Functionality integration in stereolithography 3D printed microfluidics using a "print-pause-print" strategy

Abstract

Stereolithography 3D printing, although an increasingly used fabrication method for microfluidic chips, has the main disadvantage of producing monolithic chips in a single material. We propose to incorporate during printing various objects using a "print-pause-print" strategy. Here, we demonstrate that this novel approach can be used to incorporate glass slides, hydrosoluble films, paper pads, steel balls, elastic or nanoporous membranes and silicon-based microdevices, in order to add microfluidic functionalities as diverse as valves, fluidic diodes, shallow chambers, imaging windows for bacteria tracking, storage of reagents, blue energy harvesting or filters for cell capture and culture.

Fig. 1. Concept illustration of the print-pause-print strategy. a) Printing of a first part (pre-pause part). b) Pausing, removal of the building platform, removal of resin excess and positioning of the object to integrate. c) Resuming of the print (post-pause part). d) Cleaning and developing of the detached chip.

Fig. 2. Precision of the realignment during the PPP process. a) Picture of an alignment structure. b) Schematic of the measurement with an exaggerated misalignment (left) and a control structure (right): α angle between the inner and outer cross; position of the centre of mass of the inner cross (yellow) and outer cross (blue). c) Angle and shift between the inner and outer crosses, measured with 12 samples per conditions, 4 samples per print. Error bars represent ± one standard deviation.

Fig. 3. Imaging windows and shallow chambers. a) Tomographic cross section of the integration of a coverslip before printing the channels. b) Cross section of the integration of a coverslip after printing the channels, with a zoom-in in insert. c) Cross section of the double coverslip chip, with a thin channel between the two coverslips. In insert, vertical grey values profile (averaged over 1700 μm). d) DIC and GFP imaging of SP15 pFVP25.1 E. coli. bacteria inside the glass–resin chip (illustrated in b) and the glass–glass chip (illustrated in c). e) Histogram of the fluorescent background noise for the glass–resin chip (grey) and the glass–glass chip (black). Higher grey values correspond to higher light intensities. f) Growth curves of bacteria imaged on the coverslip surface in the glass–glass chip, for 5 different locations in the imaging windows. Error bars are standard deviations.

Fig. 4. Shallow channels with sacrificial films. a) Pictures of the xurographed soluble films before integration. b) Pictures of red dye in the chips after film integration and solubilisation. c) SEM image of the chip in b-left, cut in half following the red line on b.

Fig. 5. Reagent storage. a) Tomographic cross section of the chip with paper pads after ink loading. b) Time-lapse of the ink diffusion after water addition in the channel. c) Time lapse of the film solubilisation and ink diffusion after water addition in the channel.

Fig. 6. Valves and fluidic diodes. a) Tomographic cross section of the valve chip containing a PDMS elastic membrane masked with tape frames. b) Temporal variation of the flow rates for 3 different chips during actuation pressure pulses. c) Tomographic cross section of a check valve. d) Flow rate in the open direction depending on the pressure difference, for three pressure ramps in both directions, for 3 diode chips.

Fig. 7. Nanoporous membranes. a): Configuration of the 3D printed electro-chemical cell for membrane characterisation. The mounted membrane (1) separates two electrolyte reservoirs of concentration c₁ and c₂. The electrical circuit is closed by silver-chloride electrodes (2) allowing a current I to flow and to measure the voltage across the cell. Electrical characterization of b and c) nanoporous PET (non-selective) at two different concentrations and d) Nafion membranes in a salt gradient (cation selective). n = 3 for clamped membranes and n = 4 for PPP membranes.

Fig. 8. Microfabricated filters. a) Pictures of microfabricated filters exhibiting the porous circular membrane in the centre and 12 electrical contact pads. b) SEM micrograph of the porous circular membrane supporting sensing electrodes and surrounded by fluidic slits formed by the silicon supporting structure. c) Tomographic cross section showing the subsequent integration of a glass coverslip and a microfabricated filter within a 3D printed fluidic channel. d) Pictures of the 3D printed chip. e) Fluorescence microscopy during the capture of PC3 GFP cells in PBS. f) Bright field image of trapped cells on the membrane at day 0 and day 2, after media renewal.