Thermal Analysis During the Commercial Phase for a Large Global Life Sciences Company
Our client’s lyophilized protein diagnostic product had been successfully launched and sales exceeded expectations. Therefore, they were facing the decision whether to expand their lyophilization capacity (and by how much) to meet demand. However, they suspected their formulation and lyophilization cycle had not been optimized due a low collapse temperature of -48°C and lower than expected yields during commercial production. They sought a collaborative partner who could assess their current lyophilization cycle and recommend meaningful (rather than small incremental) changes. They wanted to minimize formulation changes, reduce cycle length, increase yields and improve quality. Because the partner would be suggesting changes to a top selling product, they realized choosing a reputable partner was key to making their case for improvement to internal stakeholders.
As an initial step of what was to become a much larger lyophilization cycle development project, thermal analysis by differential scanning calorimetry (DSC) and freeze dry microscopy (FDM) was performed on the current formulation to determine the critical thermal temperatures and pressures. This data was then compared to the existing lyophilization cycle parameters.
DSC thermograms produced using two methods failed to identify critical temperatures – neither glass transition nor eutectic melt. Working collaboratively with the client, it was theorized that the unusually low protein concentration of <10 mg/mL might make it difficult to detect a low-energy thermal event, such as a glass transition, using DSC.
FDM results were unique as well due to the low protein concentration and the resulting freeze-dried product was lacking in structure and substance and exhibited a very thin and spongy nature. However, the onset of collapse was found to be -48°C/37mTorr and complete collapse occurred at -40.5°C/37mTorr. Other noteworthy findings were:
- A change in the morphology of the freeze-dried layer was observed in addition to the presence of bubbles at the sublimation front. The phenomena indicate the melt of at least one component of the solution and speculation that the physical changes were indicative of a glass transition not detectable by DSC.
- At full collapse, there was no longer any observable structure to the freeze-dried layer.
- A large temperature range between the onset of and full collapse is unusual. It is possible the lack of significant structure and/or the presence of multiple proteins in the formulation may have contributed to a complex collapse process. .
Thermal analysis results indicate that a lyophilization cycle:
- Should ensure the product is frozen to at least -60°C to make certain the ice and interstitial space are solid.
- That product temperature at the start of primary drying should be approximately -53°C.
- That a chamber pressure of less than 10 mTorr should be maintained to ensure pressure differential between the vapor pressure of ice at this temperature and the vapor pressure at the condenser.
The current lyophilization cycle which consumes 60+ hours in use is not optimized. The current dilute formulated solution, low fill volume and low collapse temperatures of the product result in critical temperatures that are not readily achieved by commercial lyophilizers, result in low freezing and primary drying temperatures and vapor pressures resulting in a low sublimation rate. These are the drivers for the very long and difficult to control freeze dry cycle and low product yield. BioConvergence suggested the client change their formulation by adding a bulking agent that would yield a discernable cake structure during freeze-drying and increase the collapse temperature to a level achieved by most commercial lyophilizers.