IMPLANT AND METHOD FOR ITS MANUFACTURE

Description

[0001] The present invention relates to an implant and a method for manufacturing this implant. The implant of the invention is intended to come into direct contact with bone tissue, without the use of cement, resin, glue, etc. The objective is for the bone tissue to develop and regrow on the surface and in depth of the implant by osseointegration. An implant is understood to mean any part, set of parts or devices intended to be implanted, partially or completely, in a human or animal body. Examples include dental implants, hip prostheses, knee prostheses, shoulder prostheses, intervertebral cages, etc.

[0002] In femoral implants, for example, we know of titanium or titanium alloy acetabular cups intended to be implanted in a cavity of the iliac bone. The titanium or titanium alloy constituting the acetabular cups is very dense: it is not porous. These acetabular cups generally have a hemispherical external shape intended to come into contact with the bone cavity. The hemispherical external surface of the acetabular cup can be structured, for example with a grid network of grooves, thus delimiting small protruding blocks. This macrostructure increases the specific surface area of ​​contact with the bone, which reinforces the stability of the acetabular cup in the bone cavity, but is not sufficient to allow bone regrowth. It is common to coat the external surface of the acetabular cup (structured or not) with hydroxyapatite, a mineral component naturally present in bone, in order to increase its osseointegration.However, this hydroxyapatite coating does not allow a controlled host response and a "foreign body" reaction may occur.

[0003] On the other hand, it is known from document EP2032663 to graft PolyNaSS (sodium polystyrene sulfonate) onto titanium or titanium alloy implants, with the aim of promoting the biointegration of the implants into the tissues by allowing bone regeneration, while preventing infections, thanks to its chemical characteristics of mimicking glycosaminoglycans, which prevent the adhesion of bacteria and the creation of bacterial biofilm.

[0004] It is not possible to graft PolyNaSS onto a hydroxyapatite-coated acetabulum. However, it is possible to graft PolyNaSS onto acetabulum without hydroxyapatite.

[0005] The present invention aims to overcome the aforementioned drawbacks by defining a titanium or alloy implant having optimal roughness, so as to be able to be coated with PolyNaSS by grafting, in order to allow controlled bone regrowth and avoid bacterial biofilm and infection.

[0006] In the prior art, we know the document FR2789315A1 from 1999 which describes a titanium alloy implant which is coated: of an inner porous layer having a thickness of 60 to 100 µm, a porosity of less than 10% and a roughness of less than 50 µm, and of an outer porous layer having a thickness of 60 to 100 µm, a porosity of 10 to 20% and a roughness of 100 to 150 µm.

[0007] The implant thus formed is then coated with calcium hydroxyapatite.

[0008] In the prior art, the 2008 publication entitled Mayingi et al: "Synthesis and grafting of bioactive polymers on titanium surfaces to promote osseointegration", IRBM, ELSEVIER, AMSTERDAM NL, vol.29, n°1, March 1, 2008 (2008-03-01), pages 1-6, XP022832498, ISSN: 1959-0318, DOI: 10.1016 / J.RBMRET.2007.10.001 (extracted on 2008-03-04) is also known. ). This 2008 publication describes the grafting of PolyNaSS onto titanium or a titanium alloy. The characteristics of titanium (or titanium alloy) are not specified in this publication.

[0009] Document FR2902102A1 from 2006 also deals with the grafting of PolyNaSS onto titanium. The research report for this document FR2902102A1 cites a document EP0893164A2 from 1998 which already deals with the grafting of NaSS.

[0010] The present invention provides an implant comprising a dense body of titanium or titanium alloy, which is coated with a porous layer of titanium or titanium alloy, similar to that of document FR2789315A1 of 1999, but on which PolyNaSS has been deposited by grafting, as in document EP0893164A2 of 1998, instead of calcium hydroxyapatite.

[0011] It can thus be noted that more than 20 years have passed between the publication of documents FR2789315A1 and EP0893164A2 and the filing of this application. And if we consider document FR2902102A1 from 2006, 15 years have still passed. This implies that the grafting of PolyNaSS onto a porous layer of titanium is not at all obvious to specialists in the field of implants. Otherwise, this technology would have been described and implemented a long time ago. This long period must be seen as a clear indication of inventive activity.

