Microfluidic one-step fabrication of radiopaque alginate microgels with in situ synthesized barium sulfate nanoparticles

In this work, we report a new strategy to fabricate monodispersed radiopaque alginate (Ba-alginate) microgels by a one-step microfluidic method. Alginate droplets containing sulfate ions are first formed by a flow focusing microfluidic setup. These alginate droplets are subsequently solidified by barium ions in a collection bath. During the solidification process, excessive barium ions in the collection bath also react with sulfate ions in the alginate droplet, resulting in barium sulfate (BaSO₄) nanoparticles in situ synthesized (acting as radiopaque imaging agents) within the Ba-alginate microgels. Scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDX) illustrate that 800 nm BaSO₄ nanoparticles are uniformly distributed inside the 30 μm Ba-alginate microgels, with 62 wt% of elemental barium (Ba). In addition, X-ray diffraction (XRD) measurements indicate that the BaSO₄ nanoparticles consist of 10 nm in situ synthesized BaSO₄ crystallites. The alginate microgels act as a soft and porous template to prevent the precipitation and aggregation of BaSO ₄ nanoparticles. The Ba-alginate microgels are also visible under X-ray radiation. The facile route to fabricate alginate microgels as radiopaque embolic materials is of particular importance for endovascular embolization and localized diagnostic imaging applications. Similar approaches can also be adopted for synthesizing other inorganic nanoparticles in microgels.