Method for obtaining a crosslinked ultrahigh molecular weight polyetylene, a prosthesis for internal application as well as application of ultrahigh molecular weight polyethylene subjected to radiation

The subject of the invention is a method for obtaining crosslinked ultra high molecular weight polyethylene, a medical prosthesis for use inside the body, and the use of radiation treated ultra high molecular weight polyethylene. This invention relates generally to the orthopedic field, in particular to prostheses such as hip and knee implants.

The use of synthetic polymers, e.g. ultra-high molecular weight polyethylene, in combination with metal alloys has revolutionized the field of prosthetic implants, e.g. by using them to completely replace a hip or knee joint. However, abrasion of the synthetic polymer on the metal of the joint can lead to serious, adverse effects, which mostly manifest themselves after several years. Various studies have found that such rubbing can lead to the release of ultra-thin polyethylene particles into prosthetic tissues. It has been suggested that attrition extends the corrugated crystallite chain, forming anisotropic fibrous structures on the articular surface. Stretched fibrils can then tear, leading to the formation of submicron particles. In response to the increasing entry of these polyethylene particles between the prosthesis and the bone, resorption of periprosthetic bone begins, induced by the macrophage. Macrophage, which is often unable to digest these polyethylene particles, synthesizes and releases large amounts of cytokines and growth factors that can eventually lead to bone resorption through osteoclasts and monocytes. This bone melting atrophy can contribute to the mechanical loosening of prosthesis components, which sometimes requires surgical intervention with associated problems.

The object of the invention is to provide an implantable medical prosthesis, manufactured at least in part from radiation-treated ultra-high molecular weight polyethylene (UHMWPE), which has essentially no detectable free radicals to reduce the formation of fine particles from the prosthesis during wear of the prosthesis.

Another object of the invention is to reduce bone loss and inflammatory reactions associated with prosthetic implants.

Yet another object of the invention is to provide a medical prosthesis that can remain implanted inside a person for a longer period of time.

Still another object of the invention is to provide an improved UHMWPE that can be used in medical prostheses with the above purposes and / or in parts of the prostheses.

Yet another object of the invention is to provide an improved UHMWPE that has a high crosslink density and no detectable free radicals.

Another object of the invention is to provide an improved UHMWPE that has improved abrasion resistance.

According to the invention, the method for obtaining ultra-high molecular weight cross-linked polyethylene is characterized in that steps are carried out in which (a) an ultra-high molecular weight polyethylene is provided having polymeric chains which is at room temperature or below room temperature; (b) irradiating ultra-high molecular weight polyethylene with radiation greater than 5.0 Mradów, cross-linking the polymer chains; (c) heating the irradiated ultra-high molecular weight polyethylene to obtain, after the heating step, a final ultra-high molecular weight polyethylene temperature higher than the melting point of the ultra-high molecular weight polyethylene; and (d) cooling the heated ultra-high molecular weight polyethylene.

In the process of the invention, ultra-high molecular weight polyethylene is preferably fed to the irradiation step, which is preferably at a temperature of about 20 ° C.

Preferably, in the process of the invention, ultra-high molecular weight polyethylene which is at a temperature of about 25 ° C is fed to the irradiation step.

Preferably, in the process of the invention, after the irradiation step, the final temperature of the ultra-high molecular weight polyethylene is lower than the melting point of the ultra-high molecular weight polyethylene.

189 246

In the process of the invention, the ultra-high molecular weight polyethylene is irradiated at a temperature below the melting point of the ultra-high molecular weight polyethylene.

Preferably, the ultra-high molecular weight polyethylene of the present invention is irradiated to about 0.5 to 1000 Mrads.

Preferably, the ultra-high molecular weight polyethylene in the process of the invention is irradiated to about 15 Mrads.

Preferably, in the process of the invention, ultra-high molecular weight polyethylene is irradiated at a dose rate of about 0.05 to 0.2 Mrads per minute.

Preferably the ultra high molecular weight irradiated polyethylene is heated to a temperature from about 137 ° C to about 300 ° C.

Preferably, in the process of the invention, the ultra-high molecular weight irradiated polyethylene is heated to a temperature of about 150 ° C.

According to the invention, the method for obtaining ultra-high molecular weight cross-linked polyethylene is characterized in that steps are carried out in which (a) an ultra-high molecular weight polyethylene is provided having polymeric chains which is at room temperature or below room temperature; (b) irradiating ultra-high molecular weight polyethylene with radiation greater than 5.0 Mradów (i) cross-linking polymeric chains and (ii) generating enough heat to at least partially melt ultra-high molecular weight polyethylene; and (c) cooling the heated ultra-high molecular weight polyethylene.

Preferably, the process furthermore carries out a step in which the irradiated ultra-high molecular weight polyethylene is heated to obtain, after the heating step, a final ultra-high molecular weight polyethylene temperature higher than the melting point of the ultra-high molecular weight polyethylene.

Preferably, in this method, ultra-high molecular weight polyethylene which is at a temperature of about 20 ° C is fed to the irradiation step.

Preferably, ultra-high molecular weight polyethylene that is at a temperature of about 25 ° C is fed to the irradiation step.

Preferably, in the process of the invention, the ultra-high molecular weight irradiated polyethylene is heated to a temperature from about 13'7 ° C to about 300 ° C.

Preferably, the ultra-high molecular weight irradiated polyethylene is heated to a temperature of up to about 150 ° C.

Preferably, the methods of the invention result in cross-linked ultra-high molecular weight polyethylene which has a polymer structure with less than 50% crystallinity.

Preferably, the methods of the invention result in crosslinked polyethylene with an ultra-high molecular weight that has a polymeric structure with a less than 940 MPa elastic stretching ratio.

According to the invention, the medical prosthesis for use inside the body is characterized in that it is made of radiation-treated ultra-high molecular weight polyethylene having cross-linking bonds and two or three melting peaks, wherein this ultra-high molecular weight polyethylene is obtained by the methods of the invention.

Preferably, the ultra-high molecular weight polyethylene in the prosthesis of the invention has two melting peaks.

Preferably, the ultra-high molecular weight polyethylene in the prosthesis of the invention has three melting peaks.

Preferably, the ultra-high molecular weight polyethylene in the prosthesis of the invention has been subjected to irradiation heating.

Preferably, the polymeric structure of the prosthesis according to the invention has extensive crosslinking bonds, so that a substantial part of this polymeric structure does not dissolve in xylene at 130 ° C or decalin at 150 ° C for 24 hours.

189 246

Preferably, in the prosthesis of the invention, ultra-high molecular weight polyethylene has an initial average molecular weight greater than 1 million.

Preferably, a portion of this prosthesis according to the invention is in the form of a cup-shaped or disc-shaped element that has a load-bearing surface.

Preferably, in the prosthesis of the invention, its load-bearing surface is made of ultra-high molecular weight polyethylene.

More preferably, in a denture according to the invention, its load-bearing surface is in contact with a second part of the prosthesis that has a cooperating load-bearing surface made of metallic or ceramic material.

Preferably, the prosthesis according to the invention is constructed and adapted to replace a joint selected from the group consisting of the hip joint, knee joint, elbow joint, shoulder joint, ankle joint and finger joint.

Preferably, in the prosthesis of the invention, the ultra-high molecular weight polyethylene has a polymeric structure with less than 50% crystallinity and less than 940 MPa elastic stretching ratio; the prosthesis obtained results in reduced production of fine solid particles from the prosthesis during wear of the prosthesis.

Preferably, the ultra high molecular weight polyethylene of the prosthesis according to the invention has a hardness of less than 65 on the Shor D scale.

Preferably, in the prosthesis of the invention, the ultra-high molecular weight treated polyethylene has high entanglement density.

Preferably, in the prosthesis of the invention, ultra-high molecular weight polyethylene has a polymeric structure with less than 50% crystallinity.

Preferably, in the prosthesis of the invention, the ultra-high molecular weight polyethylene has a polymeric structure with a crystallinity in the range of 40% to 50%.

Preferably, the ultra high molecular weight polyethylene in the prosthesis of the invention is substantially resistant to oxidation.

Preferably, the ultra-high molecular weight polyethylene in the prosthesis of the invention has a high specific light transmission.

Preferably, in the prosthesis according to the invention, the ultra-high molecular weight polyethylene is in the form of a thin film or foil, the thin film or foil being transparent and wear-resistant.

Preferably, the ultra-high molecular weight polyethylene in the prosthesis of the invention is substantially free of detectable free radicals.

The invention also relates to the use of ultra-high molecular weight treated polyethylene obtained by the methods of the invention for the manufacture of a medical prosthesis.

Preferably, polyethylene is used to manufacture a medical prosthesis that is primarily in the form of a raw rod to be processed, capable of being shaped by machining.

Preferably, polyethylene is used to make a medical prosthesis that has a load-bearing surface.

Preferably, polyethylene is used to manufacture the manufactured part, which is a medical prosthesis.

Thus, according to the invention, there is provided a medical prosthesis for use inside the body, which is made of radiation-treated ultra-high molecular weight polyethylene (UHMWPE) which has essentially no detectable free radicals. The radiation may be e.g. gamma radiation or electron radiation. UHMWPE has a cross-linked structure '. Preferably, UHMWPE is substantially non-oxidized and substantially resistant to oxidation. Variants include, e.g. UHMWPE, which has three melting peaks, or two melting peaks. In some embodiments, UHMWPE has a polymeric structure with less than about 50% crystallinity, less than about 290 A plate thickness, and less than about 940 MPa elastic stretching ratio to reduce the production of fine particles from the prosthesis during its

189 246 use. Part of the prosthesis may e.g. be in the form of a hemispherical recess or cup-shaped element having a load-bearing surface made of UHMWPE. This load-bearing surface may come into contact with a second part of the prosthesis having a mating bearing surface of metal or ceramic material.

Another aspect of the present invention is exposed to UHMWPE radiation, which has essentially no detectable free radicals. This UHMWPE has a cross-linked structure. Preferably, this UHMWPE is substantially non-oxidized and substantially oxidation-resistant. Variants include, e.g., UHMWPE having three melting peaks, or two melting peaks.

Other aspects of the present invention include parts of the medical prosthesis manufactured, e.g., with a support surface and abrasion resistant coatings made of such UHMWPE. One embodiment relates to the case where the manufactured part of the medical prosthesis is in the form of a raw rod which can be shaped by conventional methods, e.g. by machining.

In yet another aspect, the present invention relates to a method of producing crosslinked UHMWPE which has essentially no detectable free radicals ··. Standard UHMWPE with polymeric chains is supplied. This UHMWPE is irradiated to cross-link said polymer chains. Next,. UHMWPE is heated to a temperature above the melting point of UHMWPE, so there are essentially no detectable free radicals'. Then, UHMWPE is cooled to room temperature. In some embodiments, cooled UHMWPE is machined and / or sterilized.

One preferred embodiment of the method of the invention is called CIR-SM, i.e. cold irradiation and subsequent melting. The UHMWPE supplied is at room temperature or below the room temperature.

Another method for making UHMWPE that is not related to the invention is called WIR-SM, i.e., heat irradiation and subsequent melting. The UHMWPE supplied is preheated to below the UHMWPE melting point.

Another method for making UHMWPE that is not related to the invention is called WIR-AM, i.e., heat irradiation and adiabatic melting. In this method, the supplied UHMWPE is preheated to a temperature below the melting temperature of UHMWPE, preferably between about 100 ° C and a temperature below the melting temperature of UHMWPE. Preferably, UHMWPE is in the insulating material to reduce heat loss from UHMWPE during its processing. The preheated UHMWPE is then irradiated, with a sufficiently high total dose and with a sufficient dose rate to generate sufficient heat in the polymer to melt essentially all the crystals of the material and thereby ensure the elimination of substantially all detectable free radicals generated e.g. during the irradiation step. To cause adiabatic heating, it is preferable to use electron radiation during the irradiation step.

Still another embodiment of the method for producing crosslinked UHMWPE, known as MIR, is known, i.e., after melting irradiation. Standard UHMWPE is provided. Preferably, UHMWPE is surrounded by an inert material that is substantially oxygen free. Then, UHMWPE is heated above the melting point of UHMWPE to completely melt the entire crystalline structure. Heated UHMWPE is irradiated, and after irradiation it is cooled to about 25 ° C.

In the MIR version, highly crosslinked and entangled UHMWPE is formed. Standard UHMWPE is provided. Preferably, UHMWPE is surrounded by an inert material that is substantially oxygen free. Then, UHMWPE is heated above the melting point of UHMWPE, for a period of time sufficient to allow the formation of entangled polymer chains in UHMWPE. The heated UHMWTE is then irradiated to trap the polymer chains in a tangled state, after which the irradiated UHMWPE is cooled to a temperature of about 25 ° C.

189 246

From the UHMWPE-treated radiation, which has essentially no detectable free radicals, and obtained by various related methods, a medical prosthesis can be made that results in reduced particle formation from the prosthesis during wear. UHMWPE is supplied after treatment with radiation that has essentially no detectable free radicals. A UHMWPE is used to make a medical prosthesis to reduce the amount of particles that form from the prosthesis when worn, where UHMWPE forms the bearing surface of the prosthesis. The prosthesis can be manufactured using standard techniques known to those skilled in the art, e.g., by machining.

The medical prosthesis of the invention is used to treat a person who requires such a medical prosthesis. A shaped prosthesis is provided, made of UHMWPE treated with radiation, which has essentially no detectable free radicals. A prosthesis, with a reduced amount of particles forming during its wear, is put on to the person who requires it. In preferred embodiments, UHMWPE is the bearing surface of the prosthesis. .

Both this and other objects, characteristics and advantages of the present invention will become clearer when reading the following description in connection with the accompanying drawings.

