IMPLANT WITH CERAMIC COATING, METHOD OF FORMING AN IMPLANT, AND METHOD OF APPLYING A CERAMIC COATING

Abstract

An implant comprises a metal body having a ceramic coating comprising monoclinic and orthorhombic phases of zirconium oxide ZrO2 and at least one multi-metal phosphate from the group comprising l-IV metal phosphates. A method of forming an implant is provided. A method of applying a ceramic coating to a metal body comprises the step of electrochemical oxidation of at least a portion of the surface of a metal body in aqueous electrolyte; in which the electrolyte contains at least two elements from a group consisting of zirconium, titanium, magnesium, phosphorus, calcium, fluoride, potassium, sodium, strontium, sulphur, argentum, zinc, copper, silicon, gallium; in which electrochemical oxidation is conducted in a plasma discharge (PEO) mode for at least one interval of time, and non-discharge modes for at least two intervals of time.

Claims

1-38. (canceled)

39. An implant comprising a metal body having a ceramic coating, in which the ceramic coating material contains monoclinic and orthorhombic phases of zirconium oxide ZrO.sub.2, and at least one multi-metal phosphate from the group comprising I-IV metal phosphates.

40. An implant according to claim 39, in which the ceramic coating is formed at least in part by electrochemical oxidation of a portion of the surface of the metal body.

41. An implant according to claim 39 in which the ceramic coating material contains at least four, or five, elements from the group consisting of: zirconium, titanium, magnesium, oxygen, phosphorus, calcium, fluoride, potassium, sodium, strontium, sulphur, argentum, zinc, copper, silicon, gallium.

42. An implant according to claim 39, in which the multi-metal phosphate comprises an alkali-metal phosphate, such as an alkali-metal zirconium phosphate, or an alkali-metal titanium phosphate.

43. An implant according to claim 42, in which the ceramic coating material comprises potassium zirconium phosphate of kosnarite type KZr.sub.2 (PO.sub.4).sub.3, sodium zirconium phosphate NaZr.sub.2(PO.sub.4).sub.3, or silver sodium zirconium phosphate AgNaO.sub.8P.sub.2Zr.

44. An implant according to claim 42 in which the ceramic coating material comprises sodium titanium phosphate NaTi.sub.2(PO.sub.4).sub.3 or potassium titanyl phosphate KTiOPO.sub.4.

45. An implant according to claim 39, in which the ceramic coating is a nanoceramic coating, and has a nano-crystalline structure with having an average grain size of between 20 and 100 nanometres.

46. An implant according to claim 39, in which the metal body is selected from a group consisting of titanium, zirconium, magnesium, tantalum or an alloy or intermetallic of any of these metals.

47. An implant according to claim 39, in which the ceramic surface has a roughness Ra of greater than or equal to 0.4 μm, or 0.5 μm, or 0.6 μm, and less than or equal to 1.2 μm, or 1.5 μm, or 2 μm.

48. An implant according to claim 39, in which the ceramic coating has a thickness of between 5 micrometres and 40 micrometres, preferably between 7 micrometres and 30 micrometres, particularly preferably between 10 micrometres and 40 micrometres.

49. An implant according to claim 39, in which the ceramic coating is impregnated or top coated with one or more anti-inflammatory drugs or bone stimulating materials, for example with antibiotics, hydroxyapatite, fluorides, bisphosphonates, bioactive lipids, lysophosphatidic acids, osteogenic growth factors, bone morphogenetic proteins (BMPs), and/or in which the ceramic coating is impregnated or top coated with a material such as bone healing enhancement drugs, or cancer treatment materials such as P32 isotope or caesium chloride.

50. An implant according to claim 39, in which the ceramic coating comprises: a top surface layer, an intermediate layer, and a barrier layer at an interface with the metal body, optionally in which the surface layer of the ceramic coating has a bone-like colour with CIELAB colour space values of L* from 65 to 80, a* from −3 to +3 and b*from −2 to +5 and reflectance in the visible wavelength range above 30%, preferably in which the surface layer of the ceramic coating has a porosity of greater than 25%.

