ABSTRACT
Load-bearing implants (e.g., endoprosthesis, dental implants, orthopedic fixation devices), which are in direct contact to bone, should ideally bond to their bony surrounding without the formation of a fibrous tissue interface. However, this is often observed for various bioinert materials (e.g., titanium alloys). Calcium phosphates, in particular hydroxyl apatite (HA, Ca10(PO4)6(OH)2), could fulfill this requirement due to its close resemblance to the inorganic part of bone tissue. However, due to its weak mechanical properties HA cannot be considered for load-bearing applications. For this reason, several physico-chemical [9], morphological [10], and bioorganic [11] modifications of metallic implant surfaces have been investigated to provide materials with osteoconductive and osteoinductive behavior, respectively. The commercially most widespread method to realize this is plasma spraying of HA. However, these coatings show some disadvantages compromising their long-term stability [12-14]. The problems are mainly related to delamination, an insufficient adhesion of the coating and in controlling the composition of calcium phosphates at process temperatures exceeding 10,000°C. Moreover, the method cannot be used to coat porous materials due to its line-of-sight characteristic.It is generally accepted that the in vitro apatite formation from simulated body fluid (SBF), which resembles the inorganic part of human blood plasma, represents an indicator for the in vivo bioactivity of a material [15]. Beyond that, the utilization of SBF allows to coat materials surfaces with a biomimetic apatite whose structure and composition is close to biological apatite. 5.2 Biomimetic Apatite
Definition: Biomimetic apatite, precipitated under physiological conditions from a simulated body fluid (SBF), mimics the chemical, physical and structural properties of biological bone apatite. After an implantation into a bony defect it adopts the metabolic function of bone and allows the substantial integration of the implant.The bone tissue of vertebrates represents a composite material grown by a biomineralization process. It consists of 65 mass-% carbonated hydroxy apatite (CHA), 25 mass-% proteins (mainly collagen I) and water [16]. The main function of bone is related to the structural and mechanical support of the skeletal apparatus.