Short description of the drawings

Figure 1 is a cross-sectional view of the medical hip prosthesis according to a preferred embodiment of the present invention;

Figure 2 is a side view of the hemispherical recess insert as shown in Figure 1;

Figure 3 is a cross-sectional view taken along the line 3-3 of Figure 2;

Figure 4 is a graph of crystallinity and melting point, molten irradiated UHMWPE, for different irradiation doses;

Figure 5 is a scanning electron micrograph of an etched surface of a standard UHMWPE showing its crystalline structure;

Figure 6 is a scanning electron micrograph of an etched surface of molten-irradiated UHMWPE showing its crystalline structure, at approximately the same magnification as in Figure 5; and

Figure 7 is a graph of crystallinity and melting point at different depths of hemispherical well from molten-irradiated UHMWPE.

Figure 8 is a graph showing DSC melting endotherms for HoechstCelanese GUR 4050 UHMWPE, prepared using heat irradiation and partially adiabatic melting (WIR-AM), with subsequent heating and without heating, respectively.

Figure 9 is a graph showing DSC melting endotherms for HoechstCelanese GUR 1050 UHMWPE, prepared using heat irradiation and partially adiabatic melting (WIR-AM), with subsequent heating and without heating, respectively.

Figure 10 is a graph showing adiabatic UHMWPE heating after WIR-AM treatment with a preheating temperature of 130 ° C.

Figure 11 is a graph showing the tensile deformation behavior of non-irradiated UHMWPE, UHMWPE after CIR-SM treatment and UHMWPE after WIR-AM treatment.

Detailed description of the invention

The invention provides a medical prosthesis for intra-body use that is made of radiation-treated ultra-high molecular weight polyethylene (UHMWPE) that has essentially no detectable free radicals.

The medical prosthesis in the form of a hip prosthesis is generally represented as 10 in Fig. 1. The prosthesis shown has a standard spherical head 14, connected by an array part to the trunk 15, which is attached with standard cement 17 to femur 16.

189 246

The spherical head may be of a standard design and may be made of stainless steel or other alloy as known in the art. The radius of the spherical head closely corresponds to the inner radius of the acetabular cavity of the hemispherical recess 12, which can be attached in cement 13, directly to the pelvis 11. Alternatively, the metal acetabular cover may be cemented to the pelvis 11, and the acetabular recess 12 may form a coating or insert that are connected to the metal acetabular cover by means known in the art.

The specific form of the prosthesis can vary greatly, as is known in the art. Many structures of the hip and other prostheses are known, such as knee joints, shoulder joints, ankle joints, elbow joints and finger joints. All such prior art prostheses can become more advantageous by making at least one bearing surface of such a high molecular weight polyethylene prosthesis according to the invention. Such bearing surfaces may be in the form of layers, linings or entire devices, as shown in Fig. 1. In all cases, it is preferred that the bearing surface engages with the associated metal or ceramic part of the prosthesis so that a sliding surface forms between them .

Such sliding surfaces are subjected to severe damage to polyethylene, as is known in the art. This type of serious damage can be significantly reduced by using the materials of the present invention.

Figure 2 shows the acetabular cavity 12 in the form of an hollow hemisphere, the device more clearly visible in cross section in Fig. 3. As previously shown, there is no need for the outer surface of the acetabular cavity to be spherical or hemispherical, since it can be square or any configuration to adhere directly to the pelvis or to the pelvis through a metal cover, as is known in the art. The radius of the acetabular recess 21 in Fig. 3, in a preferred embodiment, varies from about 20 mm to about 35 mm. The thickness of the acetabular recess, from its generally hemispherical hollow portion to the outer surface 20, is preferably about 8 mm. The outer radius is preferably in the order of from about 20 mm to about 35 mm.

In some cases, the ball joint may be made of UHMWTE according to the present invention, and the acetabulum cavity formed of metal, although it is preferred to make a acetabular recess or a cylindrical basin insert of uHmWPE to mate with the metal ball. The detailed method of attachment of prosthesis components to body bones can vary significantly, which is known in the art.

The prosthesis according to the invention comprises the whole or part of the prosthetic device, e.g. an element, layer or padding. Such prostheses include, e.g., orthopedic joint and bone replacement parts, e.g., hip, knee, shoulder, elbow, ankle or finger. The prosthesis may take the form of, e.g., hemispherical hollow or cup shaped parts having a bearing surface. Other forms known to those skilled in the art are also within the scope of the invention. The term "medical prostheses" also includes within its meaning any bearing surface of a prosthesis, e.g. a coating on the surface of a prosthesis made of a material other than UHMWPE according to the invention.

The prostheses according to the invention are suitable for contact with metal-containing parts formed, e.g., from a cobalt-chromium alloy, stainless steel, titanium or nickel-cobalt alloy, or ceramic parts. For example, a hip joint is produced in which a hemispherical cavity portion having an inner diameter of 25 mm is contacted with a metal ball with an outer diameter of 25 mm to work closely with the hemispherical cavity portion. In this example, the support surface of the hemispherical recess portion is made of UHMWPE, preferably at least about 1 mm thick, more preferably at least about 2 mm thick, particularly preferably at least about 6.35 mm thick, and especially at least about 8.47 mm thick.

The prostheses may have any standard known form, shape or configuration or customary design, but have at least one UHMWPE bearing surface according to the present invention.

189 246

The prostheses of the present invention are non-toxic to humans. They are not degraded by normal body components, e.g. blood or interstitial fluids. They can be sterilized by standard means, including e.g. heating or ethylene oxide.

UHMWPE means linear, unbranched ethylene chains that have molecular weights above about 500,000, preferably above about 1,000,000, and especially above 2,000,000. Often, molecular weights may exceed about 8,000,000. By initial average molecular weight is meant molecular weight of the UHMWPE starting material, before any irradiation.

Conventional UHMWPE is normally produced by Ziegler-Natta catalysis as the polymer chains are generated from the catalytic surface side, they crystallize and combine as chain-shaped crystals. Examples of known UHMWPE powders include Hifax Grade 1900 polyethylene (available from Montell, Wilmington, Delaware), having a molecular weight of about 2 million g / mol and no calcium stearate; GUR 4150, also known as GUR 415 (available from Hoescht Celanese Corp., Houston, TX), having a molecular weight of about 4-5 million g / mol and containing 500 ppm calcium stearate; GUR 4050, (available from Hoescht Celanese Corp .; Houston, TX), having a molecular weight of about 4-5 million g / mol and not containing calcium stearate; GUR 4120 (available from Hoescht Celanese Corp., Houston, TX), having a molecular weight of about millions of g / mol and containing 500 ppm calcium stearate; GUR 4020 (obtained from Hoescht Celanese Corp., Houston, TX), having a molecular weight of about 2 million g / mol and not containing calcium stearate; GUR 1050 (available from Hoescht Celanese Corp., Germany), having a molecular weight of about 4-5 million g / mol and not containing calcium stearate; GUR 1150 (available from Hoescht Celanese Corp., Germany), having a molecular weight of about 4-5 million g / mol and containing 500 ppm calcium stearate; GUR 1020 (available from Hoescht Celanese Corp., Germany), having a molecular weight of about 2 million g / mol and not containing calcium stearate; and GUR 1120 (available from Hoescht Celanese Corp., Germany), having a molecular weight of about 2 million g / mol and containing 500 ppm calcium stearate. For medical applications, the preferred UHMWPE are GUR 4150, GUR 1050 and GUR 1020. Resin is understood to be a powder.

UHMWPE powder can be solidified using a wide variety of techniques, e.g. extrusion molding, compression molding or direct compression molding. During extrusion molding, the UHMWPE powder is held under increased pressure in a heated cylinder, where it solidifies into a further processing rod, i.e. a raw processing rod (it can be obtained, e.g. from Westlake Plastics, Lenni, PA). During compression pressing, UHMWPE powder is solidified under high pressure into a mold (it can be obtained e.g. from Poly-Hi Solidur, Fort Wayne, IN or Perplas, Stanmore, UK). The mold may have the shape of e.g. a thick sheet. Direct compression pressing is preferably used for the production of shaped products, e.g. acetabular components or knee tibial inserts (can be obtained e.g. from the company Zimmer, Inc., Warsaw, IN). With this technique, powdered UHMWPE can be pressed directly into the final shape. "Hockey pucks" or pucks are generally cut from raw extrusion-molded bars or from a compression-molded sheet.

By UHMWPE after radiation treatment, is meant UHMWPE that has been subjected to radiation, e.g., gamma radiation or electron radiation, to cause cross-linking between UHMWPE polymeric chains.

The expression, no essentially no detectable free radicals, means no essentially no free radicals, based on electron paramagnetic resonance measurements as described by Jahan et al in J. Biomedical Materials Research 25: 1005 (1991). Free radicals include, e.g., unsaturated trans-vinylene free radicals. UHMWPE, which has been irradiated below its melting point, is crosslinked by ionizing radiation and contains trapped free radicals with a long survival time. These free radicals react with oxygen over a long period of time, causing

189 246 as a result of oxidative degradation, brittleness UHMWPE. The advantage of UHMWPE and the medical prostheses of the present invention is that irradiated UHMWPE is used that has essentially no detectable free radicals. Free radicals can be removed by any method that leads to this, e.g. by heating UHMWPE above its melting point, which means that essentially no residual crystal structure remains. By eliminating the crystal structure, free radicals are able to recombine and thus be removed.

The UHMWPE that is used according to the present invention has a crosslinked structure. The advantage of a cross-linked structure is that the production of particles from the prosthesis is reduced when worn.

It is preferred that UHMWPE is substantially non-oxidized. By the term, substantially non-oxidized, it is meant that the ratio of the area under the carbonyl peak at 1740 cm '¹ in the FTlR spectrum, to the area under the peak at 1460 cm '¹ in the FTIR spectrum of the crosslinked sample, it is of the same order of magnitude as the ratio for the sample before crosslinking.

It is preferred that UHMWPE is substantially oxidation resistant. The phrase, essentially oxidation-resistant, means that it remains substantially non-oxidized for at least about 10 years. Preferably, it remains substantially non-oxidized for at least about 20 years, more preferably for at least about 30 years, even more preferably for at least about 40 years, and especially throughout the patient's lifetime.

In the process of the invention, UHMWPE is obtained, which has three melting peaks. The first melting peak is preferably in the temperature range from about 105 ° C to about 120 ° C, more preferably in the temperature range from about 11 ° C to about 120 ° C, and especially at about 118 ° C. The second melting peak is preferably in the temperature range from about 125 ° C to about 140 ° C, more preferably in the temperature range from about 130 ° C to about 140 ° C, even more preferably at a temperature of about 135 ° C and especially at a temperature of about 137 ° C. The third melting peak is preferably in the temperature range from about 140 ° C to about 150 ° C, more preferably in the temperature range from about 140 ° C to about 145 ° C, and especially at about 144 ° C. Sometimes UHMWPE is obtained, which has two melting peaks. The first melting peak is preferably in the temperature range from about 105 ° C to about 120 ° C, more preferably in the temperature range from about 110 ° C to about 120 ° C, and especially at a temperature of about 118 ° C. The second melting peak is preferably in the temperature range from about 125 ° C to about 140 ° C, more preferably in the temperature range from about 130 ° C to about 140 ° C, even more preferably at about 135 ° C and especially at about 137 ° C.

UHMWPE can also be obtained, which has one melting peak (this does not apply to the present invention). Such a melting peak is in the temperature range from about 125 ° C to about 140 ° C, and sometimes in a temperature range from about 130 ° C to about 140 ° C, most often at about 135 ° C, and especially at about 137 ° C .

Preferably, UHMWPE has two melting peaks. The number of melting peaks is determined by differential scanning calorimetry (DSC) at a heating rate of 10 ° C / min.

UHMWPE with a polymeric structure used in the prostheses of the invention leads to a reduction in the production of UHMWPE particles from the prosthesis during wear. As a result of the limited amount of particles discharged into the body, the dentures have a longer implant life. Preferably, the prosthesis may remain implanted in the body for at least 10 years, more preferably for at least 20 years, and especially throughout the patient's lifetime.

The UHMWPE obtained by the process of the invention can be used to shape parts produced therefrom, wherein such UHMWPE after radiation treatment, generally has no detectable free radicals. Preferably, used to shape the manufactured parts, UHMWPE has a crosslinked structure. Preferably, UHMWPE is substantially resistant to oxidation. Such UHMWPE after radiation treatment has three melting peaks. Such a UHMWPE may also have two melting peaks. UHMWPE which has one melting peak does not apply to the present invention. preferably,

189 246

UHMWPE has two melting peaks. Manufactured parts include shaped and unshaped parts, including, e.g., machined parts, e.g., hemispherical cavities, gears, nuts, sled skids, pins, clamps, ropes, tubes and the like, and raw machining rods, membranes, cylindrical rods, foils, panels and fibers. Shaped parts can be made, e.g. by machining. The manufactured part may be, e.g. in the form of a raw rod that is suitable for shaping another part by machining. Manufactured parts are particularly suitable for applications where loads are transferred, e.g. in applications where high abrasion resistance is needed, e.g. as a load-bearing surface, e.g. articulated surface, and as metal replacement parts. Thin films or films of UHMWPE obtained by the method of the invention can also be attached, e.g. with adhesive on bearing surfaces and thus used as a wear-resistant load-bearing surface.

UHMWPE after radiation treatment generally has no detectable free radicals. The UHMWPE obtained according to the invention has a cross-linked structure. Preferably, UHMWPE is substantially non-oxidized and is substantially resistant to oxidation. The UHMWPE obtained according to the invention preferably has two or three melting peaks. Most preferably UHMWPE has two melting peaks. Depending on the type of process used to manufacture UHMWPE, some impurities may be present in the UHMWPE by the process of the invention, including, e.g., calcium stearate, form release agents, fillers, antioxidants and / or other standard additives used for polyethylene polymers.

