Category: Formulation and Quality
Purpose: Freeze drying (lyophilization) is a common method of stabilization for protein-based therapeutics and vaccines. While lyophilization is considered more gentle than other drying methods, proteins are often formulated with amorphous saccharides or polymers, which can serve not only to prevent denaturation during processing but also as a rigid matrix that provides some physical stabilization in the dried state. However, it has been established that environmental conditions such as temperature and humidity have a strong impact on product performance under selected storage conditions. In this study, the influence of different protein-excipient ratios during lyophilization on the glass transition, water sorption behavior and mechanical properties has been studied.
Methods: Dynamic Vapor Sorption (DVS) is a well-established gravimetric method for the determination of vapor sorption isotherms. In the current study, water sorption and glass transition behavior of different proteins, co-lyophilized with different saccharides at a series of ratios, were investigated at 25°C. Also, the inclusion of glycerol was investigated to see if it affected the end product’s hydrophilicity. In addition, mechanical properties and robustness of the lyo cakes were studied using a MicroPress. The MicroPress uses a linear actuator to gently compress the cake while a load cell measures the force applied.
Results: The protein-excipient samples typically showed three distinct phase transitions as the relative humidity was linearly ramped from 0 to 95% RH. First, a surface rearrangement/relaxation was observed at low RH conditions (5-15% RH). Second, a moisture-induced glass transition was observed at moderate RH conditions (~25-35% RH). Finally, clear evidence of an amorphous to crystalline transformation was observed at higher humidities (above 50% RH). For formulations using sucrose, a deliquescence event was also observed above 90% RH. The transition that was most affected by protein-excipient ratio was the amorphous-crystalline transformation humidity. The addition of glycerol did have a measurable effect on the overall product hydrophilicity. The mechanical properties of the freeze-dried cakes were determined by measuring Young’s Modulus (robustness) and max stress at failure (strength).
Conclusion: Different processing conditions and protein-excipient ratios had a strong effect on the moisture-sorption behavior of the final lyophilized product. Multiple moisture-induced phase transitions were observed, while the amorphous to crystalline transformation points were most affected by product formulation.
Frank Thielmann– Novartis Pharma AG, Basel, Basel-Landschaft, Switzerland
Jerry Heng– Reader, Imperial College London, London, England, United Kingdom
Kevin Ward– Winchester, England, United Kingdom
Andrew Bright– Winchester, England, United Kingdom
Joshua Robinson– Winchester, England, United Kingdom