Some implications of structural collapse during freeze-drying using Erwinia caratovora L-asparaginase as a model

Comparison of the Design Space of Products with Different Initial Saturation

Vacuum freeze-drying is a promising technology widely used in pharmaceuticals. Preparing products with prebuilt porosity has attracted considerable attention due to its potential in shortening process duration. However, the design space for the primary drying of initially unsaturated products remains unclear. A novel index, average power, was proposed in this paper to represents the collapse risk. And a multiphase model was employed in this paper to build the design space for the products with initial voids. The simulation results show that both the drying time and average power show higher sensitivity to the temperature variation than pressure. In addition, the initial saturation has significant impacts on the design space, with small initial saturation resulting in vast design space and vice versa, which implies that small initial saturation is more beneficial for the actual production. This paper would be helpful for the development of freeze-drying.

Characterization techniques: The stepping stone to liposome lyophilized product development

The primary drying is the longest step of the freeze-drying process and becomes one of the focuses for lyophilization cycle development inevitably, which is often approaching through a "trial and error" course and requires a labor-intensive and time-consuming endeavor. Nevertheless, drawing support from characterization techniques to understand the physic-chemical properties changing of the sample during lyophilization and their correlation with process conditions comprehensively, the freeze-drying development and optimization will get more from less. To get the optimal lyophilization cycle in the least time, the instrumental methods assisting primary drying design are summarized. The techniques used for estimating the collapse temperature of products are reviewed at first, aiming to provide a reference on the primary drying temperature setting to guarantee product quality. The instrumental methods for primary drying end prediction are also discussed to get optimal freeze-drying protocol with higher productivity. This review highlights the practicality of the above techniques through expounding basic principles, typical measurement conditions, merits and drawbacks, interpretation of results and practical applications, etc. At last, the techniques used for residual moisture detection of lyophilized products and size determination after liposome rehydration are briefly introduced.

On the Use of Infrared Thermography for Monitoring a Vial Freeze-Drying Process

Monitoring a vial freeze-drying process without interfering with product dynamics is a challenging issue. This article presents a novel device constituted by an infrared camera designed to be placed inside the drying chamber, able to monitor the temperature of the vials, very close to that of the product inside. By this way it is possible to estimate the ending point of the primary drying, the heat transfer coefficient to the product (K_v), and the resistance of the dried product to vapor flux (R_p). Experiments were carried out in a pilot-scale freeze-dryer, processing 5% and 10% sucrose solutions at different values of shelf temperature and chamber pressure, using both thermocouples and the IR camera to track product dynamics. Results evidence that the measurements (of temperature) and the estimates (of the ending point of the main drying and of K_v and R_p) obtained using the 2 systems are very close, thus validating the IR camera as an effective process analytical technologies for the freeze-drying process. Besides, it was shown that the presence of the IR camera in the chamber is not responsible for any additional heating to the product and that monitored vials are representative of the majority of the vials of the batch.

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.

Model-Based PAT for Quality Management in Pharmaceuticals Freeze-Drying: State of the Art

Model-based process analytical technologies can be used for the in-line control and optimization of a pharmaceuticals freeze-drying process, as well as for the off-line design of the process, i.e., the identification of the optimal operating conditions. This paper aims at presenting the state of the art in this field, focusing, particularly, on three groups of systems, namely, those based on the temperature measurement (i.e., the soft sensor), on the chamber pressure measurement (i.e., the systems based on the test of pressure rise and of pressure decrease), and on the sublimation flux estimate (i.e., the tunable diode laser absorption spectroscopy and the valveless monitoring system). The application of these systems for in-line process optimization (e.g., using a model predictive control algorithm) and to get a true quality by design (e.g., through the off-line calculation of the design space of the process) is presented and discussed.

On the Design of a Fuzzy Logic-Based Control System for Freeze-Drying Processes

This article is focused on the design of a fuzzy logic-based control system to optimize a drug freeze-drying process. The goal of the system is to keep product temperature as close as possible to the threshold value of the formulation being processed, without trespassing it, in such a way that product quality is not jeopardized and the sublimation flux is maximized. The method involves the measurement of product temperature and a set of rules that have been obtained through process simulation with the goal to obtain a unique set of rules for products with very different characteristics. Input variables are the difference between the temperature of the product and the threshold value, the difference between the temperature of the heating fluid and that of the product, and the rate of change of product temperature. The output variables are the variation of the temperature of the heating fluid and the pressure in the drying chamber. The effect of the starting value of the input variables and of the control interval has been investigated, thus resulting in the optimal configuration of the control system. Experimental investigation carried out in a pilot-scale freeze-dryer has been carried out to validate the proposed system.

