Dissolvable Calcium Alginate Microfibers Produced via Immersed Microfluidic Spinning.

Fabrication of micro- and nanofibers are critical for a wide range of applications from microelectronics to biotechnology. Alginate microfibers with diameters of tens to hundreds of microns play an important role in tissue engineering and fibers of these diameters are impossible to fabricate via electrospinning and can only be produced via fluidic spinning. Typically, microfluidic spinning based on photopolymerization produces fibers that are not easily dissolvable, while fluidic spinning with chemical cross-linking employs complex setups of microfabricated chips or coaxial needles, aimed at precise control of the fiber diameter; however, fluidic spinning introduces significant cost and complexity to the microfluidic setup. We demonstrate immersed microfluidic spinning where a calcium alginate microfiber is produced via displacement of alginate solution through a single needle that is immersed in a cross-linking bath of calcium chloride solution. The resulting diameter of the fiber is characterized and the fiber diameter and topology of the deposited fiber is related to the concentration of the alginate solution (2 wt%, 4 wt%, and 6 wt%), needle gauge (30 g, 25 g, and 20 g), and the volumetric flow rate of the alginate solution (1 mL/min, 2 mL/min, and 2.7 mL/min). The resulting fiber diameter is smaller than the internal diameter of the needle and this dependence is explained by the continuity of the flow and increased rate of fall of the liquid jet upon its issuing from the needle. The fiber diameter (demonstrated diameter of fibers range from 100 microns to 1 mm) depends weakly on the volumetric flow rate and depends strongly on the needle diameter. It also seems that for a smaller needle size, a greater concentration of alginate results in smaller diameter fibers and that this trend is not evident as the needle diameter is increased. In terms of topology of the deposited fiber, the higher wt% alginate fiber produces larger loops, while smaller wt% alginate solution yields a denser topology of the overlaid fiber loops. These fibers can be dissolved in DMEM/EDTA/DSC solution in 20-30 min (depending on the fiber diameter), leaving behind the hollow channels in the hydrogel matrix. We believe that the demonstrated simple setup of the immersed microfluidic spinning of the calcium alginate microfibers will be useful for creating tissue constructs, including the vascularized tissue implants.