Coating for improved wear resistance of orthopedic implants

Abstract

A medical implant includes a titanium-based component and a ceramic coating on the component, the ceramic coating including A12O3, TiO2, or a mixture of both A12O3 and TiO2, that is compressively stressed.

Description

COATING FOR IMPROVED WEAR RESISTANCE OF ORTHOPEDIC IMPLANTSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to co-pending U.S. Provisional Patent Application No. 63 / 683,931 filed on August 16, 2024, the entire content of which is incorporated herein by reference.FIELD OF THE INVENTION

[0002] The present invention relates to medical implant components, and more particularly to a medical implant component with a ceramic coating under compressive stress.BACKGROUND

[0003] Metal hypersensitivity is a common problem with many orthopedic implants. Metal allergy (or hypersensitivity) is an excessive immune response to certain metals. Many of these metals are common in orthopedic implants. Metals are thought to produce an immune response by the metal surface becoming attached to natural serum proteins and changing them enough to look foreign to the implantee’s immune system. This can result in an infection, which may cause the patient excessive pain and potentially result in implant failure. The metals that are common sensitizers include nickel, cobalt and chrome. Nickel is the most common sensitizing metal followed by cobalt and then chrome.

[0004] A solution to address metal hypersensitivity is to use titanium as the base metal for implants. Alloys having a composition of Ti, 6%V, 4%A1 have the strength to replace common implant materials such as CoCr. This alloy also has the advantage that metal hypersensitivity is extremely low. However, compared to more common CoCr alloys, Ti alloys often have decreased wear resistance and titanium alloys do not hold up as well to abrasive or adhesive wear, both wear mechanisms are found in articulating surfaces of orthopedic implants.SUMMARY

[0005] This disclosure addresses the wear performance of Ti alloys by the addition of a wear resistant coating applied to the Ti implants on surfaces that see wear. Example surfaces include hip femoral heads and acetabulum (sockets), knee femoral component and tibial inserts, and shoulder humeral heads and glenoid components. The coatings included under this disclosure are hard ceramic materials that are deposited using unique thermal spray deposition methods.

[0006] New ceramic coatings and a coating method to produce the coatings for orthopedic implants are provided. These ceramic coatings have properties to maximize their performance as wear resistant surfaces to articulating implant surfaces. The method used to develop these coatings produces ceramic coatings that have low porosity content, high hardness, high adhesion, high fracture toughness, are compressively stressed and can be finished to extremely smooth surface finishes. All these coating properties are desired for providing excellent wear resistance and longevity for an orthopedic implant wear surface.

[0007] Thermal sprayed ceramic coatings are commonly produced using a plasma spray process. The very high temperatures generated in the plasma spray process works well in melting ceramic materials that typically have high melting points. The present disclosure is directed to ceramic coatings produced using a unique high-velocity oxy-fiiel (“HVOF”) deposition process, not plasma spraying. Most HVOF thermal spray processes do not create ceramic coatings well due to their high gas velocities and relatively lower process temperatures compared to plasma spraying. This combination of temperature and limited dwell time of the ceramic powder particles in the HVOF flame do not provide enough energy to melt the ceramic powders properly. The present disclosure is directed to creation of unique coatings using an HV-2000 HVOF torch or gun assembly and related support systems, manufactured by Thermach of Appleton, Wisconsin. This is a system that axially injects the feedstock powder into the combustion chamber and has a slower gas velocity than most HVOF processes. The axial injection into the combustion chamber in combination with the slightly slower gas velocity allows sufficient heating of the ceramic powder for deposition of the ceramic material. The higher gas velocities of this process, relative to plasma spray processes, provides significantkinetic energy to propel the particles on the surface being coated to create well-adhered coatings that are compressively stressed, have very low porosity (less than 1.0% by area), high hardness, and high fracture toughness. Materials such as pure aluminum oxide, pure titanium oxide, and mixtures and alloys of aluminum oxide and titanium oxide can be deposited by the HV 2000 HVOF System with the proper process parameters to produce dense well adhered coatings.

[0008] The present disclosure provides, in one aspect, a medical implant component including: a titanium-based component: and a ceramic coating on the component, the ceramic coating including A12O3, TiO2, or a mixture of both A12O3 and TiO2, that is compressively stressed.

[0009] The present disclosure provides, in another aspect, a method of coating a medical implant component, the method including: providing a medical implant component; and applying a ceramic coating to the component using an HVOF process.

