Layer-by-layer assembly of responsive polymeric nanofilms: Characterizations and new applications



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Layer-by-layer (LbL) assembly is a film fabrication technique where material species are deposited on a substrate in order of alternating charge or other complementary interactions. The past decades have witnessed a remarkable increase in LbL assembly related research, owing to its simple operation, flexibility in selecting building materials and substrates, and precise control over film structure and thickness at the nanoscale. In this dissertation, responsive polymeric nanofilms are developed by LbL assembly for various applications. In Chapter 2, a simple benchtop version of the capillary flow layer-by-layer (CF-LbL) platform was developed for high throughput film fabrication and screening. Using a common polyelectrolytes combination, the effect of flow rates and channel sizes on film thickness and surface roughness were systematically investigated. In addition, the platform was used to study the biocompatibility and degradation behaviors of a series of enzymatically degradable nanofilms made from naturally derived polymers. Finally, microfluidic chip modified by one optimized film was used for capture and rapidly release of cancer cells from the blood sample. In Chapter 3, a simple yet effective cell isolation platform was established by applying optimized enzymatically degradable nanofilm and antibodies on the surface of hollow glass microspheres (HGMS). Thus, modified HGMSs can specifically capture cancer cells and float to the top of the blood sample hereby isolating targeted cancer cells. To reduce non-specific adhesion of blood cells, polyethylene glycol (PEG) molecules were incorporated onto the thin film coating. Using cancer cells spiked blood as a mode system, isolation and recovery of cancer cells was performed and the effect on cell viability or proliferative potential was investigated. In chapter 4, in order to enhance the interactions between cancer cells and the HGMS’ surface, nanostructured HGMS (NSHGMS) was prepared by applying LbL assembly of negatively charged SiO2 nanoparticles and positively charged polymer. The NSHGMS was then modified with the enzymatically degradable LbL film and antibodies for cancer cell isolation. The effect of the sizes of the nanostructure, isolation time, and cell concentration was systematically studied. The optimized NSHGMS was lastly used to isolated several common cancer cell lines, such as MCF7, SK-BR-7, and PC-3. In chapter 5, LbL assembly was used to develop thin films that can dynamically respond to environmental relative humidity (RH). To achieve this, polyelectrolytes films were fabricated by two neutrally derived polymers, chitosan (CHI) and carboxymethyl cellulose (CMC), through Layer-by-layer (LbL) assembly. The swelling behavior of CHI/CMC film was studied by measuring film thickness under different RH. In addition, three cross-linking methods, thermal, glutaraldehyde and EDC cross- linking, were carried out to form cross-linked CHI/CMC films whose swelling behavior were also studied. In chapter 6, thin films that can reversibly display and hide patterns in response to RH changes were further developed. Specifically, UV cross-linkable functional groups were grafted on CMC molecules for the fabrication of thin films which can be selectively cross-linked upon UV radiation. The thickness of cross-linked and uncross-linked films are equivalent at low RH whereas the uncross-linked regions swell more than the cross- linked ones at high RH, generating a strong structural color difference. It is demonstrated that this structural color is highly reproducible and can also be tuned to produce a wide range of colored films. By photo cross-linking certain regions of films, patterns can be reversibly hidden and displayed simply through human breath. Chapter 7 will conclude this dissertation and present several prospective works for future study.



Thin film, Layer-by-layer assembly