Meso-ordered soft hydrogels

Abstract

Many factors such as cross-link density are known to dictate the properties of hydrogels; however, less is known about the microstructure and how it can be tailored to control the properties. Here we demonstrate a method of forming microstructured hydrogels using a soft template that allows us to control and modify the microstructure. Meso-ordered hydrogels were formed by chemically cross-linking poly(ethylene glycol)-diacrylate (PEG-DA) segments via photopolymerization in the presence of poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) (EO_xPO_yEO_x) block co-polymers. The results showed that hydrogels with lamellar mesostructured regions were formed when high concentrations of PEG-DA segments (50%) were used in combination with block co-polymers having certain ratios of the hydrophilic and hydrophobic blocks (P123, EO₂₀PO₇₀EO₂₀). Only lamellar mesostructures were observed, independent of the PEG molecular weight (1500 or 3400 g mol⁻¹) or block co-polymer concentration (10–50%). This finding demonstrates that it is possible to form soft meso-ordered hydrogels using block co-polymers as templates, and they do not follow the same meso-phase behavior as the purely self-assembled block co-polymers.