Advanced micromolding approach toward scaling-up smart hydrogel microvalves

Smart hydrogel valves are a promising technology for autonomous process control. At the macroscale, hydrogel valves offer high flow rates with slow response times, whereas hydrogel microvalves offer low flow rates with fast response times. This contradiction limits the practical applicability of these valves, particularly in industry. Scaling-up refers to the process of transferring the benefits and results of microfluidics from the laboratory scale to the production scale. In this paper, we present advanced fabrication methods and corresponding promising concepts toward scaling-up responsive hydrogel microvalves to achieve higher throughput while maintaining fast response times. Using selective laser-induced etching (SLE), precise three-dimensional (3D) microfluidic structures and corresponding molds can be produced from fused silica, allowing hydrogel to be molded and anchored directly within the microchannel. This method enables the sizing-up of hydrogel microstructures in both horizontal and vertical directions. The influence of this scaling, in the form of various hydrogel dimensions up to 1500 μm, was investigated with regard to their suitability for an autonomous hydrogel valve. As a proof-of-principle, three hydrogel valves with different depths were fabricated using this method, whereby the response time decreases with increasing depth while the flow rate is increased simultaneously.