FITC-dextran with different Mw (150 and 2000 kDa) were mixed with the emulsion phase at a concentration of 0.03% (w/v). Microcapsules were prepared using the previously described method using this solution. For expansion and release studies, a microcapsule was initially transferred into an isotonic 15% (w/v) dextran solution dissolved in the normal saline. A certain amount (2050 L) of the solution in external phase was slowly replaced by normal saline with the same volume using the pipette, and then placed for over 10 min to make the expansion of microcapsule reach equilibrium and imaged using the fluorescence microscope. At the same time, the release of FITC-dextran was monitored. The operation was repeated until the final concentration of dextran in external phase less than 1% (w/v). The diameters of the microcapsules at different stages were measured using ImageJ image analysis software (NIH, USA).