Electron beam sterilization of medical devices

ES 2 413 655 T3

DESCRIPTION

Electron beam sterilization of medical devices

The present invention relates to medical devices comprising bioactive surfaces, provided with a bioactive heparin coating and, more particularly, to procedures for sterilizing medical devices comprising bioactive surfaces, while in their packaging, using beam sterilization techniques. of electrons.

Numerous metallic materials and polymeric materials have been used in the manufacture of implantable medical devices, as well as coatings in implantable medical devices. Often times, coatings and surface modifications of the same or different compositions are used to further improve the biocompatibility, hemocompatibility, and functionality of implantable medical devices. Typically, the coating or surface modification of these devices requires the performance of various processing steps. The substrates modified by each of these procedures, as well as the surface coatings require some form of terminal sterilization to ensure the sterility of the products for use on a patient. Sterilization procedures used today for metal devices can have potential drawbacks, for example, decreased stability and coating functions, when used on coated devices, as the coating materials may not be compatible with these procedures. traditional sterilization systems.

Different surface modification procedures have been documented in the literature in order to obtain a favorable host-material response. Coating techniques for medical devices, particularly those that come into contact with blood, such as stents, that do not address the problem of subsequent sterilization are described in documents US-4656083, US-5034265, US-5132108, US- 5244654 and US-5409696. Palmaz et al., In a review of intravascular stents, are skeptical about the use of stent coatings (Palmaz, J., F. Rivera and C. Encamacion. Intravascular Stents, Adv. Vasc. Surg., 1993, 1: 107-135). However, Kocsis et al. Report that the use of heparin-coated stents was effective in reducing the thrombogenicity of the stent surface (Kocsis,

J., G. Llanos and E. Holmer. Heparin-Coated Stents, J. of Long-Term Effects of Medical Implants, 2000, 10 19-45).

Typical surface modifications include hydrophilic and / or hydrogel coatings, such as polyvinyl pyrrolidone (PVP), polyethylene glycol (PEG), or hyaluronic acid (HA), on the surface of cardiovascular implants, such as stents and pacemakers, or permanent medical devices. prolonged, topical wound healing applications, contact lenses, intraocular lenses, etc. Hydrophobic or lubricating coatings are used for medical devices, such as coronary or neurovascular guide wires, sutures, needles, catheters, and trocars. Bio-active coatings are used for a targeted cellular response, such as cell adhesion molecules (CAMs, such as RGD (Arg-Glu-Asp amino acid sequence), laminin, collagen, etc.) in tissue engineering applications or adhesion prevention coatings for use in medical devices, such as vena cava filters or small diameter vascular grafts. The coating materials also include infection resistant agents or antimicrobial agents. Some coatings also allow for sustained drug release, such as sustained drug release from stents, or as a hydrophobic coating to extend the release time of a drug loaded reservoir. Bioactive coatings containing therapeutic agents, such as heparin, phosphorylcholine (PC), urokinase, and the like, can be used for antithrombogenic properties.

