In spite of beneficial properties of magnetic particles with non-spherical shapes such as anisotropic responses to external fields, large surface areas, and unique structure formation, anisotropic magnetic particles with uniform morphology have not been available. A T-junction microfluidic device in combination with an ultraviolet (UV) light reflector has been developed to controllably synthesize magnetic hydrogel microparticles in spherical and non-spherical forms. Sphere, disk, and plug shapes of magnetic emulsion droplets in confined microchannel geometries were locked-in without deformation via UV-initiated photopolymerization. The reflector mode approach offers significantly enhanced UV-based polymerization conditions for microfluidic-based particle synthesis via an increase UV energy flux and a uniform distribution of UV energy. Thus, this method will be very effective and useful to generate not only general polymeric particles but also various novel composite materials. Magnetic nanoparticles were uniformly encapsulated in the microhydrogels, giving the microparticles a superparamatic behavior which is highly desirable in most biological applications. Additionally, the non-spherical microparticles show anisotropic responses under an applied external magnetic field. This unique magnetic response of anisotropic microparticles has great potential for many microscale applications such as rheological probes for microrheological characterization of complex fluids and biological materials and also basic components of portable microfluidic devices (mixers). Additionally, biocompatibility, high surface area, and high target capturing capacity due to porous structure of the non-spherical magnetic hydrogels will offer the advantages in biomedical applications such as sorting and separation of biological materials.

Figure 1. Optical images of collections of magnetic hydrogels: (a) spheres, (b) disks, and (c) plugs. The scale bars are (a-c) 30μm.