Microfluidic on-chip production of microgels using combined geometries

Abstract

Microfluidic on-chip production of microgels using external gelation can serve numerous applications that involve encapsulation of sensitive cargos. Nevertheless, on-chip production of microgels in microfluidic devices can be challenging due to problems induced by the rapid increase in precursor solution viscosity like clogging. Here, a novel design incorporating a step, which includes a sudden increase in cross-sectional area, before a flow-focusing nozzle was proposed for microfluidic droplet generators. Besides, a shielding oil phase was utilized to avoid the occurrence of emulsification and gelation stages simultaneously. The step which was located before the flow-focusing nozzle facilitated the full shielding of the dispersed phase due to 3-dimensional fluid flow in this geometry. The results showed that the microfluidic device was capable of generating highly monodispersed spherical droplets (CV < 2% for step and CV < 5% for flow-focusing nozzle) with an average diameter in the range of 90–190 μm, both in step and flow-focusing nozzle. Moreover, it was proved that the device could adequately create a shelter for the dispersed phase regardless of the droplet formation locus. The ability of this microfluidic device in the production of microgels was validated by creating alginate microgels (with an average diameter of ~ 100 μm) through an external gelation process with on-chip calcium chloride emulsion in mineral oil.

Microfluidic on-chip Production of Alginate Hydrogels Using Double Co-flow Geometry

“…6a & b). The production of teardrop-shaped microgels indicated that complete gelation process or most of it occurred outside of the micro uidic device in the outlet tube [14], [34]. An observation that veri es this theory is the formation of spherical alginate droplets during our experiments.…”

“…The micro uidic production of the microgels typically consists of two steps, including micro uidic emulsi cation of forerunner solutions and gelation of the produced droplets, which can be done in either on-chip or off-chip mode. The on-chip gelation method is commonly favored since it has numerous advantages over off-chip gelation, including simpli ed manipulation of the microgels' morphologies, facilitated way for loading a wide diversity of cargos, and continuous production of the microgels with an extraordinary degree of monodispersity [13], [14]. Yet, there are several outstanding challenges with the on-chip gelation method, one major factor being the immediate development of the cross-linking process, which may result in the occlusion of the microchannels and/or inlets and outlets.…”

“…Yet, there are several outstanding challenges with the on-chip gelation method, one major factor being the immediate development of the cross-linking process, which may result in the occlusion of the microchannels and/or inlets and outlets. The production of microgel with controlled morphology and dispersity also requires the inclusion of a time lag between the emulsi cation and gelation processes [14]. Several research groups have come up with some innovative ideas to solve this issue.…”

Microfluidic Chip Device for In Situ Mixing and Fabrication of Hydrogel Microspheres via Michael-Type Addition

“…Shieh et al . incorporated a shielding oil phase to avoid simultaneous emulsification and gelation of microspheres . Several groups have used the controlled release of calcium ions to trigger gelation on the chip for alginate systems. , Hou et al .…”

Microfluidic On-Chip Production of Alginate Hydrogels Using Double Coflow Geometry

“…The microfluidic production of the microgels typically consists of two steps, including microfluidic emulsification of forerunner solutions and gelation of the produced droplets, which can be done in either on-chip or off-chip mode. The on-chip gelation method is commonly favored since it has numerous advantages over off-chip gelation, including simplified manipulation of the microgels’ morphologies, facilitated way for loading a wide diversity of cargos, and continuous production of the microgels with an extraordinary degree of monodispersity. , Yet, there are several outstanding challenges with the on-chip gelation method, one major factor being the immediate development of the cross-linking process, which may result in the occlusion of the microchannels and/or inlets and outlets. The production of microgel with controlled morphology and dispersity also requires the inclusion of a time lag between the emulsification and gelation processes .…”