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

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

9.3.5.2 Disposability Engineering

Medical nanodevices should incorporate appropriate disposal pathways as explicit design criteria. For instance, morcellator wear during bulk materials processing will accumulate as a complicated function of v_blade, T_sample/T_blade, and numerous other factors, until the blade fails. Proper morcellator design may include some ready means for blade replacement, recycling, or elimination, or else the entire subunit must be abandoned or discarded. Other internal nanorobotic structures such as diamondoid binding sites, sensor fittings, broken tool tips, or reconfigurable metamorphic drive elements also may require recycling if interior refuse storage volume is limited or if onboard fabrication materials are in short supply.

Additionally, disabled or malfunctioning whole nanodevices may require disposal. Drexler [personal communication, 1995] has suggested that nanodevices and their subassemblies could have frangible mechanical links incorporated into their structure to enable easy device disassembly for disposal. One can imagine a complex nanorobot comprised of strong and closely fitted subassemblies which are held in place by pins or tenons in the vacuum environment of the functional nanodevice interior. If the pins are soluble in water, or are readily unlocked by enzymatic agents, or are otherwise easily removable, then large strong devices may be rapidly dismantled into their constituent subassemblies with only modest effort, or automatically upon infiltration of the external environment. Of course, final disassembly or disposal of the subassemblies is still required to achieve complete biodegradability. Construction using special nonisotropic materials such as foamy diamond (containing patterned vacuum holes) or biodegradable fiber windings that are easily unraveled might also simplify this mode of disassembly (Chapter 11).

However, even setting aside biocompatibility issues, a major difficulty with the above-described "Chinese Puzzle Box" approach to disposability engineering is that no matter how clever the disposal design, there will always be some occasions when the "puzzle box" becomes jammed or sealed shut, or has been mechanically compromised, or is actively resisting normal disassembly procedures. Design for disposal thus must include provision of capabilities to allow the partial or complete dismantlement of disabled or uncooperative devices.

Finally, there is the problem of nonbiological waste disposal. Such wastes might include accidental releases into the in vivo environment (external to the nanorobot) of raw feedstock materials, specialized fuel elements, pressurized nanocontainers, or nanodevice components such as tool tips, sensors, integument plates, or hard-material work products in various stages of completion. All manner of nanorobot-related detritus might plausibly be found freely floating in the tissues or bloodstream, from the smallest diamondoid parts up to and including detached whole manipulator arms, major subassemblies following a major device breach, or debris resulting from the execution of a voluntary autodestruct protocol (Chapter 12). While reliable and clean operation is an essential design objective in nanomedical systems, it would be irresponsible to ignore the need for an explicit nonbiological materials waste scavenging and disposal capability (Chapter 16).

Last updated on 21 February 2003