Preparation of uniform and large sized agarose microspheres by an improved membrane emulsification technique

The SPG (Shirasu porous-glass) membrane emulsification technique has been subject to much attention for the preparation of uniform emulsions. However, so far primarily used for the production of droplets with sizes below approximately 60 μm. A production bottleneck occurred if the desired size was further increased, especially when highly viscous dispersed phases were involved. To this end, an improved membrane emulsification technique was proposed and has been applied to the preparation of large agarose microspheres, with a size of around 90 μm and with a narrow size distribution. The effects of important emulsification parameters, including the pore size of the SPG membrane, the operating pressure, the stirring rate of the continuous phase, the composition of the continuous oil phase, and the concentration of agarose in the dispersed water phase, have been extensively studied. Under optimum conditions, uniform-size agarose microspheres with an average diameter of 93 μm and a size distribution index of 0.65 were successfully prepared. The average particle size of the home-made agarose microspheres was almost identical to that of the commercial product Sepharose 4 Fast Flow (4FF), which is produced by mechanical stirring and an additional sieving process. However, the size distribution of the former was much narrower than that of the latter. Therefore, the improved membrane emulsification technique presented here is promising for the application of high viscosity systems such as agarose solutions, and the production scale can be further enhanced by increasing the number of membrane units attached to the experimental apparatus.