T. Habijan, M. Köller, Universitätsklinik Bergmannsheil, Bochum, Germany; T. Simon, T. Glogowski, Ruhr-University Bochum, Bochum, Germany
Corrosion of orthopedic implants is a relevant clinical problem. It was postulated that osteoclasts were responsible for corrosion and failure of explanted nickel titanium stents. Nickel titanium shape memory alloys (NiTi-SMA) are of increasing biomedical interest due to an unusual pseudo-elasticity and the shape memory effect. There are still concerns because of the potential release of nickel ions from NiTi-SMA (50%at Ni/ 50%at Ti). The surface of NiTi-SMA is well passivated because titanium is more readily oxidized than Ni. Therefore, NiTi-SMA devices exhibit a Ti-based oxide layer which acts as an effective barrier to nickel ion release. The integrity of the outermost surface layer is of crucial importance for the biocompatibility of NiTi-SMA. However, the high nickel content of NiTi-SMA may result in adverse tissue reactions under corroding conditions. When the passivating surface of NiTi-SMA is damaged the nickel ion release increases dramatically. Bone-resorbing osteoclasts secrete hydrochloric acid, locally reducing the pH. Osteoclasts will adhere on the implant surface during bone remodeling. In consequence, local destruction of the passivating TiO2 layer seems possible. Osteoclasts were differentiated from PBMCs using Dexamethasone, M-CSF, TGF-ß and RANKL. Resorbing osteoclasts were cultured onto calcium phosphate coated glass slides (positive control) and NiTi-SMA specimens for 8 weeks. The interface between osteoclasts and the substrate was visualized using focused ion beam. The interface was analyzed by SEM. Nickel ion release was determined using atomic absorption spectroscopy. There was no evidence for a corrosion of the NiTi-SMA specimens. This method enables studies on cell-biomaterial reactions directly at the interface site.
Summary: The ability of osteoclasts to corrode Nickel-titanium shape memory alloys (NiTi-SMA) was investigated. Bone resorbing osteoclasts secrete hydrochloric acid, which reduces the pH locally. Thus, they are considered to be cell prototypes for the induction of implant corrosion in the human body. Therefore, resorbing osteoclasts were cultured on calcium phosphate coated glass slides (positive control) and NiTi-SMA specimens for 8 weeks. The interface between osteoclasts and the substrate was visualized using focused ion beam. The interface was analyzed by scanning electron microscopy. Nickel ion release was determined using atomic absorption spectroscopy. There was no evidence for corrosion of the NiTi-SMA specimens induced by osteoclasts.
