C flex laboratory tubing

Gelatin microemulsions were first fabricated using the microfluidic flow-focusing device. The syringes containing the oil phase (20 wt% Span 80 in mineral oil) and the aqueous phase (5 wt% Type A gelatin solution), respectively, were connected with fluidic ports, using plastic tubing (0.8 mm inner diameter and 1.6 mm outer diameter, C-Flex^® laboratory tubing, Sigma). The surrounding temperature was maintained at around 30 °C to prevent the gelatin solution from pre-gelation. The syringes were equipped with syringe pumps (New Era) to control the flow rate of the oil phase at 18.8 μl/min and the aqueous phase at 3 μl/min. The mixture containing gelatin microemulsions and mineral oil was drained out from the chip outlet and was collected in a container. The gelatin microemulsions were maintained at 15 °C and crosslinked to acquire gelatin microspheres (MSs) by adding 10 ml of 5% glutaraldehyde (Sigma) for at least 5 h. MSs were washed with ethanol, cyclohexane, and deionized (DI) water repeatedly, and the excessive aldehyde groups on MSs were blocked in 25 mM glycine solution (Sigma) for 1 h. MSs were lyophilized and kept at room temperature. In order to swell MSs, 10 mg of MSs were immersed in 50 μl of buffers. The mean size of buffer-swollen MSs was observed using an optical microscope and recorded.