Droplet Microfluidics‐Assisted Fabrication of Shape Controllable Iron‐Alginate Microgels with Fluorescent Property

Droplet‐based microfluidics‐assisted fabrication of alginate microgels has extensive applications in biomaterials, biomedicines, and related fields. This approach is typically achieved by crosslinking droplets of an aqueous solution of sodium alginate with various divalent and trivalent ions, such as Ca2+, Ba2+, Sr2+, etc. Despite the exceptional features exhibited by bulk alginate hydrogels when using iron ions as the crosslinking reagent, including stimulus responsiveness and complex chemistry, no attention has been given to studying the fabrication of Fe‐alginate microgels through droplet microfluidics. In this work, a facile method is presented for fabricating Fe‐alginate microgels using single emulsion droplets as templates and an off‐chip crosslinking technique to solidify the droplets. The morphologies of the resulting microgels can be systematically adjusted by manipulating different parameters such as viscosities and ionic strength of the collecting solutions. It should be noted that these resulting microgels undergo a color change from light brown to dark brown due to presumed self‐oxidation of iron ions within their skeleton structure. Furthermore, these Fe‐alginate microgels are functionalized by decorating them with a positively charged linear polymer via electrostatic interactions to impart them with stable fluorescent property. These functionalized Fe‐alginate microgels may find potential applications in drug delivery carriers and biomimetic structures. Droplet microfluidics produced spherical droplets of an aqueous solution of sodium alginate can be deformed and generate Fe‐alginate/Ca‐alginate microgels with different morphologies and color intensities when collected in aqueous solutions with different concentrations of glycerol, CaCl2, and FeCl3. The microgels can be further endowed with stable fluorescence property when reacted with a linear pNIPAAm‐co‐Ru(bpy)3 polymer simply via the electrostatic interaction.