Bijels-derived hydrogel hybrid membranes for medical applications

Abstract

Bicontinuous interfacially jammed emulsion gels (bijels) are new structures discovered recently. They are composed of two interwoven networks, with each being a liquid-phase material that is immiscible with the other. Bijels can be solidified through processes such as polymerization, resulting in materials with bicontinuous structures. Since distinctive release behaviors of bio-agents with different functions from the same carrier are often required in the biomedical field, the bicontinuous architectures make bijels-derived materials very attractive for applications such as controlled release in tissue engineering. Traditionally, bijels are made via thermal quenching. However, this technique can be applied only to certain pairs of liquids and delicately prepared colloids with relatively low thermal stability. The batch process of thermal quenching also limits the potential of bijels. Solvent transfer-induced phase separation (STRIPS), which provides a facile way to continuously fabricate bijels in various shapes (particles, fibers and films) with high thermal stability, thus becomes very appealing. A major issue for applying bijels-derived materials in tissue engineering is the biocompatibility of most of current bijels systems. To make bijels-derived materials useful in tissue engineering, biocompatible hydrogels may be used in bijels systems. In this study, the fabrication of biocompatible hydrogel hybrid membranes via bijels using the STRIPS technique was investigated. To produce bijels structures, a ternary liquid mixture was made by adding ethanol, hexanedioldiacrylate (HDA), 2-hydroxy-2-methylpropiophenone, distilled water, Ludox TMA, and CTAB in ethanol (0.2 M). HCL was added to this mixture to adjust pH. A polystyrene plate was immersed in the ternary mixture for forming a mixture film on its surface. It was taken out and then immersed in a water bath (10-3 M CTAB) to form bijels film. A high-intensity UV light cured HDA monomer, solidifying the bijels structure. After curing, bijels films were immersed in Na-alginate solution, taken out and immersed in CaCl2 solution for crosslinking. The products were freeze-dried. The bicontinuous structure of bijels films (before introducing Na-alginate) could be clearly seen under SEM. This microstructure was composed of solidified HDA and liquid water. The water phase was evaporated after freeze-drying, leaving continuous channels in bijels-derived structure. The channel diameter was 3-10 µm. After adding Na-alginate and crosslinking, these channels were filled with cross-linked Ca-alginate hydrogel, leading to successful fabrication of bijels-derived hydrogel hybrid membranes. For controlled release, a bio-agent could be incorporated in Ca-alginate hydrogel. It could be released when a dilute sodium citrate solution broke down Ca-alginate. This study has demonstrated that it is feasible to produce biocompatible bijels-derived membranes for potential biomedical applications.