[0010] Other features and aspects of the invention will become apparent by consideration of the following detailed description and accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1A is an exploded perspective view of components of a femur in a total hip replacement.

[0012] FIG. IB is a perspective view of the assembled components of a femur in a total hip replacement of FIG. 1A.

[0013] FIG. 1C is a perspective view of a total hip replacement of FIG. 1 A.

[0014] FIG. ID is a perspective view of the medical implants of a total knee replacement.

[0015] FIG. IE is a perspective view of the medical implant components of a total shoulder arthroplasty.

[0016] FIG. IF is a perspective view of the medical implant components of a reverse shoulder arthroplasty.

[0017] FIG. 2 is a section view of a high-velocity oxy-fuel gun depositing a ceramic coating on a medical implant component.

[0018] FIG. 3A is a diagram illustrating the Vickers microhardness measurement procedure used to measure fracture toughness, including a cross-section showing load application and a top view showing indentations at various loads.

[0019] FIG. 3B is a diagram illustrating the Vickers microhardness measurement process used to measure fracture toughness and an exemplary' image illustrating measurements used in the hardness calculation.

[0020] FIG. 4 is a chart illustrating bar deflection as a function of coating thickness and the coating process.

[0021] FIG. 5A is an illustration of a scratch testing process.

[0022] FIG. 5B is an illustration of a scratch testing process.

[0023] FIG. 5C is an illustration of a scratch testing process.

[0024] FIG. 6 is an exemplary cross-section of a sample tested using the scratch testing process of FIGS. 5A-5C.

[0025] FIG. 7 is a set of cross-sections of samples of a medical implant component with a plasma- or HVOF-deposited coating tested using the scratch testing process of FIGS. 5A-5C.

[0026] FIG. 8 is a chart illustrating a comparison of interfacial crack length resulting from a scratch load for plasma- and HVOF-deposited coatings.

[0027] FIG. 9 is a chart illustrating a comparison of cone area resulting from a scratch load for plasma- and HVOF-deposited coatings.

[0028] FIG. 10 is a cross-section of a medical implant component with a TiO2 coating deposited by an HVOF process.

[0029] FIG. 11 is a perspective view of a femoral head coated with a Ti02 coating having a polished surface finish of less than 1 pin. Ra.

[0030] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology7used herein is for the purpose of description and should not be regarded as limiting.DETAILED DESCRIPTION

[0031] FIGS. 1A-1F illustrate medical implant components in joints that are frequently the subject of component replacement surgeries. FIGS. 1 A-1C illustrate components of a total hip replacement in which a coated femoral head implant 10 (e.g., the replacement “ball” of a “ball and socket joint”) is coupled to the femur stem 14. An acetabular component 18 (the replacement “socket,” or hip acetabulum) is coupled to the pelvis 22. The femoral head implant 10 is positioned in the acetabular component 18 and a plastic liner 26 is positioned in the acetabular component 18 between the femoral head implant and the acetabular component 18. FIG. ID illustrates components of a total knee replacement including a stemmed tibial plate 30 or tibial insert that is coupled to the tibia, a coated knee femoral component 34 (e.g., the replacement for the lower end of the femur), and a polyethylene articulating surface 38 positioned on the stemmed tibial plate 30 and along which the knee femoral component 34 articulates. FIG. 1 E illustrates a total shoulder arthroplasty procedure in which a coated humeral head 40 replaces the head, or upper end, of the humerus 44 and contacts the glenoid 48, or glenoid disc. FIG. IF illustrates a reverse shoulder arthroplasty procedure in which a glenoid 48 is replaced with a coated glenoid sphere 52 and contacts a humeral cap 56 coupled to the humerus 44.

