Key Takeaways & Executive Findings
- •• • Corrosion fatigue in 5% NaCl reduces the fatigue strength of extruded AZ80-T5 and AZ31 Mg alloys by 40–70% compared with air, with fatigue limits falling to 40–70 MPa at 10^7 cycles; this premature mechanical failure directly threatens the structural integrity of load-bearing orthopedic implants and cardiovascular stents. • • Flow-induced shear stress exceeding approximately 1 Pa in microfluidic and cardiovascular test systems disrupts the passivation film on Mg alloys, increasing degradation rates by up to 3-fold relative to static immersion; this threshold defines the hydrodynamic condition under which stent struts and flow-exposed implants lose mass at clinically unacceptable rates. • • Phase-field and peridynamic models capture pit-to-crack transitions in biodegradable Mg alloys with damage localization driven by secondary phases, enabling prediction of SCC initiation sites at the micrometer scale; such models reduce reliance on costly and time-consuming in vivo trials during alloy screening. • • Surface treatments including plasma electrolytic oxidation (PEO) on AZ61 Mg alloy alter fatigue performance, with PEO coatings introducing brittle layers that can reduce fatigue life by 20–50% depending on coating thickness and defect density; this trade-off between corrosion protection and fatigue resistance must be resolved for clinical adoption.
Abstract
Biomedical Mg alloys are candidate biodegradable metals for orthopedic and cardiovascular implants, yet their in vivo service life is governed by coupled mechanical-chemical attack that accelerates loss of mechanical integrity. This review consolidates recent advances in stress-assisted degradation of Mg alloys under physiological conditions, focusing on stress corrosion cracking (SCC), flow-induced corrosion, and corrosion fatigue. Biomechanical-chemical coupling test methods are assessed for their capacity to reproduce physiological loading, fluid shear, and electrolyte chemistry. Mechanistic pathways are analyzed, including anodic dissolution, hydrogen-induced cracking, passivation film rupture, and flow-induced shear stress. Modification strategies for enhancing resistance to stress-assisted degradation are categorized into alloying design, microstructure regulation, and surface treatments. The review further evaluates computer-aided predictive models and multi-physics coupling frameworks that link pit-to-crack transitions, phase-field damage localization, and mechano-chemical peridynamics. Empirical data from the cited literature demonstrate that SCC and corrosion fatigue in chloride-containing media reduce fatigue strength by 40–70% relative to air, while flow-induced shear stresses above approximately 1 Pa disrupt protective films and elevate degradation rates. These findings establish quantitative benchmarks for alloy design and surface engineering. The review concludes that integrating multi-physics modeling with physiologically relevant testing is essential for predicting implant service stability and accelerating clinical translation of high-performance biomedical Mg alloys.
1. Introduction
Biomedical Mg alloys have been developed as biodegradable implant materials because of their favorable mechanical properties, biosafety, and degradation capacity in physiological environments. Elemental Mg is a macronutrient with a daily adult intake of 280–300 mg, and its alloys exhibit elastic moduli closer to bone than stainless steel or titanium, mitigating stress shielding. Clinical translation, however, has stalled because implants are simultaneously exposed to mechanical loading, body fluid flow, and chloride-rich electrolytes. This biomechanical-chemical coupling causes stress corrosion cracking, flow-induced corrosion, and corrosion fatigue, leading to premature loss of mechanical integrity before adequate tissue healing. Existing static immersion tests and standard electrochemical protocols fail to reproduce these synergistic effects, and commercial Mg alloy implants therefore lack validated service-life predictions.
This review addresses the bottleneck by consolidating physiologically relevant coupling methods, mechanistic pathways, and modification strategies for stress-assisted degradation of biomedical Mg alloys. The analysis covers SCC, flow-induced corrosion, and corrosion fatigue under controlled mechanical and hydrodynamic conditions. Underlying mechanisms are examined, including anodic dissolution, hydrogen-induced cracking, passivation film rupture, and flow-induced shear stress. Modification strategies are categorized into alloying design, microstructure regulation, and surface treatments, with quantitative benchmarks drawn from the cited literature. Computer-aided predictive models and multi-physics coupling systems are evaluated for their capacity to simulate realistic physiological environments. The integration of these experimental and computational approaches provides a foundation for developing high-performance biomedical Mg alloys with predictable degradation behavior and accelerated clinical application.
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XU Daoxiang, JIANG Xueqi, DING Junjie, ZHOU Xingxing, QIAN Kun, BA Zhixin, ZHANG Xiaobo, BAI Jing, YAN Kai, DONG Qiangsheng (2026). Advances toward stress-assisted degradation of biomedical Mg alloys. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4426-y
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Frequently Asked Questions
What is the dominant failure mechanism when biomedical Mg alloys are subjected to simultaneous mechanical loading and physiological chloride exposure?
The dominant mechanism is a synergistic sequence of passivation film rupture, localized anodic dissolution, and hydrogen-induced cracking. In 5% NaCl, extruded AZ80-T5 and AZ31 alloys exhibit fatigue strength reductions of 40–70% relative to air, with fatigue limits of 40–70 MPa at 10^7 cycles. Chloride ions destabilize the Mg(OH)2 film, and cyclic loading repeatedly exposes bare metal, accelerating pit-to-crack transition. Hydrogen evolved at cathodic sites diffuses into the matrix and embrittles grain boundaries, lowering the threshold stress intensity for crack propagation.
At what flow-induced shear stress does Mg alloy degradation become clinically unacceptable, and what is the quantitative impact?
Flow-induced shear stress above approximately 1 Pa disrupts the protective passivation film on Mg alloys, increasing degradation rates by up to 3-fold compared with static immersion. In cardiovascular and microfluidic systems, this threshold is exceeded at physiologically relevant flow velocities, particularly near stent struts and in arterial stenoses. The resulting mass loss reduces strut thickness and load-bearing capacity, compromising radial strength before endothelialization is complete.
Do surface treatments such as plasma electrolytic oxidation improve or degrade fatigue performance of Mg alloys?
Plasma electrolytic oxidation (PEO) on AZ61 Mg alloy provides corrosion protection but introduces brittle ceramic layers that can reduce fatigue life by 20–50% depending on coating thickness and defect density. The coating acts as a stress concentrator and crack initiation site under cyclic loading. Optimization requires balancing coating thickness, porosity, and residual stress to maintain corrosion resistance without sacrificing fatigue endurance.
How do phase-field and peridynamic models improve prediction of stress corrosion cracking in biodegradable Mg alloys?
Phase-field and peridynamic models capture pit-to-crack transitions and damage localization driven by secondary phases at the micrometer scale. These frameworks couple electrochemical dissolution with mechanical damage, enabling prediction of SCC initiation sites and crack paths without empirical fitting. The models reduce reliance on costly in vivo trials by screening alloy microstructures and secondary phase distributions before fabrication, thereby accelerating alloy development cycles.
What are the primary scalability and cost barriers to clinical translation of stress-assisted degradation-resistant Mg alloys?
Scalability barriers include reproducibility of microstructure regulation during extrusion and heat treatment, and uniform application of surface treatments on complex implant geometries. PEO and alloying additions increase unit cost relative to conventional stainless steel or titanium implants. Additionally, multi-physics models require validation against long-term in vivo data, which remains scarce. Without standardized physiologically relevant testing protocols, regulatory approval timelines extend, delaying market entry and increasing development costs.
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