Multiscale Mechanics of Composite Hydrogels Exposed to Shock Waves

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This grant will support research to examine the response of hydrogels to shock waves, which is not well understood. A hydrogel (e.g. Jell-O, styling gel) is a material that consists of a water soluble polymer that can swell to form an interconnected three-dimensional network. Hydrogels have also been used as surrogate material for soft biological tissue due to their similarity in mechanical properties. The passage of a shock wave through hydrogels may serve as a model for investigating blast-induced traumatic brain injury as, for example, sustained by United States’ military service members. However, characterizing the mechanical response of shocked hydrogels is first needed. The project will test the hypothesis that the energy from shock waves disrupt the hydrogel network, leading to changes in hydrogel mechanical properties. An understanding of the behavior of shocked hydrogels would aid material scientists in developing tissue surrogate materials for blast studies, along with more resilient hydrogel formulations for wearable sensor and soft robot applications. Additionally, this research project will be complemented by engaging with existing organizations such as Iowa State University’s Academic Program for Excellence and the Program for Women in Science and Engineering. Initiatives that support the recruitment and retention of underrepresented students in the field of engineering will be established through outreach activities that introduce students to topics such as rheology and biomaterials.The specific goal of the research is to fundamentally understand the effect of shock wave exposure on the bulk and microstructural properties of composite hydrogels that act as tissue simulants. Molecular dynamic simulations of shock waves in hydrogels have shown a decrease in local concentration of water, leading to changes in bulk mechanical properties. However, experimental observations of hydrogel exposure to shock waves are needed for validation. Thus, the research objectives of this project include: (1) probing hydrogel microstructure at quasistatic conditions using optical video microscopy to measure viscoelastic behavior; (2) measurement of hydrogel mechanical response before and after shock wave exposure to connect microstructural changes to modified bulk mechanical behavior; and (3) quantification of the conformational changes of hydrogel due to shock wave exposure at the microstructural level. The overarching focus will be on the use of experiments to (i) obtain a better understanding of the macrostructural and microstructural changes that hydrogels undergo when exposed to a shock wave and (ii) correlating the structural changes with viscoelasticity behavior. This project will advance knowledge in mechanics and material science, along with computational science.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.