Pharmaceutical Freeze-drying Research Articles

Development of a Single Vial Mass Flow Rate Monitor to Assess Pharmaceutical Freeze Drying Heterogeneity.

During pharmaceutical lyophilization processes, inter-vial drying heterogeneity remains a significant obstacle. Due to differences in heat and mass transfer based on vial position within the freeze drier, edge vials freeze differently, are typically warmer and dry faster than center vials. This vial position-dependent heterogeneity within the freeze dryer leads to tradeoffs during process development. During primary drying, process developers must be careful to avoid shelf temperatures that would result in overheating of edge vials causing the product sublimation interface temperature to rise above the critical (collapse) temperature. However, at lower shelf temperatures, center vials require longer to complete primary drying, risking collapse or melt-back due to incomplete drying. Both situations may result in poor product quality affecting drug stability, activity, and reconstitution times. We present a new approach for monitoring vial location-specific water vapor mass flow based on Tunable Diode Laser Absorption Spectroscopy (TDLAS). The single vial monitor enables measurement of the gas flow velocity, water vapor temperature, and gas concentration from the sublimating ice, enabling the calculation of the mass flow rate which can be used in combination with a heat and mass transfer model to determine vial heat transfer coefficients and product resistance to drying. These parameters can in turn be used for robust and rapid process development and control.

Computational and intelligence modeling analysis of pharmaceutical freeze drying for prediction of temperature in the process

Accurate temperature prediction is crucial for various scientific and engineering applications, yet it remains challenging due to the complex relationships between spatial coordinates and temperature variations. This study addresses this challenge by exploring advanced machine learning models to improve prediction accuracy, filling the research gap in optimizing predictive models for temperature estimation in freeze drying of pharmaceuticals. We employed Support Vector Regression (SVR), Poisson Regression (POR), and Adaptive Neuro-Fuzzy Inference System (ANFIS) models, each enhanced using the Cheetah Optimizer (CO), to estimate temperature based on spatial coordinates (X, Y, Z) in the domain of process. The methodology involved training and testing these models on a dataset comprising spatial and temperature data, with a focus on improving accuracy through optimization techniques. Validation of the models showed that the CO-SVR model outperformed the others, achieving an R2 score of 0.953, Mean Squared Error (MSE) of 9.893, and Mean Absolute Error (MAE) of 2.549. This represents a significant improvement over the CO-ANFIS model, which obtained an R2 of 0.863, MSE of 23.583, and MAE of 3.912. The CO-POR model showed the lowest predictive capability, with an R2 score of 0.753, MSE of 57.608, and MAE of 6.756. These findings underscore the effectiveness of the Cheetah Optimizer in enhancing the accuracy of SVR models for temperature prediction, suggesting its potential for broader applications in predictive modeling where accuracy is paramount.

The Freeze-Drying of Pharmaceuticals in Vials Nested in a Rack System-Part II: Primary Drying Behaviour.

The freeze-drying of biopharmaceuticals is a common strategy to extend their shelf-life and facilitate the distribution of therapeutics. The drying phase is the most demanding one in terms of energy consumption and determines the overall process time. Our previous work showed how the loading configuration can impact freezing. This paper focuses on primary drying by comparing the thermal behaviour of vials loaded in direct contact with the shelf or nested in a rack system. The overall heat transfer coefficient from the apparatus to the product was evaluated at different chamber pressures (5-30 Pa) and shelf temperatures (from -10 °C to +30 °C), and in the case of various vial positions (central, semi-border, and border vials). Because of the suspended configuration, the heat transfer coefficient was less affected by chamber pressure in vials nested in a rack system. The two loading configurations displayed comparable heat transfer efficiency below 10 Pa. For higher chamber pressure, the heat transfer coefficients of nested vials were lower than those of vials in direct contact with the shelf. Nevertheless, the rack system was beneficial for reducing the inter-vial variability as it promoted higher uniformity in the heat transfer coefficients of central vials. Eventually, thermal image analyses highlighted limited temperature differences between the vials and the rack system.

