CAREER: Mechanics of Fluid-Saturated Soft Materials Under Externally Applied Stress Fields

This Faculty Early Career Development Program (CAREER) award will advance the fundamental understanding of how soft elastic materials behave when they contain an internal fluid that can move, reorganize, and separate into distinct phases within the solid network. Fluid-saturated soft solids arise in a wide range of engineered and natural systems, including hydrogels, solid–liquid composites, biological tissues, and geological media. When these materials are subjected to mechanical loading, the embedded fluid can redistribute, interact with the surrounding elastic matrix, and in some cases undergo phase separation, thereby strongly influencing stiffness, stability, and resistance to failure. Despite their prevalence in both natural and technological contexts, the coupled relationship between mechanical deformation and fluid organization remains poorly understood, particularly when large deformations and evolving microstructures are involved. This project addresses this critical knowledge gap by developing a predictive framework that captures the two-way coupling between mechanical response and fluid organization in soft materials. In addition to advancing fundamental science, the knowledge generated through this research will support the design of next-generation soft composite materials, flexible biomedical implants, engineered tissue scaffolds, and emerging materials for energy storage. This CAREER award will also support an integrated educational program that strengthens the domestic Science, Technology, Engineering, and Mathematics pipeline through middle-school outreach, undergraduate research experiences in soft matter, and the integration of research discoveries into undergraduate and graduate curricula, while training students in modern computational and theoretical tools. The CAREER project will support research aimed at establishing a predictive theoretical and computational framework for the mechanics of fluid-saturated soft solids subjected to external stresses. The central objective is to develop a continuum modeling approach that captures the interplay between finite-strain elasticity, fluid transport, and thermodynamic phase stability in deformable porous networks. To achieve this goal, a phase-field formulation will be developed to describe how internal and external stresses drive fluid migration, alter phase boundaries, and control microstructural evolution within the solid matrix. The framework will enable systematic investigation of regimes that remain largely unexplored, including materials containing moderate to large fluid volume fractions where elastic interactions among fluid-rich domains become significant, as well as phase instabilities that generate droplets, bicontinuous morphologies, and stress-driven structural transitions. The models will be implemented within a finite-element computational framework and validated through analytical benchmarks, numerical verification, and comparison with existing experimental observations. Building on these predictive simulations, the project will further develop a machine-learning–assisted inverse-design capability that identifies material parameters and loading protocols capable of producing targeted internal microstructures, thereby providing a general pathway for the rational design of fluid-saturated soft materials with tailored mechanical and functional properties. 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. NSF Award ID: 2543637 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Mrityunjay Kothari | Institution: University of New Hampshire, DURHAM, NH | Award Amount: $635,061 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2543637 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2543637.html