Figure 7.

Geometry control during fabrication by using laminar flows. (a) A schematic of the fabrication method using laminar flows to control geometry. (b) Steady laminar flows are obtained before UV irradiation. The outer streams of prepolymer mixture contain acrylic acid, EGDMA, water, and a photoinitiator. The middle stream consists of glycerin. The channel fabrication is the same as described in Fig. 5a. (c) After UV irradiation for 2 min, pH-sensitive hydrogel walls are formed while the center of the channel remains open. (d) When exposed to a basic solution, the pH-sensitive hydrogels expand to seal off the channel. (Bars = 500 μm.)