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

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.

Nature‐Inspired Stimuli‐Responsive Self‐Folding Materials

“…Bending could be achieved either (i) by applying gradients of field to homogenous materials or (ii) by applying non-gradient stimuli to inhomogeneous materials. The example of the first case is the bending of polyelectrolyte hydrogel during electrolysis [8]. The examples of the second case are the bending of liquid crystalline films [9], hydrogel with the lateral gradient monomer concentration [10], cantilever sensors [11], and shape-memory polymers [12].…”

Selective deposition of chemically-bonded gold electrodes onto PDMS microchannel side walls

“…For example, silver wires have been introduced through guide channels, resulting in electrode wires laying along the bottom corners of the microfluidic channels [21]. One possible difficulty with this approach is poor precision in the electrode placement, which can lead to misalignment with side walls, reduction in efficacy, and short-circuiting.…”

Smart Microfluidics: The Role of Stimuli- Responsive Polymers in Microfluidic Devices

“…To prevent this problem, Kwon and co-workers implemented an electro-responsive hydrogel sorter based on 4-Hydroxybutyl acrylate (4-HBA), which was able to operate at low driving voltages.(G.H. Kwon et al, 2010) Beebe et al designed and realized microvalves by either patterning a pH-sensitive hydrogel along the walls of a channel or creating an array of the same hydrogel inside the microfluidic devices. The swelling of these hydrogel structures blocked a channel when a high pH solution flowed into the channel, whereas when the pH value was appropriately decreased, the contracted state of hydrogel allowed the fluid to pass.…”