This trend towards 3D cell culture can no longer be overlooked. Over the past decade, the number of publications in the field of 3D culture has grown exponentially. While around five thousand publications on this topic existed a decade ago, today there are more than 22,000 publications addressing three-dimensional cell culture. And new publications are currently running at almost three thousand a year.
The reason for this trend is the substantial limitations which apply to two-dimensional cell culture. Cells grown under flat (2D) conditions do not behave like the cells which grow in the natural organism. The activity, growth and intercellular communication observable in the host are all different from those same attributes as displayed via 2D cell culture.
In addition, the trypsinization of cells during passage destroys their extracellular matrix and thus part of the mechanism controlling cell activity. As a result, only limited physiologically relevant data can be obtained from a 2D cell culture.
In contrast, more complex cell models such as spheroids and organoids are able to depict the physiological properties of the native tissue. However, it is difficult to cultivate these multi-layered cell models over a long period of time, because the cell clusters often vary in shape and size, which makes experiments more difficult to reproduce.
Systems with scaffolds, gels, or other types of additives have evolved to preserve the physiological properties of cells and increase the viability of 3D cell models. These, in turn, can unbalance natural gene expression, once again reducing the functionality of 3D cultures.
In order to promote the functionality of large three-dimensional tissue-mimetic structures, the cells must therefore be maintained in an environment as close as possible to in vivo conditions. A simulated microgravity system is a solution for maintaining the function, architecture and ultrastructure of three-dimensional cell cultures.
Gravity has the great advantage that the cells are then exposed to very low shear forces. A rotating bioreactor keeps cells in a state of suspension by allowing gravitational forces to act on the cells from all sides. This creates an environment which positively promotes the functionality of large 3D structures such as spheroids, organoids, acini and other aggregates. Thus large spheroids of uniform size can be created.
Furthermore, this active diffusion creates very good gas and nutrient exchange, and oxygen can easily reach the core of a cell cluster. Active transport mechanisms require a lot of energy, and this metabolic activity of cells shows just how alive and viable the 3D clusters in a microgravity system actually are.
Compared to the classic 2D standard cell culture, the proliferation of cells in the ClinoStar gravity system decreases dramatically. For example, HepG2 cells in 2D are already 100% confluent after 5 days, while the same cells in the 3D system only reach a size of 1400 µm and a proliferation rate of >60 days after 42 days in culture. This slower cell growth reflects the actual in vivo situation, and due to this more relaxed growth, the cells can then invest their energy in functional tasks instead of in growth activity.
If you measure the functionality in hepatocytes – for example, in terms of urea, cholesterol and glycogen production – you can see there is almost no production of these substances in a 2D cell culture.
However, in the ClinoStar cultures, urea and cholesterol levels rise to in vivo levels during maturation. And after 21 days, the cells reach the in vivo situation.
The ClinoStar system thus makes it possible to imitate the true state of a tissue or organ.
These physiological changes and restoration of in vivo functionality make it possible to cultivate spheroids, organoids or other aggregates which can realistically replicate the characteristics of a living organism.
The ClinoStar is a CO2 incubator with a microgravity system which makes the cultivation of three-dimensional structures easy and reproducible. And this gain in the in-vivo-like physiological properties greatly improves the informative value of scientific studies. A clinostat can thus increase the effectiveness of toxicological studies – both acute and chronic (single dose or repeated doses). It can also be used in cancer research, regenerative medicine and for the discovery of new drugs.
The ClinoStar enables the production of uniform, reproducible and functional spheroids and organoids. These spheroids realistically imitate the function, structure and architecture of the living organism. Under laboratory conditions, this creates an unprecedented correlation between cell culture and cell function.