Bio-corrosion of stainless steel by osteoclasts--in vitro evidence

Most metals in contact with biological systems undergo corrosion by an electrochemical process. This study investigated whether human osteoclasts (OC) are able to grow on stainless steel (SS) and directly corrode the metal alloy leading to the formation of corresponding metal ions, which may cause inflammatory reactions and activate the immune system. Scanning electron microscopy analysis demonstrated long-term viable OC cultures and evident resorption features on the surface of SS discs on which OC were cultured for 21 days. The findings were confirmed by atomic emission spectrometry investigations showing significantly increased levels of chromium, nickel, and manganese in the supernatant of OC cultures. Furthermore, significant levels of pro-inflammatory cytokines IL-1beta, IL-6, and TNF-alpha, which are considered to be major mediators of osteolysis, were revealed in the same cultures by cytometric bead array analysis. Within the present study, it was shown that human osteoclast precursors are able to grow and differentiate towards mature OC on SS. The mature cells are able to directly corrode the metal surface and release corresponding metal ions, which induce the secretion of pro-inflammatory cytokines that are known to enhance osteoclast differentiation, activation, and survival. Enhanced corrosion and the subsequently released metal ions may therefore result in enhanced osteolytic lesions in the peri-prosthetic bone, contributing to the aseptic loosening of the implant.