Coatings can be used to deliver therapeutic and pharmaceutical agents including natural products including antiproliferative / antimitotic agents, such as vinca alkaloids (i.e. vinblastine, vincristine and vinorelbine), paclitaxel, epidipodophyllotoxins (i.e. etoposide, teniposide), antibiotics ( dactinomycin (actinomycin D) daunorubicin, doxorubicin and idarubicin), anthracyclines, mitoxantrone, bleomycins, plicamycin (mithramycin) and mitomycin, enzymes (L-asparaginase that systemically metabolizes L-asparagine and deprives cells that do not have the ability to synthesize their own asparagine; antiproliferative / antimitotic alkylating agents, such as nitrogen mustards (mechlorethamine, cyclophosphamide and analogs, melphalan, chlorambucil), ethyleneimines and methylmelamines (hexamethylmelamine and thiotepa), alkyl sulfonates-busulfan, nitrosoureas (carmustine), and analogs -dacarbazinine (DTIC); antiproliferative / antimitotic antimetabolites such as folic acid analogs (methotrexate), pyrimidine analogs (fluorouracil, floxuridine, and cytarabine), purine analogs, and related inhibitors (mercaptopurine, thioguanine, pentostatin, and 2-chlorodeoxyadenosine}); {cladribine}; platinum coordination complexes (cisplatin, carboplatin), procarbazine, hydroxyurea, mitotane, aminoglutethimide; hormones (i.e. estrogen); anticoagulants (heparin, synthetic heparin salts, and other thrombin inhibitors), fibrinolytic agents (such as tissue plasminogen activator, streptokinase, and urokinase), aspirin, dipyridamole, ticlopidine, clopidogrel, abciximab; antimigration; antisecretory (breveldin), anti-inflammatory: such as adrenocortical steroids (cortisol, cortisone, fludrocortisone, prednisone, prednisolone, 6c (-iTiethylprednisolone, triamcinolone, betamethasone and dexamethasone), non-steroidal agents (i.e. aspirin derivatives, salicylic acid derivatives) para-aminophenol ie acetaminophen; Indole and indene acetic acids (indomethacin, sulindac and etodalac), heteroaryl acetic acids (tolmetin, diclofenac and ketorolac), arylpropionic acids (ibuprofen and derivatives), anthranilic acid (mefenamic acid and meclofenamic acid), enolic acids (piroxicam, tenoxicam, phenylbutazone, phenylbutazone and oxyphentatrazone), nabumetone,

ES 2 413 655 T3 gold compounds (auranofin, aurothioglucose, gold sodium thiomalate); immunosuppressants: (cyclosporine, tacrolimus (FK-506), sirolimus (rapamycin), azathioprine, mycophenolate mofetil); angiogenic: vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF); nitric oxide donors; antisense oligonucleotides and their combinations.

Coatings can be formulated by mixing one or more therapeutic agents with the polymeric coating mixture. The therapeutic agent can be present as a liquid, a finely divided solid, or any other appropriate physical form. Optionally, the coating mixture can include one or more additives, for example non-toxic auxiliary substances such as diluents, carriers, excipients, stabilizers or the like. Other suitable additives can be formulated with the polymer and the pharmaceutically active agent or compound. For example, a hydrophilic polymer can be added to a biocompatible hydrophobic coating to modify the release profile, or a hydrophobic polymer can be added to a hydrophilic coating to modify the release profile. An example would be the addition of a hydrophilic polymer selected from the group consisting of polyethylene oxide (PEO), PVP, polyethylene glycol (PEG), carboxymethyl cellulose and hydroxymethyl cellulose to a coating of hydrophobic (co) polymer to modify the profile of release. Appropriate relative amounts can be determined by monitoring the in vitro and / or in vivo release profiles for the therapeutic agents.

Typically, surface modification procedures include a surface activation step followed by the coupling of the desired molecule. Typically, surface activation is achieved by an energy-assisted gas phase reaction (plasma, pulsed plasma, flow discharge reactive chemistry (FDRC), corona discharge, etc.) and / or substrate activation with a highly reactive leaving group (N-OH of succinimide, imidazole, etc.); surface functionalization with self-assembling molecules (SAMs, functional silanes and thiols); controlled hydrolysis of esters and amides on the surface (polyethylene terephthalate (PET), polylactic acid (PLA), polyglycolic acid (PGA), PLGA, etc.). Typically, coupling reactions are performed by carbodiimide chemistry, reductive amination, maleimide-thiol reactions, etc.

Typically, photochemical surface modifications are preferable since typically this procedure does not require a prior surface activation step. Aryl ketone-based chemistry, azide-based chemistry, and acrylate-based chemistry may be suitable for surface modification.

