COMPUTATIONAL TASKS IN MEDICAL NANOROBOTICS - Bio-Inspired and Nanoscale Integrated Computing - page 417

their impact on safety, the likelihood of a rapid change in status, their computa-
tional overhead (the more often the protocol is run, the fewer computer resources
are available for primary tasks), and data acquisition time (e.g., detecting a very
rare molecule in the bloodstream might take many seconds or minutes; the
reprotocol cycle time should be significantly longer than the maximum practical
sensing period). Some protocols might be checked continuously—biochemical
processes may occur in milliseconds, other biological responses may require seconds
or minutes (e.g., automobile fuel gauges are rechecked electronically about once
every second.)
It is worth noting that theater protocols are found in natural human cell
biology. For example, most tissue cells require attachment to the ECM and
subsequent spreading on the ECM, for proper growth, function, and even
survival, a feature known as anchorage dependence [66]. Upon losing this
anchorage and departing from the desired theater of operation, cells often die
by undergoing apoptosis or programmed cell death. (Only the cells circulating in
the blood are designed to survive without attachment and spreading—some tumor
cells acquire this ability and leave their original tissue site to form metastases, a
pathological state.) In this theater protocol, the cell is designed to default to
suicide, but defers this action as long as a survival signal is received, indicating
continued residence in the permitted theater of operations. The survival signal is
generated as long as the cell maintains integrin attachment to a basement surface
or ECM. This protocol trigger is called an apoptotic switch [67]. T-cells employ a
similar theater protocol via the ''immunological synapse'' [68].
There are at least six basic classes of theater protocols.
1. Locational. Nanorobot activities may be locationally restricted to certain
specific regions of the body (e.g., heart, liver, epidermis, skull, ear canal,
right arm, big toe, or bloodstream). They may be restricted negatively—
allowed to operate only as long as they are not present in a particular
location—or may have a combination such that they exhibit two distinct
modes of behavior (e.g., location A behavior vs. location B behavior, or
location A versus location not-A behaviors). Thus a nanorobot that has
been bled out of the body or has been surreptitiously syringed from one
body to another would automatically deactivate. Since nanorobots can
contain reliable onboard geographic location and gravity sensors [1ax],
nanorobots could vary their activities as the patient moved across the
surface of the Earth, and astronaut-implanted nanorobots could vary
their behaviors according to whether the human is (a) on the ground,
(b) experiencing high-acceleration during boost phase, or (c) experiencing
on-orbit weightlessness.
2. Functional. Nanorobots may include theater protocols to restrict their
actions according to functional criteria, such as where a set of specified
conditions exists (e.g., only in a cancer tumor secreting certain biochemical
factors), or only where blood composition lies within certain preset limits,
or only in bloodstreams in which large amounts of alcohol, nicotine,