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Author

Qi LuFollow

Author ORCID Identifier

https://orcid.org/0000-0001-7821-9035

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Polymer Science and Engineering

Year Degree Awarded

2020

Month Degree Awarded

May

First Advisor

Ryan C. Hayward

Subject Categories

Nanoscience and Nanotechnology | Polymer and Organic Materials | Polymer Science | Statistical, Nonlinear, and Soft Matter Physics

Abstract

This thesis aims to extend the understanding and explore the application of temperature-responsive hydrogel systems by integrating microelectromechanical systems (MEMS). Stimuli-responsive hydrogel systems are immensely investigated and applied in numerous fields, and interfacing with micro- and nano-fabrication techniques will open up more possibilities.

In Chapter 2, the first biologically relevant, in vitro cell stretching device based on hydrogel surface instability was developed. This dynamic platform is constructed by embedding micro-heater devices under temperature-responsive surface-attached hydrogels. The fast and regional temperature change actuates the stretching and relaxation of the seeded human artery smooth muscle cell (HASMC) via controllable surface creasing instability. This device is engineered to mimic the in vivo environment of HASMCs, with independent control over substrate stiffness, mechanical cues and peptide attachment chemistry, and the response of HASMCs is inspected by the differentiation marker expression change.

In Chapter 3, the swelling and deswelling kinetics of hydrogel sheets with high polymer content is inspected, with micro-heaters providing abrupt local temperature change. Poly(N-isopropylacrylamide) (PNIPAM) molecules can form hydrogen bonds with both water molecules and polymer chains, while poly(N,N-diethylacrylamide) (PDEAM) molecules can only form hydrogen bonds with water. The kinetics of the two hydrogel systems are systematically compared, revealing that while PDEAM shows one-step mass transport-limited kinetics, PNIPAM shows two-step kinetics behavior, presumably reflecting the strong influence of inter-molecular hydrogen bonding.

The following two chapters document the attempts to further investigate into the hydrogel/MEMS interface. In Chapter 4, photo-patterning technique assists the study of regional modulus contrast influencing the formation of creases on the soft hydrogel surface, and it is demonstrated that the dimensions of the stiff patterns are relevant in directing the creasing direction. In Chapter 5, a photo-patternable sacrificial layer is designed based on crosslinking chemistry and gelation physics to potentially enable the construction of more complex MEMS devices.

Available for download on Saturday, May 08, 2021

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