Functionally-Responsive Hydrogels: from Dynamic Coloration to Biosensing Restricted; Files & ToC

Dong, Yixiao (Spring 2022)

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There are numerous examples of living creatures taking advantage of various responsive mechanisms to adapt to their environment. For example, chameleons change their skin color for mating or intimidating predators. Mimosa pudica folds its leaves inward upon mechanical perturbation as a defense mechanism, and the Venus flytrap closes its trapping leaves in response to the minute force of an insect landing on it. These examples have inspired numerous works developing responsive and “smart” materials. To date, scientists have built a library of responsive hydrogels according to their various response types, such as pH, heat, biomolecules, magnetic field, salt gradient, etc. In this dissertation, we have further expanded this library of responsive hydrogel materials to address specific challenges in the field, including strain-accommodation, on-demand assembly, and cellular force sensing.

   In chapter one, a comprehensive overview is given regarding previously developed responsive hydrogels with different functionalities. The overview is focused on three major aspects, including the components, responsibilities, and latent applications. The diversity of the materials demonstrates the great potential of functionally-responsive hydrogels in addressing different challenges in materials science and engineering.

   In chapter two, the design of strain-accommodating smart skin (SASS) is proposed based on the inspiration of a chameleon. Both finite element analysis and experimental results confirm the strain accommodating behavior of SASS material which is different from previously developed responsive photonic hydrogels with accordion-type structure. In the end, the SASS design demonstrates latent applications such as camouflage and anti-counterfeiting.

   In chapter three, a more challenging topic about on-demand assembly is proposed. In this case, the chromatic response of photonic hydrogel is no longer rely on the swelling/deswelling of hydrogel matrix, but rather the in situ assembly of magnetic nanoparticles. The on-demand assembly mechanism can not only avoid the volumetric change of common responsive hydrogels, but also sheds light on novel rewritable technology, information storage, and encryption technology.

   In chapter four, a responsive hydrogel was developed to measure cellular forces at the pico-newton level. We chemically modify single molecular tension probes on a PEG hydrogel surface. This responsive hydrogel provides a physiologically identical environment while measuring the cellular tension surface. Attempts of cellular tension imaging beyond 2D surface has also been introduced.

   The final chapter provides comprehensive summary and outlook about functionally-responsive hydrogels, beyond the scope of what is described in this dissertation. The prospective discussions include alternative material design, characterization, and other potential applications.

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