Direct and green production of sterile aerogels using supercritical fluid technology for biomedical applications

Aerogels based on natural polymers are of increasing interest in the biomedical field due to their biocompatibility, bioactivity, biodegradability and, in certain cases, extracellular matrix biomimicry. However, sterility has been a critical quality attribute limiting the use of aerogels in biomedicine. This work introduces a new and environmental-friendly technique based on the use of CO2 called in situ sterilization that enables the manufacturing of sterile aerogel in a one-pot process. Starch aerogel cylinders and alginate aerogel beads enclosed within sterilization pouches were produced using this approach. The study involved the redesign of the flow diagram for aerogel production and the study of the effect of key parameters in the process (additive type and content, agitation, CO2 flow regime type and duration) on the resulting material. The obtained materials were evaluated regarding their texture (helium pycnometry, N2 adsorption-desorption analysis, SEM) and their sterility against three standardized bioindicators. Finally, the sterile aerogel materials were put in contact with NIH-3T3 cells assessing their cytocompatibility. Under the optimal operating conditions with 4.5 h of processing time, the aerogels were sterile, cytocompatible and had a porosity of ca. 80 % and a specific surface area of ca. 80 m2/g and 200 m2/g, for starch and alginate aerogels, respectively. Results allowed to identify the feasible operating region as well as the optimum processing values to obtain the typical nanostructure of aerogels, whilst ensuring suitable regulatory sterilization levels for aerogel implantation and cytocompatibility of the sterile material with fibroblastic cells.