GB2315690A - 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 silane functionalised prepolymer where the prepolymer is formed by a chain growth mechanism.

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 water, 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 resin systems 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 resin systems the 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 resins are fully reacted.

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

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

We have found a way of overcoming the above mentioned disadvantages by utilising a silane functionalised prepolymer with pendant hydrolysable groups where the prepolymer is formed via a chain growth mechanism.

Therefore according to the present invention there is provided an orthopaedic splinting material comprising a flexible substrate carrying a water hardenable resin system where the resin system comprises a water hydrolysable organo-oxy silane functionalised prepolymer having the general formula: (I)

wherein: a) X comprises a water hydrolysable organo-oxy group based on C1 to C6 hydrocarbon group.

b) Y is H, alkyl, aryl, halide, or X c) z = O to 50 d) Q may be H, Si(Ym)(Xm) e) R2, R4, R5, R7, and R8 may be the same or different and may be H, R'.

f) R1, R3, and R6 may be the same or different, substituted or unsubstituted and are groups based on the following C1 - C12 alkyl, alkene, aryl, cycloalkyl, heteroalkyl, heteroaryl, heterocycloalkyl all of which may be optionally interrupted by -O-, -S-, -NR2, -C(O)-, > Si < .

The prepolymers of general formula (I) may be polymers formed from a single monomer species, block copolymers, alternating copolymers or random copolymers.

Organo-oxy silanes are suitably defined as a group including alkoxysilanes [-Si-OR], acyloxysilanes [-Si-O-C(O)-R], cyclic alkoxysilanes, where R is an alkyl group aptly containing up to 6 carbon atoms.

Preferably the hydrolysable organo-oxy group is a C2 to C4 hydrocarbon alkoxy group and most preferably the hydrocarbon group is an ethoxy group.

During the curing reaction of the prepolymers the organo-oxy silane groups are hydrolysed to form hydroxsilane groups which condense together. The reaction may be exemplified by the following formulae: i) Prepolymer-Si(OR)3 + H20 < Prepolymer Si(OR)20H ii) Prepolymer-Si(OR)20H + Prepolymer-Si(OR)3 o Prepolymer-Si(OR)2-O-Si(OR2)-Prepolymer + ROH.

iii) 2 Prepolymer-Si(OR)20H o Prepolymer-Si(OR)2O-Si(OR)2-Prepolymer + H20 until all or most of the Si(OR) have reacted to give a cross linked system.

The prepolymers for use in the present invention may be prepared via the polymerisation of suitable unsaturated momomers.

Polymerisation may occur by any chain - growth mechanism, for example free radical, anionic or cationic mechanisms.

A preferred mechanism is polymerisation via a free radical mechanism.

Examples include the polymerisation of methacryloyl silyl alkyl: CH2=CH(CH9 C(O) CH2 CH2 CH2Si(OR)3 i) With itself to give a polymer ii) With vinyl alkyls RCH=CH2 to give a copolymer iii) With divinyl alkyls R(CH=CH2)2 to give a copolymer Further examples include the polymerisation of acrylolysilyalkyl CH2 =CH(CH Si(OR)3.

i) With itself to give a polymer.

ii) With vinyl alkyls R(CH=CH2) to give a copolymer.

iii) With divinyl alkyls, R(CH=CH2)2 to give a copolymer The use of divinyl alkyls under apt conditions may result in a polymer with pendant vinyl groups. These pendant vinyl groups may be polymerised subsequently by the same or a different mechanism.

Another example includes the reaction of bisacrylamide with aminoalkylylenesilane to give an acryloyl terminated monomer which may be subsequently polymerised to give a prepolymer.

The reaction of acryloyl chloride with aminoalkylenesilane also gives an acryloyl terminated monomer which may be subsequently polymerised to give a prepolymer. In this example the acryloyl terminated monomer further comprises amino ionic centers -+NH2which aid wetting out of the resulting prepolymer. Wetting out is defined as the uptake of water by the prepolymer on initiating hydrolysis of the organo-oxy silane groups.

Building up the monomers allows the polymerisation rate and hence the molecular weight and viscosity of the resulting prepolymers to be controlled.

The polymerisation of the vinyl groups may require an initiator.

Suitable examples include, but are not limited to: AIBN: azobis(isobutyronitrile), BCHPC: bis(4-t-butylcyclohexyl) peroxydicarbonate and benzoyl peroxide.

The initiator if present, is preferably used in an amount of 0.01% w/w to 50% w/w. Most preferably in an amount of 0.5% w/w to 25% w/w. The hydrolysis reaction of the alkoxy or acyloxy silane group may be catalysed. Suitable catalysts include, but are not limited to: organotin salts, chloroacteic acid, MSA: methane sulphonic acid, phosphoric acids, DBN: 1,5-diazabicyclo [4.3.0] non-5-ene, DBU: 1,8-diazabicylo[5.4.0]undec-7-ene, p-toluene sulphonic acid, bismorpholino dialkyl ethers, for example dimorpholinodiethylether, water soluble organic and inorganic halides for example potassium fluoride and tetrabutylammonium fluoride.

