Strategies for the design of hydrophilic microspheres with controlled size and microstructure

Synthesizing hydrophilic microspheres is a subject of great interest for a variety of applications. However, there is difficulty in the control of the microspheres' size. In this study, the combination of membrane emulsification and droplets swelling method is utilized to prepare poly(2-hydroxyethyl methacrylate) (PHEMA) microspheres, a kind of hydrophilic material. The former is used to prepare monodisperse seed droplets, which include hydrophobic monomer (ethylenedimethacrylate, EDMA) and some assistant agents, whereas the latter is used for the absorption of hydrophilic monomer (HEMA). After a polymerization process, PHEMA microspheres with desired size can be obtained. It is found that large membrane pore size or high swelling ratio tended to increase the final particle size. At the same time, smaller particle size is got at higher EDMA concentration in the seed droplets. In addition, microstructure of the microspheres is also controlled by using this method. Nonporous, porous, nonporous/porous half-moon, or macroporous microspheres can be obtained easily by changing the total oil composition in swollen droplets.