Fabrication of alginate fibers using a microporous membrane based molding technique

Tubular structures made of alginate and similar hydrogels have been extensively investigated for drug delivery, tissue engineering and other biomedical applications. Alginate fibers are usually fabricated using complicated techniques such as coaxial flow extrusion or electro-spinning. This paper discusses the fabrication of hollow and solid alginate fibers using a simple membrane based molding technique. A hollow-fiber microfiltration membrane served both as the mold as well as reservoir for the cross-linking agent. The pores of the membrane were first filled with the cross-linker (i.e. calcium chloride) solution, after which the lumen was filled with sodium alginate solution. The calcium ions diffused from the membrane pores into the lumen, cross-linking the alginate in a radially inward direction. Solid alginate fibers were obtained by cross-linking all the alginate within the lumen, while hollow fibers were fabricated by pushing out un-cross-linked alginate from the central core using calcium chloride solution. The alginate fibers fabricated as described above were expelled from the membrane mold using water under pressure. These were then characterized by optical, fluorescence and scanning electron microscopy. The most attractive features of this fabrication method are its simplicity and flexibility with regards to alginate concentration. The fibers obtained were straight with excellent definition and uniform thickness, and could be fabricated in a highly reproducible manner. Other complicated solid and hollow 3-dimensional structures suitable for biomedical, and indeed other applications could also potentially be fabricated using similar membrane-based molding techniques.