Size Dependent Mechanical Properties for Elastic Polymer Gels

该项目由材料研究部的聚合物计划和土木，机械和制造创新部的材料力学计划支持，将开发超软材料机械性能的基础知识。主要目标将是实验研究尺寸尺度对超软材料实现大应变、弹性机械响应的影响。 具有这些属性的超软材料对于从保护装置到组织工程的许多应用都很重要。 最近，许多模拟天然存在的凝胶的新型聚合物，如节枝弹性蛋白，已经证明取得了一些成功，但这些聚合物通常是复杂的，并且可能难以实际实施。通过了解超软材料在小尺寸尺度下的机械性能，可以找到一种替代策略。 这种策略是由金属和陶瓷的一个众所周知的属性，大小可以影响机械负载下的缺陷的敏感性。 因此，在小尺寸尺度上制造的金属和陶瓷可以显示出非凡的机械性能。 对于超软材料，这些效应尚未通过实验测量。在所提出的研究中，标度关系提供了指导性假设，预测溶胀聚合物网络的大应变可逆变形的优化尺寸尺度的存在。 这些假设将使用标准和新的表征方法对两种不同的凝胶材料进行实验证实。这项研究的结果将导致新的表征方法和理解的合成凝胶和活组织，以及新的材料策略，创造超软材料，可以实现高应变，高强度，高弹性。非技术总结：超软材料是有吸引力的许多技术，从防护装备到组织工程。 目前，这些材料要么很脆，不允许它们伸展得很远，要么它们能够通过耗散能量伸展得很远，类似于橡皮泥的工作方式。 最近的努力集中在创造新的聚合物，模仿生物蛋白质的结构和性质，如节枝弹性蛋白。 然而，这些新材料是复杂的并且可能难以实际实施。 克服这些挑战的一种可能的策略是利用小尺寸尺度下的预测机械性能增强。 众所周知，金属和陶瓷在相对于其分子尺寸尺度的小尺寸尺度上显示出改善的机械性能;然而，尚未对超软材料进行类似的实验研究。 拟议的研究将通过实验研究小尺寸超软材料的机械性能，以实现高应变，高强度和高弹性。预计所吸取的经验教训将影响新保护装置的开发;影响包括活组织在内的软材料的表征;并引发与软生物组织（如大脑）创伤性损伤相关的新问题。 此外，将开发一个关于生物启发材料设计的创新研讨会项目，以激励来自不同背景的高中生追求未来的科学和工程职业。该计划将使学生和公众在西马萨诸塞州认识到材料和力学研究的重要性，创造力在科学和工程发现的作用，以及当没有基本原则的情况下使用生物灵感时出现的困难。

TECHNICAL SUMMARY:This project, supported by the Polymers Program of the Division of Materials Research and the Mechanics of Materials Program of the Division of Civil, Mechanical, and Manufacturing Innovation, will develop fundamental knowledge of mechanical properties for ultra-soft materials. The primary goal will be to experimentally investigate the effect of size scale on achieving large strain, resilient mechanical responses in ultra-soft materials. Ultra-soft materials with these attributes are important for numerous applications, from protective devices to tissue engineering. Recently, many novel polymers which mimic naturally-occurring gels, such as resilin, have been demonstrated with some success, but these polymers are often complex and potentially difficult to implement practically. An alternative strategy may be found by understanding the mechanical properties of ultra-soft materials at small size scales. This strategy is motivated by a well-known property for metals and ceramics that size can influence the sensitivity to defects under mechanical loading. Thus, metals and ceramics fabricated on small size scales can display extraordinary mechanical properties. For ultra-soft materials, these effects have not been experimentally measured. In the proposed research, scaling relationships provide guiding hypotheses that predict the existence of optimized size scales for large strain reversible deformations for swollen polymer networks. These hypotheses will be experimentally confirmed using standard and novel characterization methods on two different gel materials. The results of this research will lead to new characterization methods and understanding for both synthetic gels and living tissues, as well as new materials strategies for creating ultra-soft materials that can achieve high strains, high strength, and high resiliency.NON-TECHNICAL SUMMARY:Ultra-soft materials are attractive for many technologies, from protective gear to tissue engineering. Currently, these materials are either brittle, not allowing them to stretch very far, or they are able to stretch far by dissipating energy, similar to the way Silly Putty works. Recent efforts have focused on creating new polymers that mimic the structure and properties of biological proteins, such as resilin. However, these new materials are complex and may be difficult to implement practically. One possible strategy for overcoming these challenges is to take advantage of predicted mechanical property enhancements at small size scales. It is well known that metals and ceramics display improved mechanical performance on small size scales relative to their molecular size scale; however, similar experimental investigations have not been conducted on ultra-soft materials. The proposed research will experimentally investigate the mechanical properties of ultra-soft materials at small sizes to achieve high strains, high strength, and high resiliency. The lessons learned are anticipated to impact the development of new protective devices; to influence the characterization for soft materials including living tissues; and to provoke new questions related to traumatic damage in soft biological tissues, such as the brain. In addition, an innovative workshop program on Bioinspired Materials Design will be developed to inspire high school students from diverse backgrounds to pursue future careers in science and engineering. This program will allow students and the general public in Western Massachusetts to realize the importance of materials and mechanics research, the role of creativity in scientific and engineering discovery, and the difficulties that arise when bioinspiration is used without foundational principles.