Octane pro

The set discs were analyzed by SEM/EDX (Octane pro, 7.2/15252, EDAX, Ametek Material Analysis Division, Mahwah, NJ, USA) to determine the surface morphology and composition of each sealer before immersion in deionized water. At the end of the final immersion period (i.e., after 28 days), the discs were reexamined to determine the surface and composition changes consequent to solubility. The microporosities in each image were measured using ImageJ software, a Java-based image processing program, (version 1.44, 64-bit Java 1.8.0_112, National Institutes of Health, Bethesda, MD, USA).

Microstructures of non-galvanized and galvanized steel specimens were observed by optical microscopy (Eclipse LV150, Nikon, Tokyo, Japan), and the grain sizes were compared. The hardness values of the specimens were obtained by a micro-Vickers hardness testing machine (HM-200, Mitutoyo, Kawasaki, Japan) using a load of 0.02 kgf for 10 s. The specimens were tested for mechanical properties under static loading using a tensile testing machine (Shimadzu Autograph no. 79641, Shimadzu, Kyoto, Japan) at an initial strain rate of 4.76 × 10⁻⁴ s⁻¹ and a crosshead speed of 1 mm/min. Fatigue testing experiments were carried out using a laboratory fatigue testing machine (Servopulser EHF-EUB5, Shimadzu, Kyoto, Japan) with a sine wave cyclic loading at a frequency of 10 Hz and stress ratios, R, ( $${\sigma }_{min}$$ / $${\sigma }_{max}$$ ) of −1.0, 0.01, and 0.5. The experiment was deliberately terminated when the specimen reached 10⁷ cycles without failure. The microstructure of the galvanizing layer and the morphologies of the fracture surfaces were examined using a scanning electron microscope (S-3500N, Hitachi, Tokyo, Japan) coupled with an energy-dispersive X-ray spectroscope (Octane pro, EDAX, Mahwah, NJ, USA). The crack initiation sites were identified on the fracture surfaces by observing the ratchet marks, ridges, and morphologies of the crack propagation area (stage II region).

The surface morphology and the elemental composition of the hydrogel crescent microswimmers were characterized using scanning electron microscopy (SEM, ZEISS, Merlin, OR, USA) at 5 keV and 1 nA and energy-dispersive spectrometry (EDS, EDAX, Mahwah, NJ, USA, Octane Pro), respectively.