Thermoplastic cast material

Patented Nov. 4, 1952 2,616,418

UNITED STATES PATENT OFFICE

2,616,418

THERMOPLASTIC CAST MATERIAL

James J. Eberl, Bound Brook, N. J., assignor to Johnson & Johnson, a corporation of New Jersey

No Drawing. Continuation of abandoned application Serial No. 557,386, October 5,1944. This application July 8, 1948, Serial No. 37,521

Ciaims.

This invention relates to thermoplastic cast forming material in the form of a bandage which is useful in surgery for the maintenance of immobilization and fixation following reduction of fractures and dislocations, the maintenance of approximation of bone fragments following reduction of fractures, the maintenance of fixation and immobilization to promo te healing in instances of compound fractures and bone disease, the immobilization of inflamed ox^- injured joints in disease or trauma, and the support and immobilization of ligamentous and muscular structures in instances of sprains and strains. The improved cast material also may be used as an occlusive dressing for wounds of the extremities by encasing the limb or part to reduce motion and accelerate healing; as a support splint in paralysis or weakness of muscles; as a means to maintain correction of deformities, either congential or acquired, and as an artificial capillary wall in closed cast technique for burns to prevent abnormal capillary leakage. Outside of the surgical field, the improved cast material has many uses, such as in the manufacture of dress forms, tailor’s dummies and protectors for athletes, to mention a few.

The most popular type of cast material currently used in surgery is one made from a fabric bandage impregnated with plaster of Paris. In use, this bandage is moistened, then wrapped around the injured member in a series of layers and allowed to harden. While a cast of this type has proved adequate, it does nevertheless possess many undesirable features. For instance, plaster of Paris bandages are messy in application. The wetted plaster slurry runs out of the bandage and may soil clothing and the room. Much time is required for a plaster cast to assume its ultimate strength; that is, until all the water has dried out. A plaster of Paris cast has poor X-ray penetrability. It is sensitive to water and will weaken from continued exposure thereto. If handled too much by the physician during the so-called critical stage, a rubber-like cast results. It is extremely bulky and must be very thick when high strength is a factor.

In accordance with the present invention there is provided a cast material in the form of a bandage which is quite devoid of the disadvantages just enumerated and which will readily conform to the shape of the body or member to which it is applied. The improved cast material has a melting temperature low enough to cause no added discomfort to the patient during application and a setting temperature high enough to eliminate the possibility of cold flow at normal temperatures. Strength equivalent to that in a plaster cast may be obtained with substantially less bulk. X-ray penetrability is good, there is no water sensitivity; and depending upon the (CI. 128—90) ingredients used, there will be no odor or skin toxicity.

Essentially the cast material comprises a base sheet of flexible material serving as a carrier for 5 a cast forming composition which includes essentially a crystalline organic compound having a sharp melting point preferably within the range of 45° C. to 100° C. and a high molecular weight thermoplastic substance compatible with or 10 soluble in the crystalline organic compound to add strength, provide a super-cooling effect, and increase the viscosity of the cast forming composition. It is also preferred that there be added to the cast forming composition a filler 15 to impart surface hardness and increase viscosity, and in some cases, a low molecular weight thermoplastic substance when additional super-cooling is desired.

Suggested crystalline organic compounds for 20 preparing cast forming compositions of the type herein contemplated include:

Μ. P. (°C.)

Dicyclohexyl phthalate 66

Diphenyl phthalate69-70 •25 Triphenyl phosphate 19

Benzophenone 48 para-Nitro anisole 54

Phenyl para-tolyl ketone 60

Phenyl urethane 52 ortho-Isopropyl benzoic acid 51

Isocinnamic acid 58

Oxamic acid, N-acetyl-ethyl ester 54

Benzyl 1-naphthyl ketone66-67

1,4-Dimethoxy benzene___________) 56

As will be observed, all of the crystalline organic compounds mentioned have a melting point well within the desired range.

The selection of a suitable strength imparting high molecular weight thermoplastic substance, such as a high molecular weight polymer, a resin, or a cellulose derivative, will depend upon the crystalline organic compound used as the base. The important factor is of course compatibility, and it will be found that, fox- the purposes of the ^4o invention, at least one of the following high molecular weight thermoplastic substances is sufficiently compatible with one or another of the crystalline organic compounds listed above:

Polyamides Acrylates Polyvinyl compounds Cellulose esters Cellulose ethers

Specific acrylates including ethyl acrylate, n-butyl acrylate, , methyl methacrylate, ethyl methacrylate, and n-butyl methacrylate; specific polyvinyl compounds including polyvinyl chloride, polyvinyl acetate chloride copolymer, poly60 vinyl formal, polyvinyl acetal, and polyvinyl

2,618,418 butyral; and specific cellulose esters and ethers including cellulose acetate, cellulose propionate, cellulose butyrate, ethyl cellulose, and benzyl cellulose are examples of celluose esters and ethers which have been found suitable as high molecular weight thermoplastic substances in preparing the cast forming composition.

As in the case of the high molecular weight thermoplastic substance, the chief requisite in a low molecular weight thermoplastic substance used to provide additional super-cooling effect is compatibility with the other ingredients of the cast forming composition. A suitable low molecular weight thermoplastic substance for the purpose may be selected from the group comprising rosin, modified rosins, rosin esters, coumarone, coumarone-indene resins, polymerized beta-pinene resins, and others which will suggest themselves to those skilled in the art.

