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

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

5.3.2.5 Block Exchange Model

The most difficult surface to construct is also the most volume-efficient and indefinitely extensible configuration -- a surface consisting entirely of replaceable blocks or prisms of fixed geometry. In this model, surface blocks connected by snap-together interfaces are disconnected, rotated, exchanged, moved, and reconnected by subsurface block-moving mechanisms which may include manipulator arms (Section 9.3.1), conveyor systems (Section 3.4.3), and the like. Cytoskeletal components (e.g., subsurface actin microfilaments; Section 8.5.3.11) are similarly lengthened or shortened by adding or subtracting monomeric units during movement and various intracellular transport processes. Blocks combining at least one pentagonal, hexagonal, and heptagonal face can be removed, rotated to expose a new face, then refastened in a new relationship to their neighbors to alter surface concavity or convexity at will. Design constraints include a requirement that each edge of the surface faces must be of the same length, and that blocks should have angles < 90° on all edges of the face that will form the surface, so that the face can be flush with adjacent faces [C. Phoenix, personal communication, 1999]. Blocks containing different "letters" from a pattern "alphabet" on various faces (e.g., different Braille-like dots on each surface, like spots on dice cubes) can also be used to post tactile-readable information mechanically on the nanorobot surface, or individual rods in rod arrays can be selectively extended or retracted from the surface to create tactile-readable displays similar to refreshable Braille displays used by the deafblind (Section 7.4.6.1).

Block-built tubular members or protrusions of any other shape may be extruded, lengthened, rotated, or reabsorbed, as required. Internal block exchange allows periodic antifouling maintenance to be performed, eliminating biomatter contamination of the external nanorobot surface. Careful design should permit a waterproof boundary to be maintained throughout the reconfiguration process (Fig. 5.16). The extensibility and reactivity of efficient block exchange models has already been explored in Section 5.3.1.

Last updated on 18 February 2003