The impact of sterilization upon extracellular matrix hydrogel structure and function

Extracellular matrix (ECM) hydrogels represent a growing subset of injectable biomaterials for tissue engineering and regenerative medicine applications. Whilst two-dimensional scaffolds composed of ECM have been in routine clinical use for decades, the clinical translation of ECM hydrogels has been limited to date. Evaluation of the stability and function of ECM hydrogels after sterilization and storage is necessary to advance therapeutic use of these materials. In the present study, a new form of ECM material, specifically, ‘lyophilized digest’ was introduced to mitigate potential storage issues and investigate the effects of sterilization. Both ECM powders and lyophilized digests were subjected to sterilization by gamma irradiation, electron beam irradiation, ethylene oxide and supercritical carbon dioxide prior to hydrogel formation. The efficacy and effect of sterilization upon mechanical properties, macrophage response and stem cell chemotaxis was determined. Independent of the form of ECM exposed to sterilization, irradiation at 30 kGy altered ECM properties and inhibited subsequent gelation. Interestingly, the form of the ECM exposed to sterilization had a dramatic impact upon hydrogel rheological properties. Hydrogels formed from sterilized powders had reduced mechanical properties whereas hydrogels formed from sterilized lyophilized digest had mechanical properties equivalent to the non-sterilized control. Sterilization did not affect the bioactivity of ECM hydrogels as measured by stem cell chemotaxis and macrophage response. Together these data provide practical insight required for the translation of ECM based hydrogels.