Stimuli-Responsive Shape-Changing Molecular Brushes

University Of Tennessee Knoxville, Knoxville TN

Investigators

Abstract

PART 1: NON-TECHNICAL SUMMARY Molecular brushes are a class of very long, chain-like molecules consisting of a polymer backbone with densely attached side molecules, so the whole molecular assembly looks like a brush. Their dimensions and shapes are determined by the backbone and side-chain lengths and the interactions of side chains with themselves and their environment. These giant molecules exhibit intriguing properties and are found in the human body performing a wide variety of functions, including joint lubrication, lung clearance, and cell signaling. This project will design, synthesize, develop, and study in detail molecular brushes that can change their sizes and shapes in water in response to environmental variations and stimuli. They will be designed to emulate the behavior of a natural protein in our bodies called the "von Willebrand factor", which causes our blood to clot at the site of an injury, thus stopping the bleeding. The synthetic strategies, properties, and fundamental understanding of such macromolecules will have potential impact to many technologies, including material surface modification, lubrication, medication delivery, etc., thus benefiting society. The research program will also have societal impact via human-resource development. It provides a platform to train next-generation scientists (postdoctoral researchers, graduate and undergraduate students). Outreach activities will be organized in collaboration with local high school teachers, aimed at stimulating the interest of high school students toward STEM fields. PART 2: TECHNICAL SUMMARY This project is aimed at synthesizing and studying molecular brushes that can exhibit controllable changes in size and shape upon application of external stimuli. Its behavior is inspired by the von Willebrand factor, which enables blood clotting in response to an injury by unraveling from a non-sticky soluble globular shape to an extended nano-object exposing a large number of binding sites to form a clot at the site of an injury. Specifically, the research program will develop general strategies to prepare responsive molecular brushes using state-of-the-art polymer synthesis techniques, investigate stimuli-triggered changes in molecular dimension, conformation, and shape in aqueous solution, and elucidate the effects of various molecular parameters on stimuli-responsive properties. A series of molecular brushes with various molecular architectures, chemical compositions, grafting densities, and molecular weights will be prepared, and their stimuli-responsive behavior in water will be characterized by a broad range of techniques, including dynamic light scattering (DLS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). DLS can conveniently provide in-situ information on molecular dimensions under different conditions; AFM and TEM allow for directly visualizing the brush molecules. The control of interactions of these giant molecules with other macromolecules and solid materials will be demonstrated via external stimuli. The knowledge gained from this study will be used to guide the design and synthesis of functional molecular brushes.