As a company focused on 3D cell culture models and assays, we routinely have researchers ask us about organoid models and typically we always ask the researcher what exactly they mean by organoid. The reason for this is that many researchers tend to use the term organoid to refer to any model of cells grown into a three-dimensional type structure such as patient-derived cancer cells or primary human hepatocytes. However, organoid actually refers to a very specific type of 3D cell culture model which is a model that has been generated from induced pluripotent stem cells (iPSCs) or primary stem cells.
The confusion around these terms stems from the newness of the 3D cell culture field as well as the current definition for organoid which is “an artificially grown mass of cells or tissue that resembles an organ.” Below are the definitions we use at Visikol to describe different types of models and that many of the experts in the space are using:
- 3D cell culture model – broad all-encompassing term for any three-dimensional cell culture model where cells are organized into a three-dimensional construct. These models can be generated using a wide array of approaches from bio-printing to magnetic levitation and can be comprised of a single cell type or highly organized co-culture models.
- Spheroid – this is a 3D cell culture model that is roughly spherical and can be comprised of a single cell type or multiple cell types. These cells can be primary cells, cancer cell lines, iPSCs or stem cells. In practice, spheroids can be generated one per well or multiple spheroids per well for use in assays.
- Organoid – a 3D cell culture model that is derived from iPSCs or primary stem cells. These models tend to show significant organization and multiple cell types.
- Bioprinted tissue – while not exactly tissue, these 3D cell culture models are comprised of cells within an extracellular matrix that is extruded from a bioprinter to provide spatial organization. These models can vary significantly in how they are generated and structured from simple to highly complex.