Preparation of large-sized highly uniform agarose beads by novel rotating membrane emulsification

A novel rotating membrane emulsification setup incorporating a 100 μm pore diameter stainless steel hydrophobic membrane is used to produce W/O emulsions consisting of 4 wt% hexaglycerin penta ester (PO-500) as emulsifier, the mixture of liquid paraffin (LP) and petroleum ether (PE) in 11:1 (v/v) as continuous oil phase and agarose solution as the dispersed phase. The agarose beads of average sizes between 108.4 and 385.4 μm can be obtained after the emulsion solidification process. The membrane rotational speed (500–2000 rpm), agarose concentration (2–4 wt%) and oil phase composition are all investigated as to their effect on emulsion droplet size and size uniformity of agarose beads. The optimal conditions for producing uniform agarose beads are an agarose solution of 3 wt%, a mixture of liquid paraffin and petroleum ether in 11:1 (v/v) and a membrane rotational speed of 900 rpm, under which the average bead diameter is 220 μm with a very narrow size distribution value of 0.76 (Span value). A model describing the operation is presented to predict droplet size under a certain condition and the prediction results fit with the experimental data fairly well. The emulsification reproducibility and stable beads properties demonstrate that the rotating membrane emulsification is a manufacturing protocol for uniform droplets and beads of controlled size.