Nanomedicine, Volume I: Basic Capabilities
© 1999 Robert A. Freitas Jr. All Rights Reserved.
Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999
Numerous simple actuators have been developed for microelectromechanical systems or MEMS.1232,1253-1255,1267-1269 A few of these designs might possibly be useful in early nanomedical systems. All major components of an articulated micromanipulator having multiple degrees of freedom, workspaces on the order of 1 mm3, positional resolution up to ~10 nm, operating frequencies up to 10 KHz, and slewing speeds up to 4 mm/sec have been demonstrated experimentally; complete systems have even been proposed.346,1253,1254
Actuation and manipulation may be very broadly defined. For example, self-assembling and self-disassembling ~300 micron gold foil cubes have been fabricated and cycled repeatedly at ~1 Hz;1251 "silicon origami" has also been described.1382 Nonmechanical actuation has also been explored. In the Magnetic Stereotaxis System,1256 a helmet with a cubic array of six superconducting coils is used to apply a 0.2 N force to a 3.2-mm wide, 4.7-mm long permanently magnetized cylindrical pellet that is embedded in brain material, causing stepped movement of the pellet through the brain material to a specified location with ~1 mm placement accuracy without any direct physical contact.
However, in the usual definition of a manipulator, an ergomechanical transducer (e.g., motors; Chapter 6) converts chemical, electrical, mechanical, acoustical, or some other form of energy into the mechanical energy of a manipulatory device which then exerts useful forces on objects or materials in the environment. In most cases a force-transmitting physical structure is required which may include both heavy load-bearing elements such as girders, struts, pneumatic tubes or rotary joints, and fine control elements such as stress cables, valves or switches (Section 9.3.1). An end-effector (e.g., gripper, cutter or molecular jig) is usually employed to focus and redirect the application of force at the distal end of the manipulation device (Section 9.3.2), or to perform specialized tasks. Sensors permit feedback control of manipulator motions as well as verification that the assigned manipulatory task has been properly executed (Section 9.3.3). Large numbers of manipulators can form ciliary arrays, allowing convenient mass transport of materials (Section 9.3.4); other classes of manipulators may be useful in bulk disassembly of materials (Section 9.3.5).
The diverse concepts outlined in this Section demonstrate the enormous range of possible nanomanipulator designs. These concepts are not intended as specific engineering proposals but rather as illustrations of certain useful classes of manipulators representing alternative design pathways that could provide the desired capability. No effort has been made to produce optimal systems that minimize energy dissipation, maximize speed, minimize parts count, or simplify manufacture. Biocompatibility issues3234 will be addressed in Chapter 15.
Last updated on 20 February 2003