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Jakob Beirowski - Articles and news items

Figure 1 Schematic illustration of a particle stabilised by a steric stabiliser. Note that it has been reported that both the degree of adsorption and the density / thickness of the steric barrier are essential factors to mitigate freezing and drying stresses

Stabilisation of nanoparticles during freeze drying: The difference to proteins

Issue 4 2011, Lyophilisation / 31 August 2011 / Jakob Beirowski and Henning Gieseler, University of Erlangen-Nuremberg, Division of Pharmaceutics, Freeze Drying Focus Group

The underlying concept for the stabilisation of proteins during freeze drying is the formation of a glassy matrix in which the macromolecules remain isolated and immobilised. The concept relies on the so-called ‘vitrification hypothesis’ which assumes that the formation of an amorphous phase by lyoprotectants is mandatory to interact with the amorphous protein molecule. The use of lyoprotectants has also been found to be beneficial to preserve the original particle size distribution of nanoparticles during freeze drying. Until today, it has been speculated that the predominant mechanism to suppress physical instabilities of such colloidal particle systems is their embedment in a rigid glass. Today, there are various types of colloidal particles used in drug development, and sometimes the scientific literature gives evidence that glass formation was not necessarily required for stabilisation during freezing thawing or even freeze drying. The purpose of this article is therefore to briefly provide the latest insight into potential stabilisation mechanisms when freeze drying nanoparticles, a key knowledge for rational formulation and process design for such systems.

Application of DSC and MDSC in the development of freeze dried pharmaceuticals

Issue 6 2008, Past issues / 3 December 2008 / Jakob Beirowski, Pharmacist and Dr. Henning Gieseler, Assistant Professor, Division of Pharmaceutics, University of Erlangen-Nuremberg

Freeze drying of pharmaceuticals requires an adequate formulation design to prevent low-temperature, freezing and drying stresses. The goal is to achieve a final product with long storage stability and elegant appearance. To meet these specifications the product temperature must be controlled below the critical formulation temperature during the freeze drying cycle. DSC is an established tool to measure this critical formulation property in the development of freeze dried pharmaceuticals as it allows rapid sample preparation and analysis time. The introduction of modulated DSC (MDSC) by Reading in 1992 has greatly facilitated the interpretation of DSC results. The overlapping transitions in the same temperature range can be distinguished and characterisation of the nature of transitions is facilitated.


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