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
9.3.4 Manipulator Arrays
Arrays of micron or submicron-scale manipulator elements can be used to create 1-, 2-, or 3-dimensional programmable motion fields. In the simple 1-dimensional case, a single row of manipulators alternately grasp, transfer, and release a load, passing the payload down the line like a bucket brigade. In the 2-dimensional case, surfaces may be coated with closely-packed manipulators, allowing rapid and continuous transfers of multiple payload streams along multiple surface vectors simultaneously. In biology, ciliated epithelium is found in respiratory, excretory, digestive, circulatory, genital, and nervous systems of various animal groups, to drive fluid flow.1617,1618 Examples in human physiology include the ciliated air passages of the bronchi (Section 8.2.2) and the villiated surfaces of the small intestine (Section 8.2.3). In these natural systems, payload transport speeds are typically 10-100 microns/sec. For instance, experiments with ciliated bullfrog gullet tissue show maximum transport efficiency when moving a load of ~5 grams/cm2 at a speed of 27 microns/sec.526 Ciliary arrays used by protozoa for locomotion also display time-synchronized wave patterns3558 (Section 188.8.131.52.1), which may be analogous to the operation of submicron motion fields.
There are many possible applications of manipulator arrays in nanomedicine. Ciliary arrays inside hollow nanofactory workspaces can regulate throughput of physical materials for manufacturing (Chapter 19). Arrays can establish specified flows of environment fluids such as blood plasma across sensors, or may be used in device locomotion (both crawling and swimming; Section 9.4) or in self-cleaning activities. Medical nanosystems may incorporate complex three-dimensional manipulator arrays to control the transport of biocomponents in cell mills and organ mills (Chapter 21), to move chyme across an artificial stomach lining (Chapter 26), or to move fluids through artificial organs designed for chemical processing or filtration such as an artificial liver or kidney (Chapter 26). Ciliary transport systems may also support unique and highly sophisticated artificial whole-body nutrient transport systems such as the vasculoid class devices described in Chapter 30. These nanomechanical arrays can be operated at transport speeds (1-100 cm/sec), flexure frequencies (up to 1 MHz), and power levels (0.1-100 pW per array element) characteristic of individual nanoscale manipulators (Section 9.3.1).
In 1998, the prototyping and testing of ciliary arrays in MEMS work was an active research area. Ataka et al1274 fabricated and operated a 1 cm2 array of 512 cantilever-type bimorph manipulators (each one 500 microns long, 100 microns wide, and 6 microns thick) and operated it at 10 Hz in a coordinated fashion to transport a 2.4 mg piece of silicon wafer at 27-500 micron/sec using ~100 micron strokes and a 4 milliwatt input power to each actuator. Bohringer et al1639 fabricated a prototype array of 1024 cilia called the "cilia chip" that moves silicon chips at speeds up to 200 microns/sec with a placement accuracy of ~3 microns and a lifting capacity of 250 N/m2. Individual ciliary pixel control allows movement of multiple components on different trajectories, enabling the performance of various assembly tasks. A larger manipulator chip (M-chip) consisting of ~10,000 microactuator "resonators" (5-micron tall cilia) has also been fabricated on a few cm2 of silicon substrate and tested at ~5 KHz.1645 A part dropped onto the array is propelled forward at a constant speed of ~800 microns/sec.1646 Bohringer et al1643,1644 also created a theory of programmable force fields to model the actions of a ciliary array; simulations have uncovered numerous important operational design issues.1646 Analogously in experimental biology, an array of kinesin motors fastened to a fixed surface transported microtubules hand-over-hand when ATP was added.2425,2426
Peter Will et al1640 developed a software toolkit to allow researchers to program Intelligent Motion Surfaces1641,1642 to perform a variety of simple functions including centering parts, spiraling a part to center in a convergent field array, spiraling a part away from the center in a divergent field array, rotating a part about the center using four triangular fields, orienting a part in a programmable field array, and sorting two parts using a hole as a trap for a part being translated past it. Properly arrayed, such surfaces can form an assembly pipeline in which parts may enter at one end and be successively sorted, spaced (so parts flow through at a constant rate), centered, aligned and, ultimately, inserted into other parts.
Last updated on 21 February 2003