COMPUTATIONAL TASKS IN MEDICAL NANOROBOTICS - Bio-Inspired and Nanoscale Integrated Computing - page 397

these same rotors reverse their direction of rotation, recharging the device with
fresh oxygen and dumping the stored CO 2 , which diffuses into the lungs and can
then be exhaled by the patient. The onboard nanocomputer and numerous
chemical and pressure sensors enable complex device behaviors remotely repro-
grammable by the physician via externally applied ultrasound acoustic signals.
There is also a large internal void surrounding the nanocomputer which can be a
vacuum, or can be filled or emptied with water. This allows the device to control
its buoyancy very precisely (Section 2.1.2) and provides a crude but simple method
for removing respirocytes from the blood using a centrifuge, a procedure called
nanapheresis [1n].
Various sensors are needed to acquire external data essential in regulating gas
loading and unloading operations, tank volume management, and other special
protocols. It is also convenient to include internal pressure sensors [1k] to monitor
O 2 and CO 2 gas tank loading, ullage (container fullness) sensors [1o] for ballast and
glucose fuel tanks, and internal/external temperature sensors [1i] to help monitor
and regulate total system energy output. The attending physician can broadcast
signals to molecular mechanical systems deployed inside the human body most
conveniently using modulated compressive pressure pulses received by mechanical
transducers embedded in the surface of the respirocyte. Converting a pattern
of pressure fluctuations into mechanical motions that can serve as input to a
mechanical computer requires transducers that function as pressure-driven actua-
tors [1p, 12e]. Data transmitted at 10 7 bits/sec) using peak-to-trough

10-atm pressure pulses (the same as medical pulse-echo diagnostic ultrasound
systems [30]) should attenuate only

10MHz (

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10% per 1 cm of travel [1q], so whole-body
broadcasts should be feasible even in emergency field situations. Internal commu-
nications within the respirocyte itself can be achieved by impressing modulated low-
pressure acoustical spikes [1r] on the hydraulic working fluid of the power
distribution system [1s], or via simple mechanical rods and couplings [1t].
Onboard power is provided by a mechanochemical engine [1u] or fuel cell [1v]
that exoergically combines ambient glucose and oxygen to generate mechanical or
electrical energy to drive molecular sorting rotors and other subsystems, as
demonstrated in principle in a variety of biological motor systems [1w]. Sorting
rotors absorb glucose directly from the blood and store it in an internal fuel tank.
Oxygen is tapped from onboard storage. The power system is scaled such that each
glucose engine can fill the primary O 2 tank from a fully empty condition in
10 seconds, requiring a peak continuous output of 0.3 pW. The glucose fuel tank
is scaled such that one tankful of fuel drives the glucose engine at maximum output
for 10 seconds, consuming 5% of the O 2 gas stored onboard and releasing a volume
of waste water approximately equal to the volume of the glucose consumed. Power
is transmitted mechanically or hydraulically using an appropriate working fluid,
and can be distributed as required using rods and gear trains [1x] or using pipes and
mechanically operated valves, controlled by the nanocomputer.
A 5 cc therapeutic dose of 50% respirocyte saline suspension containing
5 trillion nanorobots would exactly replace the gas carrying capacity of the
patient's entire 5.4 liters of blood. If up to 1 liter of respirocyte suspension can

B