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
18.104.22.168 Surface Electrical Thrombogenicity
An early hypothesis held that surface charge was the primary physicochemical feature of blood-contact material surfaces in determining thromboresistance. Cell coats with negatively charged sialic acid termini on both the glycoproteins and gangliosides, and macromolecules in all known flowing biological fluids, carry a slightly negative charge, thus should be repelled by bloodborne nanodevice surfaces bearing a net negative charge, or negative electrochemical potential, reducing the risk of thrombosis.
However, it is now known that immersion of adherent particles in liquid virtually eliminates electrostatic image forces (Section 9.2.2), greatly reduces electrostatic contact potential forces (Section 9.2.2), and can reduce van der Waals forces (Sections 9.2.1 and 9.2.3) by at least a factor of six at organic-water interfaces . The early hypothesis is further weakened when the immersion fluid is not neutral or insulating, but rather consists of the high ionic strength, salty, highly conductive (“dead short”) biofluids actually found in vivo. Careful experiments designed to measure surface potential and surface charge find that the choice of surface electrical properties of materials intended to be brought into contact with blood or other salty aqueous fluids has little influence on biological adhesion . Indeed, there is growing evidence that any state of surface electrification is associated with greater rather than lesser accumulations of biological debris on such surfaces. While there is an obvious accentuation of adhesive induction by net positive surfaces , negatively-charged surfaces may activate contact factors initiating the intrinsic coagulation pathway (Section 15.2.5). Hence a net neutral nanorobot surface may be preferable in order to minimize surface electrical thrombogenicity.
G.M. Fahy notes that an electric charge of oscillating polarity might discourage biological accumulations on nanorobot surfaces. A negative charge would repel most proteins; if this led to positive items clustering on the surface, an oscillating surface charge might get rid of those items before they become a problem.
Detailed calculations of nanorobot electrical characteristics  should be a part of every complete design analysis.
Last updated on 30 April 2004