A solution of 1% (w/v) 2-hydroxy -1-(4(hydroxyethoxy)phenyl) -2-methyl -1propanone (Irgacure2959) photo-initiator was dissolved in MilliQ water at 80°C and stirred until fully dissolved. The freeze-dried functional gelatin macromer was weighed and dissolved in the above solution containing a photo-initiator to prepare prepolymer solutions with the desired protein concentration of 10% (w/v) under stirring at 40°C.