[0032] FIG. 2 illustrates an HV-2000 HVOF torch 60 used to deposit a ceramic coating64 on a medical implant component, illustrated in FIG. 2 as a femoral head 10. The HVOF torch 60 includes a torch body 68 defining a plurality of passages. The passages include a first passage 72 through which a powdered ceramic material axially travels from a powder source (not shown)to a combustion chamber 76. The powdered ceramic material is combined with a carrier gas (e.g., a non-combustible gas such as nitrogen or argon) prior to travelling through the first passage 72. The torch body 68 also defines a second passage 80 through which a fuel / oxygen mixture is introduced into the combustion chamber 76. The fuel in the fuel / oxygen mixture may be hydrogen, propylene, or other appropriate fuel. Other passages may be defined in the torch body 68, such as a coolant passage 84 through which a coolant (e.g., water or other appropriate coolant) travels to maintain the proper operating temperature of the torch 60. The combustion chamber 76 defines a nozzle portion 88 having a decreasing cross-section. An outlet passage 92 extends through the torch body 68 from the nozzle portion 88 to a torch outlet 96. In the combustion chamber 76, the fuel / oxygen mixture and the powder / carrier gas are combined and the fuel / oxygen mixture is ignited to melt the powdered ceramic as well as to propel the melted ceramic powder through the outlet passage 92 and out of the torch outlet 96. The stream 100 of melted powdered ceramic is directed to and deposited on a substrate, e.g., a titanium-based medical implant component such as a femoral head implant 10 (shown in FIG. 2), knee femoral component 34 (FIG. ID), humeral head 40 (FIG. IE), glenoid sphere 52 (FIG. IF), or other implant component. In other embodiments, the medical implant component may instead be stainless steel, CoCr (cobalt-chromium), Ta (tantalum), or Ta alloys.

[0033] The torch 60 is ideal for HVOF deposition of ceramic materials such as aluminum oxide, titanium oxide, as well as mixtures and alloys of these materials due to the axial feeding of powder into the combustion chamber 76 (via first passage 72, conducted at subsonic gas velocities) and because the torch 60 utilizes a converging nozzle 88 for lower gas velocities compared to other HVOF systems that use converging-diverging nozzles. These features result in longer dwell times of the powders for greater heating but also supersonic gas velocities for high impact velocities at the target. Other manufacturers of torches for HVOF coating deposition include GTV Verschliessschutz GmbH of Luckenbach, Germany, which manufacturers the Top Gun HV OF torch.

[0034] Table 1 below illustrates exemplary operational parameters of the HV-2000 HVOF system including the torch 60. The HV-2000 HVOF system utilizes higher velocities gas and lower heat inputs in comparison to plasma spray processes and can use finer ceramic powders while still sufficiently heating the particles prior to impact with the target substrate.The ceramic powder sizing for aluminum oxide, titanium oxide, as well as mixtures and alloys of these materials should be in the range of 5-35 pm (micrometers) with feed rates between 7-15 g / min (grams per min). Furthermore, for adequate heating of the powder during deposition, nozzles with combustion chamber depths 108 of 19-22 nun are used. The gas flow conditions for deposition of aluminum oxides, titanium oxide, as well as mixtures and alloys of these ceramics are hydrogen flow rates of 1200-1550 scfh (standard cubic feet per hour) with a supply pressure of 90-110 psi (pounds per square inch), oxygen flow rates of 400-700 scfh with a supply pressure of 140-160 psi. The typical distance from the target, stand-off distance 112, is 7-13 inches for these coating materials. These parameters are summarized in Table 1.Table 1: HV-2000 HVOF Spray Parameters for Producing Ceramic Coating

[0035] The ceramic powders used for the ceramic deposition process can be readily-available chemistries, such as A12O3-3%TiO2 (meaning 3% by weight TiO2 with the balance being A12O3), A12O3-13%TiO2, A12O3-40%TiO2, pure TiO2 and pure A12O3. The term “pure” with regard to the powder chemistries should be understood to mean a powder in which the main component, i.e., TiO2 or A12O3, comprises greater than or equal to 98% by weight of the main component. Other ceramic powders can be custom made by mechanically blending TiO2 and A12O3 to make different weight percentages. One such example is a custom-made composition of TiO2-20%A12O3. In yet other embodiments, small amounts of other ceramics at lower percentages can be added to the mixture of A12O3 (aluminum oxide or alumina) and TiO2 (titanium oxide, or titanium dioxide), such as MgO (magnesium oxide or magnesia), ZrO2 (zirconium dioxide or zirconia), SiO2 (silicon dioxide or silica), and / or Cr2O3 (chromium (III) oxide, chromia, or dichromium trioxide).

