GB2315687A - 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, Wherein an organo-oxy group is attached to Se, Al, Sn, B or Ti.

Description

ORTHOPAEDIC MATERIALS In particular this invention relates to 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 shorter time as possible consistent with requirements for moulding and shaping the splint.

The isocyanate cross linking reaction is usually an exothermic reaction. In meeting the working requirements for such resin systems the resin chemistry has to be carefully controlled so as to allow the resins 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 thus desirable to make a suitable splinting materials without utilising isocyanate functionalised prepolymers and thus considerable care has to be taken in both the preparation of the splinting or casting material and in its use to ensure that all the isocyanate functionalities are fully reacted.

In US Patent No. 4411262 (von Bonin et al) there are disclosed splinting and casting materials comprising substrates impregnated or coated with a reactive one component system, wherein inter alia the system 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 polyurethane/polyurea 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 one component resin system which avoids the use of free isocyanate groups as the water activated reactive groups, thus eliminating any health hazard which may be associated with the use of materials containing free isocyanate groups.

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

(a) wherein A is a polymeric residue, optionally interrupted by (II)

(b) X comprises a water hydrolysable organo-oxy group based on C, to C6 hydrocarbon group or water hydrolysable halide.

(c) Y is alkyl, aryl based on C1 to C6 hydrocarbon group, halide, H or X.

(d) Z is Se, Al, Sn, B or Ti.

(e) n = 1 to 20, m=Oto2, p= 1 to2.

(f) Q comprises residues based on the following formulae (III).

~G~(CH2)q~D~ or ~D~(CH2)q~G~ (III) where G = -CH(OH)-, -C(O)-, -CH(NH2)-, -CH(SH)- and Dis -NH-, -N < , -0-, -S- and q = 1 or 2 (g) R' and R" may be the same or different, substituted or unsubstituted and are groups based on the following C1 - 012 alkyl, aryl, cycloalkyl, heteroalkyl, heteroaryl, heterocycloalkyl all of which may be optionally interrupted by -0-, -S-, -NH-, -C(O)- ,further units of Q, with the proviso that urea NHC(O)NH-, urethane -NHC(O)-, carbamylthio -SC(O)NH- are not represented.

The prepolymers employed in the present invention are end capped with a water hydrolysable organo-oxy group (X). Organooxy groups are suitably defined as alkoxy [-O-R] acyloxy [-O-C(O)-R] and halide groups.

Favoured end capping groups have the general formula -Z(OR)n, -Z(OCOR)nX -Z-O-Z(OR)n, Z-O-Z(R1)3.n(OR)n, Z(OC(R3)=C(R1)(R2)n where n has a maximum value of 3 and each of R, R,, R2 and R3 may be the same or different and are alkyl groups aptly containing up to 6 carbon atoms. Preferably the hydrolysable alkoxy or acyloxy group is a Cr-C3 hydrocarbon group.

More preferably the hydrolysable group is a C1-C3 hydrocarbon alkoxy group and most preferably the hydrolysable group is an ethoxy group. Z as hereinbefore described comprises a member of the group containing Se, Al, Sn, B and Ti.

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,casts, bandages, supports and braces, where such splints, casts, supports, bandages and braces do not necessarily surround the whole limb or other body portion.

During the curing reaction of the prepolymers the alkoxy or acyloxy groups are hydrolysed to form hydroxy groups which condense together. The reaction may be exemplified by the following formulae:

OR OR i) Prepolymer -OR + H20 . Prepolymer t OH + ROH OR OR OR OR ii) Prepolymer t-OH + Prepolymer --OH OR OR OR Prepolymer i~o~* ~ Prepolymer + H20 OR OR OR OR iii) Prepolymer t OH + Prepolymer --OR OR OR OR OR Prepolymer t i~O~+ Prepolymer + ROH OR OR until all or most of the organo-oxy groups have reacted to give a cross-linked system.

The resins system for use in the invention can be made by a nucleophilic addition reaction. Suitable examples of nucleophilic addition reactions are Michael - Type reactions and the reaction of nucelophiles with activated carbon-carbon based moieties.

Michael -Type reactions may be defined as the reaction of a nucleophile with an a, ss-unsaturated carbonyl moiety. Michael Type reactions may be exemplified by the reaction of acrylates or acrylamides with reagents terminated with -SH, -NH2, -NH-NH2, > NH moieties.

According to an embodiment of the present invention suitable Michael - Type reactions include the reaction of acrylate or acrylamide reagents with reagents terminated with -SH, -NH2, -NH NH2, > NH moieties where at least one of the reagents is further terminated with a hydrolysable organo-oxy group.

In another embodiment of the present invention apt nucleophilic reactions comprise the reaction of nucleophiles with activated carbon-carbon based moieties. These include the reaction of reagents terminated with three membered heterocycles for example epoxides or aziridenes with reagents terminated with SH-, -NH2, -NH-NH2, > NH moieties where at least one of the reagents is further terminated with a organo-oxy group.

