COMPUTATIONAL TASKS IN MEDICAL NANOROBOTICS - Bio-Inspired and Nanoscale Integrated Computing - page 416

that result in breaking free from splenic captivity and returning to the bloodstream
(Section 2.2.2).
Numerous other biocompatibility situations requiring specialized protocols
are identified elsewhere [2]. One interesting example involves the commandeering
of natural motile cells by medical nanorobots, a procedure known as cytocarriage
[1bn], as an alternative mode of in vivo transport. During cytocarriage, one or
more medical nanorobots may enter a motile cell, ride or steer the cell to a desired
destination inside the human body, then vacate the cell upon arrival. When
macrophages and other leukocytic cells become infected, they express B7 on their
membrane surface which can be recognized by a T-cell CD28 receptor protein,
triggering an immunologic response. In the ''infected cytovehicle protocol,''
nanorobot pilots would inspect the cell surface of a prospective cytovehicles for
B7 and similar flags prior to cytopenetration to avoid choosing an infected cell for
cytocarriage that could then spread the infection. If the cell subsequently becomes
infected and begins expressing B7 or other warning substances during the journey,
the protocol would direct the nanorobot pilot to abort the mission and steer the
cytovehicle to a nearby disposal site, or implement immediate therapeutic
measures; failing this, the pilot should abandon the vehicle at once.
15.4.3. Theater Protocols
A theater protocol is a control process by which the nanorobot verifies that it is
performing its tasks in the intended location or in the desired circumstances, as
prescribed by the attending physician. If the nanorobot determines that its present
location is inappropriate or the necessary conditions to enable action no longer
exist, the protocol triggers an appropriate corrective or defensive response. When
a nanorobot detects an out-of-theater condition (e.g., bled out of body), the most
appropriate response may often be to safe the device and then shut down.
Subsequent reentry into theater after shutdown (e.g., bled-out devices find their
way back into the bloodstream) normally should not allow reactivation of the
device because during its absence from theater, the nanorobot may have been
subjected to unknown forces, chemicals, radiation, or even reprogramming that
could render it harmful to the patient upon reentry, if reactivated. Even if a full
pre-restart self-diagnostic routine could be performed after an out-of-theater
excursion, unwanted modifications may be too subtle to detect via internal sensors
and the risk of malicious tampering is too great. One possible exception is where
the violated theater of operation is a functional condition such as ''patient is
asleep,'' ''patient is drunk,'' or ''patient is sexually aroused.'' In these cases, it is
less likely that switching on or off in response to theater protocols would pose
significant risk either to the devices or to the patient because these conditions are
normally cyclical volitional states that define inherently ephemeral or periodic
theaters of action.
The longer a therapeutic nanorobotic medical procedure takes to complete, the
more times a theater protocol should be executed during the mission. Protocols
might be checked more or less frequently depending upon their mission criticality,