Regardless of the type of coating, sterilization of the final product, as noted above, can cause potential problems. Conventional sterilization procedures, such as hot water vapor, radiation (gamma and electron beam), and ethylene oxide, can adversely affect the activity of the coating. For example, medical devices are typically sterilized by a terminal sterilization procedure, such as ethylene oxide (EtO) sterilization, gamma sterilization, or, more recently, electron beam sterilization. EtO sterilization does not significantly affect metal- or polymer-based medical products, such as first-generation catheters, metal stents, and drug-eluting stents. EtO is a lengthy and often cumbersome procedure that requires fine tuning of procedure parameters such as duration, temperature, humidity, carrier gas to moisture ratio, and extensive degassing procedures to remove residual EtO after the procedure. More importantly, the very mechanism by which EtO kills pathogens (nucleic acid disruption) in the presence of moisture can also be detrimental to sensitive chemicals and most biological molecules. Proteins, peptides, and gene products are the most prone to destruction by EtO. Gamma sterilization, which does not involve moisture, involves an extremely high amount of energy, which may make it undesirable for use in sterilizing most devices containing biologics and drug device combination products. Electron beam sterilization, which is electrically generated gamma radiation, also involves a large amount of energy and is also known to be potentially destructive to many biologically active materials.

Ethylene oxide sterilization (using EtO mixed with steam) is known to reduce the activities of biologically active surfaces, such as heparin-coated surfaces. Furthermore, the presence of water vapor in the EtO process is also known to have a negative impact on the shelf life of sterile medical devices containing heparin surfaces. Other energy-intensive procedures such as gamma and electron beam sterilization procedures have been shown to cause a reduction in the activity of bioactive coatings, for example, as described in US6787179.

Experience with heparin-coated stents and EtO sterilization has shown that this type of sterilization procedure is difficult to control and can cause a considerable reduction in heparin activity. EtO can also cause fluctuations in heparin activities from one manufacturing plant to another. Small changes in EtO sterilization conditions could lead to wide variation in heparin activity and, consequently, specification of release and shelf life of heparin-coated stents.

ES 2 413 655 T3

In the age of the drug eluting stent, heparin and other bioactive coatings or surfaces will be close to a drug, such as sirolimus, and the drug carrier, such as PLGA polymers. In addition to the sensitivity of heparin towards EtO, both sirolimus and biodegradable polymers are known to retain substantial amounts of EtO after processing. Furthermore, PLGA degrades by hydrolysis by the moisture required in the EtO process. Therefore, it is advantageous to use alternative methods, such as electron beam, to terminally sterilize heparin-coated drug elution devices. In the literature, the use of a high energy method, such as electron beam, to sterilize a pharmaceutical product containing a biological substance and / or device-drug combination products is generally not advised. Instead, expensive, aseptically manufactured filtration / lyophilization procedures are typically used to ensure the sterility of the final packaged products.

WO-A-2004/066876 discloses a method of packaging a coated stent in which a moisture scavenger is included in the package. The container is treated with an inert gas and evacuated. It is then sealed and sterilized by exposure to gamma radiation or using ethylene oxide.

Given the above limitations of conventional sterilizations that include ethylene oxide, electron beam, and gamma radiation procedures, these have not been routinely used to sterilize medical devices that contain a biologically active component, such as a heparin coating. Consequently, there is a need for a convenient terminal sterilization procedure that ensures both the sterility of a medical device and the activities of its biological coating.

The present invention relates to a method of sterilizing a medical device having a surface that includes a bioactive material including heparin, as defined in claim 1.

The present invention relates to an electron beam process, which is a process involving large amounts of energy that is normally used to sterilize medical products with or without a biological component, which can be used to maintain the biological activities of a coating. superficial heparin. Within an optimal range, the energy of the electron beam unexpectedly retains and reactivates the biological functions of a heparin coating. This procedure can also be used as an effective means of extending the shelf life of immobilized and probably free forms of heparin. The present invention has broad applications in the sterilization of medical devices with a heparin surface and other heparin-based pharmaceuticals.

The present invention also demonstrates that the electron beam process, when properly controlled, not only maintains the biological activity of the heparin coating, but also reverses the loss of heparin activity during a manufacturing process of an elution stent. drug involving exposure to solvents and prolonged drying at elevated temperatures. In a controlled experiment, it was also found that an electron beam procedure at a dose of 25 kGy recovered the lost biological activity of heparin during and / or after long-term storage. Thus, the present invention may have potential for the maintenance of heparin in other forms, and may become a simple procedure for extending the shelf life of the product by reprocessing using an electron beam procedure.

