Electrophoretic deposition of calcium polyphosphate on metal substrates

Abstract

Methods of producing calcium polyphosphate coatings on surfaces of a metal substrates are described herein. The methods include providing calcium polyphosphate particles in a powdered form; forming an electrochemical solution by mixing the calcium polyphosphate particles with an alcohol; immersing the substrate into the electrochemical solution; and applying a voltage to the electrochemical solution to form an electric field within the electrochemical solution, the electric field driving the calcium polyphosphate particles within the electrochemical solution to deposit onto the surface of the substrate and produce the calcium polyphosphate coating. Implants having calcium polyphosphate coatings are also described herein.

Description

Title: Electrophoretic Deposition of Calcium Polyphosphate on Metal SubstratesRelated Applications

[0001] The present application claims priority to United States Provisional Patent Application No. 63 / 703,465 entitled “Electrophoretic Deposition of Calcium Polyphosphate on Metal Substrates” filed on October 4, 2024, the contents of which are hereby incorporated by reference in their entirety.Technical Field

[0002] This disclosure relates generally to calcium polyphosphate coatings, and, more specifically, to electrophoretic deposition of calcium polyphosphate on metal substrates.Background

[0003] Total hip arthroplasty (THA) is an orthopedic procedure performed to relieve hip pain due to multiple physiological or physical causes that ultimately lead to the degeneration of the hip joint.

[0004] To mimic the “ball-and-socket” nature of a normal hip joint, a typical hip implant includes four major components: an acetabular cup, a wear-resistant liner, a femoral head, and a femoral stem.

[0005] When these components are introduced into a body, there are generally three ways to add fixation between the implant and the body: cemented, uncemented, and hybrid.

[0006] The cemented method uses bone cement to provide strong and long-term fixation between the implant and the bone surface. Bone cement typically consists of poly (methyl methacrylate) (PMMA), methyl methacrylate monomer and a polymerization initiator (benzoyl peroxide). The formulation may also contain an accelerator and an inhibitor to enhance curing and stability. The mixing of powder polymer-containing component and liquid monomer-containing component forms a high viscosity paste and ultimately a fully cured and rigid material. The cemented method is widely applied for THA, especially for aged patients. Aged patients have a relatively lower rate of bone1Error! No document variable supplied.regeneration, and bone cement can provide fast and stable fixation. However, many patients are reported to have bone cement implantation syndrome (BCIS). BCIS is characterized by hypoxia, hypotension or both and / or unexpected loss of consciousness occurring around the time of cementation, prosthesis insertion, reduction of the joint or, occasionally, limb tourniquet deflation in a patient undergoing cemented bone surgery. Meanwhile, for younger aged patients, rigid bone cement may also cause stress-shielding and potentially leads to bone loss.

[0007] To avoid BCIS and stress-shielding caused by bone cement, uncemented methods of fixing the implant and the bone surface are rising among THA cases. An uncemented implant has a fine mesh of holes on the surface designed to contact the bone directly. This mesh provides for bone growth into the mesh and forms stable fixation overtime. The direct connection between living bone and a load-carrying implant is generally referred to as osseointegration.

[0008] Bioactive materials like titanium, calcium phosphate, and hydroxyapatite are widely used in hip implant applications. These materials can stimulate a biological response from the body and bone growth along the implant surface. Uncemented osseointegrated implants improve quality of life, prosthetic use, hip motion range, and walking ability.

[0009] However, due to aseptic loosening, uncemented implants have a higher risk of revision. Uncemented implants also have a higher risk of wear-related problems. As a result, there is a need to develop a new uncemented implant solution with lower loosening and wear risk, ultimately with lower revision risk.

[0010] To avoid stress-shielding, the physical properties of the load-bearing component should be similar to the natural bone. Meanwhile, good implant performance is also directly related to its flexibility, ductility, corrosion resistance and biocompatibility. Commonly used metallic materials for hip implants include stainless steel, cobaltchromium alloys and titanium alloys.

[0011] Titanium (Ti) and Ti-based alloys have lower elastic modulus, good fatigue strength, excellent corrosion resistance, low density and a high strength / weight ratio than other metallic materials. Ti-6AI-4V (ASTM F 136, Ti64) is one of the most popular choices2Error! No document variable supplied.for hip joint implants. Its two-phase microstructure consists of small, equiaxed a grains with a uniform distribution of isolated [3-phase particles at the a-phase grain boundaries. Ti and Ti-alloy are also bioactive and have a proven osseointegration property after surface modification.

[0012] Bioceramics is a term commonly used to refer to ceramic materials applied in biomedical applications. The first generation of bioceramics focuses on high-strength bioinert materials (such as but not limited to alumina and / or zirconia). Although they have low biotoxicity and stable properties, these materials are generally non-biodegradable and require secondary surgery for revision. Moreover, bioinert materials cannot form biological bonds or induce bone regeneration.

[0013] Through the development of arthroplasty, a second generation of bioceramics has emerged in the implant industry. Second generation bioceramics enable bone to grow onto the ceramic surface and form a strong bond. Second generation bioceramics are expected to be biodegradable and have been designed to match the speed of bone repair and avoid stress shielding.

[0014] Polyphosphate (PolyP) is a linear polymer of tens to hundreds of orthophosphate residues linked via phosphoanhydride P-O-P bonds. PolyP can promote mesenchymal stem cell differentiation into osteoblasts, accelerate osteoblast mineralization and eventually increase a rate of osseointegration. PolyP can also combine with calcium to form calcium polyphosphate (CPP). CPP has good bioactivity, biocompatibility, degradability and mechanical properties.

[0015] There is a need for new techniques to produce a bioactive CPP coating on a metal substrate surface.Summary

[0016] In accordance with a broad aspect, a method of producing a calcium polyphosphate coating on a surface of a metal substrate is described herein. The method includes: providing calcium polyphosphate particles in a powdered form; forming an electrochemical solution by mixing the calcium polyphosphate particles with an alcohol; immersing the substrate into the electrochemical solution; and applying a voltage to the3Error! No document variable supplied.electrochemical solution to form electric field within the electrochemical solution, the electric field driving the calcium polyphosphate particles within the electrochemical solution to deposit onto the surface of the substrate and produce the calcium polyphosphate coating.

[0017] In at least one embodiment, forming the electrochemical solution further comprises mixing the calcium polyphosphate particles with an anhydrate isopropyl alcohol.

[0018] In at least one embodiment, the electrochemical solution is about a 1 -2 wt% suspension of the calcium polyphosphate particles in the anhydrate isopropyl alcohol.

[0019] In at least one embodiment, forming the electrochemical solution further comprises mixing the calcium polyphosphate particles and the alcohol with a conductivity adjuster.

[0020] In at least one embodiment, the conductivity adjuster is HNOs.

[0021] In at least one embodiment, the conductivity adjuster is H3PO4.

[0022] In at least one embodiment, mixing the calcium polyphosphate particles and the alcohol with the conductivity adjuster includes mixing the calcium polyphosphate particles and the alcohol with an amount of the conductivity adjuster to provide for the electrochemical solution to have a pH of about 7.

[0023] In at least one embodiment, mixing the calcium polyphosphate particles and the alcohol with the conductivity adjuster includes mixing the calcium polyphosphate particles and the alcohol with an amount of the conductivity adjuster to provide for the electrochemical solution to have a pH of about 7.

[0024] In at least one embodiment, the conductivity adjuster is NaCI.

[0025] In at least one embodiment, the conductivity adjuster is KCI.

