Carbon coated400 square mesh copper grids

Transmission electron microscopy (TEM) imaging was carried out by first glow discharging carbon-coated 400 square mesh copper grids (Electron Microscopy Sciences). Particle suspensions (25 μL) were left on the grid for 1 min before being washed off with 10 drops of water. Grids were then negatively stained with 3 drops of 1% uranyl acetate (Sigma Aldrich). For filtration study, the polymerization precursor solution was added with calcein (excitation/emission = 495/515 nm) (5 mg/mL), followed by the same synthesis procedure. Unencapsulated calcein was removed by dialysis using a dialyzer (Harvard Apparatus, Holliston, USA) equipped with a dialysis membrane (0.05 μm Isopore Membrane filters, Merck Millipore Ltd. Billerica, USA). The RBC membrane-derived vesicles and the RBC membrane-coated nanogel samples were then treated with Trition X-100 and filtered through an Amicon ultra filter with a molecular weight cutoff of 100 kDa. The fluorescence intensity of the filtrates was measured with a fluorescent spectrophotometer (Infinite M200, TECAN, Switzerland). The dynamic light scattering (DLS) measurements were carried on a Zetasizer Nano ZS (model ZEN3600 from Malvern Instruments). To dissolve RBC membranes, the solutions were added with 0.25 mL 5 wt% Triton X-100 together with 20 μg Proteinase K (New England Biolabs, Inc., Beverly, USA).