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
22.214.171.124 Diffusion-Limited Broadcast Rate
Given Imessage ~ 109 bits for rmessage = 0.2 micron from Eqn. 7.2, it is clear that onboard stores of messenger molecules will be quickly exhausted at the highest broadcast bit rates unless the communication system architecture makes substantial use of messenger molecule recycling. Without recycling, emission of hydrofluorocarbon message molecules is fluorine-limited, because carbon and hydrogen atoms are readily available from glucose and water molecules. The bloodstream concentration of fluoride is ~4.5 x 10-7 gm/cm3 (Appendix B) or ~1.4 x 1022 F atoms/m3. From Eqn. 3.4, the maximum diffusion current to the entire surface of a spherical nanodevice of radius R = 1-micron and diffusion constant D ~ 2 x 10-9 m2/sec (est. from Table 3.3) is J = 3.6 x 108 F atoms/sec or 1.1 x 10-17 kg/sec, enough fluorine to manufacture 2.7 x 10-17 kg/sec representing a continuous long-term maximum broadcast rate of 'I ~ 7.2 x 108 bits/sec of (CHX)n 1-bit/unit hydrofluorocarbon messenger molecules.
Even in the unlikely event that all 8.3 x 1022 atoms of fluorine present in the human body (Table 3.1) were somehow converted to hydrofluorocarbon messenger molecules and released into the bloodstream simultaneously, the bloodstream concentration would reach ~1.2 gm/liter, well below the ~700 gm/liter LD50, though admittedly exceeding the ~0.1 gm/liter limit that occasionally triggers anaphylactoid-type reactions.
In 1963, Bossert and Wilson703 completed the first systematic analysis of chemical communication in the context of animal olfactory communication in air, later extended by Bossert725 in an analysis of maximum possible bit rates. In the following discussion, their results are adapted to the problem of in vivo chemical communication among medical nanodevices.
Last updated on 18 February 2003