Fabrication of Waterproof Artificial Compound Eyes with Variable Field of View Based on the Bioinspiration from Natural Hierarchical Micro-Nanostructures

Abstract

Planar and curved microlens arrays (MLAs) are the key components of miniaturized microoptical systems. In order to meet the requirements for advanced and multipurpose applications in microoptical field, a simple manufacturing method is urgently required for fabricating MLAs with unique properties, such as waterproofness and variable field-of-view (FOV) imaging. Such properties are beneficial for the production of advanced artificial compound eyes for the significant applications in complex microcavity environments with high humidity, for instance, miniature medical endoscopy. However, the simple and effective fabrication of advanced artificial compound eyes still presents significant challenges. In this paper, bioinspired by the natural superhydrophobic surface of lotus leaf, we propose a novel method for the fabrication of waterproof artificial compound eyes. Electrohydrodynamic jet printing was used to fabricate hierarchical MLAs and nanolens arrays (NLAs) on polydimethylsiloxane film. The flexible film of MLAs hybridized with NLAs exhibited excellent superhydrophobic property with a water contact angle of 158°. The MLAs film was deformed using a microfluidics chip to create artificial compound eyes with variable FOV, which ranged from 0° to 160°.

Keywords: Bioinspired; E-jet printing; Hierarchical MLAs and NLAs; Microfluidics chip; Waterproof artificial compound eyes.

Fig. 1

Illustration of artificial compound eyes inspired by the compound eyes of dragonfly and the superhydrophobic surface of lotus leaf. a A dragonfly, whose eyes have a wide FOV (see inset). b A lotus leaf, whose surface morphology leads to its superhydrophobic property. c SEM images of the lotus leaf with nanotomenta. d SEM images of the lotus leaf without nanotomenta. e Schematic diagram for the fabrication of the waterproof artificial compound eyes with variable FOV

Fig. 2

Schematic illustration of the fabrication process for the waterproof artificial compound eyes with variable FOV. a Fabrication of hierarchical micro-/nanodroplets via the stable cone-jet and electrospray printing modes using an E-jet printing system. b Fabrication of hierarchical MLAs and NLAs on the flexible PDMS film. c Flexible deformation of the MLAs film using an integrated microfluidics chip to fabricate artificial compound eyes

Fig. 3

Hierarchical fabrication of MLAs and NLAs by E-jet printing. a Finite-element method model of the electric field (E) distribution around the nozzle tip and substrate during the ejection process. b and c The variation in E at the apex of the printing nozzles, with different inner diameters, for various voltages and gap distances, respectively. d E-jet printing modes for NOA61 using different printing nozzles and voltages. e–h SEM and AFM images of MLAs with different sizes obtained via the stable cone-jet mode. i–l Diameter, height, and volume of the microlenses as functions of the amplitude and duration of applied voltage. m and n AFM images of NLAs fabricated via the stable cone-jet and electrospray modes, respectively. o and p AFM images of various hierarchical MLAs combined with NLAs

Fig. 4

Characterization and statistical analysis of the fabricated artificial compound eyes. a–d Statistical analysis of the fabrication frequency and diameter distribution of the nanolenses printed by nozzles with diameters of 1, 2, and 10 μm. e Relative densities of nanolenses as a function of the densities of printing routes for a nozzle with inner diameter of 1 μm. f WCAs of the surface of PDMS films covered with different densities of nanolenses printed via a nozzle with inner diameter of 1 μm. The inset images show the WCA measurements for the corresponding PDMS film. g Statistics for the WCAs of the artificial compound eyes fabricated using a flexible MLAs film. The MLAs film was modified through different treatments (T1–T4) via nanolenses fabricated with different parameters. h The corresponding images of the WCA measurements for the surface of artificial compound eyes fabricated using T1–T4, respectively. i and j SEM images of the artificial compound eyes fabricated utilizing a flexible MLAs film. The inset images in (i) and (j) show the magnified details of the hierarchical micro–nanolenses. k and l Two-dimensional AFM image and the corresponding AFM profiles of the hierarchical micro–nanolenses. The inset images in (l) are the corresponding profiles of the nanolenses shown in (k)

Fig. 5

Schematic and analysis of the deformation mechanism and focusing properties of the artificial compound eyes. a Deformation mechanism of the artificial compound eyes via a microfluidics chip. b Deformation of planar MLAs to curved MLAs. c and d Height and the radius of curvature of the tunable artificial eyeball as functions of the volume of liquid injected in the chamber, respectively. e and f FOV, focal length and NA of the eyeball as functions of the volume of injected liquid, when the diameter of eyeball is 1 mm. g–j FDTD simulation results for the light intensity distribution of focal spots via single microlens of planar MLAs, (g) and (h), and curved MLAs, (i) and (j), at various incident angles

Fig. 6

Characterization of the optical imaging performance and focusing ability of the artificial compound eyes. a Optical system for characterizing the artificial compound eyes. b–d Optical images of the letters “SIA” focused by MLAs distributed in the center, middle, and edge regions of the artificial compound eyes, as indicated at the areas enclosed by the red, blue, and green dashed lines in a. e–g Focusing ability test for the tunable artificial compound eyes with variable FOVs of 0°, 128°, and 161°, respectively. h–j Normalized light intensity distribution obtained from the focal spots indicated by the circled positions shown in (e–g)

Fig. 7

Characterization of the FOV properties of planar and curved MLAs of artificial compound eyes. a Schematic of the characterization of the FOV of the artificial compound eyes. b and c Normalized light intensity distribution (along x- and y-directions, respectively) of focal spots for a planar MLAs observed by the optical system at incident angles of 0°, 20°, 40°, 60°, and 80°. For each case, the inset optical image shows the focal spot for a single microlens of a planar MLAs at an incident angle of 40°. d and e Normalized light intensity distribution (along x- and y- directions, respectively) of focal spots for a curved MLAs observed at incident angles of 0°, 20°, 40°, 60°, and 80°. For each case, the inset optical image shows the focal spot for a single microlens of a curved MLA at an incident angle of 40°. f Normalized light intensity distribution of focal spot for the same single microlens of the curved MLAs observed at incident angles ranging from -80° to 80°. The inset optical images show the focal spot for the same MLAs at incident angles of 0° and 40°