Scientists have developed a synthetic substance that can 1. be used to replace damaged brain tissue 2. conduct, or transmit, nerve impulses 3. replace damaged nerve tissue 4. grow artificial limbs

replace damaged nerve tissue

Related, anabolic steroids is the common name for synthetic substances related to the male sex hormones e.g. testosterone. They promote the growth of skeletal muscle (anabolic effect) as well as development of male sexual characteristics ( androgenic effect) in both male and females.

During the 1930s, scientists discovered that anabolic steroids could facilitate the growth of skeletal muscle in lab animals.  This led to the abuse (inappropriate use)  of the compounds first by body builders then by athletes in other sports.