Claims:WE CLAIM
1. A process of providing a coating (100) of bioactive material on a medical implant (10), the process comprising:
providing a substrate;
etching the substrate to provide a rough substrate;
coating a first layer (100a) of a bioactive material on the rough substrate;
sintering the substrate coated with the first layer (100a);
annealing the substrate coated with the first layer (100a);
coating a second layer (100b) of bioactive material on the substrate;
annealing the substrate coated with the second layer (100b);
wherein the first layer (100a) includes nano hydroxyapatite particles and is coated by a process of electrophoretic deposition; and
wherein the second layer (100b) includes powdered hydroxyapatite particles and is coated by a process of plasma spray coating.
2. The process of providing the coating (100) of bioactive material on a medical implant (10) wherein the size of the nano hydroxyapatite particles is 100nm to 5000nm.
3. The process of providing the coating (100) of bioactive material on a medical implant (10) wherein the size of the powdered hydroxyapatite particles is 45µm to 130µm.
4. The process of providing the coating (100) of bioactive material on a medical implant (10) wherein first layer (100a) have a thickness ranging from 5.00 micron to 15.00 micron.
5. The process of providing the coating (100) of bioactive material on a medical implant (10) wherein the second layer (100b) have a thickness ranging from 110 micron to 190 microns.
6. The process of providing the coating (100) of bioactive material on a medical implant (10) wherein the hydroxyapatite includes calcium and phosphate ions in a range of 1.65 to 1.82.
7. The process of providing the coating (100) of bioactive material on a medical implant (10) wherein the substrate is pre cleaned using ultrasonic cleaning process.
8. The process of providing the coating (100) of bioactive material on a medical implant (10) wherein the substrate is masked before subjecting to the etching process. , Description:FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(Section 10 and Rule 13)

1. TITLE OF THE INVENTION:
PROCESS OF HYDROXYAPATITE COATING ON ORTHOPAEDIC IMPLANT

2. APPLICANT:
Meril Healthcare Pvt. Ltd., an Indian company of the address, Bilakhia House, Muktanand Marg, Chala, Vapi-Gujarat 396191, India

The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF INVENTION
[1] The present invention relates to a coating on an orthopedic implant, more specifically, relates to a method of providing a coating on the orthopedic implant.
BACKGROUND
[2] Osteoarthritis is the most common form of arthritis which affects millions of people worldwide. It is an age-related disorder which primarily affects people over the age of 70 and can be identified by symptoms or clinical pathology. Though, osteoarthritis can damage any joint, the said disorder most commonly affects the joints of knee (up to 41%), hands (up to 30%), hips (up to 19%) and/or spine. Other reasons for damaged joints may include infection, injury genetic disorder, etc. The damaged joints may cause trauma and pain thereby reducing mobility of a patient. Moreover, in severe cases, pain may also persist even while resting.
[3] In order to restore mobility and relieve pain, joint replacement is proven to be the most effective treatment over any other form of treatments. In the joint replacement surgery, a doctor surgically removes a painful joint and replaces it with an artificial joint implant. The key requirement for such implant is that the bone grows onto and/or into the implant surface. Such requirement may be met by providing a coating of an osteoconductive material (bioactive material/coating) onto the implant’s surface.
[4] Hydroxyapatite has been widely used as an osteoconductive material for such implants. However, adequate adhesion of the bioactive material on the implant has been a crucial factor which directly impacts the effectiveness of such implants. Adhesion of the bioactive material on the implant largely depends upon the coating method. Conventionally, various coating methods have been used to coat the surface of the orthopaedic implants such as sputtering, rf-suspension plasma spray, micro-plasma spray, sol gel, pulsed-laser, electro-deposition, hydrothermal electrochemical method, thermal spraying techniques, etc.
[5] However, conventional coating methods have proven to show various limitations such as formation of amorphous coating layer which results in decrease in adhesion capacity of the coating with the implant surface. Such a reduction in adhesion capacity further leads to reduced long-term stability of the implant. One such conventional coating method is disclosed in the patent publication US9682170B2. The aforesaid publication discloses an electrostatic spray coating method to provide a coating of hydroxyapatite on the orthopedic implant. The electrostatic spray coating method may form a thicker and non-uniform coating on the implant. This may lead to formation of micro cracks in the coating which results in delamination of the coating from the implant.
