Sebastian Hofmann, M.Sc.


Eißendorfer Str. 38

Building N, Room 1.083

21073 Hamburg

Phone +49 40 42878 - 3106

Mail Sebastian Hofmann


Research

DFG Priority Program SPP 2170 “InterZell” – Project “CHOLife”: Multiscale experimental analysis and simulation of lifelines in bioreactors to study their impact on the cultivation performance of Chinese Hamster Ovary (CHO) cells

Large-scale bioreactors with working volumes up to 22,000 L are frequently exposed to dynamic cultivation conditions that create spatial and temporal gradients in mixing. These variations cause a decline in cellular performance, which ultimately results in lower product quality and quantity. Precise and reliable process control is critical for biopharmaceutical production of vaccines and monoclonal antibodies, as well as for understanding the impact of dynamically changing environments on cells. For the detailed understanding of cultivation processes it is indispensable to get deep insights into the overall and local hydrodynamics with high spatial and temporal resolution.

CHOLife tackles the scale-up problem linking the unique access to a transparent 15,000 L cell culture bioreactor (Institute of Multiphase Flows, TUHH Hamburg, IMS) with the development of a novel scale-up device (Institute of Biochemical Engineering, Stuttgart, IBVT) in order to predict industrial-scale performance of IgG1 producing CHO cells. In essence, three dimensional flow trajectories and lifelines will be measured at the IMS and mimicked in the novel scale-up simulator of IBVT. The close cooperation of both parties ensures a successful scale-down of large-scale conditions and an equally successful prediction of large-scale performance of CHO cells cultured in the novel scale-up simulator.

One method of gaining insight into complex hydrodynamic flow patterns and compartmentalization is by means of the (de)colorization method, which is based on phenolphthalein or bromothymol blue in an acrylic glass bioreactor. However, the lack of optical access into generic bioreactors requires an alternative analysis. Industrially used fixed probes at the reactor wall cannot provide information on spatiotemporal gradients or the cell's residence time in different zones of the reactor.

To overcome this limitation, Lapin et al. proposed the "Traveling along the Lifelines of Single Cells" approach, which uses a numerical method. This Lagrangian analysis was recently experimentally scrutinized on laboratory-scale through the 4D-Particle Tracking Velocimetry (4D-PTV) method demonstrating detailed results regarding the flow-following capability of Lagrangian particles.

On production scale, a combination of sensor systems integrated into a mobile, enclosed and neutrally buoyant Lagrangian Sensor Particle (LSP) offers a deeper understanding of complex flow patterns inside a bioreactor by recording data alongside its trajectory and thereby mimicking the movement of a cell.

Science Communication
Awards
  • Maximilian Kamp as the winner of the “Karl H. Ditze Award of the TUHH to graduates of the TUHH” in the category of outstanding Bachelor thesis. The thesis convinced the committee in terms of theoretical-scientific quality, practical relevance and interdisciplinarity, which was written within the framework of the priority program SPP 2170 “InterZell” (funded by the DFG).

  • Winner of the I3 Junior Project: Flow-following Lagrangian Sensor Particles - Development of a novel measurement technique with conductivity sensors for a novel macro-mixing and lifeline analysis; Hofmann, S.; Kamp, M.; Buntkiel, L.; Reinecke, S.; I3-Programm, sponsored by the Hamburg University of Technology for the project period 01/2023 - 03/2024

Research Projects
  • DFG Priority Program 2170 – InterZell – CHOLife
Education

Undergraduate courses

  • Reactor Design Using Local Transport Processes (Winter Semester 2022/23)

  • Reactor Design Using Local Transport Processes (Winter Semester 2021/22)

  • Grundlagen des Technischen Zeichnens (Summer Semester 2021)

Supervised Theses

  • "Measurement and modelling of carbon dioxide and oxygen partial pressures over the height of a 15,000 L acrylic glass reactor", working title, Noah von Schnitzler, Master thesis (supervision in cooperation with Marc Maly and Nicolas Nickel), ongoing

  • "Effect of a Phosphate-Buffered System on the Determination of the Volumetric Mass Transfer Coefficient kLa for CO2", Lara Offermann, Bachelor thesis (supervision in cooperation with Marc Maly and Nicolas Nickel), ongoing