[0012] This long period is also explained by technical considerations, and in particular an optimization of oxidation due to the porosity of the layer, which allows for grafting rates 10 to 20 times higher, an essential factor in bone regeneration. In addition, we thus obtain a hybrid material composed of titanium and living bone tissue, perfectly integrated thanks to the presence of polyNaSS, which will at the same time prevent any bacterial adhesion and therefore infection. This true composite material has a progressive modulus of elasticity between dense titanium and cortical or cancellous bone. This structure is not obvious, even for specialists in the field.

[0013] Advantageously, the dense body can have a roughness Ra of 4 µm to 8 µm. Indeed, the roughness of the dense body, which is not porous, allows better adhesion of the porous layer.

[0014] Advantageously, the porous layer may have a thickness of the order of 200 µm to 400 µm, advantageously of the order of 300 µm to 400 µm.

[0015] According to a successful embodiment, the porous layer may comprise a porous inner layer in contact with the dense body and a porous outer layer in contact with the porous inner layer, the two inner and outer porous layers having different porosities, the porous outer layer advantageously having a porosity greater than that of the porous inner layer.

[0016] The inner layer with small particles improves adhesion to the dense body and the outer layer with larger particles allows for pore diameters and therefore high volume porosity, factors essential for all-round blood vascularization and consequently optimal bone colonization.

[0017] Preferably, the porous outer layer may have a porosity of the order of 10% to 25%, advantageously of the order of 20%. Furthermore, the porous outer layer may have a thickness of the order of 150 µm to 300 µm. Furthermore, the porous outer layer may consist of titanium or titanium alloy powder having a particle size of between 90 µm and 250 µm. The porous outer layer preferably has an average roughness Ra of the order of 30 to 70 µm and a maximum roughness Rz of the order of 150 to 300 µm.

[0018] The porous outer layer is the optimal osseointegration layer due to its roughness and porosity. It also provides an optimal impregnation layer for PolyNaSS.

[0019] For its part, the porous inner layer can have a thickness of the order of 50 µm to 100 µm. It can be made of titanium powder or titanium alloy having a particle size between 40 µm and 100 µm. The porous inner layer can have an adhesion greater than or equal to 22 MPa. The porous inner layer can be described as an optimal adhesion layer allowing both good adhesion to the dense body and good adhesion of the porous outer layer. It should be noted that the porous inner layer can be deposited on the external surface of an acetabulum with a macrostructure, as explained above.

[0020] The present invention also defines a method for manufacturing an implant comprising a dense body of titanium or titanium alloy, characterized in that a porous layer of titanium or titanium alloy is deposited using a plasma torch on the dense body, PolyNaSS then being deposited by grafting onto the porous layer.

[0021] Preferably, the manufacturing method comprises the following steps: a- depositing titanium powder with a plasma torch having an average particle size of the order of 40 to 100 µm, so as to form on the dense body a porous internal layer having a thickness of the order of 50 µm to 100 µm, b- depositing titanium powder with a plasma torch having an average particle size of the order of 90 to 250 µm, so as to form on the porous internal layer a porous external layer having a thickness of the order of 150 µm to 300 µm, and advantageously a porosity of 10 to 25%, c- grafting PolyNaSS onto the porous external layer.

[0022] The plasma torch allows the titanium powder grains to be deposited at a temperature high enough for their external surface to be at least partially molten, so that the powder grains will stick to each other, leaving cavities between them, hence the desired porosity. The PolyNaSS is then deposited on the uneven external surface of the external porous layer, penetrating more or less into the cavities. It can be considered that the specific surface is at least multiplied by 2 or 3, in comparison with a classic macrostructured acetabulum coated with hydroxyapatite. Thus, a significant quantity of PolyNaSS can be deposited with quality adhesion.

[0023] The spirit of the present invention lies in creating a rough external titanium surface, in order to be able to apply PolyNaSS, which will adhere perfectly to this external titanium surface and which will be able to fully fulfill its function of bone regrowth by osseointegration and its function of anti-bacterial adhesion.

