Electrically-driven hydrogel actuators in microfluidic channels: fabrication, characterization, and biological application

TLDR

Electro‑responsive smart materials are limited by bubble generation during electric field application and biocompatibility concerns. The study designs a device that overcomes these limitations by integrating material properties, novel design concepts, and microtechnology. Using a 4‑hydroxybutyl acrylate hydrogel, the authors characterize its bending force and elasticity, design the actuator to operate below 1.2 V to avoid bubbles, and embed it in a microfluidic channel for particle sorting in cell‑culture media. The device successfully sorted mouse embryoid bodies, which retained pluripotency and differentiated into endoderm, mesoderm, and ectoderm, demonstrating the practical use of smart materials in cell biology.

Abstract

The utility of electro-responsive smart materials has been limited by bubble generation (hydrolysis) during application of electrical fields and by biocompatibility issues. Here we describe the design of a device that overcomes these limitations by combining material properties, new design concepts, and microtechnology. 4-hydroxybutyl acrylate (4-HBA) was used as a backbone hydrogel material, and its actuating behavior, bending force, and elasticity were extensively characterized as a function of size and acrylic acid concentration. To prevent bubble generation, the system was designed such that the hydrogel actuator could be operated at low driving voltages (<1.2 V). A microfluidic channel with an integrated electroactive hydrogel actuator was developed for sorting particles. This device could be operated in cell culture media, and the sorting capabilities were initially assessed by sorting droplets in an oil droplet emulsion. Biocompatibility was subsequently tested by sorting mouse embryoid bodies (mEBs) according to size. The sorted and collected mEBs maintained pluripotency, and selected mEBs successfully differentiated into three germ layers: endoderm, mesoderm, and ectoderm. The electroactive hydrogel device, integrated into a microfluidic system, successfully demonstrated the practical application of smart materials for use in cell biology.