[6] Therefore, there is exists a need for an improved coating method on orthopaedic implant in order to overcome limitations of the conventional ones.
SUMMARY
[7] The present invention discloses a process of providing a coating of bioactive material on a medical implant. The process comprises etching a substrate in order to provide a rough substrate. Further, the rough substrate is coated by a first layer of a bioactive material. The first layer of bioactive material includes nano hydroxyapatite particles. Further, the first layer is coated by a process of electrophoretic deposition. Post coating the first layer, the substrate is subjected to a process of sintering and annealing. Following, the process of annealing, the substrate is coated with a second layer of powdered hydroxyapatite material. The second layer is coated by a process of plasma spray coating.
BRIEF DESCRIPTION OF DRAWINGS
[8] The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those in the art will understand that the drawings are not to scale.
[9] FIG.1 represents a hip implant 10 in accordance with an embodiment of the present invention.
[10] FIG.2 represents coating on the implant 10 in accordance with an embodiment of the present invention.
[11] FIG.3 represents a flow chart of a process involved in coating the implant 10 in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF DRAWINGS
[12] Prior to describing the invention in detail, definitions of certain words or phrases used throughout this patent document will be defined: the terms "include" and "comprise", as well as derivatives thereof, mean inclusion without limitation; the term "or" is inclusive, meaning and/or; the phrases "coupled with" and "associated therewith", as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have a property of, or the like; Definitions of certain words and phrases are provided throughout this patent document, and those of ordinary skill in the art will understand that such definitions apply in many, if not most, instances to prior as well as future uses of such defined words and phrases.
[13] Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment, but mean “one or more but not all embodiments” unless expressly specified otherwise. The terms “including,” “comprising,” “having,” and variations thereof mean “including but not limited to” unless expressly specified otherwise. An enumerated listing of items does not imply that any or all of the items are mutually exclusive and/or mutually inclusive, unless expressly specified otherwise. The terms “a,” “an,” and “the” also refer to “one or more” unless expressly specified otherwise.
[14] Although the operations of exemplary embodiments of the disclosed method may be described in a particular, sequential order for convenient presentation, it should be understood that the disclosed embodiments can encompass an order of operations other than the particular, sequential order disclosed. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Further, descriptions and disclosures provided in association with one particular embodiment are not limited to that embodiment, and may be applied to any embodiment disclosed herein. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed system, method, and apparatus can be used in combination with other systems, methods, and apparatuses.
[15] Furthermore, the described features, advantages, and characteristics of the embodiments may be combined in any suitable manner. One skilled in the relevant art will recognize that the embodiments may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments. These features and advantages of the embodiments will become more fully apparent from the following description and appended claims, or may be learned by the practice of embodiments as set forth hereinafter.
[16] The present invention relates to a method of providing a coating on a medical implant. In various embodiments, the medical implant may include one or more of, an orthopedic implant, dental implant, craniotomy implant and craniofacial implant etc. In an embodiment, the medical implant is an orthopedic implant for knee (or knee implant). Though the below description relates to providing a coating over a hip implant as an exemplary application, it should be noted that the teachings of the present invention also extend to providing coatings on other orthopedic implants such as a knee implant, an elbow implant, a spine implant, etc.
[17] The coating may include at least two layers including a first layer and a second layer. The first layer may include nano Hydroxyapatite (HA) particles and may be coated by a technique of electrophoretic deposition. The said technique of coating may help in formation of thin coating having enhanced crystallinity and adhesion to the implant surface. Further, the nano hydroxyapatite particles may be easily coated on a rough surface of the implant and result in uniform/even coating on the implant surface.
[18] The second layer may include powdered HA particles and may be coated by a process of plasma spray technique. The aforesaid techniques followed for proving the multi-layered coating on the implant provide enhanced adhesion of the coating with the implant surface and avoid formation of any microcracks on the implant surface thereby leading to increased durability of the coating. Further, the coating provides early osseointegration and confers enhanced stability to the implant.
[19] Now referring to figures, FIG. 1 discloses a medical implant 10 (or implant 10) provided with a multi-layered coating 100 (or coating 100). As provided above, the implant 10 may be one or more of hip implant and knee implant.
