Tubular multi-bilayer polysaccharide biofilms on ultra-thin cellulose fibers

Multiple bilayered polysaccharide biofilms have been assembled by electrostatic layer-by-layer (LBL), alternating deposition of cationic chitosan (CS, M_v = 405 kDa) and anionic dextran sulfate (DXS, M_w = 500 kDa) onto ultra-fine cellulose (CELL) and partially hydrolyzed cellulose acetate fibers with diameters ranging from 350 to 410 nm. While the surfaces of partially hydrolyzed (degrees of substitution of 1.14 or 0.2) and CELL fibers were equally hydrophilic, higher surface charges on the more hydrolyzed fibers afford thicker bilayers. The elestrostatic interactions between CS and DXS were enhanced by the presence of NaCl in the dipping and rinsing solutions to allow uniform deposition of sequential polysaccharide bilayers. At 0.25M NaCl, each CS/DXS bilayer averaged 6.4 to 9.0 nm thick with the total thickness of the five bilayer (CS/DXS)₅ varied from 64 to 77 nm. The CS/DXS bilayers exhibited much reduced BET surface area and pore volume indicating that these polysaccharides were much more densely packed on the fully hydrolyzed CELL fibers. The findings proofed the concept that long chain polysaccharide electrolytes can be self-assembled as nanometer scale tubular bilayers on ultra-fine cellulose fibers to afford wholly polysaccharidic fibrous architecture. The electrolytic nature, chemical reactivity, and structural versatility of these ultra-high specific surface polysaccharides are advantageous and can be further tuned to serve biological functions and for biomedical applications.