Complex Adaptive Matter
Professor Ralph Nuzzo
University of Illinois
Chemistry Department
505 South Mathews Avenue
Urbana, IL 61801
(217) 244-0809
From the vantage of a chemist, how might one
define a set of principles or properties that would serve to differentiate complex
adaptive systems from the better-established foci of current chemical research? The list
given below is not intended to be an exhaustive elaboration of possibilities. It is merely
a range of ideas that I find intriguing. It will be immediately evident that many of these
notions have very obvious analogies in living systems.
Directed Organization
The term self-organization (or self-assembly) has been much discussed. Typically one envisions a thermodynamically mediated evolution of structure, as directed by small energy differences. The area of Self-assembled Monolayers is now very well developed but much potential for progress remains. Emerging research areas include 3D hierarchical organization, synthesis via templates (including crystal engineering via the mediation of nucleation), and ìunconventionalî means of effecting micro- and nano-scale patterning (e.g. of cells, proteins, etc.). A very substantial need in the field is to develop a range of tools that are useful for patterning a much broader range of materials (or the assembly of structures) over a vast range of length scales. As an example, what methods would be useful for merging electronic systems (with devices patterned at sub-micron scales) to larger biological or microfluidic components (where the organization needed may range to many microns or more)? How might microelectronic systems be integrated in a truly three-dimensional way? An interesting notion to consider, especially in the context of fabricating functional systems (see below), is the research aimed at developing assembly processes which harvest and/or are driven by chemical energy. Is there a non-biological analogy of a directed assembly process that can be driven by a non-thermal energy source (it seems to me that some examples of electrochemically driven nano-fabrication may come close to successfully realizing this concept)?
Recognition/Actuation/Signaling
The construction of functional molecular systems makes complex demands on the enabling chemistries. Using sensors and diagnostic systems as examples, it is seen that several direct functions are needed. One desires that molecules be recognized with high specificity and at extreme levels of detection. This recognition (for example, by binding) must then be communicated, either as an electrical signal or other complex chemical response. Ideally, the signal arising in a selective but low-frequency recognition event must be greatly amplified. Inherently non-linear systems may provide needed mechanisms for achieving such responses. Catalysts, as suggested by the explicit example of enzyme-linked assays, can also be envisioned as a means of effecting chemical amplification. The key challenge in the chemistry, then, is to deduce useful ways for harvesting such properties as an enabling component of a functional structure.
Replication
There is currently no class of ìunnaturalî material that can mimic in a substantial way this essential aspect of a living system. Can macromolecules be made to template their own synthesis (macromolecules displaying no distributions of composition or molar mass)? Not all goals need be this extraordinary. Using an essential property of bone as another example, can we devise structural materials that actively adapt to the nature of the mechanical forces to which they are subjected?
Memory and Intelligence
Some rudimentary examples of this complex property are known in materials systems. Gels and Martensite alloys come to mind as notable examples of materials displaying a specific (here shape) memory effect. Such notable examples provide a rational and motivation to establish broad-based programs of research which develop/identify/exploit materials displaying this property. For example, can we design molecular systems that would demonstrate utility as a medium for encoding and reading information in digital form? More broadly, can we develop molecular systems which will usefully process this type of (or related) information?