[20] The implant 10 may be made of any metallic material. The metal used for fabricating the implant 10 may include, without limitation, aluminum, titanium, nickel, vanadium, other metallic alloys and their combinations. In an embodiment, the implant 10 is made of an alloy of titanium, aluminum and vanadium. The aforesaid metals are opted due to their excellent strength, low modulus of elasticity, high corrosion resistance, and heat resistivity. In an exemplary embodiment, the implant 10 is made of Ti-6Al-4V ELI. The said alloy consists of 90% titanium, 6% aluminum, 4% vanadium, 0.25% iron and 0.2% oxygen.
[21] The implant 10 may include one or more components depending upon the type and nature of the implant 10. As indicated in FIG. 1, the implant 10 is a hip implant which includes a stem 10a, a head 10b, a liner 10c and a shell 10d.
[22] The diameter of the shell 10d may be in a range of 40mm to 70mm. In an embodiment, the diameter of the shell 10d is 50mm. The diameter of the liner 10c may range from 35mm to 52mm. In an embodiment, the diameter of the liner 10c is 44mm. Further, the diameter of the head 10b may be in a range of 22m to 40mm. In an embodiment, the diameter of the head 10b is 32mm.
[23] In order to achieve effective and early osseointegration, it is necessary that the coating 100 is applied over a substrate i.e a pre-defined surface of the implant 10 that has minimal friction or no friction with other parts of the implant 10. In an embodiment, the coating 100 (explained below) is applied over the stem 10a. The coating 100 is applied over the stem 10a as the stem 10a is a bone contacting component and leads to osseointegration which is one of the crucial requirements for performance of such implants.
[24] Now referring specifically to drawings, FIG. 2 represents the coating 100 which is applied over the substrate “S”.
[25] The coating 100 may be formulated in a predefined proportion. The formulation of the coating 100 may include any bioactive and osteoconductive material such as without limitation, hydroxyapatite, apatite-wollastonite (A-W), glass ceramic etc. In an embodiment, the coating 100 includes hydroxyapatite (HA). The hydroxyapatite is used as the coating 100 material on the substrate ‘S’ due to its properties to induce early osseointegration, i.e., bone ingrowth and strong bonding between the natural bone and the implant 10.
[26] Hydroxyapatite includes calcium and phosphate ions in a predefined ratio. The ratio of calcium and the phosphate ions may be in a range of 1.65 to 1.82. In an embodiment, the ratio of calcium and phosphate ions is 1.70. Further, hydroxyapatite has predefined crystallinity raging from 45% to 99%. In an embodiment, the crystallinity is 99%.
[27] The coating 100 may include at least two layers. In an embodiment, the coating 100 includes two layers, a first layer 100a and a second layer 100b. In an embodiment, the first layer 100a is coated on the substrate ‘S’ and the second layer 100b is coated on the first layer 100a. Alternately, the second layer 100b may be coated over the substrate ‘S’ while the first layer 100a may be coated over the second layer 100b.
[28] The layer coated over the substrate ‘S’ acts as an adhesive layer for the other layer. For example, the first layer 100a may act as an adhesive layer for the second layer 100b. Moreover, the first layer 100a acts a barrier between the substrate ‘S’ and the second layer 100b, thereby protecting the second layer 100b from stress caused by expansion and contraction of the substrate ‘S’ during annealing (explained below). The first layer 100a facilitates to achieve a crack free second layer 100b.
[29] The first layer 100a includes hydroxyapatite particles in a predefined formulation. The size of hydroxyapatite particles in the first layer 100a may play a crucial role in determining mechanical strength of the coating 100. Further, the nano sized particles can be easily attached to peaks and valleys of the rough surface of the substrate leading to enhanced adhesion of the first layer 100a on the substrate. In an embodiment, the first layer 100a includes hydroxyapatite particles in the form of nano particles. The size of the particles may be in a range of 100nm to 5000nm. In an embodiment, the size of particles ranges from 200nm to 1000nm.
[30] The first layer 100a acts as an adhesion layer for the subsequent second layer 100b and/or helps to prevent the substrate ‘S from direct contact with the bodily fluids. The effectiveness of the first layer 100a depends upon the coating 100 thickness and crystallinity of the first layer 100a. The first layer 100a may have a thickness ranging from 5.00 micron to 15.00 micron. In an embodiment, the thickness of the first layer 100a is 10.00 micron. The crystallinity of the first layer 100a may be in a range of 60% to 80%. In an embodiment, the crystallinity of the first layer 100a is 77%.