[0026] In at least one embodiment, the conductivity adjuster is CaCh

[0027] In at least one embodiment, mixing the calcium polyphosphate particles and the alcohol with the conductivity adjuster includes mixing the calcium polyphosphate4Error! No document variable supplied.particles and the alcohol with an amount of the conductivity adjuster that has about a same weight, or less than about the same weight, as the calcium polyphosphate particles.

[0028] In at least one embodiment, mixing the calcium polyphosphate particles and the alcohol with the conductivity adjuster includes mixing the calcium polyphosphate particles and the alcohol with the conductivity adjuster and an amount of distilled water.

[0029] In at least one embodiment, the amount of distilled water is less than an amount of the alcohol.

[0030] In at least one embodiment, the amount of distilled water provides for a ratio of the amount of alcohol to the amount of distilled water to be about 3:1 .

[0031] In at least one embodiment, forming the electrochemical solution includes, after mixing the calcium polyphosphate particles with the alcohol, ultrasonicating the electrochemical solution for a period of time of at least 180 seconds.

[0032] In at least one embodiment, the period of time is about 180 seconds.

[0033] In at least one embodiment, after ultrasonicating the electrochemical solution, forming the electrochemical solution includes stirring the electrochemical solution at about 800 rpm for about 30 minutes.

[0034] In at least one embodiment, the stirring the electrochemical solution is by an electromagnetic stirrer.

[0035] In at least one embodiment, during the application of voltage, the platinum coated titanium electrode is connected to an anode and the titanium alloy substrate is connected to a cathode.

[0036] In at least one embodiment, during the electrophoresis, the electrochemical solution is continuously stirred.

[0037] In at least one embodiment, the electrochemical solution is continuously stirred at a rate of about 300 rpm.

[0038] In at least one embodiment, the calcium polyphosphate particles have a size distribution in a range of about 1 to 100 pm, or of about 1 to 50 pm, or of about 1 to 20 pm.5Error! No document variable supplied.

[0039] In at least one embodiment, the voltage applied is in a range of about 10 volts (V) to about 100 V, or in a range of about 20 V to about 50 V, or is about 20 V, or is about 30 V, or is about 40 V.

[0040] In at least one embodiment, the voltage applied is for a period of time in a range of about 5 minutes to about 30 minutes, or is in a range of about 10 minutes to about 20 minutes, or is about 10 minutes, or is about 20 minutes.

[0041] An implant having a calcium polyphosphate coating is also described herein. The calcium polyphosphate coating may have been produced by any one of the methods described herein.

[0042] In at least one embodiment, the implant is an orthopedic implant or a dental implant.

[0043] In at least one embodiment, the implant is a hip implant.

[0044] These and other features and advantages of the present application will become apparent from the following detailed description taken together with the accompanying drawings. It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the application, are given by way of illustration only, since various changes and modifications within the spirit and scope of the application will become apparent to those skilled in the art from this detailed description.Brief Description of the Drawings

[0045] For a better understanding of the various embodiments described herein, and to show more clearly how these various embodiments may be carried into effect, reference will be made, by way of example, to the accompanying drawings which show at least one example embodiment, and which are now described. The drawings are not intended to limit the scope of the teachings described herein.

[0046] FIG. 1 is a diagram of an electrophoretic deposition system according to at least one embodiment described herein.6Error! No document variable supplied.

[0047] FIG. 2 shows the steps in a method of producing a CPP coating on a metal substrate by electrophoretic deposition.

[0048] FIG. 3A shows an XRD pattern of calcium phosphate powder.

[0049] FIG. 3B shows an XRD pattern of uncoated Ti-6AI-4V alloy (Ti64) substrates.

[0050] FIG. 4 is a picture comparing different polished surface coating qualities.

[0051] FIG. 5 is a picture showing a comparison of coating qualities for different stirring rates.

[0052] FIG. 6 is a picture showing a comparison of coating qualities for different voltages.

[0053] FIG. 7 is an upview of five different positions of a Ti64 substrate in a beaker.

[0054] FIG. 8 is a picture showing a comparison of coating qualities for different positions of the substrate relative to the electrode.

[0055] FIG. 9 is a picture showing a comparison of coating qualities for different deposition times.

[0056] FIG. 10 is a picture showing the effect of annealing for different times on coatings.

[0057] FIG. 11 is a picture showing a comparison of samples as-coated, as- annealed and as-water washed for various times.

[0058] FIG. 12 is a picture showing a comparison of coatings for different voltages and different times.

[0059] FIG. 13 is another picture showing a comparison of coatings for different voltages and different times.

[0060] FIG. 14A is another picture showing a comparison of coatings for different voltages and different times (optical microscope).

[0061] FIG. 14B is another picture showing a comparison of coatings for different voltages and different times (optical microscope).7Error! No document variable supplied.

[0062] FIG. 15 is another picture showing a comparison of coatings for different voltages and different times.

[0063] FIG. 16 is a picture of laser powder bed fusion (LPBF) Ti64 blocks, as- printed (left: Photo, right: optical microscope).

[0064] FIG. 17 is a SEM image of a LPBF Ti64 block, as printed.

[0065] FIG. 18 is a picture of LPBF Ti64 blocks, as-coated.

[0066] FIG. 19 is a picture of Bulk Kokubo Solution (left), and merged samples in the oven (right).

[0067] FIG. 20 is a picture showing surface characterization of Ti64 sheets and 3D printed substrates before and after soaking.

[0068] FIG. 21 is a picture showing surface characterization of HNOs adjusted as- coated sample after soaking.

[0069] FIG. 22 is a group of pictures showing surface characterization of H4PO3 adjusted as-coated sample after soaking.

[0070] FIG. 23 is a group of pictures showing the coating quality of different voltage and time applied on Ti64 sheet substrate in NaCI-adjusted system.

[0071] FIG. 24 is pictures showing surface morphology of NaCI-adjusted system coated on Ti64 sheet by electrophoretic deposition (EPD) at 20 volts (V) with different deposition times. Photo (left), OM (middle), SEM (right).

[0072] FIG. 25 is pictures of as-annealed Ti64 sheet samples. Photo (left), OM (right).

[0073] FIG. 26 is pictures showing surface morphology of NaCI-adjusted system coated on a LPBF Ti64 substrate by EPD at 20 V with different deposition times.

[0074] FIG. 27 is pictures showing characterization of as-annealed LPBF Ti64 samples.

[0075] FIG. 28 is a picture of CPP powder.8Error! No document variable supplied.

[0076] FIG. 29 is a picture of initial trials of CPP deposited on LPBF Ti64 samples by EPD.

[0077] FIG. 30 is a picture of initial trials of CPP deposited LPBF Ti64 samples by EPD at 20 V.

[0078] FIG. 31 A is pictures showing surface morphology of CPP on a LPBF Ti64 substrate as-deposited by EPD at 10 V using a KCI-adjusted system and as-annealed thereafter at different deposition times.

[0079] FIG. 31 B is pictures showing surface morphology of CPP on a LPBF Ti64 substrate as-deposited by EPD at 10 V using a KCI-adjusted system and as-annealed thereafter at different deposition times.

[0080] FIG. 32 is pictures showing surface morphology of CPP on a LPBF Ti64 substrate as-deposited by EPD using a KCI-adjusted system at different deposition voltages.

[0081] FIG. 33 is pictures showing surface morphology of CPP on a LPBF Ti64 substrate as-deposited by EPD using a KCI-adjusted system at different deposition voltages.

[0082] FIG. 34 is pictures showing surface morphology of CPP on a LPBF Ti64 substrate as-deposited by EPD at 10 V using a KCI-adjusted system at different deposition times.

[0083] FIG. 35 is pictures showing surface morphology of CPP on a LPBF Ti64 substrate as-deposited by EPD at 10 V using a KCI-adjusted system at different deposition times.

