BRIGE: Hindered-Diffusion Grayscale Surface Functionalization

The PI’s long-term research goal is to expand the knowledge, capabilities, precision, and affordability of micro- and nanoscale fabrication methods. In pursuit of this goal, the research objective of this BRIGE proposal is to utilize hindered diffusion of chemical solutes through polymers to create nanofabrication methods capable of generating “grayscale” functionalized surface patterns with spatially-variable chemical density. This work represents a significant advancement over currently available patterning technology, which is limited to generating either “binary” patterns or simple unidirectional gradients. The functionally graded surface patterning will enable scientific and technological breakthroughs in fields ranging from targeted drug delivery to tissue engineering. Intellectual Merit: Selective deposition of chemical solutes can be used to modify a number of surface properties, including binding affinity, etch susceptibility, hydrophobicity, and immune response. While the ability to locally vary chemical density in these patterns would be an invaluable tool in many fields, the state-of-the-art in surface patterning only enables the user to make microscale “binary” patterns, where regions are either completely absent of chemical modification or contain a single uniform chemical density. The research proposed here aims at gaining the knowledge required to generate grayscale surface patterns in a highly controllable way using low-cost, widely-available materials, making it immediately accessible to a large number of researchers. The two approaches proposed are: (1) exploring threedimensional polymer substrates as masks to control the diffusion path length of molecules from a liquid reservoir to the target patterning surface, and (2) exploring the use of a deformable polymer stamp and variable contact pressure to locally control which regions of stamp are in contact with the target patterning surface as a function of time. The proposed research will: (1) experimentally characterize mesh density and solute transport rates through polymers, (2) derive predictive relationships correlating hindered diffusion rate to basic polymer and solute properties, (3) generate numerical models of the proposed patterning mechanisms and validate them experimentally, and (4) develop deterministic algorithms for selecting optimized polymer geometry and mesh density for any desired solute/pattern combination. Broader Impact: Applications for controlled-density surface patterning are numerous and varied, including high-throughput binding studies for pharmaceuticals, portable biosensors for medical testing, control of fluid movement for microfluidics and self assembly, and quantitative studies of cell behavior. In addition, the hindered-diffusion studies and analytical models developed in this research will provide invaluable tools in the large number of fields governed by this transport mechanism, including tissue engineering, targeted drug delivery, chromatography, and medical diagnostics. Broadening Participation: This work would be used to provide educational and research opportunities to underrepresented groups, supporting the PI’s long-term educational goal of increasing the diversity of individuals pursuing careers in STEM disciplines, particularly in nanoscale engineering. The PI will continue her involvement with the University of Kentucky’s AMSTEMM (Appalachian & Minority Science, Technology, Engineering, & Mathematics Majors) and SWE (Society of Women Engineers) groups to actively mentor and recruit Appalachian, minority, and female students to participate in undergraduate research on this project. The results of this research will be integrated into two existing engineering courses in order to increase the exposure of students to nanoscale science and engineering as undergraduate students. Finally, a series of lectures and interactive activities designed to introduce K-12 students to the field of nanotechnology will be developed in collaboration with the Department of Curriculum and Instruction in UK’s College of Education. These materials will be presented as a part of the campus GEMS (Girls Enjoying Math and Science) program, made available online, and presented at high schools which traditionally have large minority and Appalachian populations.