[31] The second layer 100b includes hydroxyapatite particles in a predefined formulation. The size of hydroxyapatite particles in the second layer 100b may play a crucial role in determining mechanical strength of the coating 100. In an embodiment, the second layer 100b includes the hydroxyapatite in the form of powder particles. The size of the particles may vary in a range of 45µm to 130µm. The greater size of the hydroxyapatite particles may lead to enhanced crystallinity of the second layer 100b which results in enhanced adhesion strength of the second layer 100b on the first layer 100a.
[32] The second layer 100b acts as an osteoconductive layer which helps in early osseointegration of the implant 10 with the bone and also protects the first layer 100a from the direct contact of the body fluid. The second layer 100b may have a thickness ranging from 110 micron to 190 microns. In an embodiment, the thickness of the second layer 100b is 140µm. The crystallinity of the second layer 100b may be in a range of 60% to 80%. In an embodiment, the crystallinity of the second layer 100b is 70%. s
[33] Further, the desired porosity of the second layer 100b helps in achieving greater penetration of bone cells in the implant 10 leading to enhanced cell attachment resulting in early osseointegration of the implant 10. The porosity of the second layer 100b may be in a range of 5% to 20%. In an embodiment, the porosity is 14%.
[34] Further, the substrate ‘S’ may have a predefined overall thickness after coating 100 the first layer 100a and the second layer 100b. The overall thickness of the substrate ‘S’ may be in a range of 110µm to 190µm. In an embodiment, the overall thickness of the substrate ‘S” is 150 microns.
[35] FIG. 3 represents a flow chart depicting a process involved in providing the coating 100 on the substrate ‘S’.
[36] The process of providing coating 100 on the substrate ‘S’ commences at step 201. At the step 201, the substrate is subjected to a process of pre-cleaning. The substrate ‘S’ may be cleaned by means of ultrasonic cleaning process. The said process may be performed by using purified water at a predefined temperature for predefined time duration. The predefined temperature may be in a range of 50°C to 60°C and predefined time duration is 8 minutes to 12 minutes.
[37] Post the cleaning process, the substrate ‘S’ is subjected to a process of masking at step 203. Masking may be performed at predefined portions of the substrate ‘S’. The predefined portions may be the stem 10a. The process of masking helps in avoiding coating 100 on the predefined portions of the substrate ‘S’. Masking may be performed with the help of medical grade PTFE (polytetrafluoroethylene) tape owing to its compatibility with high temperature plasma used in subsequent steps of the process.
[38] The condition of the substrate ‘S’ significantly affects adhesion capacity of the first layer 100a and the second layer 100b. The condition of the substrate ‘S’ may include surface finish, texture and topography. In order to achieve enhanced adhesion of the first layer 100a and the second layer 100b to the substrate ‘S’, surface roughening of the substrate ‘S’ is performed at the step 205.
[39] The surface roughening may be performed by means of grit blasting. The process of grit blasting may be performed by propelling a stream of an abrasive material under high pressure against the substrate ‘S’. During the aforesaid process, some of the abrasive particles are embedded in the substrate ‘S’. The abrasive material may include without limitation white alumina, glass beads, silicone carbide and plastics etc. In an embodiment, the process of grit blasting is performed using pure white alumina, Al2O3. The pressure may be maintained in a range of 3 bar to 4 bar. The grit blast surface may be again cleaned using ultrasonic cleaning process.
[40] Further at step 207, the cleaned substrate is subjected to an etching process. The process of etching may be performed by photochemical machining process.
[41] The aforesaid process may involve fabricating a surface using photo resist and etchants by machining away elected portion of the surface. The etching process may be performed in order to provide more roughness to the substrate ‘S’.
[42] Post etching process, the substrate ‘S’ is coated with the first layer 100a at step 209. The first layer 100a is coated using technique of electrophoretic deposition at the substrate ‘S’. The aforesaid process may be performed at a voltage ranging between 10V to 30V. The electrophoretic deposition technique avoids problems related to formation of amorphous phases in the first layer 100a. Further, the said technique may provide a uniform coating 100 on complex geometries of the substrate. Moreover, the aforesaid technique helps to provide thin coating 100 having enhanced adhesion capacity. The composition details of the first layer 100a are as described in earlier diagrams.