[0084] FIG. 36 an x-ray diffraction (XRD) graph for calcium polyphosphate.

[0085] FIG. 37 is a particle size distribution chart of the CPP.

[0086] FIG. 38A is an SEM image showing the surface morphology of an as- received Ti-6AI-4V surface.

[0087] FIG. 38B is an SEM image showing the surface morphology of an as- sandblasted Ti-6AI-4V surface.9Error! No document variable supplied.

[0088] FIG. 38 C is a three-dimensional (3D) topography analysis of the as- sandblasted Ti-6AI-4V surface of FIG. 38B with a maximum depth of 18.47 pm.

[0089] FIG. 39A is an optical image showing the surface morphology for a 30V sample.

[0090] FIG. 39B is an SEM image showing the surface morphology at a first magnification for a 30V sample.

[0091] FIG. 39C is an SEM image showing the surface morphology a second magnification for a 30V sample.

[0092] FIG. 39D is an optical image showing the surface morphology for a 40V sample.

[0093] FIG. 39E is an SEM image showing the surface morphology at a first magnification for a 40V sample.

[0094] FIG. 39F is an SEM image showing the surface morphology a second magnification for a 40V sample.

[0095] FIG. 39G is an optical image showing the surface morphology for a 50V sample.

[0096] FIG. 39H is an SEM image showing the surface morphology at a first magnification for a 50V sample.

[0097] FIG. 39I is an SEM image showing the surface morphology a second magnification for a 50V sample.

[0098] FIG. 39J is an optical image showing the surface morphology for a 60V sample.

[0099] FIG. 39K is an SEM image showing the surface morphology at a first magnification for a 60V sample.

[0100] FIG. 39L is an SEM image showing the surface morphology a second magnification for a 60V sample.10Error! No document variable supplied.

[0101] FIG. 40A shows one micropore on 30V as-deposited sample with a diameter of around 7.6 pm.

[0102] FIG. 40B shows one micropore on 60V as-deposited sample with a diameter of around 115.7 pm.

[0103] FIG. 41A is an optical image showing the surface morphology of an as- annealed 30V sample.

[0104] FIG. 41 B is an SEM image showing the surface morphology of an as- annealed 30V sample at a first magnification.

[0105] FIG. 41 C is an SEM image showing the surface morphology of an as- annealed 30V sample at a second magnification.

[0106] FIG. 41 D is an optical image showing the surface morphology of an as- annealed 40V sample.

[0107] FIG. 41 E is an SEM image showing the surface morphology of an as- annealed 40V sample at a first magnification.

[0108] FIG. 41 F is an SEM image showing the surface morphology of an as- annealed 40V sample at a second magnification.

[0109] FIG. 41 G is an optical image showing the surface morphology of an as- annealed 50V sample.

[0110] FIG. 41 H is an SEM image showing the surface morphology of an as- annealed 50V sample at a first magnification.

[0111] FIG. 411 is an SEM image showing the surface morphology of an as- annealed 50V sample at a second magnification.

[0112] FIG. 41 J is an optical image showing the surface morphology of an as- annealed 60V sample.

[0113] FIG. 41 K is an SEM image showing the surface morphology of an as- annealed 60V sample at a first magnification.11Error! No document variable supplied.

[0114] FIG. 41 L is an SEM image showing the surface morphology of an as- annealed 60V sample at a second magnification.

[0115] FIG. 42 is an XRD pattern of CPP powder before and after annealing.

[0116] FIG. 43 is an XRD pattern of an as-coated sample under different applied voltages.

[0117] FIG. 44 is an XRD pattern of an as-annealed sample under different applied voltages.

[0118] Further aspects and features of the example embodiments described herein will appear from the following description taken together with the accompanying drawings.Detailed Description

[0119] Various systems, devices and methods are described below to provide an example of at least one embodiment of the claimed subject matter. No embodiment described below limits any claimed subject matter and any claimed subject matter may cover systems, devices and methods that differ from those described below. The claimed subject matter are not limited to systems, devices and methods having all of the features of any one systems, device or method described below or to features common to multiple or all of the systems, devices and methods described below. It is possible that a system, device or method described below is not an embodiment of any claimed subject matter. Any subject matter that is disclosed in a system, device or method described herein that is not claimed in this document may be the subject matter of another protective instrument, for example, a continuing patent application, and the applicant(s), inventor(s) and / or owner(s) do not intend to abandon, disclaim, or dedicate to the public any such invention by its disclosure in this document.

[0120] Furthermore, it will be appreciated that for simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the example embodiments described herein. However, it will be understood by those of ordinary skill in the art that the example embodiments described herein may be practiced without these12Error! No document variable supplied.specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the example embodiments described herein. Also, the description is not to be considered as limiting the scope of the example embodiments described herein.

[0121] It should be noted that terms of degree such as "substantially", "about" and "approximately" as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of the modified term, such as 1 %, 2%, 5%, or 10%, for example, if this deviation does not negate the meaning of the term it modifies.

[0122] Furthermore, the recitation of any numerical ranges by endpoints herein includes all numbers and fractions subsumed within that range (e.g., 1 to 5 includes 1 , 1.5, 2, 2.75, 3, 3.90, 4, and 5). It is also to be understood that all numbers and fractions thereof are presumed to be modified by the term "about" which means a variation up to a certain amount of the number to which reference is being made, such as 1 %, 2%, 5%, or 10%, for example, if the end result is not significantly changed.

[0123] The following description is not intended to limit or define any claimed or as yet unclaimed subject matter. Subject matter that may be claimed may reside in any combination or sub-combination of the elements or process steps disclosed in any part of this document including its claims and figures. Accordingly, it will be appreciated by a person skilled in the art that an apparatus, system or method disclosed in accordance with the teachings herein may embody any one or more of the features contained herein and that the features may be used in any particular combination or sub-combination that is physically feasible and realizable for its intended purpose.

[0124] Recently, there has been a growing interest in developing new and improved techniques to produce a bioactive coating on metal substrates, such as but not limited to three-dimensionally (3D) printed metal substrates and / or structures. These 3D printed metal substrates and / or structures may include, but are not limited to, metal alloy substrates and / or structures, and these metal alloy substrates and / or structures may include stainless steel, cobalt-chromium alloys and titanium alloys.13Error! No document variable supplied.

[0125] in particular, the CPP coatings on titanium alloy substrate surfaces described herein offer enhanced material properties when compared to CPP coatings produced using other techniques, and therefore offer a versatile platform for potential applications in cementless implants and dental implants. The integrated materials contribute to improved implant osseointegration and biocompatibility, aligning with evolving standards in biomedical engineering.

[0126] The following description describes the synthesis and manufacturing of CPP powder, the production of conducting CPP coatings on metal substrates, including but not limited to Ti-alloy substrates, by electrophoretic deposition (EPD). The following description also discusses post-deposition annealing, sample characterization, and in- vitro biocompatibility assessment.

[0127] EPD is one type of electrodeposition technique. Here, charged ceramic particles are suspended in a liquid medium and an electric field is applied to the medium. The charged particles migrate in the electric field and deposit on an electrode. In the examples described herein, the electrode is a metal substrate. Hydroxyapatite, for example, often uses isopropyl alcohol as a suspension medium for the EPD process. The alcohol solvent, as a proton donor, plays a vital role in charging ceramic colloidal particles.

[0128] Magnetic stirring may occur during EPD to maintain suspension stability. Based on several EPD mechanism models, the deposit yield is positively related to the electric field strength, electrophoretic mobility, electrode surface area, particle mass concentration, and Zeta potential of the particle. Conversely, deposit yield is generally negatively related to the viscosity of the suspension and the distance between the electrodes.

