To prepare microparticles, 65g of prepolymer solution was poured into an aluminum dish and was photo-polymerized as described above. The crosslinked hydrogel was suspended in 30 mL of Milli-Q water and was poured into a commercial laboratory blender (Waring, USA) for chopping into finer particles. The slurry was blended at 15,000 rpm speed for 5 min.