The emergence of drug delivery using water stable metal-organic frameworks has elicited a lot of interest in their biocompatibility. However, few studies have been conducted on their stability in common buffers, cell media, and blood proteins. For these studies, single crystal ZIF-8 approximately 1 um in diameter were synthesized, incubated with common laboratory buffers, cell media, and serum, and then characterized by PXRD, IR, DLS, and SEM. Time-resolved SEM and PXRD demonstrate that buffers containing phosphate and bicarbonate alter the appearance and composition of ZIF-8; however, cargo inside the ZIF-8 does not appear to leak out, in most of these buffers, even when the ZIF-8 itself is displaced by phosphates. On the other hand, blood proteins in serum dissolve ZIF-8, causing trapped biomolecules to escape. The study presented here suggests that ZIF-8 can undergo dramatic surface chemistry changes that may affect the interpretation of cellular uptake and cargo release data. On the other hand, it provides a rational explanation as to how ZIF-8 neatly dissolves in vivo.
Keywords: MOF; ZIFs; biocompatibility; in vitro; in vivo; metal-organic frameworks; zeolitic imidazole frameworks.