COMPUTATIONAL TASKS IN MEDICAL NANOROBOTICS - Bio-Inspired and Nanoscale Integrated Computing - page 402

its minor axis, consisting of 610 billion precisely arranged structural atoms in a
gross geometric volume of 12.1 micron 3 and a dry mass of 12.2 picograms. This
size helps to ensure that the nanorobot can safely pass through even the narrowest
of human capillaries and other tight spots in the spleen (e.g., the interendothelial
splenofenestral slits [2e]) and elsewhere in the human body [2f]. The microbivore
has a mouth with an irising door, called the ingestion port, where microbes are fed
in to be digested. The microbivore also has a rear end, or exhaust port, where the
completely digested remains of the pathogen are harmlessly expelled from the
device. The rear door opens between the main body of the microbivore and a tail-
cone structure. The device may consume up to 200 pW of continuous power while
completely digesting trapped microbes at a maximum throughput of 2 micron 3 of
organic material per 30-second cycle, which is large enough to internalize a single
microbe from virtually any major bacteremic species in a single gulp. This ''digest
and discharge'' protocol [1ab] is conceptually similar to the internalization and
digestion process practiced by natural phagocytes, except that the artificial process
should be much faster and cleaner. For example, it is well-known that macro-
phages release biologically active compounds during bacteriophagy [41], whereas
well designed microbivores need only release biologically inactive effluent.
The first task for the bloodborne microbivore is to reliably acquire a pathogen
to be digested. If the correct bacterium bumps into the nanorobot surface,
reversible species-specific binding sites on the microbivore hull can recognize
and weakly bind to the bacterium. A set of 9 distinct antigenic markers should be
specific enough [1ac], since all 9 must register a positive binding event to confirm
that a targeted microbe has been caught. There are 20,000 copies of these 9-marker
receptor sets, distributed in 275 disk-shaped regions across the microbivore
surface. Inside each receptor ring are more rotors to absorb ambient glucose
and oxygen from the bloodstream to provide nanorobot power. At the center of
each 150-nm diameter receptor disk is a grapple silo. Once a bacterium has been
captured by the reversible receptors, telescoping robotic grapples [1ad] rise up out
of the microbivore surface and attach to the trapped bacterium, establishing
secure anchorage to the microbe's plasma membrane. The microbivore grapple
arms are about 100 nm long and have various rotating and telescoping joints that
allow them to change their position, angle, and length. After rising out of its silo, a
grapple arm can execute complex twisting motions, and adjacent grapple arms can
physically reach each other, allowing them to hand off bound objects as small as a
virus particle. Grapple handoff motions can transport a large rod-shaped
bacterium from its original capture site forward to the ingestion port at the front
of the device. The captive organism is rotated into the proper orientation as it
approaches the open microbivore mouth, where the pathogen cell is internalized
into a 2 micron 3 morcellation chamber.
There are two concentric cylinders inside the microbivore. The bacterium is
minced into nanoscale pieces in the morcellation chamber [1ae], the smaller inner
cylinder, then the remains are pistoned into a separate 2 micron 3 digestion

chamber, a larger outer cylinder. In a preprogrammed sequence, 40 different

engineered digestive enzymes are successively injected and extracted six times

B