Silk Sponges (Step 24, Options L and M)
Silk sponges provide a versatile 3D porous scaffolding material for several applications as shown in Table 1. Here we provide protocols to form aqueous-based or HFIP-based scaffolds. The aqueous-based sponges have excellent interconnectivity between the pores and have the benefit of not requiring an organic solvent. This may be of interest if a bioactive molecule will be incorporated into the silk matrix during processing. The HFIP-based sponges have smoother surfaces along the pores and have higher mechanical strength. Through this processing method, reinforcing agents can be added to the silk matrix to further increase mechanical properties23. In addition, it has been shown that aqueous-based sponges degrade faster than HFIP-based sponges14 which enables the user to tailor these scaffolds to project specifications. Both of these sponge types may be sterilized by either immersing them in 70 v/v% ethanol overnight or by autoclaving. The first protocol will produce aqueous-based silk sponges 15 mm in diameter and 10 mm in height and the second protocol will produce at least 9 scaffolds approximately 12 mm in both height and diameter. SEM can be used in order to characterize the morphology and pore structure of these materials. Porosity can be determined via liquid displacement.