Stimuli-Responsive Shape-Changing Molecular Brushes

分子刷是一类非常长的链状分子，由聚合物主链和密集附着的侧分子组成，所以整个分子组合看起来像一个刷子。它们的尺寸和形状取决于主链和侧链的长度以及侧链与自身及其环境的相互作用。这些巨大的分子表现出有趣的特性，在人体中被发现具有多种功能，包括关节润滑、肺清除和细胞信号传导。该项目将详细设计、合成、开发和研究分子刷，这些分子刷可以根据环境变化和刺激改变其大小和形状。它们将被设计成模仿我们体内一种叫做“血管性血友病因子”的天然蛋白质的行为，这种蛋白质会使我们的血液在受伤部位凝结，从而止血。这些大分子的合成策略、性质和基本认识将对许多技术产生潜在的影响，包括材料表面改性、润滑、药物输送等，从而造福社会。该研究项目还将通过人力资源开发产生社会影响。为培养下一代科学家（博士后、研究生和本科生）提供了一个平台。将与当地高中教师合作组织外展活动，旨在激发高中生对STEM领域的兴趣。本项目旨在合成和研究能够在外部刺激下表现出大小和形状可控变化的分子刷。它的行为受到了冯氏血液病因子的启发，该因子通过从非粘性可溶性球状物向扩展的纳米物体展开，使血液在损伤部位凝结，从而暴露出大量的结合位点，从而在损伤部位形成血块。具体来说，该研究项目将开发利用最先进的聚合物合成技术制备反应性分子刷的一般策略，研究水溶液中刺激引发的分子尺寸、构象和形状的变化，并阐明各种分子参数对刺激响应特性的影响。将制备一系列具有不同分子结构、化学组成、接枝密度和分子量的分子刷，并通过动态光散射（DLS）、原子力显微镜（AFM）和透射电子显微镜（TEM）等广泛的技术表征其在水中的刺激响应行为。DLS可以方便地提供不同条件下分子尺寸的原位信息；原子力显微镜和透射电镜允许直接可视化电刷分子。这些大分子与其他大分子和固体材料的相互作用的控制将通过外部刺激来证明。本研究所获得的知识将用于指导功能分子刷的设计和合成。

PART 1: NON-TECHNICAL SUMMARYMolecular 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 SUMMARYThis 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.