Phase Crosslinking Strategy to Construct Impact-Resistant and Buffer-Enhanced Bilayer Hydrogels with High Interfacial...

Area of Science:

• Materials Science
• Biomimetics
• Polymer Chemistry

Background:

• Developing advanced composite materials with integrated soft and hard components is crucial for applications requiring both structural integrity and energy absorption.
• Mimicking natural structures, like the exoskeleton and tissues of crustaceans, offers a promising design strategy for novel materials.

Purpose of the Study:

• To develop a novel bilayer gel with high interfacial adhesion, combining rigidity and cushioning properties.
• To establish a versatile platform for fabricating gradient materials with controlled concentration profiles.
• To demonstrate the potential of this material in biomechanical applications, such as impact protection.

Main Methods:

• A stepwise solid-liquid phase crosslinking strategy using polyvinyl alcohol (PVA) solutions was employed.
• Partial thawing of a prefrozen high-concentration PVA gel allowed for molecular chain interpenetration with a subsequently cast low-concentration PVA solution.
• Freeze-thaw cycles, controlled molecular penetration, and salt-induced crystallization (1 M Na2SO4) were utilized to enhance interfacial adhesion and rigidity.

Main Results:

• A bilayer gel with high interfacial adhesion (1060 ± 40 J m⁻²) was successfully fabricated.
• The rigid layer exhibited a compressive modulus of 1493 ± 94 kPa at 50% strain, while the soft layer provided energy dissipation.
• The fabrication method allowed for programmable gradient control, independent of gravity, enabling unidirectional or multidimensional concentration gradients.
• A helmet-like structure demonstrated effective impact resistance and shock absorption.

Conclusions:

• The developed strategy provides a universal platform for constructing complex soft-hard composites via interfacial molecular entanglement and crystallization.
• This approach addresses challenges in gradient material fabrication for diverse biomechanical applications.
• The gravity-independent gradient control and dual-phase integration mechanism offer new avenues for designing multifunctional biomimetic materials.