Carbon coater

Scanning electron microscopy (Carl Zeiss Inc., Oberkochen, Germany) was utilized to observe and capture the image of prepared dry powders. Approximately 5 mg of powder samples (raw materials and dry powder formulations) were kept on a carbon adhesive tape using a carbon coater (Quorum Technologies Ltd., Sussex, UK) and coated with gold–palladium alloy. The images were captured, and the particle size was analyzed from the captured image by measuring the geometric diameter of no less than 300 particles. To determine the geometric diameter, ImageJ software (Version 1.53e, National Institutes of Health, Bethesda, MD, USA) was used.

The powder morphology of prepared formulations was investigated by scanning electron microscopy (Carl Zeiss Inc., Oberkochen, Germany). Briefly, 5 mg powder of each sample was spread on a carbon adhesive tape and then coated with gold/palladium alloy by carbon coater (Quorum Technologies Ltd., Sussex, UK). The images of powder samples were captured at an accelerating voltage (5 kV). The diameters of at least 300 particles for each sample were measured to determine the average geometric diameter by an image analyzing software ImageJ (National Institutes of Health, Bethesda, MD, USA).