Fabrication of microbial cellulose nanofiber network sheets hydrophobically enhanced by introduction of a heat-printed surface

Acetobacter xylinum, a Gram-negative bacterium, secretes a cellulose nanofiber into the culture medium, and thereafter the individual secreted nanofibers are assembled to form a 3D network structure as termed "pellicle." The pellicle has unique properties including high water retention ability, biocompatibility, high strength and so on. Therefore, a hydrophobic cellulose nanofiber network sheet was attempted to be fabricated by heat-pressing of metal molds having a micro pattern in order to open further pathways of the pellicle towards potentially versatile materials. From the contact angle measurements, a heating condition at 130°C for 24 hours was the optimal condition for the treatment. ESCA analyses indicated that the increase in hydrophobicity was due to introduction of the ether bonds on the surface. Furthermore, a structural hydrophobic effect such as "Lotus effect" on this sheet was examined by introduction of micro -lattice patterns onto the surface. Finally, the synergistic effect of the heating and micro-patterning was examined. The surface of the sheet was more hydrophobic when the two effects were combined together. This successful method could be generally extended for bio-based materials to provide nano/micro structures with a surface hydrophobic property.