Yihan Wang, et al. Carbohydrate Polymers, 2015, 122(20), 18-25.
Ultrasonic atomization combined with freeze casting can easily prepare oriented chitosan nanofibers with a diameter less than 100 nanometers. The obtained chitosan nanofibers can be used in biomedicine and food engineering.
Preparation procedure
· A 0.4 wt% aqueous chitosan solution (molecular weight = 22 kDa) was poured into the atomization device's reservoir and atomized multiple times until a complete mist was produced by the nozzle. A stainless steel dish was filled with either liquid nitrogen, an ice/NaCl mixture, or dry-ice/ethanol, and then a silicon wafer was placed on top until its surface started to freeze. The PSAF nozzle tip was positioned 5 cm from the center of the wafer and aligned with its edge, remaining parallel to the wafer while a single layer was atomized along this edge. The wafer was then promptly transferred to a freeze dryer, where it was lyophilized under vacuum for approximately 5 hours at -52 ◦C.
· To enable atomization at different temperatures, the chitosan solution was divided into three small beakers. The first beaker was kept in the freezer compartment of a refrigerator at roughly 0 ◦C until it formed an ice-water mixture. The second beaker remained at room temperature (around 25 ◦C), and the third was heated to 37 ◦C. Additionally, a common household sprayer and an airbrush, equipped with a 0.2 mm nozzle and a 2.5 ml cup, were utilized for atomization. The airbrush operated under a pressure range of 0.1-0.6 MPa, using a small air pump and a pressure control valve.
Treviño-Garza, et al. Postharvest Biology and Technology, 2017, 128, 63-75.