GB2315689A - Orthopaedic splinting material - Google Patents

Abstract

An orthopaedic splinting material comprises a flexible substrate carrying a resin system comprising at least a water hydrolysable organo-oxy functionalised prepolymer where the organo-oxy groups are attached to Si, Ti, Zr, Hf, Ge, Sn, Pb, As, Bi, Mn, B or Se.

Description

ORTHOPAEDIC MATERIALS This invention relates to orthopaedic casting and splinting materials. In particular this invention relates to orthopaedic casting and splinting materials based on synthetic resins which, upon contact with water1 will cross-link and harden to form a weight bearing support for a limb or body portion and to such resins which on contact with water will cross-link and harden.

Resin based splinting and casting materials find wide use in the immobilisation of limbs, for example the fixation of fractured bones, immobilisation of injured joints and for the support of ligaments and muscles where it is necessary to encase the limb in a partially or completely surrounding rigid form or cast.

There are several major considerations for a casting or splinting material. A suitable material should be easily handleable, with a reasonable setting time to allow sufficient time in the case of casting bandages to mould the bandage about the limb and it should be flexible and free of offensive chemicals which may affect the patient or practitioner applying the material. In addition it is desirable that during the forming of the cast the material does not generate an uncomfortable exothermic reaction and that it sets within a relatively short time under mild conditions.

Splinting and casting materials comprising water activated synthetic polymers in which a cross-linkable prepolymer resin system is coated onto a suitable substrate are well known. The most favoured and commercially developed systems are those based on prepolymers which contain isocyanate functional groups and which in the presence of cold water will cross-link to form urea bridges. The prepolymers usually also contain a catalyst to speed up the cross-linking reaction and so that a weight bearing cast may be formed in as short a time as possible consistent with requirements for moulding and shaping the splint.

The isocyanate linking reaction is usually an exothermic reaction. In meeting the working requirements for such systems the prepolymers chemistry has to be carefully controlled so as to allow the prepolymers to cure in a period of time which is acceptably short and yet not cure under conditions in which so much heat is evolved that the applied cast is uncomfortable to the wearer.

A disadvantage of such systems is the relatively high exotherm generated on curing and that there is a perceived health hazard with the use of orthopaedic bandages comprising isocyanate functionalised prepolymers. It is therefore desirable to make a suitable splinting material without utilising isocyanate functionalised prepolymers.

Examples of this approach include US Patent No. 4411262 (von Bonin et al) wherein there are disclosed splinting and casting materials comprising substrates impregnated or coated with a reactive one component system, wherein inter alia the systems includes organic compounds with molecular weights greater than 10,000, comprising reactive groups which may be alkoxysilane groups. It is taught that the organic compounds themselves were produced by an isocyanate functionalised reaction and thus any perceived health risk associated with isocyanate functionalised resins is not entirely removed without ensuring that the prepolymers are fully reacted.

US Patent No. 5,423,735 also describes materials of this type, where the water reactive prepolymer is an alkoxysilane functionalised polyurethanelpolyurea prepolymer, produced by reacting isocyanate functionalised precursors. Such materials potentially have the same problems which may be associated with other prepolymers produced from isocyanate functionalised precursors.

The present invention seeks to provide an improved orthopaedic splinting material with a prepolymer system which overcomes the above mentioned disadvantages.

Although the splinting and casting material of the present invention is described in terms of "an orthopaedic splinting material" the term is also intended to embrace splints, bandages, casts, supports and braces, where such materials do not necessarily surround the whole limb or body portion.

