While magnesium implants are already commercially available, exploring new manufacturing methods and alloy designs is essential to enhance their properties and clinical safety. This study assesses the in vitro and in vivo degradation of disc-shaped implants of the Mg-1Ca-0.5Zn-0.1Y-0.03Mn (at.%) alloy prepared by the rapidly solidified ribbon consolidation (RSRC) and hot extrusion of cast material (ingot metallurgy, IM). Electrochemical measurements and 28-day in vitro immersion tests were carried out under simulating physiological conditions. The cytotoxicity was evaluated by exposing L929 fibroblasts to RSRC Mg extracts. For the first time, the biocompatibility and degradation of the Mg-1Ca-0.5Zn-0.1Y-0.03Mn at.% alloy was assessed in a partial thickness calvaria defect model on male Wistar rats after 7 and 28 days of implantation. In vitro results showed that the RSRC alloy exhibited a more homogeneous microstructure and significantly lower corrosion rates compared to IM samples, with corrosion rates below 0.12 mm/year. The RSRC specimens exhibited lower pH and osmolality, and cytotoxicity assays confirmed that extracts from the RSRC alloy were non-toxic to L929 fibroblasts. In vivo, the RSRC alloys demonstrated slow degradation with corrosion rates remaining below 0.25 mm/year compared to pure Mg. Despite the presence of hydrogen gas cavities, new bone formation was observed suggesting that the RSRC alloy is a suitable material for the potential use as medical-grade absorbable Mg implants.

A novel metal matrix composites (MMC) with Mg matrix reinforced with natural filler in the form of Didymosphenia geminata frustules (algae with distinctive siliceous shells) are presented in this work. Pulse plasma sintering (PPS) was used to manufacture Mg-based composites with 1, 5 and 10 vol.% ceramic filler. As a reference, pure Mg was sintered. The results show that the addition of 1 vol.% Didymosphenia geminata frustules to the Mg matrix increases its corrosion resistance by supporting passivation reactions, and do not affect the morphology of L929 fibroblasts. Addition of 5 vol.% the filler does not cause cytotoxic effects, but it supports microgalvanic reactions leading to the greater corrosion rate. Higher content than 5 vol.% the filler causes significant microgalvanic corrosion, as well as increases cytotoxicity due to the greater micro-galvanic effect of the composites containing 10 and 15 vol.% diatoms. The results of contact angle measurements show the hydrophilic character of the investigated materials, with slightly increase in numerical values with addition of amount of ceramic reinforcement. The addition of Didymosphenia geminata frustules causes changes in a thermo-elastic properties such as mean apparent value of coefficient of thermal expansion (CTE) and thermal conductivity (λ). The addition of siliceous reinforcement resulted in a linear decrease of CTE and reduction in thermal conductivity over the entire temperature range. With the increasing addition of Didymosphenia geminata frustules, an increase in strength with a decrease in compressive strain is observed. In all composites an increase in microhardness was attained.

The results clearly indicate that filler in the form of Didymosphenia geminata frustules may significantly change the most important properties of pure Mg, indicating its wide potential in the application of Mg-based composites with a special focus on biomedical use.