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

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

15.5.3.4 Nanorobotic Destructive Mechanical Vasculopathies

The physical configurations or activities of medical nanorobots and their aggregates could in some circumstances be destructive to vascular tissue [3897]. Owens and Clowes [3898] point out that the severity of arterial injury is important in determining the ultimate pathophysiologic response. They describe a classification system [3899] based on the immediate histologic effect of the injury:

Type I injuries involve no significant loss of the vessel’s basic cellular architecture, although there may be a slight change in endothelial architecture and associated cellular adhesion. Examples include the fatty streak (an early atherosclerotic lesion), hemodynamic factors and flow disturbances which produce, at most, only a modification of the established cellular architecture.

Type II injuries involve loss of the endothelial layer, perhaps inducing platelets to adhere and begin forming a thrombus at the area of loss, but the internal elastic lamina remains intact and there is little or no damage to the media. Examples include injuries incurred during simple arterial catheterization, endovascular procedures, vein graft preparation, or gentle filament-induced endothelial denudation of the carotid artery in a rat model [3900].

Type III injuries involve transmural damage in which the endothelium is removed, the internal elastic lamina is often disrupted, and a significant portion of the medial cells are killed [3900, 3901]. In these situations, platelets deposit and a thrombus forms at the site of endothelial loss. An inflammatory response (vasculitis) including intimal hyperplasia [3898] is initiated within the vessel wall. Examples include spontaneous vascular dissection and various forms of surgical repair or reconstruction such as balloon angioplasty, endarterectomy, and atherectomy.

Nanorobot device and mission designs should always seek to avoid causing Type II and Type III injuries, although in some special circumstances the potential even for Type III injuries may be inescapable. Destructive vasculopathies which might be caused by medical nanorobots may be classified as ulcerative (Section 15.5.3.4.1), lacerative (Section 15.5.3.4.2), or concussive (Section 15.5.3.4.3).

Last updated on 30 April 2004