GB2099702A

GB2099702A - Water-soluble prosthesis

Info

Publication number: GB2099702A
Application number: GB8117141A
Authority: GB
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1981-06-04
Filing date: 1981-06-04
Publication date: 1982-12-15
Also published as: GB2099702B

Abstract

A temporary prosthesis comprising a body of non-toxic material, e.g. a glass, soluble in body fluids over an extended period of time. The prosthesis provides post-operative support of bone or tissue members. As healing proceeds the prosthesis slowly dissolves into the body fluids thus obviating the need for surgical removal. Typically the prosthesis is formed from a phosphorus pentoxide/calcium oxide/alkali metal oxide glass the dissolution rate of which can be controlled to the desired value.

Description

SPECIFICATION Prosthesis This invention relates to water soluble structural compositions and in particular to water soluble surgical support structures.

Surgical operations of an orthopaedic nature frequently involve the provision of a temporary support structure during the post-operative healing process. The exact nature of the support structure will of course depend on the nature of the particular operation performed, but in many cases the use of such a structure necessitates a further operation for its removal. This involves the patient in further discomfort and risk of infection and is of course relatively costly. Furthermore, the need for this 'followup' operation disturbs the healing process and may give rise to a variety of medical complications.

The object of the invention is to minimise or to overcome these advantages.

According to the invention there is provided temporary prosthesis for providing post-operative support of skeletal or tissue members, the prosthesis comprising a rigid body of a non-toxic material soluble in body fluids, and wherein the dissolution rate of the material is such that the prosthesis retains its supportive properties for a period sufficient for the skeletal or tissue member to become self supporting.

This prosthesis provides post-operative support of skeletal members, or tissue members such as blood vessels, for a sufficient period of time for healing of the damaged member to be effectively complete. Over the weeks or months following the operation the prosthesis slowly dissolves in the body fluids to leave substantially no solid residue thus obviating the need for a secondary or 'follow-up' operation.

Advantageously the prosthesis is made from a water soluble glass the composition of which can be tailored to provide a dissolution period which, according to the nature of the operation performed, can range from a few days to several months. Typically such glasses comprise phosphorus pentoxide as the principal glass forming oxide together with any one or more glass modifying oxides of non-toxic metals, such as sodium oxide (Na2O), potassium oxide (K2O), magnesium oxide (MgO) and calcium oxide (CaO). Other glass modifying oxides which may also be included in the glass include alumina (Al203) and ferric oxide, these latter oxides having a relatively large effect on the dissolution rate of the glass.

The rate at which a prosthesis made from such glasses will dissolve in body fluids is determined primarily by the glass composition. It is determined by the ratio of glass-modifier to glass-former oxides and in particular by the relative proportions of glass-modifying oxides in the glass. Thus, for example, the addition of one or more of calcium oxide, ferric oxide or alumina produces a corresponding decrease in the dissolution rate. By suitable adjustment of the glass composition dissolution rates ranging from substantially zero to 25 mg/cm2/hr in water at 380C and above can be obtained. The techniques of glass dissolution rate control are more fuliy described in our co-pending application No. 79 30041 (C. F.

Drake 70).

We have found that glass compositions of the type described above are non-toxic and substantially non-irritant to human or animal tissue. In particular we have found that there is minimal tissue reaction when the proportion of phosphorus pentoxide in the glass is less than 50 mole % and there is no detectable interaction when this proportion is below 48 mole %. The lower limit of the phosphorus pentoxide concentration is determined by the limits, of the glass-forming region and is about 30 mole %, the exact value of the lower limit being determined by the proportion and nature of the glass-modifying oxides present in the glass.

Glass compositions from which a prosthesis can be formed may be made by co-melting suitable quantities of the constituent oxides or precursors of those oxides for a sufficient period of time to produce an homogenous melt. Suitable oxide precursors include e.g. those carbonates or nitrates that break down during the melting process to form the corresponding oxides. Also some or all of the phosphorus pentoxide may be added in the form of ammonium phosphate or phosphoric acid which again decompose at the temperatures at which melting is performed. The composition of the glass is determined either by weighing the individual constituent or by subsequent chemical analysis of the finished glass. If the former method is used due allowance must be made for loss of some of the phosphorus pentoxide by evaporation.

