In-Line Monitoring of the Freeze-Drying Process by Means of Heat Flux Sensors

Shear stress as a driver of degradation for protein-based therapeutics: More accomplice than culprit

Protein degradation is a major concern for protein-based therapeutics. It may alter the biological activity of the product and raise the potential for undesirable effects on the patients. Among the numerous drivers of protein degradation, shear stress has been the focus around which much work has revolved since the 1970s. In the pharmaceutical realm, the product is often processed through several unit operations, which include mixing, pumping, filtration, filling, and atomization. Nonetheless, the drug might be exposed to significant shear stresses, which might cooperatively contribute to product degradation, together with interfacial stress. This review presents fundamentals of shear stress about protein structure, followed by an overview of the drivers of product degradation. The impact of shear stress on protein stability in different unit operations is then presented, and recommendations for limiting the adverse effects on the biopharmaceutical formulations are outlined. Finally, several devices used to explore the effects of shear stress are discussed.

Root Cause Analysis of An Inverse Relationship Between The Ice Nucleation Temperature, Process Efficiency And Quality of A Lyophilized Product

The aim of this study was to probe an unexpected relationship between the ice nucleation temperature (TIN), process efficiency and product attributes in a controlled ice nucleation (CIN) lyophilization process. An amorphous product was lyophilized with (CIN-5 °C, CIN-7 °C or CIN-10 °C) or without (NOCIN) control of ice nucleation. Process parameters and product attributes were monitored and compared using a series of advanced in-line and off-line process analytical technology (PAT) tools. Unexpectedly, an indirect relationship was observed between TIN and primary drying efficiency for the CIN processes. Further, the CIN-5 °C process was associated with higher product resistance to mass flow than corresponding CIN-7 °C and CIN-10 °C processes. Surprisingly, the air voids in some NOCIN products were larger than CIN-5 °C products but comparable to CIN-7 °C. Heat flux analysis revealed an indirect relationship between TIN and the minimum hold time required to complete solidification. The heat flux analysis also revealed all products underwent complete solidification prior to primary drying. The order of homogeneity in water activity of the products was CIN-5 °C ≥NOCIN>CIN-7 °C. The higher homogeneity in water activity of CIN-5 °C than corresponding CIN-7 °C processes indicated that the lower process efficiency of CIN-5 °C could not be attributed to unsuccessful induction of ice nucleation during CIN-5 °C. High resolution micro-CT imaging and Artificial Intelligence Image analysis revealed cake wall deformation in CIN-7 °C and NOCIN products but not in CIN-5 °C. In addition, NOCIN products had bimodal distribution in air voids with median size range of 4-5 µm and 151.9-309 µm, respectively, hence the lower process efficiency of NOCIN despite the higher D90. Thus, the observed relationship between TIN and process efficiency may be attributed to microstructural changes post freezing. This hypothesis was corroborated by visible macroscopic cake collapse in NOCIN products but not in CIN products after lyophilization at a higher shelf temperature. In conclusion, the advantages of controlling the ice nucleation temperature of a lyophilization process may only be attained through a robust process design that takes into consideration the primary and secondary drying process parameters. Further, combined use of advanced in-line and off-line PAT tools for process and product characterization may hasten the at scale adoption of advance techniques such as CIN.

Heat Flux Analysis and Assessment of Drying Kinetics during Lyophilization of Fruits in a Pilot-Scale Freeze Dryer

Vacuum freeze-drying as a process for achieving high product quality has attracted increasing attention in the last decade. Particularly in the pharmaceutical field and food processing industries, lyophilization can produce high-quality products compared to samples dried by conventional methods. Despite its benefits, lyophilization is a time-consuming and costly process that requires optimization of a number of process parameters, including shelf temperature, chamber pressure, freezing rate, and process time. This paper reports on the implementation of heat flux measurements that allow noninvasive real-time determination of the endpoint of the primary drying stage as an essential parameter for the effective optimization of the overall drying time. Quantitative analysis of the drying kinetics of five fruits (kiwifruit, avocado, Asian pear, persimmon, and passion fruit) was assessed by comparing the heat flux and temperature profiles of samples during the lyophilization process. For a 24 h lyophilization cycle, average heat fluxes in the primary drying phase ranged from 250 to 570 W/m2. A significant correlation was found between the temperature and heat flux distributions at the estimated endpoint of the sublimation process and the corresponding transition into the secondary drying stage. Furthermore, good agreement was also found for the freezing phase. The use of real-time heat flux measurements proved to be a cost-effective experimental method to better understand the process variables in order to reduce the lyophilization cycle time and overall energy consumption.

