Activity Microscopy: From single filament to bulk mechanics in biopolymer networks

我们身体的主要部分是由构成纤维网络的蛋白质组成的。这些网络完成了许多基本功能，比如为我们的皮肤提供弹性，防止它过度拉伸。因此，了解这些宏观特性是如何从网络的各个组成部分中产生的，对于我们理解基本生理过程、治疗疾病的能力以及未来设计模仿生物组织的新型材料至关重要。然而，这种理解仍然是难以捉摸的，因为缺乏实验技术，可以用单丝分辨率解决纤维网络，同时也量化它们对大规模网络的贡献。提出的研究旨在建立一种显微镜技术，可以解决每个细丝对网络整体大尺度特性的贡献。它将应用于有或没有细胞的胶原蛋白网络，以及生物人工心脏瓣膜的组织样本。提出的研究有望为材料研究人员提供更好地理解纤维生物聚合物网络中的微机械过程。这项工作可能会导致新材料的发展，用于指导细胞生长，人造皮肤和器官，以及依赖于机械应力下生物组织行为的药物递送新方法。研究生和本科生将在一个跨学科的环境中接受一种独特的最先进的仪器的培训，女高中生将参与研究，作为推广计划的一部分。这些高中生还将通过参观实验室和研究报告与大学的其他研究人员直接接触，从而受益。新型光学显微镜技术的发展和应用有望实现生物聚合物网络中从单个纤维到整体特性转变的可视化和量化。关于这类重要材料的微观力学行为的理论假设将得到检验。由于该方法有衍射限制，因此将选择比焦点尺寸大的网格。网络将被成像，沿细丝的应力分布将被量化和可视化。纤维精确分辨率将用于研究胶原蛋白凝胶中细胞的力生成。生物假体心脏瓣膜的纤维组织样本将被测试是否有退化的迹象。更详细地了解生物聚合物网络所表现出的微力学行为，为通过合理设计生物相容性和可生物降解材料来控制细胞生长和组织形成提供了新的机会。这种新的显微镜技术将使研究单丝分辨率纤维网络中细胞的力产生以及观察它们的力介导通信成为可能。对细胞外基质中细胞间的机械信号传导以及生物人工心脏瓣膜组织的退化有了新的认识。研究生和本科生将在一个跨学科的环境中学习最先进的仪器，这一领域直接有利于国家的健康和繁荣。

Non-technical summaryA major part of our body consists of proteins that form fiber networks. These networks fulfill a multitude of essential functions, such as providing elasticity to our skin and preventing it from overstretching. Understanding how these macroscopic properties arise from the networks' individual components is thus crucial to our understanding of basic physiological processes, our ability to treat diseases, and the future design of novel materials that mimic biological tissue. Such an understanding remains elusive, however, due to a lack of experimental techniques that can resolve fibrous networks with single filament resolution, while also quantifying their contribution to the large-scale network. The proposed research aims to establish a microscopy technique that can resolve the contribution of each filament to the overall large-scale properties of the network. It will be applied to collagen networks with and without cells, and to tissue samples from bioprosthetic heart valves.The proposed research is expected to provide material researchers with a better understanding of micromechanical processes in fibrous biopolymer networks. This work could result in the development of novel materials for guiding cell growth, artificial skin and organs, and new methods for drug delivery that rely on the behavior of biological tissue under mechanical stress. Graduate and undergraduate students will be trained in an interdisciplinary environment on a unique state-of-the-art instrument, and female high-school students will participate in research as part of an outreach program. These high-school students will furthermore benefit from direct contact with other researchers at the university through lab visits and research presentations. Technical summaryThe development and application of the novel optical microscopy technique is expected to result in the visualization and quantification of the transition from individual fiber to bulk properties in biopolymer networks. Assumptions made in theories about the micromechanical behavior of this important class of materials will be tested. Because the method is diffraction limited, networks with mesh sizes larger than the dimensions of the focal spot will be chosen. Networks will be imaged and the stress distribution along filaments will be quantified and visualized. The fiber-precise resolution will be used to study the force generation of cells in collagen gels. Fibrous tissue samples of bioprosthetic heart valves will be tested for signs of degeneration. The more detailed understanding of the micromechanical behavior displayed by biopolymer networks opens a new opportunity to control cell growth and tissue formation by rationally designed biocompatible and biodegradable materials. The novel microscopy technique will enable the study of force generation of cells in fibrous networks with single filament resolution, as well as the observation of their force-mediated communication. New insight into mechanical signaling between cells in the extracellular matrix is expected, as well as into the degeneration of bioprosthetic heart valve tissue. Graduate and undergraduate students will be trained in an interdisciplinary environment on state-of-the-art instrumentation in a field that directly benefits national health and prosperity.