Impact of post-freeze annealing on shrinkage of sucrose and trehalose lyophilisates

Freeze-drying of pharmaceuticals produces lyophilisates with properties that depend on both the formulation and the process. Characterisation of the lyophilisate in terms of appearance is necessary not only to produce a visually appealing product, but also to gain insight into the freeze-drying process. The present study investigates the impact of post-freeze annealing on the volume of lyophilisates. For this purpose, sucrose and trehalose solutions were freeze-dried with different annealing conditions and the resulting lyophilisates were analysed with a 3D structured light scanner. The external structure of the lyophilisates was found to be dependent on the bulk materials as well as the choice of vials, while the volume was influenced by the annealing time and temperature. Additionally, differential scanning calorimetry was used to determine glass transition temperatures of frozen samples. As a novelty, the volumes of the lyophilisates and their corresponding glass transition temperatures were compared. This resulted in a correlation supporting the theory that the shrinkage of lyophilisates depends on the amount of residual water in the freeze-concentrated amorphous phase before drying. Understanding the volume change of lyophilisates, in combination with material properties such as glass transition temperature, forms the basis for relating physicochemical properties to process parameters in lyophilisation.

Experimental validation of multi-vial control for primary drying in a pilot-scale unit

Primary drying is the bottleneck of pharmaceutical lyophilization, as it represents the most time and energy-consuming stage and largely determines the quality of the final product. The common practice runs the process under pre-calculated input profiles while considering average drying dynamics for the batch. This results in conservative and underperforming cycles. In this regard, the paper proposes and experimentally validates an in-line control strategy for primary drying. It explicitly accounts for intra-lot drying heterogeneity using three models, each one calibrated for a reference vial position in the chamber. Two separate experiments evaluate the proposed framework: offline and in-line process control. Validation on a pilot-scale unit shows a cycle time reduction of the proposed approaches compared to standard drying protocol at constant operating conditions. The input profiles obtained by offline control lead to a 16% shorter cycle time; however, the lack of feedback during the cycle impedes addressing potential parametric variations and model mismatches. Conversely, in-line control yields a reduction of 13% while allowing careful monitoring of the product status, ensuring a more dependable cycle. In both cases, the visual quality inspection confirms the acceptability of the final product without visible degradation.

Freeze-Drying of Pharmaceuticals in Vials Nested in a Rack System—Part I: Freezing Behaviour

The distribution of biopharmaceuticals often requires either ultra-cold conditions or lyophilisation. In both cases, the drug product is frozen and, thus, exposed to similar stress conditions, which can be detrimental to its quality. However, these stresses can be inhibited or mitigated by a suitable formulation and/or an appropriate freezing design. This paper addresses how the key freezing parameters, i.e., ice nucleation temperature and cooling rate, impact the freezing behaviour of a sucrose-based formulation. The analysis included two loading configurations, vials directly resting on the shelf and nested in a rack system. The loading configuration affected the product freezing rate and the ice nucleation temperature distribution, resulting in larger ice crystals in the case of vials nested in a rack system. SEM micrographs and specific surface area measurements confirmed the different product morphology. Eventually, the different product morphology impacted the bioactivity recovery of lactate dehydrogenase.

A non-invasive multipoint product temperature measurement for pharmaceutical lyophilization

Monitoring product temperature during lyophilization is critical, especially during the process development stage, as the final product may be jeopardized if its process temperature exceeds a threshold value. Also, in-situ temperature monitoring of the product gives the capability of creating an optimized closed-loop lyophilization process. While conventional thermocouples can track product temperature, they are invasive, limited to a single-point measurement, and can significantly alter the freezing and drying behavior of the product in the monitored vial. This work has developed a new methodology that combines non-invasive temperature monitoring and comprehensive modeling. It allows the accurate reconstruction of the complete temperature profile of the product inside the vial during the lyophilization process. The proposed methodology is experimentally validated by combining the sensors’ wirelessly collected data with the advanced multiphysics simulations. The flexible wireless multi-point temperature sensing probe is produced using micro-manufacturing techniques and attached outside the vial, allowing for accurate extraction of the product temperature.