The present invention also relates to a method for producing crosslinked UHMWPE which has essentially no detectable free radicals. Preferably, this UHMWPE is intended for use as a load-bearing part with high abrasion resistance. Standard UHMWPE with polymeric chains is supplied. The standard UHMWPE can be in the form of e.g. a raw machining rod, a shaped machining rod, e.g. a disc, a shell or a manufactured part, e.g. in the shape of a hemispherical cavity or cup for use in a medical prosthesis. By standard UHMWPE, it is meant commercially available high density (linear) polyethylene with a molecular weight greater than about 500,000. Preferably, the starting UHMWPE has an average molecular weight greater than about 2 million. Initial average molecular weight means the average molecular weight of the original UHMWPE before any radiation. UHMWPE is then irradiated to cross-link the polymer chains. Irradiation can be carried out in an inert or non-inert environment. Preferably, the irradiation is carried out in a non-inert environment, e.g. air. After irradiation, UHMWPE is heated to a temperature above the melting point of UHMWPE, as a result of which there is essentially no detectable free radicals in UHMWPE. Then, heated UHMWPE is cooled to room temperature. Preferably, the cooling step is carried out at a rate greater than about 0.1 ° C / min. Cooled UHMWPE can optionally be machined. For example, if any oxidation occurs during the irradiation step, it may be machined, as appropriate, by any method known to those skilled in the art. And possibly, chilled UHMWPE. or UHMWPE after machining, can be sterilized by any method known to those skilled in the art.

One preferred embodiment of this method is called CIR-SM, i.e. cold irradiation followed by melting. In this embodiment, the supplied UHMWPE is at or below room temperature. Preferably, it is about 20 ° C. UHMWPE irradiation can take place by means of e.g. gamma irradiation or electron irradiation. Generally, gamma irradiation gives a large penetration depth, but it takes more time, which creates the possibility of greater oxidation at depth. In general, electron irradiation gives a more limited penetration depth, but requires a shorter time and the possibility of more severe oxidation is reduced. Irradiation is carried out to cross-link the polymer chains. The irradiation dose can be variable, which allows you to control the degree of crosslinking and crystallinity of the final UHMWPE product. preferably,

189 246 the total absorbed dose of radiation is from about 0.5 to about 1000 Mrad, more preferably from about 1 to about 100 Mrad, even more preferably from about 4 to about 30 Mrad, even more preferably about 20 Mrad and especially about 15 Mrad. Preferably, a dose rate is used that does not generate enough heat to melt the UHMWPE. If gamma irradiation is used, the preferred dose rate is from about 0.05 to about 0.2 Mrad / minute. If electron irradiation is used, preferably the dose rate is from about 0.05 to about 3000 Mrad / minute, more preferably from about 0.05 to about 5 Mrad / minute, especially from about 0.05 to about 0.2 Mrad / minute. minute. The dose rate in the case of electron radiation is determined by the following parameters: (i) the accelerator power in kW, (ii) the conveyor speed, (iii) the distance between the irradiated surface of the sample and the scanning nozzle, (iv) the scanning width. The dose rate in the e-beam device is often measured in Mrady to pass under the raster e-beam. The indicated dose intensities as Mrad / minute can be converted to Mrad / transition using the following equation:

DMrad / min ^— DMrad / XC transition_c 4- 1 where D \ 4rad / mm is the dose rate in D ^ rad / min, DMrad / transition is the dose rate in Mrad / transition, v_c is the conveyor speed and 1 is the length of the sample that passes through the raster surface of the e-beam. If electron irradiation is used, the electron energy may be different to change the depth of electron penetration. Preferably, the electron energy is from about 0.5 MeV to about 12 MeV, more preferably from about 5 MeV to about 12 MeV. This manipulation capability is especially useful when the irradiated object is a part of varying thickness or depth, e.g. a hemispherical joint cavity for a medical prosthesis.

After irradiation, UHMWPE is heated above the melting point of UHMWPE, and it also has essentially no detectable free radicals in UHMWPE. Heating provides particles with sufficient mobility to eliminate bonds from UHMWPE crystals, which allows virtually all of the remaining free radicals to recombine. Preferably, the UHMWPE is heated to a temperature from about 137 ° C to about 300 ° C, more preferably to a temperature from about 140 ° C to about 300 ° C, even more preferably to a temperature from about 140 ° C to about 190 ° C, even more preferably to temperatures from about 145 ° C to about 300 ° C, even more preferably to a temperature from about 145 ° C to about 190 ° C, even more preferably to a temperature from about 146 ° C to about 190 ° C, especially to a temperature of about 150 ° C . Preferably, the temperature at the heating stage is maintained for a period of time from about 0.5 minutes to about 24 hours, more preferably for a period of time from about 1 hour to about 3 hours, especially for about 2 hours. Heating may be carried out, e.g. in air, in an inert gas, e.g. nitrogen, argon or helium, in a sensitizing atmosphere, e.g. in acetylene or under vacuum.

Another method not related to the present invention is called WIR-SM, i.e. heat irradiation and subsequent melting. In this method, the supplied UHMWPE is preheated to a temperature below the melting point of UHMWPE. Pre-heating can be carried out in an inert or inert environment. It is preferred to carry out this preheating in air. Preferably, the UHMWPE is pre-heated to a temperature from about 20 ° C to about 135 ° C, more preferably to a temperature higher than about 20 ° C to about 135 ° C, and especially to a temperature of about 50 ° C. The remaining parameters are as described for the CIR-SM implementation with the difference that the dose rate at the irradiation step using electron irradiation is preferably from about 0.05 to about 10 Mrad / minute, and more preferably from about 4 to about 5 mrad / minute; and the dose rate at the irradiation step using gamma irradiation, preferably is from about 0.05 to about 0.2 Mrad / minute, and more preferably is about 0.2 Mrad / minute.

Another method not related to the present invention is called WIR-AM, i.e. heat irradiation and adiabatic melting. In this method, the supplied UHMWPE is preheated to a temperature below the melting point of UHMWPE. Pre-heating can

189 246 be carried out in an inert or inert environment. It is preferred to carry out this preheating in air. Pre-heating can be carried out, e.g. in an oven. Preferably, the UHMWPE is preheated in a temperature range from about 100 ° C to a temperature below the melting point of the UHMWPE. Preferably, the UHMWPE is pre-heated to a temperature from about 100 ° C to about 135 ° C, more preferably to a temperature of about 130 ° C, and especially to a temperature of about 120 ° C. Preferably, UHMWPE is in an insulating material to reduce heat loss from UHMWPE during the process line. Heat includes, e.g., heat supplied during pre-heating prior to irradiation and heat generated during irradiation. Insulation material means any type of material that has insulation properties, e.g. a fiberglass bag.

The preheated UHMWPE is then irradiated with a sufficiently high total dose and with a sufficiently high dose rate to generate a sufficient amount of heat in the polymer to melt essentially all crystals in the material and thereby ensure the elimination of substantially all detectable free radicals produced e.g. during the irradiation step. During the irradiation step, it is preferable to use electron radiation, because in this way such adiabatic heating is generated. Adiabatic heating means no heat loss to the environment during irradiation. Adiabatic heating results in adiabatic melting if the temperature is higher than the melting point. Adiabatic melting means complete or partial melting. The minimum total dose is determined by the amount of heat necessary to heat the polymer from its initial temperature (i.e. the preheating temperature discussed above) to its melting point and the amount of heat necessary to melt all crystals and the amount of heat necessary to heat the polymer to a predetermined temperature above its temperat ury point. The equation below describes how the total dose is calculated:

Total dose = Cp_S(T_m-T,) + AH_m + Cp_m(T_rT_m) where: cp_S(= 2 J / g / ° C) ac_pm(= 3 J / g / ° C), mean thermal capacities of UHMWPE in solid state and after melting, AH respectively_m (= 146 j / g) means the heat of fusion of the non-irradiated crude Hoescht Celanese GUR 415 rod, Tj is the initial temperature and Tf is the final temperature. The final temperature should be higher than the melting point of UHMWPE.

Preferably, the end temperature of UHMWPE is from about 145 ° C to about 200 ° C, more preferably from about 145 ° C to about 190 ° C, even more preferably from about 146 ° C to about 190 ° C, especially 150 ° C. Above 160 ° C, bubbles and cracks begin to form in the polymer. Preferably, the electron irradiation dose rate is from about 2 to about 3000 Mrad / minute, more preferably from about 2 to about 30 Mrad / minute, even more preferably is from about 7 to about 25 Mrad / minute, even more preferably is about 20 Mrad / minute , especially 7 Mrad / minute. Preferably, the total absorbed dose is from about 1 to about 100 Mrad. Using the equation presented above, the absorbed dose, at an initial temperature of 130 ° C and an final temperature of 150 ° C, was calculated to be about 22 Mrad.

In this embodiment, the heating step results from the adiabatic heating described above.

In some embodiments, adiabatic heating causes the UHMWPE to completely melt. In some embodiments, adiabatic heating causes only partial melting of UHMWPE. Preferably, additional heating of the irradiated UHMWPE is carried out after irradiation, causing adiabatic heating, so that the final UHMWPE temperature, after additional heating, is above the melting point of UHMWPE, which ensures the complete melting of the UHMWPE. Preferably, the UHMWPE temperature from the additional heating step is from about 140 ° C to about 200 ° C, more preferably from about 145 ° C to about 190 ° C, even more preferably from about 146 ° C to about 190 ° C, especially 150 ° C.

189 246

Still another embodiment of the present invention is called CIR-AM, i.e. cold irradiation and adiabatic heating. In this embodiment, UHMWPE at room temperature or below room temperature, melts by adiabatic heating, with or without subsequent heating as described above.

The invention also relates to the use of the UHMWPE product obtained by the CIR-SM method and the CIR-AM method.

The invention also relates to a method for producing a medical prosthesis from UHMWPE which has essentially no detectable free radicals, resulting in reduced production of particles from the prosthesis during wear of the prosthesis. It is delivered treated with UHMWPE radiation, which has essentially no detectable free radicals. With this UHMWPE, a medical prosthesis is formed to reduce the production of particles from the prosthesis during wear of the prosthesis, wherein UHMWPE forms a load-bearing denture surface. Shaping of the prosthesis can be carried out using standard procedures known to those skilled in the art, e.g., by machining.

The medical prosthesis according to the invention is used to treat a person who requires the use of such a prosthesis. A shaped denture is made, made of irradiated UHMWPE, which has essentially no detectable free radicals. This prosthesis is put on to a person who requires it. The prosthesis reduces the production of fine particles from the prosthesis as the prosthesis wears. In preferred embodiments, ultra-high molecular weight polyethylene forms a load-bearing denture surface.

In yet another embodiment of the present invention, a medical prosthesis is provided for use inside the body which is made of ultra-high molecular weight polyethylene (UHMWPE) which has a polymeric structure with less than about 50% crystallinity, less than about 290 A platelet thickness and less than about 940 MPa elastic stretching ratio to reduce the production of fine particles from the prosthesis during wear of the prosthesis.

In this embodiment, UHMWPE has a polymeric structure with less than about 50% crystallinity, preferably less than about 40% crystallinity. Crystallinity means the polymer fraction which is crystalline. The crystallinity is calculated by knowing the weight of the sample (in, in grams), the heat absorbed by the sample during melting (E, in inch) and the calculated heat of melting polyethylene at 100% crystallinity (AH ° = 69.2 cal / g) and using the following equation:

% crystallinity = νν · ΔΗ °

In this embodiment, UHMWPE has a polymeric structure with less than about 290 A plate thickness, preferably less than about 200 A plate thickness, and especially less than about 100 A plate thickness. Plate thickness (1) means the calculated thickness of the assumed plate structures in the polymer using the following expression:

2, σ ~ .Τ e · ^χπι where: oy is the energy of the final free surface of polyethylene (2.22 x x 10 '° inch / cm)²), AH ° means the calculated heat of melting polyethylene at 100% crystallinity (AH ° = 69.2 cal / g) / p means the density of the crystalline areas (1.005 g / cm³),

189 246

T_m° means the melting point of a perfect polyethylene crystal (418.15 K) and T_m experimentally means the melting point of the sample.

In this embodiment, the UHMWPE has less than about 940 MPa elastic stretching ratio, preferably less than about 600 MPa elastic stretching ratio, more preferably less than about 400 MPa elastic stretching ratio, and especially less than about 200 MPa elastic stretching ratio. The elastic stretching ratio is the ratio of the nominal stress to the corresponding stress for strains less than 0.5% as determined using the standard ASTM 638 M HI test.

Preferably, in this embodiment, UHMWPE has a polymeric structure with about 40% crystallinity, about 100 A, plate thickness, and an elastic stretching ratio of about 200 MPa.

In this embodiment UHMWPE has no trapped free radicals, e.g. unsaturated trans-vinylene free radicals. It is preferred that the UHMWPE in this embodiment has a hardness less than about 65 on the Shore D scale, more preferably less than about 55 on the Shore D scale, and especially less than about 50 on the Shore D scale. Hardness means the hardness of the first cut, measured on the Shore D scale, using the hardness tester described in ASTM D2240. It is preferred that the UHMWPE in this embodiment is substantially non-oxidized. The polymeric structure has such extensive crosslinking that a substantial part of the polymeric structure does not dissolve in decalin. The essential part means at least 50% by dry weight of the polymer sample. The term insoluble in decalin means that it is insoluble in decalin at 150 ° C for 24 hours. Preferably, the UHMWPE in this embodiment has a high entanglement density such as to induce imperfect crystal formation and reduce crystallinity. Entanglement density means the number of entanglement points of polymer chains in a unit of volume; wherein a higher entanglement density indicates polymer samples unable to crystallize to the same degree as the standard UHMWPE, which leads to a lower degree of crystallinity.

