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

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

15.5.5.1.2 Erythrocyte Surface Fluctuations and Elasticity

Low frequency submicron fluctuations of the cell membrane, known as cell membrane fluctuations or CMF [4075], have been shown to be characteristic for different cell types [4076-4082] and to occur in the 0.3-30 Hz frequency range [4075]. For erythrocytes [4085], these fluctuations typically exhibit displacement amplitudes of 160 nm for deoxygenated red cells and 290-400 nm for oxygenated red cells [4082-4084] (236 nm in diabetic patients [4084]) as observed over 0.25-micron² membrane surface patches [4082, 4086]. These fluctuations apparently provide a dynamic control of bending deformability of the membrane-skeleton complex [4086] and assist red cells in performing their function of oxygen delivery [4087] by improving their efficiency in passing through capillaries narrower than the cellular diameter [4084].

Nanorobots might incidentally alter red cell membrane mechanical properties by their presence or activities at the cell surface, as in cytocarriage (Section 9.4.7), or might purposely alter those properties by locally extracting, releasing or injecting specific chemical species. For example, nanorobots could elevate the amplitude of red cell bending fluctuations by the local release of human atrial natriuretic peptide [4087]. Adrenaline (epinephrine) and isoprenaline [4086] increase maximum fluctuation amplitude by +45%, although adrenaline stimulates only the low-frequency component at 0.3-3 Hz, reaching maximum effect after 20-30 minutes and fully dissipating after 60 minutes [4086]. Increasing extracellular solvent macroviscosity by adding macromolecules such as dextrans, polyethylene glycol, or carboxymethylcellulose diminishes cell membrane fluctuations [4075]. Wheat germ agglutinin diminishes fluctuations tenfold, and fluctuations are totally suppressed by a 0.01% solution of glutaraldehyde, which also decreases RBC adhesivity to glass by twofold [4088]. Increasing the cholesterol content of the RBC phospholipid bilayer causes large reductions in internal fluidity of membrane and a change in its preferred direction of bending without changing the gross mechanical rigidity. On the other hand, an increase in intracellular (cytosolic) concentration of polyamines (especially spermine) adds to the cohesion of the membrane cytoskeleton and increases the mechanical rigidity of the membrane [4089]. Amphipathic drugs also modify the mechanical properties of the cell plasma membrane [4090]. The tension required to smooth out the thermal undulations or Brownian motions of the outer membrane of artificial phospholipid vesicles 10-20 microns in diameter (~typical cell size) has been determined experimentally as 0.01-0.1 x 10^-3 N/m [4091] (Section 9.4.3.2.1).

Last updated on 30 April 2004