Advancing Processability and Material Performance of Synthetic Polyamino Acids with Transformable Secondary Structures

非技术总结：许多生物材料的性质和性能取决于其组成分子的结构和组织，这些分子可以是螺旋或片层的形式。有趣的是，纤维状蛋白质从螺旋到片状的动态转变促进了强度、刚度和能量耗散能力的显著增加。先进和多样化的材料性能可以通过非常简单的结构块及其转换来实现，这一事实激励研究人员开发基于相同概念的新聚合物材料。聚氨基酸（PAA），也称为合成多肽，可以采用类似的结构。然而，在高分子量（MW）的固体PAA中诱导结构转变在很大程度上是未满足的挑战。因此，许多PAA材料要么具有差的热机械性能，要么与聚合物加工技术如挤出和压缩成型不相容。该项目旨在开发一种通用策略，通过利用PAA的亚稳，可转化结构和控制其原位转变和分级组织，显着改善合成PAA的热机械性能和加工性能。该研究的成功完成将打破溶液工艺的限制，并使用标准聚合物加工技术在熔体中制备新的PAA材料，用于大规模生产具有形态和性能控制的薄膜/棒材/纤维。研究生和本科生将接受生物启发聚合物材料的培训，并获得聚合物合成，材料表征，力学和计算机模拟方面的技能。该计划将把研究融入新的和现有的课程，促进跨学科教育和高质量的研究经验，并通过讲座和研讨会为公众展示材料研究的应用。技术概要：高分子量PAA是由氨基酸N-羧酸酐单体开环聚合而成的多肽模型体系，可形成稳定的α-螺旋或β-折叠结构。近年来，随着活性协同聚合等策略的发展，具有复杂结构和可控分子结构的聚丙烯酸已被大规模、高收率、高纯度地合成。尽管如此，由纤维蛋白质制成的结构生物材料具有更先进的材料性能，并且它们具有比有机对应物更多样化的机械行为。借助关于如何合成能够从α-螺旋转化为β-片层的PAA共聚物的新知识，计划中的研究旨在提高固体PAA材料的机械性能和加工性能。控制有序的二级结构的PAA，其原位转化和分级组织在固态是本研究的核心。精心设计的含有可转化二级结构的PAA共聚物将用于制备硬热固性材料、半硬应变硬化材料和在低应力下柔软但具有高拉伸强度和延展性的材料。该项目的发现可能使聚合物系统的产生接近自然界一些生物材料中发现的复杂性和多功能性水平。该研究还提供了具有内在二级结构的合成聚合物的模型系统，其中分子内和分子间网络的不同划分决定了材料的宏观性质，该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的评估来支持。影响审查标准。

NON-TECHNICAL SUMMARY:The properties and performance of many biological materials rely on the structures and organization of their constituent molecules, which can be in the form of helices or sheets. Interestingly, dynamic transition from helices to sheets in fibrous proteins facilitates a remarkable increase in the strength, stiffness, and energy dissipation capacity. The fact that advanced and diverse material performance can be achieved by remarkably simple structural blocks and their transformations has inspired researchers to develop new polymeric materials based on the same concept. Polyamino acids (PAAs), also known as synthetic polypeptides, can adopt analogous structures. However, inducing the structural transitions in the solid PAA of high molecular weights (MWs) is a largely unmet challenge. As a result, many of the PAA materials either have poor thermomechanical properties or are incompatible with polymer processing techniques such as extrusion and compression molding. This project aims to develop a general strategy to significantly improve the thermomechanical properties and processability of synthetic PAAs by taking advantage of metastable, transformable structures of PAAs and control over their in-situ transition and hierarchical organization. Successful completion of the research will break the constraint of solution process and prepare new PAA materials in the melt for large-scale production of films/bars/fibers with morphological and properties control, using standard polymer processing techniques. Graduate and undergraduate students will be trained on bioinspired polymeric materials and acquire skills in polymer synthesis, material characterization, mechanics, and computer simulations. The program will integrate the research into the new and existing course, promote interdisciplinary education and high-quality research experiences, and demonstrate the application of materials research through lectures and workshops for the public. Emphasis will be given to involving underrepresented students at all levels.TECHNICAL SUMMARY:Prepared by ring-opening polymerization of amino acid N-carboxyanhydride monomers, high-MW PAAs are polypeptide model systems that form stable alpha-helix or beta-sheet structures. With the recent development of living cooperative polymerization and other strategies, PAAs with complex architectures and controlled molecular structures have been synthesized on large scales at high yield and purity. Still, structural biological materials made from fibrous proteins have far more advanced material performance, and they have more diverse mechanical behaviors than their organic counterparts. Equipped by a new knowledge on how to synthesize PAA copolymers capable of transforming from alpha-helices to beta-sheets, the planned research seeks advancements in the mechanical properties and processability of solid PAA materials. Control over ordered secondary structures of PAAs, their in-situ transformation and hierarchical organization in the solid state are central to this study. Carefully designed PAA copolymers containing transformable secondary structures will be utilized to make hard thermoset materials, semi-hard strain-stiffening materials, and materials that are soft at low stress but have high tensile strength and extensibility. The findings from this project may enable the generation of polymeric systems that will approach the level of sophistication and versatility found in some of nature’s biomaterials. The research also provides a model system of synthetic polymers with intrinsic secondary structures in which the different partitioning of intramolecular and intermolecular networks determines the macroscopic properties of materials, enabling comparison of the experimental results with predictions from simulations and modeling.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.