Despite the high success rates of hip replacements, implant-wear mediated periprosthetic osteolysis remains the most prominent cause of long-term implant failure. Other adverse tissue reactions including hypersensitivity reactions and pseudotumors have also recently been reported as a cause for short-term implant failures. The objectives of this thesis were: 1.) To analyze the effects of Co2+ and Cr3+ released from CoCrMo alloys used in hip implants on macrophage chemokine release; 2.) To determine if Co2+, Cr3+, and the chemokines in cultures of macrophages exposed to Co2+ and Cr3+ can induce migration of T and B lymphocytes; and 3) To analyze the potential modulation of macrophage response to Cr3+ using simvastatin as an anti-inflammatory agent. Results showed that the release of TNF–α and CC chemokines were ion-specific and dose-dependent. Results also suggested that Co2+ and Cr3+ may be capable of directly stimulating the migration of T cells, but not that of B cells, suggesting the potential of these ions to create a micro-environment that would favour a T cell-mediated response in vivo. Results also showed that simvastatin was capable of decreasing chemokine release in macrophages exposed to Cr3+, suggesting its potential to modulate the Cr3+-induced inflammatory response. Together, these studies improve the understanding of the role metal ions play in ion-mediated adverse tissue reactions and potential therapies that may modulate the immune response to metal ions.

Advanced alloys often present precipitated carbides and nitrides in their microstructure following exposure to elevated temperatures. These secondary phases are usually undesirable, because potentially deleterious for the corrosion and mechanical performances of the material. Carbides and nitrides are enriched in key alloying elements that are subtracted from their surrounding matrix areas, creating alloying element depleted zones, which might become initial sites for corrosion initiation. In this study, the influence of micro- and nano-sized precipitated carbides and nitrides on the corrosion initiation of biomedical CoCrMo alloys and duplex stainless steels has been investigated at microscopic scale, by using a combination of local probing techniques. The microstructures of the alloys were first characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and magnetic force microscopy (MFM). The Volta potential mapping of carbides and nitrides revealed their higher nobility compared to the matrix, and particularly compared to their surrounding areas, suggesting the occurrence of some alloying element depletion in the latter locations, which may lead to a higher susceptibility for corrosion initiation. In-situ electrochemical AFM studies performed at room temperature showed passive behavior for large potential ranges for both alloy families, despite the presence of the precipitated carbides or nitrides. At high anodic applied potential, at which transpassive dissolution occurs, preferential dissolution started from the areas adjacent to the precipitated carbides and nitrides, in accordance with the Volta potential results. Thus, the presence of carbides and nitrides doesn’t largely affect the corrosion resistance of the tested advanced alloys, which maintain passive behavior when exposed to highly concentrated chloride solutions at room temperature with no applied potential. The effect of nitrides on the corrosion initiation of duplex stainless steels was investigated also at temperatures above the critical pitting temperature (CPT). Depending on the type, distribution and size range of the precipitated nitrides different corrosion behaviors were observed. Intragranular (quenched-in) nano-sized nitrides (ca. 50-100 nm) finely dispersed in the ferrite grains have a minor influence on the corrosion resistance of the material at temperatures above the CPT, while larger intergranular (isothermal) nitrides (ca. 80-250 nm) precipitated along the phase boundaries cause a detrimental reduction of the corrosion resistance of the material, in particular of the austenite phase / <p>QC 20130927</p>