© 2003 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Nanomedicine, Volume IIA: Biocompatibility, Landes Bioscience, Georgetown, TX, 2003

15.5.5.2.1 Nanorobotic Thrombocytolysis

Collisions between platelets and medical nanorobots in the bloodstream will take place at similar velocities and frequencies as collisions that normally take place between platelets and other natural blood elements. Hence nanorobots should not significantly increase the risk of mechanical thrombocytolysis and subsequent thrombosis. For example, each ~2-micron diameter platelet [4100] present in human blood that contains a 10% Nct of 2-micron diameter nanorobots may experience ~2 collisions/sec with neighboring nanorobots at a mean collision velocity of ~2 mm/sec but may also experience ~0.5 collisions/sec at ~2 mm/sec with other platelets, ~110 collisions/sec at ~3 mm/sec with nearby red cells, and ~100 collisions/sec at 0.5-5 mm/sec with capillary walls (Section 9.4.2.2). Such high nanorobot dosages induce the highest collision rates because red cells disproportionally occupy blood vessel axial regions [4100] (forcing platelets and nanorobots together preferentially toward the periphery; Section 9.4.1.3) and because erythrocyte flip-flop motions [4094] impart additional radial energy to platelets and nanorobots.

Even with the extra collisional energy, the maximum shear stress per collision is only <0.1 N/m² (Section 9.4.2.2). This is far less than: (1) the time-averaged shear stress of 1.5-2.0 N/m² [4101, 4103] (range 0.5-5.6 N/m² [4094]) for blood circulation in normal vessels, (2) the threshold limit of 6-9 N/m² for shear stress-induced platelet aggregation [4102-4107], (3) the >14 N/m² shear stress required for large platelet aggregate (>10-micron diameter) formation [4109], and (4) up to 10-40 N/m² reached when small arteries and arterioles are partially occluded as by atherosclerosis or vascular spasm [4105-4108]. So thrombocytolysis by free-floating nanorobots in the bloodstream seems extremely unlikely.

Last updated on 30 April 2004