In this study, we report the microfluidic-based synthesis of a multifunctional Janus hydrogel particle with anisotropic superparamagnetic properties and chemical composition for the bottom-up assembly of hydrogel superstructures. In a uniform magnetic field, the resulting Janus magnetic particles fabricated in the present method exhibit chainlike or meshlike superstructure forms, the complexity of which can be simply modulated by particle density and composition. This controllable field-driven assembly of the particles can be potentially used as building blocks to construct targeted superstructures for tissue engineering. More importantly, we demonstrated that this method also shows the ability to generate multifunctional Janus particles with great design flexibilities: (a) direct encapsulation and precise spatial distribution of biological substance and (b) selective surface functionalization in a particle. Although these monodisperse particles find immediate use in tissue engineering, their ability to self-assemble with tunable anisotropic configurations makes them an intriguing material for several exciting areas of research such as photonic crystals, novel microelectronic architecture, and sensing.

Spherical and non-spherical magnetic hydrogel particles were synthesized in a microfluidic device containing an embedded UV light reflector. Monodisperse magnetic emulsion droplets were generated in a T-junction and allowed to relax into spheres, disks, and plugs in confining microchannel geometries. Particle morphology was locked-in via UV-initiated photopolymerization. The role of the reflector in the microchannel is to provide a uniform distribution of UV energy to the magnetic emulsion droplets and to increase the UV flux, which significantly improves UV polymerization conditions for microfluidic-based particle synthesis. Magnetic nanoparticles were uniformly encapsulated in the hydrogel, giving the microparticles superparamagnetic behavior. Additionally, the non-spherical particles show anisotropic responses under an applied external magnetic field.

Microgel particles capable of bulk-degradation have been synthesized from a solution of diacrylated triblock copolymer composed of poly(ethylene glycol) (PEG) and poly(lactic acid) (PLA) in a microfluidic device using stop flow lithography (SFL). It has been previously demonstrated that SFL can be used to fabricate particles with precise control over particle size and shape. Here we have fabricated hydrogel particles of varying size and shape and examined their mass-loss and swelling behavior histologically and mechanically. We report that these features in addition to the degradation behavior of the hydrogel particles may be tailored with SFL. By decreasing the applied UV dose during fabrication, hydrogel particles can be made to exhibit a distinct deviation from the classical erosion profiles of bulk-degrading hydrogels. At higher UV doses, a saturation in cross-linking density occurs and bulk-degrading behavior is observed. Finally, we synthesized multifunctional composite particles, providing unique features not found in homogeneous hydrogels.