Biotechnology is a key technology of the 21st century and will have a greater and more sustainable impact on life than most innovations created before. The development of new vaccines and medications, effective treatment of chronic diseases, and the breeding of new plants are just one facet of research in this field. Prosthetics are already being developed to restore vision to blind individuals. Computer scientists are considering developing biologically-based computers (DNA computers), and biosensors are already in use for environmental protection. The cultivation of tissue and replacement organs is being intensively researched. The development of biofuel cells and the integration of biotechnology and nanotechnology are also considered promising. There are approximately 5,000 biotechnology companies worldwide.