[0036] With reference to FIGS. 3A and 3B, maximizing toughness of a coating designed for articulating surfaces of an implant component ensures a coating will not develop cracks or chips when implanted into a human body and subjected, especially, to impact-type loading (e.g.,impacts resulting from jumping, running, or other sudden contact between the coated medical implant component and its mating component). The fracture toughness of HVOF deposited ceramic coatings produced with pure TiO2 and mixtures of TiO2 and A12O3 were measured and compared directly with the same ceramic coating compositions produced with a plasma spray system. FIG. 3 A illustrates the method of testing the fracture toughness of a material and the size and spacing of indentations for different applied loads. A load 116 is applied through a contact tip (not shown) to the coating 120 applied to the substrate 124. Depending on the load applied (e.g., 300 gf, or grams-force, 500 gf, 1000 gf, or 2000 gf), the indentations are spaced to provide sufficient room to allow crack propagation between test locations. FIG. 3B illustrates a sample test location illustrating the indentation 128 at which the load was applied, and measurements of crack length cl, c2 propagating from the indentation 128. FIG. 3B also includes the formula for calculating fracture toughness. The equation can be found in J. Am. Ceram. Soc., 64 [9] (1981) 533-538, or in “A Critical Evaluation of Indentation Techniques for Measuring Fracture Toughness: I, Direct Crack Measurements” by G. Anstis, P. Chantikul, B. Lawn, and D. Marshall, and is produced below:

[0037] K = Calculated fracture toughness

[0038] E = Elastic modulus (200 GPa used for 100% TiO2 )

[0039] H = the Vickers hardness

[0040] P = indentation load

[0041] C = the crack length (measured with in an optical microscope; the c value was an average of c 1 and c2)

[0042] Table 2 below includes calculated fracture toughness based on measurements conducted on HVOF- and plasma-spray -deposited pure TiO2 coatings deposited on 1018 steel in two different coating thicknesses. 0.005 inches and 0.010 inches.Table 2. Fracture Toughness of Pure Ceramic TiO2 Coatings Deposited by HVOF and Plasma Spray Processes

[0043] The fracture toughnesses of the TiO2 coatings were calculated using the equation described above. Measurements were made using different indent loads and the average fracture toughness was determined over the different loads. Table 2 shows the facture toughness values calculated for each coating deposition process. The HVOF-produced coatings showed higher fracture toughness values compared to the plasma sprayed coatings at every indent load.

[0044] The fracture toughness of a TiO2 ceramic coating deposited using the HVOF process is significantly greater than ceramic TiO2 coatings deposited by' plasma spray. The significantly higher fracture toughness provides a more durable coating for articulating surfaces of medical implants. Based on the test data above, the illustrated embodiment has a fracture toughness greater than 2.4 MPa m*l / 2, with test values ranging between 2.54 and 3.41, and averaged test values ranging from 2.90-3.05 MPa m*l / 2.

[0045] With reference to Table 3 below, the coating hardness of the ceramic alloys in this disclosure are maximized by the HVOF deposition process. The coating hardness of the materials was measured with the coating in cross-section that had been ground and polished to asmooth finish and Vickers microhardness testing was used to measure the coatings har dness for the coating materials applied by the coating deposition processes listed in the table.Table 3. Coating Hardness (Vickers Microhardness Scale)

[0046] Based on the test data in Table 3 above, the tested TiO2 and AL2O3-TiO2 alloys have a microhardness of greater than at least 800 Vickers, with the data showing even higher hardnesses in a range between approximately 917 and 1167.

[0047] With reference to Table 4 below, the coating adhesion of the materials described in this disclosure were measured by the test method described by ASTM C633 standard. ASTM C633 tests the adhesion and cohesion of the coating in uniaxial tension. Hie coating is deposited onto one surface of a first titanium plug, and a second plug is then adhered to the coating using a high strength adhesive. The adhered plugs are then pulled in tension until failure and the adhesion is measured. The adhesive between the coating and the second plug will typically fail when the pressure (e.g., the tensile force applied divided by the area of the coating / adhesive interface) is in a range of 10,000-12,000 psi.Table 4. Measured Adhesion for Coating Materials Applied by an HVOF Deposition Process

[0048] As shown by the data in Table 4, the illustrated embodiments have adhesion greater than approximately 8,750 psi as measured by the process of ASTM C633 standard, with the data showing even higher adhesions, and may be between 9,000 and 11,010.

