Bioreactor systems for cultivating cells in Life Sciences have been widely used for decades. Recently, there is a trend towards miniaturization, disposables and even micro platforms that fulfill increasing demands strongly aiming for production and testing of novel pharmaceutical products. Miniaturized bioreactors allow low power consumption, portability and reduced space requirements and utilize smaller volumes of reagents and samples [1,2]. A recursive strategy is necessary for optimizing the design and the manufacture of such miniaturized bioreactors. For the fabrication of these prototypes utilized micro-milling. Micro milling is a mechanical process which is commonly applied to create micro-structures in metals, e.g. aluminum and steel, or polymers, e.g. poly carbonate substrates. The structures and geometries are generated by utilizing computer aided design. By means of computer-aided manufacturing, the machining operations are implemented and then transferred to the machine tool. The machine tool moves the cutting tools with certain speeds, feeds and traverse ranges to the substrate. Micro milling has the advantage that the materials are generally not degraded by chemical substances, heating procedures or electromagnetic radiation.

Conventional Bioreactor systems for cultivating cells in Life Science have been widely used for decades. An in vitro cell cultivation bioreactor should reliably and reproducibly mimic the in vivo microenvironment of the cultured cells. Normally, mammalian cell cultures are performed in conventional bioreactor devices such as culture flasks and culture-dishes. However, these tools have fundamental limitations due to being inappropriate for high throughput screening and consume a considerable amount of resources and time [1]. Therefore, there is a trend towards miniaturization, disposables and even micro platforms that fulfill increasing demands strongly aiming for production and testing of novel pharmaceutical products. Here we present the development and manufacture of a disposable miniaturized flow-through bioreactor system that can be produced in large numbers at low costs. nanoporous hollow fibers are located at the fluidic sources and drains of the miniaturized bioreactors and retain cells. The necessary mixture of oxygen and carbon dioxide is provided via diffusion through a semi-permeable membrane. Fluidic connections allow the continuous feeding of the cells adding nutrient solution at constant rates at the inlet of the micro bioreactor and removing the solution at the same rate at the outlet. This medium can be collected and used for subsequent analysis. Different designs and concepts for such bioreactors were carried out with varying numbers of plates, and integrated or joined miniaturized reactor chambers. First tests show full technical and biological functionality, cells could successfully be cultivated at high viability rates for some days.

A bioreactor is a device simulating physiological environments for different biotechnological applications. In highly promising research fields like tissue engineering micro-sized bioreactors were utilized successfully promoting mammalian cells to grow and build 3D cell structures similar to in vivo environments. For any practical application and even for improved R&D it is necessary to generate and maintain a physiological environment over the whole cultivation period (hours, days or weeks, in case of artificial organs even up to months). Depending on the field of application physiological environments can comprise different parameters. In case of mammalian cell lines these parameters require a complex supply and monitoring system. Thus, we developed a semi-automated bioreactor-system for long-term cultivation of different mammalian cell types imitating physiological conditions. The system included detection and control of the following parameters: temperature, pH-value, gas concentration and the continuous supply with nutrients. A micro fluidic network was established enabling a high through-put cultivating system as bioreactor-system. The bioreactor-system consists of several micro-sized chambers in a microliter scale (the related article discussing the micro-sized chambers “Miniaturized Flow-Through Bioreactor for Processing and Testing in Pharmacology” by Boehme et al is published within this issue). The chambers were placed in a polymeric slide each with an individual medium supply and disposal. Every single chamber thus was connected to an individual syringe-based micro-pump setup and supplied by nutrients solution with a velocity of 100μl/h. The pH-value was observed optically and controlled via CO2 supply. All gas interchanges into every single chamber were realized via semi permeable membranes. The required temperature was adjusted via an appropriate custom-fit heating system utilizing MOSFETs allocated on an aluminum board along the slides. Two slides each were housed in a PMMA case. This bioreactor-system is a first prototype for larger systems aiming for the parallel operation of up to 100 micro-sized reaction chambers.