[0129] When compared with thermal spray, one of the current techniques that is used for forming coatings on metal substrates, EPD provides for coating onto complex geometric structures with strong bonding. Further, EPD provides a uniform strong coating on the metal substrate by forming both mechanical and chemical connections.

[0130] As discussed above, CPP has higher osseointegration properties compared with apatite. Further, Ti-alloys are also proven for good biocompatibility when used in14Error! No document variable supplied.implants. For these reasons, the combination of these two materials are used in the examples described herein.

[0131] It should be understood that the materials described herein may be used with orthopedic implants and / or dental implants, such as but not limited to hip implants, knee implants, ankle implants, shoulder implants, elbow implants, endosteal implants, zygomatic implants, and / or subperiosteal implants.

[0132] Turning now to the figures, FIG. 1 is a diagram of an electrophoretic deposition system 100. System 100 includes a vessel 102 housing an electrochemical solution 104. A metal substrate, such as but not limited to a titanium alloy substrate, 106 is immersed in the electrochemical solution 104 together with a platinum-coated titanium electrode 108. Substrate 106 is connected to a cathode 110 and platinum-coated titanium electrode 108 is connected to an anode 112 for the electrophoretic deposition. As shown in FIG. 1 , the substrate 106 and the platinum-coated titanium electrode 108 are separated by a distance d.

[0133] As an electric field is applied to the electrochemical solution 104, charged CPP particles within the electrochemical solution 104 move out of the electrochemical solution 104 and onto the negatively charged substrate 106, thereby providing a coating on the substrate 106.

[0134] The electric field may be created by any power supply 116, including but not limited to a direct current (DC) power supply that provides for the voltage and current supplied to be adjusted and controlled to control, for example, the deposition rate and the final thickness of the coating.

[0135] Physical properties of the coating produced on the titanium alloy substrate 106 are further described in the Examples section below, however, it should be noted that the coating generally has a highly organized honeycomb structure, which is desired for bioactive coatings that stimulate a biological response from the body and bone growth along the implant surface (e.g., osseointegration).

[0136] Turning now to FIG. 2, shown therein are steps of a method 200 for producing a CPP coating on a metal substrate.15Error! No document variable supplied.

[0137] At a first step 202, CPP particles are produced in a powdered form. CPP synthesis may be conducted through any previously described method. Generally, the CPP particles have particle size distribution in a range of about 1 to 20 pm.

[0138] At a second step 204, electrochemical solution 104 is formed by mixing the CPP particles with an alcohol. In at least one embodiment, the alcohol may be an anhydrate isopropyl alcohol. In at least one embodiment, the electrochemical solution is about a 1 wt% suspension of the calcium polyphosphate particles in the anhydrate isopropyl alcohol.

[0139] At a third step 206, substrate 106 is immersed in the electrochemical solution 104. As described above, substrate 106 is connected to a cathode 110 and platinum-coated titanium electrode 108 is connected to an anode 112 for the electrophoretic deposition. Optionally, prior to immersing the substrate in the electrochemical solution, the substrate may be sandblasted (e.g., using 80 grit aluminum oxide with a hand-held gun). Sandblasting the outer surface of the substrate may increase surface roughness and adhesion of the coating to the substrate.

[0140] At a fourth step 208, an electric field is applied to the electrochemical solution 104 by a power supply 116. Application of the electric field drives the CPP particles within the electrochemical solution 104 to deposit onto at least one surface of the substrate 106 and produce the calcium polyphosphate coating.

[0141] To apply the electric field, a voltage is applied by the power source 116 to the electrochemical solution 104. Power source 116 is generally a DC power source.

[0142] Application of a moderate voltage, for example in a range of about 10 V to about 100 V, may be used to create the electric field within the electrochemical solution 104 to produce a uniform ceramic coating on a Ti-6AI-4V alloy (Ti64) substrate. Different voltages may provide for a uniform ceramic coating on a Ti64 substrate based on the conductivity adjuster that is used in the solution. For example, a voltage of 20 V may provide a uniform coating of CPP on a Ti64 substrate when used with a HNOs system (as described below). In another example, a voltage of 40 V may provide a uniform coating of CPP on a Ti64 substrate when used with a H3PO4 system (as described below). In another example, a voltage of 20 V may provide a uniform coating of CPP on a Ti6416Error! No document variable supplied.substrate when used with a NaCI system (as described below). In another example, a voltage of 10 V may provide a uniform coating of CPP on a Ti64 substrate when used with a KCI system (as described below). In another example, a voltage of 40 V may provide a uniform coating of CPP on a Ti64 substrate when used with a CaCl2 system (as described below).

[0143] In at least one embodiment, increasing the applied voltage may enable a higher deposition rate of the CPP, but lower coating uniformity. In at least one embodiment, lower applied voltages enable a lower deposition rate but higher coating uniformity. Higher voltages may also result in increased porosity of the coating, but also results in lower stability (i.e. , the coating may peel off of the substrate easily).

[0144] Further, if the voltage is too low (e.g., below a minimum voltage threshold), the deposition process will not be initiated.

[0145] In at least one embodiment, the step 204 of forming the electrochemical solution 104 includes mixing the CPP particles with an alcohol and with a conductivity adjuster. The conductivity adjuster may be, for example, HNOs, H3PO4, NaCI, KCI, or CaCI2.

[0146] When the conductivity adjuster is HNO3 or H3PO4, the amount of the conductivity adjuster that is added to form the electrochemical solution 104 may be sufficient to provide for the electrochemical solution to have a pH of about 3.

[0147] When the conductivity adjuster is NaCI, KCI, or CaCl2, the amount of the conductivity adjuster that is added to form the electrochemical solution 104 may be sufficient to provide for the electrochemical solution to have a pH of about 7.

[0148] When the conductivity adjuster is NaCI, the amount of the conductivity adjuster that is added to form the electrochemical solution 104 may be about a same weight, or less than about the same weight, as the CPP particles in the electrochemical solution 104. For example, the concentration may be about 0.9 wt%.

[0149] Distilled water may also be added to the electrochemical solution 104. The amount of distilled water may be equal to or less than an amount of the alcohol. For17Error! No document variable supplied.example, the amount of distilled water may provide for a ratio of the amount of alcohol to the amount of distilled water in the electrochemical solution 104 to be about 3:1 .

[0150] After mixing the CPP particles with the alcohol, the electrochemical solution 104 may be ultrasonicated, for example for a period of time of about 180 seconds, or at least 180 seconds. Mixing of the solution may occur at a stirring rate of about 800 rpm.

[0151] After ultrasonicating the electrochemical solution 104, the electrochemical solution 104 may be continuously stirred, for example during the application of the electric field at step 208. For example, the electrochemical solution 104 may be stirred during the application of the electric field (i.e. , during deposition) at a stirring rate of about 300 rpm. For example, the electrochemical solution 104 may be stirred during the application of the electric field for a period of time, for example for about 30 minutes. The stirring may be by an electromagnetic stirrer.

[0152] The voltage applied by the power source 116 may be in a range of about 10 volts (V) to about 100 V, or in a range of about 10 V to about 50 V, or be about 10V, or be about 20 V, or be about 30 V, or be about 40 V.

[0153] The voltage applied by the power source 116 may be for a period of time in a range of about 5 minutes to about 30 minutes, or be about 10 minutes to about 20 minutes, or be about 10 minutes, or about 20 minutes.

[0154] For example, when the conductivity adjuster is HNOs, and the electrochemical solution 104 optionally has a pH of about 3, the voltage applied may be about 20 V.

