Scheme 1. Schematic illustration of electrostatic condensation of mRNA with PEI and one-pot coprecipitation of mRNA complexes inside ZIF-8 (mRPZ), creating a polymer core-MOF shell particle (A). mRNA@ZIF-8 is unable to deliver mRNA due to leakage, while delivery with mRPZ retains mRNA and leads to the successful, delayed expression of enhanced green fluorescence protein (eGFP) in vitro (B) and firefly luciferase in vivo (C).