Microfluidic Synthesis of Complex Alginate Fibers for the Direction Control of Cell Growth

We report herein a simple system for continuously synthesizing complex Ca-alginate fibers using a uniformdepth, co-flowing microchannel. The continuous flow of sodium alginate (NaA) solution is gradually gelled in the microchannel by the diffusion of Ca ions from the outer gelation solutions. Introduction of thin buffer layers between the NaA and the gelation solutions could regulate the gelation speed of alginate and prevent the microchannel clogging, and the highly viscous multiphase flows were stabilized with a help of a thickener. We applied the presented system for fabricating complex alginate fibers with a cross section composed of multiple regions, including two or three-component fibers, spiral fibers composed of solid and soft regions, and fibers incorporating oil droplets. In addition, the microscopic solid-soft anisotropy of the hydrogel fibers made from NaA and propyleneglycol alginate (PGA, a non-gelling derivative of alginate) was utilized to control the direction of cell growth, demonstrating a unique application for the formation of linear tissues or cell networks.