[0155] For example, when the conductivity adjuster is H3PO4, and the electrochemical solution 104 optionally has a pH of about 3, the voltage applied may be about 40 V.

[0156] For example, when the conductivity adjuster is NaCI, and the electrochemical solution 104 optionally has a pH of about 7, and the concentration of the conductivity adjuster is optionally about 0.9 % w / v NaCI, the voltage applied may be about 20 V.18Error! No document variable supplied.

[0157] For example, when the conductivity adjuster is CaCl2, and the electrochemical solution 104 optionally has a pH of about 7, the voltage applied may be about 40 V.ExamplesCalcium Polyphosphate Synthesis

[0158] Calcium polyphosphate (CPP) synthesis was conducted through a previously described method. Precursor powder, calcium phosphate monobasic monohydrate (calcium dihydrogen phosphate hydrate, 97%, Thermo Scientific Chemicals), was calcined at 500°C for 10 hours in the air to form pure CPP through a condensation reaction. It was then melted at 1100 °C for one hour. The molten CPP was then quenched into distilled water, and washed with anhydrous ethanol to remove excess water. After completely drying from water and ethanol, CCP frit was milled in a high- energy ball mill to reach the desired particle size. The preferred particle size was 1 - 20 pm. The reaction formula for CPP synthesis is: n Ca(H2PO4)2H2O — [Ca(PO3)2]„ + 3nH2O 500 C

[0159] The obtained ACPP frit was milled in a high-energy 3D ball mill (MSK-SFM- 3-II, MTI Corporation). Each milling cycle took 5 minutes for 800 rpm forwards and 5 minutes for 800 rpm backwards. 8 cycles were completed in total. The particle size distribution of the prepared CPP powder was confirmed by the laser scattering particle size distribution analyzer (LA-950V2, HORIBA) in deionized water.

[0160] In general, it should be understood that any process that provides CPP having an average particle size of less than about 100 pm, or an average particle size of less than about 20 pm, may be used.

[0161] The Ti-6AI-4V substrate (High-Strength Grade 5 Titanium Sheet, 0.032” thick, McMASTER-CARR) was sandblasted using 80 grit aluminum oxide with a handheld gun to increase surface roughness. The surface roughness was then measured through the 3D topography by digital optical microscopy (VHX-7000N, KEYENCE).19Error! No document variable supplied.Electrochemical Solution Preparation

[0162] Four electrochemical solution systems were tested: HN Os-adjusted, H3PO4- adjusted, NaCI-adjusted, KCI-adjusted and CaCl2-adjusted. The liquid environment consisted of ceramic (e.g., CPP) powder mixed with anhydrate isopropyl alcohol to make 1 -2 wt% suspension. Acid and salt were added to improve the solution's conductivity. Table 1 , below, provides four example solution recipes. The solutions were first ultrasonicated for 180 seconds, then stirred at 800 rpm by an electromagnetic stirrer for 30 minutes. Since the manufacturing cost of CPP powder was relatively high and there was a delay in raw material delivery, most EPD experiments were conducted using commercial calcium phosphate dibasic dihydrate powder as the theory verification.Table 1 : Electrochemical solution recipesElectrophoretic Deposition (EPD)

[0163] EPD was conducted in a 200 mL beaker with a DC power supply. The Pt- coated Ti electrode was connected to the positive (anode), and the Ti64 substrate was connected to the negative (cathode). A 300 rpm continuous stirring was applied during the EPD process. The temperature was controlled at 30°C.

[0164] The horizontal distance between the cathode and anode was 35 mm. The EPD was performed under various voltages for a fixed 10-minute deposition duration.20Error! No document variable supplied.Table 2 shows each EPD parameter set. The as-coated samples would be dried in air for 24 hours at room temperature.

[0165] After EPD, a heat treatment was performed at 750 °C for 4 hours in a tube furnace with a continuous 400 cc / min argon gas flow, heating rate of 5 °C / min, and cooling rate of 3 °C / min. Alternate heating and cooling rates are also possible. The annealing temperature can range between 500 °C and 1000 °C.Table 2: Applied voltage and respective current density for each condition

[0166] Parts were then annealed using one of two methods. In a first method, parts with enough coating thickness were rinsed in water and sintered in a muffle furnace at 800°C for two hours.

[0167] In a second annealing process, parts with enough coating thickness may be annealed using vacuum annealing performed using a tube furnace. Here, the tube of the tube furnace was washed using argon (Ar) gas three times (e.g., continuous Ar gas was flowed through the tube for two minutes). The clean tube was maintained at vacuum at -0.1 MPa during the annealing process. Annealing occurred first at 585 °C for one hour and then at 785 °C for one hour. Cooling and OM characterization then followed.Error! No document variable supplied.Additive Manufacturing

[0168] LPBF technique was used to manufacture metal substrates. The standard testing substrate dimension according to ISO23317 was 10 mm x 10 mm x 2 mm. In the future, the AM technique will also be used to produce parts with complex geometry, various internal structures, different surface roughness, heterogeneous chemical composition, etc.Kokubo Solution for Osseointeqration (ISO 23317)

[0169] This experiment aimed to determine the osseointegration property of the product as an in-vitro technique. This simulated body fluid (SBF) recipe described in this standard was adapted from “How useful is SBF in predicting in vivo bone bioactivity?” by T. Kokubo et al. in 2006. This type of SBF is also called the “Kokubo Solution”. The whole soaking process took four weeks. Characterization would be performed using thin-film X- ray Diffraction and Scanning Electron Microscopy.CharacterizationOptical Microscopy (OM)

[0170] Optical microscopy is a useful tool to characterize the microstructure of the sample surface with the ability to zoom in from 50x to 1000x. It is the primary characterization technique to examine the coating quality and thickness.X-ray diffraction (XRD)

[0171] XRD is a nondestructive technique that provides detailed information about the crystallographic structure, chemical composition, and physical properties of a material

[0038] , It is used to determine the coating material (CP from CPP), and crystal structure. For as-coated samples and Kokubo Solution-soaked samples, thin-film XRD should be applied instead of conventional XRD. The machine used was Phillips PW3710 Powder X-ray Diffractometer (XRD) , Cu - Ceramic X-ray tube. 2 Theta from 20° to 80° with step size 0.02°.22Error! No document variable supplied.Scanning Electron Microscopy (SEM)

[0172] SEM is useful to characterize the microstructure of the sample surface in micro- and nanometer scales with high contrast. The embedded Energy-dispersive X-ray spectroscopy (EDS) is a powerful tool to analyze the element composition.Porosity calculation

[0173] Imaged is utilized in this project to measure the porosity and average pore size. The porosity is calculated by the threshold method. The average pore size is taken from all observed pores in SEM images, together with the maximum, minimum, median, and standard deviation.ResultsHNOs-adjusted SystemXRD Results for Calcium Phosphate, Ti64, and EPD-coated samples

[0174] Calcium phosphate EPD coated samples, calcium phosphate powder, and uncoated Ti64 substrates were examined by XRD technique. FIG. 3A shows the XRD pattern of calcium phosphate powder, and FIG. 3B shows the uncoated Ti64 substrates’ XRD pattern. EPD-coated samples showed the same XRD pattern as the uncoated samples. The main reason was the X-ray penetrated through the thin coating and the system retrieved the data from the Ti64 substrate instead of the coating. As a result, thin- film XRD is required for future research. pH and EPD Coating Quality

