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Rechargeable aqueous zinc (Zn) metal batteries (ZMBs) have gained tremendous attention because of their intrinsic safety and low cost. However, the lifespan of ZMBs is seriously limited by severe Zn dendritic growth in aqueous electrolytes. Despite the feasibility of Zn deposition regulation by introducing Zn-alloying sites at the Zn plating surface, the activity of the Zn-alloying sites can be seriously reduced by side reactions in the aqueous environment. Here, we propose a facile but efficacious strategy to reinforce the activity of the Zn-alloying sites by introducing a low quantity of polar organic additive in the electrolyte that can be self-adsorbed on the Zn-alloying sites to form a molecular crowding layer against the parasitic water reduction during Zn deposition. As a consequence, stable cycling of the Zn anode can be maintained at such a multifunctional interfacial structure, arising from the synergism between the seeded low-overpotential Zn deposition on the stabilized Zn-alloying sites and a Zn 2+ redistributing feature of the self-adsorbed molecular crowding layer. The interfacial design principle here can be widely employed due to the great variety of Zn-alloy and polar organic materials and potentially be applied to improve the performance of other aqueous metal batteries.

Zn-based alloys are promising biodegradable implants for bone defect repair due to their good mechanical performance and degradability. However, local Zn 2+ released from Zn-based implants can seriously affect adhering cell behaviors as well as new bone formation on implant surfaces. To address this issue, we have fabricated a bone-mimetic extracellular matrix (ECM)-like surface on Zn-1Ca implants using a hybrid process of anodization, hydrothermal treatment (HT), and fluorous-curing. The ECM-like surface consisted of Zn 2 SiO 4 nanorods layered with collagen I (Col-I). The Zn 2 SiO 4 nanorods were hemicrystallized and transformed by the reaction of Zn(OH) 2 and SiO 4 4- during the HT. The Zn 2 SiO 4 nanorods effectively protected the substrate from corrosion; the Col-I layer decreased the degradation of Zn 2 SiO 4 nanorods and further reduced Zn 2+ release into the medium. This ECM-like surface generated a microenvironment with appropriate Zn 2+ levels, nanorod-like topography, and Col-I. It significantly improved adhesion, proliferation, and differentiation of osteoblasts on implant surfaces and vascularization of endothelial cells in the extract medium. The in vivo results are in good agreement with in vitro tests, with the ECM-like surface significantly enhancing new bone formation and bone-implant contact compared to the bare implant surface. Overall, this bone-mimetic ECM-like material of Col-I layered Zn 2 SiO 4 nanorods is a promising scaffold that promotes the bone regeneration of Zn-based implants.

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/mm 2 , 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.