In accordance with the present invention there is provided an orthopaedic splinting material comprising a flexible substrate carrying a water curable resin system, wherein the resin system comprises at least a water curable organo-oxy functionalised prepolymer having the general formula (I):

i) where n is an integer up to 30 ii) where M may be the same or different in each repeat unit and M is from the group comprising metals Si, Ti, Zr, Hf, Ge, Sn, Pb, As, Bi, Mn, B, Se.

iii) where X3 may be -H, halide,X1 , -OH, C1 - Cg alkyl, aryl, iv) where R1 may be -H, -OH, halide, -NH2, -SH, C, to C6 alkyl, aryl, v) where R2 may be the same or different in each repeat unit: substituted, unsubstituted, based on C, - C,2 alkyl, aryl, cycloalkyl, heteroalkyl, hetereocycloalkyl, all of which may be optionally interrupted by -O-, -S-, -NH-, -C(O)-, -NR2-, -NH2±, > NH±, vi) where X1 and X2 may be the same or different and may be a water hydrolysable organo-oxy group based on C1 - C,.

Aptly X', X2 comprise at least one water hydrolysable organooxy group. Organo-oxy groups are suitably defined as a group including for example alkoxy [-ORl, acyloxy [-OC(O)R] and cyclic alkoxy groups.

Preferably M is from the group comprising Si, Ti, Zr.

During the curing reaction of the prepolymers any hydrolysable groups on the prepolymer are hydrolysed to form metal-hydroxy groups which condense together. The reaction may be exemplified by the following formulae: (Polymer)2 M(OR)2 + H20 o (Polymer)2M(OR)(OH) (Polymer)2 M(OR)(OH) + (Polymer)2M(OR)2 < (Polymer)2 M(OR)-O-M(OR)(Polymer)2 Which continues until all or most of the hydrolysable groups have reacted to give a crosslinked ploymer.

Furthermore the metal centres may have a catalytic efect on the hydrolysislcondensation reaction. Different metal centres with different catalytic effects may be employed to provide a controlled rate of cure.

The prepolymer for use in the reaction may be made by suitable polymerisation reactions, for example the progressive transesterification of an alkoxymetal and a polyhydric alcohol.

Further examples include the reaction of halide alkoxy metals with polyhydric alcohols where the halide functional groups are displaced.

The use of combinations of polyhydric alcohols alllows the hydrophiliclhydrophobic balance of the prepolymer to be controlled.

Furthermore the use of tri-or tetrahydric alcohols allows the viscosity of the prepolymer to be increased.

The preparation of the prepolymers may be catalysed.

Suitable catalysts include sodium alkoxides, titanic acid esters for example tetraethyltitanate, sulphuric acid, trifluoroacetic acid, tertiary amines and quaternary ammonium hydroxides.

Aptly additional catalysts may be added to catalyse the hydrolysis reaction of the prepolymer. Suitable catalysts include organotin salts, chloroacetic acid, methane sulphonic acid [MSA], 1 ,5aiazabicyclo[4.3.0] non-5-ene [DBN], 1,8-diazabicyclo (5.4.0] undec-7-ene (DBU), bismorpholino dialkyl ethers and potassium fluoride.

The catalysts as hereinbefore described may be present as a single chemical species or as a mixture, and when used, are aptly present in an amount up to 20% w/w, more aptly up to 10% w/w of the prepolymer. Aptly, if used, they should comprise at least 0.05% w/w of the resin.

The prepolymer used in the invention may be precured by the addition of water to crosslink a small percentage of the hydrolysable groups. The advantage gained would be an increase in molecular weight, leading to an increase in viscosity.

Preferred formulations of the prepolymer system may include a variety of additives conventional in the art. These additives may comprise fillers, pigments, fragrances, surfactants, lubricants or mixtures thereof.

Suitable powdered fillers include talc, calcium carbonate, fumed silica sold under the trade name Cab-o-SilTM, alumina and fibrous reinforcing fillers such as wollastonites (calcium metasilicate), to impart desirable viscosity and handling characteristics.

The fillers may be present as single chemical species or as mixtures and, when used, are aptly present in an amount of up to 50% w/w, preferably up to 20% w/w and aptly at least 1.0% wiw of the resin.

