Supercritical carbon dioxide induces sterilization of PLLA scaffolds contaminated by E. coli.

The common sterilization techniques are based on physical processes that involve, for example, the use of autoclaves or systems to radiation such as γ-rays that can cause a structural change of the polymer treated. Therefore, the use of supercritical carbon dioxide (scCO2) is an excellent alternative, as it does not induce any variation of biomaterials treated (Perrut M., 2012). It's a good candidate because is readily available at low cost, non-toxic and non-flammable, it has an easily accessible critical point (7.38 MPa and 304.2 K) and excellent transport properties and wettability (White A. et al., 2005). We report the development of a supercritical CO2 based process capable of sterilization of PLLA [poly(L-lactic acid)] scaffolds that can be used for tissue engineering applications. The PLLA scaffolds were contaminated by the gram negative bacterium E. coli or environmental microorganisms: the amount of bacteria in each scaffold was determinated by colony-forming unit (CFU). Than they were subjected to different (for temperature or pressure values) supercritical CO2 processes. A good sterilization was obtain with a pressure of 150 bar for only 15 minutes of treatment at 37°C. The process does not alter crystallinity and melting temperatures of the scaffolds, as demonstrated by DSC analysis (differential scanning calorimetry) of the scaffolds treated and not. Therefore, the treatment does not significantly alter the properties of the sample. The CO2 treatment does not intact the biocompatibility of the scaffolds as demonstrated by MTS assay (viability assay) of SK-HEP-1 tumour cells growth on the surface and the internal pores of the scaffolds. These results suggest that the scCO2 can be used as a perfect method of sterilization for PLLA scaffolds for their possible use for tissue engineering applications.  Michel Perrut, 2012 Sterilization and virus inactivation by supercritical fluids. The Journal of Supercritical Fluids. 66: 359-371.  White A. et al., 2006, Effective terminal sterilization using supercritical carbon dioxide. Journal of Biotechnology. 123(4):504-15.