Freezing- and Drying-Induced Micro- and Nano-Heterogeneity in Biological Solutions

This chapter focuses on experimental detection and quantification of heterogeneity such as freezing-induced heterogeneity and drying-induced heterogeneity, in systems of pharmaceutical interest. In general, the main experimental methods that have been applied to detect heterogeneity and phase separation are conventional microscopy (transmitted light and fluorescence microscopy), electron microscopy (scanning/transmission electron microscopy (SEM/TEM)), thermal analysis (differential scanning calorimetry (DSC)), and spectroscopy (mainly, Fourier transform infrared (FTIR) and Raman spectroscopy). Once the degree of freezing- and desiccation-induced heterogeneity in products of industrial and commercial value is established, it is believed that the demand for the development of techniques to minimize heterogeneity (and they do exist) will increase exponentially.