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

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

5.4.2 Transbumper Communication

Besides occluding and anchor junctions, mutually attached biological cells use gap junctions²⁹²² or "communicating junctions" to exchange inorganic ions and other small water-soluble molecules like sugar and ATP. Connexons are hexagonal transmembrane proteins with tiny pores; when connexons in the membranes of two cells are aligned, they form a continuous aqueous channel linking the two cell interiors that can open and close in a way similar to the acetylcholine receptor channel described in Section 3.3.3. When the calcium level of a cell rises -- often a signal that the cell is sick or compromised -- connexons close and quarantine the unhealthy neighbor.³¹² A force of 6-10 pN is required to physically pry apart each connexin-32 hepatic cell gap junction unit, each unit a combined pair of hexagonal cylinders ~7.5 nm in height and 7 nm in diameter with a 2-nm pore through the center.¹²²³ Another communicative adhesive mechanism is provided by bacterial sex pili,^1588,3549 filamentous surface adhesive organelles that are long thin hollow protein tubes (typically ~300 per cell) with sticky receptors on their ends that bind to recipient cell walls, allowing DNA to pass from cell to cell.²³²⁸ Integrins (Section 8.5.2.2) mediate cell binding to extracellular matrix and anchorage-dependence mechanical signals.⁷¹⁸

Similar mechanisms may be employed in metamorphic bumper walls to establish stable physical conduits among neighboring nanorobots in an array. Such conduits may transmit information, materials, nanoscale components, power (acoustic or hydraulic), or even structural forces (including tension, compression or torsion) to provide stability or movement of the entire nanotissue assemblage. Hinges⁵³⁴ and related mechanisms allow contact to be maintained as the metamorphic surface expands, contracts, twists or translates.

Last updated on 18 February 2003