The catalyst may be present as a single chemical species or a mixture and, when used, is aptly present in an amount of up to 20% w/w, more aptly up to 10% w/w and most preferably up to 5% w/w of the resin. Aptly, if present, it should be at least 0.01% w/w of the prepolymer.

Alternatively water soluble catalysts may be added to the water used for setting of the hydrolysis reaction.

The prepolymers used in the invention may be precured by the addition of water to the cross-link a small percentage of the available organo-oxy silane groups. The advantage gained would be an increase in molecular weight1 leading to a increase in viscosity.

The hardenable resin system as herein before described may aptly be used to prepare a splinting material.

The term " splinting material " as used herein is intended to embrace splints, bandages casts and braces where such materials do not necessarily surround the whole limb or body portion.

Preferred formulations of the resin 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 but are not limited to talc, calcium carbonate, fumed silica sold under the trade name Cab-o-SilTU, alumina and fibrous reinforcing fillers such as wollastonites (calcium metasilicate), to impart desirable viscosity and handling characteristics. Aptly the resins have viscosities from 10,000 to 100,000 mPas", more preferably from 40,000 to 60,000 mPas' .

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% w/w of the resin.

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

The resin system may be coated, laminated, sprayed or impregnated onto a suitable substrate using conventional methods in the art. Aptly the splinting 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 and aid 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 80% 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% wlw 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 or body member to be treated. Preferably the limb is covered by a conventional underlying stockinette or padding.

An alternative 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 a soluble catalyst, thus forming a solution.

According to the invention there is also provided a method of treatment for injured body member comprising wetting the splinting material as herein before described, shaping the material around the body member and allowing the material to harden.

Suitably the injured body member is a fractured or broken limb.

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 prepolymers employed in the present invention possess the advantage that no methanol is generated during the curing reaction, and the further advantage in that the curing reaction is only slightly exothermic thus causing no harm or discomfort to the patient.

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

The orthopaedic splinting 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 250 cm3 flask, fitted with a drying tube and stirrer was charged with methylenebiscacrylamide [25.8 g, 0.17 mol ] and 3-aminopropyltriethoxysilane 174.1 g, 0.33 mol ]. The mixture was heated to 70"C for 48h and AIBN [0.06 g , 0.06 % wlw ] was added as the initiator.

The mixture was heated further at 70"C for 6h. A viscous prepolymer was formed, to which 3% wlw KF was added as the catalyst for hydrolysis.

The prepolymer was coated onto a dry glass fibre bandage by passing the substrate through the prepolymer followed by passing the coated bandage through a nip roller, adjusted to a suitable pressure obtaining a coating weight of 5060% w/w. The prepolymer was set of by dipping the coated bandage in cold water and squeezing several times before application to a mandrel representing a limb.

Example 2 A 100 cm3 flask, fitted with a drying tube and stirrer was charged with methacryloylsilylalkyl (50g, 0.22 mol) and AIBN [39, 6% wlw] as the initiator. The mixture was heated to 70 C for 6h to give a prepolymer. KF (1 .5g, 3% wlw] was added as a catalyst for hydrolysis.

Examples 3 to 6

Materials used Example Example Example Example 3 4 5 6 Trimethoxysilylpropyl 20% wlw 40% w/w 50% wlw 20% whnr methacrylate 2-Ethyl hexylacrylate 40% w/w 30% w/w 25% w/w 20% w/w n-Butyl acrylate 40% wlw 30% wlw 25% wlw 40% whv Acrylic Acid 20% w/w General method for examDles 3 - 6: A 700cm3 flask fitted with a reflux condenser and a dropping funnel was charged with trimethoxysilylpropylmethacrylate [209], butylacrylate [40g], 2-ethylhexylacrylate [409] and ethyl acetate [500cm3]. The mixture was bought to reflux under N2. On establishment of reflux initiator BCHPC [2% w/w] in ethylacetate [50cm3] was added via the dropping funnel. The mixture was maintained at reflux for 4 hours. The resultant solution was concentrated by rotary evaporation to give a viscous prepolymer.

Preparation of a splintinn material: The prepolymer was coated onto a dry glass fibre bandage by passing the substrate 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% wiw. The prepolymer was set of 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 hardenable resin system, where the resin system comprises at least a water hydrolysable organo-oxy silane functionalised prepolymer having the general formula (I):

wherein: a) X comprises a water hydrolysable organo-oxy group based on Ci to C6 hydrocarbon group.

b) Y is H, alkyl, aryl, halide, or X c) z = 0 to 50 d) Q may be H, -Si(Ym)(Xgm) e) R2, R4, R5, R7, and R8 may be the same or different and may be H, R1 f) R1, R3, and R6 may be the same or different, substituted or unsubstituted and are groups based on the following C1 - C12 alkyne, alkyl, aryl, cycloalkyl, heteroalkyl, heteroaryl, heterocycloalky all of which may be optionally interrupted by O-, -S-, -NR2, -C(O)-, > Si < .

2. A material according to claim 1 wherein the water hydrolysable group is from the group comprising alkoxy silanes (-Si-OR), acyloxy silanes (-Si-OCOR), cyclic alkoxy silanes 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 C, 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-diazabicyclo[4.3.0] non -5-ene, 1 ,8-diazabicyclo[5.4.O]undeo7-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 1 as an orthopaedic casting bandage or splint.