Suitable organo-oxy terminated reagents include but are not limited to sodium orthoborate, aminopropyltriethoxytin and tin IV halide.

The resin system of the present invention can also be prepared by employing a mixture of the reactions as herein before described.

The preparation of the prepolymer may be catalysed.

Suitable nucleophilic addition acceptors, such as acrylates, acrylamides and epoxides have a reaction functionality of at least 2 and will preferably be hydrophilic enough to render the resin system water absorbent to facilitate the hydrolysis of the organo-oxy groups when it is desired to cause the resin system to set.

The preferred prepolymers resin systems are free of isocyanate moieties and thus any perceived health hazards associated therewith are avoided.

The hydrolysis reaction of the organo-oxy silane group may be catalysed. Suitable catalysts include but are not limited to organotin salts, chloroacetic acid, methane sulphonic acid (MSA), phosphoric acids, 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 1 ,8-diazabicyclo[5.4. O]undec-7~ene (DBU), potassium fluoride, p-toluene sulphonic acid and bismorpholino dialkyl ethers such as dimorpholinodiethylether.

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 0.1% wlw of the resin.

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

Preferred formulations of the resin system according to the present invention can 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 Silts 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% wlw and aptly at least 1.0% wlw of the resin.

The resin system as hereinbefore described may be carried on any substrate suitable for a casting, splinting, support or bracing material.

The resin system employed in the invention may be coated, laminated, sprayed or impregnated onto a suitable substrate using conventional methods in the art. Aptly the bandages of the invention are prepared by nip-coating the resin system 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 resin system of the invention 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 resin 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 bandages1 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 parts of the resin system. 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 resin system.

The amount of resin carried by the substrate may vary depending on the instrinsic properties of the resin system and should be sufficient to ensure that the resultant cast has adequate strength.

Suitable amounts range from 30 to 80% w/w of the resin system which is calculated using the equation: weight of (substrate + resin) - weight of (substrate) x 100% weight of (substrate + resin) Preferably 40 to 70% w/w and most preferably 50 to 60% w/w of the resin system are used.

The material of the invention, for example in the form of a bandage, may be used to form a hardened cast by wetting and shaping the wet bandage around a body member or part thereof and allowing the bandage to cure.

Aptly wetting is achieved by immersing the bandage in water1 and removing any excess water1 for example, by squeezing the bandage several times before application to the body member.

When removed from the water the bandage can be readily wrapped about a body member or limb. Preferably the limb is covered with a conventional underlying stockinette or padding before application of the bandage.

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

The curing reaction of the resin system should be sufficiently slow to allow the bandage of the invention to be positioned and shaped before the bandage becomes unworkable. Suitable working times are aptly 1 to 6 minutes more aptly 2 minutes to 4 minutes.

The curing reaction of the resin system 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 bandage will set and become supportive between 5 and 30 minutes1 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 resin systems employed in the present invention possess 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 convention vibrating sawtooth disc.

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

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

Example 1 3-Aminopropyltrimethoxy tin (77g) was mixed with methylene bisacrylamide (30g) in an oven dried reaction vessel. The mixture was stirred and heated at 700C for a total of 48 hours. After this time a resin prepolymer was formed. The prepolymer was coated onto a dry glass fibre bandage by passing the bandage through the resin system 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. The resin 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 Polyvinyl alcohol (100 parts) was mixed with a plasticiser until homogeneous. Sodium borate (5 parts) was added and mixed in to give a resin. The resin was coated onto a dry glass fibre bandage by passing the bandage through the resin system 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. The resin was set of by dipping the coated bandage in cold water1 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 organo-oxy functionalised resin system, wherein the resin system comprises at least a prepolymer having a general formula (I):

(a) wherein A is a polymeric residue, optionally interrupted by (II)

(b) X comprises a water hydrolysable organo-oxy group based on C, to Cg hydrocarbon group or water hydrolysable halide.

(c) Y is alkyl, aryl based on C, to C6 hydrocarbon group, halide, H or X.

(d) Z is Se, Al, Sn, B or Ti.

(e)n= 1 to20, m = Oto2, p= 1 to2.

(f) Q comprises residues based on the following formulae (III).

-G-(CH2)q-D- or ~D~(CH2)q~G~ (III) where G = -CH(OH)-, -C(O)-, -CH(NH2)-, -CH(SH)- and Dis -NH-, -N < , -0-, -S- and q = 1 or 2 (g) R' and R" may be the same or different, substituted or unsubstituted and are groups based on the following C1 - 012 alkyl, aryl, cycloalkyl, heteroalkyl, heteroaryl, heterocycloalkyl all of which may be optionally interrupted by -0-, -S-, -NH-1 -C(O)-, further units of Q, with the proviso that urea -NHC(O)NH-, urethane -NHC(O)-, carbamylthio -SC(O)NH- are not represented.

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

3. A material according to claim 2 wherein the water hydrolysable alkoxy or acyloxy group is a C, to C3 hydrocarbon group.

4. A material according to claim 2 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 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 1 as an orthopaedic casting bandage or splint.