Thiolated collagen was prepared as described elsewhere. A collagen/PEG hydrogel was prepared by mixing thiolated collagen with PEG-maleimide at 1:1 ratio between thiol and maleimide in a syringe mixing system. EVs at a concentration of 8.5510 9 particles/mL was added to the hydrogel and mixed. Approximately 125 mg of gel was added to each cuvette (which corresponds to ~1.07 10 9 EVs) and left to cure O/N with lid at RT. Hydrogels without EVs were used as negative control. The next day 3 mL of PBS was added on top of the gels and fluorescence of the solution on top of gels were measured on day 0, 1, 2, 10, 14, 20, 30, 35. A calibration curve of fluorescently stained EVs was used to determine the percentage of release. Gels containing stained EVs were done in quadruplicates and gels without EVs were done in triplicates.