| Rapid developments in surgical and implantable device technology challenge current sterilization methods. This is particularly true for temperature-sensitive biopolymers. In this work, we investigate a new sterilization process based on liquid and supercritical carbon dioxide (CO2) technology. We studied the effect of exposure to liquid CO2 and select additives on the mechanical properties of selected medical polymers. Gas uptake, swelling, and distortion were observed for the more amorphous polymers while polymers with higher crystallinity showed much less sensitivity to CO2 exposure. These results are relevant to evaluating the potential of liquid CO2 -based sterilization technology. We evaluated the novel 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. The gels were hydrated and inoculated with Staphylococcus aureus and Escherichia coli, and then treated with supercritical CO2 (40°C, 27.6 MPa). Complete killing was achieved with pure CO2 at 60 minutes and with CO2 plus H2O 2 at 30 minutes. Incomplete kill was achieved at lesser times in both cases. Several physical properties of the gel were evaluated before and after treatment. These were largely unaffected by the process. We also quantified high level disinfection of the model hydrogel by the liquid-CO2 process. To assess mass transfer limitations in the process, both 6 mm and 23 mm thick hydrogel slabs were treated. In a thin slab, complete inactivation occurred after 90 minutes of CO2 contact. Very little deactivation occurred when a thick layer of hydrogel was treated for the same times. For longer treatment times, a slow and significant induction time was required, followed by accelerating then decelerating rate of kill. Finally an accelerated rate occurred characterized by a sharp increase in log-reduction leading to complete kill. Physical and biological properties of the gel were largely unaffected by the process. In the last part of the study biocompatibility of titanium implants sterilized by SC CO2 in a rat subcutaneous implantation model were evaluated. Overall the soft tissue response to the implants was similar among different methods of sterilization, indicating SC CO2 treatment did not compromise the biocompatibility of titanium. |
