Printing of Viscous Microdroplets by laser induced flow focusing

摘要

We present a drop on demand system based on light actuation. Viscous micro droplets are ejected from a thin capillary. This is accomplished by focusing light from a pulsed nanosecond laser in a liquid-filled glass capillary (< 500 micrometer). The acoustic wave generated by the focus spot inside the capillary is able to eject droplets thanks to a flow-focusing phenomenon. This effect was shown by another group to generate highly focused supersonic jets. Here, this technique was implemented for the generation of low-velocity micro-droplets and with a wide range of viscosity (0.6-200 mPa.s). We investigated parameters such as the viscosity of the fluid, the capillary diameter, the meniscus contact angle and the pulse energy on the ejection speed, the droplet(s) size and the printing accuracy. Several ejection regimes were demonstrated depending on the pulse energy and liquid viscosity. Micro-droplets of photopolymer inks were generated with a diameter less than 20% that of the nozzle for the least viscous liquid, resulting in ejected volumes from ten to 100 picoliters. This technique combines the advantages of inket technology (thin nozzles) and the high viscosity droplet ejection of Laser assisted forward transfer (LIFT) technology. Thus a wide range of material for drug delivery can be precisely ejected without clogging the capillary. Two-dimensional patterns were printed with a good controllability and consequently cured, which opens up new possibilities beyond drug delivery for the additive manufacturing of microstructures.