Nanomedicine, Volume I: Basic Capabilities
© 1999 Robert A. Freitas Jr. All Rights Reserved.
Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999
10.1.4 Dedicated Chronometer Organs
Just as the hypothalamus is the physical locus of the natural circadian clock (Section 10.1.1), it may be convenient to establish artificial chronometer organs inside the human body for various purposes. Dedicated nano-organs have been described previously in connection with power (Section 6.4.4), communication (Section 7.3.4), and navigational (Section 8.3.6) systems.
Chronometer organs, which would likely be millimeter-scale or smaller, could be used as endogenous clocks to regulate the precise administration of time-release substances or devices. Such organs could serve as highly accurate timers to improve the natural human interval timing sense from ±15% accuracy in biological systems (Section 10.1.1) to parts per million accuracy, or better, using artificial systems. If linked to the patient or user through various outmessaging channels (Section 7.4.6), chronometer organs can provide a continuously-available, consciously-accessible unfailing "time sense" of extraordinary precision for time of day, calendar date, and other time-related information.
Dedicated chronometer organs can be used to synchronize chronocytes or mobile communication networks at the nodes (Section 7.3.2). For example, chronocytes with lower-stability crystal oscillators could be repeatedly recalibrated as they passed near larger embedded chronometer organs during each blood circulation cycle (e.g., once per minute). Such chronometer organs might incorporate higher-stability onboard atomic frequency standards. Alternatively, chronometer organs could serve as transdermal data ports through which timing synchronization signals can be injected into fiber-based in vivo communication networks (Section 7.3.1) from external timing sources, similar to the autoclock pulse (containing time and date information) that is added to most contemporary television broadcast signals. Hard connectors, centimeter-scale rf wireless antennas, and other types of links are possible (Sections 6.4.2 and 7.2.3). In 1998, a desk clock could be purchased for $50 that automatically recalibrated itself by picking up WWVB radio signals anywhere in North America, several times a night, using a few centimeters of rod antenna.1711 WWV's carrier frequency is regulated to Dn / n ~ 5 x 10-12, ultimately providing a time synchronicity at the receiver of ~100 microsec/day. With a slightly larger in vivo antenna, satellite GPS signals may be received, providing <~20 nanosec time error.1711 If buildings and vehicles are rewired to permit dissemination of time synchronization pulses and other useful information via continuous rf or IR channels, chronometer organs could employ smaller in vivo antennas and still achieve very precise results.
Although it has been informally speculated3025 that nanorobots could use biological nerve fibers as rf antennas to receive electromagnetic time recalibration signals from outside the human body, such as from WWV, this concept is probably unworkable for several reasons. First, the axoplasm is only ~10-7 as electrically conductive as a metal wire of equivalent size, because axoplasmic charge carrier density and mobility are much lower than for electrons in a wire.799 Second, passively conducted axonal currents are quickly attenuated by leakage through ion channels in the membrane, which is a very poor insulator. From cable theory applied to neurons,799,3022 the length constant ln is defined as the distance over which an applied potential depolarizes to 1/e (~37%) of its maximum value; ln = (dneuron rmem / 4 raxo)1/2 ~ (0.04 dneuron)1/2, where dneuron is axonal diameter in meters, rmem is the specific membrane resistance (~0.2 ohm-m2 in human neurons) and raxo is the specific resistance of the axoplasm (~1.25 ohm-m in human neurons). For a typical human axon with dneuron ~ 1 micron, then ln ~ 200 microns (~internodal distance between nodes of Ranvier) and an external signal is >99% attenuated in ~1 mm of longitudinal travel. Third, short pulses (e.g., rapidly-oscillating rf signals) are severely distorted and attenuated by the electrical capacitance of the cell membrane. The capacitive time constant in human nerves and muscle cells ranges from 120 millisec,799 thus limiting any possible electromagnetic reception to frequencies under 50-200 Hz, although pulsed microwaves directed through the brain can induce auditory effects in animals and humans.3473-3481
Last updated on 23 February 2003