Bioaccessibility and reactivity of alloy powders used in powder bed fusion additive manufacturing

Exposure to metal particles via the inhalation route unavoidably takes place at occupational settings during additive manufacturing of metals and alloys. This calls for investigations on possible adverse health effects. This study focuses on virgin and reused powders of three iron- and nickel-based alloy powders (316L, IN718, 18Ni300) widely used in additive manufacturing, and dust powder of 18Ni300 generated during laser melting. Investigations were performed from a physico-chemical and toxicological perspective assessing their bioaccessibility in artificial lysosomal fluid (ALF, simulating lung exposure to respirable particles), corrosion behavior, surface morphology and composition, microstructure, hydrodynamic size distribution in ALF, and in-vitro toxicity towards cultured human lung cells. Less than 1% of the powder mass was dissolved from the passive alloys (316L, IN718) under simulated physiological conditions (pH4.5, 37 °C, 24 h), whereas the 18Ni300 iron-nickel alloy showed an active behavior and dissolved completely. Reused powders of 18Ni300 and IN718 showed no, or only minor, differences in surface oxide composition, metal release pattern, and corrosion behavior compared with virgin powders. After reuse, the 316L powder showed an enrichment of manganese within the outermost surface, an increased corrosion current, increased amounts of released iron and an increased fraction of particles with ferritic microstructure, which increased the extent of particle aggregation. All powders showed low, or negligible, cytotoxic potency and reactive oxygen species formation. Powder bed fusion using laser melting can hence affect the chemical, physical, and surface properties of non-fused powders, which, if reused, could influence the properties of the printed part. Keywords: Corrosion; Metal and alloys; Microstructure; Powder processing; Rapid prototypin

Location of cobalt impurities in the surface oxide of stainless steel 316L and metal release in synthetic biological fluids

Since 2021, cobalt (Co) is in Europe classified as carcinogen in quantities exceeding 0.1 wt-%. This affects nickel-rich stainless steels, which contain about 0.2 wt-% Co impurities. Previous findings show the bioaccessibility of Co in stainless steel to be primarily determined by the corrosion resistance. It has been unclear whether Co is distributed heterogeneously in the alloy and the outermost surface and whether a specific location would pose a risk for Co release under specific exposure conditions. This study aimed at locating Co in stainless steel 316L (0.2 wt-% Co) surfaces prior to and after exposure to different synthetic body fluids for 24 h at 37 °C. Time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma mass spectrometry (ICPMS) investigated the location of Co in the surface oxide and extent of release along with other metals (iron, chromium, nickel, and manganese) into synthetic biological fluids (gastric fluid, pH 1.5; lysosomal fluid, pH 4.5; phosphate buffered saline-PBS, pH 7.4). Co was homogeneously distributed along with metallic nickel beneath the surface oxide and co-released with other metals upon surface reformation and passivation. Exposure in PBS resulted in the incorporation of both Co and phosphate in the oxide

Surface–rain interactions: Differences in copper runoff for copper sheet of different inclination, orientation, and atmospheric exposure conditions

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Metal Release from a Biomedical CoCrMo Alloy in Mixed Protein Solutions Under Static and Sliding Conditions: Effects of Protein Aggregation and Metal Precipitation

Biomedical materials made of cobalt-chromium-molybdenum (CoCrMo) alloys are commonly used in artificial prostheses and dental implants, which are exposed to friction and load. The release of Co, Cr, and Mo from these surfaces is governed by physical and chemical 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 h. 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

Metal bioaccessibility in synthetic bodyfluids–A way to considerpositive and negative alloying effects in hazard assessments

Hazard classification of metal alloys is today generally based on their bulk content, an approach that seldom reflects the extent of metal release for a given environment. Such information can instead be achieved via bioelution testing under simulated physiological conditions. The use of bioelution data instead of bulk contents would hence refine the current hazard classification of alloys and enable grouping. Bioelution data have been generated for nickel (Ni) and cobalt (Co) released from several stainless steel grades, one low-alloyed steel, and Ni and Co metals in synthetic sweat, saliva and gastric fluid, for exposure periods from 2 to 168 h. All stainless steel grades with bulk contents of 0.11–10 wt% Ni and 0.019–0.24 wt% Co released lower amounts of Ni (up to 400-fold) and Co (up to 300-fold) than did the low-alloyed steel (bulk content: 0.034% Ni, 0.015% Co). They further showed a relative bioaccessibility of Ni and Co considerably less than 1, while the opposite was the case for the low-alloyed steel. Surface oxide- and electrochemical corrosion investigations explained these findings in terms of the high passivity of the stainless steels related to the Cr(III)-rich surface oxide that readily adapted to the fluid acidity and chemistry

A bio-tribocorrosion comparison between additively manufactured and forged Ti6Al4V parts

