Effect of steam sterilisation on physico-chemical properties of antibacterial covalently cross-linked ε-polylysine/hyaluronic acid hydrogels

Sterilisation of implantable biomaterials such as hydrogels remains a key step towards their clinical translation. Standard sterilisation methods can significantly alter hydrogels' physicochemical and biological performance. Previously, we developed composite hydrogels based on ε-polylysine (ε-PL) and hyaluronic acid (HA). The developed hydrogels demonstrated promising antibacterial activity and in vitro cell viability and their variable properties depending on the chosen ε-PL to HA ratio. In this study, we fabricated a series of chemically cross-linked ԑ-PL/HA hydrogels with expanded ԑ-PL to HA mass ratios. Using small-angle X-ray scattering (SAXS), we unravelled the topological differences between physically and chemically crosslinked hydrogels. We then selected the chemically crosslinked hydrogel ԑ-PL/HA series of 60:40 wt%, 70:30 wt%, and 80:20 wt% ratios, with similar network topologies, to evaluate the impact of steam sterilisation on their physicochemical and viscoelastic properties. The antibacterial activity of the sterilized hydrogels was also evaluated against Gram-negative and Gram-positive bacteria. Our results showed that steam sterilisation minimally affects structure and physicochemical properties of ԑ-PL/HA hydrogels. Furthermore, the developed hydrogel ԑ-PL/HA series of 60:40 wt%, 70:30 wt%, and 80:20 wt% ratios showed pronounced antibacterial activity against Gram-negative and Gram-positive pathogenic bacteria. We expect our results will contribute to the growing understanding of using sterilisation methods for antibacterial hydrogels that have the potential for wider tissue engineering applications.