Effect of Product Temperature During Primary Drying on the Long-Term Stability of Lyophilized Proteins

Development of a Stable Lyophilized Cyclophosphamide Monohydrate Formulation Using Non-Aqueous Solvents

To ensure product stability, it is critical to maintain the monohydrate state of cyclophosphamide following lyophilization, as this is the most stable solid form of the Cyclophosphamide. On the other hand, because of their limited aqueous solubility and stability, non-aqueous solvents are preferred for determining the composition and stability of bulk solutions. Hence, the purpose of this study was to use non-aqueous solvents for determining the composition and stability of bulk solutions, and to shorten the lyophilization process by retaining the cyclophosphamide monohydrate. Furthermore, prior to selecting the solvent for the bulk solution consisting of 90:10 tertiary butyl alcohol (TBA) and acetonitrile (ACN), various factors were taken into account, including the freezing point, vapor pressure of solvents, solubility, and stability of cyclophosphamide monohydrate. The concentration of the bulk solution was adjusted to 200 mg/mL in order to optimize the fill volume, enhance sublimation rates at lower temperatures during primary drying, and eliminate the need for secondary drying. The differential scanning calorimetry (DSC) measurements of bulk solution were used to improve the lyophilization cycle. The lyophilization cycle opted was freezing at a temperature of -55 °C with annealing step at -22 °C by which the reconstitution time was significantly reduced. The drying was performed at below - 25 °C while maintaining a chamber pressure of 300 mTorr. The complete removal of non-aqueous solvents was achieved by retaining water within the system. The presence of cyclophosphamide monohydrate was confirmed using X-ray diffraction (XRD). The reduction of lyophilization process time was established by conducting mass transfer tests and evaluating the physicochemical properties of the pharmaceutical product. Using non-aqueous solvents for freeze-drying cyclophosphamide is a viable option, and this study provides significant knowledge for the advancement of future generic pharmaceuticals.

Part I: Significant reduction of lyophilization process times by using novel matrix based scaffolds

To improve the long-term stability of drugs with limited stability (e.g., biologicals such as monoclonal antibodies, antibody drug conjugates or peptides), some pharmaceuticals endure a lengthy and cost-intensive process called lyophilization. While the shelf life of lyophilized drugs may be prolonged compared to their liquid form, the drawbacks come in the form of intensified manufacturing, preparation, and dosing efforts. The use of glass vials as the primary container unit for lyophilized products hinders their complication-free, fast and flexible use, as they require a skilled healthcare professional and an aseptic environment in which to prepare them. The feasibility of substituting glass vials with novel container designs offering the complete transfer of the lyophilizate cake into modern administration devices, while reducing the economic footprint of the lyophilization process, was investigated. The lyophilization process of a monoclonal antibody solution was studied by assessing primary drying conditions, homogeneity of the drying process, and critical quality attributes after successful lyophilization. The creation of novel container designs utilized vacuum-forming to generate confined containers with removable bottoms and rapid prototyping, including subtractive and additive manufacturing methods, to generate porous 3D structures for drug housing. The novel container designs generated lyophilizates twice as fast and achieved a threefold faster reconstitution compared to their vial counterparts, without adaptation of the processing conditions. We conclude that the use of intermediate process containers offers significant relief for healthcare professionals in terms of reduced probability of handling errors, while drug manufacturers benefit from the accelerated processing times, increased batch homogeneity, and sustainability.

Storage and Lyophilization of Pure Proteins

This chapter outlines empirical procedures for the storage of pure proteins with preservation of high levels of biological activity. It describes simple and workable means of preventing microbial contamination and proteolytic degradation and the use of various types of stabilizing additives. It sets out the principles of lyophilization (a complex process comprising freezing, primary drying, and secondary drying stages, otherwise known as freeze-drying). There follows a general procedure for the use of lyophilizer apparatus with emphasis on best practice and on pitfalls to avoid. The use of modulated differential scanning calorimetry to measure the glass transition temperature, a key parameter in the design and successful operation of lyophilization processes, is described. This chapter concludes with brief summaries of interesting recent work in the field.

