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 Cytosolic Leakage During Transit

If the nanorobot-membrane interface is not tight, some leakage of material into or out of the cell (depending upon relative hydraulic and osmotic pressures) may occur during nanodevice transit. For example, from Eqn. 3.1 the Brownian diffusion distance during a ttransit ~ 10 millisec transit time is ~3 microns for small molecules like amino acids (MW ~ 100 daltons), ~1 micron for large protein molecules (MW ~ 100,000 daltons). An annular leakage ring of width hleak ~ 10 nm around the circumference of a nanorobot of radius Rnano ~ 1 micron may pass Vleak ~ 2 p Rnano hleak vleak ttransit ~ 0.006 micron3 of cytosolic fluid during each transit (~0.00008% of cell volume), assuming vleak ~ 10 microns/sec for random hydrodynamic flows induced by thermal fluctuations inside a cell (Section Alternatively, modeling the leak as a ring of Npipe = 2 p Rnano / rtube = 1257 nanopipes each of radius rtube ~ hleak/2 and length ltube ~ 10 nm, and taking Dp ~ 0.001 atm for the interstitial/cellular pressure differential (Section, then from Eqn. 9.25 the total leakage volume from the ring of nanopipes is Vleak ~ Npipe 'VHP ttransit ~ 0.03 micron3 of cytosolic fluid during each transit, or ~0.0004% of cell volume. Leakage may be reduced by encouraging a tighter seal during transit using a dynamic ring pattern of lipophilic semaphores at the nanorobot surface (Section that tracks the device's passage through the plasma membrane. In some cases such as nerve cells, significant ionic leakage could produce depolarization and thus should be avoided.


Last updated on 21 February 2003