Complex-shaped particle fabrication from inertial microfluidics

Abstract

Next, a modification of optofluidic fabrication is introduced to break the top-down symmetry observed in all of the original 3D particle shapes. By introducing the time dimension into our existing optofluidic fabrication process, we break this top-down symmetry, generating fully asymmetric 3D particles with a process termed Four-dimensional (4D) optofluidic fabrication. After pillar induced inertial flow shaping, the time dimension is incorporated by stopping the flow and allowing denser UV-reactive fluids to settle by gravity to create asymmetric flow cross-sections. Patterned UV light illumination then polymerizes fully asymmetric 3D particles. In order to maximize the generated particle utility, a solution is then presented to enable sub-100 micron particle generation by adding a tapered reduction channel after pillar-induced inertial flow shaping that reduces the channel size 10-fold. 3D particles with dimensions 50 x 35 x 30 µm3 and minimum feature sizes of 15 µm are shown. All experimental results involving inertial flow shaping are compared to and validated with finite element based simulations. Although a limited number of particles are presented, by adjusting flow rates, pillar configurations, and photomasks, an infinite set of particle shapes are possible.

Complex shaped particles have shown great potential for applications such as drug delivery, tissue engineering, and structural materials; however, the ability to fabricate custom particle shapes with current manufacturing methods remains limited. A variety of techniques can create two-dimensional shaped particles such as cubes and cylinders, although it is expected that fully three-dimensional (3D) shaped particles can enhance their utility due to increased surface-area-to-volume ratios and altered structural properties. Here, we present a novel inertial microfluidic technology called optofluidic fabrication for the generation of complex 3D-shaped polymer particles based on two coupled processes: inertial flow shaping and ultraviolet light (UV) polymerization. While flowing at finite Reynolds numbers in microfluidic channels, secondary flows generated near pillars within the channel deterministically alter the flow cross-section of UV-reactive and inert fluid streams coflowing through the channel. The channels are then illuminated with patterned UV light to polymerize the UV curable fluid, creating particles with multi-scale 3D geometries. The effect of pillar location, number of pillars, Reynolds number, and photomask pattern is investigated for the creation of a variety of 3D particle shapes at the millimeter scale.