The Influence of Local Microstructure Inhomogeneities on Local Drying Kinetics during Freeze-Drying

Freeze-drying is a gentle drying technique to dry high value products, such as pharmaceuticals, without impacting the quality of the product. However, this method is very time and cost intensive. It is known that larger pores reduce the duration of primary drying due to facilitated mass transport. However, next to the pore size, other structural parameters exist whose influence on drying kinetics is still unknown. Therefore, the aim of this article is to investigate the influence of the microstructure (pore size, shape and orientation) on local primary drying kinetics. In the study, freeze-drying experiments on maltodextrin and sucrose solutions (c₁ = 0.05 and c₂ = 0.15 w/w) were carried out in a lyomicroscope. Two-dimensional images were recorded during the whole drying process and in the dry state and analyzed on the movement of the sublimation front, pore size, orientation and shape. Different microstructures were created by using different freezing parameters, namely two different cooling rates and solid concentrations. It could be shown that for pores with a high aspect ratio, the pore orientation was more important for the drying kinetics than the pore size, while for pores with a lower aspect ratio the pore size was the decisive parameter.

Cycle Development in a Mini-Freeze Dryer: Evaluation of Manometric Temperature Measurement in Small-Scale Equipment

The objective of this research was to assess the applicability of manometric temperature measurement (MTM) and SMART™ for cycle development and monitoring of critical product and process parameters in a mini-freeze dryer using a small set of seven vials. Freeze drying cycles were developed using SMART™ which automatically defines and adapts process parameters based on input data and MTM feedback information. The freeze drying behavior and product characteristics of an amorphous model system were studied at varying wall temperature control settings of the cylindrical wall surrounding the shelf in the mini-freeze dryer. Calculated product temperature profiles were similar for all different wall temperature settings during the MTM-SMART™ runs and in good agreement with the temperatures measured by thermocouples. Product resistance profiles showed uniformity in all of the runs conducted in the mini-freeze dryer, but absolute values were slightly lower compared to values determined by MTM in a LyoStar™ pilot-scale freeze dryer. The resulting cakes exhibited comparable residual moisture content and optical appearance to the products obtained in the larger freeze dryer. An increase in intra-vial heterogeneity was found for the pore morphology in the cycle with deactivated wall temperature control in the mini-freeze dryer. SMART™ cycle design and product attributes were reproducible and a minimum load of seven 10R vials was identified for more accurate MTM values. MTM-SMART™ runs suggested, that in case of the wall temperature following the product temperature of the center vial, product temperatures differ only slightly from those in the LyoStar™ freeze dryer.

Lyophilization of Small-Molecule Injectables: an Industry Perspective on Formulation Development, Process Optimization, Scale-Up Challenges, and Drug Product Quality Attributes

Lyophilization is a pivotal manufacturing process to obtain a stable drug product that is unstable as a ready-to-use formulation. Some formulations may require the addition of drug-specific excipients such as stabilizers, buffers, and bulking agents to support the cake appearance and ensure long-term stability of the drug product. Optimization of the lyophilization process parameters at each stage including freezing and primary and secondary drying is important because these parameters can have a direct impact on the process efficiency (shortened cycle time) and product performance (cake appearance and homogeneous moisture content). Several parameters of the formulation, including properties of the active pharmaceutical ingredient, excipients, solvent system, and container closure, determine the success of lyophilization. Development, scale-up, and transfer of the lyophilization cycle are challenging; hence, a comprehensive understanding of the critical parameters related to the formulation, lyophilization process, and lyophilizer design allows designing a quality drug product. One approach for a successful transfer of the lyophilization cycle between the laboratory and commercial-scale lyophilizer is using vial heat transfer coefficient and ice slab test to establish a maximum sublimation rate. This review provides a general overview of the lyophilization process and discusses several key considerations and product development aspects of formulation, process optimization, container closure system, scale-up principles, and drug product quality attributes from the industrial viewpoint. Grapical abstract.

