Experimental Study of the Impact of Pore Structure on Drying Kinetics and Sublimation Front Patterns

Freeze-drying frozen maltodextrin solutions with solid contents of 5% and 30% (w/w) was experimentally investigated using neutron imaging at PSI Villigen/Switzerland. Different solid contents, as well as annealing at −5 °C for 11 h, were used to modify the porous structure of the samples, which was...

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Bibliographic Details
Published in:Pharmaceutics 2022-07, Vol.14 (8), p.1538
Main Authors: Thomik, Maximilian, Gruber, Sebastian, Kaestner, Anders, Foerst, Petra, Tsotsas, Evangelos, Vorhauer-Huget, Nicole
Format: Article
Language:English
Subjects:
Aluminum
Chemical properties
Chemical reaction, Rate of
drying rates
Energy consumption
Experiments
Freeze-drying
Heat
image processing
in operando visualization
lyophilization
Methods
neutron imaging
Oligosaccharides
Pharmaceutical research
Pore size
Porosity
Porous materials
Sublimation (Physics)
Temperature
Tomography
X-ray tomography
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Summary:Freeze-drying frozen maltodextrin solutions with solid contents of 5% and 30% (w/w) was experimentally investigated using neutron imaging at PSI Villigen/Switzerland. Different solid contents, as well as annealing at −5 °C for 11 h, were used to modify the porous structure of the samples, which was quantified using X-ray computed tomography. Annealing of the 5% (w/w) sample, with a pore size distribution (PSD) of 23.7 ± 11.1 µm, yielded a very open pore space with high porosity (ε = 0.96) and a PSD of 33.0 ± 27.0 µm. In contrast, the higher solid content resulted in small, lamellar, narrow pores with high anisotropy and a porosity of ε = 0.65, as well as a PSD of 13.5 ± 4 µm. In operando neutron imaging was used to show the impact of the structure of frozen maltodextrin on the overall drying kinetics and shape of the sublimation front during freeze-drying. For this purpose, a freeze-drying stage was employed, which allowed a novel approach to time- and space-resolved monitoring of the ice phase. The sublimation front propagation was quantitatively analyzed based on ice saturation profiles and sublimation rates. The dependence of drying velocity on structure is nicely demonstrated by the data. In addition, it is shown that the sublimation front widened during freeze-drying, resulting in either rather concave or convex shape depending on morphological parameters.
ISSN:1999-4923
1999-4923
DOI:10.3390/pharmaceutics14081538