Microstructure analysis of hydroxyapatite coating on stainless steel 316L using investment casting technique for implant application

Osteoporosis and traffic accidents are a significant factor that causes a bone fracture in Indonesia. One solution for the bones fracture treatment is by using fixation implant that has similar characteristics with the human bones. Stainless Steel (SS) 316L is one of biomaterial that has been used as an implant material due to its corrosion resistance, excellent biocompatibility, and excellent mechanical properties. However, the bioactivity properties of the material are needed to improve by coating it with hydroxyapatite (HA). In this research, HA was coated to the surface of 316L SS by using investment casting technique. A slurry of HA was poured into the casting cavity surface prior to the metal casting process and then followed by sintering at temperatures of 850°C, 900°C, and 950°C. Characterization of HA coating layer on specimen surface was conducted by Optical Microscope, Scanning Electron Microscope (SEM), and Energy Dispersive X-Ray (EDX). The hardness of the samples was measured by Vickers Hardness Tester. The result of the experiment shows that the investment casting is successfully to coat the HA on the SS 316L surface. Pouring method produces HA layer with thickness (spongy and porous surface) in the range of 60 μm - 110 μm. The increasing of sintering temperature increases the hardness number of the surfaces, and affect the purity of HA, but it is not related to coating thickness. The optimum sintering temperature is obtained at 900°C which produces the best calcium and phosphate ratio. The investment casting method is found as a simple and non-expensive technique that can be used to coat HA powder to SS 316L that produces good properties and optimum crystallinity of HA that suitable for orthopaedic implant application

Microstructure Analysis of Hydroxyapatite Coating on Stainless Steel 316L Using Investment Casting Technique for Implant Application

Osteoporosis and traffic accident are major factor that causes bone fracture in Indonesia. One of solution for the bones fracture treatment is by using fixation implant that has similar characteristics with the human bones. Stainless Steel (SS) 316L is one of biomaterial that has been used as an implant material due to its corrosion resistance, good biocompatibility, and excellent mechanical properties. However, the bioactivity properties of the material is needed to improve by coating it with hydroxyapatite (HA). In this research, HA was coated to the surface of 316L SS by using investment casting technique. A slurry of HA was poured into casting cavity surface prior to metal casting process, and then followed by sintering at temperatures of 850oC, 900oC, and 950oC. Characterization of HA coating layer on specimen surface was conducted by Optical Microscope, Scanning Electron Microscope (SEM), and Energy Dispersive X-Ray (EDX). Hardness of  the samples was measured by Vickers Hardness Tester. Result of the experiment shows that the invvestment casting is successfully to coat the HA on the SS 316L surface. Pouring method produces HA layer with thickness (spongy and porous surface) in the range of 60 µm – 110 µm. The increasing of sintering temperature increases the hardness number of the surfaces, and affect the purity of HA, but it is not related to coating thickness. Optimum sintering temperature is obtained at 900oC which produces the best calcium and phosphate ratio. The investment casting method is found as a simple and non-expensive technique that can be used to coat HA powder to SS 316L that produces good properties and optimum crystallinity of HA that suitable for orthopedic implant application

Optimisation of electrophoretic deposition parameters in coating of metallic substrate by hydroxyapatite using response surface methodology

Hydroxyapatite bioactive coating was deposited on treated medical grade stainless steel 316L by electrophoretic deposition. Two independent variables including deposition voltage and time span were evaluated in order to investigate their effect on substrates’ corrosion potential and coating mass. After deposition, coated substrates were post-treated in a vacuum furnace at 800 °C. The experimental plan was based on a central composite design to create a precision of the mathematical models. The precision of mathematical model and relative parameters were evaluated by variance analysis. Optimum parameters value, considered as simultaneous minimum ion release and maximum coating mass, were predicted at the deposition voltage of 25.93 V and deposition time span of 159 s. The validity of the model generated by response surface methodology was evaluated by comparing the predicted and experimental results. In addition, close agreement between experimental and predicted results was observed

Effect of calcium content on the microstructure, hardness and in-vitro corrosion behavior of biodegradable Mg-Ca binary alloy

Effect of calcium addition on microstructure, hardness value and corrosion behavior of five different Mg-xCa binary alloys (x = 0.7, 1, 2, 3, 4 wt. (%)) was investigated. Notable refinement in microstructure of the alloy occurred with increasing calcium content. In addition, more uniform distribution of Mg2Ca phase was observed in a-Mg matrix resulted in an increase in hardness value. The in-vitro corrosion examination using Kokubo simulated body fluid showed that the addition of calcium shifted the fluid pH value to a higher level similar to those found in pure commercial Mg. The high pH value amplified the formation and growth of bone-like apatite. Higher percentage of Ca resulted in needle-shaped growth of the apatite. Electrochemical measurements in the same solution revealed that increasing Ca content led to higher corrosion rates due to the formation of more cathodic Mg2Ca precipitate in the microstructure. The results therefore suggested that Mg-0.7Ca with the minimum amount of Mg2Ca is a good candidate for bio-implant applications