ZIF-8 Nanoparticles: Zinc Ion Release, In Vitro Biocompatibility, and Evaluation in Galleria mellonella

Abstract Metal–organic frameworks (MOFs), and Zeolitic Imidazolate Framework-8 (ZIF-8) in particular, have found wide application in the therapeutic field. Their structure, size, and porosity can be tuned, and they can be synthesized using various methods. However, their biocompatibility and potential cytotoxicity remain insufficiently investigated. In this study, ZIF-8 nanoparticles were synthesized at room temperature using a rapid method with methanol as the solvent and characterized in terms of their chemical composition, structural properties, ion release behavior, and biocompatibility. The Zn ion release profile of ZIF-8 particles into Tris-HCl buffer medium was obtained through inductively coupled plasma optical emission spectroscopy (ICP-OES) under dynamic flow conditions, indicating a gradual and continuous release over 48 h. According to in vitro assays, MC3T3-E1 mouse preosteoblast cells maintained high viability at concentrations up to 100 μg·mL–1, while direct exposure of VH10 human fibroblast cells to 100 μg·mL–1 ZIF-8 reduced metabolic activity without significant membrane damage. However, no evident toxicity was observed in the eluate-based assay at this concentration. The findings were supported by the outcomes from the static ion release studies in DMEM cell culture medium, where ICP-OES showed that the level of Zn cations was lower than 9.5 μg·mL–1 in 100 μg·mL–1 ZIF-8 samples. The DNA fragmentation assay also indicated no detectable fragmentation at 100 μg·mL–1, suggesting the absence of apoptotic DNA damage in MC3T3-E1 cells under indirect exposure conditions. In addition, ZIF-8 was evaluated in vivo using the Galleria mellonella larval model, and samples up to 100 μg·mL–1 showed 100% survival and only minor reductions in health index score. The study underscores the importance of selecting appropriate methods for biocompatibility assessment, while also demonstrating the cytocompatibility of the investigated ZIF-8 nanoparticles, which may be associated with the relatively low measured Zn ion release.