Observing Spheroids and Organoids

What are spheroids?

Spheroids are cellular aggregates. With typical culturing methods, cells are cultured in single, two-dimensional layers. However, in living bodies, cells are formed as three-dimensional structures. Growing cells as 3D lumps instead of flat layers is believed to reproduce intercellular interaction and operation with the extracellular matrix, resulting in an environment that is similar to a living body.

While 2D cell layers have their benefits, there are certain instances where a 3D culture in necessary - e.g. drug discovery and evaluation. Spheroids can reproduce the complicated environments within living bodies, making them better suited for screening tests and evaluating the toxicity of medicines. Additionally, research into spheroid transplantation as a treatment is ongoing, including their usefulness for treating ischemic and liver diseases.

There are two primary methods for creating spheroids: the shaking culture method using a container with a non-adherent base and the method of rotating the culture chamber. These methods both require the use of microfabricated containers; however, the spheroid arrays, used to create large quantities of uniform spheroids, are sold by multiple companies and can vary in size.

What are organoids?

Organoids are evolved spheroids that have been given functions as specific organs. It's not possible to culture actual organs because it is difficult to supply them with continuous nutrition. Organoids are smaller and simpler, so they are able to be cultured. The difference between organoids and spheroids is that while spheroids are lumps of 3D-cultured cells, organoids are more complex tissues composed of multiple cells that function as an organ.

Organoids are being researched for various organs, such as the brain, spinal cord, lungs, kidneys, stomach, and digestive tract. Even in the field of cancer research, organoids can be formed from the tumor cells of a patient and then used as the target model.

Example of spheroid observation

In the following example, KEYENCE's All-in-One Fluorescence Microscope BZ-X800 is used to observe a HEK293 spheroid that has been cleared through the use of Scale, a reagent that turns tissue transparent. Dead cells are colored red and fluoresce, making it possible to observe the distribution of dead cells, as well as the increase and decrease of them when the conditions are changed.

Conventionally, a laser confocal microscope was commonly used to observe spheroids and organoids, particularly given their 3D structure. However, there were several limitations with this approach, such as: 1) imaging took too long, 2) equipment was difficult to operate, and 3) cells were photobleached.

The optical sectioning function of the BZ-X Series can be used to observe thick samples without the influence of scattered or background fluorescence and do it much faster, easier, and with less damage. Compared to the standard wide-field image below, you can see just how clear of an image can be produced when using this function.

Using the All-in-One Fluorescence Microscope BZ-X800