Ingrid Burrington: "While the key materials of tissue engineering, like scaffolding, cells, and nutrient sources to help the cells grow, technically don’t need to be mined from the earth, they do have to come from somewhere. For example, when it comes to generating human skin—a practice currently used in burn grafting and for more niche lab applications, like cosmetics testing—you need collagen and fibroblast cells. Bovine collagen is typically extracted as part of the end process of livestock slaughter via a hydrolysis process used to turn cow hides into leather. Rat tail tendons, presumably obtained from deceased lab rats, are also a common collagen source. But if you’re looking for human sources of collagen, the supply chain gets a bit murkier. Neonatal foreskin is one of the most commonly used sources for generating human skin in the lab. No one in my reporting seemed able to point me to the vendor who 'just does foreskin,' but most likely it involves recovering materials that would otherwise end up in medical waste streams."