A Stimuli-Responsive Hydrogel Array Fabrication Scheme for Large-Scale and Wearable Microfluidic Valving

Abstract

Programmable microfluidic valving enables controlled routing and compartmentalized manipulation of fluid within networks of microfluidic channels-capabilities which can be harnessed to implement an automated, massively parallelized, and diverse set of bioanalytical operations in large-scale microfluidics (lab-on-a-chip) and wearable (labon-the-body) applications. Stimuli-responsive hydrogels are suitable base materials to construct programmable microfluidic valving interfaces: once embedded in a microfluidic channel, their volumetric shrinkage/expansion (in response to stimulus) can be exploited to open/close microfluidic channels. However, to adapt them for the envisioned applications, critical fabrication challenges including robustness (e.g., complete channel sealing), scalability (forming arrays of valves with high yield and throughput), miniaturization of the valve actuation interface, and mechanical compatibility (flexibility for wearability) must be addressed. Here, we devise a simple and low-cost fabrication scheme to create arrays of stimuli-responsive hydrogels (e.g., thermo-responsive) and optional stimulus embodiments (e.g., microheaters) with compact footprints and within complex microfluidic networks. Within the framework of this fabrication scheme, we specifically: 1) introduced an ex situ hydrogel hydroconditioning step to achieve full channel sealing; 2) optimized the valve performance to achieve maximal volumetric response; and 3) utilized mechanically flexible and thin device layers to ensure compatibility for wearable applications. We illustrated the scalability of the fabricated valves and their enabling microfluid management capabilities, by demonstrating fluid routing/compartmentalization within valve-gated square matrix and radial tree matrix microfluidic networks.