2019 · Zhu — Mechanical Strength, Biodegradation, and in Vitro and in Vivo Biocompatibility of Zn Biomaterials.
Super-Abstract
Zinc (Zn)-based alloys were evaluated as a new class of biodegradable metal implant materials — notable specifically because they degrade without producing hydrogen gas, unlike magnesium-based implants. Alloying Zn with small amounts of Sr or Mg significantly improved mechanical strength, while corrosion rate, cytotoxicity, and in-vivo immune response remained acceptable in cell culture and animal testing. (ACS Applied Materials & Interfaces, 2019.)
Commentary
Like PMID 30853611, this is fundamentally a biomaterials engineering paper. Its relevance to H₂ biology is inverse: the key advantage of Zn-based implants over magnesium-based ones is the absence of H₂ gas evolution during degradation. Hydrogen gas bubbles from Mg implants have historically caused gas pockets, tissue irritation, and degradation instability. Zn corrodes at a moderate rate (~0.4 mm/year) without this H₂ by-product. The study demonstrates good biocompatibility across multiple human primary cell lines, low platelet activation, acceptable hemolysis, and an in-vivo immune response comparable to the benchmark Mg alloy AZ31. The key finding regarding H₂ is that its absence is a feature. This paper is useful context for understanding why H₂ management in implant design matters — but it contributes no data on therapeutic molecular hydrogen.
Key quotes
- „Compared to other degradable metallic biomaterials (i.e., Mg- or Fe-based), Zn biomaterials have a more appropriate corrosion rate without hydrogen gas evolution.“ — key advantage of Zn implants: no H₂ gas production during degradation
- „The measured cell viability and proliferation of three different human primary cells fared better for Zn-based biomaterials than AZ31 using both direct and indirect culture methods.“ — Zn alloys showed better in-vitro biocompatibility than the Mg benchmark
- „Zn-based biomaterials may have a great potential as promising candidates for medical implants.“ — authors' overall conclusion on the potential of Zn-based implants
Our assessment
This is a preclinical biomaterials study — not a therapeutic H₂ study. The H₂ connection is that Zn implants are positioned as superior to Mg implants precisely because they avoid H₂ gas release. The study is in-vitro and early-phase in-vivo; no human implantation data exist. It does not contribute evidence for or against therapeutic molecular H₂ — it is implant materials science with a note about H₂ as an unwanted by-product in the competing technology.
Study design
- Type: preclinical biomaterials study (in vitro + in vivo) · Model: three human primary cell lines (direct/indirect culture); rat subcutaneous, bone, and vascular implantation · H₂ relevance: absence of H₂ gas evolution from Zn corrosion (in contrast to Mg alloys)
- Result: Zn-alloy corrosion rate ~0.4 mm/year; better cell viability than AZ31 (Mg benchmark) in vitro; minimal platelet activation; hemolysis <0.5 %; in-vivo acute toxicity and immune response minimal/moderate, comparable to AZ31; no H₂ gas evolution during degradation
Abstract
Zn-based biomaterials have emerged as promising new types of bioresorbable metallics applicable to orthopedic devices, cardiovascular stents, and other medical applications recently. Compared to other degradable metallic biomaterials (i.e., Mg- or Fe-based), Zn biomaterials have a more appropriate corrosion rate without hydrogen gas evolution. Here, we evaluated the potential of Zn-based metallics as medical implants, both in vitro and in vivo, alongside a standard benchmark Mg alloy, AZ31. The mechanical properties of the pure Zn were not strong enough but were significantly enhanced (microhardness > 70 kg/mm2, strength > 220 MPa, elongation > 15%) after alloying with Sr or Mg (1.5 at. %), surpassing the minimal design criteria for load-bearing device applications. The corrosion rate of Zn-based biomaterials was about 0.4 mm/year, significantly slower than that of AZ31. The measured cell viability and proliferation of three different human primary cells fared better for Zn-based biomaterials than AZ31 using both direct and indirect culture methods. Platelet adhesion and activation on Zn-based materials were minimal, significantly less than on AZ31. The hemolysis ratio of red cells (<0.5%) after incubation with Zn-based materials was also well below the ISO standard of 5%. Moreover, Zn-based biomaterials promoted stem cell differentiation to induce the extracellular matrix mineralization process. In addition, in vivo animal testing using subcutaneous, bone, and vascular implantations revealed that the acute toxicity and immune response of Zn-based biomaterials were minimal/moderate, comparable to that of AZ31. No extensive cell death and foreign body reactions were observed. Taken together, Zn-based biomaterials may have a great potential as promising candidates for medical implants.
Source & links
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