Sterilization of silicone-based hydrogels for biomedical application using ozone gas: Comparison with conventional techniques

Abstract

Sterilization of hydrogels is challenging due to their often reported sensitivity to conventional methods involving heat or radiation. Although aseptic manufacturing is a possibility, terminal sterilization is safer in biological terms, leading to a higher overall efficiency, and thus should be used whenever it is possible.The main goal of this work was to study the applicability of an innovative ozone gas terminal sterilization method for silicone-based hydrogels and compare its efficacy and effects with those of traditional sterilization methods: steam heat and gamma irradiation. Ozone gas sterilization is a method with potential interest since it is reported as a low cost green method, does not leave toxic residues and can be applied to thermosensitive materials.A hydrogel intended for ophthalmological applications, based on tris(trimethylsiloxy)silyl] propyl methacrylate, was prepared and extensively characterized before and after the sterilization procedures. Alterations regarding transparency, swelling, wettability, ionic permeability, friction coefficient, mechanical properties, topography and morphology and chemical composition were monitored. Efficacy of the ozonation was accessed by performing controlled contaminations and sterility tests. In vitro cytotoxicity testes were also performed.The results show that ozonation may be applied to sterilize the studied material. A treatment with 8 pulses allowed sterilizing the material with bioburdens≤103CFU/mL, preserving all the studied properties within the required known values for contact lenses materials. However, a higher exposure (10 pulses) led to some degradation of the material and induced mild cytotoxicity. Steam heat sterilization led to an increase of swelling capacity and a decrease of the water contact angle. Regarding gamma irradiation, the increase of irradiation dose led to an increase of the friction coefficient. The higher dose (25kGy) originated surface degradation and affected the mechanical properties of the hydrogel by inducing a significant increase of the Young's modulus.Overall, the results show that ozonation may be considered as a valid and promising alternative for the sterilization of silicon-based hydrogels for biomedical applications.