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
10.4.2.5.1 Desiccate, Sequester and Transport (DST)
After the target bacterium has been identified by chemosensory pads binding, the nanorobot secures itself to the cell exterior. The first objective is to desiccate the bacterium. An efficiently designed molecular sorting rotor for water may require ~30 nm2/receptor of exposed surface with 600 nm3/rotor which includes 50% volume overhead for housings and other mechanical elements, and transports ~106 molecules/sec at a cost of ~0.01 pW/rotor (Section 3.4.2). Of total bacterial water, ~2/3 is freely diffusible as bulk water and ~1/3 is loosely bound as hydration water (Section 220.127.116.11). Thus to accomplish the desiccation, the nanorobot inserts a 0.3-micron wide, 2-micron long cylindrical water extraction probe into the cell interior. Taking the experimentally measured3149 failure strength of the wet peptidoglycan wall as ~3 x 106 N/m2 (Table 9.3), a probe tip configured as a core sampler tool (Section 9.3.2) with an annular cutting edge of thickness Wedge = 1 nm (Section 18.104.22.168) can penetrate the bacterial wall by applying a force of ~3 nN perpendicular to the surface; a rotating serrated cutting edge requires even less force. In the alternative, a chemical or enzymatic cutting tool may be employed.3150-3152
The extraction probe is tiled with ~66,000 sorting rotors of volume ~0.04 micron3. Extraction probe volume is ~0.14 micron3, which leaves ~0.10 micron3 for probe structure, probe plumbing manifold, pipes and pumps, and probe control mechanisms. All bulk water is extracted from the bacterium in ~1 sec, shrinking the cell by half from ~4 micron3 to a volume of ~2 micron3. (Sorting rotors covering ~2 micron2 remove ~3 x 1010 molecules/sec-micron2, far outpacing possible backflows which may be crudely estimated from maximum macrophage water-ingestion rates (Section 10.4.2.1), suggesting at most ~107 molecules/sec-micron2 across a ~13 micron2 bacterial surface.) Engulf formations of metamorphic nanorobots (Section 5.3.4) could be especially useful in this application.
Its volume halved, the bacterium is packed into a nanorobot storage cannister of volume ~2 micron3 and is delivered to an appropriate dedicated biodisposal organ or other biodisposal facility (Section 10.4.2.4) -- one dead bacterium per nanorobot. (A rigid wet hollow peptidoglycan sphere of diameter ~2 microns and thickness ~20 nm can be compacted into a 2-micron wide storage cylinder by a 2 micron piston by applying an Euler buckling force (Eqn. 9.44) of ~1540 nN, or ~5 atm; a dry peptidoglycan sphere of this size would require ~10,000 atm to crush.) Serious infections of ~107 bacteria/cm3 (mean separation ~50 microns) thus require a minimum therapeutic dose of >~107 nanorobots/cm3. Bacterial clearance time for infected tissue at minimum dosage is dominated by entry and withdrawal times (Chapter 16) for single-cell-payload nanorobots, which may require several blood circulation times, but is certainly less than 1000 sec.3233 An alternative suggestion is that a desiccated bacterium could be "shrink-wrapped," possibly using a tightly wound surface webbing consisting of polymerized glucose (e.g., cellulose or "string"), then flagged for phagocytic removal (Section 10.4.1.2) and released, with the objective of improving the microbe-processing speed of nanorobots. Unfortunately this incautious approach allows bacterial DNA to remain intact. If the wrapping is easily digestible, the prokaryote might escape confinement prior to disposal, and reinflate; if not easily digestible, blockade of the macrophage system could result.
Note that cellular RNA synthesis and protein synthesis stop below 70%-80% hydration. All metabolism of small molecules, lipid synthesis, amino acid synthesis, and CO2 fixation into organic molecules ceases below ~35% hydration.941
Last updated on 24 February 2003