Fig. 6. Preparation methods of silk hydrogels.

Silk hydrogels that can hold large amounts of water are attractive for implantable applications. The intermolecular and intramolecular interactions of macromolecular protein chains inside silk fibroin make these molecular chains physically crosslinked, resulting in the formation of a silk hydrogel. Some methods are usually implemented to accelerate the gelation process, such as (a) ultrasonic induction¹⁰⁶, (b) electric field induction¹⁰⁷, (c) ultraviolet (UV) exposure¹⁰⁸, (d) vortex induction, and (e) pH lowering. Reproduced with permission from Springer Nature (2017) and Wiley (2016) and (2017). f, g Photographs of some samples of silk hydrogels^100,109. Reproduced with permission from ACS (2016) and RSC (2017)