Zr-Based MOFs Shielded with Phospholipid Bilayers: Improved Biostability and Cell Uptake for Biological Applications
For practical biomedical applications, the stabilization of nanoscale metal–organic frameworks (NMOFs) in the presence of phosphate is of prime importance but remains a significant challenge because of the inevitable and strong driving force between metal clusters and phosphate species to form metal-phosphate in physiological environments. Through shielding Zr-NMOFs within the continuous phospholipid bilayers (PBLs), herein, we figured out a unique way to protect the vulnerable coordination bonds in their frameworks from the attack of phosphate. To exemplify the facility of constructing PBLs on Zr-NMOFs core, a porphyrinic NMOF of PCN-223 (standing for a platform with broad biological applications) was elaborated using a triethylamine (TEA)-modulated strategy. TEA could not only control the phase transformation of porphyrinic MOFs to achieve pure-phase PCN-223 crystals but also minimize their particles size down to sub-200 nm. Negative-stained TEM, FT-IR and XPS techniques revealed that PBLs could be closely coated onto the surface of nanoPCN-223, thanks to the strong Zr–O–P chemical complexation between Zr-NMOFs and phospholipid. The resultant coated nanoPCN-223 exhibited significantly enhanced phosphatic-resistance in phosphate buffer solution (PBS) and presented exceptional stability in harsh chemical environments. Furthermore, the MOFs-supported PBLs could effectively provide a stable biocompatible interface for subsequent cell culture and improve their biocompatibility, cellular uptake efficiency and real biostability of NMOFs in cellular environments. This study offers an alternative system for forming stable PBLs supported on NMOFs, and represents the first example of stabilizing Zr-NMOFs free from the attack of phosphate species in biological media.
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