Evaluation of CO2-based cold sterilization of a model hydrogel

The purpose of the present work is to evaluate a novel CO(2)-based cold sterilization process in terms of both its killing efficiency and its effects on the physical properties of a model hydrogel, poly(acrylic acid-co-acrylamide) potassium salt. Suspensions of Staphylococcus aureus and Escherichia coli were prepared for hydration and inoculation of the gel. The hydrogels were treated with supercritical CO(2) (40 degrees C, 27.6 MPa). The amount of bacteria was quantified before and after treatment. With pure CO(2), complete killing of S. aureus and E. coli was achieved for treatment times as low as 60 min. After treatment with CO(2) plus trace amounts of H(2)O(2) at the same experimental conditions, complete bacteria kill was also achieved. For times less than 30 min, incomplete kill was noted. Several physical properties of the gel were evaluated before and after SC-CO(2) treatment. These were largely unaffected by the CO(2) process. Drying curves showed no significant change between treated (pure CO(2) and CO(2) plus 30% H(2)O(2)) and untreated samples. The average equilibrium swelling ratios were also very similar. No changes in the dry hydrogel particle structure were evident from SEM micrographs.