The Study of Amorphous Phase Separation in a Model Polymer Phase-Separating System Using Raman Microscopy and a Low-Temperature Stage: Effect of Cooling Rate and Nucleation Temperature

Trehalose or Sucrose: Which of the Two Should be Used for Stabilizing Proteins in the Solid State? A Dilemma Investigated by In Situ Micro-Raman and Dielectric Relaxation Spectroscopies During and After Freeze-Drying

“…10,11 It was shown that micro-Raman Spectroscopy (mRS) is a suitable technique to monitor the secondary structure of protein 12 and to estimate the degree of stabilization by the excipient [13][14][15] during each stage of the FD process. Furthermore, mRS makes it possible to detect the phase separation, considered as source of protein denaturation, 13,16 and to clearly describe the preferential interactions between disaccharides, water and protein.…”

Amorphous-Amorphous Phase Separation in API/Polymer Formulations

“…Formulations which undergo APS usually show two distinguishable glass-transition temperatures as long as the pure component glass-transition temperatures differ to a certain extend [ 7 ]. The presence of two glass-transition temperatures is therefore considered as the main qualitative proof for the immiscibility of API/polymer formulations [ 8 ], polymer blends [ 9 , 10 , 11 ] and amorphous mixtures of APIs and small-molecule excipients, e.g., indomethacin/citric acid [ 12 ]. However, due to the high viscosity of the formulations, demixing may take very long time and therefore the quantitative analysis of APS and determining the equilibrium compositions of the two amorphous phases is quite challenging.…”

“…Koningsveld cooled polymer/solvent mixtures of certain feed compositions until turbidity was detected visually [ 13 ], which is the proof of reaching the APS region in the phase diagram. Immiscibility of solvent-free and API-free polymer blends has also been qualitatively evaluated by atomic force microscopy [ 14 ], X-ray powder diffraction [ 15 ], and micro Raman mapping [ 11 ]. Purohit and Taylor applied atomic-force microscopy combined with nanoscale infrared imaging to qualitatively evaluate the immiscibility in the system itraconazole/hydroxypropyl methylcellulose [ 16 ].…”

Heterogeneity of Protein Environments in Frozen Solutions and in the Dried State

“…An extreme case of heterogeneity would be a phase separation between a protein and excipients, resulting in two amorphous phases, protein-rich and excipient-rich [23][24][25]. A potential protein/polymer phase separation in human brain-derived neurotropic factor (BDNF) and BDNF-polyethylene glycol (PEG) co-lyophilized with dextran was suggested based on scanning electron microscopy [26].…”