Strength enhanced hydrogels constructed from agarose in alkali/urea aqueous solution and their application

As a breakthrough to the traditional method of dissolving with heat, agarose aqueous solution was successfully obtained in alkali/urea system via freezing/thawing for the first time. The agarose dissolution was a physical process, proved by 13C NMR. The results of dynamic light scattering and atomic force microscopy demonstrated that agarose existed as extended chains in the solution and easily aggregated in parallel to form nanofibers. The viscosity and rheology measurements indicated that the agarose solution exhibited higher stability at room temperature than that traditionally dissolved in hot water, favoring the processing of agarose to fabricate various materials. Moreover, the new agarose hydrogels were fabricated directly from the agarose solution, showing more homogenous structure, enhanced thermal stability and mechanical properties than that prepared by hot water. The compression fracture stress of the agarose hydrogels was 3.7 times of that by hot water, as a result of the reinforcement by the nanofibers, leading to greater applicability. Furthermore, the agarose hydrogels displayed excellent biocompatibility, showing potential applications in wider fields. Especially, the agarose hydrogel exhibited effective germination and growth for the use as soilless culture medium, superior to the hydrogel prepared by hot water. This work provided not only new insights of dissolving agarose with cooling temperature and fabricating strength enhanced hydrogels, but also significance for the dissolution and green conversion of biomass which fits sustainable strategy about utilizing the products from agriculture and ocean.