Scanning Electron Microscopy freeze drying

Fig. 1.42. Photographs of different freeze-dried products obtained by scanning electron microscopy, (a) 1 % trehalose solution, 1 °C/ min, cut out of the surface (b) 1% trahalose solution, 150 °C/min, cut out of the center ...

Fig. 2 Shape and structure of BC. a molecular cellulose chain, b scanning electron microscopy (SEM) of freeze-dried nanofiber network (magnification 10000), c pellicle of bacterial nanocellulose from common static culture...

Murase, N. Echlin, P. Franks, F. The structural states of freeze-concentrated and freeze-dried phosphates studied by scanning electron-microscopy and differential scanning calorimetry. Cryobiology 1991, 28 (4), 364—375. 

Fig. 3 Scanning electron microscopy (SEM) of (A) a freeze-dried lysozyme sample and (B) the same sample prepared via SEDS. (From Ref. l)...

For scanning electron microscopy, the carhon samples from the middle part of the column were freeze dryed, coated with gold, and viewed under Jeol — JSM-35 SEM. 

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). 

Freeze drying biological specimens Freeze drying may be used to prepare specimens for scanning electron microscopy (SEM). Formerly, soft biological materials were chemically fixed and then air dried. Tissue structure coUapsed and smaller appendages... 

Figure 9.12 Fast-freeze cryogenic scanning electron microscopy for visualizing structure development In drying or curing coatings...

The study of the rehydration ratios of forced air-dried compressed carrots after partially freeze-drying to different moisture levels showed the drying treatment significantly affected rehydration ratios in all cases [66]. The sample that was freeze-dried to 50% moisture, compressed, and then air-dried had the highest ratio and was the quickest to rehydrate. In comparison, the totally freeze-dried and hot air-dried compressed carrots showed much lower values of rehydration ratios. These observations were supported by scanning electron microscopy (SEM), which showed collapse of cellular structure and tissue coagulation to act as a barrier for rehydration. 

P Dawson, D Hockley. Scanning electron microscopy of freeze-dried preparations relationship of morphology to freeze-drying parameters. Developments in Biological Standards 75 185, 1991. 

AP MacKenzie. Freezing, freeze-drying and freeze-substitution. Proceedings of the Workshop on Biological Specimen Preparation Techniques for Scanning Electron Microscopy, IIT Research Institute, April, 1972. 

T Inoue, H Osatake. A new drying method of biological specimens for scanning electron microscopy the t-butyl alcohol freeze-drying method. Arch Histol Cytol 51 53-59, 1998. 

H Akahori, H Ishii, I Nonaka, H Yoshida. A simple freeze-drying device using tert-butyl alcohol for SEM (scanning electron microscopy) specimens. J Electron Microsc 37(6) 351-352, 1988. 

T Hojo. Specimen preparation of the human cerebellar cortex for scanning electron microscopy using a t-butyl alcohol freeze-drying device. Scanning Microsc, Suppl 10 (Science of Biological Specimen Preparation for Micro-scopy) 345-348, 1996. 

P Meredith, AM Donald, RS Payne. Freeze-drying in situ observations using cryoenvironmental scanning electron microscopy and differential scanning calorimetry. J Pharm Sci 85 631-637, 1996. 

Figure 14.16 Scanning electron microscopy of a freeze-dried hydrogel made by polyacrylic acid and polyethylene glycol (a and c) compared to the same type of gel functionalized with arginine-glycine-aspartic acid (b and d).

Fig. 5.7 Scanning electron microscopy images of mannitol (metallized samples) that have been freeze-dried from a 5% (w/w) water solution with (a) spontaneous nucleation and (b) forced nucleation. Samples processed in research laboratories of Telstar S.A., Terrassa, Spain.

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