A bioreactor is defined as any device or system that supports a biologically active environment. They are designed and used to grow and maintain cells or tissues under controlled conditions. In tissue engineering, bioreactors are usually used to guide the development and maturation of lab-grown tissue constructs.

On the more basic side, a bioreactor can refer to something as simple as a petri dish filled with media which can grow cells. However, bioreactor design can get complicated based on the application. For instance, bioreactors can be designed to control fluid or air flow occur,  provide electrical stimulation, or apply various types of mechanical forces.