Physical properties of TEMPO-oxidized bacterial cellulose nanofibers on the skin surface

Water-dispersed bacterial cellulose nanofibers were prepared via an oxidation reaction using 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (TEMPO) as a catalyst. It was found that TEMPO-oxidized bacterial cellulose nanofibers (TOCNs) synthesized via sodium bromide-free methods are similar to those synthesized using sodium bromide. The TOCNs retained their unique structure in water as well as in emulsion. TOCNs adhere to the skin surface while maintaining nanofibrous structures, providing inherent functions of bacterial cellulose, such as high tensile strength, high water-holding capacity, and blockage of harmful substances. When gelatin gels as model skin were coated with TOCNs, the hardness representing the elasticity was increased by 20% compared to untreated gelatin gel because TOCNs could tightly hold the gelatin structure. When porcine skin was treated with TOCNs, carboxymethyl cellulose, and hydroxyethyl cellulose, the initial water contact angles were 26.5°, 76.5°, and 64.1°, respectively. The contact angle of TOCNs dramatically decreased over time as water penetrated the fibrous structure of the TOCN film. When observed by scanning electron microscopy and confocal microscopy, TOCNs on the skin surface provided physical gaps between particles and the skin, blocking the adsorption of particulate matter to the skin surface. On the contrary, the structure of water-soluble polymers was disrupted by an external environment, such as water, so that particulate matter directly attached to the skin surface. Characterization of TOCNs on the skin surface offered insight into the function of nanofibers on the skin, which is important for their applications with respect to the skin and biomedical research.