FR2664501A1 - Composite material for osseous implant and method for using it as a covering - Google Patents

Abstract

Composite material (10) for osseous implant, characterised by the fact that it comprises at least one flexible metal latticework layer, onto which there is moulded, frozen then lyophilised, a mixture comprising at least collagen and at least one calcium phosphate. Application in particular as insert in a cavity (2) of an implant (1) or as a covering for such an implant.

Description

Composite material for bone implant and method of use as a coating
The present invention relates to a composite material for bone implant, and in particular for osteoarticular implant fixed without cement; it also relates to a process for using this material as a coating.

 It is known in fact that the fixation of the osteoarticular implants with a cement of polymethyl methacrylate type poses a certain number of problems - Exothermic polymerization which brings about a more or less significant tissue necrosis.

- Release of the monomer in the cardiovascular system generating pressure drops.

- Release of cement particles causing tissue reactions.

- Resistance to fatigue quite low causing ruptures of the cement case with a risk of loosening.

- Difficulties in removing this cement during a reintervention.

 All of these problems have led surgeons and researchers to develop solutions for fixation by bone regrowth on the implant. These solutions involve perfect mechanical blockage of the implant during the first post-operative weeks. To achieve this result, it has already been proposed to implement - Implants with simple corrugations of variable, longitudinal, circular shapes, in which the bone is supposed to regrow.

- Implants with external macropores, obtained by microfusion technology.

- Implants on which surface treatments have been carried out, for example sandblasting, in order to obtain a high surface roughness and therefore allow bone "hooking".

- Implants onto which beads or particles of titanium, cobalt-chromium have been sprayed with a plasma torch, which create either a porous structure or a surface roughness, depending on the thickness deposited.

- Implants that have been coated with a plasma torch with calcium phosphates, such as hydroxyapatite.

- Implants on which metallic textures have been fixed by mechanical-thermal treatment.

 All of these solutions pose significant problems with regard to the long-term behavior of the metal alloy of the implant, because the macroporosities and the microporosities are points of weakness which can lead to initiations of rupture by fatigue-corrosion.

 On the other hand, the coatings of calcium phosphates by plasma torch have only a purely mechanical adhesion and can be the object of flaking causing a salting out of particles and its multiple consequences in terms of friction components, tissue reactions, periprosthetic ossifications ...

 In addition, the surfaces of the implants are treated with a relatively small thickness and do not allow all-round vascularization: bone regrowth cannot therefore take place in the crevices and will be insufficient. There is only a simple apposition of bone which does not create an interface whose elasticity module is adapted to both that of the bone tissue and of the implant: this results in long-term holding difficulties. sealing of the prosthesis.

 The present invention aims to avoid these drawbacks.

 The subject of the present invention is a composite material for bone implant, characterized in that it comprises at least one layer of flexible metal mesh on which is overmolded, frozen and then lyophilized a mixture comprising at least collagen and at least one phosphate of calcium.

 Collagen can be of animal or human origin; it is absorbed in a few weeks.

 Preferably, calcium phosphates, sintered or not, will be used, based on absorbable tricalcium phosphate, a particularly osteogenic material, since its calcium and phosphate ions complement the natural intake.

 The chemical composition of the phosphates can be chosen according to the desired rate of resorption.

 It is also possible to use a mixture of absorbable tricalcium phosphate and non-absorbable hydroxyapatite, the latter contributing, with the lattice, to serve as a support for the bone tissue in formation.

 It may be advantageous to add to the mixture of active principles such as antibiotic, antimitotic, growth factor these products are directly released into the area of the infection or of the tumor as the collagen and the absorption of calcium phosphate.

 The material according to the invention preferably has a sandwich structure with several layers of lattice arranged parallel to each other. Each layer is formed of expanded or woven metal, chosen from titanium, tantalum, niobium.

 The different trellises can be crossed, for example at 450 or 900.

 The material according to the invention can be intended to be used as an insert held in an implant without cement. This implant, preferably with a smooth surface and without porosity, no longer presents the risks of metallic embrittlement and of corrosion, like the implants of the prior art.

Thus, in the thickness of the implant, a cavity is made in which the material insert according to the invention is housed. It can be maintained there by any means, for example a trellis system, itself fixed with the aid of rings of the same metal as the trellis. The whole can be overmolded with a collagen and calcium phosphate compound which may or may not have the additives mentioned above. This overmolding plays a protective role in the trellis, for example during the forced insertion of a hip femoral implant into the metaphysso-diaphyseal zone.

 Collagen and the external mesh layer, perfectly compatible materials, not only play a protective role, but also allow better blocking of the implant, given the significant deformations they may undergo. On the other hand, the very hydrophilic collagen, exhibits swelling and ensures better adaptation and better tightening against the bone walls.

 After the resorption of collagen which takes place in a few weeks, the material according to the invention is reduced to an assembly formed by the lattice, the non-absorbed calcium phosphates and possibly the active principles. This very porous texture allows an all-round vascularization, internal and external to the implant, resulting in faster and more significant regrowth of the bone.

This texture creates an interface between the bone and the metal implant, a real composite material with a thickness of around 2 mm, formed of an inert phase, the prosthetic materials, and a living phase, the bone. . The elastic modulus of this composite is relatively close to that of bone tissue and makes it possible to avoid the problems encountered with current prostheses, where bone regrowth is limited to a simple apposition of thin bone on a rigid porous texture. .