The prepolymer system used for casting materials according to the invention may be carried on any substrate suitable for a casting1 splinting or bracing material.

The prepolymer system may be coated, laminated, sprayed or impregnated onto a suitable substrate using conventional methods in the art. Aptly the casting materials of the invention are prepared by nip-coating the prepolymer on to the substrate.

A preferred substrate is a flexible fabric carrier which may be a woven, knitted or non woven fabric which can carry enough of the prepolymer to ensure that the resultant cast has adequate strength.

The substrate should be sufficiently porous to allow water to come into contact with the carried prepolymer when the formed bandage is immersed in water. The substrate may be in the form of tapes, bandages, sheets or other conventional forms, apt for preparing orthopaedic casting bandages, splinting materials or braces.

Suitable materials for forming the substrate include polyester, nylon, polypropylene, polyamides, polyolefins and glass fibre or mixtures thereof. Examples of such substrates are disclosed in Patent Nos. US 4,427,002, US 4,627,424 and EP 326, 285.

Aptly the substrate may be a mesh having openings through it to enable the water to penetrate into the rolled bandage to contact all of the prepolymer. The openings will also permit circulation of air to and evaporation of moisture from the skin beneath the cured cast.

Preferably the mesh is of a loose weave or knit so as to allow at least partial impregnation as well as coating by the prepolymer.

The amount of prepolymer carried by the substrate before curing may vary depending on the intrinsic properties of the prepolymer and should be sufficient to ensure that the resultant cast has adequate strength.

Suitable amounts range from 30 to 70% w/w which is calculated using the equation: weight of (substrate + prepolymer) - weight of (substrate) x 100 weight of (substrate + prepolymer) Preferably 35 to 70% w/w and most preferably 40 to 65% w/w of prepolymer are used.

A hardened cast may be formed by wetting and shaping the wet material around a body member or part thereof and allowing the material to cure.

Aptly wetting is achieved by immersing the material in water, and removing any excess water, for example, by squeezing the material several times before application to the body member.

When removed from the water the material can be readily wrapped about a limb wherein the conventional underlying stockinette or padding is employed.

An altemative method for forming a cast or splint comprises applying the material to the body member followed by spraying the material with water.

The water used to wet the material may contain the catalyst to catalyse the hydrolysis reaction thus forming a catalytic solution.

The curing reaction of the prepolymer should be sufficiently slow to allow the material to be positioned and shaped before the material becomes unworkable. Suitable working times are aptly 1 to 6 minutes more aptly 2 minutes to 4 minutes. The curing reaction of the prepolymer should, however, be sufficiently fast to permit the formed cast or splint to become supportive and load-bearing as soon as possible after completion of working. Aptly the material will set and become supportive between 5 and 30 minutes, more aptly within 15 minutes and particularly in the case of a cast, will aptly become load-bearing within 60 minutes, more aptly after 10 minutes.

The cast may be readily removed by conventional means such as by cutting with a conventional vibrating sawtooth disc.

The orthopaedic casting material should be protected during storage from water and moisture vapour to prevent a premature setting taking place. The material can be conventionally packaged in heat sealed pouches such as metal foil polyethylene laminate pouches.

The invention will now be described by way of example only and it should be understood that normal precautions for excluding moisture during chemical reactions were employed.

Example 1: A 500cm3 flask, fitted with a short fractionating column and a distillation head was charged with polyethylene glycol (1509, 0.5mol], tetraethylorthosilicate [at 10% mol excess, 114.69, 0.55mol] and tetraethyl titanate [2.289, 1 %w/w].

The mixture wass protected from atmospheric mositure and gradually heated to 1500C with stirring. Ethanol was distilled progressively and the reaction continued until approximately 50g was collected. A viscous prepolymer was produced.

Example 2: A prepolymer was prepared as in Example 1 utilising polydimethyl siloxane [0.5mol] instead of polyethylene glycol.

