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

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

10.4.2.5.3 Liquefy, Digest and Discharge (LDD)

After identification and docking, the nanorobot extends a retractible, self-cleaning, flexible diamondoid filament rotating "eggbeater" tool (Section 9.3.2 (7)) into the bacterial interior and sweeps the tool around inside the cell. A mechanical sensor that serves as a registration bumper detects the presence of cell wall, allowing the rapidly rotating mechanism to avoid damaging the bacterial outer perimeter. A beater with four tines of length 500 nm, tine width 50 nm, and forward cutting edge 10 nm, bowed to a 200 nm diameter and rotating at ~100 Hz has an equatorial velocity of ~60 micron/sec and can cut material having tearing strength ~10⁸ N/m² (~maximum for soft biological materials; Table 9.3) while consuming ~30 pW (Eqn. 9.75) in continuous operation in highly viscous E. coli cytoplasm (absolute viscosity h ~ 1000 kg/m-sec; Table 9.4). As liquefaction proceeds, the protoplasm may become less viscous, allowing rotation rates to be increased and input power to be reduced.

After 1-10 sec, the appropriately liquefied material is pumped from the exemplar 4 micron³ bacterium interior into the 1 micron³ enzymatic reaction chamber in ~0.01 micron³ aliquots and is processed as described earlier in ~100 millisec cycles consuming ~30 pW (Section 10.4.2.4.2). However, the LDD chamber also includes lipases to digest lipids, amylases and related enzymes to digest carbohydrates, and molecular sorting rotors able to transport and discharge fatty acids, sugars, and inorganic ions. A few specialized additional enzymes may be required to fully digest unusual or rare metabolites that might already be present or might appear during processing. Processing time for ~400 cycles is ~40 sec. Finally, the bacterial coat, plasma membrane, and flagella (another ~0.3 micron³ plus ~0.001 micron³/flagellum) are sectioned, drawn into the reaction chamber, processed in like fashion, and then discharged in an additional 30 chamber cycles or ~3 sec. Care should be taken not to fragment the coat until nearly all of the cell contents are evacuated, thus minimizing contamination of the extracellular environment. A few additional sorting rotors and special processing may be required for endotoxins, native cellular enzymes, indigestible bacterium-resident poisons and heavy metals, and so forth. Operating simultaneously and in parallel, all 10¹¹ water molecules are discharged in ~50 sec by 2000 sorting rotors drawing 20 pW. Thus, total processing time is ~50 sec, consuming ~50 pW.

Table 10.6 also compares the composition of bacterial digestion products to natural bloodstream concentrations of those same products (Appendix B), and shows that the (extremely conservative) maximum "safe" bacterium material discharge rate is nucleotide-limited to ~10⁷ microbes/cm³, which is near the typical microbial number density in serious infections. Digested-bacterium material discharges should not significantly augment natural serum concentrations of most of these substances. (See also microbivores for more details.)

Processing 20-micron tissue cells may proceed by similar, but more cautious, means, and will require on the order of one nanorobot-day to digest and discharge each such cell. A cooperative group of ~100 LDD nanorobots occupying ~10% of a tissue cell surface can perform a complete disassembly and discharge in ~1000 sec, employing a group power draw of ~5000 pW for the duration.

Last updated on 24 February 2003