© 1999 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999

9.4.7.3 Cytocarriage Initiation

There are ~7000 leukocytes/mm³ in adult human blood (Appendix B) with a mean separation of ~50 microns, providing numerous and readily-available cytovehicles. A white cell that is cytoambulating at ~10 microns/sec moves only ~0.02 micron during the ~2 millisec required to establish identity (Section 8.5.2.2), and another ~0.1 micron during the ~10 millisec required for the piloting nanorobot to penetrate the plasma membrane (Section 9.4.5). Nevertheless, it may be desirable to temporarily halt the progression of the cytovehicle during the period in which nanorobot control is being established. This is readily accomplished by biochemical means. For example, when leukocytes are placed in an isotonic solution containing EDTA, active spontaneous movement stops and the cells respond passively to external loads.³⁶² Excess zinc immobilizes macrophages.³⁵⁹ Integrins respond to intracellular messages, altering both selectivity and binding strength: the a₂b₁ integrin can be inactive, a receptor for collagen, or a receptor for both collagen and laminin, depending on the type of cell that produces it and the signals received from inside the cell.¹⁵¹¹

Once inside a 10-micron diameter leukocyte, a nanorobot traveling at ~1 micron/sec may require ~5 sec to migrate to an appropriate location near the center of the cell and establish control. Leukocyte towing harnesses may be quite simple in design but must be nondestructive. A required towing force of 0.01 nN (Section 9.4.7.1) requires only ~5 noncovalent bonds (breaking strength ~2 pN/bond; Section 9.4.4.2) to the glycocalyx or plasma membrane; a single 100 nm² footpad (Section 9.4.3.3) can provide up to 0.3 nN of harness anchoring force.

Last updated on 21 February 2003