51. An implant according to claim 50, in which the intermediate layer of the ceramic coating is a scratch-resistant layer, and/or in which the intermediate layer of the ceramic coating has a porosity of between 5% and 15%, and/or in which the barrier layer of the ceramic coating has a porosity below 5%.

52. A method of forming an implant comprising a metal body having a ceramic coating, comprising: electrochemical oxidation of at least a portion of the surface of a metal body in aqueous electrolyte, in which the metal body and/or the electrolyte contains zirconium, and in which the electrolyte contains phosphorus and at least one of sodium or potassium, such that the electrochemical oxidation forms a ceramic coating on the metal body, the ceramic coating containing monoclinic and orthorhombic phases of zirconium oxide ZrO.sub.2, and at least one multi-metal phosphate from the group comprising I-IV metal phosphates.

53. A method according to claim 52, in which the electrochemical oxidation process comprises the step of electrically biasing the metal body with respect to the electrolyte by applying a sequence of voltage pulses of alternating polarity, preferably in which the pulse frequency is greater than 1 kHz.

54. A method according to claim 52, in which the electrolyte contains at least two elements from a group consisting of zirconium, titanium, magnesium, phosphorus, calcium, fluoride, potassium, sodium, strontium, sulphur, argentum, zinc, copper, silicon, and gallium.

55. A method according to claim 52, in which electrochemical oxidation is conducted in a plasma discharge (PEO) mode for at least one interval of time, and non-discharge modes for at least two intervals of time, and/or in which the energy density of the electrochemical oxidation process exceeds 20 kW/dm.sup.2, preferably in which the energy density of the electrochemical oxidation process exceeds the value of 20 kW/dm.sup.2 for an interval of time of at least 1 minute.

56. A method according to claim 52, in which the process of electrochemical oxidation comprises the following consecutive steps: a) pre-discharge energy ramping step, b) plasma electrolytic oxidation step in which the process energy density exceeds the value of 20 kW/dm.sup.2, c) post-discharge energy decrease step, optionally comprising the additional step of: d) low energy quasi stationary step in which the process energy density does not exceed the value of 5 kW/dm.sup.2, preferably in which the duration of step a) is between 0.1 and 2 minutes, and/or in which the duration of step b) is between 1 and 20 minutes, and/or in which the duration of step c) is between 2 and 20 minutes, and/or in which the duration of step d) is between 1 and 5 minutes.

57. A method according to claim 52, in which the implant is an implant according to claim 1.

58. A method according to claim 52, comprising the step of manufacturing of the metal body by at least one method from a group comprising forging, casting, thixomolding, machining, turning, milling, additive manufacturing or chemical vapour deposition, wire erosion and spark erosion, and/or comprising the step, before electrochemical oxidation, of surface preparation of the metal body by at least one method from a group comprising polishing, blasting, etching or cleaning.

Description

PREFERRED EMBODIMENTS OF THE INVENTION

[0124] Preferred embodiments of the invention will now be described with reference to the figures, in which:

[0125] FIG. 1 is a schematic illustration of an electrolytic apparatus suitable to form a coating embodying the invention;

[0126] FIG. 2 illustrates a preferred energy density diagram to form a coating embodying the invention;

[0127] FIG. 3 is a scanning electron micrograph of a nanoceramic coating surface on titanium grade 5 alloy;

[0128] FIG. 4 is a scanning electron micrograph of a cross-section of nanoceramic coating on titanium grade 5 alloy;

[0129] FIG. 5 is an X-ray diffraction (XRD) pattern of a nanoceramic coating on titanium grade 5 alloy;

[0130] FIG. 6 is a photographic image of three titanium Grade 5 dental implants: 1—with etched surface; 2—with anodised surface; 3—with nanoceramic coating embodying the invention.