[0175] The mixture of Isopropyl Alcohol and Calcium Phosphate is in neutral condition, and has very low electric conductivity. Based on the review, the preferred pH condition for this system to conduct EPD is pH = 3~5. By adding HNOs to make the solution reach a pH of 3, the system showed better electrodeposition quality than the neutral condition. Table 3, below, shows the coating qualities for various voltages and pHs.23Error! No document variable supplied.Table 3: pH value and coating quality pH Voltage Current Coating7 10 V 0.00 A No coating7 20 V 0.00 A No coating7 30 V 0.00 A No coating3 10 V 0.00 A Thin coating3 20 V 0.01 A Good coating3 30 V 0.02 A Thick coatingSurface Roughness and EPD Coating Quality

[0176] The unpolished Ti64 surface was coated by a matte oxide layer. After polishing, Ti64 became shiny and smoother. FIG. 4 shows the coating quality for different roughness surfaces. The roughness was created by different sandpapers (ANSI 60, 320, 400, 600, and 800 grits). The smoother surface had a thinner but finer coating after EPD. The rougher surface had a thicker but unevenly distributed coating. However unpolished samples had better coating quality than all polished samples. The solution was pH=3 adjusted by HNO3, and samples were coated at 20 V for 1 minute.Stirring Rate

[0177] An electromagnetic stirrer was used to maintain the suspension of particles in a liquid environment. A high stirring rate may affect the traveling stability of particles in the electric field. Low stirring rate may result in the precipitate of particles and cause bad coating quality. Different sizes in the beaker and stirrer may lead to different stirring effects at the same speed (rpm) In this project, a 200 mL beaker and a 30 mm stirrer were used, and 200 and 300 rpm were tested. The result showed that a 300 rpm stirring rate was preferred. FIG. 5 shows a coating quality comparison at different stirring rates.Voltage and EPD Coating Quality

[0178] Higher voltage resulted in a higher deposition rate, but lower coating quality. Lower voltage had a lower deposition rate, but the coating was uniformly distributed with a finer surface than others. 20 V showed the most balanced deposition rate and quality. FIG. 6 shows a coating quality comparison at different voltages.24Error! No document variable supplied.Distance between Electrodes

[0179] FIG. 7 shows an upview of five different positions of Ti64 substrate in the beaker. No.1 is 10 mm away from the anode, Nos. 2, 4 and 5 are 20 mm away, and No. 3 is 30 mm away. The blue arrows represent the fluid flow directions, and the red arrows represent the electrical field direction. Coating quality will improve if the direction of the electrical field and fluid flow match. A moderate distance (e.g., 20 mm) between electrodes appears to improve coating quality and the position should avoid high turbulence (e.g., No. 2 at the whirlpool center). EPD parameters were 20 V, 300 rpm, pH = 3 (nitric acid), unpolished. FIG. 8 shows coating qualities at different positions.Deposition time and Coating Quality

[0180] In these examples, EPD parameters were 20 V, 300 rpm, pH = 3 (nitric acid), unpolished, position No. 4. The uniformity and thickness of the coating increased as time increased. However, around 3% of the area remained uncoated after long-time deposition. This might be because of the hydrogen bubbles formed from the surface during the electrodeposition. The initialization spot of the movement of bubbles blocked the deposition and left the area uncoated. FIG. 9 shows coating qualities at different deposition times.Annealing after EPD

[0181] Durations of 15 and 20 minutes EPD coated samples were annealed using a tube furnace for 2 hours slowly heated up to 800°C, 2h temperature kept at 800°C, 2h slowly cooled down to 200°C, and air-cooled to room temperature. The temperature range for annealing samples may be in a range of about 500 °C of about 800 °C. FIG. 10 shows the pictures of the annealed samples. The annealed samples formed large cracks in the coating, delamination between layers. The annealed samples were then washed with distilled (DI) water. FIG. 11 shows the surface morphology of as-coated, as-annealed, and as-washed samples characterized by optical microscopy. The yellowish area indicates an oxidation film formed on the Ti64 substrate surface during the annealing.H4PO3-adjusted System25Error! No document variable supplied.EPD Voltage

[0182] Since nitric acid is a strong acid, it may change the microstructure of ceramics in the liquid environment. Meanwhile, nitric acid residuals may decrease the biocompatibility of the coated parts. As a result, phosphoric acid was used to adjust pH in the following experiments. As a weak acid, the H4P Os-adjusted system required a higher voltage to perform EPD. FIGs. 12, 13, 14A and 14B show coatings formed by EPD under 20 V, 30 V, 40 V, and 50 V for 1 minute, 5 minutes and 10 minutes. The results showed that 40 V was the preferred voltage for the H4POs-adjusted system.Deposition Time

[0183] For 40 V phosphoric acid system EPD, the edge quality decreased as the deposition time went from 1 to 30 minutes, increased from 30 minutes to 1 hour, and continuously decreased after 1 hour. The coating thickness did not have an obvious increment after 2 hours 50 minutes. Compared with the HNOs-adjusted system, the HsPCM-adjusted system has poorer macro-level coating quality, but has smoother microlevel coating quality. FIG. 15 shows coatings formed under 40 V H3PO4-adjusted system EPD for different durations, from 10 minutes to 4.5 hours.Laser Powder Bed Fusion (3D printed) Ti64 SampleLPBF Ti64 blocks, as-printed

[0184] The LPBF Ti64 blocks were printed. The dimension was 10 mm x 10 mm x 3 mm. The surface was coarse and unpolished, had a large surface area, and a higher oxide area percentage compared with the Ti64. This is shown in FIG. 16 and FIG. 17 (SEM image).LPBF Ti64 Blocks, as-coated

[0185] The 3D printed Ti64 blocks were EPD coated in the HsPCM-adjusted system at 40 V for 30 minutes, 2 hours, 3 hours, and 4 hours. Results (see FIG. 18) showed that 3D-printed parts had better coating quality compared with Ti64 sheets. Coating thickness did not increase significantly after 3 hours.26Error! No document variable supplied.Body Simulated Fluid Experiment for Osseointeg ration

[0186] Kokubo solution was freshly made and preserved at 7 °C. Each sample was soaked in 20 mL SBF for 4 weeks at 37°C. The samples are Ti64 sheet coated in HNOs- adjusted system, Ti64 sheet coated in H3PO4-adjusted system, LPBF Ti64 coated in HsPCM-adjusted system, uncoated Ti64 sheet, 3D printed Ti64 block, and Kokubo Solution only. FIG. 19 shows bulk Kokubo Solution (left), and merged samples in the oven (right).

[0187] After the 4-week soaking, a thin film of calcium was observed on the uncoated sample surface (see FIG. 20). Since Ti64 is a material with good biocompatibility proven by literature, the observed calcium film indicates that the prepared Kokubo solution is capable of determining osseointegration properties.