Lyophilization cycle design for highly concentrated protein formulations supported by micro freeze-dryer and heat flux sensor

High-concentration protein formulations (HCPFs) represent a common strategy and freeze-drying can mitigate the stability challenges of HCPFs. In general, an in-depth characterization of the lyophilization process is essential to not impair the product quality by inappropriate process parameters. The aim of this study was to create a primary drying design space for lyophilized HCPFs by utilizing the heat flux sensor (HFS) integrated in a MicroFD with a minimum number of cycles and product vials. All the necessary data to obtain the design space were determined starting from only two lyophilization cycles, each holding 19 vials. The vial heat transfer coefficient (Kv) was determined by the HFS and compared to gravimetric values. The results indicate a consistant offset between the HFS and the gravimetry based values for annealed samples with higher protein content. This work highlights a possibility of integrating new technologies, the HFS and the MicroFD to generate a design space for lyophilization of HCPFs, which enables to implement a QbD approach at minimal material and time investment.

A New Model-Based Approach for the Development of Freeze-Drying Cycles Using a Small-Scale Freeze-Dryer

This paper presents a model-based approach for the design of the primary drying stage of a freeze-drying process using a small-scale freeze-dryer (MicroFD® by Millrock Technology Inc.). Gravimetric tests, coupled with a model of the heat transfer to the product in the vials that account also for the heat exchange between the edge vials and the central vials, are used to infer the heat transfer coefficient from the shelf to the product in the vial (Kv), that is expected to be (almost) the same in different freeze-dryers. Differently from other approaches previously proposed, the operating conditions in MicroFD® are not chosen to mimic the dynamics of another freeze-dryer: this allows saving time and resources as no experiments are needed in the large-scale unit, and no additional tests in the small-scale unit, apart from the three gravimetric tests usually needed to assess the effect of chamber pressure on Kv. With respect to the other model parameter, Rp, the resistance of the dried cake to mass transfer, it is not influenced by the equipment and, thus values obtained in a freeze-dryer may be used to simulate the drying in a different unit, provided the same filling conditions are used, as well as the same operating conditions in the freezing stage, and cake collapse (or shrinkage) is avoided. The method was validated considering ice sublimation in two types of vials (2R and 6R) and at different operating conditions (6.7, 13.3 and 26.7 Pa), with the freeze-drying of a 5% w/w sucrose solution as a test case. An accurate estimate for both Kv and Rp was obtained with respect to the values obtained in a pilot-scale equipment, determined through independent tests for validation purposes. Simulation of the product temperature and drying time in a different unit was then possible, and results were validated experimentally.

Comparison of vial heat transfer coefficients during the primary and secondary drying stages of freeze-drying

This study uses a heat flux sensor and temperature probes to directly measure vial heat transfer coefficients (K_v) during primary and secondary drying stages of lyophilization. It is observed that K_v is 40-80% smaller during secondary drying than primary drying, and this value exhibits a weaker dependence on chamber pressure than in primary drying. These observations arise because water vapor in the chamber significantly decreases between primary and secondary drying, which alters the gas conductivity between the shelf and vial. This study tabulates K_v values for secondary drying for different vials and different chamber pressures, and demarcates the contributions from gas conduction. Lastly, the study performs an energy budget analysis on two different vials (10R glass vial and 10 mL plastic vial) to determine the major factors that contribute to vial energy consumption. During primary drying, the majority of energy supplied goes towards sublimation, while for secondary drying, the majority of energy goes towards heating the vial wall rather than desorbing bound water. We discuss the consequences of this behavior for heat transfer modeling. During secondary drying, the heat of desorption can be neglected in thermal modeling for some materials (e.g., glass) but not others (e.g., plastic vials).