[0131] FIG. 1 is a schematic illustration of an electrolytic apparatus suitable to form a coating embodying the invention.

[0132] The implant 1 on which it is desired to form a ceramic coating is placed in a chemically inert tank 2, for example a tank formed from a polypropylene plastic, which contains an electrolyte solution 3. The electrolyte solution 3 is an aqueous solution, for example an aqueous solution of zirconium sulphate Zr(SO.sub.4).sub.2, potassium pyrophosphate K.sub.4P.sub.2O.sub.7 and potassium hydroxide KOH. The electrolyte may be a colloidal electrolyte comprising solid particles, for example zirconium oxide ZrO.sub.2 nano powder.

[0133] The implant 1 is electrically connected to one output of a pulse power supply 4. An electrode 5, for example formed from stainless steel, is connected to a second output of the pulse power supply 4, and both the electrode 5 and the implant 1 are immersed in the electrolyte solution 3 contained within the tank 2. The pulse power supply 4 is capable of supplying electrical pulses of alternating polarity in order to electrically bias the implant 1 with respect to the electrode 5.

[0134] To control electrolyte temperature within optimal range between 20 and 25° C. the tank 2 is connected by tubes 6 with a pump 7 and a chiller 8.

[0135] FIG. 2 illustrates a preferred energy density diagram to form a coating embodying the invention. Diagram presents 4 stages of the coating forming process.

[0136] Stage 1 is a pre-discharge stage characterised by ramping up process energy from zero up to a discharge threshold level W1 at which first microarc discharge appears on the surface. During this phase a ceramic coating begins to form on the metal body, as the metal of the metal body is oxidised. Zirconium oxide in monoclinic phase is formed from the zirconium in the electrolyte and consolidated into the ceramic layer.

[0137] At stage 2 the energy density is increased above discharge threshold W1 value and the process can be classified as plasma electrolytic oxidation (PEO) or micro arc oxidation (MAO). PEO mode forms rough surface of ceramic coating due to multiple discharge events. Roughness can be controlled through control of applied energy and duration of PEO stage.

[0138] Further increase of energy density during second stage 2 enables to reach level W2 at which formed zirconium oxide phase starts to transform from monoclinic to orthorhombic phase. That transformation starts at energy densities exceeding 20 kW/dm.sup.2.

[0139] After reaching maximum process value of energy density W3 the process energy is made to reduce to a discharge threshold level W1 until the discharge effect disappears.

[0140] Stage 3 is a post-discharge oxidation during which process energy is gradually decreased until quasi stationary level W4. Absence of discharge allows to form more compact oxide ceramic which is positioned underneath porous top layer built during PEO stage.

[0141] Stage 4 of the process is characterised by maintaining energy density at relatively low level W4. During stage 4 the barrier layer on the interface with metal is formed.

[0142] FIG. 3 is a scanning electron micrograph of a nanoceramic coating surface on titanium Grade 5 alloy. It demonstrates a highly developed surface with micro and nano roughness pattern. The mean roughness value is 0.8 micrometres. The pore size ranges from 0.1 to 2 micrometres. Achieved roughness and presence of nano- and micro pores are beneficial for osseointegration (Le Guehennec et al, Surface treatments of titanium dental implants for rapid osseointegration, Dental materials 23 (2007) 844-854).

[0143] FIG. 4 illustrates typical 3 layer structure of nanoceramic coating formed on titanium grade 5 alloy by invented multi stage electrochemical oxidation method. The mean average total thickness of ceramic layer is 13 micrometres. The top layer 1 has the mean average thickness of 3 micrometres, highly developed surface and average roughness of 0.8 micrometres. The middle layer 2 has the mean average thickness of 6 microns and is more compact and dense than the top layer 1. The bottom layer 3 has the mean average thickness of 4 micrometres. It has a very low porosity and serves as a barrier against migration of ions from substrate material 4.

