Size control of calcium alginate beads containing living cells using micro-nozzle array

Size-controlled small (i.e. less than 300 μm) polyelectrolyte complex gel beads are urgently desired for wide-spread application, including use in medical, pharmaceutical, and bioengineering fields. However, it was impossible to obtain smaller beads less than 300 μm with conventional apparatuses. We developed a novel microfluidics device that utilizes silicon micro-nozzle (MN) array, enabling to produce 50–200 μm calcium alginate beads with a narrow size distribution. Alginate aqueous solution was extruded through a precisely fabricated thin (30 μm×30 μm) and short (500 μm) MN and was sheared by the viscous drag force of oil flow to form alginate droplets. Alginate droplets were immediately reacted with CaCl2 droplets at the downstream of oil flow to form calcium alginate gel beads. This device enabled us to successfully encapsulate living cells into 162 μm calcium alginate beads with maintaining viability, which was confirmed by the expression of marker protein.