A Novel Immobilization Method of Urease in Silk Fibroin Scaffolds by Annealing at Constant Temperature and Humidity

Temperature and humidity (TH) post-treatment is a relatively mild way to change the silk fibroin (SF) secondary structure. Here, urease is immobilized in SF scaffold (SFS) by TH post-treatment, and the effects of annealing on the immobilized urease activity are examined. Fourier transform infrared indicates that the SFS secondary structure started to transform when the scaffold is annealed at 35 degrees C with 100% relative humidity for 20 min. The higher the temperature, the lower the treatment time is required to change SFS structure. Compared to methanol annealing, TH post-treatment maintains the original form of the sample, and the scaffold shows better water-binding abilities. The maximum recovery ratio of immobilized urease is 98.4 +/- 7.0%, which is obtained after the scaffold is postprocessed at 35 degrees C for 60 min, and the relative recovery ratio of the urease activity is still as high as 80.6 +/- 12.1% after repeatedly measuring 10 times. In addition, the relative recovery ratio of urease is not significantly decrease within 4 weeks of storage. Therefore, TH annealing is a relatively mild and effective way to immobilize urease in SFS. The urease-immobilized SFS with hydrophilic properties and prolonged enzyme activity may be used for peritoneal dialysate regeneration systems.