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

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

15.5.3.6 Non-Occluding Indwelling Vascular Obstructions

In some applications it may be deemed useful to extend foreign objects into the vascular lumen, as for example power tethers (Section 6.4.3.6) and energy teats from dedicated energy organs (Section 6.4.4), communications fiber networks (Section 7.3.3), temporary or permanent nanocannula (Chapter 19), stents (Section 15.5.3.2), and luminal surface coatings or nanoaggregates including vasculoid-class systems ([4609]; Chapter 30). Nanoscale cables, wires, and other fiberlike protrusions into the bloodstream could induce red cell hemolysis (Section 15.5.5.1.1). By analogy, forcing living cells through a finely-holed rigid strainer destroys them, and red cells can be torn in half by fibrin strands as the cells traverse platelet-fibrin plugs in arterioles and capillaries [4023, 4064]. Hemolytic anemia may result from mechanical shearing damage to erythrocytes by microangiopathic fibrin strands in peripheral microvessels [4060-4064]. Indwelling materials that detach or migrate can occlude vital vascular structures, causing significant morbidity and even death (Section 15.4.1).

It is possible that mechanical stress from improperly-engineered vascular-indwelling foreign objects could produce a nucleation site for inflammation, infection, or calcification, and could eventually result in the rupture [5212-5214] or growth [5215-5220] of arteriosclerotic plaque. However, vascular platelet/leukocyte adhesion and smooth muscle proliferation is readily inhibited [5221]. Also, the chronic presence of long strandlike Dirofilaria heartworms* lying lengthwise along the luminal walls of canine pulmonary arteries without immediate bloodflow-related pathological consequences (though there is considerable vascular damage [5222-5226]) suggests that it should be possible to design vascular indwelling nanosystems having near-permanent biocompatibility and mechanical stability, possibly involving actual [5226] or biosimulated re-endothelialization. Interestingly, endovascular coil occlusion of vascular aneurysms (in which a platinum wire coil is permanently emplaced inside an aneurysm sac) seems well tolerated clinically [5685-5687].

* In vivo canine microfilariae are typically ~300 microns long and ~6 microns wide [3959], but larvae have been grown to 100 microns x 25 microns in vitro [3960] and in vivo sloth Dirofilaria parasites have been reported as large as 214 mm in length and 360 microns in width [3961].

Last updated on 30 April 2004