At this point it should be noted that although the glass compositions are described in terms of their constituent oxides, the discrete oxides are not necessarily present in the composition. This method of defining glasses in terms of theoretical oxide constituents is however preferred and will also be familiar to those skilled in the art.

A prosthesis made from a glass described herein may be formed by a number of methods. Thus the prosthesis may simply be cast by conventional or centrifugal casting, or it may be prepared via one or more stages or rod, fibre or tube drawing. Other preparation techniques include comminution ofthe glass followed by pressing and sintering into a solid body and preparation in the form of a foamed glass.

In further applications the prosthesis may comprise a composite material containing one or more water soluble glass compositions.

Advantageously the glass may also contain elements having a therapeutic effect. Thus the glass may contain zinc oxide which promotes healing of damaged tissue and/or traces of fluoride ions which encourage bone regrowth.

We have found that glasses suitable for prosthesis construction can be formed from glasses in the calcium oxide/alkali metal oxide/phosphorus pentoxide system. A number of such glasses have been prepared by melting quantities of the mel nl oxides together with phosphoric acid. The finished glasses were analysed for their molar compositions and their dissolution rates in water at 380C were measured.

The results are summarised in the following table.

Dissolution Rate K20 Na20 CaO P205 mg/cm2/hr Oxide Mole % 0 33.0 26.1 40.9 0.17 0 33.5 22.3 44.2 0.35 0 32.2 20.2 47.5 0.90 0 34.0 27.0 39.0 0.50 0 27.8 29.8 42.4 0.25 2.0 25.0 30.0 43.0 0.19 These glasses release ions that are non-toxic to human and animal tissue and have dissolution rates suitable for use as a temporary prosthesis.

The form of the prosthesis will of course depend on the function that it has to perform. Thus, for example, plate or rod members may be used to support bone and/or cartilage, and tubular structures may be used for supporting blood vessels and the like. Other structures may be used to prevent undesired adhesion between adjacent tissues following an operation. Yet other applications include the use of the glass in the form of a tube or assembly of tube to provide a temporary connection between cut vessels or fibres and simultaneously to define a space in the surrounding tissue into which said vessel or fibre can subsequently grow. Fine single or woven fibres of the glass can be used as a ligature in surgery or microsurgery.

Claims

1. A temporary prosthesis for providing post-operative support of skeletal or tissue members, the prosthesis comprising a rigid body of non-toxic material soluble in body fluids, and wherein the dissolution rate of the material is such that the prosthesis retains its supportive properties for a period sufficient for the skeletal or tissue member to become self supporting.

2. A prosthesis as claimed in claim 1 , wherein said material comprises wholly or partially a water soluble glass.

3. A prosthesis as claimed in claim 2, wherein said glass comprises a phosphorus pentoxide/calcium oxide/alkali metal oxide glass.

4. A prosthesis as claimed in claim 3, wherein said glass contains alumina.

5. A prosthesis as claimed in claim 2, 3 or 4, wherein said glass contains zinc oxide.

6. A prosthesis as claimed in any one of claims 2 to 5, wherein said glass contains one or more fluorides.

7. A prosthesis as claimed in any one of the preceding claims, and wherein the dissolution rate of said material in water at 38CC is less than 25 mg/cm2/hr.

8. A prosthesis as claimed in any one of the preceding claims and in the form of a tube.

9. A temporary prosthesis substantially as hereinbefore described.

1 0. A method of performing a surgical operation, including supporting injured tissue or bone with a temporary prosthesis comprising a body of non-toxic material soluble in body fluids at a dissolution rate sufficiently low that the supportive function of the prosthesis is maintained until the tissue or bone becomes self supporting.

11. A method of performing a surgical operation substantially as hereinbefore described.

12. A method of making a temporary prosthesis substantially as hereinbefore described.

New claims or amendments to claims filed on 22nd September 1981 Superseded claim:-- claim 1 New or amended claim:

1. A temporary prosthesis for providing post-operative support of skeletal or tissue members, the prosthesis comprising a rigid body of non-toxic amorphous material soluble in body fluids, and wherein the dissolution rate of the material is such that the prosthesis retains its supportive properties for a period sufficient for the skeletal or tissue member to become self supporting.