The invention also relates to other manufactured parts made of UHMWPE, including an embodiment having a polymeric structure with less than about 50% crystallinity, less than about 290 A plate thickness and less than about 940 MPa elastic stretching ratio. Such parts include shaped and unshaped parts, including. e.g. machined items, e.g. hemispherical cavities, gears, nuts, toboggan runners, pins, clamps, ropes, tubes and the like, and raw machining bars, films, cylindrical bars, films, panels and fibers. Shaped parts can be made, e.g. by machining. The manufactured parts are particularly suitable for applications where loads are transferred, e.g. as a load-bearing surface and as metal replacement parts. Thin films or films of UHMWPE that has been melted-irradiated can also be attached, e.g. with glue, to bearing surfaces and thus used as a transparent, abrasion-resistant load-bearing surface.

The invention also includes an embodiment in which UHMWPE has a unique polymeric structure characterized by less than about 50% crystallinity, less than about 290 A plate thickness, and less than about 940 MPa elastic stretching ratio. Depending on the particular process used to make UHMWPE, some impurities may be present in the UHMWPE according to the present invention including, e.g. calcium stearate, form release agents, fillers, antioxidants and / or other standard additives used for polyethylene polymers. In some embodiments, UHMWPE has high specific light-transmission, preferably light transmission greater than about 10% of light by 517 nm, through a 1 mm thick sample, more preferably greater than about 30% of light by 517 nm, through a 1 mm thick sample, and especially greater than about 40% of light by 517 nm, by a sample 1 mm thick. This type of UHMWPE is particularly useful for thin films or films that can be attached to the supporting surface of various parts, the films or films being transparent and abrasion resistant.

189 246

Another UHMWPE cross-linking method that is not related to the present invention is called the MIR method. This method is called melting-irradiation (or MIR). Standard UHMWPE is provided. Preferably, in this method, UHMWPE is surrounded by an insulating material that is substantially free of oxygen. UHMWPE is heated above the melting point of UHMWPE, so as to completely melt the entire crystal structure. The heated UHMWPE is then irradiated and the irradiated UHMWPE is cooled to 25 ° C.

Preferably, the UHMWPE prepared by this method has a polymeric structure with less than about 50% crystallinity <less than about 290 A plate thickness and less than 940 MPa elastic stretching ratio. A standard UHMWPE is supplied, e.g. raw bar, shaped bar, coating or manufactured part. Standard UHMWPE means commercially available high density (linear) polyethylene with a molecular weight greater than about 500,000. Preferably, the UHMWPE starting material has an average molecular weight greater than 2 million. Initial average molecular weight means the average molecular weight of the original UHMWPE before any radiation. It is preferred that this UHMWPE is surrounded by an inert material that is substantially oxygen free, e.g. nitrogen, argon or helium. In some embodiments, an inert environment may be used. UHMWPE is heated to a temperature above its melting point, for a time sufficient to melt all the crystals. Preferably, the temperature is from about 145 ° C to about 230 ° C, and more preferably from about 175 ° C to about 200 ° C. Preferably, the heating is carried out so as to keep the polymer at a preferred temperature for a time period from about 5 minutes to about 3 hours, and more preferably a time period from about 30 minutes to about 2 hours. Then, UHMWPE is irradiated by gamma irradiation or electron irradiation. Generally, gamma irradiation gives a large penetration depth, but requires a longer period of time, creating the possibility of some oxidation. Generally, electron irradiation gives a more limited penetration depth, but it takes less time and therefore creates less oxidation potential. The irradiation dose can be varied, allowing control of the degree of crosslinking and crystallinity of the final UHMWPE product. Preferably, a dose greater than about 1 Mrad, more preferably greater than about 20 Mrad, is used. If electron irradiation is used, the electron energy can be different to change the depth of electron penetration, thus controlling the degree of crosslinking and crystallinity of the final UHMWPE. Preferably, this energy is from about 0.5 MeV to about 12 MeV, more preferably from about 1 MeV to about 10 MeV, especially about 10 MeV. This manipulation capability is particularly useful when the irradiated object is a part of varying thickness or depth, e.g. a hemispherical articular cavity for a medical prosthesis. The irradiated UHMWPE is then cooled to a temperature of about 25 ° C. Preferably, the cooling rate is equal to or greater than about 0.5 ° C / minute, more preferably equal to or greater than about 20 ° C / minute. In some embodiments, cooled UHMWPE may be machined. In preferred embodiments, the cooled UHMWPE has essentially no detectable free radicals. ' Examples 1,3 and 6 describe some preferred embodiments of the method. Examples 2, 4 and 5 and Fig. 4 to 7, illustrate some of the properties of fused-irradiated UHMWPE obtained in these preferred embodiments, compared to standard UHMWPE.

In the MlR embodiment, UHMWPE is produced with a high degree of entanglement and crosslinking. Standard UHMWPE is provided. Preferably, UHMWPE is surrounded by an inert material that is substantially oxygen free. Then, UHMWPE is heated above the melting point of UHMWPE, for a time sufficient to allow the formation of entangled polymer chains in UHMWPE. The heated UHMWPE is then irradiated to trap the polymer chains in a tangled state. Irradiated UHMWPE is cooled to a temperature of about 25 ° C.

The invention relates to a method for producing a medical prosthesis from UHMWPE, and thanks to its use it is possible to reduce the formation of fine particles from the prosthesis during its wear. Supplied is UHMWPE treated with polymeric radiation

189 246 structure with less than 50% crystallinity, less than 290 A plate thickness and less than 940 MPa elastic stretching ratio. This UHMWPE-treated prosthesis is made into a prosthesis, whereby UHMWPE forms the load-bearing surface of the prosthesis.

Shaping of the prosthesis can be carried out using standard procedures known to those skilled in the art, e.g. by machining.

The medical prosthesis of the invention is used to treat a person who requires a prosthesis. A shaped denture is provided, made of ultra-high molecular weight polyethylene, having a polymer structure with less than 50% crystallinity, less than 290 A plate thickness, and less than 940 MPa elastic stretch ratio. This prosthesis is put on to a person who requires a prosthesis. The prosthesis reduces the formation of fine particles from the prosthesis when worn. In preferred embodiments, the ultra-high molecular weight polyethylene is the load-bearing denture surface.

The products and methods described above may also apply to other polymers such as high density polyethylene, low density polyethylene, linear low density polyethylene and polypropylene.

The following non-limiting examples further illustrate the present invention and related methods.

Examples

Example 1: Method for preparing fused-irradiated UHMWPE (MIR method).

This example is a comparative illustration of molten UHMWPE electron irradiation.

A 10 mm x x 12 mm x 60 mm cube sample (pucek) prepared from a piston-pressed raw UHMWPE rod (raw rod Hoescht Celanese GUR 415, obtained from Westlake Plastics, Lenni, PA) is placed in the chamber. The atmosphere inside the chamber is low oxygen gas (<0.5 ppm oxygen gas) (obtained from AIRCO, Murray Hill, NJ). The chamber pressure is about 100 kPa (1 atm). The temperature of the sample and the irradiation chamber are controlled using a heating element, a variator and a thermocouple reading (manually) or a temperature controller (automatically). The chamber is heated with a 270 W heating jacket. The chamber is heated (controlled by a crazy person) at such a rate that the steady-state temperature of the sample is about 175 ° C. The sample is kept at a steady temperature for about 30 minutes before the irradiation begins.

Irradiation is carried out using a van de Graaff generator with 2.5 MeV electron energy and a dose rate of 1.67 MRad / min. The sample is irradiated with a 20 MRad dose using an electron beam bombarding the sample over an area of ​​60 mm x 12 mm. After irradiation, the heating element is turned off and the sample is allowed to cool inside the chamber in an inert atmosphere of nitrogen gas, to a temperature of 25 ° C, at a rate of approximately 0.5 ° C / minute. Similar samples from the unheated and non-irradiated UHMWPE raw rod were prepared as controls.

Example 2: Comparison of the properties of the raw UHMWPE GUR 415 rod and the fused-irradiated (MIR) raw UHMWPE GUR 415 rod (20 Mrad).

This example illustrates the different properties of irradiated and non-irradiated UHMWPE (GUR 415) raw rod samples obtained in Example 1. The following samples were tested: the test sample was a raw rod that was melted and then irradiated during melting; the control sample was a raw rod (no heating-melting, no irradiation).

(A) Differential scanning calorimetry (DSC)

A Perkin-Elmer DSC7 apparatus with water-ice heat removal and a heating and cooling rate of 10 ° C / minute, with continuous nitrogen removal, was used. crystallinity

189 246 samples obtained in Example 1 were calculated based on sample weight and heat of fusion of polyethylene crystals 289.7 J / g (69.2 cal / g). The temperature corresponding to the endotherm peak was taken as the melting point. The plate thickness was calculated assuming crystalline plate morphology and known values, AH ° heat of melting 100% crystalline polyethylene 289.7 J / g (69.2 cal / g), perfect melting temperature 145 ° C (418.15 ° K) , density of crystal areas (1.005 g / cm²) and the final energy of the free surface of polyethylene 9.29 x 10 '⁶ J / cm2 (2.22 x 10 '⁶ cal / cm2). The results are shown in Table 1 and in Figure 4.

Table 1: DSC (10 ° C / min)

<td></td><td>GUR 415 (not fixed)</td><td>GUR 415 (fused repair *)</td>

<td>Properties</td><td>område</td><td>20 MRad</td>

<td>Crystallinity (%)</td><td> 50,2</td><td> 37,8</td>

<td>Top temperature (° C)</td><td> 135,8</td><td> 125,5</td>

<td>Plate thickness (A)</td><td> 290,0</td><td> 137,0</td>

* Stress. = irradiated

The results indicate that the melted-irradiated sample has a higher degree of entanglement and less crystallinity in the polymeric structure than the non-irradiated sample, as shown by lower crystallinity, lower plate thickness and lower melting point.

(B) Swelling rate

The samples were cut into cubes 2 mm x 2 mm x 2 mm and immersed in decalin at 150 ° C for 24 hours. To prevent sample degradation, an antioxidant (1% N-phenyl-2-naphthylamine) was added to decalin. The degree of swelling and the percentage of extract were calculated by weighing the sample before the experiment, after 24 hours of swelling and after vacuum drying the swollen sample. The results are shown in Table 2.

Table 2:

Swelling in decalin for 24 hours at 150 ° C with the addition of an antioxidant

<td></td><td>GUR 415 (not fixed)</td><td>'GUR 415 (fused repair *)</td>

<td>Properties</td><td>område</td><td>20 MRad</td>

<td>Degree of swelling</td><td>dissolves</td><td> 2,5</td>

<td>Extract (%)</td><td>about 100%</td><td> 0,0</td>

* Stress. = irradiated

The results indicate that the melted-irradiated sample was higher crosslinked and hence the polymer chains did not dissolve in the hot solvent, even after 24 hours, while the non-irradiated sample at the same time dissolved completely in the hot solvent.

189 246 (C) Elastic stretching ratio

The samples were tested in accordance with ASTM 638 M HI. The feed speed was 1 mm / minute. The experiment was carried out on an MTS machine. The results are shown in Table 3.

Table 3:

Elasticity test (ASTM 638 M III, 1 mm / min)

<td></td><td>GUR 415 (not fixed)</td><td>GUR 15 (melted repair *)</td>

<td>Properties</td><td>0 MRad</td><td>20 MRad</td>

<td>Elastic stretching ratio (MPa)</td><td> 940,7</td><td> 200,8</td>

<td>The yield point</td><td> 22,7</td><td> 14,4</td>

<td>Stress at break (%)</td><td> 953,8</td><td> 547,2</td>

<td>UTS technique (MPa)</td><td> 46,4</td><td> 15,4</td>

The results indicate that the UHMWPE fused-irradiated sample has a much lower elastic stretching ratio than the non-irradiated control sample. Less plasticity and breakage of the fused-irradiated sample is further evidence of cross-linking of sample chains.

(D) Hardness

The hardness of the samples was measured using a Shore D scale hardness tester. The hardness was registered for the first incision. The results are shown in Table 4.

Table 4: Hardness (Shore D)

<td></td><td>GUR415 (Nienapr).</td><td>GUR 415 (fused repair *)</td>

<td>Properties</td><td>område</td><td>20 MRad</td>

<td>Hardness (D scale)</td><td> 65,5</td><td> 54,5</td>

The results indicate that melted-irradiated UHMWPE was softer than non-irradiated in the control sample.

(E) Light transmission (transparency)

The transparency of the samples was. measured as follows. Light transmission was tested for light at 517 nm, passing through a sample about 1 mm thick, sandwiched between two glass slides. The samples were prepared by polishing the surface with a 600 grain size paper. Then, silicone oil was spread on the sample surfaces, and then the sample was placed between two slides. Silicone oil was used to reduce the light scatter resulting from the surface roughness of the polymer sample. To this end, two similar glass slides separated by a thin layer of silicone oil were used as reference.

189 246

Transmittance was measured using a Perkin Elmer Lambda 3B uv spectrophotometer. The absorption coefficient and sample permeability of exactly 1 mm thick were calculated on the basis of Lambert-Beer law. The results are shown in table 5.

Table 5:

517 nm light transmission

<td></td><td>GUR 415 (not fixed)</td><td>GUR 415 (fused repair *)</td>

<td>Properties</td><td>0 MRad</td><td>20 MRad</td>

<td>Transmittance (%) (1 mm sample)</td><td> 8,59</td><td> 39,9</td>

<td>Absorption coefficient (c ^ '1</td><td> 24,54</td><td> 9,18</td>

The results indicate that the UHMWPE fused-irradiated sample transmits a lot more light than the control sample, and is therefore much more transparent than the control sample.

