Mixing and Dissolution Processes of Pharmaceutical Bulk Materials in Stirred Tanks: Experimental and Numerical Investigations

The quest for down scale representativeness: how to exploit CFD to design a shear study for vaccines

In this work, we exploit computational fluid dynamics (CFD) to evaluate stirred tank reactor (STR) process engineer parameters (PEP) and design a scale-down system (SDS) to be representative of the formulation and filling process steps for an Aluminum adjuvanted vaccine drug product (DP). To study the shear history in the SDS we used the concept of number of passages, combined with an appropriate stirring speed down scale strategy comprising of either (i) tip speed equivalence, widely used as a scale-up criterion for a shear-sensitive product, or (ii) rotating shear, a shear metric introduced by Metz and Otto in 1957 but never used as scaling criterion. The outcome of the CFD simulations shows that the tip equivalence generates a worst-case SDS in terms of shear, whereas the rotating shear scaling approach could be used to design a more representative SDS. We monitored the trend over time for "In Vitro Relative Potency" as DP Critical Quality Attribute for both scaling approaches, which highlighted the crucial role of choosing the appropriate scaling-down approach to be representative of the manufacturing scale during process characterization studies.

Optimized Design of Solid-Liquid Dual-Impeller Mixing Systems for Enhanced Efficiency

Flow interferences occur in the dual-impeller stirred tank between paddles as well as between paddles and baffles and the tank wall, leading to inefficient utilization of the stirring energy. To address this issue, this study investigates the flow characteristics within the mixing tank using Euler-Euler numerical simulation and the particle image velocimetry (PIV) experimental method. The three-dimensional nonconstant flow characteristics are analyzed to optimize the critical stirrer geometry. By employing the Sobol method, an approximate model is established for sensitivity analysis to identify key parameters affecting the solid-liquid dual-impeller stirred tank's performance. Numerical simulations demonstrate that the optimized stirred tank exhibits a significantly improved solid-liquid suspension capacity and considerably reduces flow losses near the wall and baffle areas. Under the designated conditions, the cloud height is increased by 8.7%, and power consumption is reduced by 15.6% compared to the prototype. PIV tests performed on the stirred tank before and after optimization confirmed the reliability of the obtained optimization results. The primary objective of this study is to enhance mixing efficiency and homogeneity in solid-liquid mixing tanks while concurrently minimizing energy consumption and cost. These results validate the feasibility of employing a multiobjective optimal design approach that combines the RBF agent model with the Sobol method. The findings offer valuable insights for the design of similar mixing tanks.

Towards robust cell culture processes - Unraveling the impact of media preparation by spectroscopic online monitoring

Biopharmaceutical manufacturing processes can be affected by variability in cell culture media, e.g. caused by raw material impurities. Although efforts have been made in industry and academia to characterize cell culture media and raw materials with advanced analytics, the process of industrial cell culture media preparation itself has not been reported so far. Within this publication, we first compare mid-infrared and two-dimensional fluorescence spectroscopy with respect to their suitability as online monitoring tools during cell culture media preparation, followed by a thorough assessment of the impact of preparation parameters on media quality. Through the application of spectroscopic methods, we can show that media variability and its corresponding root cause can be detected online during the preparation process. This methodology is a powerful tool to avoid batch failure and is a valuable technology for media troubleshooting activities. Moreover, in a design of experiments approach, including additional liquid chromatography-mass spectrometry analytics, it is shown that variable preparation parameters such as temperature, power input and preparation time can have a strong impact on the physico-chemical composition of the media. The effect on cell culture process performance and product quality in subsequent fed-batch processes was also investigated. The presented results reveal the need for online spectroscopic methods during the preparation process and show that media variability can already be introduced by variation in media preparation parameters, with a potential impact on scale-up to a commercial manufacturing process.

Investigation of dissolution rate kinetics of bulk pharmaceutical feed streams within a stirred tank vessel and a twin screw extruder

The introduction of continuous manufacturing of pharmaceuticals has highlighted the challenging area of continuous dissolution of solids for work ups to flow chemistry systems. In this study, the use of a 16 mm twin screw extruder (TSE) as a platform technology for solid feeds is investigated using four solid pharmaceutical ingredients (PI) in a mixture of water and IPA. In order for comparison, the same experiments were also carried out in a batch traditional stirred tank vessel (STV). The objectives of this work are to gain further scientific understanding on dissolution kinetics and to compare kinetics in both a batch and continuous system. The concentration of each PI during dissolution is monitored using an in-line UV-ATR probe, allowing the extraction of dissolution kinetics. Faster dissolution rates are achieved in the TSE than in the STV due to higher power dissipation generated by the aggressive shear mixing and thermal energy within the TSE. Complete dissolution of paracetamol is obtained within the residence time of the TSE; complete dissolution of benzoic acid and acetylsalicylic acid are achieved at higher barrel temperatures; however full dissolution of nicotinic acid is not achievable in the TSE under the experimental conditions.