Feature Papers in Biobased and Biodegradable Metals

1. Introduction and Scope

Biodegradable metals (Mg, Zn, Fe) represent a transformative approach for biomedical implants and special industrial applications. This Special Issue features nine cutting-edge studies advancing understanding of these systems, highlighting key material challenges: magnesium alloys exhibit excellent biocompatibility but suffer rapid corrosion and hydrogen evolution, zinc alloys offer moderate degradation rates yet have poor mechanical strength, and iron-based systems show superior mechanical properties but degrade too slowly for physiological needs. The research encompasses novel alloy design, thermomechanical processing, microstructure, mechanical properties, corrosion characterization, and in vitro degradation/cytocompatibility assessment. These interdisciplinary studies integrating metallurgy, materials science, electrochemistry, and biomedical engineering address clinical translation bottlenecks, providing critical insights to overcome current limitations and guide future development of biobased and biodegradable metals.

2. Contributions

This Special Issue comprises nine original contributions, featuring one review and eight original studies on biobased and biodegradable metals including Mg, Zn, and Fe.

Fróis et al. (contribution 1) addressed the intraoral degradation of fixed orthodontic appliances and pointed out current mitigation strategies using alloy design, process, and surface treatment. This paper sets a foundational framework for understanding degradation mechanisms in biomedical metallic systems, making it essential reading for researchers in both orthodontics and broader biomaterial fields.

Larraza et al. (contribution 2) presented a novel approach of ultrasonic melt treatment to enhance the strength and corrosion resistance of magnesium-based implants through the fabrication of bioactive glass–ceramic nanoparticle-reinforced metal matrix nanocomposites. Subsequent hot rolling enhanced strength but increased corrosion rates. The study demonstrated a critical trade-off between mechanical reinforcement and degradation control in Mg implants.

Bryan et al. (contribution 3) explored the fabrication of magnesium-based bulk metallic glasses using spark plasma sintering and investigated the influence of sintering duration (15–180 min) on the structural, mechanical, and corrosion behavior of Mg₆₅Zn₃₀Ca₅ ribbons. A key finding is that sintering at 150 °C for 90 min achieves a near-net amorphous structure with 98.2% densification and minimal crystallization, resulting in optimal mechanical properties. The study revealed that prolonged sintering beyond 90 min increased densification but compromised corrosion performance.

Johanes et al. (contribution 4) introduced selenium (Se) as a novel alloying element in magnesium, synthesizing a Mg-15Se binary alloy via powder metallurgy, including microwave sintering and hot extrusion. The alloy exhibited mechanical properties significantly superior to pure Mg: 57% higher hardness, 21–51% improvements in compressive strength and ductility, and a remarkable 76% increase in damping capacity, as well as a comparable corrosion rate to pure Mg. This work provides a basis for the use of selenium as an alloying element in biomedical materials.

Jiang et al. (contribution 5) reported a rapid biodegradable Mg-Gd-Cu-Zr alloy fracture balls for oil and gas extraction, where rapid degradation is a desired feature rather than a limitation. The alloy exhibited high ultimate tensile strength (>200 MPa) and elongation (>11.1%) at 93 °C. More strikingly, its corrosion rate in 3 wt.% KCl solution reached 1660.8–1955.1 mm/y. The findings underscore the versatility of Mg alloys and expand their utility into sustainable energy technologies, where temporary structural components that dissolve after use can reduce environmental impact and operational costs.

Sutic et al. (contribution 6) investigated the effects of titanium addition (0.10–1.00 wt.%) on the microstructure, mechanical properties, and corrosion behavior of zinc-based alloys. Microstructural refinement of α-Zn dendrites and eutectic grains led to improved mechanical performance. Electrochemical tests in simulated physiological conditions showed that increasing Ti content enhanced corrosion resistance, with lower degradation rates observed for Zn–1.00Ti.

Shi et al. (contribution 7) combined alloying and pulsed magnetic field treatment to enhance the performance of Zn-3Cu-xMg alloys. The addition of Mg (0.5–1.0 wt.%) promoted precipitation along grain boundaries, refining the microstructure and improving strength–ductility synergy. The Zn3Cu0.5Mg alloy achieved the best combination of strength and ductility, moderate corrosion rate, positive cytocompatibility, and antibacterial efficacy.

Silva et al. (contribution 8) presented a new processing route for a Fe-35Mn alloy involving arc melting, homogenization, hot swaging, and solution treatment. The alloy exhibited excellent mechanical properties: ultimate tensile strength of 533 MPa, elongation of 39%, and reduced Young’s modulus of 171 GPa but a relatively low corrosion resistance. The study highlighted the role of Mn in reducing corrosion resistance due to its lower electrochemical potential, creating galvanic couples with the Fe matrix. The work demonstrated that tailored thermomechanical processing could optimize the mechanical–degradation trade-off in Fe-Mn alloys.

Kadirov et al. (contribution 9) investigated how compressive deformation at various temperatures (350–900 °C) affected the phase composition and corrosion behavior of Fe-30Mn-5Si alloy. It was found that deformation below 700 °C preserved a single-phase γ-austenite structure, while deformation at 900 °C induced a two-phase γ-austenite + ε-martensite structure, which enhanced biodegradation due to increased electrochemical activity. The corrosion rate ranged from 0.14 to 0.42 mm/year, depending on deformation conditions.

3. Conclusions and Outlook

The nine papers in this collection collectively illustrate the remarkable progress in biobased and degradable metallic alloys, showcasing innovative strategies to overcome the inherent limitations of Mg, Zn, and Fe systems from novel alloying concepts to advanced processing techniques. Future research should focus on the tunability of mechanical and degradation properties, in vivo validation, and long-term toxicity studies for clinical application. As these technologies mature, biodegradable metals are poised to revolutionize implantable medical devices, offering safer, more sustainable, and patient-centric solutions.