2019 · Liu — In vitro and in vivo studies of Mg-30Sc alloys with different phase structure for potential usage within bone.
Super-Abstract
Researchers developed a magnesium-scandium (Mg-30Sc) alloy with a body-centred-cubic (bcc) crystal structure as a biodegradable orthopaedic implant material and tested it in cell cultures and rats over 24 weeks. The β-phase bcc alloy showed superior mechanical strength (>600 MPa compressive strength), low in-vivo corrosion rate, no cytotoxicity, and good bone integration — with only limited hydrogen gas release during degradation. (Acta Biomaterialia, 2019.)
Commentary
This study is primarily a biomaterials engineering paper, not a hydrogen-medicine study in the traditional sense. Its relevance to H₂ biology lies in the fact that magnesium alloy implants inevitably release small amounts of H₂ gas as a degradation by-product — and historically this has been a concern for implant safety and gas pocket formation. The Mg-30Sc alloy is notable because its bcc structure achieves an unusually slow corrosion rate (0.06 mm/year), which limits H₂ gas evolution to levels the authors describe as acceptable. No cytotoxicity or systemic toxicity was observed in either cell or rat models. Bone contact ratio was 75 % after 24 weeks. The study is well-designed for a biomaterials evaluation, but it does not investigate any therapeutic role of H₂ — H₂ is a side product to be minimized, not a therapeutic agent here. Transferability to human orthopaedic use requires much further work including larger animal models and long-term human trials.
Key quotes
- „The β phased Mg-30 wt%Sc alloy displayed acceptable corrosion resistance in vivo (0.06 mm y-1) and maintained mechanical integrity up to 24 weeks.“ — key engineering result: slow degradation preserves mechanical function
- „No cytotoxicity and systematic toxicity were shown for β phased Mg-30 wt%Sc alloy on MC3T3 cell model and rat organisms.“ — safety finding: no detectable toxicity in cells or rats
- „Good osseointegration, limited hydrogen gas release and maintained mechanical integrity were observed after 24 weeks' implantation into the rat femur bone.“ — in-vivo result: H₂ release from implant degradation was limited and acceptable
Our assessment
This is a preclinical biomaterials study, not a study of therapeutic H₂. The H₂ aspect is specifically about minimizing incidental H₂ gas release from a degradable implant — the goal is to keep H₂ low, not to administer it therapeutically. Results are from cell culture and a rat femur model; no human implantation data exist. The alloy concept is scientifically interesting but far from clinical application. This paper is not evidence for therapeutic H₂ in any sense — it belongs to implant materials science.
Study design
- Type: preclinical biomaterials study (in vitro + in vivo) · Model: MC3T3 osteoblast cell line (cytotoxicity); rat femur implantation model, 24-week follow-up · H₂ relevance: incidental H₂ gas evolved during Mg-alloy corrosion (not therapeutic administration)
- Result: β-phase Mg-30Sc: compressive strength 603 MPa, corrosion rate 0.06 mm/year in vivo, bone-implant contact 75 % at 24 weeks; no cytotoxicity on MC3T3; no systemic toxicity in rats; limited H₂ gas release from implant degradation
Abstract
Proper alloying magnesium with element scandium (Sc) could transform its microstructure from α phase with hexagonal closed-packed (hcp) structure into β phase with body-cubic centered (bcc) structure. In the present work, the Mg-30 wt% Sc alloy with single α phase, dual phases (α + β) or β phase microstructure were developed by altering the heat-treatment routines and their suitability for usage within bone was comprehensively investigated. The β phased Mg-30 wt% Sc alloy showed the best mechanical performance with ultimate compressive strength of 603 ± 39 MPa and compressive strain of 31 ± 3%. In vitro degradation test showed that element scandium could effectively incorporate into the surface corrosion product layer, form a double-layered structure, and further protect the alloy matrix. No cytotoxic effect was observed for both single α phased and β phased Mg-30 wt% Sc alloys on MC3T3 cell line. Moreover, the β phased Mg-30 wt%Sc alloy displayed acceptable corrosion resistance in vivo (0.06 mm y-1) and maintained mechanical integrity up to 24 weeks. The degradation process did not significantly influence the hematology indexes of inflammation, hepatic or renal functions. The bone-implant contact ratio of 75 ± 10% after 24 weeks implied satisfactory integration between β phased Mg-30 wt%Sc alloy and the surrounding bone. These findings indicate a potential usage of the bcc-structured Mg-Sc alloy within bone and might provide a new strategy for future biomedical magnesium alloy design. STATEMENT OF SIGNIFICANCE: Scandium is the only rare earth element that can transform the matrix of magnesium alloy into bcc structure, and Mg-30 wt%Sc alloy had been recently reported to exhibit shape memory effect. The aim of the present work is to study the feasibility of Mg-30 wt%Sc alloy with different constitutional phases (single α phase, single β phase or dual phases (α + β)) as biodegradable orthopedic implant by in vitro and in vivo testings. Our findings showed that β phased Mg-30 wt%Sc alloy which is of bcc structure exhibited improved strength and superior in vivo degradation performance (0.06 mm y-1). No cytotoxicity and systematic toxicity were shown for β phased Mg-30 wt%Sc alloy on MC3T3 cell model and rat organisms. Moreover, good osseointegration, limited hydrogen gas release and maintained mechanical integrity were observed after 24 weeks' implantation into the rat femur bone.
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