[43] Followed by deposition of the first layer 100a on the substrate ‘S’, the substrate ‘S’ is subjected to a process of sintering at step 211. The process of sintering may be performed by heating the substrate ‘S’ coated with the first layer 100a under vacuum. The process of sintering may be performed at a temperature ranging from 600°C to 900°C for a time duration ranging from 10 minutes to 20 minutes. In an embodiment, the process of sintering is performed at a temperature of 750°C for a time duration of 15 minutes. The process of sintering may be performed in order to increase crystallinity of hydroxyapatite particles in the first layer 100a. The higher crystallinity of the hydroxyapatite particles leads to enhanced adhesion of the first layer 100a on the substrate ‘S’.
[44] Post the process of sintering, the substrate ‘S” is subjected to a process of first annealing at step 213. The process of annealing may be performed at a temperature ranging from 450°C to 650°C for a time duration ranging from 30 minutes to 120 minutes. In an embodiment, annealing is performed at a temperature of 550 °C for 45 minutes. The process of annealing helps to stabilize higher crystallinity of the hydroxyapatite particles in the first layer 100a achieved by the preceding sintering process. The higher crystallinity leads to early osseointegration and provides stability to the implant 10.
[45] Further, post the annealing step, the substrate ‘S’ is coated with the second layer 100b at step 215. The second layer 100b is provided over the first layer 100a. The composition details of the second layer 100b are as described in earlier diagrams. The second layer 100b may be coated by a process of plasma spray coating. The aforesaid process may provide higher crystallinity to the second layer 100b. The high crystallinity of the second layer 100b leads to micro cracks free coating having enhanced adhesion capacity to the first layer 100a. The process of plasma spray coating may be performed by spraying soft or heat softened hydroxyapatite particles onto the substrate ‘S’. The spraying may be performed by means of without limitation a spray gun.
[46] The process of plasma spray coating may be performed at predefined parameters. The parameters may include rate of feed and distance between the spray gun and the substrate ‘S’, etc. The rate of feed on the substrate ‘S’ may play a crucial role in determining thickness of the second layer 100b. The rate of feed may be in a range of 15.5rpm to 20.5rpm. In an embodiment, the rate of feed is 19.5rpm.
[47] Further, the distance between the spray gun and the substrate ‘S’ may play a crucial role in order to achieve uniform deposition of the hydroxyapatite particles on the substrate ‘S’. Moreover, the optimum distance helps to impart desired porosity and crystallinity to the second layer 100b. The distance between the spray gun and the substrate ‘S’ may be maintained in a range of 800mm to 1200mm, preferably 900mm to 1100mm. In an embodiment, the distance between the spray gun and the substrate ‘S’ is 1000mm.
[48] Post plasma spraying process, the substrate ‘S’ is subjected to the process of second annealing at step 217. The process of second annealing may be performed at a temperature of 500°C to 800°C for duration of 0.5 hour to 5 hours. In an embodiment, the annealing is performed at a temperature of 600°C to 700°C for time duration of 2.25 hours. The process of annealing helps to enhance fracture toughness and hardness of the coating 100 leading to long-term stability of the implant 10.
[49] Further, the substrate ‘S’ is subjected to post treatment cleaning at step 219. The cleaning may be performed to remove any residual particles from the surface before packaging. The process of cleaning involves washing the coated substrate ‘S’ with purified water at an ambient temperature for a time duration of 3 minutes to 7 minutes, followed by washing with hot water at a temperature ranging from 85°C to 90°C for time duration of 15 minutes to 20 minutes. Again, the substrate ‘S’ is rinsed with water at the ambient temperature for a time duration of 3 minutes to 7 minutes. Further, the washed implant 10 is dried at a temperature ranging from 115 °C to 125 °C for time duration of 45 minutes to 50 minutes.
[50] Post cleaning, the substrate ‘S’ is subjected to packaging at step 221. The packaging may be done by placing the substrate ‘S’ in a TPU (Thermoplastic polyurethane) sleeve. Post packaging in the sleeve, the substrate is kept in an inner tray covered with a retainer. Further, the inner tray is covered using a Tyvek lid. The covered inner tray kept in an outer tray which is covered with an outer Tyvek lid.