Be Aggressive! Amorphous Excipients Enabling Single-Step Freeze-Drying of Monoclonal Antibody Formulations

Short freeze-drying cycles for biopharmaceuticals are desirable. Formulations containing an amorphous disaccharide, such as sucrose, are prone to collapse upon aggressive primary drying at higher shelf temperature. We used 2-hydroxypropyl-betacyclodextrin (HPBCD) in combination with sucrose and polyvinylpyrrolidone (PVP) to develop an aggressive lyophilization cycle for low concentration monoclonal antibody (mAb) formulations. Glass transition temperature and collapse temperature of the formulations were determined, and increasingly aggressive cycle parameters were applied. Using a shelf temperature of +30 °C during primary drying, the concept of combining sublimation and desorption of water in a single drying step was investigated. Cake appearance was evaluated visually and by micro-computed tomography. Lyophilisates were further analyzed for reconstitution time, specific surface area, residual moisture, and glass transition temperature. We demonstrated the applicability of single-step freeze-drying, shortening the total cycle time by 50% and providing elegant lyophilisates for pure HPBCD and HPBCD/sucrose formulations. HPBCD/PVP/sucrose showed minor dents, while good mAb stability at 10 mg/mL was obtained for HPBCD/sucrose and HPBCD/PVP/sucrose when stored at 40 °C for 3 months. We conclude that HPBCD-based formulations in combination with sucrose are highly attractive, enabling aggressive, single-step freeze-drying of low concentration mAb formulations, while maintaining elegant lyophilisates and ensuring protein stability at the same time.

Effect of primary drying temperature on process efficiency and product performance of lyophilized Ertapenam sodium

The present work aimed to investigate the impact of primary drying temperature on lyophilization process efficiency and product performance of lyophilized Ertapenam sodium (EPM). Phase behavior of EPM formulation (200 mg/mL) using differential scanning calorimetry (DSC) and freeze drying microscopy (FDM) showed Tg' at -28.3 °C (onset) and Tc at -25.0 °C (onset), respectively. The formulation was freeze dried at different product temperature (Tp) during primary drying, using (a) conservative cycle (CC) where the maximum Tp (-31.9 °C) <Tg', (b) aggressive cycle 01 (AC01) where the maximum Tp (-24.8 °C) >Tg', and (c) AC02 where the maximum Tp (-21.0 °C) >Tc. The drying kinetics revealed that the sublimation rate was increased from 0.128 g/h/vial in CC to 0.159 and 0.182 g/h/vial in AC01 and AC02, respectively. This ultimately reduced the primary drying time of 208 min in CC to 145 min in AC01 and to 103 minutes in AC02. Morphological evaluation of cake using scanning electron microscopy (SEM) and texture analysis revealed that AC01 lead to induction of microcollapse, whereas AC02 resulted in collapsed cake. Furthermore, the microcollapsed formulations showed similar physicochemical stability to CC formulation, whereas collapsed cake showed significant degradation of EPM and increased degradation on stress stability. The study highlights that primary drying with microcollapse can be utilized to improve the process efficiency without compromising product quality of amorphous EPM.

Sensitivity Study to Assess the Robustness of Primary Drying Process in Pharmaceutical Lyophilization

The objective of this work is to apply a sensitivity study to assess the robustness of the primary drying step of pharmaceutical lyophilization with respect to deviations in process parameters. The sensitivity study can provide valuable information regarding the effect of process input parameters on the product quality that can aid in designing robust lyophilization processes. In this study, the output response is related to its inputs using Smolyak sparse grid generalized polynomial chaos method, and the sensitivity was calculated using elementary effects method. Sensitivity of chamber pressure and shelf temperature on product temperature of 2 sucrose-based and one mannitol-based formulation was studied, and the results were analyzed in terms of risk of adverse effects due to process deviations on the product quality. The study revealed that the sensitivity varies among formulations, and preliminary information regarding the possible impact of process deviations can be obtained from the process cycle diagram. The product temperature showed greater sensitivity toward the change in the shelf temperature than toward change in the chamber pressure for the greater part of the primary drying stage. An aggressive process-deviation scenario at the late stage of primary drying was also studied for different formulations, and the results were consistent with the sensitivity study.

