A film of osteoconductive and biocompatible material on biomedical metallic implants can create bioactivity of the implant and shorten healing time. Hydroxyapatite, that is the most important mineral part of human bone, was coated on Ti6Al4V using cathodic electrode position process. Pulse electrode position technique was used and the effects of different parameters such as potential, duty cycle (on time/ (on time+ off time)), temperature and current density on the morphology of the deposits were examined. Nano size deposits were formed under controlled temperature and optimization of voltage and current density.

This study was a preliminary study on flame spray coating with hydroxyapatite (HAp). Coating is one of the technique to improve metal resistance to corrosion. In this study, flame spray coating using HAp was performed on stainless steel 316 L as a material for medical devices. This synthetic compound contains elements which are biocompatible and bioactive in human body where they can stick to body tissues or muscles.HAp has been extensively used as a bone substitute because of its crystal structure, biocompatibility and osteoconductive nature. In this study, 316L SS was coated by HAp using flame spray method with varied oxygen flowrate and air pressure. The result of this study showed that the air pressure of 1 bar and oxygen flowrate of 25 l/min had the thickest coating which was 123.5μm and the lowest corrosion rate which was 0.0261 mm/year. The air pressureof 3 bar and oxygen flowrate of 35 l/min produced the lowest thickness which was 32.5μm and the highest corrosion rate which was 0.0761 mm/year. The use of high air pressure and oxygen flowrate decreased the coating thickness and the corrosion rate. The result revealed that flame spray method was effective to be used to coat HAp on 316L SS.

Calcium phosphate (Ca-P) based bioceramics has proved to be alluring materials for biomedical applications. Among these, particular attention has been given to hydroxyapatite (HA), Ca10(PO4)6(OH)2. Due to its favorable some physical, mechanical, chemical properties and biocompatibility, HA-coated Ti6Al4V alloy has been approved as one of the most interesting implant materials for orthopedic and dental applications. High Velocity Oxy Fuel (HVOF) is a method used to coat hydroxyapatite (HA) on metallic implants such as titanium (Ti) and its alloy (Ti6Al4V). In this work decreasing the crack occurrence and increasing adhesion strength were investigated. For this purpose, sol-gel synthesized nano sized HA, alumina (Al2O3) and Boron oxide (B2O3) powders were produced. First, a series of HA/Al2O3 HA/B2O3 coatings have been deposited on Ti6Al4V substrate by HVOF method. All specimens’ surfaces were used to characterize by using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM-EDS) and X-ray Diffraction (XRD). Adhesion strength of the samples was found to affect with increasing amount of Al2O3 and B2O3 in HA. Furthermore, water contact angles of coating layer were decreased with increasing amount of Al2O3 and B2O3 in HA. This coating surface was expected to combine the advantages of Ca-P (osseointegration) and adhesion strength.

In this study the bioactivity of hydroxyapatite/poly(ε-caprolactone)– poly(ethylene glycol) bilayer coatings on Nitinol superelastic alloy was investigated. The surface of Nitinol alloy was activated by a thermo-chemical treatment and hydroxyapatite coating was electrodeposited on the alloy, followed by applying the polymer coating. The surface morphology of coatings was studied using FE-SEM and SEM. The data revealed that the hydroxyapatite coating is composed of one-dimensional nano sized flakes and the polymer coating is uniformly covered the sublayer. Also, High resolution TEM studies on the hydroxyapatite samples revealed that each flake contains nano-crystalline grains with a diameter of about 15 nm. The hydroxyapatite monolayer coating was rapidly covered by calcium phosphate crystals (Ca/P=1. 7) after immersion in simulated body fluid confirming the bioactivity of the nanostructured flakes. However, the flakes were weak against applied external forces because of their ultra-fine thickness. Scratch test was applied on hydroxyapatite/ polymer coating to evaluate delamination of the coating from substrate. It was shown that, the polymer coating has a great influence on toughening the hydroxyapatite coating. To assess the degradation effect of the polymer layer on hydroxyapatite coating, samples were immersed in phosphate-buffered saline at 37 ᵒ C. SEM studies on the samples revealed that the beneath layer of hydroxyapatite appears after 72 h without any visible change in morphology. It seems that, application of a biodegradable polymer film on the nanostructured hydroxyapatite coating is a good way to support the coating during implantation processes.

