Stimuli-Responsive Shape-Changing Molecular Brushes

第1部分：非技术总结分子刷是一类非常长的链状分子，由聚合物主干和密集连接的辅助分子组成，因此整个分子组装看起来像刷子。它们的尺寸和形状由主链和侧链长度以及侧链与自身和环境的相互作用决定。这些巨大的分子表现出耐人寻味的特性，在人体内被发现执行各种功能，包括关节润滑、肺清除和细胞信号传递。该项目将设计、合成、开发和详细研究分子刷，这些分子刷可以在水中改变其大小和形状，以响应环境变化和刺激。它们将被设计成模仿我们体内一种名为von Willebrand因子的天然蛋白质的行为，这种因子会导致我们的血液在受伤部位凝结，从而停止出血。这些大分子的合成策略、性质和基础知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。它为培养下一代科学家(博士后研究人员、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。第二部分：技术总结本项目旨在合成和研究在外部刺激作用下可以显示可控大小和形状变化的分子刷。它的行为受到von Willebrand因子的启发，von Willebrand因子通过从非粘性可溶球状解体为延伸的纳米物体，暴露出大量结合位点，在损伤部位形成凝块，从而使血液凝结以应对损伤。具体地说，该研究计划将开发利用最先进的聚合物合成技术来制备响应性分子刷的一般策略，研究在刺激引发的分子尺寸、构象和水溶液中的形状的变化，并阐明各种分子参数对刺激响应性的影响。将制备一系列具有不同分子结构、化学组成、接枝密度和相对分子质量的分子刷，并利用动态光散射(DLS)、原子力显微镜(AFM)和透射电子显微镜(TEM)等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现场信息；AFM和TEM允许直接显示刷子分子。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演示。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.