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

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

15.5.3.1 Modulation of Endothelial Phenotype and Function

The luminal surfaces of all blood and lymph vessels consist of a thin monolayer (the endothelium) comprised of flat, polygonal squamous endothelial cells (EC) which is a part of the intima (endothelium plus basement membrane and elastic lamina), covering a much thicker layer (the media) which in turn is comprised of vascular smooth muscle cells (SMC). Both layers are subject (and respond) to tangential fluid shear stresses (Section 15.5.3.1.1) across the endothelial cell surface. These stresses are attributable to: (1) the bulk flow of blood [3782-3785], (2) normal hydrostatic pressure stress acting radially on the vessel wall due to the propagation of the pressure wave, and (3) cyclic stretch or strain (Section 15.5.3.1.2) due to blood vessel circumferential expansion in vivo [3785-3787]. As a result, these two vascular layers might also be sensitive to similar mechanical stresses that may be applied by stationary or cytoambulatory intravascular nanorobots. Increases in vessel wall rigidity could cause diastolic and systolic pressures to progressively diverge, with subsequent increased risk for a vascular event, such as a stroke.

M. Sprintz notes that another risk of nanorobots penetrating and residing in the vascular integument is a potential weakening of the vessel wall. This weakening could increase the probability of aneurysm formation or direct rupture of the vascular endothelium, a possibility that should be investigated further and minimized in mission design.

Last updated on 30 April 2004