Bacterial inactivation by using near- and supercritical carbon dioxide

Abstract

The three most common methods of sterilization in use today are ethylene oxide exposure, gamma-irradiation, and steam sterilization. Each of these methods has serious limitations for the sterilization of some materials used in medicine, especially thermally and hydrolytically sensitive polymers by themselves and in combination with proteins. In this work, we demonstrate a potential new method of sterilization by using supercritical fluid carbon dioxide. Using this method we achieve complete inactivation of a wide variety of bacterial organisms at moderate temperatures and in the absence of organic solvents or irradiation. Sterilization is a function of both the proximity to the fluid's critical point and the chemical nature of the fluid itself. When biodegradable polymers poly(lactic-co-glycolic) acid and polylactic acid were included in the sterilization process, there was no effect on the inactivation efficiency, yet no physical or chemical damage to these thermally and hydrolytically labile materials was observed.

Figure 1

Schematic of SCF sterilization apparatus. (1) CO₂ cylinder. (2) Syringe pump. (3) Pump header cooler and heater. (4) Preheating coil. (5) Heater. (6) Extraction vessel. (7) Water bath.

Figure 2

(A) Sterilization kinetics of E. coli in SCF CO₂ in the presence of water. (B) Comparison of sterilization kinetics of E. coli in the presence and absence of water at 34°C and 140 bar. (Solid lines indicate trends only.)

Figure 3

(A) PLGA microsphere before (Left) and after (Right) sterilization at 25°C and 205 bar for 1 hr. (B Upper) S. aureus before (Left) and after (Right) SCF-sterilization process. (Lower) P. aeruginosa before (Left) and after (Right) SCF process. (C) E. coli before (Left) and after (Right) SCF sterilization.

Figure 4

Fourier transform IR spectroscopy analysis of unprocessed and SCF-sterilized PLGA (t = 34°C, P = 205 bar).