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

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

9.4.3 Cytoambulation

Many applications of medical nanorobots will require the ability to "walk" across biomaterial-embedded cellular tissues, packed-cell blocks, or vascular surfaces, a process called cytoambulation. Cytoambulation may involve treading the surfaces of blood or lymph vessel walls which are lined with endothelial cells; negotiating flexible surfaces such as the walls of the urinary or gall bladders; traversing interior synovial or bursal surfaces such as the articular cartilage inside skeletal joints; and walking the walls of various excretory ducts, bulbs, tubes, and glands. Cytoambulating nanorobots may be required to cross various classes of tissue and cellular membranes. Tissue membranes are typically composed of epithelial and connective tissues and include:

a. serous membranes lining the cavities of the body and surrounding the various organs (e.g., the pericardium, pleura, peritoneum, and meninges);

b. mucous membranes lining the alimentary, respiratory, and genitourinary tracts; and

c. fibrous membranes composed entirely of connective tissues (e.g., perichondrium, periosteum, and synovial membranes).

Traversing such tissue membranes will often involve crossing the individual plasma membranes of tissue-embedded cells of various classes. Nanorobots also may cytoambulate across the surfaces of motile or free-floating cells, including individual erythrocytes and red-cell rouleaux, leukocytes, fibroblasts, platelets, large protozoa, and even some bacteria.

A comprehensive survey of all possible cytoambulatory modes and requirements is beyond the scope of this book. This Section is restricted to a discussion of basic cell-surface walking, including the single footpad contact event (Section 9.4.3.1), cell plasma membrane elasticity (Section 9.4.3.2), anchoring and dislodgement forces (Section 9.4.3.3), the physical limits of contact event cycling (Section 9.4.3.4), and examples of a few specific physical nanomechanisms for cytoambulation (Sections 9.4.3.5-9.4.3.8). The reader is encouraged to review Section 8.5.3 on cell structure before proceeding further.

Last updated on 21 February 2003