Visualization of PDMS Microparticles Formation for Biomimetic Fluids

In vitro experiments of blood flow are usually performed with blood analogue fluids due to ethical and practical considerations. The ideal analogue must match the rheology of blood in multiple scales. Ideally, the blood analogue fluid should be a suspension of transparent particles with similar properties to red blood cells. PDMS particles are an interesting candidate because they are transparent, have a low refractive index and can be produced through polymerization by heating. Here we present a study to produce PDMS microparticles, to be used in biomimetic fluids, by droplet microfluidics. A microfluidic flow focusing device was employed to produce the droplets. A polymeric fluid (PDMS) was squeezed by two counter-flowing water streams (with 2% of SDS). The flow rate of the disperse phase (Qdis) was 1 μl min-1 and that of the continuous phase (Qcont) 5 μl min-1. Both liquids were forced to flow through a narrow slit (25 μm x 100 μm) located downstream the channels where PDMS stream breaks into droplets. In these conditions, the device operated in the jetting regime, forming polydispersed droplets. Monodispersed microparticles were also obtained in the dripping regime. The droplets were then cured thermally to form microparticles. The process of droplet formation was filmed with a high-speed camera and the movies were analyzed to relate the flow pattern to particle size distribution.