The principles of freeze-drying

This chapter provides an up-to-date overview of freeze-drying (lyophilization) with particular relevance to stabilizing live cells or viruses for industrial applications as vaccines or seed culture. The chapter discusses the importance of formulation, cycle development, validation, and the need to satisfy pharmaceutical regulatory requirements necessary for the commercial exploitation of freeze-dried products.

Application of gas pycnometry for the density measurement of freeze-dried products

Gas pycnometry is applied to determine the density of solid materials. The analysis of lyophilisates is particularly challenging because of their porous structure. In this study, the density of raw materials and freeze-dried products was determined using different pycnometric methodologies and gases [helium (He), nitrogen (N2 ), sulfur hexafluoride]. The number of purges was set to 60 independent of the gas used. Intact and ground lyophilisates were examined, and major differences were found between use of He and N2 . For example, the density of sucrose lyophilisates measured using He remained almost constant before (1.51 g/cm(3) ) and after (1.52 g/cm(3) ) grinding. In contrast, the density of a sucrose lyophilisate before grinding determined with N2 was 1.33 g/cm(3) . On the basis of μCT and scanning electron microscopy pictures, it appears likely that the majority of pores are interconnected, with only a small fraction of closed pores. Helium is able to penetrate deep into the freeze-dried matrix and is supposedly absorbed by the material. The N2 molecules were not able to penetrate closed pores; therefore, the skeletal density of an intact lyophilisate was determined. Reproducibility of the established method was verified, and freeze-dried orally disintegrating tablets of different compositions were analyzed.

Determination of end point of primary drying in freeze-drying process control

Freeze-drying is a relatively expensive process requiring long processing time, and hence one of the key objectives during freeze-drying process development is to minimize the primary drying time, which is the longest of the three steps in freeze-drying. However, increasing the shelf temperature into secondary drying before all of the ice is removed from the product will likely cause collapse or eutectic melt. Thus, from product quality as well as process economics standpoint, it is very critical to detect the end of primary drying. Experiments were conducted with 5% mannitol and 5% sucrose as model systems. The apparent end point of primary drying was determined by comparative pressure measurement (i.e., Pirani vs. MKS Baratron), dew point, Lyotrack (gas plasma spectroscopy), water concentration from tunable diode laser absorption spectroscopy, condenser pressure, pressure rise test (manometric temperature measurement or variations of this method), and product thermocouples. Vials were pulled out from the drying chamber using a sample thief during late primary and early secondary drying to determine percent residual moisture either gravimetrically or by Karl Fischer, and the cake structure was determined visually for melt-back, collapse, and retention of cake structure at the apparent end point of primary drying (i.e., onset, midpoint, and offset). By far, the Pirani is the best choice of the methods tested for evaluation of the end point of primary drying. Also, it is a batch technique, which is cheap, steam sterilizable, and easy to install without requiring any modification to the existing dryer.

The principles of freeze-drying

This chapter provides an up-to-date overview of freeze-drying (lyophilization) with particulars relevance to stabilizing live cells or viruses for industrial applications as vaccines or seed culture. The chapter discusses the importance of formulation, cycle development, validation, and the need to satisfy pharmaceutical regulatory requirements necessary for the commercial exploitation of freeze-dried products.

Experimental determination of viability loss of Penicillium bilaiae conidia during convective air-drying

A study was conducted on the drying of Penicillium bilaiae, a fungal micro-organism used to promote soil-bound phosphorous uptake in several crop species, such as wheat, canola and pulse crops. A wet pellet formed from a mixture of the inoculant and a starch-based carrier was air-dried to the appropriate water activity to extend the shelf-life of the viable fungal conidia. Convective air-drying was examined as a low-energy alternative to the more expensive freeze-drying technology that is currently in use. Experiments were conducted to measure the loss of conidia viability during drying in a fixed-bed, thin-layer convective dryer. The dryer air inlet temperature and relative humidity were controlled in experiments to determine the effect of thermal and dessicative stresses on conidial viability. The measured survivor fraction was determined to be dependent on solids temperature, moisture content and drying rate. Thermal stresses became significant for process temperatures above 30 degrees C, while the survivor fraction fell sharply below a dry basis moisture ratio of 30%. Slower drying kinetics associated with high inlet air relative humidity were found to significantly improve the recovery of viable conidia. By minimising environmental stresses, survivor fractions of up to 75% could be achieved, but this result fell dramatically with the introduction of more severe conditions. A general linear statistical model is used to quantify experimental error and the significance level of each factor.

