A step towards sustainable and effective hand sanitizer formulations based on bacterial cellulose nanofibers

The widespread use of alcohol-based hand sanitizers (ABHS) formulated with carbomers after the COVID-19 pandemic has increased ecotoxicity concerns. This work explored, for the first time, bacterial cellulose nanofibers (BCN) as a sustainable alternative to carbomers in ethanol and isopropanol based ABHS formulations. This approach aimed to utilize BCN biocompatibility, biodegradability, and higher environmental safety in the final product. The sensory, rheological, physical, and antimicrobial properties of the formulated ABHS were then evaluated. Scanning electron microscopy (SEM) revealed that BCN had a micrometric length and narrow width (46 nm). BCN-containing ABHS showed intermediate viscosity (≈75 cP) compared to carbomer gels formulated with ethanol (487 ± 4 cP) and isopropanol (29 ± 0 cP), directly affecting their spreadability. Less viscous ABHS (i.e., isopropanol-carbomer) showed significantly higher spreadability (S ≈ 3.0) than the others (S ≈ 2.3). BCN also influenced evaporation rates, with values similar to ethanol-carbomer formulations (≈54 % after 60 min). Optical tests revealed lower transparency for BCN formulations (≈4 % transmittance) compared to carbomer formulations (≈66 %). Antimicrobial tests confirmed robust in vitro activity against Escherichia coli, Staphylococcus aureus, and Candida albicans. A lower Minimum Fungicidal Concentration (MFC) was observed for BCN formulations against C. albicans, suggesting interactions with the yeast cell wall. In vivo tests showed a slightly higher reduction in baseline hand microbiota (97.40 ± 0.91 %) for BCN-based ABHS compared to carbomer-based ones (96.95 ± 1.30 %). Results suggest that BCN could replace carbomers in ABHS, offering equal or superior antimicrobial efficacy while significantly reducing environmental impact.