Freeze drying scanning electron microscopic

Fig. 3.25.1. Porous structure of collagen sponge produced by freezing in a cryogenic bath at -25 °C and subsequently freeze dried (scanning electron microscope, white bar = 1 mm) (from 13.67]).

Fig. 1.42. Scanning electron-microscopic photographs of different freeze dried products.

Fig. 1.44. Scanning electron-microscopic photographs of a vial containing freeze dried trehalose solution, (a), collapsed product from the bottom of the product (b), shrunk product after 6 months of storage at +20 °C with a RM too high and stored at a too high a temperature (Fig. 6 from [ 1.29]).

Representative freeze-dried samples were mounted on aluminum stubs using conductive paint, coated with gold/palladium (60 U0) in a Technics sputter coater and examined in an ETEC Autoscan scanning electron microscope at 10 kV. 

The samples were moimted on stubs, freeze dried, coated with gold, examined, and photographed in a Scanning Electron Microscope LEICA S 360. 

The surface morphology of the granules was examined using a scanning electron microscope (Hitachi S-570). The freeze-dried granules were mounted on metal stubs, and the membranes were coated with gold for 6 min. The surfaces were then observed and photographed. 

Microscopic observations were done on a Phillips High Resolution Scanning Electron Microscope. To reveal solid material inside the microcolumn, a freeze-fracture technique was used after samples were washed with methanol and dried under normal conditions. 

Traditional electron microscopy is conducted in high vacuum, which imposes specific efforts to sample preparation. Particles from colloidal suspensions have to be deposited onto an appropriate substrate (e.g. on carbon or silica films) and dried. Alternatively, the suspensions can be shock-freezed and particles are subsequently excavated from the continuous phase by special cryo-preparation techniques (Schmidt et al. 1994, pp. 694—705). The sample preparation can be considerably reduced with environmental scanning electron microscopes (ESEM), which are operated up to 1000 Pa and, thus, even facilitate the analysis of wet surfaces. However, the ease in operation is at the expense of resolution (Danilatos 1993). 

For observing structural preservation of freeze-dried cells at greater details than provided by optical microscopy, a JOEL JSM 35 scanning electron microscope (JEOL Ltd., Tokyo, Japan) was used in this study. Eor improving the quality of SEM images, the freeze-dried cells were coated with a thin layer of Au/Pd in a sputter coater (Ted Pella Inc., Redding, CA, USA). 

At the same time, the surfactant Beycostat A B09 (an add phosphate ester of ethoxylated nonyl phenol) was mixed with a CN suspension and the pH adjusted to 7.5 before freeze-drying for apphcation in solution blending and melt compounding. Scanning electron microscope observation revealed that the Beycostat A B09-coated CNs formed a sticky mixture whereas the CNs without surfactant had a fluffy texture... 

With a cryo-scanning electron microscope, it is possible to freeze-dry a sample inside the equipment, coat it with a thin layer of conductive material, and observe the morphology when it is inunersed in a liquid. 

The stability and suitability of the formulations also needs to be determined, for example, whether the viscosity of the formulation is suitable for the administration route and is stable over time. The water content is a parameter that often has a direct influence on the stability of solid formulations and may influence the appearance of freeze-dried products immensely. Karl-Fisher titration, thermogravitometric analysis (TGA), or DSC is normally used to determine the water content. Various microscopic techniques, where both macroscopic and microscopic appearance of formulation can be determined, such as particle appearance by scanning electron microscopy (SEM) or transmission electron microscopy (TEM), are usually only needed for special formulation. There are several other methods, but which one to choose depends entirely on the formulation and the critical parameters (149,150). 

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