(F) Environmental scanning electron microscopy (ESEM)

ESEM (ElectroScan, Model 3) was carried out on 10-kV samples (low voltage to reduce radiation damage to the sample) with an extremely thin gold coating (about 20 A to increase image quality). As a result of testing the surface of the polymer under ESEM, with and without a gold coating, it was found that the thin gold coating does not produce any artifacts.

Prior to testing under ESEM, the samples were digested using a permanganate digestion reagent with a 1: 1 ratio of sulfuric acid to phosphoric acid and 0.7% (w / v) potassium permanganate.

Figure 5 shows ESEM (10,000 x magnification) etched surface of a standard UHMWPE (GUR 415; unheated; non-irradiated). Fig. 6 shows ESEM (10,000 x magnification) of the etched surface of molten-irradiated UHMWPE (GUR 415; molten; 20 MRad). ESEM indicates a reduction in crystallite dimensions and the presence of imperfect crystallization in melted-irradiated UHMWPE compared to standard UHMWPE.

(G) Fourier transform infrared spectroscopy (FTIR)

The FTIR of the samples was carried out using a micro-probe, on samples washed with hexane, to remove surface contamination.

Peaks observed at wavelengths 1740 and 1700 cm- are bands associated with oxygen-containing groups. And hence, the ratio of the area under the peak at 1740 cm- to the area under the methylene peak at 1460 cm 'is a measure of the degree of oxidation.

The FTIR spectrum indicates that the UHMWPE fused-irradiated sample shows a higher degree of oxidation than the standard, non-irradiated UHMWPE control sample, but a much lower degree of oxidation than the UHMWPE sample irradiated in air at room temperature, with the same irradiation dose as the sample of the irradiated UHMWPE irradiated.

(H) Electronic paramagnetic resonance imaging (EPR)

EPR is carried out at room temperature on samples that have been placed under a nitrogen atmosphere in an air-tight quartz tube. A Bruker ESP 300 EPR spectrophotometer and Taperlok EPR tubes obtained from Wilmad Glass Company, Buena, NJ were used.

189 246

Non-irradiated samples do not contain any free radicals because irradiation is a process that produces free radicals in the polymer. During irradiation, free radicals are produced, which may remain for several years under appropriate conditions.

EPR results indicate that the molten-irradiated sample does not contain any free radicals in the case of an immediate EPR test after irradiation, while a sample that has been irradiated at room temperature under a nitrogen atmosphere shows the presence of trans-vinylene free radicals, even after 266 days of storage in room temperature. The lack of free radicals in the UHMWPE fused-irradiated sample means that no further oxidative degradation was possible.

(I) Wear

The wear resistance of the samples was measured using a bi-pin wear tester, pin type on the dial. The wear test consists of rubbing pins with UHMWPE (diameter = 9 mm; height = 13 mm) using a Co-Cr alloy disc. These tests were carried out with a total of 2 million cycles. The irradiated pin has a wear rate of 8 mg / million cycles, while the irradiated pin has a wear rate of 0.5 mg / million cycles. The results indicate that the melted-irradiated UHMWPE has a much higher wear resistance than the non-irradiated control pin.

Example 3: Method for the production of melted-irradiated (MIR) UHMWPE standard joint hemispheric wells

This example illustrates the electron irradiation of molten UHMWPE standard articular hemispherical cavity.

Standard, semi-spherical hollow well (UHMWPE hemispheric well, non-sterilized, high compliance, from Zimmer Inc., Warsaw, IN) with an internal diameter of 26 mm, made of piston-pressed raw GUR 415 rod, irradiated under controlled atmosphere and temperature conditions, in an airtight chamber, with a titanium handle cavity at the base and a thin stainless steel foil 0.0254 mm (0.001 inch) thick on top. The atmosphere inside the chamber is nitrogen gas with low oxygen content (&lt;0.5 ppm oxygen gas) (from AIRCO, Murray Hill, NH). The chamber pressure was about 100 kPa (1 atm). The chamber is heated by means of a 270 W heating mantle, located at the base of the chamber, controlling heating with a temperature controller and a variator. The chamber is heated in such a way that the temperature on the upper surface of the well rises approximately 1.5 ° C-2 ° C / min, finally settling to an asymptotically stationary temperature state, approximately 175 ° C. Due to the thickness of the well sample and the particular design of the device used, the stationary temperature state of the well varies from 200 ° C at the base to 175 ° C at the top. The hemispherical well is maintained within this temperature range for 30 minutes before the irradiation begins.

Irradiation is carried out using a GraafFa generator with electrons with 2.5 MeV energy and a dose rate of 1.67 MRad / min. The beam enters the chamber through a thin film at the top and bombards the concave surface of the depression. The dose received by the well was such that the maximum dose of 20 MRad was received about 5 mm below the surface of the well which the electrons are bombarding. After irradiation, heating is discontinued and allows the cavity to cool to room temperature (about 25 ° C) remaining in the chamber under nitrogen. When the chamber and sample reach room temperature, the sample is removed from the chamber.

The irradiated well, as above, which increases its volume (due to the decrease in density accompanying the decrease in crystallinity due to melting-irradiation), can be machined again to the correct size · '.

Example 4: Swelling degree and percentage of extraction at different depths for melted-irradiated (MIR) UHMWPE articular hemispheric wells This example illustrates the degree of swelling and percentage of extraction at different depths for the melted-irradiated (MIR) UHMWPE articular well

189 246 hemispherical, obtained in Example 3. 2 mm x 2 mm x 2 mm samples were cut from the well at various depths along the well axis. These samples were then immersed in decalin at 150 ° C for 24 hours. To prevent sample degradation, an antioxidant (1% N-phenyl-2-naphthylamine) was added. The degree of swelling and the percentage of extraction were calculated based on measurements of the sample weight before the experiment, after 24 hours of swelling and after vacuum drying of the swollen sample. The results are shown in Table 6.

Table 6:

Degree of swelling and percentage of extraction at various depths, fused (MIR), UHMWPE joint hemispherical cavity

<td colspan="3">Degree of swelling</td>

<td>Depth (mm)</td><td>(decalin, 150 ° C, 1 day)</td><td>% Display</td>

<td> 0-2</td><td> 2,43</td><td> 0,0</td>

<td> 2-4</td><td> 2,52</td><td> 0,0</td>

<td> 4-6</td><td> 2,51</td><td> 0,0</td>

<td> 6-8</td><td> 2,64</td><td> 0,0</td>

<td> 8-10</td><td> 2,49</td><td> 0,0</td>

<td> 10-12</td><td> 3,68</td><td> 0,0</td>

<td> &gt; 12</td><td> 6,19</td><td> 35,8</td>

<td>non-irradiated</td><td>It dissolves</td><td>about 100%</td>

The results indicate that UHMWPE in the well was crosslinked to a depth of 12 mm by melting-irradiation to the extent that none of the polymer chains dissolve in hot decalin within 24 hours.

Example 5: Crystallinity and melting point at various depths, melted-irradiated (MIR), UHMWPE of articular hemispheric wells

This example illustrates the crystallinity and melting point at various depths of melted-irradiated (MIR) UHMWPE of the articular hemispheric well obtained in Example 3.

Depth samples were taken from various hemispherical depths along its axis. Crystallinity is a polymer fraction that is crystalline. The calculations were calculated based on the known sample weight (in grams), heat absorbed by the sample during melting (E, in inches, which was measured experimentally using a Differential Scanning Calorimeter, at 10 ° C / min) and the heat of melting polyethylene in 100% crystallinity (AH ° = 69.2 cal / g), using the following equation:

g% crystallinity = JATT ⁰ in-ΔΗ

The melting point is the temperature corresponding to the peak in the DS.C endotherm. The results are shown in Figure 7.

The results indicate that the crystallinity and melting point of the melted-irradiated UHMwPe in the hemispherical joint wells obtained in Example 3 are high

189 246 lower than the corresponding values ​​of the standard UHMWPE, up to a depth of 1 cm (the thickness of the hemispherical joint cavity was 1.2 cm).

Example 6: Second method for the production of melted irradiated (MIR), UHMWPE hemispherical joint cavities

A standard, extruded, raw UHMWPE rod (raw GUR 415 rod, obtained from West Lake Plastics, Lenni, PA), was machined to give a cylinder shape, 4 cm high and 5.2 cm in diameter. One of the circular sides of the cylinder has been machined so as to create a semicircular hole with a diameter of 2.6 cm, so that the axes of the hole and the cylinder closely coincide. This sample was enclosed in an airtight chamber with a thin stainless steel foil (0.001 inch thick) on top. The cylindrical sample was placed in such a way that the semicircular opening was facing the foil. Then, the chamber was purged and filled with low oxygen gas (&lt;0.5 ppm gaseous oxygen) obtained from AIRCO, Murray Hill, NJ). After flushing and filling the chamber, a slow continuous flow of nitrogen was maintained while maintaining the chamber pressure of about 1 atm. Then, the chamber was heated with a 270 W heating jacket, located at the base of the chamber, controlling the heating with a temperature controller and a freak. The chamber was heated in such a way that the temperature on the upper surface of the cylindrical sample increased approximately 1.5 ° C-2 ° C / min, finally reaching an asymptotically stationary temperature state, approximately 175 ° C. The sample was then held at this temperature for 30 minutes before irradiation began.

Irradiation was carried out using a Graaff generator with electrons with 2.5 MeV energy and a dose rate of 1.67 MRau / min. The beam enters the chamber through a thin film on top and bombards the surface of the semi-circular hole. The dose received by the sample was such that the maximum dose of 20 MRad was received about 5 mm below the surface of the polymer which the electrons bombard. After irradiation, heating is discontinued and the samples allowed to cool to room temperature (about 25 ° C), remaining in the chamber under nitrogen atmosphere. The cooling rate was approximately 0.5 ° / min. When the chamber and sample reach room temperature, the sample is removed from the chamber.

Then, this cylindrical sample is machined to give it the shape of a hemispherical joint cavity with dimensions compatible with UHMWPE hemispherical joint cavity with an internal diameter of 26 mm, manufactured by Zimmer Inc., Warsaw, IN, so that the concave surface of the hemispherical hole is re-edged to the articular surface. This method allows for the possibility of relatively large changes in dimensions during melting-irradiation.

Example 7: Electron irradiation of UHMWPE discs

This example illustrates that the electron irradiation of UHMWPE discs gives a heterogeneous absorbed dose profile.

A standard, extruded raw UHMWPE rod (raw rod Hoescht Celanese GUR 415, obtained from West Lake Plastics, Lenni, PA) was used. The GUR 415 resin used to make the rod has a molecular weight of 5,000,000 g / mol and contains 500 ppm calcium stearate. The raw rod was cut into a "hockey puck" shaped roll (height 4 cm, diameter 8.5 cm).

The discs were irradiated at room temperature with an electron beam incident on one of the circular disc bases, using a linear electron accelerator operating at 10 MeV and 1 kW (AECL, Pinawa, Manitoba, Canada) with a scanning width of 30 cm and 0.08 cm / sec. transfer rate Due to the cascade effect, electron beam irradiation leads to a heterogeneous absorbed dose profile. Table 7 shows the calculated values ​​of the observed dose at various depths of the polyethylene sample irradiated with 10 MeV. The absorbed doses were the values ​​measured on the upper surface (surface of the incident e-beam).

189 246

Table 7:

Change in absorbed dose depending on the depth of polyethylene

<td>Depth (mm)</td><td>Absorbed dose (MRad)</td>

<td> 0</td><td> 20</td>

<td> 0,5</td><td> 22</td>

<td> 1,0</td><td> 23</td>

<td> 1,5</td><td> 24</td>

<td> 2,0</td><td> 25</td>

<td> 2,5</td><td> 27</td>

<td> 3,0</td><td> 26</td>

<td> 3,5</td><td> 23</td>

<td> 4,0</td><td> 20</td>

<td> 4,5</td><td> 8</td>

<td> 5,0</td><td> 3</td>

<td> 5,5</td><td> 1</td>

<td> 6,0</td><td> 0</td>

Example 8: Production method for UHMWPE using cold irradiation followed by melting (CIR-SM)

This example is an illustration of a method for producing UHMWPE that has a crosslinked structure and which has essentially no detectable free radicals by cold irradiation followed by melting of UHMWPE.

A standard UHMWPE extruded raw rod (Hoescht Celanese GUR 415, obtained from Westlake Plastics, Lenni, PA) was used. The GUR 415 resin used to make the rod has a molecular weight of 5,000,000 g / mol and contains 500 ppm calcium stearate. The raw rod was cut into a "hockey puck" shaped roll (height 4 cm, diameter 8.5 cm).

The discs were irradiated at room temperature with a dose of 2.5 MRad per transition to 2.5; 5; 7.5; 10; 12.5; 15; 17.5; twenty; 30 and 50 MRad of the total absorbed dose as measured on the upper surface (incident electron beam) (AECL, Pinawa, Manitoba, Canada). The discs were not packaged and the irradiation was carried out in air. After irradiation, the discs were heated to 150 ° C under vacuum for 2 hours so as to melt the polymer and thereby obtain recombination of free radicals, leading to essentially no detectable free radicals. Then, the discs were cooled to room temperature at a rate of 5 ° C / min. The minimum content of free radicals was measured by electron paramagnetic resonance, as described by Jahn et al. In J. Biomedical Materials Reasearch 25: 1005 (1991).

Example 9: Method for producing UHMWPE using heat irradiation followed by melting (WIR-SM)

This example illustrates the method for producing UHMWPE, which has a cross-linked structure and which has essentially no detectable free radicals,

189 246 by irradiation of UHMWPE, which was heated below the melting point, followed by melting of UHMWPE.

