Tissue culture is a generic term that includes in vitro cultivation of organs, tissues, and cells.
The term originally applies not only to animal cells but also includes in vitro cultivation of plant cells.
Tissue culture can be subdivided into three major categories:
Organ culture
Explant culture
Cell culture
Organ culture refers to a three-dimensional culture of tissue that retains some or all histological features of the tissue in vivo.
The whole organ or part of the organ is maintained to allow differentiation and preservation of architecture, typically by culturing the tissue at the liquid-gas interface on a grid or gel.
Disadvantages of organ cultures:
Non-propagation: Organs cannot be propagated, so each piece of tissue can only be used once, making it hard to assess reproducibility.
Small cell populations: The cells of interest might be few in number, making their responses hard to detect and quantify.
Oxygen and nutrient supply: Adequate oxygen and nutrients may not be delivered to the entire tissue due to the absence of a vascular system, leading to rapid necrosis of some cells.
- Mitigation of issues:
Keeping the organ in stirred cultures or roller bottles can alternately provide air and soluble nutrients, which helps reduce necrosis.
Explant (or organotypic) culture:
In explant culture, small pieces of tissue are allowed to attach to an appropriate substrate, typically coated with collagen, and cultured in a rich medium, usually containing serum.
After attachment, cell migration occurs in the plane of the solid substrate.
- Traditional and modern approaches:
Traditionally, explants were maintained in Maximov chambers, where cells were grown on coverslips sealed over a depression in a thick glass slide. This approach is still used.
More recently, regular culture dishes are commonly used as they are more convenient and do not require disassembly at each feeding.
- Explant preparation:
Immature tissue grows best in explant cultures, so explants are often prepared from embryonic or neonatal tissue.
Tissue is usually cut with scalpels into slices 0.5 to 1.0 mm thick, but in some cases, it is fragmented by passing through a nylon mesh.
The need for diffusion of nutrients and oxygen to the centre limits the thickness of the explant to about 1 mm.
- Advantages:
Explant cultures can be maintained for months with proper experience.
Cells within the explant continue to develop more or less appropriately.
A key advantage is that some aspects of the tissue's architecture are preserved within the explant.
Cell culture refers to cultures created from dissociated cells taken from original tissue, called "primary cell culture."
The cells are separated either mechanically or enzymatically into a cell suspension.
These suspended cells can be cultured either:
As a monolayer on a solid surface, or
As a suspension in a culture medium.
Changes in Cells:
In dissociated cell cultures, cells lose their original tissue structure (histotypic architecture).
They may also lose some biochemical properties associated with the original tissue.
Benefits:
Despite these changes, the cells can be propagated (expanded and divided), allowing for the creation of replicate cultures.
Cultured cells can be preserved by freezing.
The most significant advantage is that it allows access to individual living cells.
Primary dissociated cell cultures are useful for studying cells using:
Morphological techniques (studying cell structure)
Physiological techniques (studying cell function)
These techniques can be applied on a cell-by-cell basis.
These cultures are less suitable for traditional biochemical studies because:
The quantity of material is often small.
The cell population is typically diverse (heterogeneous).
Success in primary cell culture is not guaranteed.
It requires effort to:
Find the right conditions for good cell growth and maturation.
Ensure the culture grows consistently (reproducibly).
Document and confirm the success of the process.