Alginate droplets pre-crosslinked in microchannels to prepare monodispersed spherical microgels

Monodispersed spherical calcium alginate microgels (denoted as Ca-ALG) with uniform and controllable size were prepared by using a microfluidics technique. Herein, an aqueous solution of sodium alginate (denoted as Na-ALG) was used as a dispersed phase, and the liquid paraffin containing CaCl 2 nanoparticles formed in situ was used as a continuous phase. Na-ALG droplets were first pre-crosslinked by CaCl 2 diffused from the oil phase in the microchannel, and then crosslinked completely in the collection bath containing an aqueous solution of CaCl 2 . In comparison with conventional external crosslinking, this method can avoid deformation of microgels which usually occurs in the process of external crosslinking. Due to the pre-crosslinking of Na-ALG droplets in the microchannel, the spherical morphology of the microgels could not be affected by the preparation conditions, such as types of microfluidic devices, flow rate ratios of the continuous phase and dispersed phase, size of the droplets, collection height and so on. In addition, the size of the spherical Ca-ALG microgels can be well controlled from 40 to 700 μm in diameter by changing the dimension of the microchannels and the flow rate ratios of the dispersed phase and continuous phase. Furthermore, such spherical Ca-ALG microgels can improve their movement and packing state in a microchannel, which is beneficial for their use as embolic materials for interventional therapy.