2.8 Scanning electron microscopy
The samples were placed in DI water at 37 ℃ for two days, cooled at -80
℃ for 2 hours, and then lyophilized. The cross section of the structure
was sputter coated with gold at 15 mA for 2 min (EM Ace600, Leica,
Germany) and observed under a scanning electron microscope (SEM, Flex
SEM1000, Hitachi, Japan) at 10kV. The diameters of different samples
were analyzed using image J.