Entrapment of living cells in microbeads is to protect the encapsulated cells from the host's immune system, which can be used as drug delivery vehicles, immunotherapies and engineered tissues. The main objective of the present study was to investigate the droplet formation and to better develop mono-dispersed microencapsulation of living cells with controllable size. The uniformity of microencapsulation size was realized by performing electrospray in the dripping mode and also stabilized by an additional ring electrode. Reduction of droplet diameter and increase in the dripping frequency were observed with increasing applied voltage to the nozzle using a conventional electrospray setup. The vibration of the needle was found to reduce when high voltage was applied to the nozzle. With increasing voltage applied to the ring electrode, the dripping frequency was found to decrease with the formation of slightly larger sizes of droplets. Hep G2 cell line was taken as the model cell line for encapsulation in calcium alginate microbeads. Relatively uniform microbeads could be achieved when operating under low flow rates with high voltages applied to the nozzle by using a conventional electrospray setup. In contrast, uniform microbeads can not be obtained using a similar setup under high flow rates unless the ring electrode is applied with voltage to stabilize the electrospray in the dripping mode. In this modified electrospray, microbeads with narrow size distribution and slightly larger size can be obtained even for cases under high flow rates. Phase contrast microscope images showed that the diameter of microbeads from around 200 mu m to 2 mm could be finely tuned by adjusting various operating parameters. (c) 2007 Elsevier Inc. All rights reserved.