A standard, extruded UHMWPE raw rod (Hoescht Celanese GUR 415, obtained from Westlake Plastics, Lenni, PA) was used. The GUR 415 resin used to make the rod had a molecular weight of 5,000,000 g / mol and contained 500 ppm calcium stearate. The raw rod was cut into a "hockey puck" shaped roll (height 4 cm, diameter 8.5 cm).

The discs were heated in an oven to 100 ° C in an atmosphere of air. The heated discs were then irradiated with an electron beam, to a total dose of 20 MRad, at a dose rate of 2.5 MRad per pass (E-Beam Services, Cranbury, NJ), with a scanning width of 30 cm and a transfer rate of 0.08 cm / sec. After irradiation, the discs were heated under vacuum for 2 hours to 150 ° C, which allowed free radical recombination, resulting in essentially no detectable free radicals. Then, the discs were cooled to room temperature at a rate of 5 ° C / min.

Example 10: Method for the production of UHMWPE using heat irradiation and adiabatic melting (WIR-AM)

This example illustrates the method of producing UHMWPE, which has a cross-linked structure and which has essentially no detectable free radicals, by irradiating UHMWPE, which has been heated below the melting point, to create the conditions of adiabatic melting of UHMWPE.

A standard, extruded, raw UHMWPE rod (Hoescht Celanese GUR 415, available from Westlake Plastics, Lenni, PA) was used. The GUR 415 resin used to make the rod had a molecular weight of 5,000,000 g / mol and contained 500 ppm calcium stearate. The raw rod was cut into a "hockey puck" shaped roll (height 4 cm, diameter 8.5 cm).

Two discs were packaged in a glass fiber bag (available from Fisher Scientific Co., Pittsburgh, PA) to minimize heat loss in subsequent process steps. First, the wrapped discs were heated overnight in an air convection oven at 120 ° C. Immediately after removal from the oven, the discs were placed under an electron beam, incident on one of the circular disc bases, from a linear electron accelerator operating at 10 MeV and 1 kW (AECL, Pinawa, Manitoba, Canada) and immediately irradiated to a total dose of 21 and 22.5 MRad, respectively. The dose rate was 2.7 MRad / min. And hence, for 21 MRad, the irradiation lasted 7.8 min, and for 22.5 MRad, the irradiation lasted 8.3 min. After irradiation, the discs were cooled to room temperature at a rate of 5 ° C / minute, at which point the glass fiber pouch was removed and samples were analyzed.

Example 11: Comparison of the properties of sheaves of raw bar UHMWPE GUR 415 and sheaves of raw bar, treated with CIR-SM and WIR-Am

This example illustrates the different properties of irradiated and non-irradiated samples from the raw UHMWPE GUR 415 rod obtained in Examples 8 and 10. The samples tested were as follows: (i) samples (discs) from a crude rod that was irradiated at room temperature and then heated to a temperature of about 150 ° C to completely melt the polyethylene crystals, then cooled to room temperature (CIR-SM), (ii) samples (discs) from a raw rod that were heated to 120 ° C in a glass fiber bag to minimize heat loss from the discs and then immediately irradiated, to produce adiabatic melting of polyethylene (WIR-AM) crystals and (iii) raw control bar (no heating / melting, no irradiation).

A. Fourier transform infrared spectroscopy (FTIR)

Infrared (IR) spectroscopy of the samples was performed using a BioRad UmA 500 infrared microscope on thin sections of samples obtained in Examples 8 and 10. These thin sections (50 frames) were prepared using a microtome. IR spectra of samples taken at 20 pm, 100 pm and 3 mm depth, below the surface of the irradiation of the discs, with a gap size of 10 x 50 pm were tested². Peaks were observed

189 246 from around 1740 to 1700 cm '¹, associated with oxygen-containing groups. And hence, the ratio of the area under the carbonyl peak at 1740 cm 'to the area under the methylene peak at 1460 cm, after deduction of the respective baselines, was a measurement of the degree of oxidation. In tables 8 and 9, oxidation states for the samples described in examples 8 and 10 are collected.

These data indicate that following cross-linking procedures some oxidation occurred within a thin layer of approximately 100 pm thickness. After rejecting this layer by machining, the final product could have the same level of oxidation as the non-irradiated control sample.

Table 8:

Oxidation degree of the samples of Example 8 (CIR-SM) (with vacuum melting after irradiation)

<td>A sample</td><td colspan="3">Oxidation degree at various depths (AU)</td>

<td>Non-irradiated control</td><td> 0,01</td><td> 0,01</td><td> 0,02</td>

<td>Irradiated up to 2.5 MRad</td><td> 0,04</td><td> 0,03</td><td> 0,03</td>

<td>Irradiated to 5 MRad</td><td> 0,04</td><td> 0,03</td><td> 0,01</td>

<td>Irradiated up to 7.5 MRad</td><td> 0,05</td><td> 0,02</td><td> 0,02</td>

<td>Irradiated up to 10 MRad</td><td> 0,02</td><td> 0,03</td><td> 0,01</td>

<td>Irradiated up to 12.5 MRad</td><td> 0,04</td><td> 0,03</td><td> 0,03</td>

<td>Irradiated to 15 MRad</td><td> 0,03</td><td> 0,01</td><td> 0,02</td>

<td>Irradiated to 17.5 MRad</td><td> 0,07</td><td> 0,05</td><td> 0,02</td>

<td>Irradiated to 20 MRad</td><td> 0,03</td><td> 0,02</td><td> 0,01</td>

Table 9:

Oxidation degree of the samples of Example 10 (WIR-AM)

<td>A sample</td><td>20pm</td><td>100 pm</td><td>3 mm</td>

<td>Non-irradiated counter:</td><td> 0,01</td><td> 0,01</td><td> 0,02</td>

<td>Irradiated to 21 MRad</td><td> 0,02</td><td> 0,01</td><td> 0,03</td>

<td>Irradiated to 22.5 MRad</td><td> 0,02</td><td> 0,02</td><td> 0,01</td>

B. Differential scanning calorimetry (DSC)

A Perkin-Elmer DSC7 apparatus with water-ice heat removal and a heating and cooling rate of 10 ° C / minute with continuous nitrogen removal was used. The crystallinity of the samples obtained in Examples 8 and 10 was calculated based on the weight of the sample and the heat of fusion of the polyethylene crystals measured during the first heating cycle. The percentage of crystallinity is expressed by the following equation:

% crystallinity =

E wMT

189 246 where E is the melting heat of the test sample (J or inch), w is the weight (grams) of the test sample and AH ° is the heat of melting polyethylene with 100% crystallinity, (J / gram, 291 J / g or 69.2 inch / g). The temperature corresponding to the endotherm peak was taken as the melting point. In some cases, when there were many endothermic peaks, many melting points, corresponding to these endothermic peaks, were given. The crystallinity and melting points for the samples described in examples 8 and 10 are shown in tables 10 and 11.

Table 10:

DSC at 10 ° Cnin heating rate for the samples of example 8 (CIR-SM)

<td>A sample</td><td>Krystal. (%)</td><td>Temp.top. (° C)</td>

<td>Non-irradiated control</td><td> 59</td><td> 137</td>

<td>Irradiated up to 2.5 MRad</td><td> 54</td><td> 137</td>

<td>Irradiated to 5 MRad</td><td> 53</td><td> 137</td>

<td>Irradiated up to 10 MRad</td><td> 54</td><td> 137</td>

<td>Irradiated to 20 MRad</td><td> 51</td><td> 137</td>

<td>Irradiated up to 30 MRad</td><td> 34</td><td> 137</td>

Table 11:

DSC at a heating rate of 10 ° C / min, for the samples of Example 10 (WIR-AM)

<td>A sample</td><td>Krystal. (%)</td><td>Temp.top. (° C)</td>

<td>Non-irradiated control</td><td> 59</td><td> 137</td>

<td>Irradiated to 21 MRad</td><td> 54</td><td> 120-135-145</td>

<td>Irradiated to 22.5 MRad</td><td> 48</td><td> 120-135-145</td>

The results indicate that the crystallinity does not change significantly up to the MRad dose absorbed. Thus, the elastic properties of the crosslinked material should remain substantially unchanged during crosslinking. On the other hand, it is possible to adapt the properties of elasticity to the needs, by changing the crystallinity with higher doses.

The data also indicate that the WIR-AM material has three melting peaks.

C. Pin-on-disk (POD) experiments to determine the rate of wear

The experiments (POD) were carried out on a bi-axial tester, at a frequency of 2 Hz, where the polymer pins were tested by rubbing wheels with a well-polished Go-Cr disc. Before making cylindrical pins

Find a diameter of 9 mm, nirvana through the screen and the tmlltmeltr with the OiVUlllvu Sili} i xxxxxxy_? XjVXVJilivvłUliU₅ ŁA 1X111 v, jv \ xvii iimiiiiwi t-, surface discs, to remove the outer layer that was oxidized during irradiation and prior and subsequent processing. Then, dowels were punched out of the core of the discs and tested on the POD in such a way that the Co-Cr disc was facing frontally towards the surface of the incident e-beam. These tests were carried out in bovine serum with a total of 2 million cycles. The pins were weighed every 500,000 cycles, and Tables 12 and 13 show the average weight loss values ​​(wear rate) for the samples obtained in Examples 8 and 10, respectively.

189 246

Table 12:

Wear rate POD for samples of example 8 (CIR-SM)

<td>A sample</td><td>Wear rate (mg / million cycles)</td>

<td>Non-irradiated control</td><td> 9,78</td>

<td>Irradiated up to 2.5 MRad</td><td> 9,07</td>

<td>Irradiated to 5 MRad</td><td> 4,80</td>

<td>Irradiated up to 7.5 MRad</td><td> 2,53</td>

<td>Irradiated up to 10 MRad</td><td> 1,54</td>

<td>Irradiated to 15 MRad</td><td> 0,51</td>

<td>Irradiated to 20 MRad</td><td> 0,05</td>

<td>Irradiated up to 30 MRad</td><td> 0,11</td>

Table 13:

Wear rate POD for samples of example 10 (WIR-AM)

<td>A sample</td><td>Wear rate (mg / million cycles)</td>

<td>Non-irradiated control</td><td> 9,78</td>

<td>Irradiated to 21 MRad</td><td> 1,15</td>

The results indicate that the crosslinked UHMWPE has a much higher wear resistance than the non-irradiated control sample.

D. Gel content and degree of swelling

The samples were cut into cubes 2 mm x 2 mm x 2 mm and immersed in xylene at 130 ° C for 24 hours. To prevent sample degradation, an antioxidant (1% N-phenyl-2-naphthylamine) was added to decalin. The swelling ratio and gel content were calculated by weighing the sample before the experiment, after 24 hours of swelling and after vacuum drying the swollen sample. The results are shown in Tables 14 and 15, for the samples obtained in Examples 8 and 10.

Table 14:

Gel content and swelling ratio for the samples of Example 8 (CIR-SM)

<td>A sample</td><td>Zeiu content (%)</td><td>St. spęczn.</td>

<td> 1</td><td> 2</td><td> 3</td>

<td>Non-irradiated control</td><td> 89,7</td><td> 12,25</td>

<td>Irradiated to 5 MRad</td><td> 99,2</td><td> 4,64</td>

189 246

cd of table 14

<td> 1</td><td> 2</td><td> 3</td>

<td>Irradiated up to 10 MRad</td><td> 99,9</td><td> 2,48</td>

<td>Irradiated to 20 MRad</td><td> 99,0</td><td> 2,12</td>

<td>Irradiated up to 30 MRad</td><td> 99,9</td><td> 2,06</td>

Table 15:

Gel content and swelling ratio for the samples of Example 10 (WIR-AM)

<td>A sample</td><td>Gel content (%)</td><td>St. Spęczn</td>

<td>Non-irradiated control</td><td> 89,7</td><td> 12,25</td>

<td>Irradiated to 21 MRad</td><td> 99,2</td><td> 2,84</td>

<td>Irradiated to 22.5 MRad</td><td> 100</td><td> 2,36</td>

The results indicate that the degree of swelling decreases as the absorbed dose increases, indicating an increase in crosslinking density. The increasing gel content indicates the formation of a crosslinked structure.

Example 12: Free radical concentration in UHMWPE produced by cold irradiation with subsequent melting and non-melting (CIR-SM)

This example illustrates the effect of melting, following the cold irradiation of UHMWPE, on the concentration of free radicals. Electron paramagnetic resonance (EPR) tests were carried out on a Bruker ESP 300 EPR spectrophotometer, on samples placed in an airtight tube, in a nitrogen atmosphere, at room temperature, and the tubes used were Taperlok EPR tubes (available from Wilmad Glass Co., Buena, NJ).

Non-irradiated samples do not contain any detectable free radicals. During the irradiation process, free radicals are produced that can survive for at least several years under appropriate conditions.

Cold irradiated UHMWPE samples show a strong free radical signal when tested by EPR. If the same samples were tested by EPR after the melting cycle, it was found that the EPR signal was reduced to undetectable levels. The lack of free radicals in the cold irradiated and then molten (recrystallized) UHMWPE sample means that no further oxidative degradation can occur through attack on trapped radicals.

Example 13: Crystallinity and melting point at different depths for UHMWPE produced by cold irradiation followed by melting (CIR-SM)

This example illustrates the crystallinity and melting point of the crosslinked UHMWPE samples at various depths obtained in Example 8, with a total irradiation dose of 20 MRad. Samples were taken from various depths of crosslinked UHMWPE. The crystallinity and melting point were determined using a differential scanning calorimeter as described in Example 10 (B). The results are shown in Table 16.

