Happy Passaging in the new Year
The building blocks of our body are in constant flux. Every second, millions of cells die, and even a million other cells divide. The “me/I” in the next second is different from the previous second.
The cells in our body are like bioreactors – they continually churn various hormones, proteins, and signaling molecules to communicate with other cells. They not only interact with neighboring cells but also with extracellular matrix proteins. The cells modulate the behavior based on the availability of nutrients and signaling molecules.
This new year lets us make in-vitro models more relevant by exploring new upcoming techniques:
We have been growing cells on a plastic surface (T-25, T-75 Flaks). The cells bind to this surface with a higher stiffness than the cells do in the physiological environment. Secondly, each cell in our body binds with different tenacity. If we start growing all the cells with varying tissue origins on the same type of plastic surface, we do not provide the right environment to see the cells’ real behavior. For example, the bone cells bind with a higher stiffness than the nerve cells. Lastly, the cells in our body interact with extracellular matrix proteins. Hence, it is critical to coat cell culture flasks/plates with relevant material to mimic physiological conditions. Cell culture researchers use various biological and chemical coating components to suit the research needs to recapitulate the physiological environment.
- Biological Coating: Collagen, Elastin, Laminin, Vitronectin, Fibronectin
- Chemical Coating: Poly-L-Lysine, Poly-Ornithine
Our body cells are in a 3D environment and frequently interact with cells from both apical and basolateral sides. The nutrients diffuse into the cells in a gradient fashion. The cells on the surface usually get higher amounts of nutrients, while the more profound areas may get fewer nutrients. The cells we grow in a 2D environment get an equal concentration of nutrients as they are spread uniformly on the plates.
To mimic 3D environments, cell culture researchers started growing cells with some support /scaffolds. The choice of scaffold used depends on the nature of cells and the final objective of the study. Two primary supporting methods are being used:
- The hydrogel is a polymer network extensively swollen with water. Hydrogels are either natural (ECM based hydrogels) or synthetic – each has distinct properties. Synthetically derived hydrogels are usually more reproducible as they are free of animal components.
- Polymeric Scaffolds are fibers or sponge-like structures made up of either polystyrene (compatible for imaging) or polycaprolactone (biodegradable).
Organoids are cell aggregates that exhibit organ functionality. The organoids show similar composition and architecture as primary tissue. Organoids harbor a small population of self-renewing stem cells that can differentiate into cells of all significant cell lineages, with similar frequency as in physiological conditions. Organoids are amenable to manipulate niche components and could be cryopreserved as biobanks.