Rapid Depressurization Based Controlled Ice Nucleation in Pharmaceutical Freeze-drying: The Roles of the Ballast Gas and the Vial

Controlled ice nucleation offers several key benefits to the pharmaceutical lyophilization process, including reducing lyophilization cycle time, control of ice crystal morphology, and increased consistency of lyophilized product quality attributes. The rapid depressurization based controlled ice nucleation technique is one of the several demonstrated controlled ice nucleation technologies and relies on the rapid discharge of an inert pressurized gas to induce ice nucleation. In this work, a series of custom wireless gas pressure and temperature sensors were developed and applied to this process to better understand the mechanism of controlled ice nucleation by depressurization. The devices capture highly transient conditions both in the chamber near the vial and within the vial headspace throughout the entire process. The effects of ballast gas composition, initial charge pressure, and vial size on gas pressure and headspace/chamber temperature are explored individually. We model the depressurization as an isentropic process, allowing the influence of these parameters to be evaluated quantitatively. It is demonstrated that monatomic gases (e.g. argon) with low thermal conductivity produce the most favorable conditions for ice nucleation at the end of depressurization, based on temperature drop in the vial headspace. Experimental data also reveal a correlation between initial charge pressure and vial size with the temperature drop within the vial headspace, during depressurization. These findings ultimately provide deeper insight into the rapid depressurization based controlled ice nucleation process and help lay the foundation for a more robust process development and control.

Wireless sensor networks for pharmaceutical lyophilization: Quantification of local gas pressure and temperature in primary drying

Wireless sensor networks have become prolific in a wide range of industrial processes and offer several key advantages over their wired counterparts in terms of positioning flexibility, modularity, interconnectivity, and data routing. We demonstrate their utility in pharmaceutical lyophilization by developing a series of wireless devices to measure spatial variations in gas pressure and temperature during primary drying. The influence of shelf temperature, chamber pressure, excipient concentration, and dryer configuration are explored for various representative cycles using a laboratory-scale pharmaceutical lyophilizer. Pressure and temperature variations across the shelf for these cases are shown to vary up to 1.2 Pa and 10 °C, respectively. Experimental measurements are supported by computational fluid dynamics simulations to reveal the mechanisms driving the vapor flow. The measurements and simulation data are then combined to estimate the shelf-wise sublimation rate in the inverse sense to within a deviation of 3% based on comparison with gravimetric data. We then apply the sublimation rate profile to obtain the vial heat transfer coefficient and product mass transfer resistance for a 5% w/v mannitol formulation. Finally, these parameters are applied to a one-dimensional quasi-steady heat transfer model to predict the evolution of the product temperature over the course of primary drying. Thermocouple measurements of product temperature are compared directly to the simulated data and demonstrate accuracy comparable to existing published one-dimensional models.

Molecular Insights on Successful Reconstitution of Freeze-Dried Nanofibrillated Cellulose Hydrogel.

The diversity and safety of nanofibrillated cellulose (NFC) hydrogels have gained a vast amount of interest at the pharmaceutical site in recent years. Moreover, this biomaterial has a high potential to be utilized as a protective matrix during the freeze-drying of heat-sensitive pharmaceuticals and biologics to increase their properties for long-term storing at room temperature and transportation. Since freeze-drying and subsequent reconstitution have not been optimized for this biomaterial, we must find a wider understanding of the process itself as well as the molecular level interactions between the NFC hydrogel and the most suitable lyoprotectants. Herein we optimized the reconstitution of the freeze-dried NFC hydrogel by considering critical quality attributes required to ensure the success of the process and gained insights of the obtained experimental data by simulating the effects of the used lyoprotectants on water and NFC. We discovered the correlation between the measured characteristics and molecular dynamics simulations and obtained successful freeze-drying and subsequent reconstitution of NFC hydrogel with the presence of 300 mM of sucrose. These findings demonstrated the possibility of using the simulations together with the experimental measurements to obtain a more comprehensive way to design a successful freeze-drying process, which could be utilized in future pharmaceutical applications.

Cryopreservation and Lyophilization of Pharmaceuticals and Vaccines

Cryopreservation and Lyophilization of Pharmaceuticals and Vaccines

Temperature/end point monitoring and modelling of a batch freeze-drying process using an infrared camera

Temperature monitoring and accurate drying end time determination are crucial for final product quality in vacuum freeze-drying of pharmaceuticals. Whether crystalline or amorphous solutes are used in the formulation, product temperature during ice sublimation should be kept below a threshold limit to avoid damage to the product structure. Hence, there is a need to continuously monitor product temperature throughout this process. Current monitoring tools, such as thermocouples and Pirani gauge pressure sensors, have several limitations such as affecting product dynamics or imprecise end point determination. In this work, a monitoring tool based on infrared (IR) thermography is used for batch freeze-drying processes. Batches using three different vial sizes, with up to 157 vials, were studied, allowing to extend and better describe the representativeness of IR thermography for this application. The detailed axial temperature profiles obtained through IR imaging allowed not only a comprehensive non-invasive temperature monitoring of the product, but also tracking of the sublimation interface. IR temperature measurements and primary drying end point determination were compared to standard methods and thus verified. Parameters important for freeze drying design space calculation, namely the global heat coefficient (Kv) and cake resistance to vapor flow (Rp), were also accurately estimated with the proposed method.