An unexpected discovery of the present invention is that, with the processing steps used, the activity of a heparin coating on the surface of a medical device or in reservoirs in a medical device was not reduced as predicted in the literature and it had been reported by others. Heparin activity, as determined by both modified FXa and antithrombin binding assays, has consistently shown unexpected increases after electron beam processing, proportional to the electron beam dose used, as explained in detail below.

The present invention solves a critical, long-standing problem of destroying or decreasing the activity of a biological molecule, such as heparin, associated with a medical device by means of an electron beam sterilization procedure. It is also far superior to more conventional sterilization techniques, such as ethylene oxide sterilization, which is known to severely reduce the activities of a heparin coating.

In general, the method of the present invention comprises packaging a medical device containing a bioactive heparin surface with nitrogen under vacuum conditions and drying agents, and sterilizing the medical device by an electron beam procedure with a suitable dose of radiation. . More specifically, the devices for sterilization will be packaged on a catheter spool to prevent damage during shipping and transportation. Each spool is individually sealed in a bag. When the device is positioned within the bag, it is evacuated and purged with a non-reactive gas, such as nitrogen. The vacuum is made again and the bag is sealed. Although the method can be used on any number of substrates, for the sake of ease of explanation, exemplary embodiments of the method will be described with respect to a stent.

ES 2 413 655 T3

In an exemplary embodiment of the invention, the substrate material can include a metal, a non-metal, a polymer, or a combination of metal and polymer. In a preferred exemplary embodiment, the substrate material is selected from the group including stainless steel, aluminum, nitinol, cobalt chromium, and titanium, and similar metal alloys. In an alternative embodiment, the material is selected from the group that includes glass, silica, and ceramic. A preferred embodiment includes a CoCr alloy (L605) coronary stent, which also has deposits on the struts.

Embodiments of the invention are described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is an isometric view of an expandable medical device.

Figure 2 is a graphical representation of the effect of electron beam radiation on heparin activity, as measured by the antithrombin III uptake assay.

Figure 3 is a graphical representation of the effect of electron beam radiation on heparin activity, as measured by the anti factor Xa assay.

Figure 4 is a graphical representation of the effect of electron beam radiation on the surface density of heparin.

With reference to the drawings, Figure 1 shows an expandable medical device or stent having a plurality of ports containing a beneficial agent for delivery to tissue via the expandable medical device. The expandable medical device 100 shown in Figure 1 is cut from a tube of material to form an expandable cylindrical device. The expandable medical device 100 includes a plurality of cylindrical sections 102 interconnected by a plurality of bridging elements 104. Bridge elements 104 allow the tissue support device to flex axially as it passes through the tortuous path of the vasculature to a deployment site and allow the device to flex axially when necessary to accommodate the curvature of a lumen. to endure. Each of the cylindrical sections 102 is formed by a network of elongated struts 108 that are interconnected by ductile hinges 110 and circumferential struts 112. During expansion of the medical device 100, the ductile joints 110 deform, while the struts 108 are not deformed.

As shown in Figure 1, elongated struts 108 and circumferential struts 112 include openings 114, some of which contain a benefit agent for delivery to the lumen in which the expandable medical device is implanted. In addition, other parts of device 100, such as bridge elements 104, may also include openings. Preferably, the openings 114 are provided in the non-deforming parts of the device 100, such as the struts 108, so that the openings are not deformed and the beneficial agent is delivered without risk of being fractured, ejected, or otherwise damaged. during device expansion

Devices of the invention can be further refined by using finite element analysis and other techniques to optimize the deployment of beneficial agents within apertures 114. Basically, the shape and location of apertures 114 can be modified to maximize the volume of the voids while preserving the relatively high strength and stiffness of the struts relative to the ductile joints 110. According to a preferred exemplary embodiment of the present invention, the apertures have an area of ​​at least 0.0032 mm²(5 x 10^-6 inches²) and preferably at least 0.0045 mm² (7 x 10^-6 inches²). Typically, the openings are filled from about 50 to about 95% of their full capacity with beneficial agent.

