Developing fabrication approaches for exploring dynamic response in closed-cell, osmotically-active fluid-solid composites

Spitzer, Alexandra Rose

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https://hdl.handle.net/2142/129489 Copy

Description

Title

Developing fabrication approaches for exploring dynamic response in closed-cell, osmotically-active fluid-solid composites

Author(s)

Spitzer, Alexandra Rose

Issue Date

2025-02-10

Director of Research (if dissertation) or Advisor (if thesis)

Hutchens, Shelby

Doctoral Committee Chair(s)

Hutchens, Shelby

Committee Member(s)

• Leal, Cecília
• Statt, Antonia
• Evans, Chris

Department of Study

Materials Science & Engineerng

Discipline

Materials Science & Engr

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• osmotically-active
• soft actuators
• emulsions
• DIW 3D printing
• permeability
• PDMS
• tissue mimics, fluid-solid composites

Abstract

Plant-tissue-analogs (PTAs), an osmotically-active fluid-filled soft-solid material platform developed within the Hutchens research group, exhibit forceful slow growth swelling behavior when submerged in aqueous environments, mimicking the osmotic actuation methods of nonvascular plant tissue. These materials consist of polydimethylsiloxane (PDMS) matrix phases and encapsulate aqueous osmolyte containing solutions. When placed in a high chemical potential environment (high water potential) the osmotic potential difference between the chamber and environment induces water to flow through the PDMS matrix into the osmolyte containing solutions, in turn increasing the internal volume, stretching the PDMS matrices, and inducing swelling of the bulk structure. In soft solids, large deformations significantly alter molecular structure and device geometry, which can impact other properties. In the case of mass transport, an interplay between flux and mechanical deformation results. Here we demonstrate a platform for the simultaneous characterization of mechano-permselectivity using the (slow) transport of water through polydimethylsiloxane (PDMS) as a challenging test case. The platform uses micron-sized, cylindrical, NaCl solution-filled PDMS chambers encapsulated by selectively-permeable PDMS thin film membranes. When placed in a high chemical potential environment, water flow through the PDMS membrane into the chamber is induced, resulting in membrane bulging. A model combining membrane flux and nonlinear elasticity captures the time-dependent response well, but only when a deformation-dependent permeability is used. Notably, the permeability of water through PDMS decreases by nearly an order of magnitude, from 2x10-12 to 5x 10-13 m2/s, due to primarily its thickness decreasing by nearly an order of magnitude as the average biaxial stretch increases from 1 to 2.75. Previously PTA materials were fabricated via an emulsion templating process, employing high shear mixing to emulsify NaCl solutions into PDMS. This process results in water-in-oil emulsions, where the internal aqueous phase droplets mimic the microstructure of nonvascular plant tissue, as well as the osmosis-induced swelling behavior. In order to mimic plant tissue microstructures, the aqueous phase droplets must be highly packed (≥74 vol.%), yet this was previously impossible without the use of packing emulsified droplets with centrifugation due to phase viscosity mismatch, resulting in low-yield of PTA material and high quantities of oil phase waste. Here we overcome this challenge using internal aqueous phases with improved viscosities, allowing for high internal phase emulsion (HIPE) fabrication by high-shear mixing alone, producing no waste. We report that to develop HIPEs using an osmolyte sodium alginate solution, the viscosity ηsodium alginate ≥ 22% ηPDMS Oil Phase , which practically equates to sodium alginate solutions of ≥ 5wt.%. These improved processing parameters allow for the development of yield-stress PTA emulsion formulations capable of manufacturing complex structures via direct-ink-write (DIW) 3D printing. Here we report on yield stress and formulation related printability via print maps, determining the printability as a function of resolution, draw ratio, and applied pressures. PTA emulsions with increased yield-stresses, result in trends of decreased print line thicknesses, increased draw ratios, and decreased pressure ranges, yet these trends fail at the upper limitations of printing parameters available on the DIW 3D printer utilized in this study. With improved printability, we determine 3D printed materials are capable of increased swelling in comparison to centrifuged samples, due to non-uniform swelling and new delamination based failure modes. DIW 3D printing also allows for complex structure fabrication, such as fabrication of non-planar bi-layer actuators. With the aim of using the materials as biological soft tissue mimics and support structures, we develop a formulation capable of swelling in physiological osmotic conditions using a PEG-8000 aqueous phase, show proof of benchtop sterilization techniques, mechanical cue based cell viability testing, as well as modify a technique for adhering silicone based materials to wet biological soft tissues.

Graduation Semester

2025-05

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/129489

Copyright and License Information

Copyright 2025 Alexandra Rose Spitzer

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