Biomedical application of hydroxyapatite bioceramics

Biomaterials have been used to replace or support the human organs or tissues in many years. They are classified into four groups as metals, ceramics, polymers and composites. Biocompatibility is considered as the most important feature in biomaterials, allowing the surrounding tissue to differentiate normally and preventing undesired reactions (such as infection and blood clot). Titanium and its alloys are metallic biomaterials which bond strongly with bone and are highly compatible with the surrounding tissue. Hydroxyapatite (HA:Caio(P04)6(OH)2) is a calcium phosphate based bioceramic and mostly used in clinics for making artificial bone due to its biocompatibility (to be used in various prosthesis), treating cracks and fractures in the bone and coating of metallic biomaterials. Different methods such as plasma spray, high velocity oxy fuel spray, lazer ablation, sol-gel, electrophoresis, electrochemical etc. are used to coat implants with hydroxyapatite. However, there have been some problems in the application. The major problem is the gradual weakening of the bond between coating and metal surface. This happens due to the low bonding strength of the coating material. This situation sometimes necessitates a second operation on patients with implant, which is not desired because of health and financial concerns. Strengthening and stabilizing the bond between metal surface and HA coating could prevent this from occurring. In addition to the one above, there are some inherent problems associated with these methods:. Complex preparation procedures,. Application of high temperatures which cause structural damages either on host (Tİ6AI4V) or coating (HA) material,. Getting unwanted phases in coatings,. Employing complex equipment,. High cost,. Bonding strength that depends upon coating thickness. Because of the difficulties listed above, in-situ coating method is chosen. In this method, HA coating is realized in a simple biocompatible environment (under the conditions of human body temperature of 37°C and pH=7.4) with chemical in-situ sedimentation method, where no high temperatures is applied. In this study, Synthetic/Simulated Body Fluids (SBF) were prepared in various concentrations. Then, common implant material Tİ6AI4V was submersed to coat with hydroxyapatite and the mechanical properties of the coatings were investigated. Chemical analysis of the coating material was performed by using XRD and SEM. Thicknesses of the coatings were measured with an optical microscope. Micro hardness values of coated surface interface and substrates were obtained. Surface roughness was determined. Bonding and shear strengths of hydroxyapatite layer connected to the Tİ6AI4V implant were determined according to the standards ASTM F1501-95 and ASTM F 1658-95, respectively. Scratch test equipment was used on hydroxyapatite coated test sample to measure the bonding resistance of coating to surface. Uncoated samples, testing equipment and HA coated samples were pictured by a digital camera.Key words: Biomaterials, Hydroxyapatite, Biocompatible, Synthetic Body Fluids (SBF), Tİ6AI4V, Coating, Mechanical Properties.