Different benefit agents may be provided in the various openings in the expandable device, or benefit agents may be provided in some openings and not others. Combinations of beneficial agents or therapeutic agents can be used in individual openings. Because each opening is independently filled, individual chemical compositions and pharmacokinetic properties can be imparted to the benefit agent in each opening.

The substrate material may also contain additional polymeric material that serves as a matrix to control the release of a pharmaceutical agent in or on the medical device. The polymer can be biostable, such as the group including polyacetal, polyurethane, polyester, polytetrafluoroethylene, polyethylene, polymethylmethacrylate, polyhydroxyethyl methacrylate, polyvinyl alcohol, polypropylene, polymethylpentene, polyetherketone, polycarbonyloxyphenylene, polyvinyl chloride, polyvinyl acetate, polycarbonyloxychloride, polyvinyl chloride, polycarbonate butadiene-styrene, polyetherimide, polyvinylidene fluoride and copolymers and their combinations. The material can be selected from the group including polysiloxane, fluorinated polysiloxane, ethylene-propylene rubber, fluoroelastomer, and combinations thereof. The polymeric material can be biodegradable or bioabsorbable, such as from the group including polylactic acid, polyglycolic acid, polycaprolactone, polyparadioxanone, polytrimethylene carbonate and its copolymers, collagen, elastin, chitin, coral, hyaluronic acid, bone, poly (caprolactone ), poly (co-caprolactone lactic acid); (block-ethylene oxide-block-lactide-co-glycolide) polymers of poly (PEO-b-PLGA and PEO-b-PLGA-b-PEO); poly (b-ethylene oxide-b-propylene oxide-b-ethylene oxide) poloxamers; poly (orthoesters), polysaccharides and derivatives of polysaccharides, poly (glucose), poly (alginic acid), chitosan, derivatives of chitosan; polypeptides, and proteins such as albumin, poly (lysine), poly (glutamic acid), poly 5

ES 2 413 655 T3 (anhydrides); poly (hydroxy alconates) such as poly (hydroxy valerate), poly (hydroxy butyrate), and combinations thereof.

The medical device may contain additional bioactive materials for resistance against infection, antimicrobial agents, and agents for improving the lubricity of the device.

The medical device has a heparin coating and may have additional pharmaceutically active agents integrated into the device, or on its surface, or in reservoirs and / or knockouts in the structure of the device, alone with a mixture with a matrix excipient, such as as a polymer. The pharmaceutically active agents can be selected from the groups of anti-inflammatory drugs, such as a rapamycin, eg sirolimus, and its various derivatives and analogs. Anti-proliferative drugs, such as paclitaxel, and its derivatives and analogs.

The bioactive heparin material can be an unmodified heparin, a partially degraded heparin, a low molecular weight heparin (LMWH), or the various modified forms of heparin. Heparin can be permanently attached to the surface of a medical device, for example, by means of covalent attachment, conjugation, end-point attachment, ionic complexation, salt complexing with positively charged salts.

Coatings applied to materials can be polymerized and covalently attached to the surface of the material during manufacture. The coating can be hydrophilic or hydrophobic in nature. This polymerized and grafted coating is resistant to aqueous removal (soak and rinse and / or implantation in aqueous environment) and can be sterilized prior to use. However, many applied coatings that are not covalently bonded (van der Waals forces, electrostatic, surface tension) to material surfaces during processing / manufacturing are not resistant to aqueous removal.

A polymerizable coating can be covalently bonded to the surface of the substrate through an additional processing step, while a non-polymerizable coating will not be polymerized or grafted onto the surface. One processing step that can be used to induce polymerization / grafting of a coating to a material surface and for one-step sterilization is the low temperature hydrogen peroxide gas plasma sterilization processing. Materials already polymerized and grafted with a coating should also be a good candidate for a further sterilization procedure with a hydrogen peroxide gas plasma sterilization system.

