Design and fabrication of a passive droplet dispenser for portable high resolution imaging system

Abstract

Moldless lens manufacturing techniques using standard droplet dispensing technology often require precise control over pressure to initiate fluid flow and control droplet formation. We have determined a series of interfacial fluid parameters optimised using standard 3D printed tools to extract, dispense and capture a single silicone droplet that is then cured to obtain high quality lenses. The dispensing process relies on the recapitulation of liquid dripping action (Rayleigh-Plateau instability) and the capturing method uses the interplay of gravitational force, capillary forces and liquid pinning to control the droplet shape. The key advantage of the passive lens fabrication approach is rapid scale-up using 3D printing by avoiding complex dispensing tools. We characterise the quality of the lenses fabricated using the passive approach by measuring wavefront aberration and high resolution imaging. The fabricated lenses are then integrated into a portable imaging system; a wearable thimble imaging device with a detachable camera housing, that is constructed for field imaging. This paper provides the full exposition of steps, from lens fabrication to imaging platform, necessary to construct a standalone high resolution imaging system. The simplicity of our methodology can be implemented using a regular desktop 3D printer and commercially available digital imaging systems.

In situ retrieval and correction of aberrations in moldless lenses using Fourier ptychography

“…The second approach opens up ways to tailor high performance imaging without being limited to fixed parameter determined by manufacturers. A recent surge in a variety of moldless lens techniques [2][3][4][5][6][7][8][9] opened up new lens fabrication techniques on demand, which has been proven to be economical, efficient and repeatable. This has enabled the rapid decentralization of lens-fabrication and at the same time leverage upon consumer electronics to provide high resolution imaging devices.…”

“…There have been efforts made to reduce the overall footprint of a FP microscope which would undoubtedly increase their widespread use in non-specialist laboratories [20]. Here, we built upon our prior work in developing decentralized imaging systems based on moldless lenses [5] using miniature consumer computing systems (Raspberry Pi). This aligns with the primary motivation of our work of leveraging consumer devices and low cost moldless lenses to conduct high resolution imaging at low-cost and off-optical table.…”

“…We previously established that the optical aberrations in moldless lenses have large degrees of variations (peak to valley ~0.7 µm). This is especially true for those with shorter focal lengths and higher optical magnification [4,5,7]. These aberrations are more severe than traditional lenses which could be randomly distributed across the imaging plane.…”

“…We also perform majority of the acquisition process using a fully standalone compact imaging system that is constructed using off-the-shelf components (Raspberry Pi, ICstation LED matrix -4 mm pitch). The moldless lenses were made using passive droplet approaches [5]. Here, we adopted the FP methodology proposed by Tian et al [17] who have shown that sub-level optimisation using 2nd order Newton's method are used to achieve higher speed of convergence.…”

“…In contrast, we used consumer equipment and lens made from a passive droplet dispenser. The passive droplet dispenser is a set of 3D printed tools that is capable of dispensing multiple droplets of PDMS simultaneously with minimal operator training [5]. The dispenser includes a droplet holder that is designed to balance the surface forces such that each droplet retains a parabolic shape during curing at a temperature of 70°C.…”