[0024] The invention will now be more fully described with reference to the attached drawings giving, by way of non-limiting example, an embodiment of the invention.

[0025] In the figures: There figure 1 is a perspective view slightly from above of an implant in the form of a conventional acetabulum made of titanium or titanium alloy, The figure 2 is an exploded perspective view of the acetabulum of the figure 1 , There figure 3 is a vertical cross-sectional view through the acetabulum of the figures 1 et 2 , on which the present invention has been implemented, and The figure 4 is an enlarged view of part of the figure 3 , revealing more clearly the fine structure of the acetabulum of the invention.

[0026] A cup was used to illustrate the present invention, which can be applied to all kinds of implants intended to come into contact with the bone, without the use of cement or other binder.

[0027] The implant cup of the figures 1 et 2comprises a body 1 which is made of titanium or a very dense titanium alloy: it is not porous. This body 1 has a hemispherical shell shape: its thickness can be of the order of 4 to 5 mm. The body is hollow and contains a friction component 2 which can be made of Al 2 O 3 or PE. This friction component 2 therefore forms an internal cavity, which is intended to receive the femoral head mounted on a femoral stem. Externally, the body 1 defines a hemispherical external surface 11 which can be structured, for example with a grid network of grooves 12, thus delimiting small projecting blocks 13. This macrostructure increases the specific contact surface, which reinforces the stability of the acetabulum in the bone cavity of the iliac bone. This is a completely classic design for an acetabulum. In addition, the external surface 11 of the dense body 1 preferably has a roughness Ra of 4 µm to 8 µm.

[0028] According to the invention, the external surface 11 of the acetabulum is covered by a porous layer of titanium or titanium alloy, which may have a thickness of the order of 200 µm to 400 µm, advantageously of the order of 300 µm to 350 µm. The roughness of the dense body 1 allows better adhesion of the porous layer.

[0029] According to a successful embodiment, the porous layer may comprise a porous inner layer 3 in contact with the outer surface 11 and a porous outer layer 4 in contact with the porous inner layer 3. The two porous inner 3 and outer 4 layers preferably have different porosities: the porous outer layer 4 advantageously having a porosity greater than that of the porous inner layer 3. Preferably, the porous outer layer 4 may have a porosity of the order of 10% to 25%, advantageously of the order of 20%. Furthermore, the porous outer layer 4 may have a thickness of the order of 150 µm to 300 µm. Furthermore, the porous outer layer 4 may be made of titanium or titanium alloy powder having a particle size of the order of 90 to 250 µm. The porous outer layer 4 preferably has an average roughness Ra of the order of 30 to 70 µm and a maximum roughness Rz of the order of 150 to 300 µm.Finally, the porous layer (internal and external together) can have an adhesion greater than or equal to 22 MPa.

[0030] For its part, the porous internal layer 3 may have a thickness of the order of 50 µm to 100 µm. It may be made of titanium powder or titanium alloy having an average particle size of the order of 40 to 100 µm.

[0031] Classical definitions are given to the following terms and expressions: Porosity: ratio of void volume to total volume, Grain size (average): size (average) of titanium powder grains, Average roughness Ra: average distance between peaks and valleys, and Maximum roughness Rz: maximum roughness of the profile.

[0032] The deposition of the outer layer 4 directly onto the outer surface 11 of the acetabulum is not possible, or at least not effective, because the adhesion of the large powder grains is difficult to achieve. Hence the implementation of the inner layer with smaller powder grains.

[0033] According to the invention, PolyNaSS 5 is deposited by grafting, on this porous layer 4, given that it is made of titanium or titanium alloy.

[0034] An optimal manufacturing process includes the following steps: a- depositing titanium powder with a plasma torch having an average particle size of the order of 40 to 100 µm, so as to form on the external surface 11 the porous internal layer 3 with a thickness of the order of 50 µm to 100 µm, b- depositing titanium powder with a plasma torch having an average particle size of the order of 90 to 250 µm, so as to form on the porous internal layer 3 the porous external layer 4 with a thickness of the order of 150 µm to 300 µm, and finally c- grafting PolyNaSS 5 onto the porous external layer 4.

