Tough stimuli-responsive supramolecular hydrogels with hydrogen-bonding network junctions

Area of Science:

• Materials Science
• Polymer Chemistry
• Biomaterials Engineering

Background:

• Hydrogels are water-swollen polymer networks with diverse applications.
• Developing hydrogels with enhanced mechanical properties and stimuli-responsive behavior is crucial for advanced materials.

Purpose of the Study:

• To synthesize and characterize novel hydrogels utilizing specific hydrogen-bonding units for physical cross-linking.
• To investigate the influence of polymer architecture and cross-link density on hydrogel mechanical properties.
• To explore the potential for shape memory behavior in these hydrogel systems.

Main Methods:

• Synthesis of segmented amphiphilic macromolecules with 2-ureido-4[1H]-pyrimidinone (UPy) hydrogen-bonding units and poly(ethylene glycol) (PEG) segments.
• Cryo-electron microscopy to confirm nanoscopic physical cross-links and microphase separation.
• Mechanical testing to evaluate strength, resilience, and the effect of PEG chain length.
• Differential scanning calorimetry to study thermal transitions and their relation to shape memory.

Main Results:

• Hydrogels formed stable nanoscopic physical cross-links via UPy-UPy dimers within hydrophobic domains.
• Materials exhibited high water content (w(H2O) ≈ 0.8) and tunable mechanical properties based on PEG chain length.
• The hydrogels demonstrated significant strength and resilience due to the microphase-separated network structure.
• Poly(ethylene glycol) melting transition was identified as an effective stimulus for shape memory behavior.

Conclusions:

• The UPy-crosslinked PEG hydrogels offer a robust platform for creating tough, resilient, and stimuli-responsive materials.
• The synthetic strategy allows for tunable mechanical properties and facile processing.
• These hydrogels show promise for applications requiring high performance and adaptive capabilities, including shape memory materials.