[0144] FIG. 5 is an XRD pattern of a nanoceramic coating on titanium grade 5 alloy. It demonstrates the presence of zirconia and crystalline zirconium potassium phosphate of kosnarite type (KZr.sub.2 (PO.sub.4).sub.3). Zirconia is present in two crystalline forms: monoclinic and orthorhombic.

[0145] FIG. 6 is a photographic image of three dental implants made of Ti-6Al-4V titanium grade 5 alloy: 1—with etched surface; 2—with anodised surface; 3—with nanoceramic coating embodying the invention. FIG. 6 demonstrates that implant 1 with etched surface has a dark grey metallic colour. Anodising of that grade titanium does not improve the colour due to the presence of vanadium oxide in the anodic layer. Sample 5 has a nanoceramic coating made according to this invention and it has a bone-like colour which is distinctly different from the colour of implants 1 and 2.

EXAMPLE 1

[0146] Dental implant was made of titanium grade 5 alloy (Ti-6Al-4V) rod by turning. The surface was subsequently etched in a solution of hydrofluoric acid HF and hydrochloric HCl acid. Electrochemical oxidation was conducted in an electrolytic apparatus as described above and illustrated in FIG. 1. Total coated implant surface area was 0.06 dm.sup.2. The apparatus comprised a tank containing an electrolyte, and the implant and an electrode were coupled to a pulse power supply as illustrated in FIG. 1. The substrate and the electrode were arranged in contact with the electrolyte. The electrolyte was an aqueous solution containing 1.5 g/L of zirconium sulphate Zr(SO.sub.4).sub.2, 2 g/L potassium pyrophosphate K.sub.4P.sub.2O.sub.7, 0.4 g/L potassium hydroxide KOH and 2 g/L zirconium oxide ZrO.sub.2 nano-powder, forming a stabilised colloidal solution.

[0147] The Pulse Generator applied a sequence of electrical pulses of alternating polarity between the substrate and the electrode. Pulse repetition frequency was 3 kHz. Pulse voltage amplitude was controlled in way that process energy density followed 4 stage mode required for forming 3 layer structure of ceramic coating as illustrated in FIG. 2.

[0148] At stage 1 energy density was increased from zero value to a discharge threshold level W1 equal to 12 kW/dm.sup.2 at which first microarc discharge appears on the surface. Duration of Stage 1 was 2 min.

[0149] At stage 2 of plasma electrolytic oxidation the energy density is increased above level W2 equal to 20 kW/dm.sup.2 at which formed zirconium oxide starts to transform from monoclinic to orthorhombic phase. PEO mode stage formed rough surface of ceramic coating due to multiple discharge events. After reaching the maximum process value of energy density W3 equal to 27 kW/dm.sup.2 the process energy was made to reduce to a discharge threshold level W1 until the discharge effect disappeared. Duration of stage 2 was 6 min.

[0150] At stage 3 the process energy density was gradually decreased from W1 until quasi stationary level W4 equal to 4 kW/dm.sup.2. The absence of discharge allowed to form compact oxide ceramic layer positioned underneath the porous top layer built during the PEO stage. Duration of stage 3 was 8 min.

[0151] At stage 4 the energy density was maintained at level W4. During stage 4 the barrier layer at the interface with metal was formed. Duration of stage 4 was 3 min.

[0152] Total duration of electrochemical oxidation was 19 min.

[0153] After electrochemical oxidation the implant was rinsed with deionised water in an ultrasonic tank for 20 minutes and then dried.

[0154] Scanning electron micrograph of the formed ceramic surface is illustrated in FIG. 3. The SEM image demonstrates a highly developed surface with micro- and nano-roughness pattern. The mean roughness value was 0.8 micrometres as measured by Veeco Dektak 150 Surface Profiler. The same profilometer was used for measuring surface roughness other provided examples as well. The pore size ranged from 0.1 to 2 micrometres.