The impact of standard accelerated stability conditions on antibody higher order structure as assessed by mass spectrometry

Protein therapeutic higher order structure (HOS) is a quality attribute that can be assessed to help predict shelf life. To model product shelf-life values, possible sample-dependent pathways of degradation that may affect drug efficacy or safety need to be evaluated. As changes in drug thermal stability over time can be correlated with an increased risk of HOS perturbations, the effect of long-term storage on the product should be measured as a function of temperature. Here, complementary high-resolution mass spectrometry methods for HOS analysis were used to identify storage-dependent changes of biotherapeutics (bevacizumab (Avastin), trastuzumab (Herceptin), rituximab (Rituxan), and the NIST reference material 8671 (NISTmAb)) under accelerated or manufacturer-recommended storage conditions. Collision-induced unfolding ion mobility-mass spectrometry data showed changes in monoclonal antibody folded stability profiles that were consistent with the appearance of a characteristic unfolded population. Orthogonal hydrogen-deuterium exchange-mass spectrometry data revealed that the observed changes in unfolding occurred in parallel to changes in HOS localized to the periphery of the hinge region. Using intact reverse-phase liquid chromatography-mass spectrometry, we identified several mass species indicative of peptide backbone hydrolysis, located between the variable and constant domains of the heavy chain of bevacizumab. Taken together, our data highlighted the capability of these approaches to identify age- or temperature-dependent changes in biotherapeutic HOS.

Lyophilization Process Design and Development: A Single-Step Drying Approach

High-throughput lyophilization process was designed and developed for protein formulations using a single-step drying approach at a shelf temperature (T_s) of ≥40°C. Model proteins were evaluated at different protein concentrations in amorphous-only and amorphous-crystalline formulations. Single-step drying resulted in product temperature (T_p) above the collapse temperature (T_c) and a significant reduction (of at least 40%) in process time compared to the control cycle (wherein T_p <T_c). For the amorphous-only formulation at a protein concentration of ≤25 mg/mL, single-step drying resulted in product shrinkage and partial collapse, whereas a 50 mg/mL concentration showed minor product shrinkage. The presence of a crystallizing bulking agent improved product appearance at ≤25 mg/mL protein concentration for single-step drying. No impact to other product quality attributes was observed for single-step drying. Vial type, fill height, and scale-up considerations (i.e., choked flow, condenser capacity, lyophilizer design and geometry) were the important factors identified for successful implementation of single-step drying. Although single-step drying showed significant reduction in the edge vial effect, the scale-up considerations need to be addressed critically. Finally, the single-step drying approach can indeed make the lyophilization process high throughput compared to traditional freeze-drying process (i.e., 2-step drying).

Impact of fast and conservative freeze-drying on product quality of protein-mannitol-sucrose-glycerol lyophilizates

PURPOSE

Mannitol/sucrose formulations are employed to generate lyophilizates for biopharmaceuticals with an elegant cake appearance. The aim of this study was to dry protein/mannitol/sucrose formulations as fast as possible without loss of cake appearance and protein stability. Glycerol was included as potential additional protein stabilizer. Three proteins (lysozyme and two monoclonal antibodies) at low and high concentration were analyzed comparing fast with conservative freeze-drying.

METHODS

Freeze-drying cycle development was carried out with mannitol/sucrose formulations. A product temperature (Tp) close to the Te of mannitol and clearly above the Tg' of sucrose was targeted. Protein formulations were exposed to the final fast lyophilisation process and to a conservative freeze-drying cycle. Lyophilizates were characterized by differential scanning calorimetry, Karl-Fischer titration and X-ray diffractometry. Additionally, macroscopic cake appearance and reconstitution times were evaluated. Protein stability was characterized by UV/Vis spectroscopy, light obscuration and size exclusion chromatography.

RESULTS

The fast freeze-drying cycle resulted in a primary drying time of 7 h (Tp: -10 °C) and a secondary drying time of 2 h in contrast to 47 h (Tp: -39 °C) and 12 h for the conservative cycle. Lyophilizates showed Tg values above 60 °C, a residual moisture level of 1%, reconstitution times of less than 35 s, δ-mannitol and elegant cake appearance. Mannitol/sucrose ratios below 4/1 did not lead to complete mannitol crystallization and were therefore not suitable for the selected process conditions. Characterisation of protein stability rendered low aggregation and particle levels for both, fast and conservative freeze-drying conditions.

CONCLUSIONS

It was shown that fast freeze-drying of mannitol/sucrose formulations above Tg' at a Tp of -10 °C resulted in good protein process stability and appropriate cake characteristics at maximum time reduction.

