CAREER: Mechano-Adaptive Polymers with Reversible Strain Stiffening and Softening via Active Control of Metal-Ligand Interactions

非技术总结合成聚合物的机械和弹性特性是它们在现代生活中变得无处不在的原因之一。然而，相比之下，生物材料表现出无与伦比的动力学和复杂的力学行为。这促使材料科学家和工程师多年来一直在推动合成聚合物的极限，以接近生物材料的功能。这个项目的灵感来自生物细胞的力学。肌动蛋白在支持细胞机械完整性方面起着重要作用，在机械应力作用下表现为先变硬后变软。加强保护细胞免受最初的冲击，而软化防止灾难性的骨折。这些机械反应是完全可逆的。赋予合成聚合物“硬化-软化”的机械可逆性，将实现前所未有的机械适应，并使材料能够主动调整其形状和硬度，以响应机械环境，变得耐低和高冲击。这些特性还没有在合成聚合物中实现。因此，该项目旨在开发具有定制结构和分子相互作用的聚合物材料，以实现类似的力学性能。这一结果将促进人们对复杂分子网络非线性机制控制的有限认识。它将为模拟机械生物学的材料具有力调节的传感、信号和变形功能奠定基础。该项目将与以虚拟现实(VR)演示为中心的战略教育和外联计划相结合，以吸引不同的学生群体，并促进内华达州北部的聚合物科学教育。技术综述与合成聚合物相比，生物材料表现出无与伦比的动力学和复杂的力学行为。具有可调非共价键的超分子聚合物提供了弥合这一差距的机会。人们已经进行了深入的研究，以阐明材料性质、聚合物结构和缔合基团特征之间的相互依赖关系。然而，利用机械力对缔合键的动力学进行主动控制的研究还很少。因此，本项目将通过重点研究在非平衡状态下机械扰动过程中粘贴动力学的变化来阐明该动态参数的使用，以获得响应网络的复杂的非线性粘弹性。令人感兴趣的非线性机制是活细胞的“硬化-软化悖论”。它们在低应变下变硬以抵抗初始冲击，在高应变下软化以防止灾难性断裂，并在卸载后恢复其原始形状，代表其力学性能根据周围环境的动态调整。该项目计划开发一种包含定制的非共价键的无溶剂聚合物，其缔合相互作用可以在由线性-瓶刷-线性三嵌段共聚物组装的多组分系统中随力主动调整。每个组件将提供互补的特性，以实现复杂的非线性力学。这项研究将解决基本问题，即不同的结构部件如何在一定的力范围内独立地主导宏观粘弹性，以及它们的耦合效应何时成为主导。将使用合成方法和机械和光谱表征方法相结合的方法来探索它们之间的相互作用。了解多组分系统之间的相互作用将成为模拟生物材料的跳板，生物材料依赖于多组分层次结构来优化生命功能。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYThe mechanical and elastic properties of synthetic polymers are one reason why they have become ubiquitous in modern life. However, comparatively, biomaterials exhibit unmatchable dynamics and complex mechanical behaviors. This has motivated materials scientists and engineers for years to push the limit of synthetic polymers to approach the functionalities of biomaterials. This project is inspired by the mechanics of biological cells. Actin, which plays an important role in supporting cell mechanical integrity, shows stiffening followed by softening under mechanical stress. The stiffening protects the cell from initial impact while the softening prevents catastrophic fracture. These mechano-responses are fully reversible. Imparting this mechanical reversibility of “stiffening-softening” to synthetic polymers will enable unprecedented mechano-adaptation and allow the materials to actively adjust their shape and stiffness in response to the mechanical environment, becoming resistant to both low and high impacts. These properties have not been realized in synthetic polymers. As such, this project aims to develop polymeric materials with tailored structures and molecular interactions to achieve similar mechanics. The results will advance the limited understanding of controlling the nonlinear mechanics of complex molecular networks. It will set the stage toward materials that emulate mechanobiology to have force-regulated sensing, signaling, and morphing functionalities. The project will be integrated with strategic education and outreach plans centered on virtual reality (VR) demonstrations to engage a diverse group of students and promote polymer science education in Northern Nevada. TECHNICAL SUMMARYBiomaterials exhibit unmatchable dynamics and complex mechanical behaviors compared to synthetic polymers. Supramolecular polymers with tunable noncovalent bonds provide an opportunity to bridge this gap. Intensive research has been conducted to elucidate the interdependencies of material properties, polymer architectures, and the characteristics of the associative groups. However, active control of the dynamics of the associative bonds by mechanical force is still understudied. Thus, this project will elucidate the use of this dynamic parameter by focusing on the change of sticker kinetics during mechanical perturbation in a nonequilibrium state, in order to access the complex nonlinear viscoelasticity for responsive networks. The nonlinear mechanics of interest is the “stiffening-softening paradox” of living cells. They stiffen under low strains to resist the initial impact, soften at high strains to prevent catastrophic fracture, and recover their original forms upon load removal, representing dynamic adjustments of their mechanical property according to the surrounding environment. The project plans to develop a solvent-free polymer that contains tailored noncovalent bonds, whose associative interactions can be actively adjusted with force in a multi-component system assembled from linear-bottlebrush-linear triblock copolymers. Each component would provide complementary properties to realize complex nonlinear mechanics. This study will address the fundamental question as to how different structural components independently dominate the macroscopic viscoelasticity in certain force ranges, and when their coupled effects become dominant. A combination of synthetic approaches and mechanical & spectroscopic characterization methods will be used to probe their interactions. Understanding the interplay between multi-component systems will serve as a springboard to emulate living materials, which rely on multi-component hierarchical structures to optimize living functions. .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.