Cell Metabolic Activity: HEK293t cells were plated at a seed density of 30,000 cells per well in a black-walled, clear bottom 96-well plate, phenol-red free media was used to reduce background, and one column of wells was left without cells. Resazurin was prepared for a final working concentration of 44 µM. Cells were treated with mRPZ, ZIF-8, Linear 20 kDa PEI, and lipid particles and allowed to incubate for 4-6 hours. One column of wells was treated with 70% ethanol to kill all the cells. After incubation, Resazurin solution was added to the well, and the fluorescence (excitation 560 nm, emission 590 nm) was measured between 4-24 hours after adding resazurin on the SpectraMax i3 plate reader.