Effect of Collapse on the Stability of Freeze-Dried Recombinant Factor VIII and α-amylase

Recombinant Factor VIII (rFVIII) and alpha-amylase were used as model proteins to examine the effect of freeze-drying process conditions on the long-term stability of these proteins as freeze-dried solids. The same sucrose/glycine formulation was used for all treatments. Three freeze-drying protocols were used-an "aggressive" and a "conservative" cycle that both produced pharmaceutically acceptable product, and a protocol that produced a collapsed matrix. For rFVIII, there was no difference in the biological activity versus the time profile for product freeze-dried under the three different conditions when stored at 5 or 25 degrees C. At 40 degrees C, however, the stability of the collapsed product appeared to be better than that of product freeze-dried with no collapse. Also, the level of residual moisture in the collapsed product was higher than that of the product with no collapse. For alpha-amylase, there was no significant difference in the stability profile at any of the temperatures over the time course of the study. The results support the conclusion that collapse is not necessarily detrimental to the long-term stability of freeze-dried proteins.

Protection of the enzyme L-asparaginase during lyophilisation--a molecular modelling approach to predict required level of lyoprotectant

Many novel therapeutic agents are proteins and peptides which need stabilisation due to their inherent instability in aqueous solution. Freeze-drying is an established method for protein stabilisation, although the use of additives is often necessary in order to preserve protein structure and activity during lyophilisation itself. The molecular interactions between protein and protective additive are as yet unclear. In this study, we examined the use of a range of saccharide additives to stabilise the model multi-subunit enzyme L-asparaginase during lyophilisation, assessed post-drying enzyme activity and quaternary structure, and related the extrapolated levels of additive necessary to provide full stabilisation to the theoretical levels predicted from an existing hypothesis using molecular modelling. It was found that each of the saccharides tested here displayed similar levels of protection towards L-asparaginase under the conditions used. Amounts of additive required to give full stabilisation to the enzyme were extrapolated from the activity data and were found to be in good agreement with theoretical amounts calculated from molecular modelling studies. Our data suggest that the existing hypothesis may be relevant to the prediction of optimum levels of lyoprotectant for the freeze-drying of proteins. However, further studies would be necessary in order to obtain a full picture of protein-additive interactions at the molecular level.

Optimizing the lyophilization cycle and the consequences of collapse on the pharmaceutical acceptability of Erwinia L-asparaginase

The antileukemia enzyme, Erwinia L-asparaginase, occurs as a tetramer which can be dissociated by the stresses of lyophilization into four subunits (subunit M(r) 34 000 Da). Dissociation can be reduced by adding protectants to the formulation to stabilize the biopolymer, while the product should dry to form a pharmaceutically elegant, shelf-stable cake which is readily soluble. Using analytical ultracentrifugation, HPLC, and circular dichroism we have related structural dissociation of the enzyme during lyophilization to biological activity. Additives such as mannitol prevent ablation loss of vial contents and dry to form cosmetically elegant cakes but provide little biological protection, since during freezing they crystallize and are removed from the preparation. Excipients persisting throughout the cycle in the amorphous state provide improved biological protection, although high molecular weight compounds such as Dextran (M(r) 70000 Da) are most effective only during product freezing or storage. Low molecular weight sugars are protective throughout the cycle although formulations containing monosaccharides often exhibit low collapse temperatures (Tc) measured using a freeze-drying microscope or glass transition temperatures (Tg') measured by thermal analysis, but these formulations distort as drying progresses to form a collapsed, cosmetically unacceptable cake, with reduced activity, poor stability, a high moisture content, and reduced solubility. Collapse can be avoided by formulating with disaccharides, which display higher Tc temperatures than monosaccharides, or drying below Tc. Dried samples which persist in the amorphous state can also collapse when stored above their solid-state collapse temperatures when they decay at a faster rate than predicted by Arrhenius kinetics. The solid-state collapse temperature can be significantly decreased by the diffusion of moisture from the stopper into the dry product resulting in an increase in sample water content. Lyophilization cycle times can be reduced by analyzing collapse characteristics so that the relationship between product temperature and chamber pressure can be controlled so that drying rates can be optimized while ensuring that the product does not melt or collapse during sublimation.