This invention concerns components made of biodegradable materials, a method of making such materials, such materials, and a method of making such components.
Orthopaedic surgery, craniofacial surgery and related fields of medicine require the use of materials which are suitable as implants and prostheses, for example to fill voids created by surgical removal of bone or tissue, or in the formation of screws, pins or plates to hold together bone surfaces or attach ligaments or tendons whilst natural healing takes place. Such materials must, particularly when they are used as load bearing implants, possess good mechanical strength and a sufficiently high Young's modulus to provide secure fixation. Commonly used prosthetic materials include metals such as cobalt—chromium alloys, titanium and stainless steel. Many studies however, have shown that the high rigidity of these materials can prevent complete healing since much of the load which is normally carried by the bone is transferred across the defect site by the implant i.e. producing a stress shielding effect. In addition, metallic implants can have a number of other disadvantages including long term metal ion release and often the need for further surgery to remove the implant.
Bioabsorbable polymers are a class of materials that are now being used in a wide range of medical applications. These include soft tissue support such as sutures and wound care patches and hard tissue repair and fixation such as plates, screws and pins. The rate of healing of bone and the establishment of viable haversian systems is about six weeks in man and hence materials for fracture support should maintain adequate strength and modulus throughout this time frame.
The invention provides a component made of a biodegradable material which material comprises a bioabsorbable polymer component and a bioactive filler material, wherein particles of the filler occur embedded within the surface of the component.
The component may comprise any of a screw, pin, plate, suture, wound care patch, spinal spacer, osteotomy wedge, cement restrictor, non-woven mesh or other item usable in surgery and related fields of medicine.
According to the present invention there is also provided a method of making a biodegradable material, the method comprising mixing together a bioabsorbable polymer component and a bioactive filler material.
The polymer component and filler are preferably mixed together in the form of granules each having similar particle size ranges. The particle size may be between 0.5 mm and 5 mm.
The polymer component and filler may be mixed together in the form of dry particulate materials.
Alternatively the polymer component may be coated with the filler.
The polymer component may be wetted with a solvent prior to or during mixing and the solvent may comprise chloroform. The polymer component may be sprayed onto the filler.
The material is preferably subsequently dried to remove the solvent.
The particle size of the polymer component may be reduced prior to mixing with the filler. The polymer component may be milled and may be cryogenically milled.
The particle size of the filler may be increased prior to mixing with the polymer component, and the filler material may be caused to agglomerate or granulate.
The invention further provides a biodegradable material, the material being formed by a method according to any of the preceding eight paragraphs.
The mixture is preferably substantially homogeneous.
The polymer component is preferably synthetic, and may comprise a polyester.
The polymer component preferably comprises one or more polymers or co-polymers of lactic acid (L and/or D), glycolic acid, hydroxybutyric acid, hydroxyvaleric acid, poly dioxanone, poly caprolactone, poly ethylene oxide or poly butylene terephthalate.
The filler may comprise alone or in combination, a calcium phosphate, calcium sulphate or carbonate bioceramic filler, or a bioactive glass. The filler preferably comprises hydroxyapatite and/or beta tri-calcium phosphate.
The filler preferably has a particle size of substantially less than 100 microns. The filler preferably constitutes between 1% and 50% of the mixture by weight, and desirably between 15% and 35%.
The filler may additionally comprise, alone or in combination, a sacrificial porosifier. The sacrificial porosifier may comprise a water soluble, heat stable inorganic salt. The inorganic salt may comprise sodium chloride. The sodium chloride may be in the form of a finely divided powder. The sodium chloride may constitute between 1% and 50% by weight of the material.
The material preferably substantially comprises no mechanically free filler particles with a diameter less than 100 microns.
The invention also provides a method of making a component, the method comprising moulding a material according to any of said preceding eight paragraphs.
The moulding may be in the form of injection moulding, compression moulding, extrusion, extrusion followed by drawing, melt spinning or other melt forming technique.
The material is preferably fed to a moulding machine, with at least a substantial proportion of the material in the form of granules with a diameter of between 0.5 and 5 mm.
The material may be dried prior to moulding.
The component may be annealed subsequent to moulding.