Synthesis and Purification of GelMA Polymers

The protocol for synthesizing GelMA polymers with the medium substitute degree followed our previous studies [28 (link),29 (link)]. Briefly, 10% type A gelatin powders from porcine skin were added into Dulbecco’s phosphate-buffered saline (DPBS) at 50 °C and then stirred at 240 rpm until the gelatin powder dissolved completely. Subsequently, MA was gently added into the gelatin solution drop by drop, and the final concentration of MA was 1.25 v/v%. After 2 h of reaction at 50 °C under a low-speed stirring process, an equal volume of pre-warm DPBS was added into the gelatin/MA solution, followed by another stirring process for 10 min. Afterward, the mixture was moved to the dialysis membrane (Spectra/Por molecular porous membrane tubing, MWCO 12,000–14,000, Thermo Fisher Scientific Inc., Waltham, MA, USA) to execute a purification process. In the purification process, the GelMA mixture in the dialysis membrane was placed in distilled water (DI water) at 40 °C at 500 rpm, and the DI water was changed twice daily. After 5 days of dialysis, the purified GelMA polymers were moved to the centrifugal tubes and further stored at −80 °C. The GelMA polymers were obtained via a 4-day freeze-dried process to remove the DI water before experiments.