Generating Alginate microspheres using microfluidics for cell encapsulation purposes

Cell encapsulation within polymeric microspheres allows two-way mass transfer of molecules such as oxygen, nutrients, growth factors between cells and environment. These cell-laden microgels are used in a variety of applications, such as 3D cell cultures, wound healing and bioink. One of important techniques to encapsulate cells is droplet-based-microfluidics that generates uniform diameter microspheres in the range of nanometers to micrometers, with a high frequency and good control of the size.In this research, a flow-focusing microfluidic chip was designed and fabricated in PDMS. Then we used the water as the dispersed phase and mineral oil as the continuous phase to generate aqueous droplets in oil to check the device.Droplet formation at junction is managed by the competition of shear stress and surface tension stress that these factors are related together in capillary number. So, by changing the capillary No. and dispersed phase flow rate, we obtained four flow patterns including dripping, laminar, jetting and fluctuation for 1% alginate solution as the dispersed phase and mineral oil as the continuous phase. Finally, we generated alginate droplets in our flow-focusing microfluidic chip and the crosslinking process was done off chip with Ca2+ ions dispersed in oil. According to previous studies, the best size for microgels in cell encapsulation is 100 μm in diameter. As the result, we found that to get 100 μm microspheres of 1% alginate, the alginate phase flow rate and the oil phase flow rate should be around 0.2 ml/h and 0.7 ml/h, respectively

Keywords:

Hydrogel , Cell encapsulation , Droplet-based-microfluidic