Emerging PAT for Freeze-Drying Processes for Advanced Process Control

Lyophilization is a widely used drying operation, but long processing times are a major drawback. Most lyophilization processes are conducted by a recipe that is not changed or optimized after implementation. With the regulatory demanded quality by design (QbD) approach, the process can be controlled inside an optimal range, ensuring safe process conditions. Process analytical technology (PAT) is crucial because it allows real-time monitoring and is part of a control strategy. In this work, emerging PAT (manometric temperature measurement (MTM), comparative pressure measurement, heat flux sensors, and ice ruler) are used for measurements during the freeze-drying process, and their potential for implementation inside a control strategy is outlined.

Design of freeze-drying cycles: The determination of heat transfer coefficient by using heat flux sensor and MicroFD

The complexity of biopharmaceuticals requires often the freeze-drying as stabilizing process. Inadequate parameters in the primary drying phase can impair product quality, besides, increasing time and costs. Therefore, the process requires a thorough characterization and with this purpose, heat flux sensor (HFS) and miniaturized freeze-dryers conceived to emulate larger equipment, were recently introduced. Our study investigates, for the first time, the use of HFS and miniaturized freeze-dryer (MicroFD) in combination to obtain the heat transfer coefficient (K_v) for two formulation types and freezing protocols. First, as the MicroFD presents the possibility to set the temperature of vial surrounding (LyoSIM), it was determined which set-up was representative for a lab-scale freeze drying process. Additionally, the HFS-based results were compared with the data obtained by the most accurate, but time-consuming and invasive gravimetric method. Second, the role of atypical heat transfer was evaluated for HFS and gravimetric methodology with gold-coated and un-coated vials. Obtained results revealed the HFS and the MicroFD can be used in combination to obtain K_v real-time with much less effort that gravimetrically, to study different vial scenarios, and to design lyophilization processes with a limited amount of material and experiments.

Surface Treatment of Glass Vials for Lyophilization: Implications for Vacuum-Induced Surface Freezing

Freeze-drying is commonly used to increase the shelf-life of pharmaceuticals and biopharmaceuticals. Freezing represents a crucial phase in the freeze-drying process, as it determines both cycle efficiency and product quality. For this reason, different strategies have been developed to allow for a better control of freezing, among them, the so-called vacuum-induced surface freezing (VISF), which makes it possible to trigger nucleation at the same time in all the vials being processed. We studied the effect of different vial types, characterized by the presence of hydrophilic (sulfate treatment) or hydrophobic (siliconization and TopLyo Si–O–C–H layer) inner coatings, on the application of VISF. We observed that hydrophobic coatings promoted boiling and blow-up phenomena, resulting in unacceptable aesthetic defects in the final product. In contrast, hydrophilic coatings increased the risk of fogging (i.e., the undesired creeping of the product upward along the inner vial surface). We also found that the addition of a surfactant (Tween 80) to the formulation suppressed boiling in hydrophobic-coated vials, but it enhanced the formation of bubbles. This undesired bubbling events induced by the surfactant could, however, be eliminated by a degassing step prior to the application of VISF. Overall, the combination of degasification and surfactant addition seems to be a promising strategy for the successful induction of nucleation by VISF in hydrophobic vials.

Understanding Heat Transfer During the Secondary Drying Stage of Freeze Drying: Current Practice and Knowledge Gaps

Currently, there is a lack of robust models for secondary drying with comparable accuracy and flexibility as primary drying models. In order to better understand heat transfer during secondary drying, sucrose and mannitol solutions were freeze-dried in vials in a lab-scale lyophilizer under various drying conditions. Several distinct thermal characteristics for secondary drying were experimentally observed: (1) the vial heat transfer coefficient can change significantly between primary and secondary drying due to the change in water vapor content in the freeze dryer; (2) the thermal mass of the vial plays a major role in determining the cake temperature as roughly 95% of the heat supplied is absorbed by the vial walls. From a theoretical perspective, three different models of secondary drying were examined with varying degrees of complexity (full 3D simulation, 1D-averaged equations, and lumped-capacitance 0D approach). In these models, the desorption of bound water is treated as a one-way coupling with temperature. It is found that although a simple lumped-capacitance approach can capture many of the vital features of cake temperature and moisture profile, near quantitative agreement with experiments can be made by employing a 1D-averaged equation approach, where the effective thermal conductivities of the vial are determined by thermal circuits.