Detection of Collapse and Crystallization of Saccharide, Protein, and Mannitol Formulations by Optical Fibers in Lyophilization

The collapse temperature (Tc) and the glass transition temperature of freeze-concentrated solutions (Tg') as well as the crystallization behavior of excipients are important physicochemical characteristics which guide the cycle development in freeze-drying. The most frequently used methods to determine these values are differential scanning calorimetry (DSC) and freeze-drying microscopy (FDM). The objective of this study was to evaluate the optical fiber system (OFS) unit as alternative tool for the analysis of Tc, Tg' and crystallization events. The OFS unit was also tested as a potential online monitoring tool during freeze-drying. Freeze/thawing and freeze-drying experiments of sucrose, trehalose, stachyose, mannitol, and highly concentrated IgG1 and lysozyme solutions were carried out and monitored by the OFS. Comparative analyses were performed by DSC and FDM. OFS and FDM results correlated well. The crystallization behavior of mannitol could be monitored by the OFS during freeze/thawing as it can be done by DSC. Online monitoring of freeze-drying runs detected collapse of amorphous saccharide matrices. The OFS unit enabled the analysis of both Tc and crystallization processes, which is usually carried out by FDM and DSC. The OFS can hence be used as novel measuring device. Additionally, detection of these events during lyophilization facilitates online-monitoring. Thus the OFS is a new beneficial tool for the development and monitoring of freeze-drying processes.

Application of Optical Coherence Tomography Freeze-Drying Microscopy for Designing Lyophilization Process and Its Impact on Process Efficiency and Product Quality

Optical coherence tomography freeze-drying microscopy (OCT-FDM) is a novel technique that allows the three-dimensional imaging of a drug product during the entire lyophilization process. OCT-FDM consists of a single-vial freeze dryer (SVFD) affixed with an optical coherence tomography (OCT) imaging system. Unlike the conventional techniques, such as modulated differential scanning calorimetry (mDSC) and light transmission freeze-drying microscopy, used for predicting the product collapse temperature (Tc), the OCT-FDM approach seeks to mimic the actual product and process conditions during the lyophilization process. However, there is limited understanding on the application of this emerging technique to the design of the lyophilization process. In this study, we investigated the suitability of OCT-FDM technique in designing a lyophilization process. Moreover, we compared the product quality attributes of the resulting lyophilized product manufactured using Tc, a critical process control parameter, as determined by OCT-FDM versus as estimated by mDSC. OCT-FDM analysis revealed the absence of collapse even for the low protein concentration (5 mg/ml) and low solid content formulation (1%w/v) studied. This was confirmed by lab scale lyophilization. In addition, lyophilization cycles designed using Tc values obtained from OCT-FDM were more efficient with higher sublimation rate and mass flux than the conventional cycles, since drying was conducted at higher shelf temperature. Finally, the quality attributes of the products lyophilized using Tc determined by OCT-FDM and mDSC were similar, and product shrinkage and cracks were observed in all the batches of freeze-dried products irrespective of the technique employed in predicting Tc.

Highly Stable Lyophilized Homogeneous Bead-Based Immunoassays for On-Site Detection of Bio Warfare Agents from Complex Matrices

This study shows the development of dry, highly stable immunoassays for the detection of bio warfare agents in complex matrices. Thermal stability was achieved by the lyophilization of the complete, homogeneous, bead-based immunoassay in a special stabilizing buffer, resulting in a ready-to-use, simple assay, which exhibited long shelf and high-temperature endurance (up to 1 week at 100 °C). The developed methodology was successfully implemented for the preservation of time-resolved fluorescence, Alexa-fluorophores, and horse radish peroxidase-based bead assays, enabling multiplexed detection. The multiplexed assay was successfully implemented for the detection of Bacillus anthracis, botulinum B, and tularemia in complex matrices.

Stability of S-HBsAg in long-term stored lyophilised plant tissue

A potent plant-derived oral vaccine against Hepatitis B Virus (HBV) requires a durable and compact form for efficacious and convenient distribution and delivery. In the previous study we have devised a successful freeze-drying process of plant material containing the HBV small surface antigen (S-HBsAg) for the purpose of an oral vaccine against the virus, but product storage stability was limited to 4 °C. The aim of this study was to upgrade a freeze-dried product formula to facilitate successful long-term storage of S-HBsAg assembled into Virus-Like Particles (VLPs) at elevated temperatures. Series of additional excipients and storage conditions were tested. Atmosphere of nitrogen proved to preserve S-HBsAg VLPs most efficiently, with only minor degradation at the highest temperature of 37 °C. As a result, a semi-product for the oral plant-derived vaccine against HBV with good storage capabilities was obtained.

