COMPUTATIONAL TASKS IN MEDICAL NANOROBOTICS - Bio-Inspired and Nanoscale Integrated Computing - page 393

nanoscale-component nanorobots remains largely at the concept feasibility stage.
Since 1998, the author has published seven theoretical nanorobot scaling studies
[4-10], several of which are briefly summarized below. Such studies are not
intended to produce an actual engineering design for a future nanomedical
product. Rather, the purpose is merely to examine a set of appropriate design
constraints, scaling issues, and reference designs to assess whether or not the basic
idea might be feasible, and to determine key limitations of such designs, including
the many issues related to biocompatibility of medical nanorobots as extensively
discussed elsewhere [2].
Complex medical nanorobots probably cannot be manufactured using the
conventional techniques of self-assembly. As noted in the final report [19] of the
recently completed congressionally-mandated review of the U.S. National Nano-
technology Initiative by the National Research Council (NRC) of the National
Academies and the National Materials Advisory Board (NMAB): ''For the
manufacture of more sophisticated materials and devices, including complex
objects produced in large quantities, it is unlikely that simple self-assembly
processes will yield the desired results. The reason is that the probability of an
error occurring at some point in the process will increase with the complexity of
the system and the number of parts that must interoperate.''
The opposite of self-assembly processes is positionally controlled processes, in
which the positions and trajectories of all components of intermediate and final
product objects are controlled at every moment during fabrication and assembly.
Positional processes should allow more complex products to be built with high
quality and should enable rapid prototyping during product development.
Positional assembly is the norm in conventional macroscale manufacturing
(e.g., cars, appliances, houses) but has not yet been seriously investigated experi-
mentally for nanoscale manufacturing. Of course, we already know that positional
fabrication will work in the nanoscale realm. This is demonstrated in the
biological world by ribosomes, which positionally assemble proteins in living cells
by following a sequence of digitally encoded instructions (even though ribosomes
themselves are self-assembled). Lacking this positional fabrication of proteins
controlled by DNA-based software, large, complex, digitally specified organisms
would probably not be possible and biology as we know it would cease to exist.
The most important inorganic materials for positional assembly may be the
rigid covalent or ''diamondoid'' solids, since these could potentially be used to
build the most reliable and complex nanoscale machinery. Preliminary theoretical
studies have suggested great promise for these materials in molecular manufactur-
ing. The NMAB/NRC Review Committee recommended [19] that experimental
work aimed at establishing the technical feasibility (or lack thereof) of positional
molecular manufacturing should be pursued and supported: ''Experimentation
leading to demonstrations supplying ground truth for abstract models is appro-
priate to better characterize the potential for use of bottom-up or molecular
manufacturing systems that utilize processes more complex than self-assembly.''
Making complex nanorobotic systems requires manufacturing techniques that can
build a molecular structure by positional assembly [3]. This will involve picking