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Hyperelastic Swelling of Stiff Hydrogels
1Emory University, Department of Physics, 400 Dowman Drive, Atlanta, Georgia 30322, USA.
Physical Review Letters
|April 25, 2025
Summary
Stiff hydrogels swell when sheared, unlike softer ones that contract. This hyperelastic dilatancy, observed in polyacrylamide and polyacrylic acid, may explain tissue rehydration and rejuvenation.
Area of Science:
- Materials Science
- Polymer Science
- Biophysics
Background:
- Hydrogels are polymer networks with coupled elastic deformation and fluid flow.
- They exhibit nonlinear, hyperelastic properties and can withstand large strains.
- Low-modulus hydrogels contract when sheared over long timescales.
Purpose of the Study:
- Investigate the shear-induced behavior of stiff hydrogels.
- Characterize the poroelastic relaxation and dilatancy in these materials.
- Explore the implications of hyperelastic dilatancy in biological tissues.
Main Methods:
- Rheological and tribological measurements were employed.
- Strain-controlled compression was used to examine poroelastic relaxation.
- Normal stress and volumetric changes during shearing were quantified.
Main Results:
- Stiff hydrogels (10-100 kPa moduli) exclusively swell (dilate) when sheared.
- A volumetric diffusion constant of ~10^-9 m²/s was determined.
- Shearing induced a persistent, quadratically strain-dependent increase in normal stress.
- Tribological sliding resulted in hydrogel swelling and fluid imbibement.
Conclusions:
- Stiff hydrogels exhibit inherent, hyperelastic dilatancy under shear.
- This swelling behavior contrasts with the contraction of softer hydrogels.
- Hyperelastic dilatancy may be crucial for understanding rehydration and mechanical rejuvenation in biological tissues like cartilage.
