Study Capturing Advances in Hydrogel Technology Draws Inspiration from Nature’s Designs

The inspiration for the study on hydrogel technology comes from nature, particularly Jellyfish which are almost entirely water yet maintain a delicate balance between softness and mechanical strength.

January 2025 I By Dave DeFusco
A research team led by two UNC chemistry professors has tackled a long-standing challenge in hydrogel technology: creating materials that hold large amounts of water without losing strength. Their findings, published in the Advanced Functional Materials study, “Bottlebrush Hydrogels with Hidden Length: Super-Swelling and Mechanically Robust,” could have significant applications in agriculture, water purification and biomedicine.
Hydrogels are celebrated for their unique combination of softness, elasticity and high water retention. These properties make them indispensable in diverse fields, from wound healing and drug delivery to water filtration and soil hydration. However, the very trait that makes hydrogels desirable—their ability to absorb large amounts of water—often leads to brittleness, limiting their practical utility.
“Enhancing the mechanical resilience of hydrogels has traditionally come at the expense of their softness and swelling capacity,” said Dr. Sergei Sheiko, George A. Bush, Jr. Distinguished Professor, who co-authored the study with Dr. Andrey Dobrynin, Mackenzie Distinguished Professor, “creating a trade-off that has frustrated scientists for decades.”
The research team’s solution lies in the innovative use of bottlebrush polymer architectures. These structures consist of a water-resistant central backbone made of poly(2-hydroxyethyl methacrylate) (PHEMA) with densely grafted water-loving side chains made of poly(2-methyl-2-oxazoline) (PMOx), resembling the bristles of a bottlebrush plant. This design prevents the chains from getting tangled, which is a common problem in regular hydrogels, and adds hidden length reservoirs that allow the material to stretch more and become stronger while preserving the tissue-like softness.

“This combination of features is unique in synthetic hydrogels,” said Dr. Sheiko.
The inspiration for this work comes from nature. Jellyfish, for instance, are almost entirely water yet maintain a delicate balance of softness and mechanical strength. This is achieved through the hierarchical organization of collagen scaffolds, which provides strain-stiffening behavior and resilience. The bottlebrush hydrogels mimic this natural architecture by incorporating hidden length reservoirs within their backbone. These reservoirs allow for uniform stress distribution during deformation, enhancing the material’s extensibility and toughness.
The key to the bottlebrush hydrogel’s performance lies in its unique structure:
- Hidden Length Reservoirs: The hydrophobic PHEMA backbones form microphase-separated domains within the hydrogel. These domains of coiled and aggregated backbones act as hidden length reservoirs, unraveling under stress to dissipate energy and prevent fracture.
- Hydrophilic Side Chains: The PMOx side chains create a strong hydration shell, promoting water uptake and softness. The interplay between backbone aggregation and side chain hydration enables the hydrogel to achieve high swelling ratios, up to 125, while maintaining mechanical integrity.
- Modular (Programmable) Design: By systematically varying the cross-linking density, side chain length and grafting density, the researchers could fine-tune the hydrogel’s mechanical and swelling properties to meet specific application needs.
The study’s findings reveal that these bottlebrush hydrogels outperform conventional hydrogels , with a modulus comparable to soft tissues like the brain and extracellular matrix; and despite their softness, the hydrogels can endure up to tenfold elongation, a feat unmatched by existing materials.
“The development of bottlebrush hydrogels marks a significant step forward in materials science,” said Dr. Dobrynin. “By overcoming the long-standing trade-off between softness, swelling and strength, the study’s findings advance our understanding of polymer networks that draw inspiration from nature’s designs.”