Photo-responsive hydrogel for controlling flow on a microfluidic chip

Abstract

One technological challenge in microfluidic system design has been controlling the directional flow of minute amounts of fluid through various narrow channels. Stimuli-responsive polymers can be used as micro control devices such as valves because these materials significantly change their volumetric properties in response to small environmental changes in pH, temperature, solvent composition, or electric field. In this paper, a bi-layered hydrogel structure is introduced as a light activated microactuator. The first layer of the device is a light sensitive polymer network containing poly(vinyl alcohol) (PVA) and the retinal protein bacteriorhodopsin (bR). The second layer is a blend of PVA hydrogel and a pH sensitive polymer polyethylenimine (PEI). When exposed to a light source with a peak response at 568 nm, the bR molecules in the first layer undergo a multistage photocycle that cause protons to be pumped into the surrounding medium. The diffusion of these similarly charged ions through the adjoining pH responsive hydrogel generates electrostatic repulsive and attractive forces which alter the osmotic pressure within the cross-linked polymer network. Depending upon the type of electrostatic forces generated, the pH sensitive hydrogel layer will swell or, alternatively, collapse. The multi-layered structure can be fabricated and inserted into the microchannel. The expanding volume of the actuating hydrogel is used to regulate flow or control leakage. Preliminary experiments on a 625mm 3 optical actuating device are presented to identify key response characteristics and illustrate the mechanism for actuation.

e‐Beam Nanopatterned Photo‐Responsive Bacteriorhodopsin‐Containing Hydrogels

“…Addition of bR does not appear to introduce any significantly different features or artefacts under AFM imaging. Our deswelling results are also akin to a recent report [17] showing actuation of poly(ethylenimine) (PEI, another pH sensitive polymer) hydrogels by bR via long-term light exposure. We find that the de-swelling properties of the crosslinked PAA-bR hydrogels strongly depend on the energy of the electron dose used during EBL.…”

Soft Actuators for Small‐Scale Robotics

“…Photoresponsive gels typically show a combination of sensitivities to light, temperature, and pH values . For example, the actuator presented by Al‐Aribe et al combines photo‐ and pH‐sensitive gels in a bilayer structure to create microfluidic valves that contract by up to 28% . Photothermally activated gel actuators were discussed in Section .…”

Hydrogels Classification According to the Physical or Chemical Interactions and as Stimuli-Sensitive Materials

“… [ 162 , 163 , 164 , 165 ] Light-responsive Microfluidic devices, drug delivery, soft robotic, actuators. [ 166 , 167 , 168 ] Magnetic-responsive Cancer therapy, regenerative medicine, drug delivery. [ 169 , 170 ] Electro-responsive Actuators, drug delivery.…”