Inkjet Printing of Viscous Monodisperse Microdroplets by Laser-Induced Flow Focusing

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Inkjet Printing of Viscous Monodisperse Microdroplets by Laser-Induced Flow Focusing

Paul Delrot, Miguel A. Modestino, François Gallaire, Demetri Psaltis, and Christophe Moser

Phys. Rev. Applied 6, 024003 – Published 8 August 2016

Abstract

The on-demand generation of viscous microdroplets to print functional or biological materials remains challenging using conventional inkjet-printing methods, mainly due to aggregation and clogging issues. In an effort to overcome these limitations, we implement a jetting method to print viscous microdroplets by laser-induced shockwaves. We experimentally investigate the dependence of the jetting regimes and the droplet size on the laser-pulse energy and on the inks’ physical properties. The range of printable liquids with our device is significantly extended compared to conventional inkjet printers’s performances. In addition, the laser-induced flow-focusing phenomenon allows us to controllably generate viscous microdroplets up to 210 mPa s with a diameter smaller than the nozzle from which they originated ( $200 μ m$ ). Inks containing proteins are printed without altering their functional properties, thus demonstrating that this jetting technique is potentially suitable for bioprinting.

Received 18 May 2016

DOI:https://doi.org/10.1103/PhysRevApplied.6.024003

This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Drop interactions Flow confinement Microfluidic devices Non-Newtonian fluids Shock waves Viscosity Wakes & jets

Laser applications

Fluid DynamicsPhysics of Living SystemsGeneral PhysicsPolymers & Soft Matter

Authors & Affiliations

Paul Delrot^1,*, Miguel A. Modestino^1,2, François Gallaire³, Demetri Psaltis², and Christophe Moser¹

¹Laboratory of Applied Photonics Devices, School of Engineering, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
²Laboratory of Optics, School of Engineering, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
³Laboratory of Fluid Mechanics and Instabilities, School of Engineering, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland

^*Corresponding author. paul.delrot@epfl.ch

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Issue

Vol. 6, Iss. 2 — August 2016

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Images

Figure 1
Experimental setup. (a) Top view of the time-resolved imaging setup; the capillary axis is perpendicular to the graph. $λ / 2$ , half-wave plate; PBS, polarizing beam splitter; EM, energy meter; OD, optical density. (b) Side view of the microcapillary in which the droplets are generated and a description of the experimental parameters impacting the droplet size and velocity.
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Figure 2
(a) Series of time-resolved images of the flow-focusing phenomenon. The $300 − μ m$ capillary is filled with a mixture of water and glycerol at 80% (v/v), corresponding to a 67-mPa s viscosity at $25 ° C$ . The liquid-air interface is highlighted with, respectively, a solid and dashed white line for clarity on the first two images corresponding to prefiring and postfiring of the laser. The contact angle of the meniscus is also highlighted. The lateral borders of the images correspond to the inner capillary walls. Distortion, due to the glass thickness of the capillary, is responsible for the black surroundings below the meniscus. Scale bar, $200 μ m$ . (b) Jet dynamics corresponding to the droplet formation depicted in (a). The blue circles are the data points corresponding to the pictures in (a). The dashed line is a spline interpolation of the jet dynamics. The dotted lines delimitate the phases of jetting.
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Figure 3
Jetting regimes of inks with various dynamic viscosities for the same capillary diameter ( $300 μ m$ ). The $y$ axis has a logarithmic scale, and the distance $Z$ between the laser focal spot and meniscus is kept constant at $500 μ m$ . (a) Newtonian water-glycerol solutions. (b) Non-Newtonian polymer solutions.
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Figure 4
Conventional inkjet-printability region adapted from Refs. [5, 8] superimposed with the experimental data points obtained with our laser-assisted flow-focusing device in the satellite-free jetting regime and with the water-glycerol Newtonian mixtures. Red, yellow, and blue dots are, respectively, obtained for 300-, 200-, and $100 − μ m$ capillary diameters. Error bars are omitted for clarity, and each data point is the results of at least ten experiments.
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Figure 5
Satellite-free drop diameter of water-glycerol mixtures as a function of the Ohnesorge number for different capillary sizes. The distance $Z$ between the laser focal spot and the meniscus is kept constant at $Z = 500$ , 400, and $350 μ m$ , respectively, for $D = 300$ , 200, and $100 μ m$ . Power-law fits are also displayed. Each data point is the results of at least ten experiments.
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Figure 6
(a) Array of droplets [60% (v/v) of glycerol in PBS] with rabbit and mouse IgGs imaged with a bright-field microscope prior to droplet drying. All droplets appear red due to the light-absorbing dye. Further details on the inks’ content can be found in the Appendix. (b) The same array imaged under fluorescence after drying the droplet and performing an immunoassay with fluorescent-labeled secondary anti-IgGs against rabbit (in blue) and mouse (in green) (false colors).
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