Table 1.

Summary of findings for the effect of different sterilization techniques on the properties of silk fibroin protein solution and lyophilized silk fibroin scaffolds.

	Technique	Sterilization conditions	Sterilization principle	Advantages	Disadvantages
Liquid silk fibroin	Autoclaving	High pressure saturated steam; 121°C, 20 min, liquid cycle	Coagulation of vital microbial proteins and cellular components	Readily available Non-cytotoxic Cost-effective	Changes physical properties of silk fibroin protein: ↓ MW, ↑ protein aggregation Alters mechanical properties of scaffolds formed from autoclaved silk fibroin
	Sterile filtration	0.22 μm sterile filter	Size exclusion of microbes	Readily available Non-cytotoxic Cost-effective	Only applicable to low viscosity silk fibroin solutions- ie. low MW, low concentration Losses in sample volume & sample concentration with ↑ MW and concentration
Silk fibroin scaffolds	Autoclaving	High pressure saturated steam; 121°C, 20 min, solid cycle	Coagulation of vital microbial proteins cellular components	Readily available Non-cytotoxic Cost-effective	Changes physical properties of silk fibroin scaffolds- ↓ degradation rate, ↑ compressive modulus Not applicable for silk fibroin scaffolds functionalized with biological molecules
	Gamma irradiation	Ionizing gamma rays 16.6×103 rad/min until 1.5 Mrad	Creation of free radicals that cause intracellular damage	Commonly used in hospitals & laboratories Non-cytotoxic	Not readily available Costly ↑ protein degradation rate Potential protein damage and cross-link formation
	Dry heat	High temperature 20 min, 160- 170°C	Oxidation and coagulation of cellular components	Readily available Cost-effective	Not applicable for silk fibroin scaffolds functionalized with biological molecules
	Ethylene oxide (EtO)	EtO gas for 10 h at room temperature, 2 h degassing in the sterilizer chamber, 24 h degassing in a vacuum oven at room temperature	Alkylation reactions with cellular components	Commonly used to sterilize heat- sensitive materials and equipment	Not readily available Highly toxic ethylene oxide material, risk to users Cytotoxic- ↓ cell attachment and proliferation rate- can be improved by pre-leaching ethylene oxide out of silk fibroin scaffolds
	Hydrogen Peroxide (H2O2) gas plasma	H2O2 vaporized into the chamber followed by generation of gas plasma using the STERRAD sterilization system	Oxidation of cellular components	Commonly used in hospitals & laboratories Low- temperature technique	Not readily available