[0049] With reference to FIG. 4, coating deposition on a substrate results in either a compressive or tensile residual stress that is generated by the plasma and HVOF thermal spray processes. The residual stress can be evaluated by measuring the change in curvature of a 0.125” thick steel bar after coating deposition on one face of the bar. For a coated sample, with the coating facing up, a convex curvature (i.e .. positive deflection, that is, the center of the bar deflects upward relative to the ends) indicates the coating is in compression, while a concave curvature (i.e., negative deflection, the ends deflect upward while the center of the bar is lower in comparison) indicates the coating is in tension. If the coated bar remains flat, the stress is neutral. FIG. 4 shows the change in bar deflection normalized to coating thickness after TiO2 coatings were deposited using plasma and HVOF processes to three different coating thicknesses. The plasma spray process produces a coating under a tensile residual stress due to quenching stresses generated by the solidification of molten particles. The tensile residual stress may result in a deflection of between -0.5 and -1.0 inches-per-inch of deflection per thickness of the coating. In contrast, high-velocity peening effects taking place during HVOF deposition produce a compressively stressed coating resulting in compressive deflection of between about 1.5 and 2.0 inches of deflection per inch of thickness. The compressive state of the HVOF coating contributes to its higher fracture toughness and stronger adhesive strength.

[0050] FIGS. 5A - 5C illustrate a scratch testing process to measure the adhesion and cohesion of coatings in compression (e.g., the coatings of the present disclosure deposited by an HVOF deposition process using an HV2000 HVOF system) or tension (a plasma spray deposited coating). Following deposition, a cross-section 132 of a sample of a substrate 136, a coating 140, and an epoxy resin covering 144 is taken and metallurgically mounted. Using an indenter 148, (e.g., a Rockwell C indenter), a load 152 is applied to the cross-section 132 and traversed across the substrate 136, coating 140, and epoxy covering 144, in a scratch direction 154 using different scratch loads (e.g., three scratch loads of 1,000 gf, 1,500 gf, and 2,000 gf). A scratch test was performed on TiO2 coatings to demonstrate the differences in adhesion and cohesion of coatings in compression or tension. Adhesion is the measure of the coating’s adhesive strengthand is indicated by the length of a crack 156 at the interface between the substrate 136 and the coating 140. A coating’s cohesive strength is indicated by the projected cone size A produced in the coating 140 (shown in FIG. 5B). The projected cone size is calculated using the following formula:

[0051] Where:

[0052] A = projected cone size

[0053] Lx= the length of the cone

[0054] Lv= half of the width of the cone

[0055] FIG. 5C illustrates the cohesive zone 160 often produced during testing (e.g., illustrated as a trapezoid). FIG. 6 shows a sample cross-section that has been tested, including the substrate 136, coating 140, and epoxy resin covering 144, the crack 156 indicating the adhesive zone between the substrate 136 and coating 140, and the cohesion zone 160.

[0056] FIG. 7 shows scratch test results demonstrating that a coating’s adhesive strength and cohesive strength is significantly better when the coating is in compression (i.e., when the coating is applied using an HVOF deposition process) in comparison to when the coating is in tension (e.g., the coating has been applied using a plasma spray system). The plasma sprayed coating shows more damage both at the interface (i.e., at the crack, indicating lower adhesive strength) and within the coating (i.e., the cohesive zone, indicating lower cohesive strength) compared to HVOF deposited coating. FIGS. 8 and 9 graphically illustrate the measured crack length and cone area, indicating the adhesive and cohesive strengths, respectfully, of tire plasma- sprayed and HVOF-deposited coatings.

[0057] With reference to FIG. 10, the thicknesses of the coatings described in this disclosure are substantially thicker than other coatings used for improved wear resistance. Other wear- resistive coatings include TiNbN, TiN, and CrN, which are produced by physical vapor deposition, chemical vapor deposition or plasma enhanced physical vapor deposition often havea thickness of 3 pm or less. Oxinium®, another coating / surface treatment for orthopedic medical implants offered by Smith and Nephew, which is a thin surface made of zirconium oxide, has a thickness of a few micrometers. The coatings described in the present disclosure are 50 pm to 500 pm in thickness (i.e., a factor of 10 or 100 higher than other medical implant coatings). This increased thickness provides more material to prevent wear of the titanium base metal and improves, that is, prolongs, the life of the implant when compared to existing thin film coatings on the market today. Figure 10 shows a cross section of TiO2. The thickness of this coating is over 263 pm.

