The following nanomedicine FAQ and their answers have been compiled by Robert A. Freitas Jr.
5. Can you give a concrete example of a simple medical nanorobot?One very simple nanorobot that I designed a few years ago is the artificial mechanical red cell, which I call a "respirocyte." The respirocyte measures about 1 micron in diameter and just floats along in the bloodstream. It is a spherical nanorobot made of 18 billion atoms. These atoms are mostly carbon atoms arranged as diamond in a porous lattice structure inside the spherical shell. The respirocyte is essentially a tiny pressure tank that can be pumped full of up to 9 billion oxygen (O2) and carbon dioxide (CO2) molecules. Later on, these gases can be released from the tiny tank in a controlled manner. The gases are stored onboard at pressures up to about 1000 atmospheres. (Respirocytes can be rendered completely nonflammable by constructing the device internally of sapphire, a flameproof material with chemical and mechanical properties otherwise similar to diamond.)
The surface of each respirocyte is 37% covered with 29,160 molecular sorting rotors (Nanosystems, page 374) that can load and unload gases into the tanks. There are also gas concentration sensors on the outside of each device. When the nanorobot passes through the lung capillaries, O2 partial pressure is high and CO2 partial pressure is low, so the onboard computer tells the sorting rotors to load the tanks with oxygen and to dump the CO2. When the device later finds itself in the oxygen-starved peripheral tissues, the sensor readings are reversed. That is, CO2 partial pressure is relatively high and O2 partial pressure relatively low, so the onboard computer commands the sorting rotors to release O2 and to absorb CO2.
Respirocytes mimic the action of the natural hemoglobin-filled red blood cells. But a respirocyte can deliver 236 times more oxygen per unit volume than a natural red cell. This nanorobot is far more efficient than biology, mainly because its diamondoid construction permits a much higher operating pressure. (The operating pressure of the natural red blood cell is the equivalent of only about 0.51 atm, of which only about 0.13 atm is deliverable to tissues.) So the injection of a 5 cm3 dose of 50% respirocyte aqueous suspension into the bloodstream can exactly replace the entire O2 and CO2 carrying capacity of the patient's entire 5,400 cm3 of blood!
Respirocytes will have pressure sensors to receive acoustic signals from the doctor, who will use an ultrasound-like transmitter device to give the respirocytes commands to modify their behavior while they are still inside the patient's body. For example, the doctor might order all the respirocytes to just stop pumping, and become dormant. Later, the doctor might order them all to turn on again.
What if you added 1 liter of respirocytes into your bloodstream, the maximum that could possibly be safe? You could then hold your breath for nearly 4 hours if sitting quietly at the bottom of a swimming pool. Or if you were sprinting at top speed, you could run for at least 15 minutes before you had to take a breath!
It is clear that very "simple" medical nanodevices can have extremely useful abilities, even when applied in relatively small doses. Other more complex devices will have a broader range of capabilities. Some devices may have mobilitythe ability to swim through the blood, or crawl through body tissue or along the walls of arteries. Others will have different shapes, colors, and surface textures, depending on the functions they must perform. They will have different types of robotic manipulators, different sensor arrays, and so forth. Each medical nanorobot will be designed to do a particular job extremely well, and will have a unique shape and behavior.
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