Comparative in vitro analysis of vacuum plasma-sprayed titanium implants--evaluation of OPG, Osteokalzin and AP expression

INTRODUCTION: The purpose of this study was to evaluate the influence of different surface topographies on the expression of bone cell-associated proteins, such as osteoprotegerin (OPG), osteocalcin and alkaline phosphatase (AP), and the production of the extracellular matrix (ECM) in vitro. Another aspect was the question as to whether a hydroxyapatite (HA) coating offers additional advantages. Vacuum plasma-sprayed (VPS) pure titanium was used to generate different surface topographies. MATERIALS AND METHODS: The in vitro response of human bone marrow cells to VPS implants (porosity ranging from 25 to 50%, pore size ranging from 50 to 200 microm and roughness ranging from 0.191 to 0.547 mm) and cancellous structured titanium (cs-Ti) as a reference material (55% porosity, pore size of 500 microm, roughness 0.836 mm) were compared. The expression of bone cell-associated proteins, such as OPG, osteocalcin and alkaline phosphatase (AP), was evaluated. Scanning electron microscopy (SEM) was used to judge the production of ECM. RESULTS: All implant materials induced the release of OPG, osteocalcin and AP. Significant differences were evident between the cs-Ti and the different VPS-Ti surface structures. There was no difference in the response between the VPS-Ti surfaces. SEM showed a dense and increased production of ECM on the VPS-Ti surfaces. An additional HA coating caused a faster production of ECM and higher levels of OPG. CONCLUSIONS: The in vitro data presented here demonstrate the superiority of VPS-Ti surfaces over cs-Ti, which is already in clinical use. Differences between the VPS-Ti surfaces were not evident. Presumably, VPS-Ti surfaces offer good prerequisites for a successful integration of the implant in the surrounding tissue. An additional HA coating could influence these events positively.