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Production of microfluidic systems using high-resolution 3D printing

AK Janina Bahnemann

In recent years, three-dimensional (3D) printing has aroused increasing scientific interest. Due to the remarkable technical progress, it is now possible to print high-resolution structures in the range of a few micrometers. This development can also be applied to the field of microsystems technology and is increasingly being used for 3D printing of microfluidic prototypes and disposable systems. A major advantage of 3D-printed microsystems over traditional manufacturing methods is that desired prototypes can be printed within a few hours after 3D design and modeling. This allows necessary modifications for the optimization of the systems to be quickly implemented and tested.

Using modern, high-resolution 3D printers, Dr. Janina Bahnemann's working group produces microfluidic prototypes that are used in cell culture technology. As part of the DFG's Emmy Noether funding, the junior research group is currently working on the development of an integrated microfluidic system that will enable the flexible production of recombinant proteins. By efficiently mixing and incubating the host cells with the plasmid, the system will ensure continuous transient transfection of mammalian cells. An integrated separation unit will then separate the transfected cells from the transfection medium and simultaneously transfer them into fresh culture medium. In this way, the transfected cells can be cultivated directly in the bioreactor and used for the production of target proteins.

One subproject is concerned with the design and production of so-called micromixers, which allow for a gentle and efficient mixing of suspension cells with a desired reagent within a very short time. These micromixers can be integrated directly into a cell culture process and enable continuous and flexible manipulation of mammalian cells.

Publication: https://onlinelibrary.wiley.com/doi/epdf/10.1002/smll.20180432

Cell culture technology with CHO suspension cells

AK Janina Bahnemann

Another focus of current research is the flexible production of recombinant proteins using mammalian cell cultures. The research group is currently working on the development of a flow-through system that enables continuous transient transfection of mammalian cells. The main host cells used for transfection are CHO (Chinese Hamster Ovary) suspension cells, which are widely used in industrial protein production.

In order to create a basis for the use of 3D-printed materials in cell culture, a subproject is investigating the biocompatibility of different 3D-printed materials. These investigations are particularly important because the 3D-printed prototypes and microfluidic systems are in direct contact with the cells.

A Fluorescence Activated Cell Sorting (FACS) flow cytometer is available for process monitoring and analysis of the cell culture experiments. Cell samples are analyzed for their morphological and fluorogenic properties and then selected cell populations are selected and recultivated. Current applications are, for example, investigations of cell size distribution as well as the analysis of apoptosis, necrosis and cell cycle phases. In addition, FACS is used to determine the efficiency of transient transfection by quantitatively analyzing the expression of the green fluorescent reporter protein (GFP).

Development of electromechanical and electrochemical biosensors

AK Janina Bahnemann

Furthermore, the working group deals with the development of new sensors for the process monitoring of cell culture systems. Current research focuses on the development of electrochemical and electromechanical, aptamer-based biosensors for the rapid analysis of target proteins (e.g. antibodies) as well as for an early detection of potential microbial contaminations. Aptamers are oligomeric, single-stranded nucleic acids that have highly affine and selective bonds to a target object via their three-dimensional structure. In comparison to antibodies, the in vitro selection of suitable nucleic acid sequences (SELEX) makes it possible to target non-immunogenic substances amongst others.

The combination of electrochemical and electromechanical methods with aptamers enables label-free and continuous real-time process monitoring, which combines the outstanding sensitivity of electrical measurement methods with the selective affinity of aptamers. In addition to voltammetric measurement strategies, electrochemical impedance spectroscopy is one of the electrochemical methods specified or further developed by Dr. Janina Bahnemann's junior research group. This electromechanical method is based on the oscillation of piezoelectric quartz crystals using an alternating voltage, better known as Quartz Crystal Microbalance (QCM). If the mass of bound components on the crystal surface changes, the oscillation frequency also changes.

Since electrochemical and electromechanical methods can be combined in one approach, more flexible and thus more robust detections are possible with regard to concentration ranges and detection limits.