Tuning microfluidic flow by pulsed light oscillating spiropyran-basedpolymer hydrogel valves

A method for microfluidic flow control based upon polymer hydrogel valves with rapid and reversible actuation properties is described. The platform allows for contactless optical flow control based upon pulsing light, resulting in a forced oscillating and control over the valve through photo-isomerisation of a spiropyran derivative, co-polymerised within an N-isopropylacrylamide (NIPAm) hydrogel. Application of pulsed light (450 nm) to the valves allows the valves to be held at an intermediate position for extended periods of time. Varying the extent of pulsing of the light source enables the flow rate to be regulated within a microfluidic flow rate range of 0–27 μL/min. Due to the pulsed light, a small period change in the flow rate is observed that corresponds to the pulse sequence as a corresponding oscillation in the hydrogel valves