Microstructural Analysis of ISFIs

The microstructures of ISFIs were analyzed using SEM imaging [16 (link)]. Drug-loaded formulations (30 µL) were individually injected into 200 mL of release medium (0.1 M PBS with 2% solutol, pH 7.4) and incubated for 7 days at 37 °C. ISFIs were subsequently collected, flash-frozen using liquid nitrogen, and lyophilized for 24 h (SP VirTis Advantage XL-70, Warminster, PA, USA). The lyophilized samples were mounted on an aluminum stub using carbon tape, and sputter-coated with 5 nm of gold–palladium alloy (60:40) (Hummer X Sputter Coater, Anatech USA, Union City, CA, USA). The coated samples were then imaged using a Zeiss Supra 25 field emission scanning electron microscope with an acceleration voltage of 5 kV, 30 µm aperture, and an average working distance of 10 mm (Carl Zeiss Microscopy, LLC, Thornwood, NY, USA).