Stem cells are a class of undifferentiated biological cells that can develop, through a process called differentiation, into many different types of specialized cell types in the body such as skin cells, brain cells, etc. They appear to be one of the body’s best tools for self-repair. Given the right stimulation, stem cells differentiate into cells that make bone, tendon, cartilage, and ligaments. They may be used to replace cells and tissues that have been damaged or lost due to disease.