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

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

9.4.5.3 Solvation Wave Drive

The lipid bilayer membrane is hydrophilic on the outermost and innermost surfaces, and lipophilic in the interior (Fig. 8.37). Much like the physical screw described in the previous Section, the hydrophilicity of the nanorobot exterior surface may also be manipulated to produce a traveling helical solvation wave that establishes temporary noncovalent bonds with elements of the plasma membrane, allowing the nanorobot to pull itself through the lipid bilayer (Fig. 9.30). The plasma membrane is typically 6-10 nm thick (Section 8.5.3.2). The cholesterol-poor lipid membranes of the mitochondria and the endoplasmic reticulum have a 2.5 nm inner hydrophobic region, while cholesterol-rich lipid membranes like those of the plasma membrane and the endosomes have a 3.1 nm wide hydrophobic region.^1113-1115 Each contact point may be envisioned as a semaphore-like mechanism (Section 5.3.6) by which lipophilic or hydrophilic moieties are rotated into an exposed position (facilitating noncovalent bonding with a particular lipid bilayer phase), then moved a short distance relative to the nanorobot body (transmitting force to the nanorobot), then rotated back into a nonexposed position (breaking the bond to the lipid membrane).

From Eqn. 9.73, a 1-micron nanorobot traveling at ~100 microns/sec must generate ~2 pN of motive force in order to overcome the viscous resistance of plasma-like fluid at 310 K. Given a single-lipid extraction force of F_lipid ~ 1 pN (Section 9.4.3.1), ten simultaneous contacts producing a total of 2 pN reduces applied force per contact to a reasonably safe ~20% F_lipid. Assuming 10 simultaneous contacts spaced around the nanorobot perimeter and 10 nm of available longitudinal travel for each bonded semaphore mechanism, a 1-micron nanorobot requires ~1000 surface semaphores in staggered configuration. Allowing ~300 nm² per semaphore presentation face (Section 5.3.6), the entire solvation wave drive system occupies just 5% of nanorobot surface area. Breaking ~1000 noncovalent semaphore-membrane bonds, assuming ~100 zJ/bond (Section 3.5.2), during a 10 millisec transit requires ~0.01 pW of power; the same figure is obtained for 300,000 nm² of semaphores dissipating ~0.03 pW/micron² (Section 5.3.6). Total power required to overcome viscous resistance is ~0.0002 pW during the ~10 millisec transit time (Section 9.4.2.4).

Last updated on 21 February 2003