189 246

Table 16:

DSC at a heating rate of 10 ° C / min, for the sample of Example 8, irradiated with a total dose of 20 MRad (CIR-SM)

<td>Depth (mm)</td><td>Krystal. (%)</td><td>Temp.top. (° C)</td>

<td> 0-2</td><td> 53</td><td> 137</td>

<td> 6-8</td><td> 54</td><td> 137</td>

<td> 9-11</td><td> 54</td><td> 137</td>

<td> 14-16</td><td> 34</td><td> 137</td>

<td> 20-22</td><td> 52</td><td> 137</td>

<td> 26-28</td><td> 56</td><td> 137</td>

<td> 29-31</td><td> 52</td><td> 137</td>

<td> 37-40</td><td> 54</td><td> 137</td>

<td>Non-irradiated control</td><td> 59</td><td> 137</td>

The results indicate that the crystallinity changes with depth from the surface. A sudden drop at a depth of 16 mm is a consequence of the cascade effect. The peak of absorbed dose was located at a depth of about 16 mm, where the dose level could be so high that reaching 27 MRad.

Example 14: Comparison of UHMWPE, prepared CIR-SM in the air melting variant, with the vacuum melting variant

This example illustrates that the oxidation degrees of UHMWPE discs made by the CIR-SM method, regardless of whether they are melted in air or under a vacuum, are the same as the non-irradiated discs 3 mm below the disc surface.

A standard, extruded, raw UHMWPE rod (Hoescht Celanese GUR 415, available from Westlake Plastics, Lenni, PA) was used. The GUR 415 resin used to make the rod had a molecular weight of 5,000,000 g / mole and contained 500 ppm calcium stearate. The raw rod was cut into a "hockey puck" shaped roll (height 4 cm, diameter 8, 5 cm).

The two discs were irradiated at room temperature with a 2.5 MRad dose per transition to 17.5 MRad total absorbed dose, measured on the upper surface (incident e-beam) (AECL, Pinawa, Manitoba, Canada), at a scanning width 30 cm and a sliding speed of 0.07 cm / sec. The discs were unpackaged and the irradiation was carried out in an air atmosphere. After irradiation, one of the discs was heated under vacuum to 150 ° C for 2 hours and the other was heated in an air atmosphere to 150 ° C for 2 hours to achieve an undetectable crystalline residue and undetectable free radicals. Then, the discs were cooled to room temperature at a rate of 5 ° C / minute, after which they were analyzed for the degree of oxidation as described in Example 11 (A). Table 17 summarizes the oxidation state results collected.

189 246

Table 17:

Oxidation degree of molten samples in air and vacuum

<td colspan="2"></td><td colspan="3">Oxidation degree at various depths (AU)</td>

<td>A sample</td><td>Environment</td><td>20pm</td><td>100 pm</td><td>3 mm</td>

<td>Nienapromien. counter.</td><td>ON</td><td> 0,01</td><td> 0,01</td><td> 0,02</td>

<td>Nienapromien. up to 17.5 MRad</td><td>Vacuum</td><td> 0,07</td><td> 0,05</td><td> 0,02</td>

<td>Nienapromien. up to 17.5 MRad</td><td>Air</td><td> 0,15</td><td> 0,10</td><td> 0,01</td>

The results indicate that within 3 mm below the free surfaces, the oxidation level in the UHMWPE irradiated samples decreases to the level of oxidation observed in the non-irradiated UHMWPE control sample. It was a case independent of the atmosphere (air or vacuum), carried out after irradiation, melting. Thus, melting, which is carried out after irradiation, could be carried out in an air convection oven without oxidizing the core of the irradiated disc.

Example 15: Method for preparing UHMWPE using cold irradiation followed by melting using gamma irradiation (CIR-SM)

This example illustrates a method for producing UHMWPE that has a crosslinked structure and which has essentially no detectable free radicals by cold irradiation with gamma radiation followed by melting of UHMWPE.

A standard, extruded, raw UHMWPE rod (Hoescht Celanese GUR 415, available from Westlake Plastics, Lenni, PA) was used. The GUR 415 resin used to make the rod had a molecular weight of 5,000,000 g / mol and contained 500 ppm calcium stearate. The raw rod was cut into a "hockey puck" shaped roll (height 4 cm, diameter 8.5 cm).

The discs were irradiated at room temperature with a dose of 0.05 MRad / minute to 4 MRad total absorbed dose measured on the upper surface (incident gamma radiation) (Isomedix, Northboro, MA). The discs were unpackaged and the irradiation was carried out in an air atmosphere. After irradiation, the discs were heated under vacuum to 150 ° C. within 2 hours to melt the polymer and thereby obtain recombination of free radicals, which means that there is essentially no detectable free radicals'.

Example 16: I. Method for producing UHMWPE using heat irradiation and partial adiabatic melting with subsequent complete melting (WIR-AM)

This example illustrates a method for producing UHMWPE that has a crosslinked structure, two distinct melting endotherms in a differential scanning calorimeter (DSC) and which has essentially no detectable free radicals, by irradiation of UHMWPE that has been heated to a temperature below the melting point to produce adiabatic partial melting of UHMWPE and by subsequent melting of UHMWPE.

The GUR 4050 crude rod (made of extruded Hoescht Celanese GUR 4050 resin, available from Westlake Plastics, Lenni, PA), was machined into hockey pucks with 8.5 cm diameter and 4 cm thickness. Twenty-five disks, 25 aluminum handles and 25 20 cm x 20 cm fiberglass covers, are preheated to 125 ° C overnight in an air convection oven. Then, each of the preheated discs is placed in a preheated aluminum holder, which is covered with a preheated glass fiber sheath to minimize heat loss to the environment during irradiation. Then, the discs are irradiated

189 246 in air, using 10 MeV, 1 kW electron beam with 30 cm scanning width (AECL, Pinawa, Manitoba, Canada). The travel speed was 0.07 cm / sec, which gave a dose rate of 70 kGy per pass. The discs were irradiated in two passes under the beam to achieve a total, absorbed dose of 140 kGy. In the second pass, the movement of the sliding belt was reversed as soon as the disks were outside the raster area of ​​the electron beam to avoid any heat loss from the disks. After heat irradiation, 15 discs were heated to 150 ° C in 2 hours to achieve complete melting of the crystals and substantial free radical removal.

A. Thermal properties (DSC) of the samples prepared in Example 16

A Perkin-Elmer DSC 7 apparatus with water-ice heat removal and a heating and cooling rate of 10 ° C / minute with continuous nitrogen removal was used. The crystallinity of the samples obtained in Example 16 was calculated based on the sample weight and heat of fusion of polyethylene crystals (69.2 cal / gm). The temperature corresponding to the endotherm peak was taken as the melting point. For several endothermic peaks, several melting points were given.

Table 18 shows changes in the melting behavior and crystallinity of the polymer, depending on the distance from the incident e-beam surface. Figure 8 shows representative DSC melting endotherms obtained 2 cm below the incident e-beam surface obtained before and after further melting.

<td colspan="8">Table 18: Crude bar GUR 1050 after WIR-AM, total dose = 140 kGy, 75 kGy / pass</td>

<td>Depth (Mm)</td><td>T of the 1st peak after irradiation (° C)</td><td>T of the 2nd peak after irradiation (° C)</td><td>T of the 3rd peak after irradiation ( 'C)</td><td>T of the 1st peak after further melting (° C)</td><td>T of the 2nd peak after further melting (° C)</td><td>Kiysta- number after irradiated nating (1)</td><td>crystalline number after further melting (%</td>

<td> 1,77</td><td> 109,70</td><td>NW</td><td> 145,10</td><td> 116,35</td><td> 139,45</td><td> 53,11</td><td> 45,26</td>

<td> 5,61</td><td> 118,00</td><td>NW</td><td> 147,80</td><td> 117,10</td><td> 141,60</td><td> 52,61</td><td> 45,46</td>

<td> 9,31</td><td> 113,00</td><td>NW</td><td> 146,40</td><td> 117,30</td><td> 141,10</td><td> 50,13</td><td> 44,42</td>

<td> 13,11</td><td> 113,47</td><td> 138,07</td><td> 145,23</td><td> 116,03</td><td> 139,83</td><td> 47,29</td><td> 43,33</td>

<td> 16,89</td><td> 113,40</td><td> 137,40</td><td> 144,80</td><td> 115,90</td><td> 139,30</td><td> 47,68</td><td> 43,05</td>

<td> 20,95</td><td> 113,70</td><td> 138,33</td><td> 145,70</td><td> 115,17</td><td> 139,63</td><td> 44,99</td><td> 43,41</td>

<td> 24,60</td><td> 112,40</td><td> 134,20</td><td> 143,90</td><td> 114,90</td><td> 138,70</td><td> 49,05</td><td> 44,40</td>

<td> 28,57</td><td> 112,30</td><td>NW</td><td> 145,70</td><td> 115,90</td><td> 139,90</td><td> 50,84</td><td> 44,40</td>

<td> 31,89</td><td> 111,20</td><td>NW</td><td> 144,50</td><td> 114,90</td><td> 138,80</td><td> 51,88</td><td> 45,28</td>

<td> 34,95</td><td>NW</td><td>NW</td><td> 143,90</td><td> 112,00</td><td> 138,45</td><td> 50,09</td><td> 45,36</td>

<td> 39,02</td><td>NW</td><td>NW</td><td> 139,65</td><td> 114,95</td><td> 138,30</td><td> 49,13</td><td> 46,03</td>

<td colspan="8">* NW: Peak does not occur</td>

These results indicate that in the WIR-AM embodiment, the melting behavior of UHMWPE changes rapidly after a further melting step. Prior to further melting, the polymer shows three melting peaks, whereas after subsequent melting it shows two melting peaks.

B. Electronically magnetic resonance (CEPR) samples of intra-axial samples of influence a6

The EPR test was carried out at room temperature on samples • obtained in example 16, after placing the samples in an air-tight quartz tube

189 246 nitrogen filled. A Bruker ESP 300 EPR spectrophotometer and Taperlok EPR tubes (available from Wrlmad Glass Co., Buen a, NJ) were used.

Non-irradiated samples do not contain any detectable free radicals. When irradiated, they generate free radicals that can survive for at least several years under appropriate conditions.

Before further melting, the EPR results showed a composite peak of free radicals, consisting of both peroxy radicals and primary free radicals. After subsequent melting, the EPR signal of free radicals was reduced to an indeterminable level. These results indicate that the free radicals generated during irradiation were substantially eliminated after a further melting step. Thus, UHMWPE was very resistant to oxidation.

Example 17: II. Method for producing UHMWPE using heat irradiation and adiabatic partial melting with subsequent complete melting (WIR-AM)

This example illustrates a method for producing UHMWPE that has a crosslinked structure, two distinct melting endotherms in DSC, and which has essentially no detectable free radicals, by irradiating UHMWPE, which has been heated to a temperature below the melting point, to cause adiabatic partial melting of UHMWPE and further UHMWPE melting.

The raw GUR 4020 rod (made of extruded Hoescht Celanese GUR 4020 resin, available from Westlake Plastics, Lenni, PA), was machined into hockey pucks 8.5 cm in diameter and 4 cm thick. Twenty-five discs, 25 aluminum handles and 25 (20 cm x 20 cm) fiberglass covers are preheated to 125 ° C overnight in an air convection oven. Then, each of the preheated discs is placed in a preheated aluminum holder that has been covered with a preheated glass fiber sheath to minimize heat loss to the environment during irradiation. Next, the discs are irradiated in an air atmosphere, using 10 MeV, 1 kW electron beam with 30 cm scanning width (AECL, Pinawa, Manitoba, Canada). The travel speed was 0.07 cm / sec, which gave a dose rate of 70 kGy per pass. The discs were irradiated in two passes under the beam to achieve a total, absorbed dose of 140 kGy. In the second pass, the movement of the sliding belt was reversed as soon as the disks were outside the raster area of ​​the electron beam to avoid any heat loss from the disks. After heat irradiation, 15 discs were heated to 150 ° C in 2 hours to achieve complete melting of the crystals and substantial free radical removal.

Example 18: 1Π. Method for producing UHMWPE using heat irradiation and adiabatic partial melting followed by complete melting (WIR-AM)

This example illustrates a method for producing UHMWPE that has a crosslinked structure, two distinct melting endotherms in DSC, and which has essentially no detectable free radicals, by irradiating UHMWPE, which has been heated to a temperature below the melting point, to cause adiabatic partial melting of UHMWPE, and then melting UHMWPE.

The raw GUR 1050 rod (made of extruded Hoescht Celanese GUR 1050 resin, available from Westlake Plastics, Lenni, PA), was machined into hockey pucks 8.5 cm in diameter and 4 cm thick. Eighteen discs, 18 aluminum handles and 18 (20 cm x 20 cm) fiberglass covers, preheated to 125 ° C, 90 ° C or 70 ° C overnight in an air convection oven. Six discs were preheated at each temperature. Then, each of the preheated discs is placed in a preheated aluminum holder that has been wrapped in a preheated glass fiber sheath to minimize heat loss to the environment during irradiation. Then, the discs are irradiated in the atmosphere

189 246 air, using 10 MeV, 1 kW electron beam with 30 cm scanning width (AECL, Pinawa, Manitoba, Canada). The travel speed was 0.06 cm / sec, which gave a dose rate of 75 kGy per pass. The discs were irradiated in two passes under the beam to achieve a total absorbed dose of 150 kGy. In the second pass, the movement of the sliding belt was reversed as soon as the disks were outside the raster area of ​​the electron beam to avoid any heat loss from the disks. After heat irradiation, half of the discs were heated to 150 ° C within 2 hours to achieve complete melting of the crystals and the actual elimination of free radicals.

A. Thermal properties of the samples produced in example 18

A Perkin-Elmer DSC 7 apparatus with water-ice heat removal and a heating and cooling rate of 10 ° C / minute with continuous nitrogen removal was used. The crystallinity of the samples obtained in Example 18 was calculated based on the sample weight and heat of fusion of polyethylene crystals (69.2 cal / g). The temperature corresponding to the endotherm peak was taken as the melting point. For several endothermic peaks, several melting points were given.

