Designing Highly Stretchable Resilient Hydrogels

第1部分：非技术SUMMARY水凝胶被用于许多应用，包括在生物医学领域、药物配方和食品材料中。开发具有高度伸缩性和弹性的水凝胶可以开辟这些材料的更多应用，例如在人造肌肉、假肢设备中，以帮助行动受限的个人、能量收集和软机器人的功率放大过程。生物弹性体蛋白质，如resilin，表现出高的延伸性和弹性，但由合成单体制备的含水聚合物网络通常不表现出这样的特性。生物弹性体蛋白质的高延伸性和弹性归因于由亲水和疏水片段的存在而产生的熵和热弹性的平衡组合。在拟议的研究中，受这些生物聚合物的启发，将使用一种简便的化学合成路线来合成具有亲水性和疏水性的水凝胶。本项目将开发和实施的合成策略和表征技术将适用于其他软材料。由于该项目的跨学科性质，拟议的研究将影响许多学科，即聚合物科学、物理、机器人和生物学。除了本科生和研究生直接参与拟议的研究活动外，教育和推广部分还将包括实验室演示和K-12学生积极参与研究活动，目的是向他们介绍聚合物科学和工程，并鼓励他们对STEM感兴趣。 第2部分：技术总结在本项目中，将研究由疏水和疏水成分组成的水凝胶的弹性来源和性质。特别是，本项目所考虑的水凝胶将通过丙烯酸(AAc)、甲基丙烯酰胺(MAAM)和聚丙二醇二丙烯酸酯(PPGDA)的自由基聚合来获得。PPGDA在室温下溶于水，具有疏水嵌段的作用。这些嵌段的倍数可以结合在一起，在这些凝胶中形成疏水结构域。生成的水凝胶具有高度的可伸缩性和弹性，并且在从拉伸状态释放时可以获得非常高的回缩速度。有人假设，在拉伸过程中，亲水嵌段表现出熵弹性，而疏水结构域的解离、折叠的聚丙二醇嵌段在水介质中的解离和拉伸将产生显著的热罚。与在蛋白质弹性体中观察到的类似，热弹性和熵弹性的平衡将使水凝胶变得僵硬、可拉伸和有弹性。然而，将这些水凝胶的结构和性质联系起来的基本了解尚不清楚。在计划中的研究中，将通过系统地改变单体浓度、疏水含量、疏水嵌段分子量和溶剂质量或温度来解决这一问题。这些条件的变化可能会导致凝胶结构的变化，然后这将与凝胶特性，特别是延伸性和弹性联系在一起。系统的理解将导致建立从合成聚合物合成可伸缩和有弹性的水凝胶的设计原则。该奖项反映了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。

PART 1: NON-TECHNICAL SUMMARYHydrogels are being used in many applications including in the biomedical field, pharmaceutical formulations, and food materials. Developing highly stretchable and resilient hydrogels could open up additional applications of these materials, for example in artificial muscles, in prosthetic devices towards assisting individuals with restricted mobility, energy harvesting, and enabling power amplification process in soft-robots. Biological elastomeric proteins such as resilin display high stretchability and resilience, but water-containing polymer networks prepared from synthetic monomers typically do not display such properties. High stretchability and resilience in biological elastomeric proteins have been attributed to the balanced combination of entropic and enthalpic elasticity originating from the presence of hydrophilic and hydrophobic segments. In the proposed research, taking inspiration from these biopolymers, hydrogels with hydrophilic and hydrophobic contents will be synthesized using a facile chemical synthesis route. The synthesis strategy and characterization techniques that would be developed and implemented in this project will be applicable to other soft materials. Because of the cross-disciplinary nature of the project, the proposed research will impact many disciplines viz., polymer science, physics, robotics, and biology. In addition to the direct involvement of undergraduate and graduate students in the proposed research activities, the educational and outreach component will also include laboratory demonstrations and active involvement of K-12 students in research activities with the goal of introducing them to polymer science and engineering and encouraging interest in STEM. PART 2: TECHNICAL SUMMARYIn this project, the origin and nature of elasticity in hydrogels consisting of both hydrophilic and hydrophobic components will be investigated. Particularly, the hydrogel considered for this project will be obtained by using free-radical polymerization of acrylic acid (AAc), methacrylamide (MAAm), and polypropylene glycol diacrylate (PPGDA). PPGDA is sparsely soluble in water at room temperature and will act as a hydrophobic block. Multiples of those blocks can associate to form hydrophobic domains in these gels. The resultant hydrogel is highly stretchable, resilient, and can achieve very high retraction velocity when released from a stretched state. It has been hypothesized that during stretching, the hydrophilic blocks display entropic elasticity, whereas dissociation of the hydrophobic domains, unwinding and stretching of the collapsed polypropylene glycol blocks in the aqueous media will have a significant enthalpic penalty. Similar to that observed in protein elastomers, a balance in enthalpic and entropic elasticity will render a hydrogel stiff, stretchable, and resilient. However, a fundamental understanding linking the structure and properties of these hydrogels is not clearly available. In the planned research, such will be addressed by systematically varying the monomer concentrations, hydrophobic content, hydrophobic block molecular weight, and solvent quality or temperature. Variation of these conditions will likely lead to the change in gel structure, which will then be linked to gel properties, particularly stretchability and resilience. A systematic understanding will lead to establishing design principles for synthesizing stretchable and resilient hydrogels from synthetic polymers..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.