Physical and chemical changes in Alhydrogel™ damaged by freezing

Accidental freezing of aluminum-based vaccines occurs during their storage and transportation, in both developed and developing countries. Freezing damages the freeze-sensitive aluminum adjuvanted vaccines, through separation of lattice between aluminum adjuvant and antigen, leading to formation of aluminum aggregates, and loss of potency. In this study, we examined Alhydrogel™ ([AlO(OH)]xnH₂O, aluminum hydroxide, hydrated for adsorption) stored under recommended conditions, and exposed to freezing temperature until solid-frozen. The main purpose of our research was to determine the destruction areas of the solid-frozen Alhydrogel™ using selected methods of scanning electron microscopy, energy dispersive X-ray spectroscopy, Raman spectroscopy, Fourier-transform infrared spectroscopy and transmission electron microscopy working in diffraction mode. The Zeta potential evaluation, measurements of albumin adsorption power, thermogravimetric analysis and estimation of the mass loss after drying indicated significant structural (physical) and chemical differences between the freeze-damaged and non-frozen vaccine adjuvant. The presented results are important to better understand the type and nature of damages occurring in freeze-damaged aluminum-based vaccines. These results can be used in future studies to improve the temperature stability of aluminum adjuvanted vaccines.