The prepared collagen was swollen using 1% (w/v) hydrochloric
acid at a skin/solution ratio of 1:10 (w/v) for 20 h at room
temperature with discontinuous stirring. The samples were then
washed thoroughly with distilled water until the washing water
was nearly neutral. The swollen skinwas mixed with distilledwater
at 60 C for 6 h in a skin/water ratio of 1:3 (w/v) in a SHZ-B thermostatwater
bath oscillator (Jiangren Experimental Equipment Co.,
Ltd., Shanghai, China) to extract the gelatin. The mixture was then
filtered and centrifuged at 12,800 g for 20 min using a 5810
Centrifugal Machine (Eppendorf AG, Hamburg, Germany). The supernatant
was dried under vacuum (0.07 MPa) at 50 C until the
moisture level was below 15%.