[0188] FIG. 21 and FIG. 22 show the surface morphology of HNOs-adjusted and HsPCM-adjusted samples after the 4-week soaking. All samples show a light grey film on the surface, this indicates the osseointegration property of these samples. Although all samples experienced a coating degradation after the soaking, there is still a certain percentage of the coating remains. According to the manuscript of the standard Kokubo soaking procedures, 4 weeks is the longest suggested soaking time for this experiment. To examine the coating’s long-term stability, the Hanks solution soaking experiment will be useful for future research.NaCI-adjusted System

[0189] The normal range of human blood has a pH from 7.35 to 7.45. As a result, this section mainly investigated using a neutral agent to improve the solution conductivity and electrodeposition with higher expected biocompatibility. In the NaCI-adjusted system, 1.8g NaCI was added to a mixture of 150 mL isopropyl alcohol and 50 mL DI water.Preferred EPD Voltage

[0190] Similar to the previous systems, different EPD voltages were applied and tested. FIG. 23 shows the comparison between 10, 20, and 30 V with 5, 10, and 20 minutes of deposition time. As the deposition time increased, the coating thickness increased. As the applied voltage increased, the deposition rate increased. A higher27Error! No document variable supplied.voltage (30 V) would lead to coating peel-off after 10 minutes. A lower voltage (10 V) led to an uneven distribution of coated area. 20 V was the preferred moderate voltage in the NaCI-adjusted system for EPD.EPD on Ti64 Sheet Substrate

[0191] FIG. 24 shows the surface morphology of calcium phosphate coated on Ti64 sheets at 20 V. Due to the high conductivity of the NaCI-adjusted solution, the bubble formed during the EPD process was more intense than the acid-adjusted systems. The moving bubbles behaved like a dynamic template as the ceramic particles deposited onto the substrate surface. After a 10-minute deposition, the coating showed a highly organized honeycomb structure with an average pore size of 61.57 pm, porosity of 48.11 %. The pore size increased as the deposition time increased. For the 20-minute deposited sample, the average pore size was 109.91 pm and porosity was 40.34%. Table 3 shows porosity measurements for coatings formed using various voltages and various durations.Table 4: Porosity for NaCI adjusted samples as-coated on Ti64 substrate20 V 5 mins 20 V 10 mins 20 V 20 minsAverage pore size (pm) N / A 61.57 109.91Median (pm) N / A 57.01 108.58Maximum (pm) N / A 139.74 192.87Minimum (pm) N / A 23.00 51.09Standard Deviation N / A 23.57 28.57Porosity N / A 48.11 % 40.34%28Error! No document variable supplied.

[0192] After annealing (2 hours, 800°C), the coating on Ti64 sheet samples peeled off and left an oxidized black area on the Ti64 sheet surface. This result suggests that future attempts will require lower annealing temperatures, shorter annealing time, or oxygen-free annealing. FIG. 25 shows as-annealed Ti64 sheet samples. Photo (left), OM (right).EPD on LPBF Ti64 substrate

[0193] LPBF Ti64 substrate had a higher surface area compared with the Ti64 sheet because of the coarse lack-of-fusion surface. With the same applied voltage and deposition time, LPBF samples had higher coating thickness compared with the Ti64 sheet samples. FIG. 26 shows the surface morphology of the as-coated and as-annealed samples. After the annealing (800°C, 2 hours), there was a collapse of the porous structure. FIG. 27 shows the SEM images of as-annealed LPBF samples. The structure was less organized compared with the as-coated samples and the pore size was increased. For 20 minute deposited samples, the average pore size before annealing is 45.01 pm, and after annealing was 97.47 pm. Table 5 provides porosity measurements.Table 5: Porosity for NaCI adjusted samples as-annealed on LPBF Ti64 substrate20 V 5 mins 20 V 10 mins 20 V 20 minsAverage pore size (pm) 66.45 38.26 97.47Median (pm) 65.31 34.50 93.09Maximum (pm) 122.02 85.86 207.78Minimum (pm) 24.17 10.11 30.00Standard Deviation 19.98 16.45 39.4529Error! No document variable supplied.Porosity 46.73% 39.25% 44.68%Calcium Polyphosphate (CPP) Deposition

[0194] Due to the material and equipment shipment delay, minor research was made about the calcium polyphosphate deposition. FIG. 28 shows the calcium phosphate manufactured in the lab.

[0195] FIG. 29 and 30 show the initial trials of using the NaCI-adjusted system to conduct CPP EPD on Ti64 sheet and LPBF (3D) substrate samples.KCL-System

[0196] Compared with the previously described NaCI system, the KCI system offers the following advantages. First, K+ ions have a similar radius with Cl- when compared with Na+. The ion transporting number of K+ is 0.49 and Na+ is 0.4, which means K+ is more effective in transporting through solution. Further, KCI can maintain a long-term neutrality whereas NaCI may cause ion imbalance. FIGs. 31 A and 31 B are collections of pictures showing surface morphology of CPP on a LPBF Ti64 substrates both as-deposited by EPD at 10 V using a KCI-adjusted system and as-annealed thereafter at different deposition times.

[0197] FIG. 32 is a collection of pictures showing surface morphology of CPP on a LPBF Ti64 substrate as-deposited by EPD using a KCI-adjusted system at different deposition voltages. 10 V appears to be a preferred voltage for CPP deposition in KCI systems. FIG. 33 shows magnified views of the surface morphology photos of FIG. 32.

[0198] Various deposition times were also investigated between 5 minutes and 60 minutes. 15 minutes appears to be a reasonable period for forming a uniform and stable CPP coating in a KCI system. FIG. 34 includes a collection of pictures showing surface morphology of CPP on a LPBF Ti64 substrate as-deposited by EPD at 10 V using a KCI- adjusted system at different deposition times. FIG. 35 shows magnified views of the surface morphology photos of FIG. 34.

[0199] FIG. 36 an x-ray diffraction (XRD) graph for calcium polyphosphate.30Error! No document variable supplied.Surface structure and morphology characterization

[0200] The macro surface topology and roughness were characterized through a digital optical microscope (VHX-7100N, KEYENCE) with a 3D measurement feature that stacked and synthesized images with different depths of field and analyzed the height difference of the sample surface.

[0201] The micro characterization of the sample surfaces was performed by scanning electron microscopy (SEM, 6610LV JEOL) with a Tungsten filament. Sample surfaces were gold sputtered to improve the conductivity. The secondary electron images (SEI) were acquired at 15 kV.

[0202] The phase and elemental information were acquired by X-ray diffraction (XRD, MiniFlex 600, Rigaku) with Cu Ka radiation. The scanning rate was 1 min with a step size of 0.02°, and the 29 range was from 10° to 70°.Mechanical properties of CPP coating

[0203] The adhesion strength between the CPP coating and the Ti-6AI-4V substrate was measured through a tensile testing method adapted from “ISO 13779-A”

[0016] , The testing was performed on a universal mechanical testing machine (Instron 3365, maximum 5kN). The sample dimensions were 10 mm by 10 mm and were attached to the counterpart with epoxy adhesion (J-B WELD 8265SCAN, maximum strength 27.3 MPa). The testing extension ramp rate was 0.015mm / s. 10 valid results were collected for each EPD condition.CPP powder particle size distribution analysis

[0204] Ball-milled CPP powder was diluted with DI water to achieve a transmittance of 97.8% (R) and 97.4% (B). The refractive indices of CPP and water were respectively assumed to be 1 .629 and 1 .333. Based on 3 valid measurements, ball-milled CPP had a median size of 7.034 pm, a mean size of 8.096 pm, a D10 of 3.692 pm, and a D90 of 13.161 pm. The standard deviation of the measurement was 4.916 pm. FIG. 37 shows a particle size distribution chart of the CPP.31Error! No document variable supplied.3.2 Surface morphology and structure characterization

[0205] Figure 38 shows the surface morphology of as-sandblasted of Ti-6AI-4V substrate surface. Based on the 3D depth analysis from the digital optical microscopy, the as-sandblasted substrate had a maximum depth of 18.47 pm. Sandblasting process provided higher surface roughness compared with the as-received smooth surface. This depth would interlock with the first 2 to 3 layers of deposited CPP particles and increase the overall adhesion between the coating and the substrate.

[0206] Figure 39 shows the surface of as-coated samples with deposition voltage ranges from 30v to 60v captured from optical microscopy and SEM. Higher deposition voltage resulted in a higher deposition rate, along with a more rapid hydrogen evolution reaction. The hydrogen bubble continuously generated on Ti-6AI-4V substrate, blocked the deposition of CPP coating, and resulted in the micropores across the coating. The micropore observed in 30v-deposited sample had a diameter below 10 pm and the micropore observed in 60v-deposited sample was sized over 100 pm (see Figure 4 for examples of micropores). The potential relationship among porosity, coating strength and osseointegration properties will be discussed in later section.