[0155] A cross-section of the formed ceramic layer is presented in FIG. 4. SEM image demonstrates a three-layer structure of nanoceramic coating. The total average thickness of the ceramic layer is 15 micrometres. The top layer 1 has the mean average thickness of 4 micrometres, a highly developed surface and the mean average roughness Ra of 0.8 micrometres and porosity of 32%. The intermediate layer 2 has the mean average thickness of 8 microns and porosity of 9%. It is more compact than the top layer. The bottom layer 3 has the mean average thickness of 3 micrometres and porosity of just 2%. Due to a very low porosity it serves as a barrier against ion migration.

[0156] XRD pattern of the nanoceramic coating is presented in FIG. 5. The XRD demonstrates the presence of titania TiO.sub.2 in a crystalline form of rutile; zirconia ZrO.sub.2 and crystalline zirconium potassium phosphate of kosnarite type (KZr.sub.2 (PO.sub.4).sub.3). Zirconia was presented in two crystalline forms: monoclinic and orthorhombic. Comparison of the intensities of two crystalline phases of zirconia shows that the monoclinic phase is the major component. The average crystalline size was calculated on the base of the XRD data according to the Scherrer equation (B. D. Cullity & S. R. Stock, Elements of X-Ray Diffraction, 3.sup.rd Ed., Prentice-Hall Inc., 2001, p 167-171) Produced coating had the mean crystalline size of 50 nm.

[0157] Scratch resistance of the coating was evaluated by VTT scratch tester with diamond indenter with increasing load over 15 mm distance. Indenter reached the substrate at critical load of 15 N which is a higher value compared to measured anodic oxide films (5-8N) or galvanically deposited HA (4-7N). Around 80% of the distance before the perforation the indenter ploughs through the middle layer 2 which constitutes only 50% of the coating thickness (FIG. 4). That demonstrated that a high scratch resistance of the coating is provided predominantly by the intermediate layer of ceramic material.

[0158] Produced coating has a bone like colour demonstrated in FIG. 6 which is a photographic image of three dental implants made of Ti-6Al-4V titanium grade 5 alloy: 1—with etched surface; 2—with anodised surface; 3—with ceramic coating described in this example. FIG. 6 demonstrates that implant 1 with etched surface has dark grey metallic colour. Anodising of that grade titanium does not improve the colour due to the presence of vanadium oxide in the anodic oxide layer. Implant 3 has a nanoceramic coating made according to this invention and it has a bone-like colour which is distinctly different from the colour of implants 1 and 2. Colour of ceramic surface evaluated by Datacolor 660 spectroscope provided values in CIELAB colour space corresponding to L*=70, a*=+0.3 and b*=+4. The low values of a* and b* indicated a well balanced combination between red-green and yellow-blue colours, whereas high values of lightness L* indicate a close to white light-grey shade of the surface. Optical reflectance (%) was measured by a spectrophotometer CM 2600 (Konica Minolta) in the visible wavelength range. Reflectance of teeth according to VITA Zahnfabric ranges in the interval between 30% and 70%. Mean reflectance values for non-coated Ti alloy implants with etched surface and anodised implants laid in the range of 22%-28% across visible light spectrum while produced implant with ceramic coating demonstrated surface reflectance in the range 35%-37%.

EXAMPLE 2

[0159] Magnesium alloy AZ71 was used for making a biodegradable bone implant. The implant was manufactured by die casting and cleaned in alkaline bath. Ceramic coating was applied in order to provide slower implant weight loss and reduction in Mg alloy ion release in the blood plasma.

[0160] Electrochemical oxidation was conducted in an electrolytic apparatus as described above and illustrated in FIG. 1.

[0161] The electrolyte was an aqueous solution containing 2 g/L sodium fluoride, 2.5 g/L zirconium sulphate Zr(SO.sub.4).sub.2, 3 g/L potassium pyrophosphate K.sub.4P.sub.2O.sub.7, 2.5 g/L potassium hydroxide KOH.

