The Economist: The great hope of transplant surgeons is that they will, one day, be able to order replacement body parts on demand. That possibility may be closer with the arrival of the first commercial 3D bio-printer for manufacturing human tissue and organs.The new machine, which costs around $200,000, has been developed by San Diego–based Organovo, a company that specializes in regenerative medicine, and an Australian engineering and automation firm called Invetech.To start with, only simple tissues, such as skin, muscle, and short stretches of blood vessels, will be made for research purposes.Organovo expects that within five years, once clinical trials are complete, the printers will produce blood vessels for use as grafts in bypass surgery.