GB2150147A - Materials for use in forming casts - Google Patents

Abstract

A product, for use in forming a surgical cast, is rendered flexible in the presence of liquid so that it can be moulded, and can rigidify, as the result of physical reaction, on the subsequent loss of liquid. In a modification, the product comprises both hydrophilic and thermo-labile materials, and rigidifies as the result of physical reaction involving heating, on the addition and subsequent loss of water. In a further embodiment, the product comprises a solution of a polymer in a solvent and rigidifies when there is added to the solution a liquid which is miscible with the solvent and which does not dissolve the polymer.

Description

SPECIFICATION Materials for use in forming casts The present invention relates to materials of utility in forming casts, and particularly surgical casts, the use of such materials, and the casts which can be prepared from them.

It is of course conventional practice to immobilise damaged joints and limbs. For shortterm support or emergencies, rigid wood or metal splints have been fastened to a subject with straps or bandages. For longer term treatment, plaster of Paris casts are often used. Plaster of Paris, however, suffers from the disadvantages of high weight, inconvenience of application, and considerable difficulty in removal which may be required during treatment or adjustment to the position of a damaged joint or limb. Further, plaster casts are uncomfortable for the wearer; they are essentially impermeable, so that itching is caused from sweating in the cast.

More recently, more easily applicable casts have been developed. One development has been in thermo-labile materials which are effectively rigid at room temperature, but soften at 50-60 C, thus enabling the cast to be applied and shaped as required after which it stiffens to support the limb as it cools. These materials have the advantages of rapid action and that the cast can be re-set without complete removal during treatment, if this is considered desirable. However, such materials are costly, and those presently available either need to be made uncomfortably hot during application or they do not harden completely at room temperatures. In short, the temperature coefficient of rigidity is not sufficiently large.

A second development has been in systems competitive with plaster of Paris, using chemico-sets of various types. These casting systems are variously employed, alone or in conjunction with textile or glass fibre bandages into which they are impregnated.

According to the present invention. a product which is rendered flexible in the presence of liquid so that it can be moulded, and which can rigidify, as the result of physical reaction, on the subsequent loss of liquid (which may be different from or. more usually. the same as that liquid which confers flexibility). is for use in forming a surgical cast. Products having this utility, which are novel per se, are discussed below. The casting method can also be used non-surgically, to form a cast on a member.

Products which can be used in the present invention can be applied to the body and be moulded, and then rigidify to form a light, strong and rigid cast. The cast can be easy and clean to apply, and can be a type which is easily softened for re-setting or later adjustment. In particular, the product can be used under ambient conditions, and yet the time between moulding and the formation of a satisfactory cast need not be too long.

The product may be inherently rigid, and require the addition of the necessary liquid in order to make it satisfactorily mouldable. Subsequent loss of the liquid causes rigification.

Alternatively, the product may be a liquid or liquid-impregnated substrate; such a product may be provided, for use, in an encapsulated form, and may or may not depend on the addition of the liquid for its mouldability.

In one embodiment of the invention, the product comprises a hydrophilic material.

Such materials are rigid when dry, but become soft and elastic when hydrated in water.

In use, such a product is hydrated, moulded into position, and dried to form the cast.

Suitable hydrophilic materials are cross-linked polymers or copolymers or polyblends manufactured from monomers such as hydroxylalkyl methacrylates, N-vinyllactams such as N-vinyl2-pyrrolidone, or acrylamides, with suitable dior other multi-functional cross-linking agents.

The product may consist solely of hydrophilic material, or may comprise a hydrophilic material-impregnated substrate, e.g. a fabric such as treated, textured cotton or towelling.

For simplicity, the product may be provided in the form of a strip of a size suitable for application, or of a sheet or length which can conveniently be cut to such a strip.

The time between moulding and the formation of a satisfactorily rigid cast depends on a number of factors, including the thickness and nature of the hydrophilic material, the degree of hydration of the hydrophilic at the time of application. and the provision of a drying air flow. For a number of applications. products of the type described can provide structural support in 10-30 minutes. which is acceptable. If this period is too long, it may be possible to influence factors such as those described. In particular, a preferred novel product which can be used as defined above comprises both hydrophilic and thermo-labile materials.For example. a product of the invention may comprise alternate layers or strips of such materials and. in use. this provides the rapid initial stiffening of the thermo-labile system together with the high ultimate stiffness and freedom from sensitivity to temperature which is characteristic of a dry hydrophilic material.

