Polyisocyanopeptide Hydrogels Are Effectively Sterilized Using Supercritical Carbon Dioxide

Adequate sterilization procedures for soft biomaterials such as hydrogels are known to be challenging. These materials are delicate in structure, making them sensitive to harsh conditions and prone to damage. In this study, a suitable sterilization method for hydrogels composed of tri(ethylene glycol)-functionalized polyisocyanopeptides (PIC) was explored. These high biomimetic hydrogels are temperature and strain sensitive and have been presented as novel cell culturing matrices, wound dressings, and drug carriers. The methods that were investigated include autoclaving, γ-irradiation, ultraviolet (UV) light irradiation, and supercritical CO₂ (scCO₂) treatment. The results show that autoclaving and γ-irradiation have deleterious effects on the gelation behavior and mechanical characteristics of PIC. For γ-irradiation, cooling the gels on dry ice alleviated this negative impact, but not sufficiently enough to make the method viable. In contrast, UV light and scCO₂ treatment do not affect the mechanical properties of the PIC gels. Studies with gels inoculated with 10⁷ CFU/mL Gram-positive bacteria Staphylococcus aureus show that only scCO₂ is capable of successfully sterilizing PIC hydrogels by achieving a 6-log reduction in bacterial load. It was concluded that, within the range of tested techniques, the sterilization of PIC is limited to scCO₂.