Primary Drying Optimization in Pharmaceutical Freeze-Drying: A Multivial Stochastic Modeling Framework

Primary drying is the most time-consuming and energy-intensive step in pharmaceutical freeze-drying. Minimizing the duration of this stage is of paramount importance to speed up process development...

A new mathematical model for monitoring the temporal evolution of the ice crystal size distribution during freezing in pharmaceutical solutions

The freezing step plays a key role in the overall economy of the vacuum freeze-drying of pharmaceuticals, since the nucleation and crystal growth kinetics determine the number and size distribution of the crystals formed. In this work, a new mathematical model of the freezing step of a (bio)pharmaceutical solution is developed and validated. Both nucleation and crystal growth kinetics are modeled and included in a one-dimensional population balance (1D-PBM) that describes, given the product temperature measurement, the evolution of the pore size distribution during freezing. The developed model is coupled with the real-time measurements obtained from an infrared video camera. The ending time of the primary drying stage, and the maximum temperature inside the material, simulated through a simplified model of the process and the pore distribution forecast, resulted in good agreement with experimental values. The resulting Process Analytical Technology (PAT) has the potential to boost the development and optimization of a freeze-drying cycle and the implementation of a physically grounded Quality-by-Design approach in the manufacturing of pharmaceuticals. A more general mathematical model, including the aforementioned population balance, of a vial filled with a solution of sucrose was also developed and used to further validate the approach.

On-line product quality and process failure monitoring in freeze-drying of pharmaceutical products

In this work the information provided by a noninvasive imaging sensor was used to develop two algorithms for real time fault detection and product quality monitoring during the Vacuum Freeze-Drying of single dose pharmaceuticals. Two algorithms based on multivariate statistical techniques, namely Principal Component Analysis and Partial Least Square Regression, were developed and compared. Five batches obtained under Normal Operating Conditions were used to train a reference model of the process; the classification abilities of these algorithms were tested on five more batches simulating different kind of faults. Good classification performances have been obtained with both algorithms. Coupling the information obtained from an infrared camera with that of other variables obtained from the PLC of the equipment, and from the textural analysis performed on the RGB images of the product, strongly improves the performances of the algorithms. The proposed algorithms can account for the heterogeneity of the batch and aim to reduce the off-specification products.

From Batch to Continuous: Freeze-Drying of Suspended Vials for Pharmaceuticals in Unit-Doses

In response to the current trend in the pharmaceutical industry, a new concept for the freeze-drying of pharmaceuticals in unit-doses is presented: the continuous freeze-drying/lyophilization of su...

Multi-Point Wireless Temperature Sensing System for Monitoring Pharmaceutical Lyophilization.

This work presents the design and evaluation of a fully wireless, multi-point temperature sensor system as a Process Analytical Technology (PAT) for lyophilization. Each sensor contains seven sensing elements which measure the product temperature at various positions of the contents of a glass vial. The sensor performance was studied by freeze drying experiments with sensor placement in both center and edge of full shelf of 6R glass vials with 4 ml fill volume. Product temperature profile and primary drying time measured at the bottom center position in the glass vial by the wireless sensor as well as the primary drying time are in close comparison with the thermocouple data. The drying times during primary drying were determined at the top, higher middle, lower middle and bottom positions which are 3.26 mm apart vertically in the vial by the wireless sensor based on the temperature profile measured at different positions. For a center vial, the drying time from the start of primary drying to each layer was measured at 3.9, 9.3, 14.2, and 21 h respectively, allowing to track the sublimation interface during primary drying phase. In addition, sublimation rate at each layer was calculated based on the drying time and theoretical weight loss of ice in the product. The sublimation rate at the beginning of the primary drying was similar to the sublimation rate by gravimetric method. Furthermore, the vial heat transfer coefficient (Kv) was also calculated based on the sublimation rate. Thus, allowing the use of the multi-point wireless sensor to rapidly monitor the sublimation rate and Kv for every batch as continuous process verification. Similar tests were also conducted with 3% w/v mannitol solutions and the results were consistent demonstrating potential for real-time monitoring, process verification and cycle optimization for pharmaceutical lyophilization.

