Use of supercritical CO₂ for the sterilization of liposomes: Study of the influence of sterilization conditions on the chemical and physical stability of phospholipids and liposomes

The effects of four potential supercritical carbon dioxide (ScCO₂) sterilization conditions on the chemical stability of 9 phospholipids and on the physicochemical characteristics of liposomes consisting of stable phospholipids, as well as their sterilization efficiency were evaluated. These conditions were : C1 (ScCO₂/70 °C/150 bar/240 min), C2 (ScCO₂/0.25 % water/ 0.15% H₂O₂/ 0.5% acetic anhydride/38° C/85 bar/45 min), C3 (ScCO₂/0.08 % peracetic acid/35° C/104 bar/180 min) and C4 (ScCO₂/200 ppm H₂O₂/40 °C/270 bar/90 min). The results showed for phospholipids, a significant increase in hydrolysis products of 3.77 to 14.50 % and an increase in oxidation index of 6.10 to 430.50 % with unsaturated phospholipids for all tested conditions while with saturated phospholipids, no significant degradation was observed. Concerning the liposome formulation, no change in dispersion color and no phospholipid degradation were observed. However, a decrease in liposome size from 126.90 nm to 111.80 nm, 96.27 nm, 99.60 nm and 109.13 nm and an increase in the PdI from 0.208 to 0.271, 0.233, 0.285, and 0.298 were found with conditions C1, C2, C3 and C4 respectively. For the sterilization efficiency, conditions C1, C2 and C3 achieved the required sterility assurance level (SAL) of 10^-6 for liposomes.