Fabrication and flow characteristics of monodisperse bullet-shaped microparticles with controllable structures

The preparation of microparticles with non-spherical shapes has attracted increasing interest because the special physical properties of non-spherical microparticles can increase their performance in a wide variety of industrial applications and clinical pathologies. Here a simple and flexible approach is developed to fabricate monodisperse bulletshaped microparticles with controlled structures from microfluidic droplet templates, which are deformed by both shear stress from outer fluid and spatial confinement from microchannel. The deformation of droplet templates can be simply controlled by varying the flow rate of outer fluid and the inner diameter of collection tube. By multiplying the microfluidic device, bullet-shaped microcapsules with different internal structures can be easily fabricated from deformed double emulsion droplets. The results of flow characteristics show that, the bullet-shaped microparticles have a higher velocity than the spherical microparticles with the same volume if they flow in the microchannel with smaller diameter than the length of the bullet-shaped microparticles; whereas their flowing velocity is slightly lower than that of spherical microparticles in the microchannel if the channel diameter is larger than the length of bullet-shaped microparticles. In microchannels of a model device, bullet-shaped microparticles show better embolization performance than spherical ones. The bullet-shaped microparticles and microcapsules are promising as materials candidates in the fields of embolization therapy, substance transfer and drug release systems. The proposed strategy in this study provides a facile route for fabricating bullet-shaped microparticles with controlled structures and presents intriguing possibilities for growing researches including non-spherical microparticles and micromachine systems.