[0035] The plasma torch made it possible to obtain good adhesion of powder grains to each other, while maintaining optimal porosity.

[0036] The grafting step may include the following steps: c1) Immersing the implants in an acid bath to etch them, c2) Rinsing the implants, c3) Immersing the implants in an anodizing bath to anodize them, c4) Rinsing the implants, c5) Introducing the implants into a polymerization chamber filled with inert gas, such as argon, c6) Immersing the implants in a polymerization bath present in the chamber, c7) Subjecting the polymerization bath to a polymerization catalyst to synthesize bioactive polymer on the implants, c8) Extracting the implants from the chamber, and c9) Washing the implants to remove excess ungrafted bioactive polymer.

[0037] The PolyNaSS 5 chains can thus attach to the porous layer, which is also particularly rough and porous.

[0038] Grafting PolyNaSS onto a porous titanium surface provides a dual benefit. First, PolyNaSS is better anchored in the disrupted relief of outer layer 4. Second, this disrupted relief allows for more PolyNaSS to be anchored, which promotes bone regrowth and bacterial anti-adhesion.

[0039] Although the invention has been described with reference to an acetabulum having a dense body of titanium or titanium alloy, it applies to any implant having a dense body of titanium or titanium alloy.

Claims

1. An implant comprising a dense body (1) made of titanium or titanium alloy, coated with a porous layer (3, 4) made of titanium or titanium alloy, characterized in that the porous layer (3, 4) comprises a deposition of PolyNaSS (5) applied by grafting.

2. The implant according to claim 1, wherein the dense body (1) has a roughness Ra of 4 µm to 8 µm.

3. The implant according to any one of the preceding claims, wherein the porous layer (3, 4) has a thickness of the order of 200 µm to 400 µm, advantageously of the order of 300 µm to 400 µm.

4. The implant according to any one of the preceding claims, wherein the porous layer comprises a porous inner layer (3) in contact with the dense body (1) and a porous outer layer (4) in contact with the porous inner layer (3), the two porous inner (3) and outer (4) layers having different porosities, the porous outer layer (4) advantageously having a porosity greater than that of the porous inner layer (3).

5. The implant according to any one of the preceding claims, wherein the porous outer layer (4) has a porosity of the order of 10% to 25%, advantageously of the order of 20%.

6. The implant according to any one of the preceding claims, wherein the porous outer layer (4) has a thickness of the order of 150 µm to 300 µm.

7. The implant according to any one of the preceding claims, wherein the porous outer layer (4) is made of titanium or titanium alloy powder having an average particle size of the order of 90 to 250 µm.

8. The implant according to any one of the preceding claims, wherein the porous outer layer (4) has an average roughness Ra of the order of 30 to 70 µm and a maximum roughness Rz of the order of 150 to 300 µm.

9. The implant according to any one of the preceding claims, wherein the porous inner layer (4) has an adhesion greater than or equal to 22 MPa.

10. The implant according to any one of the preceding claims, wherein the porous inner layer (3) has a thickness of the order of 50 µm to 100 µm.

11. The implant according to any one of the preceding claims, wherein the porous inner layer (3) is made of titanium or titanium alloy powder having an average particle size of the order of 40 to 100 µm.

12. A method for manufacturing an implant comprising a dense body (1) made of titanium or titanium alloy, porous layer (3, 4) made of titanium or titanium alloy being deposited using a plasma torch on the dense body (1) of the PolyNaSS (5) then being deposited by grafting on the porous layer (3, 4).

13. The manufacturing method according to claim 12, comprising the following steps: a- depositing titanium powder having an average particle size of the order of 40 to 100 µm with a plasma torch, so as to form on the dense body (1) a porous inner layer (3) having a thickness of the order of 50 µm to 100 µm, b- depositing titanium powder having an average particle size of the order of 90 to 250 µm with a plasma torch, so as to form on the porous inner layer (3) a porous outer layer (4) having a thickness of the order of 150 µm to 300 µm, and c- grafting PolyNaSS (5) onto the porous outer layer (4).