Mechanistic studies of glass vial breakage for frozen formulations. I. Vial breakage caused by crystallizable excipient mannitol.

The process of freeze-thaw not only subjects bioproducts to potentially destabilizing stress, but also imposes challenges to retain container integrity. Shipment and storage of frozen products in glass vials and thawing of the vials prior to use at clinics is a common situation. Vial integrity failure during freeze-thaw results in product loss and safety issues. Formulations of biomolecules often include crystallizable excipients, which can cause glass vial breakage during freeze-thaw operations. In this study, mannitol formulations served as models for mechanistic investigation of root causes for vial breakage. Several parameters and their impacts on vial breakage were investigated, including mannitol concentration (5% and 15%), different freeze-thaw conditions (fast, slow, and staging), fill configurations (varying fill volume/vial size ratio), and vial tray materials (plastic, stainless steel, corrugated cardboard, aluminum, and polyurethane foam). The results in this study were subjected to a statistical proportion test. The data showed that large fill volumes strongly correlated with higher percentage of vial cracks. Furthermore, the 15% mannitol was found to cause more breakage than 5% mannitol, especially with fast temperature gradient. Significantly more thawing vial breakage occurred in the fast compared to slow freeze-thaw with all types of vial trays. The freezing breakage was substantially lower than the thawing breakage using the fast temperature gradient, and the trend was reversed with the slow temperature gradient. An intermediate hold at -30 degrees C prior to further decrease in temperature proved to be a practical approach to minimize mannitol-induced vial breakage. Thermal mechanical analysis (TMA) and strain gage techniques were employed to gain mechanistic insights, and it was found that the primary causes for mannitol-induced vial breakage were partial crystallization during freezing and "secondary" crystallization of non-crystallized fraction during thawing. The strain on the vial's axial direction was significantly higher than the hoop direction, typically resulting in bottom lens of the vial coming off. Without a -30 degrees C hold, rapid volume expansions due to initial crystallization and secondary crystallization of mannitol were observed in TMA profiles, and these expansions were more apparent in 15% mannitol compared to 5% mannitol. With the introduction of a -30 degrees C hold step, abrupt expansions diminished in TMA profiles, suggesting that most of the mannitol crystallization occurred concurrently with ice solidification during the -30 degrees C holding step and, thus, secondary crystallization during thawing was minimal and the sudden expansion event was eliminated. Therefore, vial breakage during both freezing and thawing was reduced.