Fig. 2. Fabrication and characterizations of the SONIC device.

a Schematic illustration of the device fabrication (side view). b, c False-colored SEM images of the SONIC scaffold (b) and polydopamine-coated SONIC scaffold (c). One representative of 3 independent experiments is shown. d, e Digital images of water droplets (colored with food dye) and contact angle goniometer-captured images of a water droplet on a rectangular prism SONIC scaffold before (d) and after (e) polydopamine modification. f A false-colored SEM image of the polydopamine-coated SONIC scaffold with deposited CaSO₄ crystals. One representative of 3 independent experiments is shown. g Stereo microscope image of the SONIC device (top view). h SEM/EDS elemental mapping of F, N, and S on a polydopamine-coated SONIC scaffold with deposited CaSO₄ crystals. The red arrows indicate the lack of polydopamine at a coating crack location. One representative of 3 independent experiments is shown. i SEM image of the polydopamine-coated SONIC scaffold and the corresponding element N distribution profile across a polydopamine coating crack. One representative of 3 independent experiments is shown. j SEM image of the cross-sectional polydopamine-modified SONIC scaffold, showing no polydopamine inside the scaffold. One representative of 3 independent experiments is shown. k An H&E staining slice of an islet encapsulation device showing the polydopamine located at the interface between the SONIC scaffold and alginate hydrogel. One representative of 10 replicates is shown. l Captured images during the perfusion test using a cylindrical SONIC scaffold. A pump-connected needle was inserted into one end of a cylindrical SONIC scaffold, and the other end of the SONIC scaffold was immersed into a vial containing water phase (top, colored with green food dye) and chloroform phase (bottom, colored by Nile Red dye). m Schematics representing the distribution of water and chloroform during the perfusion test.