Fabrication and osmosis-mediated dynamics of a plant-inspired, fluid-filled, soft actuator

Non-vascular plant tissues constitute a special class of poroelastic solids where closed cells encapsulate the fluid. The fluid can diffuse through the semi-permeable cell walls, thereby changing the cell volume, stretching the cell wall, and consequently changing the hydrostatic pressure in the cells. The presence of this hydrostatic pressure, also known as the turgor pressure, imparts structural stiffness to the plant tissue while a systematic control of the turgor pressure drives the macroscale motion. Some examples of macroscale motion in plants are the snap closing of a Venus flytrap, the circadian opening and closing of flower petals, and the movement of plants towards sunlight or water. These osmosis-mediated motions are very energetically dense and efficient, hence provide excellent natural models for engineering inspiration. Leveraging this deformation-inducing mechanism for practical applications requires an understanding of the parameters governing the constitutive response of these materials. While classical poroelasticity theory can capture the composite response, its assumptions of an interconnected porous network and immiscible fluid-solid phases miss the underlying physics in plant tissues. Therefore, to provide a model system and therein to elucidate enhancements in performance associated with controlled variations in concentration, wall mechanical response, or mesostructure of closed-cell, fluid-filled, osmolyte-driven active materials, I fabricate and characterize synthetic plant tissue analogs (PTAs). I create these analogs by encapsulating micron-sized saltwater droplets within thin Polydimethylsiloxane (PDMS) walls at concentrations of over 80% water by volume. The semipermeability of PDMS permits the diffusion of water while retaining the salt. In a water bath, PTAs can swell to reach a state of equilibrium governed by the initial salt concentration and cell wall mechanical response. In particular, equilibrium swelling is governed by the limiting stretch of the PDMS walls. Because of their closed-cell structure and ability to sustain high internal pressures, PTAs maintain or increase their stiffness upon swelling. This behavior is in direct contrast to similar high water-content, osmotic-pressure-driven actuating materials, like hydrogels. As a proof of concept, I demonstrate that PTAs exhibit an actuation force at least 10 times higher than typical hydrogels. Therefore, PTAs hold the potential to be used as soft actuators in biomedical applications which demand high force and structural support.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Civil Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2022

Author dc:creator

• Kataruka, Amrita

Contributors dc:contributor

• Hutchens, Shelby
• Lopez-Pamies, Oscar
• Elbanna, Ahmed
• Hilgenfeldt, Sascha

• Osmosis
• Swelling
• Plant-inspired
• soft composite
• actuation

Statement dc:rights

• Copyright 2021 Amrita Kataruka

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/113278

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/113278