spheroid

A spheroid is a simple little ball of cells — one of the most basic three-dimensional tissue models. Left to clump together rather than spread out flat, cells naturally round up into a small sphere where they touch their neighbours on all sides, much closer to how cells sit inside the body than the single flat layer in an ordinary dish. Think of it as a tiny snowball of cells.

Forming one is refreshingly easy: drop cells where they cannot stick to a surface, and they huddle together into a ball on their own. Inside that ball the cells near the surface get plenty of oxygen and food while those in the centre get less — exactly the kind of gradient real tissue has. That makes a spheroid a more realistic, yet still cheap and fast, model for studying how cells grow, respond to drugs, or behave as a small tumour.

What sets a spheroid apart from an organoid is organization. A spheroid is mostly just a cluster — useful, but largely a uniform blob. An organoid goes further, with cells specializing and arranging into organ-like structures. So a spheroid is the simpler, scrappier cousin: less complex and less organized, but quick to make and ideal when you need a basic 3D model in large numbers.