Date of Award

8-9-2014

Document Type

Open Access Thesis

Department

Mechanical Engineering

First Advisor

Wally Peters

Abstract

Plants are sessile organisms that have developed methods of movement to respond to environmental stimuli. Some of the approaches feature the unequal expansion of cells and controlling deformation direction through fibers under swelling and drying. Hydrogels are three dimensional polymer networks that have the capacity for large volume changes due their affinity for water and can be tough and/or stimuli-responsive. In this paper, three preliminary plant-biomimetic hydrogel actuator designs are discussed and tested from wet to dry. The first actuator design, termed a 1%-0.1% bilayer, features two layers of different swelling and drying rates due to differences in cross-linking density. When the 1%-0.1% bilayer actuator dries, it bends towards the 0.1% layer. The 1%-0.1% bilayer is designed to mimic the plant bending movement derived from the unequal expansion of cells. The second actuator design, called a random fiber bilayer, features one layer with short randomly oriented fibers in it and a second fiber-less layer. The random fiber layer restricts the amount of shrinking/swelling that can occur and results in bending around the fiber-less layer as drying occurs. The idea for this actuator is inspired by fiber orientation and movement in the wheat awn. The third actuator design, known as a perpendicular fiber bilayer, is designed to mimic fiber actuation principles derived from pine cone scales. Long fibers are aligned on one layer to be perpendicular to long fibers in the other layer. The fibers constrain deformation to perpendicular directions only; this results in bending along two axes due to the fiber vi orientation in the two layers. All three of the designs testing from wet to dry is generally successful and these proof-of-concepts for translating plant movement principles to hydrogel actuators could be used to build more complex hydrogel actuators in the future.

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