Integrated Stimuli-Responsive Functionalities: From Bioseparation to Dynamic Optics

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Integrated Stimuli-Responsive Functionalities: From Bioseparation to Dynamic Optics

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Title: Integrated Stimuli-Responsive Functionalities: From Bioseparation to Dynamic Optics
Author: Shastri, Ankita
Citation: Shastri, Ankita. 2016. Integrated Stimuli-Responsive Functionalities: From Bioseparation to Dynamic Optics. Doctoral dissertation, Harvard University, Graduate School of Arts & Sciences.
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Abstract: Nature demonstrates the efficiency of hierarchically integrated components that work in cooperation to produce a variety of useful phenomena in organisms, such as movement or shape change. A key feature of these components is the response of multiple reconfigurable constituents to certain stimuli, partaking in a cascade of events that lead to specific outcomes. Artificial systems strive for such efficiencies and can be greatly enhanced by the assimilation of responsive soft materials that respond to various and distinct stimuli.

Here, I describe the combination of reversibly dynamic, stimuli-responsive and flexible components that are affected by its environment towards directed outputs, at the premise of which is a cross-linked hydrogel network capable of volume change in different aqueous solutions. In the first part, I will elaborate on the integration of hydrogel embedded around flexible microstructures in an aqueous microfluidic system. Chemo-mechanical activation and cooperation of the stimuli-responses of the integrated soft components and functionalities in the microfluidic can produce specific outputs, including oscillatory behavior through feedback loops that is able to maintain local temperature within a narrow range. I will show that functionalization of the system with aptamer enables the separation of target biomolecules from a solution mixture.

I will then describe a hydrogel modified with spiropyran, a molecule that isomerizes between two forms with orthogonal properties in response to multiple stimuli, including light. In the absence of light activation, the volume change of the hydrogel can influence spiropyran isomerization mechano-chemically in different aqueous solutions. Integration of the optically responsive molecule with a volume-changing hydrogel is explored further in the context of nonlinear dynamic optics. In particular, the reversible self-trapping, or lensing, of laser light in spiropyran-modified hydrogels is investigated. Furthermore, propagating two laser beams through the system is found to have highly interesting implications in studying the mechanical stresses within the hydrogel network.

From this work we come closer to the nature-inspired, adaptable reconfigurability that leads to more efficient systems with applications ranging from biomedicine to optics, while also promoting methods for fundamental studies on polymer mechanics as well as molecular-level reconfigurability that is important to all sciences.
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