Investigation of structural collapse in unidirectionally freeze cast collagen scaffolds

Though unidirectional freeze casting is a facile method for the production of structurally anisotropic biomedical scaffolds, challenges exist in optimizing the drying process that are often overlooked. In particular, structural collapse may occur if the material's frozen-state glass transition temperature (Tg') is exceeded. It was discovered that unidirectionally freeze cast collagen matrices were highly deformed following lyophilization, rendering them incapable of further use. In this study, modulated differential scanning calorimetry was performed to identify Tg's of unidirectionally freeze cast collagen scaffolds, and product temperatures during sublimation were recorded. It was observed that cast matrices from 0.5 to 0.05 M acetic acid (HAc) sublimed at a lyophilizer shelf temperature of -25 °C underwent structural collapse and exceeded their Tg's for the majority of the drying cycle. The use of a low pH suspension (0.5 M HAc) promoted the formation of a non-porous surface, which in turn contributed to the increase of the product temperature above its Tg' during drying. This study has revealed that use of a low shelf temperature (-40 °C) and a low HAc concentration (0.05 M) is effective in maintaining product temperatures under Tg' thereby preventing collapse in unidirectionally freeze cast collagen scaffolds.

Accurate prediction of collapse temperature using optical coherence tomography-based freeze-drying microscopy

The objective of this study was to assess the feasibility of developing and applying a laboratory tool that can provide three-dimensional product structural information during freeze-drying and which can accurately characterize the collapse temperature (Tc ) of pharmaceutical formulations designed for freeze-drying. A single-vial freeze dryer coupled with optical coherence tomography freeze-drying microscopy (OCT-FDM) was developed to investigate the structure and Tc of formulations in pharmaceutically relevant products containers (i.e., freeze-drying in vials). OCT-FDM was used to measure the Tc and eutectic melt of three formulations in freeze-drying vials. The Tc as measured by OCT-FDM was found to be predictive of freeze-drying with a batch of vials in a conventional laboratory freeze dryer. The freeze-drying cycles developed using OCT-FDM data, as compared with traditional light transmission freeze-drying microscopy (LT-FDM), resulted in a significant reduction in primary drying time, which could result in a substantial reduction of manufacturing costs while maintaining product quality. OCT-FDM provides quantitative data to justify freeze-drying at temperatures higher than the Tc measured by LT-FDM and provides a reliable upper limit to setting a product temperature in primary drying.

Characterizing the freeze-drying behavior of model protein formulations

The freeze-drying behavior of three model proteins, namely, lysozyme, BSA, and IgG, has been studied using a variety of techniques under two different primary drying conditions (shelf temperatures of -25°C and +25°C, respectively) in an amorphous formulation. Manometric temperature measurements were used to characterize product temperature (T (pr)), sublimation rates, and product resistance (R (p)) during primary drying. Biophysical techniques such as circular dichroism, fluorescence, and Fourier transform infrared spectroscopy were used to study protein conformation. Size exclusion chromatography was used to monitor the formation of high-molecular-weight species (HMWS) over time on storage, and cake morphology was studied using scanning electron microscopy. The differences in the freeze-drying behavior of the three proteins were more evident at higher protein concentrations, where the protein significantly influences the behavior of the formulation matrix. However, these differences were minimized in the aggressive mode and were insignificant at lower protein concentrations where excipients dominated the freeze-drying behavior. Differences in cake morphology were observed between the two drying conditions employed as well as between the three proteins studied. The stability and the protein structure, however, were equivalent for the protein cakes generated using the two different primary drying conditions.