[0162] The 4 stage oxidation process lasted 14 min and it included stage one of 1 min duration, stage 2 of 4 min, stage 3 of 6 min and stage 4 of 3 min.

[0163] Formed coating contained oxides of magnesium MgO and zirconium ZrO.sub.2 and crystalline zirconium potassium phosphate of kosnarite type KZr.sub.2(PO.sub.4).sub.3.

[0164] Formed coating had average thickness of 8 micrometres and roughness Ra=1.2 micrometres.

EXAMPLE 3

[0165] Pure tantalum Ta was used for making a porous intraosseous implant by additive manufacturing technique of 3D printing. After manufacturing, the implant was etched in a solution of nitric HNO.sub.3 and hydrochloric HCl acids.

[0166] Electrochemical oxidation was conducted in an electrolytic apparatus as described above and illustrated in FIG. 1.

[0167] The electrolyte was an aqueous solution containing 2 g/L of zirconium sulphate Zr(SO.sub.4).sub.2, 2 g/L sodium pyrophosphate Na.sub.4P.sub.2O.sub.7, 0.5 g/L sodium hydroxide NaOH, 0.1 g/L silver sulphate and 3 g/L hydroxyapatite HA nano-powder, forming a stabilised colloidal solution.

[0168] The 4 stage oxidation process lasted 26 min and it included stage one of 3 min duration, stage 2 of 8 min, stage 3 of 12 min and stage 4 of 3 min.

[0169] Formed coating contained tantalum pentoxide Ta.sub.2O.sub.5, zirconia ZrO.sub.2 and hydroxyapatite. Sodium zirconium phosphate NaZr.sub.2P.sub.3O.sub.12 and silver sodium zirconium phosphate AgNaO.sub.8P.sub.2Zr are present in the coating. Formed coating had average thickness of 16 micrometres and roughness Ra=0.7 micrometres.

EXAMPLE 4

[0170] Titanium beta alloy Ti-15Nb-8Zr (ZN1) produced by UJP PRAHA a.s. was used to manufacture dental implant prototype. Alloy was by made by vacuum arc melting with subsequent re-melting to ensure chemical homogeneity. It contained crica 15% of niobium and 8% of zirconium.

[0171] Dental implant prototype was manufactured by CNC machining.

[0172] After manufacturing implant was etched in a solution of nitric HNO.sub.3 and hydrochloric HCl acids.

[0173] Electrochemical oxidation was conducted in an electrolytic apparatus as described above and illustrated in FIG. 1.

[0174] The electrolyte was an aqueous solution containing 1 g/L of zirconium fluoride ZrF.sub.4, 12 g/L sodium pyrophosphate Na.sub.4P.sub.2O.sub.7, 1 g/L zirconium oxide ZrO.sub.2 nano-powder, forming a stabilised colloidal solution.

[0175] The 4 stage oxidation process lasted 16 min and it included stage one of 1 min duration, stage 2 of 8 min, stage 3 of 7 min and stage 4 of 2 min.

[0176] Formed coating contained titanium oxide TiO.sub.2 in a crystalline form of rutile and sodium titanium phosphate NaTi.sub.2(PO.sub.4).sub.3; zirconia ZrO.sub.2 and zirconium potassium phosphate of kosnarite type (KZr.sub.2 (PO.sub.4).sub.3). Zirconia was presented in two crystalline forms: monoclinic and orthorhombic.

[0177] Formed coating had the mean average thickness of 20 micrometres and roughness Ra=1.1 micrometres.

[0178] Scratch resistance of the coating evaluated by VTT scratch tester with diamond indenter demonstrated a critical load of 17 N.

[0179] Colour of produced ceramic surface provided values in CIELAB colour space corresponding to L*=76, a*=−0.2 and b*=+3. The low values of a* and b* indicated a well balanced combination between red-green and yellow-blue colours, whereas high values of lightness L* indicated a close to white light-grey shade of the surface. Optical reflectance measured in the visible wavelength range lied in the range of 38%-42%.