 The present invention also relates to a method of using the material defined above, as a coating for a prosthetic implant. At least one layer of mesh is then fixed on the implant; said mixture is overmolded and then freezing and lyophilization are carried out.

 Other characteristics and advantages of the present invention will appear during the following description of embodiments, which will be made with the aid of the appended drawing, given by way of illustration but in no way limiting.

 - Figure 1 is a schematic exploded view of a hip femoral implant without cement, provided with a composite material according to the invention.

FIG. 2 is a diagrammatic perspective view, partially broken away, of the composite material according to the invention associated with the implant of FIG. 1.

- Figure 3 is a schematic perspective view, partially broken away, of the implant of Figure 1.

- Figure 4 is a schematic perspective view partially broken away where the material according to the invention is used as a coating.

 We see in Figure 1 a femoral stem 1 intended to be implanted without cement in a femur. It has two housings 2 and 2 'at its upper part intended to contain respectively two inserts 10 and 10' of material according to the invention. These inserts are held in place by a trellis 4 made of unalloyed titanium, locked between two shoulders 3 and 8 and a longitudinal groove 7 by two rings made of unalloyed titanium 5 and 6. Figure 3 shows the rod 1 fitted with its insert 10 visible in more detail in FIG. 2.

 We see three flexible titanium lattices 11, 12, 13 arranged parallel to each other and crossed at 90 degrees. The wire of each trellis has a diameter of 0.1 to 0.2 mm and the diamonds of the trellis have diagonals of approximately 4mm and 2mm.

 These trellises are embedded in a frozen and lyophilized mixture comprising collagen of animal or human origin, tricalcium phosphate B, and optionally hydroxyapatite and active ingredients.

 For example, the material comprises by weight 80% of tricalcium phosphate, 12% of titanium and 8% of collagen.

 The assembly is flexible, can be compressed at the time of the placement of the femoral stem, which facilitates the introduction and avoids the risks of bursting of the femur.

 Collagen is absorbed in a few weeks, tricalcium phosphate B in two to three months with in situ release of calcium ions and phosphate ions. The hydroxyapatite possibly added to the mixture, does not dissolve; with the lattices it constitutes a support around which the bone grows and anchors.

 A process for freezing and freeze-drying a mixture comprising collagen is described in the article by D. HERBAGE "Collagens - Novelty Dermatology 4 - pages 76 to 78. 1985.

 It can be envisaged to line the housings 2 and 2 ′ beforehand with a first layer of titanium mesh; according to a variant, these housings can be coated with a layer of a few microns of non-absorbable hydroxyapatite deposited in the gas phase, this layer has greater adhesion than those produced by plasma torch and makes it possible to further improve the physicochemical bond with the 'bone.

 FIG. 4 illustrates another example of a process for using the material according to the invention as a coating. For this purpose, several layers of superimposed titanium lattice 21, 22, 23 are applied in the cavity 2 and the lattice 4 is fixed as previously using the rings 5 and 6. The whole lattice is then overmolded with the mixture 20 described above which seeps into the mesh of the trellis. Freezing and lyophilization are then carried out. It is noted that the coating thus obtained is slightly domed with respect to the surface of the femoral stem 1.

 According to another variant not illustrated, the trellis are fixed to the surface of the implant, the shape of this implant not making it possible to provide a cavity there.

 Of course, the invention is not limited to the embodiment which has just been described, both in terms of the composition of the material according to the invention and in terms of its use. The material according to the invention can be used in many types of implants, in particular acetabular cups, knee prostheses, dental prostheses .......

Claims (12)

1 / Composite material for bone implant, characterized in that it comprises at least one layer of flexible metal mesh on which is overmolded, frozen and then lyophilized a mixture comprising at least collagen and at least one calcium phosphate. 2 / composite material for bone implant according to claim 1, characterized in that said calcium phosphate is chosen according to its rate of absorption. 3 / composite material for bone implant according to one of claims 1 and 2, characterized in that said calcium phosphate is sintered. 4 / composite material for bone implant according to claim l, characterized in that it comprises absorbable tricalcium phosphate and non-absorbable hydroyapatite. 5 / composite material for bone implant according to one of the preceding claims, characterized in that said mixture further comprises at least one active principle, such as an antibiotic, an antimitotic, or a growth factor. 6 / composite material for bone implant according to one of the preceding claims, characterized in that the material of said mesh is chosen from titanium, tantalum, niobium. 7 / composite material for bone implant according to one of the preceding claims, characterized in that said mesh is made of expanded or woven metal. 8 / composite material for bone implant according to one of the preceding claim, characterized in that it comprises several layers of lattice arranged parallel to each other.  9 / composite material for bone implant according to claim 8, characterized in that said lattices are crossed at 450 or 900. 10 / Application of the composite material according to one of the preceding claims, as an insert in a bone implant. 11 / Application according to claim 10, characterized in that said insert and said implant are provided at least partially with an overmolding in a compound comprising at least collagen. 12 / A method of using the material according to one of claims 1 to 9, as a coating for a prosthetic implant, characterized in that at least one of said layers of mesh is fixed to said implant, that the the said mixture is overmolded and then frozen and lyophilized.