60 µL precursor solution of GelMA, GelMA/DbPE and GelMA/TbPE was transferred into a cylindrical PDMS mold (diameter: 5 mm, height: 3 mm) and photocrosslinked by UV light irradiation (302 nm, 8 W). The hydrogel pads were swollen in DBPS for 24 h at room temperature and weighed after carefully removing residual water from the surface. Then, the samples were lyophilized, and dry weight was measured. Mass swelling ratio -accounting the mass release within the first 24 h -was calculated from the following equation, where 𝑤 -./001' is the weight after complete swelling, and 𝑤 23* is the weight after lyophilization.