Bio‐corrosion of stainless steel by osteoclasts—in vitro evidence

Abstract

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-1b, IL-6, and TNF-a, 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. Keywords: osteoclast; bio-corrosion; stainless steel; osteolysis; TNF-a Over the last decades, significant developments have been taking place to provide suitable metal alloys for implants with optimal mechanical characteristics and good biocompatibility with minimal adverse host tissue reactions. 1 However, their permanent tendency to corrode when exposed to a physiological environment remains a serious concern. 2-4 Elevated concentrations of metal ions have been measured in clinically retrieved peri-prosthetic tissues, distal organs, and body fluids in total hip arthroplasty patients. [5][6][7] The biology behind corrosion inside the human body and the distribution of the metal ions throughout the organism is not fully understood. It has been suggested that extracellular body fluids have corrosive proprieties and contain metal binding proteins. 2,3 Furthermore, it has been debated whether osteoclasts (OC) are able to corrode pure metal when entering into contact with metal surfaces. However, direct evidence of metal corrosion by OC has been missing to date.Osteoclasts are highly specialized multinucleated cells, which are capable of bone resorption. They are formed by the fusion of marrow-derived mononuclear precursors, which circulate in the peripheral blood. Osteoclastic differentiation from hematopoietic and circulating monocytes occurs in the presence of macrophage-colony stimulating factor (M-CSF) and the receptor activator of NF-kB ligand (RANK-L) which are expressed on osteoblastic cells. 8 Mature OC display distinct morpholog...

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