OAn unusual application for MFC technology is to power implanted medical devices using glucose and oxygen from blood. An implanted MFC could provide power indefinitely and negate the need for surgery to replace batteries. Abiotic fuel cells based on noble metal catalysts and activated carbon have been demonstrated to produce energy from blood glucose in vitro and in vivo . Fuel cells based on enzymatic catalysts have also been shown to operate under physiological conditions but still require much improvement to become viable.