Bio-inspired Design of Submerged Hydrogel-Actuated Polymer Microstructures Operating in Response to pH

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Title: Bio-inspired Design of Submerged Hydrogel-Actuated Polymer Microstructures Operating in Response to pH Authors: Lauren D. Zarzar, Philseok Kim, and Joanna Aizenberg @Harvard: http://onlinelibrary.wiley.com/doi/10.1002/adma.201004231/pdf

Summary

This paper discussed the possibility of creating chemically-actuated structures by using a modified kind of hydrogel. Applications of such structures could include microfluidic devices (i.e. lab-on-a-chip devices or micro-mixing systems) and biomimetics (i.e. cilia or pedicellaria). Actuation of structures was achieved by modifying the pH of the system in such a way that osmotic pressure on the submerged hydrogel caused either contraction or swelling such that the hydrogel acts like a muscle analog while actuating an array of microposts or microfins.

Methods and Results

Some effort was made to allow for the plates to bend in a predictable direction over a large area. The first attempt (using microposts) contained many small domains of bent plates with no preferential direction observed from domain to domain. The method by which the hydrogel actuates these structures is shown in the figure below. So, anisotropy was introduced in the system by switching from microposts to microfins with a large aspect ratio such that the bending occurs preferentially in only two directions. To further allow for all of the microfins to bend in the same direction, several methods were implemented to increase the anisotropy: notably tilted plates and tilted application of the hydrogel to the structure.

Hydrogel1.jpg