Cell Culture 101
Cell culture is a method of growing cells outside of a living organism. This provides insight into the growth and development of cells for research and medical care. Cell culturing allows investigators to advance understanding at the molecular and genetic levels. The advantages of the bioreactor and the microgravity environment are best understood by looking at differences between the normal environment of cells and the microgravity environment. In each environment, living cells are exposed to complex forces that alter their development and activity at every level, from genetic expression to cell function.
Forces in Nature
The force of gravity has been constant for the 4.8 billion years that life has been present on Earth. Cells and tissues have little or no genetic memory of responding to different gravitational forces. But even modest changes in environment - from a high-altitude mountaintop to the depths of the ocean - can cause cells, tissues, and organisms to adapt.
As we learn to live and work in space, we also learn more about gravity's role in shaping evolution on Earth. The response of higher organisms to this 'new' environment may be less ordered and more complex than the response to other factors, such as thermal change. Cells are normally exposed to several forces in the human body:
- Gravitational,
- Electromagnetic,
- Strong molecular forces (forces within molecules), and
- Weak submolecular forces.
Gravity is the weakest of these forces, but it does have a huge radius of effect.
The Cell Culture Challenge
Image: Comparison of cell propagation in normal gravity and microgravity shows significant differences in cell aggregation. Cells cultured in microgravity produce aggregates that more closely resemble native tissue.
Cell culture is a method of growing cells outside of a living organism. As cells grow and develop, they form aggregates that eventually mature into tissue, such as cardiac or muscle tissue. In turn, these tissues form organs that perform dedicated functions.
Cell culture has long been an important tool for understanding how cells grow, develop, and interact, but it has a few significant limitations. In typical, stationary vessel cell culture, cells sediment to the bottom of their container and propagate as a sheet that is 1 cell thick.
Investigators have devised several ways to simulate the microgravity of space here on Earth. Each analog offers advantages and disadvantages, as described below.
The NASA Rotating Bioreactor
The NASA rotating bioreactor allows for solid body fluid rotation. The growth medium completely fills the cylindrical vessel. Rotation of the vessel along its horizontal axis suspends the cells without stirring them. In this way, cells experience less interaction with inert surfaces and experience greater three-dimensional freedom. A novel biochemical response may also result.
With the rotating bioreactor, aggregates up to 1 cubic centimeter can be cultured non-stop for hours. This affordable culturing method simulates many aspects of the microgravity of Earth orbit and is a powerful tool for cell biology research.
Many derivatives of the rotating bioreactor have been developed by NASA and it is available commercially. The bioreactor is licensed to Synthecon, Inc.
Whether used on Earth or in space, the bioreactor is a powerful tool for cell culture and tissue engineering. Key benefits of the rotating bioreactor include:
- Culture fluid rotates with the cylinder,
- Cells are in near-continuous suspension,
- Fluid shear is minimal, and
- Suspension is possible for tissue assemblies up to 1 centimeter.
+ See a video comparing cell growth on Earth and on orbit
Video: Comparison of prostate cells growing in a ground-based bioreactor (bottom) and during space flight (top) reveals visible differences in cell growth. Cells grown on Earth reach only a certain diameter, while those grown during flight form mature aggregates similar to those seen in native tissue. Although this clip shows only a short period of cell growth, the entire experiment, Bioreactor Demonstration System-05 (BDS-05), lasted nearly 16 days. BDS-05 supported studies of the cellular interaction between the prostate and bone stromal (connective tissue) cells.