The materials can also be metallic or non-metallic or elastomeric. The metallic material can be composed of a variety of metals, including but not limited to stainless steel, aluminum, nitinol, cobalt chromium, or titanium. The materials can also be elastomeric, including, but not limited to, polysiloxanes, fluorinated polysiloxane, ethylene-propylene rubber, or fluoroelastomers. Substrates can also be formed using an inorganic material, including but not limited to glass, silica, and ceramics. The material could also be biologically derived, including, but not limited to, collagen, elastin, hyaluronic acid, bone, coral, or chitin.

Example 1

Electropolished cobalt chromium stents of the design illustrated in Figure 1 were coated with surface bound heparin. The heparin coating is covalently attached to the surface of the stent through a series of intermediate layers, such as tie layers. The final heparin coating was repeatedly washed with water and had a constant final heparin surface density of approximately 13 pg.cm '². Heparin surface activity was determined to be approximately 65 pmol.cm^-2 by a competitive antithrombin III binding assay and 0.9 units of heparin / stent by a modified USP FXa inhibition assay.

The deposits on the struts of these heparin-coated stents were filled with a matrix of poly (lactide-coglycolide) (PLGA) and sirolimus by an ink jet (or nano-liquid deposition) procedure. After drying at elevated temperatures to remove excess solvent from the PLGA / sirolimus matrices in the reservoirs, the stents were compressed into matching catheter balloons with a pneumatic compressor and placed in plastic trays. The trays with plastic stents were then placed in aluminum bags equipped with sachets with a drying agent. The plastic trays were then flushed with nitrogen and a vacuum was created to remove air and remaining moisture. The procedure was repeated three times and the bag was sealed by a hot press sealer.

The vacuum sealed bags containing desiccant were then sterilized by an electron beam sterilizer at various doses: 10 kGy, 25 kGy and 40 kGy. Three stents were used in the procedure for heparin density and activity determinations at each processing point and electron beam dose. The heparin-surfaced stents in the vacuum-packed plastic bags were returned for the heparin, density, and activity assays. The results are illustrated in Figure 2 (AT uptake) and Figure 3 (FXa inhibition assay).

The data in Figure 2 clearly demonstrate that there is a temporary decrease in heparin activity from

ES 2 413 655 T3 about 65 to about 43 pmol.cm^-2. The decrease is likely caused by exposure to the processing solvent, such as DMSO, and the elevated temperature used to remove excess solvent. However once the stents were vacuum packed with additional drying agent and sterilized by electron beam radiation, the heparin surface regained its original activity. Furthermore, there also appeared to be a positive correlation with the electron beam dose used in the sterilization procedure, where a higher electron beam dose led to a higher specific heparin activity. These results are quite surprising and unexpected, considering all the reports in the literature about the destroyed or reduced activity of a bioactive coating after a sterilization procedure that involves a lot of energy, such as gamma and electron beam sterilization. . Electron beam sterilization under carefully controlled conditions achieved an even higher AT absorption value compared to the control sample stored at room temperature, as illustrated in Figure 2. The results seemed to suggest that there is a combination of processing conditions in which careful control of packaging parameters such as vacuum drying and additional drying agents inserted into the bags would prevent the heparin surface and similar bioactive surfaces from losing. its activity after the terminal sterilization procedure. The increased activity of heparin with increasing electron beam doses is probably caused by the conformational changes of heparin during energy-intensive sterilization. This hypothesis is indirectly supported by a later experiment in which the heparin coating showed increased AT absorption activity after electron beam sterilization even though the heparin surface was not subjected to solvent exposure (DMSO , IPA, etc.) and a high temperature (55 ° C). In this way, there is a set of processing conditions to ensure the sterility of a medical device and the bioactive surface activity that is prone to degradation under the conditions of conventional sterilization procedures, such as steam procedures, oxide of ethylene or gamma radiation.

The USP modified anti-factorX assay of a heparin surface directly measures the combined capacity of a heparin surface and the free forms of the heparin surface released from the surface in the test solution. The data illustrated in Figure 3 demonstrate that the electron beam procedure under carefully controlled current conditions is effective in retaining and even reversing the loss of heparin activity during the drug filling procedure. The curve differs from the trend in Figure 2 in that the control has relatively low anti-FXa activity compared to products at a later stage of manufacture. This trend points to the importance of using carefully controlled packaging and the electron beam procedure to ensure good heparin activity in the final sterile product.

