Microfluidic production of monodisperse microgels via complexation between graphene-oxide nanosheets and poly(vinyl alcohol)

Abstract

Hydrogel is one of the most famous biocompatible hydrophilic materials. The swelling and porous characteristic are their unique properties. Microgels is defined as submicroscale of hydrogel matrix. Microgels has good responsibility and compactibility compared macro-size hydrogel. Microgels have served as biological application such as microcarriers for cell and drug as they provide fast diffusion and injectable suspension. The typical generation method of microgels is using water-in-oil emulsions containing gel procursors. These emulsions are formed hydrogel matrix by cross-linking chemical reaction. However, usually used reactions are not biocompatible due to exist of small precursor molecules or high energy of reaction triggers. In this work, we propose a highly biocompativle method for fabricating microgelss using complexation of Graphene Oxide (GO) nanosheets and Polyvinyl alcohol (PVA). We prepared water-in-oil-in-water double-emulsions using a microfluidic device. The core solution contain GO and PVA solution without any cross-linker or other small molecules. The GO sheets and PVA chains are dispersed very well at the core. When double emulsions are exposured at high osmotic pressure, water in the core was selectively pumped out. During concentration of core, GO sheets formed a nematic liquid crystalline phase and concentrated at the boundary leading to increase cross-link parts with PVA chain. The complexation of GO and PVA by hydrogen bonding generate hydrogel matrix in the core. The microgels suspended in water are stable and monodisperse size and shape. This new microfluidic strategy does not use any toxic components or high energy stimuli, just using osmotic pressure. We expect not only PVA other polymer based microgels are also fabricated through this method and this will potentially provide a useful means to various biocompatible application.