organoid

An organoid is a three-dimensional, in vitro miniature tissue that models some structural and functional aspects of a real organ. Organoids arise from stem cells—usually induced pluripotent stem cells or embryonic stem cells—or from adult stem cells that differentiate and organize into tissue-like architectures. Through self-organization driven by intrinsic genetic programs and supplemented with signaling factors, cells form multiple lineages, establish lumenal cavities, and, in some cases, exhibit basic organ functions.

Organoids are typically grown in 3D cultures embedded in extracellular matrices such as Matrigel, under defined growth-factor conditions that guide regional specification. They are limited by the absence of vasculature, immune components, and full mechanical cues, which affects growth, maturation, and certain functions. They also show variability between lines and experiments.

Examples include brain organoids, intestinal organoids, liver organoids, kidney organoids, and retinal organoids, among others. Brain organoids can develop layered neural tissue and exhibit spontaneous neural activity; intestinal organoids form crypt-like structures and villus epithelium; liver organoids can show hepatocyte markers.

Organoids are used to study human development, disease mechanisms, and drug responses, to model genetic disorders using patient-derived cells, and to screen compounds for toxicity or efficacy. Researchers also employ gene editing to model or correct disease mutations. Because they recapitulate certain features in a controlled environment, organoids are valuable yet simplified models of human organs, not fully functional replacement tissues. Ethical considerations, especially for brain organoids, are discussed in the scientific community.