The data in Figures 2 and 3 point to key aspects of the present invention where a dose response curve of heparin activity can be maintained after optimal packaging and an electron beam sterilization procedure. A higher dose of electron beam can be used to achieve a higher level of heparin activity in the final sterile package, if necessary. Because the packages are sterilized sealed, it is also feasible to use an electron beam procedure to extend the shelf life of the heparin surface after various periods of storage.

The results illustrated in Figure 4 show that there is a gradual decrease in heparin surface density after an electron beam procedure, where a higher electron beam dose leads to a greater loss of heparin density. The finding is not surprising in that the high energy electron beam procedure probably caused some burning of the surface heparin chain, where a higher dose leads to a higher degree of heparin detachment from the stent surface. Thus, the following invention should be tempered to an optimum range in which heparin activity is ensured while minimizing the degree of loss of heparin content. At the ranges tested, the loss of heparin content did not affect the heparin activity of the remaining heparin surface. The traditional 25 kGy electron beam dose appears to be in the optimal range to ensure sterility, while maintaining a high level of heparin activity.

Example 2

In this study, heparin-coated stents underwent nine cycles of exposure to DMSO, which mimics the actual processing conditions of a drug-filling procedure used in the manufacture of a drug-eluting stent. The DMSO solvent, mixed with the heparin coating on the stent surface after each exposure, was removed under a combination of conditions, such as for one hour at room temperature or 55 ° C, followed by twenty-four hours of annealing at room temperature. or at 55 ° C. Following these lengthy treatment and solvent removal procedures, the heparin coated stents were vacuum packed with drying agents and sterilized by an electron beam procedure at a dose of 25 kGy. The heparin activity of stents subjected to various conditions was determined according to the standard AT III absorption test.

Table 1, below, shows the data related to the effect of the combination of DMSO, temperature, and beam.

ES 2 413 655 T3 electron on heparin activity

<td rowspan="2">Test group (N = 3)</td><td colspan="4">Process</td><td colspan="2">Test</td>

<td>Immersed in DMSO (9 x 1 min)</td><td>Drying (1 hour)</td><td>Annealed (24 h)</td><td>Sterilization</td><td>AT absorption</td><td>Residual solvent</td>

<td>TO</td><td>Do not</td><td>Do not</td><td>Do not</td><td>Do not</td><td> 51</td><td>N / A</td>

<td>B</td><td>Yes</td><td>Room temperature</td><td>Room temperature</td><td>Do not</td><td> 54</td><td>&lt;LOQ</td>

<td>C</td><td>Yes</td><td>55 ° C</td><td>55 ° C</td><td>Do not</td><td> 39</td><td>&lt;LOQ</td>

<td>D</td><td>Do not</td><td>Do not</td><td>Do not</td><td>Yes</td><td> 90</td><td>N / A</td>

<td>AND</td><td>Yes</td><td>Room temperature</td><td>Room temperature</td><td>Yes</td><td> 88</td><td>&lt;LOQ</td>

<td>F</td><td>Yes</td><td>55 ° C</td><td>55 ° C</td><td>Yes</td><td> 72</td><td>&lt;LOQ</td>

The data in Table 1 show that, compared to the baseline AT absorption value of 51 pmol.cm^-2 of the control heparin surface, prolonged drying at high temperature (55 ° C) reduces the heparin activity to approximately 39 pmol.cm^-2. The data also suggest that exposure to DMSO alone does not appear to affect heparin activity, if it is then completely eliminated. The data confirmed that an electron beam sterilization procedure is effective in maintaining heparin activity after drying both at room temperature (group B vs. group E) and at a higher temperature (group C vs. group F). The data also suggest that electron beam sterilization even reactivates lost heparin activity after coating 10 was stored at room temperature for a long period of time (group A (control) vs. electron beam treated control ( group D). Based on these findings, it is reasonable to suggest that the present invention can be used to reactivate heparin activity in packaged medical devices after various periods of storage.