Interview: Bioreactors and Surfaced-Modified 3D-Scaffolds for Stem Cell Research

My name is Karlan And I'm working as a biophysicist at the Institute for Biological Interfaces. In the Cal Screw Institute of Technology, we develop bioreactors and surface modified three dimensional scaffolds for the cultivation of functional tissues and for stem cell research, we are mainly interested in the interaction of cells with Their artificial environment. A nature editorial in 2003 asked the question by flat biology, and the question is, what is implied by this?

In the past, many in vitro culture systems, mainly monolayer cultures suffered from the disadvantages that, for example, differentiated primary cells had a relatively short lifespan and de differentiated during culture. That means they lost most of their organ specific functions very rapidly. Therefore, in order to reproduce better conditions for these cells in vitro, many different modifications and adaptations have been made in conventional monolayer cultures.

And this includes the composition of the culture medium and the create coating of culture vessels in which the cells predominantly form monolayers. And all these approaches indicate the importance of cell matrix interactions as well as cell to cell communication. Another important aspect seems to be the establishment of cell specific contexts, which are realized for example, by gap junctional complexes, which are common characteristic of many cells in vivo.

In conventional monolayer cultures gap junctional communication Is rapidly lost. For a long time. It is possible to Reestablish in vitro to some extent a tissue like arrangement of cells using the so-called steroid technique.

An example from our lab was that we could show that even adult ru hepatocytes are able to form steroids and remain viable for at least weeks in these aggregates. Hepatocytes stay in close contact to each other promoting the cellular communication resulting in the stabilization of hepatocyte specific functions. But we also found that this conventional three dimensional culture technique has several drawbacks.

The aggregate size is critical. They could induce necrosis for large aggregate diameters, and in most cases, the medium volume to cell ratio is inappropriate. Also, shearing forces and spinner cultures can be problematic.

Organs and tissues in living organisms are among others, characterized by very high cell densities, also directed active transport of substances through these tissue layers is an important characteristic. Therefore, realistic organotypic in vitro tissue models should most closely rebuild this natural architecture. And an essential determinant for the limitation of such systems is the appropriate ratio of medium to cell volume.

I mentioned before we designed a suitable cell housing Shaped as a precisely micro structured polymers scaffold, which offers evenly sized container for the three dimensional culture of cell aggregates. For the polymers scaffold, we preferably use PMMA or PC polyether, ate or polycarbonate. And this consists of a micro structured plantar device of one square centimeter, which offers a dense array of more than 1000 of these containers.

For the three dimensional culture of cell aggregates, it has been shown to be suitable for 3D cell culture over several weeks. And each of these small cubic containers in the array has an edge length of about 300 Micrometers. The special Design of this scaffold and of the periphery, that means the incubation chamber.

The ector medium and gas supply allows for different modes of medium supply. First superfusion. That means both sides of the tissue are separately supplied by nutritional medium, and secondly, perfusion.

That means medium flow is forced to penetrate the tissue layer. The perfusion mode can be used to create conditions that better mimic the in vivo vascularization, but even a mixed mode of perfusion and superfusion is possible. Different cell ship generations have been developed.

Each generation can be used with a certain design to meet the needs of any special application. For example, designs of single and double ship bioreactors have been built as well as separately addressable multi titer arrangements or highly paralleled Variance. As upscaled versions for the last generation Of these different forms, the so-called micro thermoformed containers, a certain technology has been developed, which offers the additional possibility to modify the whole surface of these 3D formed containers here herewith, even a surface patterning and a submicron scale with signaling molecules is possible.

Also, sensors and signal electrodes can be incorporated. The applications range from basic research and cell biology to toxicology and pharmacology, and also high throughput screening as possible. A very important point at the end is the fact that the last generation of our micro thermoform chips have been optimized to allow processes for cheap mass production and therefore for application In other laboratories.