Soft functional materials are fundamentally interesting from a chemistry standpoint and have exciting applications in robotics, chemical and biomolecule sensing, and biomedical engineering. In addition, soft materials are also useful in lithography, particularly cantilever-free scanning probe lithography (CFSPL). Because of their low modulus, biocompatibility, stimuli responsiveness, malleability, and other characteristics, soft materials can be used to enhance the capabilities of CFSPL, which has been primarily used to synthesize inorganic and hard materials thus far. Indeed, soft materials-enabled CFSPL approaches can be used to pattern soft substrates and organic structures, including biological ones useful for studying bio-relevant surface cellular interactions. Three key factors must be considered in performing CFSPL techniques: the pen array that delivers the ink, the types of substrates that are being patterned, and the chemistry of the ink material. Herein, findings are presented that advance aspects of each of these factors. First, a new CFSPL technique termed electrochemical polymer pen lithography is introduced, where the pen arrays are comprised of hydrogel materials. Indeed, more than 10,000 hydrogel pen tips served as the electrolyte, allowing high-throughput localized electrodeposition of electroactive materials (e.g., metal ions) with precise spatial control. By taking advantage of the hydrogel’s ability to absorb large volumes of aqueous solutions and facilitate ion diffusion, compositional gradients of bi-metallic features were generated across a single substrate. Such a technique could be used in high-throughput combinatorial screening to identify ideal catalysts for energy applications. Second, photo-responsive hydrogels were used as substrates to generate patterns of well-defined soft and stiff domains (as dictated by the local hydrogel chemistry) with sizes ranging from the sub-cellular to cell scale. These patterns were used to examine and program cellular behavior. In particular, the soft domains dictated the formation of focal adhesions and were specifically designed to be commensurate with a target cell size to maximize cell migration speed (by as much as two-fold compared to the unpatterned surfaces). The relative contribution of topography and mechanics on cell migration was also examined; it was found that cells respond to stiffness heterogeneity more than topographical variations encoded by surface patterns, contributing to our understanding of how cells differentiate physical cues in heterogeneous landscapes. Finally, small organic molecules or monomers were used as ink materials in conjunction with the polymer pen lithography (PPL) platform to synthesize covalent organic frameworks (COFs). Using this approach, the nucleation and growth mechanisms of imine-linked COFs were probed. The evaporation rate of the patterned nanoreactors was identified as the critical determining factor in synthesizing single crystal COFs, which have enhanced electronic properties compared with conventionally formed powders or amorphous aggregates. In addition, this new one-step synthetic approach does not require harsh reaction conditions, long reaction times, and multi-step processes, as do many other current synthetic methods, and enables the site-selective growth of COF crystallites with tunable sizes and morphologies that are important in the context of optoelectronic devices.

Creator

• Oh, EunBi

DOI

• https://doi.org/10.21985/n2-wdew-p445

Subject

• Chemistry

Language

• en

Alternate Identifier

• etdadmin_upload_844916
• http://dissertations.umi.com/northwestern:15750

Date created

• 2021-01-01

Resource type

• Dissertation

Rights statement

• In Copyright