Nanomedicine, Volume IIA: Biocompatibility
© 2003 Robert A. Freitas Jr. All Rights Reserved.
Robert A. Freitas Jr., Nanomedicine, Volume IIA: Biocompatibility, Landes Bioscience, Georgetown, TX, 2003
15.5.8 Nanorobot-Nanorobot Mechanocompatibility
In clinical applications involving large populations of bloodborne diamondoid nanorobots simultaneously present inside the human body, nanorobots will regularly encounter one additional class of objects in their environment towards which mechanocompatibility must be proven: other nanorobots. For example, a maximum nanocrit bloodstream infusion involving a ~1000 terabot dosage (~1015 nanorobots) implies a mean collisional frequency for each device with its nanorobotic neighbors of ~40-200 collisions/sec (Section 22.214.171.124), mostly in regions close to vessel walls even at high shear (Section 126.96.36.199). Will such nanorobots survive in sanguo collisions with their neighboring devices?
Consider an elastic collision at relative velocity vcoll between two identical spherical nanorobots of radius Rbot and density rhobot, each comprised of a diamondoid structure with failure strength sigmabot, producing at the site of interaction a collisional dimple of radius rcoll and depth xcoll, and imposing a strain scoll. The two nanorobots decelerate in a time tcoll = xcoll/vcoll with a negative acceleration of acoll = vcoll2 / (2 xcoll) = vcoll2 / (2 scoll Rbot). The collisional force of Fcoll = mbot acoll is distributed over an interaction area of Acoll = pi rcoll2, producing a collisional pressure Pcoll <~ sigmabot to avoid material failure, with mbot = (4/3) pi rhobot Rbot3. Hence the stress produced during a nanorobot-nanorobot collision is approximately scoll = (2 rhobot Rbot2 vcoll2) / (3 sigmabot rcoll2). For nanorobots of radius Rbot = 1 micron and density rhobot ~ 2000 kg/m3, thermal velocity in blood at 37 oC is ~1 mm/sec (Section 3.2.1) and the anticipated relative collision velocity is 1-2 mm/sec (Section 188.8.131.52). Conservatively taking vcoll = 1 cm/sec, sigmabot = 1000 atm (~108 N/m2) and rcoll = 10 nm, and taking the maximum allowable strain for diamond smax ~ 5%, then the collision time tcoll ~ 1 nanosec, deceleration acoll ~ 4 x 105 g’s, and strain scoll ~ 0.001% << smax ~ 5%, so such collisions appear to be easily survivable. Similar considerations may apply to interactions between individual nanorobots and macroscale nanorobotic organs or nanoaggregates. Interactions between nonspherical nanorobots having protruding surface features, extended manipulators, and the like should be examined in future studies.
Nonspecific aggregation or inelastic “clumping” of nanorobots in vivo should not be a major problem because nonbiological adhesive forces are greatly reduced in fluid environments (Section 9.2.3), and because nanorobot surface adhesive characteristics and biological adhesive forces are subject to design control and therefore to minimization (Section 15.2.2).
Last updated on 30 April 2004