  • "Development, Implementation and Testing of a Technical Solution for the Determination of Gas Partial Pressures at Different Heights of an Aerated Stirred Tank Reactor on Industrial Scale", Noah von Schnitzler, project work (supervision in cooperation with Marc Maly and Nicolas Nickel), ongoing

  • "Lagrangian Sensor Particles in a 15,000 L Bioreactor: Experimental Comparison of Different Sizes on their Flow-Following Capability", Isabel Sophie Brouwers, Master's Thesis, 2023 (still ongoing)

  • "Überblick und Bewertung von Bioprozesssensoren in Lagrangeschen Sensor Partikeln: Stand der Technik, Miniaturisierung und Weiterentwicklung", Julius Plock, Bachelor's Thesis, 2023

  • "Experimental Investigations of the Flow-Following Capabilities and Hydrodynamic Characteristics of Lagrangian Sensor Particles with Respect to their Centre of Mass", Ryan Rautenbach, Master's Thesis, 2022-2023: Python evaluation code available here.

  • "Experimental investigation of the flow behavior of Lagrangian LED Particles in a 200 l bioreactor", Maximilian Kamp, Bachelor's Thesis, 2021-2022: Thesis available here and MATLAB code available here.

  • "Design, Construction and Evaluation of Lagrangian Sensor Particles for the Flow Behavior Determination in a 200 L and 15000 L Bioreactor", Paramveer Singh GopalSingh, Master's Thesis, 2021-2023: Thesis available here and MATLAB and C++ code available here.

  • "Experimental Characterization of Modified Polyurethane Foams for Mechanical Clean Up of Oil Pollutants at Sea Surface" (in close cooperation with Daniel Niehaus), Srividya Kumar Bairamangala, Project Work, 2020-2021