The preferred filler is magnesium carbonate because of its lightness, although any other suitable filler will suffice. The amount of filler used will depend upon the viscosity desired and the particle size. The preferred viscosity is one which will permit the mixture to adhere to the carrier without excess dripping when the mixture is in the molten state. The preferred size of the filler particles ranges from 3 to 4 microns, although the larger the particle size, the greater is the amount of filler required.

The amount of high molecular weight thermoplastic substance which may be used and provide a satisfactory cast forming composition is 2% to 15% by weight of the crystalline organic compound. It is preferred, if a low molecular weight thermoplastic substance is also included in the cast forming composition, that it is present in an amount of 3% to 35% by weight of the crystalline organic compound.

In the following examples, which are merely illustrative, care has been taken to select those which will result in a cast forming composition known to be non-toxic and therefore useful in surgery.

Example I

Parts by weight

Diphenyl phthalate100

Polyvinyl acetate--------------------- 3 to10

Hydrogenated rosin (Staybelite resin) _ 3 to25

Filler —____ 10 to25

Example II

Diphenyl phthalate,100

Polyvinyl acetal______________________ 3 to10

Hydrogenated rosin (Staybelite resin) _ 3 to35

Filler—______________________________ 10 to25

Example III

Triphenyl phosphate 100

Cellulose acetate propionate--------- 3 to15

Filler__________________------------- 10 to 25

Example IV

Triphenyl phosphate-----,------- 100

Ethyl cellulose________________________ 3 to 15

Filler_______________________________ 10 to 25

Example V

Benzophenone______ 100

Ethyl cellulose________________________ 3 to11

Filler_______________________________ 10 to25

Example VI • Dicyclohexyl phthalate100

Ethyl cellulose_______________________ 2 to12

Filler_______________________________ 10 to25

Example, vil

Diphenyl phthalate100

Polyvinyl acetal—___________ 3 to10'

Coumarone-indene resin_____________ 3 to35

Filler_______________________________ 10 to25

The cast material or bandage is prepared by making a hot melt batch of the selected cast forming composition and passing the carrier sheet therethrough and then between two opposed coating knives to remove the excess material and give a uniform product. The preferred carrier may be loosely woven gauze, although the selection of the carrier will depend entirely upon the use for which the material is intended. Suggested carrier sheets include, in addition to woven fabric or gauze, knitted material and other woven or unwoven fibrous material.

Where the cast material is used for surgical purposes, it may be wound on spools in suitable lengths and widths, coated with a layer of cellulose acetate film and supplied in that form to the physician.

To use, the cast material or bandage is first immersed in boiling water until the cast forming composition has melted. When the bandage has softened, it is allowed to cool to a temperature which will facilitate handling. The excess water is wiped off, and the cellulose acetate film removed. The presence of the super-cooling agent or agents prevents spontaneous crystallization of the crystalline material and the cast forming composition during cooling. The physician then wraps the bandage on in layers to the desired thickness using a hand molding technique similar to that used in applying plaster of Paris bandages. The time required for melting the cast material in the form of a bandage will depend upon its dimensions and the melting temperatures of the cast forming composition. For instance, the melting temperatures of a cast forming composition made with diphenyl phthalate is 65° C., with triphenyl phosphate 47° C., and with benzophenone between 46° C. and 47° C.

It is neither necessary nor desirable to mould every layer of the cast material or bandage during wrapping because the layers tend to stay in place as they are wrapped. Indeed, agitation of the surface of the bandage greatly accelerates the setting time, and there is some risk that the bandage will set too rapidly if it experiences too much handling, although setting time may be controlled by regulating the amount of low molecular weight thermoplastic substance included in the cast forming composition. The average setting time, with normal surface handling of a bandage prepared with a cast forming composition made in accordance with Examples 1 to 5, is between 5 and 10 minutes.

The removal of a cast made in accordance with the invention presents no difficulty. If the cast material is made with a relatively strong fabric base, as for instance 44 x 40 gauze, it is usually possible to remove the bandage merely by unwrapping. If this cannot be done, the cast may be cut, using a pair of scissors similar to those used in cutting a plaster cast. Another very effective and rapid method of removing a thermoplastic cast consists in locating a thin metal strip longitudinally along and adjacent to the member to be placed in the cast. The metal strip is long enough to protrude slightly at the end of the cast so that its location is clearly defined. A hot knife, preferably one that is electrically heated, is drawn longitudinally along the cast on a line overlying

2,616,418 s

the metal strip. The hot knife melts the cast at the point of contact and simultaneously cuts the fibers of the base sheet carrier material. This method is extremely rapid and causes no discomfort to the patient. Obviously, the metal strip serves as a guide in the cutting operation and prevents injury from befalling the patient.

From what has been said, it will be apparent that the improved thermoplastic cast forming material embodied in this invention in the form of a bandage possesses many advantages from the standpoint of application, removal, and the comfort and well-being of the patient. Pleasing colors are available; for instance, the diphenyl phthalate bandage is light cream, the triphenyl phosphate bandage white, and the benzophenone likewise white. The surfaces of the cast may be readily washed and a clean appearance thus readily maintained.

The invention has been described herein merely by way of example and many modifications thereof are included within its spirit. It will be understood, therefore, that the invention is to be limited only by the prior art and by the scope of the appended claims.

This application is a continuation of copending U. S. Patent application Serial No. 557,386, filed October 5, 1944, now abandoned.