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

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

5.3.1.4 Reactivity

Another important parameter of nanorobot metamorphic surfaces is their reactivity -- the speed with which they can execute a full-range structural modification. Energy requirements are key, given a power budget of P_m (watts) for morphing. In particular, metamorphic block velocity is limited both by the sliding power dissipation due to sliding block surfaces of area S that are sliding at a velocity v_slide, or

{Eqn. 5.4}

where k₁ = 400 kg/m²-sec (Section 4.3.4.2), and by the drag power dissipated in driving a circular surface of radius r through a 310 K aqueous (plasma, interstitial or cytosolic) environment of viscosity h = 1.1 x 10^-3 kg/m-sec at a velocity v_drag, given³³⁷ by

{Eqn. 5.5}

Assuming we wish to restrict total morphing energy dissipation to a budget of P_m = 0.1 pW for a 1 micron³ nanorobot, then for S = 6 micron² of sliding surfaces and r ~ 0.5 micron, v_drag ~ 0.3 cm/sec (< v_slide = 0.6 cm/sec in vacuo). Using 0.3 cm/sec, the full-range morphing action to, say, double the nanorobot diameter (~0.5 micron of radial motion) requires ~0.2 millisec for the surface of the entire nanorobot to complete the motion.

The 10-finger manipulator described in Section 5.3.1.3 may also extend at v_drag ~ 0.3 cm/sec while remaining within the 0.1 pW energy budget, although a single individual finger may extend at v_drag ~ 1 cm/sec (<< v_slide = 1.6 m/sec in vacuo) allowing maximum deployment within the cytosol in ~0.3 millisec. Thus metamorphic surfaces in vivo can exhibit ~KHz frequency large-motion oscillations. By comparison, deformed erythrocytes when released from micro-pipette suction recover their normal biconcave shape in ~100 millisec.³⁷¹ Contractile gel fibers ~1 micron thick can shrink to 4% of their initial volume in ~1 millisec when triggered by an electrochemical reaction or an applied voltage of ~5000 volts/m.³⁵⁷

Last updated on 17 February 2003