Model for heat and mass transfer in freeze-drying of pellets

Lyophilizing frozen pellets, and especially spray freeze-drying, have been receiving growing interest. To design efficient and safe freeze-drying cycles, local temperature and moisture content in the product bed have to be known, but both are difficult to measure in the industry. Mathematical modeling of heat and mass transfer helps to determine local freeze-drying conditions and predict effects of operation policy, and equipment and recipe changes on drying time and product quality. Representative pellets situated at different positions in the product slab were considered. One-dimensional transfer in the slab and radial transfer in the pellets were assumed. Coupled heat and vapor transfer equations between the temperature-controlled shelf, the product bulk, the sublimation front inside the pellets, and the chamber were established and solved numerically. The model was validated based on bulk temperature measurement performed at two different locations in the product slab and on partial vapor pressure measurement in the freeze-drying chamber. Fair agreement between measured and calculated values was found. In contrast, a previously developed model for compact product layer was found inadequate in describing freeze-drying of pellets. The developed model represents a good starting basis for studying freeze-drying of pellets. It has to be further improved and validated for a variety of product types and freeze-drying conditions (shelf temperature, total chamber pressure, pellet size, slab thickness, etc.). It could be used to develop freeze-drying cycles based on product quality criteria such as local moisture content and glass transition temperature.

Non-invasive product temperature determination during primary drying using tunable diode laser absorption spectroscopy

The goal of this work was to demonstrate the application of Tunable Diode Laser Absorption Spectroscopy (TDLAS) as a non-invasive method to determine the average product temperature of the batch during primary drying. The TDLAS sensor continuously measures the water vapor concentration and the vapor flow velocity in the spool connecting the freeze-dryer chamber and condenser. Vapor concentration and velocity data were then used to determine the average sublimation rate (g/s) which was subsequently integrated to evaluate the amount of water removed from the product. Position dependent vial heat transfer coefficients (K(v)) were evaluated using the TDLAS sensor data for 20 mL vials during sublimation tests with pure water. TDLAS K(v) data showed good agreement to K(v) data obtained by the traditional gravimetric procedure. K(v) for edge vials was found to be about 20-30% higher than that of center vials. A weighted K(v) was then used to predict a representative average product temperature from TDLAS data in partial and full load freeze drying runs with 5%, 7.5%, or 10% (w/w) sucrose, mannitol, and glycine solutions. TDLAS product temperatures for all freeze-drying runs were within 1-2 degrees C of "center vial" steady state thermocouple data.

Interaction of environmental moisture with powdered green tea formulations: relationship between catechin stability and moisture-induced phase transformations

This study investigated the effect of phase transformations of amorphous and deliquescent ingredients on catechin stability in green tea powder formulations. Blends of amorphous green tea and crystalline sucrose, citric acid, and/or ascorbic acid were analyzed by X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), dynamic water vapor sorption, water activity measurements, and high-performance liquid chromatography (HPLC) after storage for up to 12 weeks at 0-75% relative humidity (RH) and 22 degrees C. The glass transition temperature (T(g)) of green tea was reduced to below room temperature (<22 degrees C) at 68% RH. Dissolution of deliquescent ingredients commenced at RH values below deliquescence points in blends with amorphous green tea, and these blends had greater water uptake than predicted by an additive model of individual ingredient moisture sorption. Catechin degradation was affected by T(g) of green tea powder and both dissolution and deliquescence of citric and ascorbic acids.

Freeze-dry microscopy: impact of nucleation temperature and excipient concentration on collapse temperature data

The objective of this study was to investigate the impact of nucleation temperature (T(n)) and excipient concentration on the collapse temperature data obtained from freeze-dry microscopy (FDM) experiments. T(n), the temperature of the onset of collapse (T(oc)), and the full collapse temperature (T(fc)) were determined for aqueous solutions of polyvinylpyrrolidone (PVP) 40 kDa and 2-(hydroxypropyl)-beta-cyclodextrin. Concentrations were varied from 1% to 20% (w/w) for PVP and from 1% to 30% (w/w) for the 2-(hydroxypropyl)-beta-cyclodextrin. Mutual correlation coefficients were calculated for the observed T(n), T(oc), and concentrations of the solutions. In addition, outliers were detected and eliminated by applying the leaving-one-out routine and calculating correlation coefficients without it. T(n) was found to be non-correlated with concentrations and only weakly correlated with T(oc). The correlation between these two temperatures was particularly poor for the solutions of the highest and lowest concentrations. In contrast, T(oc) correlated much better with the corresponding concentrations, resulting in a quadratic fit for PVP and a linear fit for 2-(hydroxypropyl)-beta-cyclodextrin.