Evaluation and optimization of the process parameters that affect the inativation of microorganisms in supercritical ambients applied to the sterilization of biomedical implants

Abstract

The existing methods used for the inactivation of microorganisms that contaminate solid surfaces, like thermal treatment with autoclaves, exposure to ethylene oxide, gamma or UV radiations are efficient but can induce damages to the materials like the degradation of thermal sensitive components, nutrients denaturation or changes in physical, biochemical or optical characteristics. The use of supercritical CO2 (CO2-SC) in the sterilization of vegetative forms of microorganisms has already produced convincing results, but its effectiveness in the decontamination of spores is still to be established. This research will evaluate the inactivation potential of combined process variables like temperature, pressure, additives and co-solvents, type of solid support, depressurizing rates, and pressure cycles by monitoring their effects on three different microorganisms. The main objective is the optimization of a CO2-SC process in order to be able to operate at moderate temperatures and pressures. This study will consider: (i) if the spores are fully inactivated or only inhibited (by counting the viable spores after storage at 4ºC for weeks), (ii) cortex ruptures, internal structure alterations of the spores and leaching of vital components, (iii) inactivation kinetics. This study can contribute to a better understanding of the mechanisms involved in the spore inactivation by CO2-SC and indicate operational conditions that allow the use of CO2-SC as a sterilizing agent, mainly for materials that need less aggressive treatments, like biomedical implants and devices. (AU)