In another embodiment of the invention, the product comprises a solution of a polymeric material in a solvent, in which rigidification is caused by the addition of an "activating" liquid with which the solvent is miscible and in which the polymeric material is insoluble. It is necessary that, in order to form a cast, the solvent should be lost to the system on the addition of the liquid. For use, the solution may be provided alone, in encapsulated form (which may be novel per se) or, advantageously, impregnated or coated on a substrate, e.g. an open-cell foam or a fabric of the type described above. Again, the impregnated or coated substrate may be encapsulated in a novel form.It will usually be flexible, and therefore mouidable, until immersed in or washed by the liquid to be added, whereupon the polymeric material is deposited as a solid, rigidifying system, either directly onto the surface of the skin or within the texture of the substrate. The rate of change of mechanical properties can be very rapid, e.g. within 30 seconds, to form a hard, rigid cast which is stable both to changes in ambient conditions and to immersion in water. A solution-impregnated substrate may suitably be provided in a form of a sheet or strip, as described above.

In general, it is preferred that the liquid added to cause rigidification and, in certain instances, mouldability, is water. Other liquids may be appropriate in certain cases, although it is of course desirable not to handle toxic materials in surgery. All materials in a product of the invention, and used in a formation of a surgical cast from such a product, should be bio-compatible. When the product comprises a polymer solution, a suitable solvent is a water-miscible ether such as diethylene glycol monomethyl ether, or alkanol such as methanol, both of which can be replaced by water.

Alternatively, the solvent can be chloroform and the added liquid an alcohol such as ethanol. Examples of suitable polymers for solution in such solvents are acrylates and methacrylates such as methylmethacrylate, and cellulose derivatives such as cellulose acetate propionate, CAB and cellulose nitrate.

The following Examples illustrate the basis of the invention.

Example 1 50 g methyl methacrylate are dissolved in 100 g diethylene glycol monomethyl ether.

The resulting viscose solution is impregnated into terry towelling and sealed in a flexible waterproof sachet. Upon removal from the packaging and immersion in water, the solvent exchanges with water and is lost to the system, resulting in the deposition of a rigid methyl methacrylate structure onto, and within, the fabric matrix. The system is subsequently rigid and stable.

Example 2 15 g cellulose acetate propionate are dissolved in 100 g methanol. The solution is impregnated into a suitable 3-dimensional matrix material and packaged, for storage. Upon removal from the package, the flexible material is immersed in water to activate the system. The methanol exchanges with water and is lost to the system, resulting in the deposition of a rigid cellulose acetate propionate structure onto and within the 3-dimensional matrix, rendering it rigid.

Claims (10)

1. A product for use in forming a surgical cast. which is rendered flexible in the presence of liquid so that it can be moulded, and which can rigidify, as the result of physical reaction, on the subsequent loss of liquid.

2. A product according to claim 1, which comprises a hydrophilic polymer.

3. A product comprising both hydrophilic and thermo-labile materials, which can be moulded and which can rigidify as the result of physical reaction involing heating, on the addition and subsequent loss of water.

4. A product according to claim 3, which comprises alternate layers or strips of each material.

5. A product for use in forming a surgical cast, which comprises a solution of a poly- meric material in a solvent, which can rigidify as the result of physical reaction, on the addition of a liquid. with which the sqlvent is miscible and in which the polymeric material is insoluble.

6. A product according to claim 5, in encapsulated form.

7. A product according to any preceding claim, which comprises an impregnated or coated substrate.

8. A method of forming a cast on a nonhuman and non-animal member, which comprises hydrating a product according to claim 3 or claim 4, applying the hydrated product to the member and moulding it in position.

9. A method for forming a cast on a nonhuman and non-animal member, which comprises applying to the member a solution of a polymeric material in a solvent, adding to the solution a liquid with which the solvent is miscible and in which the polymeric material is insoluble, and moulding the product in position.

10. A method according to claim 8 or claim 9, in which the product or solution is impregnated or coated on a substrate.