Example 3: A prepolymer was prepared as in Example 1 with dichlorodiethoxysilane (1.OmoI] and polyethylene glycol diamine [1 .OmoIJ.

Example 4: A 500 cm3 flask was charged with dichlorodiethoxy silane (1 mol) and Jeffamine EDR148 (poiyethylenediamine) (1 mol) and was heated with stirring at 70 C for 8 hours to give a viscous prepolymer.

Example 5: A 500 cm3 flask was charged with 2-hydroxyethyl acrylate (116.19) and piperazine (86.19) and was heated with stirring at 70 OC for 8 hours. The mixture was subsequently cooled to ambient temperature. Dichlorodiethoxy silane (189.19) was introduced into the flask and the mixture was heated with stirring at 80 OC for 8 hours.

Preparation of a splinting matenal utilising prepolymers prepared in examples 1 - 5.

The prepolymer was mixed with powdered potassium fluoride [3%wlwl and coated onto a dry glass fibre bandage by passing the bandage through the prepolymer, followed by passing the coated bandage through a nip roller, adjusted to a suitable pressure for obtaining a coating weight of 50-60%w/w coating.

The prepolymer was set off by dipping the coated bandage in cold water, and squeezing several times before application to a mandrel representing a limb.

Claims (12)

1. An orthopaedic splinting material comprising a flexible substrate carrying a water curable resin system, wherein the resin system comprises at least a water curable organo-oxy functionalised prepolymer having the general formula (I):

i) where n is an integer up to 30 ii) where M may be the same or different in each repeat unit and M is from the group comprising metals Si, Ti, Zr, Hf, Ge, Sn, Pb, As, Bi, Mn, B, Se.

iii) where X3 may be -H, halide,Xr, -OH, C1 - C6 alkyl, aryl, iv) where R1 may be -H, -OH, halide, -NH2, -SH, C1to C6 alkyl, aryl, v) where R2 may be the same or different in each repeat unit: substituted, unsubstituted, based on C, - C,2 alkyl, aryl, cycloalkyl, heteroalkyl, hetereocycloalkyl, all of which may be optionally interrupted by -O-, -S-, -NH-, -C(O)-, -NR2-, -NH2±, > NH±, vi) where X1 and X2 may be the same or different and may be a water hydrolysable organo-oxy group based on C, - C6.

2. A material according to claim 1 wherein the water hydrolysable groups X1 and X2 are from the group comprising alkoxys (-OR), acyloxys (-OCOR), cyclic alkoxys or mixtures thereof where R is an alkyl group based on C1 to C6 hydrocarbon group.

3. A material according to claim 1 wherein the water hydrolysable alkoxy or acyloxy group is a C1 to C3 hydrocarbon group.

4. A material according to claim 1 wherein the water hydrolysable alkoxy group is an ethoxy group.

5. A material according to claim 1 including a catalyst to catalyse the polymerisation reaction of the silane functionalised prepolymer with water.

6. A material according to claim 5 wherein said catalyst is from the group comprising: methane sulphonic acid, 1 ,5 < liazabicyclo[4.3.0] non -5-ene, 1 ,8-diazabicyclo[5.4.0]undec-7-ene, ethyl titanate, potassium fluoride, p-toluene sulphonic acid, dibutyltindilaurate, or mixtures thereof.

7. A material according to claim 1 including additives comprising pigments, fragrances, surfactants, lubricants, fillers or mixtures thereof.

8. A material according to claim 1 wherein the resin system is coated onto the flexible substrate.

9. A method for applying an orthopaedic splinting material according to claim 1 comprising wetting the material, shaping the material around a bodymember and allowing the resin system to cure.

10. An orthopaedic splinting material comprising a flexible substrate carrying a water curable silane functionalised resin as defined in claim 1.

11. An article comprising a water curable silane functionalised resin as defined in claim 1.

12. The use of a water curable silane functionalised resin as defined in claim I as an orthopaedic casting bandage or splint.