[51] Lastly, the packaged coated implant 10 is subjected to a process of sterilization at step 223. The sterilization may be performed using radiation sterilization process, such as without limitation e-beam radiation sterilization or gamma sterilization. In an embodiment, the coated implant 10 is sterilized using gamma radiation sterilization. The sterilization is done at a dose of gamma radiation in a range of 20 kGy to 30 kGy, more preferably 23 kGy to 27 kGy.
[52] The invention will now be explained with the help of following examples.
[53] Example 1: The substrate was pre-cleaned with purified water at 50°C temperature and dried at a temperature of 80°C for time duration of 10 minutes. Following the process of cleaning, masking was performed on predefined portions of the implant using PTFE tape. The PTFE tape was mounted on second area of stem 10a of the implants. Post masking, the substrate was subjected to a process of grit blasting using pure white alumina, Al2O3. The aluminum oxide was sprayed on the substrate at pressure of 4 bars. Post blasting process, the substrate was coated with hydroxyapatite powder using plasma coating 100 process. The coating constituted particle in powder form having particle size in a range of 45µm to 130µm.The process of plasma coating was performed at a voltage and current of 65 V and 500 A respectively. Further, the feed rate was 19.5rpm and distance between the spray gun and substrate was maintained at 1000mm. The thickness of the coating 100 achieved was 150 microns. Plasma coated substrate is further subjected to post annealing process at a temperature of 650°C for a duration of 2.25 hours. After that, de-masking was performed and substrate was observed under the microscope. Upon examination, the coating 100 was found to have micro cracks. Further, adhesion and crystallinity of the coating 100 was tested which was found to be 13MPa and 55% respectively.
[54] Further, the implant was tested for in-vitro evaluation, in which the substrate was placed in a beaker containing Ringer's buffered solution at a pH of 7.4, in an orbital shaker at a rotational speed of 60 rpm. The substrate was immersed for a period of two weeks and crystallinity was observed after each week using X-ray diffraction analysis. The crystallinity was found to be 57% and 59% after week 1 and week 2 respectively. Owing to less crystallinity of the coating, there will be formation of micro cracks in coating on the substrate which may lead to implant instability, failure and delay in osseointegration.
[55] In order to examine the coating 100, the substrate was evaluated under optical microscopy after 2 weeks in deteriorating medium (Ringer’s solution) wherein significant reduction was found in the coating layer. It indicated weak adhesion and delamination of coating from the substrate.
[56] EXAMPLE 2: The substrate was subjected to initial cleaning, masking & grit blasting processes with same parameters as mentioned in the above example. Grit blasted substrate was further cleaned with ultrasonic cleaning process to remove residual grit from the substrate. After cleaning, the substrate was etched using photochemical machining process. After etching process, the substrate was coated with the first layer 100a by means of electrophoretic deposition process. The first layer 100a includes hydroxyapatite particles in nano formulation having particle size ranging from 200nm to 1000nm. The electrophoretic deposition of the first layer 100a was carried at 20 V and coating 100 thickness of 10.00 micron was achieved. The substrate coated with the first layer 100a was then subjected to sintering and annealing process. Sintering process was performed by heating the substrate under vacuum at 750°C for 15 minutes at 4°C per min he
}ating and cooling rate and annealing was performed at 550°C temperature for 45 minutes. Annealed substrate is further coated with the second layer 100b by means of plasma coating process. The second layer 100b constituted particles in powder from having particle size in a range of 45µm to 130µm. Lastly; the substrate was subjected to post treatment annealing process at same parameter as mentioned in above example.
[57] The resulting coating on the substrate was found free of any micro cracks with crystallinity of 70% and adhesion strength of 23MPa. Further, the substrate was tested for in-vitro study as mentioned in above example for a period of 2 weeks and analyzed with X-ray diffraction method. The crystallinity was found to be 72% and 74% after week 1 and week 2 respectively. The higher crystallinity of the coating results in smooth surface without any micro cracks. This may result in coating to last long on the substrate leading to imparting stability to the implant and faster osseointegration.
[58] In order to support above finding, the substrate was evaluated under optical microscope after 2 weeks in deteriorating medium (Ringer’s solution) wherein it was found that there is no removal of coating layer after 2 weeks which indicates better adhesion of the coating layer to the substrate in the deteriorating medium.