Biomedical applications of nanostructured polymer films

Abstract

Functional polymeric thin films are often stratified with nanometer level structure and distinct purposes for each layer. These nanostructured polymeric materials are useful in a wide variety of applications including drug delivery, tissue engineering, controlling condensation and polymeric batteries; all of which will be discussed in this work. The first area of my thesis will detail the use of C₆₀ cluster-ion depth profiling X-ray Photoelectron Spectroscopy (XPS) to fundamentally understand how thin film structure and function relate. This method has the unique capability to determine the atomic composition and chemical state of polymeric thin films with <10nm nanometer depth resolution without any chemical labeling or modification. Using this technique, I probed the nanostructure of functional thin films to quantify the interlayer diffusion of the biopolymer chitosan as well as demonstrate methods to stop this diffusion. I also explored the role of interlayer diffusion in the design of hydrophobic yet antifogging 'zwitter-wettable' surfaces. Additionally, I probed the lithium triflate salt distribution in solid block copolymer battery electrolytes (PS-b-POEM) to understand the lithium-ion distribution within the POEM block. In the second area of my thesis, I show how the nanostructure of materials control the function of polymeric particles in vitro and in vivo. One example is a 'Cellular Backpack' which is a flat, anisotropic, stratified polymeric particle that is hundreds of nanometers thick and microns wide. In partnership with the Mitragotri group at UCSB, we show that cellular backpacks are phagocytosis resistant, and when attached to a cell, the cell maintains native functions. These capabilities uniquely position backpacks for cell-mediated therapeutic delivery and we show in vivo that immune cells attached to backpacks maintain their ability to home to sites of inflammation. In addition, we have designed polymeric microtubes that can control their orientation on the surface of living cells. Inspired by chemically non-uniform Janus particles, we designed tube-shaped, chemically non-uniform microparticles with cell-adhesive ligands on the ends of the tubes and a cell-resistant surface on the sides. Our results show that by altering the surface chemistry on the end versus the side, we can control the orientation of tubes on living cells. This advance opens the capability to control phagocytosis and design cellular materials from the bottom up.