Part 4 of a series on the history and prospects of advanced nanotechnology
concepts, prompted by the upcoming 50th anniversary of Feynman’s historic talk,
“There’s Plenty of Room at the Bottom”.
In this post, I’d like to outline the promise of fabrication technologies that are within reach of chemical and ribosome-class polymer synthesis (to make nanoscale components) in combination with the familiar mechanism of spontaneous, Brownian assembly (to put them together). These technologies can enable many applications, including productive nanosystems that are beyond ribosome-class machines, further along the path to advanced molecular manufacturing.
Where we are today
In the previous post in this sequence, on “Foldamers and Brownian Assembly”, I outlined current capabilities for designing and making molecular components that spontaneously assemble to form complex systems. Some of these components (polypeptide foldamers) have mechanical and functional properties that compare favorably with high-performance engineering polymers, and these components are compatible with others (polynucleotides) that enable facile design and fabrication methodologies that can produce new million-atom, 100-nm class structures in less than a day.
A major bottleneck today is the weakness of design software and the scarcity of integrative, cross-disciplinary work. Experimental demonstrations of foldamer design and applications show the potential for far-reaching engineering developments, but without well-targeted support for research and research-enabling software, progress will continue to lag far behind its potential. I know this both because it’s obvious from the scientific literature, and because I know several of the leading researchers in the fields I’ve mentioned, and we talk about these issues.
Toward improved components and design methods
These emerging capabilities have potential applications to a range of useful products, including ribosome-class machines that would broaden the range of accessible and economical materials, molecular components, and composite, multi-component products.
Since it is often useful to describe criteria and metrics in technology development, here is an outline of a challenging objective that I am persuaded can be achieved by creative, collaborative work:
With sufficient progress in design methodologies, existing kinds of polymers (or combinations of them) could achieve these objectives; I’m thinking here of polypeptides and polypeptoids, together with polynucleotides and their synthetic analogs.
New foldamer materials, however, could offer greater inherent rigidity and stronger intermolecular binding, with potential advantages that include low entropy of unfolding (which tends to correlate with greater predictability of folding), and greatly improved mechanical and environmental stability. Regarding greater inherent rigidity I’m thinking here of rigid-rod polymers and Chris Schafmeister’s bispeptide oligomers; regarding stronger intermolecular binding, I’m inspired by (among others) the effectiveness of extended hydrogen bond arrays [pdf] in forming strong non-covalent links [pdf], and the burgeoning field of systematic design of metal-organic frameworks [Chemical Society Reviews special issue]. All these are within the scope of current chemical synthesis methods, and are also potential target products for an early-generation of non-biological productive nanosystems.
The characteristics of advanced foldamers have the potential to facilitate design (especially if they are accompanied by fine-grained structural regularity), and adding new components to the existing toolkit is almost guaranteed to expand the scope of potential systems and system performance.
Progress will enable accelerated progress
When components become substantially easier to design, make, and assemble, and enable the engineering of more robust, highly functional products, technological progress in molecular systems engineering can be expected to accelerate.
- More effective design techniques will facilitate system architecting and more ambitious objectives.
- Quicker fabrication and assembly techniques will speed the design-build-test cycle that develops workable concepts into working systems.
- Greater product robustness and functionality will expand applications, motivating growth in research and research funding.
- Growth in research and research funding will yield both more applications and further advances in design, fabrication, and capabilities.
Thus, we can expect a virtuous circle of faster development, improved performance, broader applications, and investment in further improvement of the technology base.
For both scientific and practical reasons, there will be good reasons to pursue improvements in productive nanosystems, extending ribosome-like, 1D control of mechanosynthesis to a wider range of 1D polymers (and perhaps to row-by-row synthesis of 2D covalent-network structures). Productive nanosystems of this class have the potential to increase yields and drop costs for already-accessible synthetic structures, and to extend atomically precise control to structures that are beyond reach of unguided solution-phase chemistry.
Ribosomes are needlessly complex
Ribosomes are dauntingly complex, but mostly for irrelevant reasons. In ribosomes, the basic polymer-building mechanism has become encrusted with structural and functional features that stem from of billions of years of evolutionary tinkering, responsive to specifically biological needs. There is no need to imitate this complexity —or even the kinetic-proofreading tricks that compensate for the poor binding specificity inherent in 3-base codons.
Toward increasingly complex and capable systems
The potential advantages of implementing more complex systems are obvious in the case of hybrid digital systems (think of nanolithographic structures as providing circuit boards and sockets for increasingly complex self-assembled plug-ins), but there are also potential advantages in implementing more complex productive nanosystems.
The discussion above has considered existing fabrication methods (chemical synthesis and biological productive nanosystems), while noting the potential for ribosome-class polymer builders. Although the latter devices are deceptively dissimilar from advanced molecular manufacturing systems, this gap will shrink with increasing with complexity and performance — moving from 1D to 2D positional control of reaction locations, moving along the spectrum between self-assembly and mechanosynthesis, and expanding the range of molecular building blocks and products that can be made. Eventually, productive nanosystems can be organized in scalable arrays that feed hierarchical assembly systems. In a mature form, systems of this kind fit the criteria for high-throughput atomically precise manufacturing.
[Edited 28 Dec.]
- Part 1 — The promise that launched the field of nanotechnology
- Part 2 — Molecular Manufacturing: Where’s the progress?
- Part 3 — The Molecular Machine Path to Molecular Manufacturing (1)
- Part 5 — “There’s Plenty of Room at the Bottom” (29 December 1959)
Studies of advanced atomically precise fabrication:
- Roadmap for Atomically Precise Nanofabrication and Productive Nanosystems
- U.S. National Academies report on molecular manufacturing
- Nanosystems: Molecular Machinery, Manufacturing, and Computation,
and its precursor, my MIT dissertation:
“Molecular Machinery and Manufacturing with Applications to Computation” [pdf, 30 MB]