Stainless steel 316L (SS316L) is a good candidate for metal implants due to its excellent tensile strength and high corrosion resistance. However, its surface needs to be improved to enhance biocompatibility, bioactivity, and antimicrobial functions. Among bioceramics, hydroxyapatite (Ca10(PO4)6(OH)2) is widely used in medical applications due to its mineral composition, which is similar to the natural hard tissues of the body, and its biomimetic morphology. Chitosan possesses attractive biological properties such as good biodegradability, non-toxicity, biocompatibility, and cellular bioavailability. Graphene oxide demonstrates antibacterial activity against bacteria, fungi, and viruses, which can help limit cancer-causing infections in surgeries. Accordingly, an HA-based nanocomposite (HA-CS-GO) was deposited on SS316L sheets by electrophoretic deposition. Nanoparticle HA was synthesized via the sol-gel method. The coating was applied at 80V for 1 minute. To study the products and coating, various analyses were employed, including XRD, SEM, FTIR, electrochemical impedance spectroscopy (EIS), and polarization analysis. The results confirmed the successful synthesis of HA. The nanocomposite coating (thickness ~12.7 µm) was properly deposited on SS316L. The corrosion resistance improved with the coating; the current density decreased from 7.6 to 1.4 µA·cm⁻². The mechanism of corrosion was evaluated by EIS data. The corresponding equivalent circuit was proposed, and the dielectric capacitor and resistance values were estimated.

Electrochemical depositions of calcium phosphide layer on Ni-Ti alloy in concentrated simulated body flood (SBF×5) were carried out by cathodic electrodeposition. This layer was deposited on Ni-Ti alloy substrate under 10mA/cm2 current density for 2 hours at room temperature. Then, in order to investigate the bioactivity of the pre-calcified samples, they were put in SBF for 1 and 3 days at room temperature. The microstructure, chemical composition, and bioactivity of the coatings were evaluated using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) techniques. Results showed that the activation of the surface of the Ni-Ti alloy by electrochemical process can significantly enhance the biomimetic deposition during time. On the other hand, by increasing immersion time of pre-calcified samples in SBF from 1 to 3 days, the biomimetic coating uniformly covered the surface of the sample. The ratio of the Ca/P for the pre-calcified sample after immersion in SBF for 3 days was about 1.5 which is very close to the Ca/P ratio of stoichiometric hydroxyapatite.

Abstract. Hydroxyapatite (HA) scaffold is commonly used in the applications of bone tissue engineering due to its bioactivity and equivalent chemical composition to the inorganic constituents of human bone. The present study focused on the fabrication of porous 3D hydroxyapatite scaffold which was modified by polymer coating as a successful strategy to improve the mechanical properties. A 3D porous hydroxyapatite scaffolds were fabricated by gel-casting method by using freshly extracted egg yolk (EY) with (50 and 60)wt% of HA powder. To enhance the mechanical properties, composite PVA/ HA scaffolds were produced by using dip coating in Polyvinyl alcohol (PVA). Fourier transform infrared spectroscopy (FTIR) was used to recognize the functional group associated with the hydroxyapatite scaffolds before and after PVA coating. The physical (density and porosity) and mechanical (compressive strength and elastic modulus) properties were investigated before and after coating. SEM was used to inspect the surface morphology and pore modification of the scaffolds. Wettability was determined by using a water contact angle to analyze the scaffold hydrophobicity. Surface roughness was studied by atomic force microscopy (AFM). It was revealed that the scaffold porosity decreased with increase solid loading of HA powder in the gel and after PVA coating. The findings showed that PVA coating improved mechanical strength of scaffold to be double by covering the small pores and filling microcracks sited on the scaffold strut surfaces, inducing a crack bridging mechanism. The scaffolds’ strength was in the range of trabecular bone strength. This indicates  non-load bearing applications.