Formation of porous hydrogels by self-assembly of photo-cross-linkable triblock copolymers in the presence of homopolymers

Abstract

Hydrogels with average pore sizes ranging from 10−2–103 μm were prepared using photo-cross-linkable self-assembling amphiphilic triblock copolymers based on poly(ethylene oxide) (PEO) mixed with homopolymers of dextran or PEO. Above a critical concentration, the triblock copolymers self-assembled into a transient network, which could be rendered permanent by UV-irradiation. Phase separation occurred for mixtures with either homopolymer above a critical concentration, which was arrested by UV-irradiation before it became macroscopic. The morphology of the hydrogels was probed by confocal laser scanning microscopy or light scattering, whereas their mechanical properties were studied using oscillatory shear measurements. The porosity of the hydrogels could be varied over orders of magnitude depending on the conditions. Hydrogels with pore sizes below 1 μm were obtained in the single phase regime, whereas gels with larger pore sizes could be obtained by irradiating phase separating mixtures. Microphase separation also led to an increase of the elastic modulus of the hydrogels.