© 1999 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999

9.4.5.5 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 t_transit ~ 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 h_leak ~ 10 nm around the circumference of a nanorobot of radius R_nano ~ 1 micron may pass V_leak ~ 2 p R_nano h_leak v_leak t_transit ~ 0.006 micron³ of cytosolic fluid during each transit (~0.00008% of cell volume), assuming v_leak ~ 10 microns/sec for random hydrodynamic flows induced by thermal fluctuations inside a cell (Section 8.5.3.12). Alternatively, modeling the leak as a ring of N_pipe = 2 p R_nano / r_tube = 1257 nanopipes each of radius r_tube ~ h_leak/2 and length l_tube ~ 10 nm, and taking Dp ~ 0.001 atm for the interstitial/cellular pressure differential (Section 4.9.1.2), then from Eqn. 9.25 the total leakage volume from the ring of nanopipes is V_leak ~ N_pipe 'V_HP t_transit ~ 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 9.4.5.3) 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