Polymers such as PET can also be treated with natural or engineered enzymes to generate chemically recycled monomers. In a 2020 issue of "Nature", Tournier et al. investigated naturally occurring PETase as the basis to engineer new enzymes with higher specific activity and improved thermal stability. Using these enzymes, the researchers produced usable quantities of monomer; after additional purification, this recovered monomer was successfully used to produce PET resin with mechanical properties comparable to virgin PET. Research to improve the activity and stability of depolymerization enzymes is critical to allow this technology to be scaled industrially in a cost-effective manner.