Nonmonotonic rate-dependent adhesion of hydrogels

Area of Science:

• Materials Science
• Polymer Science
• Biomaterials Engineering

Background:

• Hydrogel adhesion is crucial for biological and engineering applications.
• The rate dependence of hydrogel adhesion is not well understood.
• Classical adhesives typically show monotonic rate dependence due to bond stress relaxation.

Purpose of the Study:

• To investigate the rate dependence of hydrogel adhesion.
• To elucidate the underlying mechanisms governing hydrogel detachment.
• To develop a quantitative model for hydrogel adhesion kinetics.

Main Methods:

• Atomic force microscopy (AFM)-based indentation across six orders of magnitude of retraction rates.
• Development of a quantitative model coupling hydrogel deformation and rate-dependent interfacial bond kinetics.
• In situ confocal microscopy to measure contact area dynamics during detachment.

Main Results:

• Hydrogel adhesion exhibits a non-monotonic rate dependence: pull-off force decreases then increases with separation rate.
• The developed model accurately reproduces the observed non-monotonic behavior and predicts contact radius evolution.
• Confocal microscopy validated the model's predictions regarding kinetic mechanisms.

Conclusions:

• Hydrogel adhesion is governed by a balance between time-dependent bond formation and limited bond relaxation.
• A novel adhesion regime in polymeric materials is identified, characterized by an intermediate rate-dependent weakening.
• Findings provide a framework for designing hydrogel interfaces with tunable rate-dependent properties.