PhD Dissertation Defense: Sangwook Chu
Thursday, August 16, 2018
301 405 3681
Name: Sangwook Chu
Professor Reza Ghodssi (Chair)
Professor Pamela Abshire
Professor Yu Chen
Professor Ryan D. Sochol
Professor James N. Culver, Dean's Representative
Date/time: Thursday, August 16, 2018 at 10am
Location: 1146 A.V. Williams Building
Title: THREE-DIMENSIONAL BIOPATTERNING TECHNOLOGY AND APPLICATION FOR ENZYME-BASED BIOELECTRONICS
In this thesis research, an innovative biomanufacturing technology has been developed enabling highly selective and scalable biomolecular assembly on 3-D device components. The successful integration of microscale 3-D device structures created via conventional microfabrication techniques with a nanoscale molecular assembly of Tobacco mosaic virus (TMV) enabled hierarchical and modular material assembly approach for creating highly functional and scalable bio-integrated microsystems components. Si-based micropillar arrays (μPAs) has been adapted as a model 3-D device structure throughout this work as it allows facile modulation of device functionalities and biomaterial interfacing properties via rational arrangement of highly ordered geometrical features. Cysteine-modified TMV (TMV1cys) has served as the biomolecular assembler based on its excellent functional features including the high surface area structure, densely arranged surface receptors, environmental robustness, and self-assembling property onto metal surfaces.
Initial efforts have focused on investigating the dependence of geometrical characteristics to the self-assembly of TMV1cys on the surface of Au-coated μPAs displaying different structural densities. The comparative studies have revealed that the self-assembly of TMV1cys on μPAs, particularly for high density pillar arrangements on the surfaces located at the deep microcavities, is limited causing failure to provide uniform surface functionality for reproducible device performance. Through a careful analysis of the surface morphology and functionalization profile within the microcavities of different pillar densities, a limited wetting property is present. In such 3-D micro/nano structured surfaces this has been identified as the key limiting factor for biomaterial integration with high surface area micro/nanodevices. In order to, evaluate the material assembly approach for scalable device performance, hierarchical electrodes assembled via combination of TMV1cys and μPAs of lower pillar densities have been characterized in a NiO-based electrochemical charge storage system, demonstrating a significant enhancement in both power and energy performances, and expanding the versatility of TMV1cys as a high-surface-area nanotemplate for assembling a wide variety of energy storage materials. The combined results indicated that an enabling method to overcome the limiting wetting property will allow biomaterial-based manufacturing methods to create fully scalable micro/nano device components.
Based on the understandings of the fundamental limitation behind the 3-D device-biomaterial integration, the surface wettability of the μPAs has been characterized using droplets of TMV1cys solution. The results, combined with the theoretical derivation based on the Cassie-Baxter equation, indicated that the wetting property can be controlled by varying the μPA geometries. The 3-D-Electro-Bioprinting (3D-EBP) technology developed by leveraging this controllable factor in which the limited wetting property of the μPA allowed selective injection of the TMV1cys droplets into the microcavities, using a capacitive surface wettability-control technique, known as electrowetting. The droplets confined within the cavities then allowed localized self-assembly of the TMV1cys onto the wetted surfaces, enabling patterning of the biomacromolecules on the 3-D device substrate. The characterizations of the structural and chemical features of TMV1cys post 3D-EBP strongly confirmed that the biofabrication technique is compatible with the biomacromolecule, and no significant disturbances to its functional integrity were observed. The proof-of-concept demonstrations of the automated and programmable 3D-EBP, via a simple system integration with a commercial bioprinter, further emphasize the significance of the technology which has strong potential to generate excellent opportunities for advancing on-demand 3-D bio-integrated devices and systems.
The last part of this research has focused on demonstrating scalable biocatalytic activities on chip by conjugating glucose oxidase (GOx) onto TMV1cys. Relying on the robust self-assembly of TMV1cys on metal surfaces, an on-chip chemical bioconjugation method has been developed for high-density immobilization of GOx on TMV1cys via a heterobifunctional crosslinker (CL). The 3D-EBP has been applied to perform the bioconjugation process on μPA electrodes towards demonstration of scalable enzymatic activities on chip. The close correspondence of the enzymatic activities (measured via colorimetric assays) with the surface area enhancement (SAE) factors (derived based on the μPA geometry) strongly supports the successful incorporation of the developed biofabrication technology, enabling high controllability over the biocatalytic activity on chip. This fundamental understanding behind the change in electrochemical kinetics associated with the TMV1cys/CL/GOx immobilization demonstrated both the biosensing and bioenergy harvesting capabilities. Particularly, a significantly higher redox current density was achieved compared to a recently published work. This strongly implies that the on-chip bioconjugation strategy was effective for high density enzyme immobilization via TMV1cys. Combining the enhanced and scalable enzymatic activity on chip with incorporation of the 3D-EBP, the developed methods provide a robust and readily employable strategy for advancing a range of enzyme-based bioelectronics and platforms.