[0058] With reference to FIG. 11 , the coatings and deposition process of the present disclosure are capable of achieving a very smooth surface finish with a TiO2 coating produced with this technology. The TiO2 coating is very dense with a porosity content of less than 1.0%, for instance, less than 0.5% by volume measured with light microscopy and image analysis software. Pure Ti02 in particular has a single-phase crystallographic structure. When the coating is ground and polished, the single phase provides a uniform structure and polishes evenly across the surface of the coating. Other materials with a single-phase crystallographic structure may provide similar benefits. Materials with multiple phases will have variations in hardness which can produce high and low areas in the polished coating that, when polished, have a surface that is not as even. The TiO2 coating has demonstrated the ability to be polished to surface finishes of less than 2 pin Ra. With multiphase ceramic coatings, it can be very difficult to achieve surface finishes less than 2 pin Ra. FIG. 11 shows a femoral head that was coated with TiO2 and has a surface finish of less than 1 pin Ra.

[0059] TiO2 coatings produced with this technology will have excellent corrosion resistance. This corrosion resistance will prevent the human body from degrading the coating by chemical attack so the longevity of the coating will not be affected by corrosion. As illustrated in a Pourbaix diagram of TiO2, Ti02 remains stable in a wide range chemical pH range. A generally available Pourbaix diagram of TiO2 shows stability of TiO2 over a pH range of 3-14 pH.

[0060] Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one ormore independent aspects of the invention as described. Various features of the invention are set forth in the following claims.

Claims

CLAIMSWhat is claimed is:

1. A medical implant component comprising: a titanium- based component; and a ceramic coating on the component, the ceramic coating including A12O3, TiO2, or a mixture of both A12O3 and TiO2, that is compressively stressed.

2. The medical implant component of claim 1, wherein the ceramic coating has a fracture toughness greater than 2.4 MPa m*l / 2.

3. The medical implant component of claim 1 , wherein the ceramic coating has a microhardness of greater than 800 Vickers.

4. The medical implant component of claim 1, wherein the ceramic coating has adhesion greater than 9,000 psi when measured by ASTM C633 standard.

5. The medical implant component of claim 1 , wherein the ceramic coating has a thickness of 50-500 pm.

6. The medical implant component of claim 1 , wherein the ceramic coating has a porosity content of less than 1.0% by volume.

7. The medical implant component of claim 1, wherein the ceramic coating comprises a single-phase crystallographic structure.

8. The medical implant component of claim 1, wherein the ceramic coating has a surface finish smoother than 2 pin Ra.

9. The medical implant component of claim 1 , wherein the ceramic coating is chemically stable and will not corrode in a pH range of 3-14.

10. The medical implant component of claim 1, wherein the component includes a hip femoral head, a hip acetabulum, a knee femoral component, a tibial insert, a shoulder humeral head, or a glenoid component.

11. The medical implant component of claim 1, wherein the ceramic coating comprises A12O3-3%TiO2, A12O3-13%TiO2, A12O3-40%TiO2, or TiO2-20%A12O3.

12. The medical implant component of claim 1 , wherein the ceramic coating comprises pure TiO2.

13. The medical implant component of claim 1 , wherein the ceramic coating further includes MgO, ZrO2, SiO2, and / or Cr2O3.

14. A method of coating a medical implant component, the method comprising: providing a medical implant component; applying a ceramic coating to the component using an HVOF process.

15. The method of claim 14, wherein the medical implant component is made out of a stainless steel, CoCr, Ta, or Ta alloy.

16. The method of claim 14, wherein applying the ceramic coating using an HVOF process includes applying the coating with a HVOF gun.

17. The method of claim 16, wherein applying the ceramic coating includes supplying a ceramic powder comprising A12O3, TiO2, or a mixture of both A12O3 and TiO2, the ceramic powder including a plurality of particles having a diameter between 5 and 35 pm, to the HVOF gun with a feed rate between 7 and 15 g / min.

18. The method of claim 17, wherein the HVOF gun is operated with a hydrogen flow rate between 1200 and 1550 scfh with a supply pressure of 90-110 psi, and with an oxygen flow rate between 400-700 scfh at a supply pressure between 140 and 160 psi.

19. The method of claim 16, wherein the HVOF gun is a Thermach HV2000 HVOF gun or a GTV Top Gun.

20. The method of claim 16, wherein a distance between the HVOF gun and the medical implant component while applying the ceramic coating is between 7 and 13 inches.

21. The method of claim 16, wherein the HVOF gun includes a nozzle with a combustion chamber depth of 19-22 mm.

22. The method of claim 14, wherein the coating is applied to have a thickness of 50-500 pm.

23. The method of claim 17, further including MgO, ZrO2, SiO2, and / or Cr2O3 in the powder.

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