Ti6Al4V has been used widely as a biomedical alloy and is increasingly manufactured by additive manufacturing due to customized shapes. As implant material, it is frequently exposed to both friction and corrosive environments. This study investigates the effect of the fabrication process (laser powder bed fusion and forging) on the tribocorrosion behavior of Ti6Al4V in various environments including diluted hydrochloric acid to simulate the acidic environment in a crevice (HCl), phosphate-buffered saline (pH 7.3) with 10 g/L bovine serum albumin (PBS+BSA), and PBS+BSA with 30 mM H2O2. While the presence of BSA hindered the repassivation (reforming of the protective passive surface oxide), the presence of H2O2 accelerated it. HCl resulted in a localized tribocorrosion process. The highest plastic deformation rate was found in the PBS+BSA solution followed by HCl and PBS+BSA+H2O2. In addition, AM parts presented a higher microhardness and smaller grain sizes compared to forged materials. There was no influence of the manufacturing process on the coefficient of friction (COF) in HCl and PBS+BSA solutions, however, a significantly higher COF was found for forged samples in PBS+BSA+H2O2 than AM samples. Tribocorrosion was more extensive for forged than AM Ti6Al4V in all solutions

Patch testing with aluminium Finn Chambers could give false-positive reactions in patients with contact allergy to aluminium

Background Earlier laboratory studies have shown that sodium tetrachloropalladate, Myroxylon pereirae, caine mix II, and palladium chloride trigger the release of aluminium (Al) from Finn Chambers (FC). Objectives To investigate whether aluminium realease from FC could influence the diagnostic outcome of patch testing with FC. Method A retrospective analysis of patch test results from 2010 to 2019 was performed. A two-sided Fisher\u27s exact test was used to calculate any overrepresentation of contact allergy to Al among patients with positive reactions to sodium tetrachloropalladate, Myroxylon pereirae, caine mix II, and palladium chloride. Results A total of 5446 patients had been tested with FC during the study period. There was a significant overrepresentation of contact allergy to Al among patients with positive reactions to sodium tetrachloropalladate, Myroxylon pereirae, caine mix II, and palladium chloride. Patients with a strong Al allergy had significantly higher amounts of concomitant reactions to sodium tetrachloropalladate, Myroxylon pereirae, caine mix II, and palladium chloride compared to patients with weak Al allergy. These results were not seen for patients tested with Finn Chambers AQUA. Conclusion In patients with contact allergy to Al, patch testing with Finn chambers could give false-positive reactions to sodium tetrachloropalladate, Myroxylon pereirae, caine mix II, and palladium chloride

Corrosion failure of titanium tubes of a heat exchanger for the heating of dissolving lye

Corrosion of titanium heat exchangers in the processing of sylvinite ore is undesirable from economic, safety, and process sustainability perspectives. Triggered by an industrial case, we investigated the extent of corrosion during simulated contact with sylvinite ore (in dissolving lye) in relevant conditions. Detailed characterization of the failed tubes and corrosion products was carried out to understand the mechanism of failure. Corrosion of titanium (Grade 2) tubes was investigated at room temperature, 60, 70, 80, and 90 °C. After electrochemical and surface morphology analysis, we found that pitting corrosion of the titanium tube material sharply increased above 80 °C in the simulated sylvinite ore environment (pH 7.1). The failure analysis revealed extensive degradation by transgranular cracking through both the oxide and metal matrix, likely caused by a combination of the high temperature, pressure, possible vibrations, the build-up of lye deposits causing crevices, the high salt content of the lye, and possibly metal (copper, iron, zinc) impurities/deposits in or on the titanium metal, which can catalyze hydrogen evolution

Skin permeation studies of chromium species - Evaluation of a reconstructed human epidermis model.

A reconstructed human epidermis (RHE) model, the EpiDerm, was investigated and compared to human skin ex vivo regarding tissue penetration and distribution of two chromium species, relevant in both occupational and general exposure in the population. Imaging mass spectrometry was used in analysis of the sectioned tissue. The RHE model gave similar results compared to human skin ex vivo for skin penetration of C

Effect of nanoparticle size on the near-surface pH-distribution in aqueous and carbonate buffered solutions

An analytical solution for the effect of particle size on the current density and near-surface ion distribution around spherical nanoparticles is presented in this work. With the long-term aim to support predictions on corrosion reactions in the human body, the spherical diffusion equation was solved for a set of differential equations and algebraic relations for pure unbuffered and carbonate buffered solutions. It was shown that current densities increase significantly with a decrease in particle size, suggesting this will lead to an increased dissolution rate. Near-surface ion distributions show the formation of a steep pH-gradient near the nanoparticle surface (\u3c6 μm) which is further enhanced in the presence of a carbonate buffer (\u3c2 μm). Results suggest that nanoparticles in pure electrolytes not only dissolve faster than bigger particles but that local pH-gradients may influence interactions with the biological environment, which should be considered in future studies