[0207] FIG. 40 shows the surface of as-annealed samples which underwent a 4- hour heat treatment at 750°C. After heat treatment, all samples exhibited coating delamination and decreasing coverage area. As the applied voltage increased, the remaining CPP coating area decreased. The delamination was mainly contributed by the coefficient of thermal expansion (CTE) difference between the Ti-6AI-4V substrate and the CPP coating. Meanwhile, the Ti-6AI-4V surface was oxidized during the heat treatment due to equipment limitations, resulting in a titanium oxide layer formed between the interface of CPP coating and Ti-6AI-4V.

[0208] FIG. 41 shows the XRD pattern of CPP powder before and after annealing at 750°C for 4 hours. Before annealing, the CPP powder showed an amorphours [3- CaP2O6 phase with a monoclinic crystal structure. After annealing, the pattern exhibited a mixture of a and [3 phases and a higher relative intensity.

[0209] FIG. 42 shows the XRD pattern of as-coated samples at different applied voltages. Different from the CPP powder, as-coated samples an extra peak at 29=51 °,32Error! No document variable supplied.indicating an addition of a (0 2 3) plane from an orthorhombic aluminum phosphate (AIPO4). One possible hypothesis is that the deposition rate of CPP was relative low at low voltage, it allowed more time for Al3+to diffuse through the thin CPP coating and form AIPO4 with PO43'. At higher voltage, the deposition rate of CPP was higher and fast covering the Ti-6AI-4V surface. The percentage of AIPO4 in the bulk coating decreased.

[0210] FIG. 43 displays the XRD pattern of as-annealed samples. Due to the coating delamination, crystallography information obtained from the as-annealed electrodeposition samples had similar patterns as the as-annealed Ti-6AI-4V sample. The signal from the substrate of as-annealed samples increased as the applied deposition voltage increased. This phenomenon indicates that higher voltage would result in a higher degree of coating delamination during the heat treatment.CPP coating tensile adhesion strength before annealing

[0211] Results from the five tested samples:Table 6: Strength Results at Various Voltages

[0212] Without the annealing, 40V-deposited samples have a coating adhesion strength that fulfills the FDA requirements (15 MPa and no samples lower than 10 MPa).33Error! No document variable supplied.

[0213] While the applicant's teachings described herein are in conjunction with various embodiments for illustrative purposes, it is not intended that the applicant's teachings be limited to such embodiments as the embodiments described herein are intended to be examples. On the contrary, the applicant's teachings described and illustrated herein encompass various alternatives, modifications, and equivalents, without departing from the embodiments described herein, the general scope of which is defined in the appended claims.34Error! No document variable supplied.

Claims

ClaimsWhat is claimed is:1 . A method of producing a calcium polyphosphate coating on a surface of a metal substrate, the method comprising: providing calcium polyphosphate particles in a powdered form; forming an electrochemical solution by mixing the calcium polyphosphate particles with an alcohol; immersing the substrate into the electrochemical solution; and applying a voltage to the electrochemical solution to form an electric field within the electrochemical solution, the electric field driving the calcium polyphosphate particles within the electrochemical solution to deposit onto the surface of the substrate and produce the calcium polyphosphate coating.

2. The method of claim 1 , wherein forming the electrochemical solution further comprises mixing the calcium polyphosphate particles with an anhydrate isopropyl alcohol.

3. The method of claim 2, wherein the electrochemical solution is about a 1 -2 wt% suspension of the calcium polyphosphate particles in the anhydrate isopropyl alcohol.

4. The method of any one of claims 1 to 3, wherein forming the electrochemical solution further comprises mixing the calcium polyphosphate particles and the alcohol with a conductivity adjuster.

5. The method of claim 4, wherein the conductivity adjuster is HNOs.

6. The method of claim 4, wherein the conductivity adjuster is H3PO4.

7. The method of any one of claims 4 to 6, wherein mixing the calcium polyphosphate particles and the alcohol with the conductivity adjuster includes mixing the calcium polyphosphate particles and the alcohol with an amount of the conductivity adjuster to provide for the electrochemical solution to have a pH of about 3.

8. The method of claim 4, wherein the conductivity adjuster is NaCI.35Error! No document variable supplied.

9. The method of claim 4, wherein the conductivity adjuster is KCI.

10. The method of claim 4, wherein the conductivity adjuster is CaCl2.11 . The method of any one of claims 8 to 10, wherein mixing the calcium polyphosphate particles and the alcohol with the conductivity adjuster includes mixing the calcium polyphosphate particles and the alcohol with an amount of the conductivity adjuster to provide for the electrochemical solution to have a pH of about 7.

12. The method of any one of claims 4 to 11 , wherein mixing the calcium polyphosphate particles and the alcohol with the conductivity adjuster includes mixing the calcium polyphosphate particles and the alcohol with an amount of the conductivity adjuster that has about a same weight, or less than about the same weight, as the calcium polyphosphate particles.

13. The method of any one of claims 4 to 12, wherein mixing the calcium polyphosphate particles and the alcohol with the conductivity adjuster includes mixing the calcium polyphosphate particles and the alcohol with the conductivity adjuster and an amount of distilled water.

14. The method of claim 13, wherein the amount of distilled water is less than an amount of the alcohol.

15. The method of claim 14, wherein the amount of distilled water provides for a ratio of the amount of alcohol to the amount of distilled water to be about 3:1 .

16. The method any one of claims 1 to 15, wherein forming the electrochemical solution includes, after mixing the calcium polyphosphate particles with the alcohol, ultrasonicating the electrochemical solution for a period of time of at least 180 second.

17. The method of claim 16, wherein the period of time is about 180 seconds.

18. The method of claim 16 or claim 17, wherein, after ultrasonicating the electrochemical solution, forming the electrochemical solution includes stirring the electrochemical solution at about 800 rpm for about 30 minutes.36Error! No document variable supplied.

19. The method of claim 18, wherein the stirring the electrochemical solution is by an electromagnetic stirrer.

20. The method of any one of claim 1 to 19, wherein, during the application of voltage, the platinum coated titanium electrode is connected to an anode and the titanium alloy substrate is connected to a cathode.

21. The method of any one of claim 1 to 20, wherein, during the electrophoresis, the electrochemical solution is continuously stirred.

22. The method of claim 21 , wherein electrochemical solution is continuously stirred at a rate of about 300 rpm.

23. The method of any one of claims 1 to 22, wherein the calcium polyphosphate particles have a size distribution in a range of about 1 to 100 pm, or of about 1 to 50 pm, or of about 1 to 20 pm.

24. The method of any one of claims 1 to 23, wherein the voltage applied is in a range of about 10 volts (v) to about 100 v, or in a range of about 20 volts (V) to about 50 V, or is about 20 V, or is about 30 V, or is about 40 V.

25. The method of any one of claims 1 to 24, wherein the voltage applied is for a period of time in a range of about 5 minutes to about 30 minutes, or is in a range of about 10 minutes to about 20 minutes, or is about 10 minutes, or is about 20 minutes.

26. An implant having a calcium polyphosphate coating, the calcium polyphosphate coating having been produced by the method of any one of claims 1 to 25.

27. The implant of claim 26, wherein the implant is a dental implant or an orthopedic implant.

28. The implant of claim 26, wherein the implant is a hip implant.37Error! No document variable supplied.

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