Size Dependent Mechanical Properties for Elastic Polymer Gels

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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.