Degradation Testing

Degradation of silk fibroin biomaterials has previously been studied using protease XIV [15]. Silk gel spun tubes weighing 10 mg from either 5, 10, 20, or 30 min extraction formulations were subjected to protease XIV enzymatic degradation under continuous orbital shaking in an incubator set to 37°C. Lyophilized protease XIV powder (Sigma-Aldrich, St. Louis, MO) was reconstituted to 1 mg/mL (0.1 U/mL in 1X PBS) with continuous stirring for one hour. Tubes were incubated in 750 μL protease solution for 14 days with complete enzyme changes occurring on days 2, 4, 7, and 10. Each day, one set of samples (N=4) was removed, rinsed for 15 seconds in deionized water, followed by two minutes of orbital shaking in fresh deionized water to completely remove enzyme and silk breakdown products. Samples were dried in a fume hood overnight to compare weights at each time point to original starting tube weights.