Substrate effect on the formation of hydrogels with heterogeneous network structure

Area of Science:

• Polymer Chemistry
• Materials Science
• Surface Science

Background:

• Aqueous polymerization on hydrophobic substrates leads to interfacial heterogeneity.
• This phenomenon, termed the "substrate effect," impacts hydrogel properties.

Purpose of the Study:

• To investigate the influence of hydrophobic substrates on hydrogel formation and properties.
• To elucidate the underlying mechanisms of the observed substrate effect.

Main Methods:

• Polymerization of vinyl monomers on various hydrophobic (polytetrafluoroethylene, polypropylene, polyethylene, polystyrene, polyvinylchloride) and hydrophilic substrates.
• Characterization of hydrogel surface properties: swelling, friction coefficient, elastic modulus, interfacial adhesion, and cell interaction.
• Development and application of novel optical methods: electric speckle pattern interferometry (ESPI) and real-time laser sheet refraction (RT-LSR).

Main Results:

• Hydrophobic substrates induced heterogeneity at the polymerization interface, unlike hydrophilic substrates.
• Hydrogels synthesized on hydrophobic substrates exhibited increased swelling, reduced friction, lower elastic modulus, weaker adhesion, and decreased cell interaction.
• These property changes correlated with a loosely cross-linked architecture and graft-like polymer chains at the surface.
• Oxygen trapped at the monomer solution-substrate interface was identified as a key factor in the substrate effect.

Conclusions:

• The substrate effect significantly alters hydrogel properties due to changes in polymer architecture at the interface.
• Novel optical techniques (ESPI, RT-LSR) provide insights into the polymerization mechanism.
• Understanding and controlling the substrate effect is crucial for designing hydrogels with tailored surface properties for specific applications.