Oral and Poster Presentations

Lectures

  • Hofmann, S.; Buntkiel, L.: Best Practices in Research Software Engineering: Working with MATLAB and Gitlab, 2nd "Technical Baldyga Seminar", 3rd "Mixing Meets Reality" Conference, Berlin, Germany, 2023, Presentation
  • Hofmann, S.; Buntkiel, L.; GopalSingh, P.; Fitschen, J.; Hoffmann, M.; Reinecke, S.; Hampel, U,; Schlüter, M.: Experimental Investigation of Circulation Times with Lagrangian Sensor Particles in a 15,000 L Acrylic Glass Reactor, 17th European Conference on Mixing (MIXING 17), Porto, Portugal, 2023, Presentation
  • Hofmann, S. - Lagrangian Particles: Experimental Determination of Lifelines in a 3 L and 15000 L Stirred Tank Reactor, Biobased Process and Reactor Technologies PhD Seminar, Hamburg University of Technology, Hamburg, 2022, Presentation
  • Hofmann, S.; Gaugler, L.: CHOLife - Multiscale Experimental Analysis and Simulation of Lifelines in Bioreactors to Study their Impact on the Cultivation Performance of CHO Cells, Annual Meeting: Priority Program Status Meeting of the SPP2170 "InterZell", organized by Uni Stuttgart, Stuttgart, 2022, Presentation
  • Fitschen, J.; Kuschel, M.; Hofmann, S.; Wucherpfennig, T.; v. Kameke, A.; Hoffmann, M.; Schlüter, M.: Characterization of Heterogeneities in Stirred Tank Reactors by Means of 4D Particle Trajectories and Numerical Flow Simulations, MIXING XXVII, North American Mixing Forum (NAMF), Online Conference 2022, Presentation
  • Hofmann, S.; Vernier-Lambert, H.; Meriguet, S.; GopalSingh, P.; Fitschen, J.; Neubauer, P.; von Lieres, E.; Ferguson, M.; Schlüter, M.: Assessment of Lagrangian Sensor Particle Designs in a Transparent 15,000 L Acrylic Glass Bioreactor, 7th BioProScale Symposium, organized by Prof. Neubauer (TU Berlin), Langenbeck-Virchow-Haus, Berlin 2022, Presentation
  • Gaugler, L.; Mast, Y.; Fitschen, J.; Hofmann, S.; Schlüter, M.; Takors, R.: Development of a single multi-compartment bioreactor (SMCB) for CHO scale-down studies in a heterogeneous cultivation environments, 7th BioProScale Symposium, organized by Prof. Neubauer (TU Berlin), Langenbeck-Virchow-Haus, Berlin 2022, Presentation
  • Weiland, C; Hofmann, S.; Fitschen, J.; von Kameke, A.; Hoffmann, M.; Schlüter, M.: Numerische Simulation Lagranger Partikeltrajektorien und Charakterisierung des Partikelfolgevermögens in einem 3 L Rührkesselreaktor, Jahrestreffen der ProcessNet-Fachgruppen Computational Fluid Dynamics + Mischvorgänge + Agglomerations- und Schüttguttechnik, DECHEMA, Hyperion Hotel Leipzig, 2022, Presentation
  • Fitschen, J.; Hofmann, S.; Hoffmann, M.; Kuschel, M.; Wucherpfennig, T.; Schlüter, M.: Lokale Mischzeitverteilung in begasten Rührkesselreaktoren im Labormaßstab, Jahrestreffen der ProcessNet-Fachgruppen Computational Fluid Dynamics + Mischvorgänge + Agglomerations- und Schüttguttechnik, DECHEMA, Hyperion Hotel Leipzig, 2022, Presentation
  • Hofmann, S.; Weiland, C.; Fitschen, J.; v. Kameke, A.; Hoffmann, M.; Schlüter, M.: Vergleich von experimentellen und numerischen Untersuchungen zur Abschätzung des Folgevermögens verschiedener Lagrange’scher Partikel in der Bioreaktorströmung, Jahrestreffen der ProcessNet-Fachgruppen Computational Fluid Dynamics + Mischvorgänge + Agglomerations- und Schüttguttechnik, DECHEMA, Hyperion Hotel Leipzig, 2022, Presentation
  • Hofmann, S.; Gaugler, L.; Fitschen, J.; v. Kameke, A.; Schlüter, M.; Takors, R.: Lagrangian Particle Tracking and Bioreactor Compartmentalization as Novel Scale-up Tools for Biopharmaceutical Processes, 13th European Congress of Chemical Engineering, 6th European Congress of Applied Biotechnology (ECCE 13 & ECAB 6), DECHEMA, Online conference, 2021, Presentation
  • Fitschen, J.; Kuschel, M.; Hofmann, S.; Hoffmann, H.; von Kameke, A.; Wucherpfennig, T.; Wutz, J.; Schlüter, M.: Validation of Numerical Flow Simulations in a 3 L Stirred Tank by Means of Real 4D Particle Trajectories 13th European Congress of Chemical Engineering, 6th European Congress of Applied Biotechnology (ECCE 13 & ECAB 6), DECHEMA, Online conference, 2021, Presentation
  • Fitschen, J.; Hofmann, S.; Hoffmann, H.; von Kameke, A.; Schlüter, M.: Measurement of Lagrangian Tracks in a 3 L Stirred Tank Reactor using 4D Particle Tracking Velocimetry with Shake-the-Box, ISPIV 21 (virtual), 2021, Presentation
  • Fitschen, J.; Kuschel, M.; Hofmann, S.; Hoffmann, H.; von Kameke, A.; Wucherpfennig, T.; Wutz, J.; Schlüter, M.: Validierung von numerischen Strömungssimulationen in einem 3L Rührkesselreaktor mittels 3D Partikel Trajektorien, Jahrestreffen der ProcessNet-Fachgruppen Computational Fluid Dynamics und Mehrphasenströmungen, 2021, Plenary Lecture
  • Hofmann, S.; Gaugler, L.: CHOLife - Multiscale Experimental Analysis and Simulation of Lifelines in Bioreactors to Study their Impact on the Cultivation Performance of CHO Cells, 2nd Annual Priority Program Status Meeting of the SPP2170 "InterZell", organized by Uni Stuttgart, Koblenz, 2021, Presentation

Poster Presentations

  • Hofmann, S.: Experimental Determination of Compartments in a 15,000 L Acrylic Glass Bioreactor by Means of Lagrangian Sensor Particles, Biobased Process and Reactor Technologies PhD Seminar, Hamburg University of Technology, Hamburg, 2022, Poster Presentation

