New Eco-Friendly and Low-Energy Synthesis to Produce ZnO Nanoparticles for Real-World Scale Applications

This paper presents an original and sustainable method for producing ZnO nanoparticles (NPs) in response to global challenges (low energy requirements, low environmental impact, short production times, and high production yield). The method is based on an ion exchange process between an anionic resin and an aqueous ZnCl2 solution; it operates in one step at room temperature/ambient pressure without the need for complex apparatus or purification steps. From the kinetics, we observed the formation of pure simonkolleite, a zinc-layered hydroxide salt (Zn5(OH)8Cl2·H2O), after only 5 min of reaction. This compound, used elsewhere as a ZnO precursor after calcination at high temperatures, here decomposes at room temperature into ZnO, allowing extraordinary savings of time and energy. Finally, in only 90 min, pure and crystalline ZnO NPs are obtained, with a production yield > 99%. Several types of aggregates resulting from the self-assembly of small hexagonal platelets (solid or hollow in shape) were observed. Using our revolutionary method, we produced almost 10 kg of ZnO NPs per week without any toxic waste, significantly reducing energy consumption; this method allows transferring the use of these unique NPs from the laboratory environment to the real world.

Simonkolleite Coating on Poly(Amino Acids) to Improve Osteogenesis and Suppress Osteoclast Formation in Vitro

Zinc can enhance osteoblastic bone formation and stimulate osteogenic differentiation, suppress the differentiation of osteoclast precursor cells into osteoclasts, and inhibit pathogenic bacterial growth in a dose-dependent manner. In this study, simonkolleite, as a novel zinc resource, was coated on poly (amino acids) (PAA) via suspending PAA powder in different concentrations of zinc chloride (ZnCl₂) solution, and the simonkolleite-coated PAA (Zn–PAA) was characterized by SEM, XRD, FT-IR and XPS. Zinc ions were continuously released from the coating, and the release behavior was dependent on both the concentration of the ZnCl₂ immersing solution and the type of soak solutions (SBF, PBS and DMEM). The Zn–PAA was cultured with mouse bone marrow stem cells (BMSCs) through Transwell^TM plates, and the results indicated that the relative cell viability, alkaline phosphatase (ALP) activity and mineralization of BMSCs were significantly higher with Zn–PAA as compared to PAA. Moreover, the Zn–PAA was cultured with RAW264.7 cells, and the results suggested an inhibiting effect of Zn–PAA on the cell differentiation into osteoclasts. In addition, Zn–PAA exhibited an antibacterial activity against both S. aureus and E. coli. These findings suggest that simonkolleite coating with certain contents could promote osteogenesis, suppress osteoclast formation and inhibit bacteria, indicating a novel way of enhancing the functionality of synthetic bone graft material and identifying the underline principles for designing zinc-containing bone grafts.