Determination of the dried product resistance variability and its influence on the product temperature in pharmaceutical freeze-drying

During the primary drying step of the freeze-drying process, mass transfer resistance strongly affects the product temperature, and consequently the final product quality. The main objective of this study was to evaluate the variability of the mass transfer resistance resulting from the dried product layer (Rp) in a manufacturing batch of vials, and its potential effect on the product temperature, from data obtained in a pilot scale freeze-dryer. Sublimation experiments were run at −25 °C and 10 Pa using two different freezing protocols: with spontaneous or controlled ice nucleation. Five repetitions of each condition were performed. Global (pressure rise test) and local (gravimetric) methods were applied as complementary approaches to estimate Rp. The global method allowed to assess variability of the evolution of Rp with the dried layer thickness between different experiments whereas the local method informed about Rp variability at a fixed time within the vial batch. A product temperature variability of approximately ±4.4 °C was defined for a product dried layer thickness of 5 mm. The present approach can be used to estimate the risk of failure of the process due to mass transfer variability when designing freeze-drying cycle.

Experimental Aspects of Measuring the Vial Heat Transfer Coefficient in Pharmaceutical Freeze-Drying

One of the current methods for cycle optimization in primary drying to is develop a graphical design space based on quality by design (QbD). In order to construct the design space, the vial heat transfer coefficient (Kv) is needed. This paper investigated experimental factors that can affect the Kv result, examined the relationship between the batch average Kv and Kv values for individual vials, and recommended best practices for measuring Kv. Factors investigated included the technique for measuring ice temperature, shelf temperature, the use of a radiation shield on the door of the freeze-dry chamber, and shelf spacing. All experiments reported here used a chamber pressure of 100mTorr. The most important factor was the technique for ice temperature measurement, where it is important to assure that any restrictions to vapor flow at the top of the vial are the same between monitored and non-monitored vials. Another factor that was found to play a role was the shelf temperature whereby the lower the shelf temperature, the larger the "edge effect," and the larger the average Kv. Factors that were found to not have a significant effect were the use of a radiation shield inside the chamber door and the shelf spacing. Being aware of these factors and knowing best practices when determining the vial heat coefficient will lead to more accurate design spaces and better cycle optimization.

Quantitative risk assessment via uncertainty analysis in combination with error propagation for the determination of the dynamic Design Space of the primary drying step during freeze-drying

Traditional pharmaceutical freeze-drying is an inefficient batch process often applied to improve the stability of biopharmaceutical drug products. The freeze-drying process is regulated by the (dynamic) settings of the adaptable process parameters shelf temperature Ts and chamber pressure Pc. Mechanistic modelling of the primary drying step allows the computation of the optimal combination of Ts and Pc in function of the primary drying time. In this study, an uncertainty analysis was performed on the mechanistic primary drying model to construct the dynamic Design Space for the primary drying step of a freeze-drying process, allowing to quantitatively estimate and control the risk of cake collapse (i.e., the Risk of Failure (RoF)). The propagation of the error on the estimation of the thickness of the dried layer Ldried as function of primary drying time was included in the uncertainty analysis. The constructed dynamic Design Space and the predicted primary drying endpoint were experimentally verified for different RoF acceptance levels (1%, 25%, 50% and 99% RoF), defined as the chance of macroscopic cake collapse in one or more vials. An acceptable cake structure was only obtained for the verification runs with a preset RoF of 1% and 25%. The run with the nominal values for the input variables (RoF of 50%) led to collapse in a significant number of vials. For each RoF acceptance level, the experimentally determined primary drying endpoint was situated below the computed endpoint, with a certainty of 99%, ensuring sublimation was finished before secondary drying was started. The uncertainty on the model input parameters demonstrates the need of the uncertainty analysis for the determination of the dynamic Design Space to quantitatively estimate the risk of batch rejection due to cake collapse.