Selective fabrication of hollow and solid polysaccharide composite fibers using a microfluidic device by controlling polyion complex formation

Natural polysaccharides are an important class of biomaterials that have attracted significant research interest for biomedical applications because of their high biocompatibility, biodegradability, and bioactivity. In this work, we fabricated water-insoluble composite hollow and solid fibers made of polyion complexes of chondroitin sulfate C (CS) and chitosan (CHI) using a single microfluidic device. A coaxial two-phase microfluidic device was constructed from stainless-steel needles and glass fibers, and CHI solutions and CS solutions were continuously infused into the core and sheath channels, respectively. The obtained fibers were flexible and homogeneous and had diameters of a few hundred micrometers. Hollow fibers were formed using water as the solvent of CS, while core-filled solid fibers were obtained using 20% (v/v) ethanol. The respective mechanisms for the fabrication of the hollow and solid fibers were discussed. An increase in the sheath flow rate or decrease in the core flow rate reduced the diameters of the fibers, while a reduction in the concentration of the CHI solution reduced the thickness of the hollow fibers. Furthermore, bovine serum albumin, used as a model protein, could be incorporated in the hollow and solid fibers by mixing them in the core flow solution. These results suggested the great potential of microfluidic techniques for the preparation of hollow and solid polysaccharide fibers.