Biomimetic Deposition of Hydroxyapatite on Titanium Implant Materials

Abstract: The clinical success of a bone-anchored implant is controlled by many factors such as implant shape, chemical composition, mechanical and surface properties. The surface properties (e.g. charge, wettability and roughness) are considered to be important parameters for the biological acceptance of the biomaterial, whereas the bulk properties control the biomechanical behaviour. For implants designed to be used in load-bearing applications in the skeletal system, the biomaterial should preferably integrate into bone tissue for a long lasting function. Lack of integration between the implant and bone increases the risk of micromotions, infections, soft tissue encapsulation, which all reduces the survival rate of the implant and makes revision surgery necessary. Coatings and surface modifications can be used to tailor properties of implant surfaces, and further improve the potential bone bonding and bone in-growth, compared to unmodified surfaces. A biomimetic method, developed by Kokubo, can be used to prepare a hydroxyapatite coating on to titanium substrates. The method is based on a solution based process where the compositions of the soaking medium and thus the formed coatings can be controlled. In this thesis, titanium (oxide) surfaces have been tailored via deposition of ion substituted hydroxyapatite coatings. Biologically relevant ions like strontium, silicon and fluoride were incorporated into apatite coatings. The substrates included well-defined rutile single crystals, as well as poly-crystalline titanium oxide surfaces and experimental Ti implants. The results showed that incorporation of substitute ions alters the morphology, crystallinity, composition and dissolution rates of apatite coatings. The in vivo effects of the ion substituted apatite coatings were also studied. The results showed that the ion substituted apatite coatings have good biocompatibility and can promote early bone formation.