Formation of supramolecular hydrogel microspheres via microfluidics

Supramolecular hydrogel microspheres are hydrogel particles formed by the self-assembly of hydrogelators in water, through non-covalent interactions. In this paper, we provide a novel strategy to prepare supramolecular hydrogel microspheres with diameters ranging from 15 to 105 microns by using microfluidics. Since the gelation temperature is ca. 64 °C, the aqueous solution containing the hydrogelator was initially set at 70 °C so the liquid mixture can be pumped into the microfluidic device. The hydrogelator solution then pinches off into uniform micron size droplets at the narrow orifice of the microfluidic device. While traveling downstream in the microchannel, the self-assembly process occurs inside the droplets and the droplets solidify into microsphere gels when the temperature drops to ca. 64 °C and below. Optical and scanning electron microscopy (SEM) demonstrate that compact, entangled, round, cage-like aggregates of hydrogelator were formed within the supramolecular hydrogel microsphere, in contrast to loose and less compact aggregates within bulk hydrogel. Thermal analysis (DSC) indicates that supramolecular hydrogel microspheres are more thermally stable and can immobilize more water molecules, owing to the compact entangled three-dimensional network structures. This observation is of particular importance for potential drug delivery and biomaterials applications.