Types, uses and limits of organ culture

Besides culturing whole organs, scientists can build tissue-like structures from cells:

• Histotypic culture: one cell type grown at high density, with soluble factors and a supporting matrix, so it forms a tissue-like structure. For example, endothelial cells form tiny capillary tubes in collagen, or cells fill collagen-coated cellulose sponges.
• Organotypic culture: cells of different kinds grown together, recreating a tissue. Mammary fibroblasts grown with mammary epithelial cells make the epithelial cells produce milk proteins, as they do in the body.
• Organoids: self-organising 3D tissues grown from stem cells, which look and work like a tiny organ. An artificial liver grown this way has been implanted in a rat.

Uses:

• As substitutes for scarce donor organs. Organs grown from a patient's own stem cells would not be rejected, so the patient would not need immunosuppressive drugs.
• To study how real tissues behave, and their biochemistry and function.
• To study hormones: the mouse mammary gland is often cultured for this.
• To study developmental biology.

Limits:

• Organ cultures do not multiply, so fresh organs are needed for every experiment.
• Results are hard to reproduce: they vary with the size and shape of the piece, how it was handled, and the proportions of its cells.
• They are costly and difficult.
• Only the integrated tissue can be studied, not single cells.

The future lies in 3D methods that bring flat (2D) laboratory tests closer to real tissue: spheroids, hydrogels, organoids, organs-on-chips, hanging drops, microfluidics, magnetic levitation, and 3D bioprinting.