The extent of metal release from implant materials that are irradiated during radiotherapy may be influenced by irradiation-formed radicals. The influence of gamma irradiation, with a total dose of relevance for radiotherapy (e.g., for cancer treatments) on the extent of metal release from biomedical stainless steel AISI 316L and a cobalt-chromium alloy (CoCrMo) was investigated in physiological relevant solutions (phosphate buffered saline with and without 10 g/L bovine serum albumin) at pH 7.3. Directly after irradiation, the released amounts of metals were significantly higher for irradiated CoCrMo as compared to nonirradiated CoCrMo, resulting in an increased surface passivation (enhanced passive conditions) that hindered further release. A similar effect was observed for 316L showing lower nickel release after 1 h of initially irradiated samples as compared to nonirradiated samples. However, the effect of irradiation (total dose of 16.5 Gy) on metal release and surface oxide composition and thickness was generally small. Most metals were released initially (within seconds) upon immersion from CoCrMo but not from 316L. Albumin induced an increased amount of released metals from AISI 316L but not from CoCrMo. Albumin was not found to aggregate to any greater extent either upon gamma irradiation or in the presence of trace metal ions, as determined using different light scattering techniques. Further studies should elucidate the effect of repeated friction and fractionated low irradiation doses on the short- and long term metal release process of biomedical materials.

Biomedical materials made of cobalt-chromium-molybdenum (CoCrMo) alloys are commonly used in artificial prostheses and dental implants that are exposed to friction and load. The release of Co, Cr, and Mo from these surfaces is governed by physical, chemical, and electrochemical processes. The extent of measured metal release from biomedical CoCrMo alloys into mixed protein solutions may be influenced by protein aggregation and metal precipitation effects. Metal release from, and the surface composition of, a CoCrMo alloy was investigated in physiological relevant solutions (phosphate buffered saline, PBS, with varying concentrations of fibrinogen from bovine plasma and/or bovine serum albumin) at pH 7.3 in static and sliding conditions for time periods between 1 and 24 hours. Cr was strongly enriched in the surface oxide of CoCrMo in all solutions, which corresponded to metal release dominated by Co. PBS and the proteins could induce significant precipitation of metals and protein aggregates, which resulted in strongly underestimated released amounts of Co and Cr, but not Mo, especially under sliding conditions. Protein aggregates were found to precipitate on the surface of CoCrMo under static conditions. The friction coefficient was greater in PBS containing physiologically relevant concentrations of fibrinogen as compared to PBS alone.

Corrosion and metal release mechanisms of the biomedical stainless steel grade Type 316L are at human-relevant biological conditions not fully understood. This study focuses on its corrosion properties and release of iron (Fe), chromium (Cr), manganese (Mn), and nickel (Ni) into simulated physiological solutions at pH 7.4 in the presence of proteins. Parallel studies were performed on stainless steel Type 303 containing a substantial amount of MnS inclusions. Metal release studies were performed in phosphate buffered saline (PBS) for 4 h and 24 h at 37 degrees C with or without different concentrations of bovine serum albumin (BSA), fibrinogen from bovine plasma (Fbn), or mixtures of the same. Studies were in addition performed after 1, 4, 6, and 24 h in solutions that were partially replenished after 5 h in order to investigate whether any Vroman effect (exchange of adsorbed proteins by proteins of higher binding affinity) could influence the extent of released metals in solution. This was performed at physiological concentrations of BSA (40 g/L) and Fbn (2.67 g/L) in PBS, and for reference solutions of PBS, PBS with 40 g/L BSA, and PBS with 2.67 g/L Fbn. Changes in open-circuit potential and linear polarization resistance were investigated for the same conditions. After exposure, the exposed surfaces were rinsed and investigated ex situ by means of x-ray photoelectron spectroscopy and infrared reflection absorption spectroscopy. Metal-protein complexation-induced metal release mechanisms were found to be most pronounced for Type 316L and the release of Fe, Cr, and Ni. Fibrinogen adsorbed differently onto Type 303 (thicker conformation of adsorbed proteins) as compared with Type 316L and occasionally induced corrosion events for Type 303. Mn was mostly released from inclusions present in the Type 303 alloy, most probably via non-electrochemical mechanisms. A Vroman effect was observed for both grades. A significant extent of precipitation of metal-rich protein aggregates influenced the metal release measurements in solution and resulted in an underestimation of the total amount of released metals from the stainless steel grades.

Stainless steel is an important transport and processing contact material for bovine milk and dairy products. Release (migration) of metals, ions, complexes or wear debris/particles, and metal-induced protein aggregation in such environments are hence important to consider both from a corrosion and food safety perspective. This study aims on investigating the release of iron (Fe), chromium (Cr), and nickel (Ni) from AISI 316L stainless steel in contact with whey protein solutions relevant for protein drinks, and on how the whey proteins are influenced by stirring with a magnetic stir bar and metal release. Mechanistic insight is gained by parallel investigations of metal release from two reference non-protein containing solutions, a metal-complexing (citrate-containing) simulated milk solution (SMS) and a low complexing phosphate buffered saline solution (PBS). All immersion exposures were conducted at pH 6.8 for 0.5, 4, 24 and 48 hat room temperature at static and stirring conditions. All solutions and samples were investigated using different chemical, spectroscopic, microscopic, and electrochemical methods. Significantly higher amounts of Fe, Cr, and Ni were released into the whey protein solution (80 g/L) as compared to SMS and PBS. Strong enrichment of Cr in the surface oxide and reduction of the surface oxide thickness were associated with a higher amount of Ni release in the metal-complexing solutions (SMS and whey protein) compared with PBS. Stirring conditions resulted in higher amounts of metal release, enrichment of Cr in the surface oxide, and clear signs of wear of the 316L surface in all solutions compared to static conditions. The wear mechanism in the whey protein solution was different as compared to corresponding processes in SMS and PBS, involving an etching-like process and larger-sized wear debris. Electrochemical measurements at static conditions confirmed observed differences between the solutions, with the lowest corrosion resistance observed for coupons exposed in the whey protein solution, followed by SMS and PBS. Released metals in solution from the 316L coupons in contact with the whey protein solution resulted in enhanced rates of protein aggregation and precipitation of protein aggregates from solution. Further studies should be made to investigate other relevant test conditions and assess toxicological risks.