Table 19 shows the effect of preheating temperature on melting behavior and polymer crystallinity. Fig. 9 shows DSC profiles of a WIR-AM processed disk with a preheat temperature of 125 ° C, both before and after further melting.

<td colspan="8">Table 19: Raw bar GOR 1050 after WIR-AM, total dose = 150 kGy, 75 kGy / pass</td>

<td>Heating preliminary (° C)</td><td>T 1st peak after irradiated nating CC)</td><td>T 2nd peak after irradiated nating (° C)</td><td>T 3rd peak after irradiated nating CC)</td><td>T 1st peak after further melting CC)</td><td>T 2nd peak after further melting CC)</td><td>crystalline cardinality after irradiated nating (%)</td><td>crystalline cardinality after further melting (and)</td>

<td> 125</td><td> 114,6</td><td> 135,70</td><td> 143,5</td><td> 114,85</td><td> 135,60</td><td> 42,81</td><td> 40,85</td>

<td> 90</td><td>NW</td><td> 142,05</td><td>NW</td><td> 116,75</td><td> 136,95</td><td> 52,39</td><td> 44,31</td>

<td> 70</td><td>NW</td><td> 141,85</td><td>NW</td><td>NW</td><td> 136,80</td><td> 51,59</td><td> 44,62</td>

<td colspan="8">* NW: Peak does not occur</td>

These results indicate that in the WIR-AM embodiment, the melting behavior of UHMWPE changes rapidly after a further melting step. Prior to subsequent melting, the polymer shows three melting peaks, whereas after subsequent melting it shows two melting peaks.

Example 19: IV. Method for producing UHMWPE using heat irradiation and adiabatic partial melting with subsequent complete melting (WIR-AM)

This example illustrates a method for producing UHMWPE which has a crosslinked structure, two distinct melting endotherms in DSC, and which has essentially no detectable free radicals, by irradiation of UHMWPE, which has been heated to a temperature below the melting point, to cause adiabatic partial melting of UHMWPE and by subsequent melting of the polymer.

189 246

The raw GUR 1020 rod (made of extruded Hoescht Celanese GUR 1020 resin, available from Westlake Plastics, Lenni, PA), was machined into 7.5 cm diameter and 4 cm thick hockey pucks. Ten discs, 10 aluminum handles and 10 (20 cm x 20 cm) fiberglass covers are preheated to 125 ° C overnight in an air convection oven. Each preheated disc is placed in a preheated aluminum holder that has been wrapped, preheated, with a fiberglass sheath to minimize heat loss to the environment during irradiation. Then, the discs are irradiated in an air atmosphere using 10 MeV, 1 kW linear electron beam accelerator (AECL, Pinawa, Manitoba, Canada). The scanning width and speed were adjusted to achieve the desired dose rate per pass. Then, the discs were irradiated to 61, 70, 80, 100, 140 and 160 kGy of the total absorbed dose. For absorbed doses of 61, 70, 80 kGy, irradiation was completed after one pass; while for doses 100, 140 and 160 it was completed after two passes. For each of the absorbed doses, six discs were irradiated. During the two pass experiments, in the second pass, the movement of the sliding tape became the reverse as soon as the discs were outside the raster area of ​​the electron beam to avoid any heat loss from the discs. After irradiation, half the discs were heated to 150 ° C for 2 hours in an air convection oven to achieve complete melting of the crystals and the actual elimination of free radicals.

Example 20: V. Method for producing UHMWPE using heat irradiation and adiabatic partial melting with subsequent complete melting (WIR-AM)

This example illustrates a method for producing UHMWPE, which has a crosslinked structure, two distinct melting endotherms in DSC, and which has essentially no detectable free radicals, by irradiating UHMWPE, which has been heated to a temperature below the melting point, to cause adiabatic partial melting of UHMWPE and by subsequent melting of the polymer.

The raw GUR 4150 rod (made of extruded Hoescht Celanese GUR 4150 resin, available from Westlake Plastics, Lenni, PA), was machined into 7.5 cm diameter and 4 cm thick hockey pucks. Ten discs, 10 aluminum handles and 10 (20 cm x 20 cm) fiberglass covers are preheated to 125 ° C overnight in an air convection oven. Each preheated disc is placed in a preheated aluminum holder that has been wrapped in a preheated glass fiber sheath to minimize heat loss to the environment during irradiation. Then, the discs are irradiated in an air atmosphere using 10 MeV, 1 kW linear electron beam accelerator (AECL, Pinawa, Manitoba, Canada). The scan width and feed rate were set to achieve the desired dose rate per pass. Then, the discs were irradiated to 61, 70, 80, 100, 140 and 160 kGy of the total absorbed dose. Six discs were irradiated for each dose absorbed. For absorbed doses of 61, 70, 80 kGy, irradiation was completed after one pass; while for doses 100, 140 and 160 it was completed after two passes.

After irradiation, three discs from each series irradiated with different amounts of absorbed doses were heated to 150 ° C for 2 hours to completely melt the crystals and reduce the concentration of free radicals to an undetectable level.

A. Properties of the samples produced in Example 20

A Perkin-Elmer DSC 7 apparatus with water-ice heat removal and a heating and cooling rate of 10 ° C / minute with continuous nitrogen removal was used. The crystallinity of the samples obtained in Example 20 was calculated based on the sample weight and heat of fusion of polyethylene crystals 289.7 J / g (69.2 cal / g). The temperature corresponding to the endotherm peak was taken as the melting point. For several endothermic peaks, several melting points were given.

189 246

The results obtained are presented in Table 20 as a function of the total absorbed dose. They indicate that the crystallinity decreases as the dose size increases. For the tested doses of absorbed doses, the polymer has two melting peaks (Tj = = 118 ° C, T2 = ~ 137 ° C) after a further melting step.

<td>Table 20:</td><td colspan="7">Raw GUR 4150 rod after WIR-AM</td>

<td>Dose</td><td>T 1st</td><td>T of the 2nd peak</td><td>T 3rd</td><td>T 1st</td><td>T 2nd</td><td>crystalline</td><td>crystalline</td>

<td>irradiated</td><td>peak after</td><td>after</td><td>peak after</td><td>peak after</td><td>peak after</td><td>cardinality</td><td>cardinality</td>

<td></td><td>irradiated</td><td>irradiated</td><td>irradiated</td><td>further</td><td>further</td><td>after</td><td>after further</td>

<td>Nanny</td><td>nating</td><td>nating</td><td>nating</td><td>melting</td><td>melting</td><td>irradiated</td><td>melting</td>

<td>(KGy)</td><td>(° C)</td><td>(° C)</td><td>(° C)</td><td>(° C)</td><td>(° C)</td><td>nating</td><td> (%)</td>

<td></td><td></td><td></td><td></td><td></td><td></td><td> (%)</td><td></td>

<td> 160</td><td> 113,4</td><td> 135,10</td><td> 143,20</td><td> 114</td><td> 135,90</td><td> 41,97</td><td> 39,58</td>

<td> 140</td><td> 114,6</td><td> 135,10</td><td> 143,60</td><td> 116,2</td><td> 138,60</td><td> 45,25</td><td> 41,51</td>

<td> 100</td><td> 118,7</td><td> 125,10</td><td> 143,50</td><td> 118,2</td><td> 138,20</td><td> 47,18</td><td> 42,58</td>

<td> 80</td><td> 115,7</td><td>NW</td><td> 143,00</td><td> 119,1</td><td> 137,60</td><td> 50,61</td><td> 44,52</td>

<td> 70</td><td> 114,8</td><td>NW</td><td> 141,40</td><td> 118,9</td><td> 137,00</td><td> 52,36</td><td> 44,95</td>

<td> 61</td><td> 114,6</td><td>NW</td><td> 140,20</td><td> 119,1</td><td> 136,00</td><td> 53,01</td><td> 45,04</td>

<td colspan="8">* NW: Peak does not occur</td>

Example 21: Temperature rise during WIR-AM

This example demonstrates that the increase in temperature during heat irradiation leads to adiabatic partial or complete melting of UHMWPE.

The raw GUR 4150 rod (made of extruded Hoescht Celanese GUR 4150 resin, available from Westlake Plastics, Lenni, PA), was machined into a hockey disc 8.5 cm in diameter and 4 cm thick. In the center of the disk a hole was drilled in which a K-type thermocouple was placed. Then, the disk was preheated to 130 ° C in a convection oven in an air atmosphere, then irradiated with 10 MeV, 1 kW electron beam (AECL, Pinawa, Manitoba, Canada). The irradiation is carried out in air, with a scanning width of 30 cm. The dose rate was 27 kGy / min, and the disc remained stationary under the beam. During irradiation, disc temperature was measured continuously.

Figure 10 shows the temperature increase in the disk during the irradiation process. The initial temperature is the pre-heating temperature (130 ° C). As soon as the beam is directed, the temperature increases and during this time the UHMWPE crystals melt. Smaller crystals melt, starting at 130 ° C, indicating that partial melting occurs when heated. At a temperature of about 145 ° C, when a sudden change in heating behavior occurs, complete melting is obtained. After exceeding this point, the temperature continues to rise in the molten material.

The example of linen shows that during the WIR-AM process, the amount of absorbed dose (during irradiation) can be adjusted, either for partial or complete melting of the polymer. In the first case, melting can be completed by an additional furnace melting step to eliminate free radicals.

Example 22: Method for the production of UHMWPE using cold irradiation and adiabatic heating with subsequent complete melting (CIR-AM)

This example illustrates a method for producing UHMWPE that has a cross-linked structure and has essentially no detectable free radicals by irradiation.

189 246

UHMWPE with a sufficiently high dose rate to induce adiabatic heating of UHMWPE and by subsequent melting of the polymer.

The raw GUR 4150 rod (made of extruded Hoescht Celanese GUR 4150 resin, available from Westlake Piastics, Lenni, PA), was machined into hockey pucks 8.5 cm in diameter and 4 cm thick. Twelve discs were irradiated stationary, in air, at a dose rate of 60 kGy / min, using 10 MeV, 30 kW electron beam (E-Beam Service, Cranbury, NJ). Six discs were irradiated with a total dose of 170 kGy, while the remaining six were irradiated with a total dose of 200 kGy. After the irradiation, the disc temperature was above 100 ° C.

After irradiation, one disc from each series was heated to 150 ° C for 2 hours to melt all crystals and reduce the concentration of free radicals to an undetectable level.

A. Thermal properties of the samples produced in example 22

A Perkin-Elmer DSC 7 apparatus with water-ice heat removal and a heating and cooling rate of 10 ° C / minute with continuous nitrogen removal was used. The crystallinity of the samples obtained in Example 22 was calculated based on the sample weight and heat of fusion of polyethylene crystals (69.2 cal / gm). The temperature corresponding to the endotherm peak was taken as the melting point,

Table 21 shows the effect of the total absorbed dose on the thermal properties of UHMWPE CIR-AM, both before and after the further melting step.

Table 21:

Raw GUR 4150 rod after CIR-AM

<td>Dose irradiation (KGy)</td><td>T peak after irradiation (° C)</td><td>T peak after further melting (° C)</td><td>Crystallinity after irradiation (%)</td><td>Crystallinity after further melting (%)</td>

<td> 170</td><td> 143,67</td><td> 137,01</td><td> 58,25</td><td> 45,27</td>

<td> 200</td><td> 143,83</td><td> 136,73</td><td> 54,74</td><td> 43,28</td>

Example 23: Comparison of tensile deformation under non-irradiated UHMWPE, cold irradiated and later molten UHMWPE (CIR-SM) and heat irradiated and partially melted adiabatically and later molten UHMWPE (WIR-AM)

In this example, the tensile deformations of UHMWPE were compared in non-irradiated form and in irradiated forms produced by the CIR-SM and WIR-AM methods.

To produce "dog bone" samples, ASTM D638 Type V was used for the tensile test. The tensile test was performed on an Instron 4120 Universal Tester with a ripper head speed of 10 mm / min. The linear tensile strain was calculated based on load displacement data in accordance with ASTM D638.

Samples of "dog bones" were produced by machining GUR 4150 hockey pucks (made of Hoescht Celanese GUR 4150 piston-extruded resin, available from Westlake Plastics, Lenni, PA), which were processed using the CIR-Sm and WIR-AM methods. For CIR-SM, the method described in Example 8 was used, and for WIR-AM, the method described in Example 17 was used. In both cases, the total dose administered was 150 kGy.

Figure 11 shows the tensile behavior obtained for the non-irradiated control, CIR-SM and WIR-AM treated samples. It shows different behavior of tensile deformation, although it was carried out in both methods

189 246 irradiation to 150 kGy. This difference is related to the two-phase structure produced using the WIR-AM method.

Those skilled in the art will be able to ascertain, by means of only routine experiments, many equivalent equivalents to the specific embodiments described. Both these and all other equivalent embodiments are covered by the following claims.

<img file="PL189246B1_D0001.tif" />

Figure 4

<img file="PL189246B1_D0002.tif" />

Figure 7

189 246

<img file="PL189246B1_D0003.tif" />

Fig. 5

<img file="PL189246B1_D0004.tif" />

Fig. 6

189 246

<img file="PL189246B1_D0005.tif" />

<img file="PL189246B1_D0006.tif" />

Temperature (° C)

Fig. 9

189 246

Stretching (ΜΡα | Temperature (%)

<img file="PL189246B1_D0007.tif" />

Fig. 10

<img file="PL189246B1_D0008.tif" />

Fig 11

deformation

189 246

<img file="PL189246B1_D0009.tif" />

Fig. 1

<img file="PL189246B1_D0010.tif" />

<img file="PL189246B1_D0011.tif" />

Fig. 3

UP Department of Publications. Circulation of 50 copies

Price PLN 6.00.