Tunable polymer microgel particles and their study using microscopy and real‐time deformability cytometry

We report the preparation and mechanical properties of highly swellable, spherical polymer microgels synthesized by precipitation copolymerization of divinylbenzene-55 (DVB), 4-methylstyrene (4MS), and maleic anhydride (MA) at different cross-linker contents, in a range of methylethylketone (MEK) and heptane solvent mixtures. Microgels were characterized by optical and confocal microscopy, and their mechanical properties tested using real-time deformability cytometry (RT-DC), a technique developed to analyze cell properties by measuring deformation under shear stress. Hydrolysis of anhydride groups gave microgels with diameters ranging from 10 to 22 μm when swollen in saline, depending on vol% MEK and cross-linker loading. Young's moduli of the microgels could be tuned from 0.8 to 10 kPa by adjusting cross-linker content and MEK/heptane solvent composition, showing an inverse relationship between the effects of vol% MEK and %DVB on microgel properties. These microgels also show strain-stiffening in response to increasing shear stresses. Extension of the RT-DC method to the study of polymer colloids thus enables high-throughput analysis of microgels with tunable mechanical characteristics.