Nanomedicine, Volume IIA: Biocompatibility
© 2003 Robert A. Freitas Jr. All Rights Reserved.
Robert A. Freitas Jr., Nanomedicine, Volume IIA: Biocompatibility, Landes Bioscience, Georgetown, TX, 2003
126.96.36.199.3 Nanorobotic Concussive Vasculopathy
If a patient experiences significant external crushing or concussive forces, resident medical nanorobots that are present in small numbers can simply slide out of the way, as described previously in connection with the risks of dental grinding (Section 9.5.1). In the case of macroscale intravascular nanoaggregates (as opposed to individual physically isolated nanorobots), however, there are several additional risks.
First, sudden external tissue compressions can significantly alter cellular function, especially in the brain . For example, tests of percussive energy transfer to cerebral endothelium found that endothelial cells subjected to 200-500 Hz pressure waves at DeltaP = 1.2-10 atm led human cerebral microvascular endothelium (HCME) cells to immediately lose their normal capacity to suppress adherence of activated platelets, with DeltaP < 6.5 atm defined as the sublethal range . Sublethal percussion trauma also causes HCME to produce inflammatory cytokines (TNF-alpha and IL-1beta)  and alters the response of HCME to cytokine-induced ICAM-1 upregulation, although the normal response is restored by oxygen free radical scavengers .
Second, there is the possibility that a sudden mechanical external tissue compression could push macroscale nanorobotic aggregates through the soft tissues, causing deep tissue penetrations, perforations, or other serious mechanical trauma. Aggregates with a density exceeding that of biological tissues could, under high acceleration, produce effects on those tissues that would be not unlike pushing gelatin through a metal wire strainer. Possibly relevant but crude analogies in the medical literature include:
(1) ulnar artery erosion, thromboemboli, digital ischemia and skin necrosis from a glass foreign body in a patient’s hand ;
(2) tantalum coil stent damage that was induced or aggravated by intravascular ultrasound inside a coronary artery ;
(3) cardiac perforation by a subclavian catheter ;
(4) pulmonary artery catheter-induced right ventricular perforation during coronary artery bypass surgery ;
(5) an ICD patch that migrated and perforated the right ventricular cavity ;
(6) a stent that migrated to an oblique position across the aorta, producing a 7-cm pseudoaneurysm after 3 years ;
(7) catheter-induced pulmonary artery rupture (a well-recognized complication of invasive monitoring) that often leads to fatal hemorrhage [3938-3940];
(8) femoral artery catheterization trauma producing hematoma, pseudoaneurysms and arteriovenous fistulas of the femoral vessels ;
(9) iatrogenic subclavian artery injury due to central venous catheterization ;
(10) repeated and prolonged vein catheterization that led to subsequent stenosis (presumably due to luminal vascular mechanical damage) ;
(11) high-pressure injection injury that induced inflammation and foreign body granulomatous reaction, progressing to necrosis ;
(12) mechanical tearing of arteries due to overstretching ; and
(13) (possibly) spontaneous coronary artery dissection (mechanical arterial wall failure) .
Third, a sudden external tissue compression could force nanorobotic aggregates into physical contact with neighboring nanoaggregates, possibly causing major structural damage or fragmentation of the devices. This risk increases as the nanodevices become more densely packed, especially along the crushing axis. Nanoorgans (as well as looser nanorobotic aggregates) can be crushed if sufficient force or mechanical shock is applied, particularly if these aggregates are adjacent to bone or other relatively incompressible materials. Again, a few possibly relevant analogies from the medical literature include:
(1) external compression of emplaced stents that produced premature stenosis ;
(2) a transabdominal Teflon stent that broke intraperitoneally during tuboplasty procedure ;
(3) a strongly-beating heart that sheared off a pericardial drainage catheter ;
(4) a Hickman catheter that ruptured and embolized during normal use ;
(5) an indwelling catheter that fractured and a distal remnant embolized to the right ventricular outflow tract and main pulmonary artery, nearly precipitating cardiopulmonary collapse ;
(6) a catheter embolism that was produced when a catheterized patient engaged in power training exercises, externally crushing the catheter, although no symptoms or complications accompanied this event ;
(7) spontaneous fracture of indwelling venous catheter, leading to vascular leakage ; and
(8) other instances of catheter fracture and embolism [3954-3957], including one case that led to cardiac arrest .
Last updated on 30 April 2004