gms | German Medical Science

Implant-associated infection is a feared complication after joint replacement. Staphylococcus epidermidis and Staphylococcus aureus are the most frequent microorganisms causing such infections. Their growth on the implant surface renders them far more resistant to the activity of antimicrobial agents. The problems associated with infected medical devices in orthopaedic surgery initiated the necessity for further research and the development of alternative treatment and prevention strategies, such as metal-ion based surface thin film with antimicrobial and biofilm-preventing properties [1]. Copper (Cu) represents a promising metal ion to exert antimicrobial effects [2], [3], [4] and with an impact on osteoblast differentiation [5]. In this in vitro study we investigated the cytotoxic and antimicrobial effects of copper based coatings on titanium alloy surfaces with human osteoblast like cells MG-63 and the biofilm forming species S. epidermidis. The surface of the cylindrical TiAl6V4 test samples was modified in a first step by titanium plasma spray (TPS, served as control). A titanium-copper-nitride (TiCuN) layer with an average Cu load of 1µg/mm² was then deposited by plasma vacuum. Two different experimental arrangements were used: (i) the MG-63 cells were directly cultivated on the TiCuN surfaces and (ii) the TiCuN samples were first rinsed in cell culture medium DMEM for 24 h and after this the cells were seeded onto the surfaces. Thereby the in vivo situation is simulated [6]. In a parallel set up S. epidermidis were cultivated with the test samples to examine the antimicrobial potential of the TiCuN coating. Planktonic S. epidermidis was centrifuged in the supernatants and quantified by colony forming units (CFU) counting. Quantification of S. epidermidis in the biofilm on the discs was performed by ultrasonic treatment and CFU counting.The concentration of Cu ions released from TiCuN films was measured by atomic absorption spectrometry.

Our results showed an initial antimicrobial effect of TiCuN films against S. epidermidis bacteria followed by growth of osteoblastic cells on the surface. The high amount of initially released Cu ions caused a non-desired cytotoxic effect on osteoblasts. The cytotoxicity of the TiCuN surfaces was significantly reduced by rinsing the materials in cell culture medium for 24 h to simulate in vivo conditions. In conclusion, copper is an interesting agent to control both bacteria and osteoblasts in the field of implant technology.