The Principles of Freeze-Drying and Application of Analytical Technologies.

Freeze-drying is a complex process despite the relatively small number of steps involved, since the freezing, sublimation, desorption, and reconstitution processes all play a part in determining the success or otherwise of the final product qualities, and each stage can impose different stresses on a product. This is particularly the case with many fragile biological samples, which require great care in the selection of formulation additives such as protective agents and other stabilizers. Despite this, the process is widely used, not least because once any such processing stresses can be overcome, the result is typically a significantly more stable product than was the case with the starting material. Indeed, lyophilization may be considered a gentler method than conventional air-drying methods, which tend to apply heat to the product rather than starting by removing heat as is the case here. Additionally, due to the high surface area to volume ratio, freeze-dried materials tend to be drier than their conventionally dried counterparts and also rehydrate more rapidly. This chapter provides an overview of freeze-drying (lyophilization) of biological specimens with particular reference to the importance of formulation development, characterization, and cycle development factors necessary for the commercial exploitation of freeze-dried products, and reviews the recent developments in analytical methods which have come to underpin modern freeze-drying practice.

Aggressive conditions during primary drying as a contemporary approach to optimise freeze-drying cycles of biopharmaceuticals.

Freeze-drying is the method of choice to dry formulations with biopharmaceutical drugs, to enhance protein stability. This is usually done below the glass transition temperature of maximally freeze-concentrated solutions (Tg'), to avoid protein aggregation, preserve protein activity, and obtain pharmaceutically 'elegant' cakes. Unfortunately, this is a lengthy and energy-consuming process. However, it was recently shown that drying above Tg' or even above the collapse temperature (Tc) is not necessarily detrimental for stability of biopharmaceuticals, and hence provides an attractive option for freeze-drying cycle optimisation. The goal of the present study was to optimise the freeze-drying cycle for a model IgG monoclonal antibody (20 mg/mL) in sucrose and sucrose/glycine formulations, by reducing primary drying time. To study the impact of shelf temperature (Ts) and chamber pressure on product temperature (Tp), one conventional and five aggressive cycles were tested. Aggressive conditions during primary drying were achieved by increasing Ts from -20 °C (conventional cycle) to 30 °C, with chamber pressure set to 0.1 mbar, 0.2 mbar or 0.3 mbar. These combinations of Ts and chamber pressure resulted in Tp well above Tg', and in some cases, even above Tc, without causing macrocollapse. Other critical quality attributes of the products were also within the expected ranges, such as reconstitution time and residual water content. Physical stability was tested using size exclusion chromatography, dynamic light scattering, and micro-flow imaging. All of the lyophilised samples were exposed to stress and the intended storage conditions, with no impacts on the product seen. These data show that implementation of aggressive conditions for the investigated formulations is possible and can significantly contribute to the reduction of primary drying times by up to 54% (from 48 to 22 h) in comparison to conventional freeze-drying.

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.

Freeze-drying microscopy in mathematical modeling of a biomaterial freeze-drying

Transplantation brings hope for many patients. A multidisciplinary approach on this field aims at creating biologically functional tissues to be used as implants and prostheses. The freeze-drying process allows the fundamental properties of these materials to be preserved, making future manipulation and storage easier. Optimizing a freeze-drying cycle is of great importance since it aims at reducing process costs while increasing product quality of this time-and-energy-consuming process. Mathematical modeling comes as a tool to help a better understanding of the process variables behavior and consequently it helps optimization studies. Freeze-drying microscopy is a technique usually applied to determine critical temperatures of liquid formulations. It has been used in this work to determine the sublimation rates of a biological tissue freeze-drying. The sublimation rates were measured from the speed of the moving interface between the dried and the frozen layer under 21.33, 42.66 and 63.99 Pa. The studied variables were used in a theoretical model to simulate various temperature profiles of the freeze-drying process. Good agreement between the experimental and the simulated results was found.

A prática da transplantação traz esperança para muitos pacientes. Uma visão multidisciplinar nessa área visa à produção de tecidos biológicos para serem utilizados como implantes e próteses. A liofilização é um processo de secagem que preserva características essenciais desses materiais, facilitando sua manipulação e armazenamento. A liofilização é um processo que requer muito tempo e energia e sua otimização é muito importante, pois permite reduzir custos de processo melhorando a qualidade do produto. A modelagem matemática é uma ferramenta que permite descrever o comportamento do produto durante o processo e, consequentemente, auxilia os estudos de otimização. Microscopia óptica acoplada à liofilização, uma técnica usualmente aplicada na determinação de temperaturas críticas de formulações líquidas, foi utilizada neste trabalho na determinação de taxas de sublimação da liofilização de um tecido biológico. As taxas de sublimação foram calculadas a partir da velocidade da interface entre a camada seca e congelada, sob pressões de 21,33, 42,66 e 63,99 Pa. As variáveis estudadas foram usadas em um modelo matemático teórico, que simula os perfis de temperatura do produto durante o ciclo de liofilização. Os resultados apresentados demonstraram boa relação entre os dados experimentais e simulados.