S 4800 sem

The morphology of microparticles was examined using SEM. The lyophilized particles were re-dispersed in nanopure water and dropped on a silicon wafer which was mounted on a SEM stub. The particles were then sputter-coated with gold-palladium for 2 minutes at 10 mA and then imaged using a Hitachi S-4800 SEM (Hitachi High-Technologies, Ontario, Canada). The size of the 12 μm microparticles was obtained from measuring the particles’ diameters (200 particles) in SEM images using ImageJ 1.44p software (Wayne Rasband, National Institutes of Health, USA). The size and zeta potential of the 0.53 μm microparticles were measured in nanopure water at 25 °C using a Zetasizer nano ZS particle analyzer (Malvern Instrument Ltd., Southborough, MA).

The morphology of the PLA-4HTB microparticles were examined using scanning electron microscopy (SEM). Briefly, microparticle samples (0.1% w/v) were suspended in nanopure water and then placed on silicon wafers and mounted on a SEM stub using double sided carbon tape. These samples were then left to dry overnight in ambient air for 24 h prior to being coated with gold-palladium using an argon beam K550 sputter coater (Emitech Ltd., Kent, England). Once coated, samples were imaged using a Hitachi S-4800 SEM (Hitachi High-Technologies). Particle size distributions were measured from SEM micrographs using ImageJ software.

After fabrication, we dried substrates and structures at room temperature overnight. We applied a gold-palladium coating using an argon beam K550 sputter coater (Emitech Ltd., Kent, England) and captured images using a Hitachi S-4800 SEM (Hitachi High-Technologies, Ontario, Canada) at an accelerating voltage of 1 kV. For parameter analysis, we analyzed vertical pores by capturing an image of each scaffold from directly above, whereas we tilted the sample stage at 30° for image capture of horizontal pores. To quantify the effect of parameters on model-to-structure fidelity, we processed images using ImageJ. Briefly, we created binary images using the software’s threshold algorithm such that the software recognized pores as dark regions. Thereafter, we measured the area (A), fitted ellipse dimensions [major axis (MjA) and minor axis] and roundness of each dark region using the ImageJ particle analysis function (for each structure, n = 19 for vertical pores, n = 6 for horizontal pores) where
$$\mathit{\text{Roundness}}=\frac{4A}{\pi {(\mathit{MjA})}^2}$$
For each vertical pore, we calculated the diameter using the average of the major and minor axes, and then calculated the diameter error by subtracting this value from the modeled pore diameter.

The morphology of the printed devices was examined using scanning electron microscopy (SEM). Samples were mounted on an aluminum stub using double-sided carbon tape. These samples were then dried overnight in ambient air for 24 h prior to being coated with gold-palladium using an argon beam K550 sputter coater (Emitech Ltd., Kent, England). Once coated, samples were imaged using a Hitachi S-4800 SEM (Hitachi High-Technologies, Tokyo, Japan) at an accelerating voltage of 1 kV with the sample stage tilted at 30°.

Alginate shell and PLGA core layers were visualized and imaged using an optical microscope. From these images, the layer diameters were measured using the open source ImageJ software. The ultra-morphology of alginate-PLGA tubes was examined using Scanning Electron Microscopy (SEM). Samples were placed on aluminum stubs and left to dry overnight in ambient air for 24 h prior to being coated with gold-palladium using an argon beam K550 sputter coater (Emitech Ltd., Kent, England). Once coated, samples were imaged using a Hitachi S-4800 SEM (Hitachi High-Technologies, Tokyo, Japan).

Membranes were rinsed with 70% ethanol, carefully dried using compressed air, then further dehydrated overnight in a desiccator. Samples were then mounted on aluminum stubs using double-sided adhesive and coated with a gold-palladium mixture using an argon beam K550 sputter coater (Emitech Ltd., Kent, England). Scanning electron micrographs were captured using a Hitachi S-4800 SEM (Hitachi High-Technologies, Ontario, Canada) at an accelerating voltage of 5 kV. Inner pore structure was examined by tilting the sample stage to 30° from horizontal.