  • Hofmann, S.; Buntkiel, L.; Reinecke, S.; GopalSingh, P.; Fitschen, J.; Hoffmann, M.; Hampel, U.; Schlüter, M.: Experimentelle Charakterisierung unterschiedlicher Lagrangescher Sensor Partikel Designs in einem 15000 L Bioreaktor, 16. Dresdner Sensor-Symposium, Dresden, 2022, Poster Presentation

  • Hofmann, S.; Weiland, C.; GopalSingh, P.; Kamp, M.; Fitschen, J.; v. Kameke, A.; Hoffmann, M.; Schlüter, M.: Experimental and Numerical Determination of Lifelines in a 3 L, 200 L and 15000 L Stirred Tank Reactor to Estimate the Flow-Following Capability of Lagrangian Sensor Particles, FTZ 3i Talk: Conference on intelligent - industrial - innovations, HAW Hamburg 2022, Poster Presentation

  • Hofmann, S.; Weiland, C.; GopalSingh, P.; Kamp, M.; Fitschen, J.; v. Kameke, A.; Hoffmann, M.; Schlüter, M.: Experimental and Numerical Determination of Lifelines in a 3 L, 200 L and 15000 L Stirred Tank Reactor to Estimate the Flow-Following Capability of Lagrangian Sensor Particles, 4th International Symposium on Multiscale Multiphase Process Engineering (MMPE), Berlin 2022, Poster Presentation

  • Hofmann, S.; Weiland, C.; GopalSingh, P.; Kamp, M.; Fitschen, J.; v. Kameke, A.; Hoffmann, M.; Schlüter, M.: Experimental and numerical determination of lifelines in a 3 L, 200 L and 15000 L stirred tank reactor, MIXING XXVII, North American Mixing Forum (NAMF), Online Conference 2022, Poster Presentation

  • Hofmann, S.; Fitschen, J.; v. Kameke, A.; Schlüter, M.: Multiscale Experimental Analysis of Lifelines in Bioreactors 1. Hamburg-Bochumer Mehrphasensymposium, Hamburg/Bochum, Online Conference, 2020, Poster Presentation

Publications

[154746]
Title: Novel Evaluation Method to Determine the Local Mixing Time Distribution in Stirred Tank Reactors.
Written by: Fitschen, J.; Hofmann, S.; Wutz, J.; Kameke, A. v.; Hoffmann M.; Wucherpfennig T.; Schlüter, M.
in: <em>Chemical Engineering Science: X</em>. May (2021).
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DOI: https://doi.org/10.1016/j.cesx.2021.100098
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Abstract: Stirred tank reactors are frequently used for mixing as well as heat- and mass transfer processes in chemical and biochemical engineering due to their robust operation and extensive experiences in the past. However, for cell culture processes like mammalian cell expression systems, special requirements have to be met to ensure optimal cell growth and product quality. One of the most important requirements to ensure ideal transport processes is a proper mixing performance, characterized typically by the global mixing time or the dimensionless global mixing time .As an evaluation method for mixing time determination, the time is usually determined until a tracer signal (e.g. conductivity) has reached a constant value after a peak has been introduced (e.g. by adding a salt). A disadvantage of this method is, that the position of tracer feeding as well as the position of the probe significantly influences the detected mixing time. Further on, the global mixing time does not provide any information about the spatial and temporal ”history” of the mixing process to identify areas that are mixed poorly or areas that form stable compartments. To overcome this disadvantage, a novel image analysis will be presented in this study for the detailed characterization of mixing processes by taking into account the history of mixing. The method based on the experimental determination of the local mixing time distribution by using a multi-color change caused by a pH-change in a bromothymol blue solution. A 3 L transparent stirred tank reactor is used for the benchmark experiment. To demonstrate the suitability of the new characterization method for the validation of numerical simulations, a calculation with a commercial Lattice-Boltzmann approach (M-Star CFD) has been performed additionally and evaluated regarding mixing time distributions. The exemplary application of image analysis to a numerical mixing time simulation shows good agreement with the corresponding experiment. On the one hand, this shows that the method can also be interesting for numerical work, especially for experimental validation, and on the other hand, this allows much deeper insights into the mixing behavior compared to conventional mixing criteria. For example the new method enables the characterization of mixing on different scales as well as the identification of micor- and macroscopic flow structures. The strong influence of the acid to base ratio on mixing time experiments becomes clearly visible with the new method.