Influence of Network Structure on the Crystallization Behavior in Chemically Crosslinked Hydrogels

Area of Science:

• Polymer Chemistry
• Materials Science
• Biomaterials Engineering

Background:

• Hydrogel properties are critically dependent on their network architecture.
• Eight-arm star-shaped poly(ethylene glycol) (8PEG) is a versatile polymer for hydrogel fabrication.
• Controlling crosslinking methods offers a pathway to tailor hydrogel morphology.

Purpose of the Study:

• To investigate the influence of crosslinking methodology on the crystallization behavior of 8PEG hydrogels.
• To compare the crystalline structures formed by photo-initiated chain-growth polymerization versus Michael addition step-growth polymerization.
• To develop a model correlating polymer network structure with hydrogel crystallization.

Main Methods:

• Synthesis of 8PEG hydrogels using two distinct crosslinking techniques: photo-initiated chain-growth polymerization (8PEG⁻UV) and Michael addition step-growth polymerization (8PEG⁻NH₃).
• Solvent drying process to prepare thin hydrogel films for analysis.
• Characterization using polarized optical microscopy (POM), scanning electron microscopy (SEM), and atomic force microscopy (AFM).

Main Results:

• 8PEG⁻UV hydrogels exhibited only nano-scaled crystallites.
• 8PEG⁻NH₃ hydrogels displayed large crystalline domains with spherulite sizes ranging from 100 to 400 µm.
• Microscopy techniques (SEM, AFM) confirmed the significant difference in crystalline domain morphology.

Conclusions:

• The crosslinking method fundamentally dictates the crystalline structure and domain size in 8PEG hydrogels.
• Michael addition polymerization promotes the formation of significantly larger crystalline structures compared to photo-initiated polymerization.
• Understanding these structure-property relationships is crucial for designing advanced hydrogel materials.