Biomedical Engineering Reference
In-Depth Information
Early molecular electronics researchers focused on molecular implementations of com-
mon microelectronic devices, such as switches. Critics from the biocomputing camp cited
the fragility of biomaterials and argued that the molecular equivalent of diodes, flip-flops,
etc., could never compete with their microelectronic predecessors. Instead, they advocated
the development of devices for nontraditional computing. While the point was well taken,
we held a different opinion (34). We believe that valuable lessons could be learned while
investigators are “imitating” microelectronic devices. Imitating microelectronics was tan-
tamount to what a beginner needs to master while ascending the learning curve.
Sometimes as art imitates life and life imitates art, humans get inspired by engineering
products. One of the most successful quantitative theories in biology—Hodgkin and
Huxley's theory of nerve conduction—was based on imitation of marine cables.
A recent report by Koçer et al. (35) presented an interesting intermediate case. These
investigators modified a mechanosensitive channel protein from
Escherichia coli
by attach-
ment of synthetic compounds that undergo light-induced charge separation and
reversibly open and close a 3-nm pore. This project was the outcome of convergence of
reverse-engineering Nature, synthetic chemistry (and perhaps chemical engineering), and
photochemistry. It is hard to decide whether it was science inspiring engineering or engi-
neering inspiring science. The implication to liposome-based drug delivery via external
photochemical control is obvious. Speaking about controlled drug delivery, Chen studied
the feasibility of using bacteriorhodopsin to mediate light-induced drug release from a
polymeric device (36). He found that the amount of released protons was insufficient to
cause a gel-sol transition of the polymer. Here, reverse engineering offers a hint for future
improvements. In visual transduction, it takes three consecutive biochemical reactions and
a host of molecular mechanism to generate the well-known 100-fold amplification of
energy (37). The lesson on bird's wings offers essentially a similar suggestion.
Bacteriorhodopsin vesicles need not supply all of the needed protons. Rather, the surface
potential associated with bacteriorhodopsin activation (38) can be used to trigger the
release of a depot of protons, much like the action of light-controlled nanovalve of Koçer
et al., which can trigger the release of drug encapsulated in liposomes.
Segregation of scientists into camps was probably fueled by human instinct of territorial
claims and reinforced by human penchant for ideology. However, such social grouping
sometimes fostered dogmatism, which could be deterrent to creativity. If we exercise the
practice of reverse-engineering Nature at this point, we are likely to find that Nature actu-
ally adhered to no ideology. Take phosphorylation of proteins as an example, Nature
recruited whatever mechanisms it could put its hands on, and enlisted a number of dif-
ferent molecular mechanisms in combination to activate a protein; the mechanisms
include electrostatic interactions, steric hindrance, and allosteric effect (39). Nature was
extremely explorative, and certainly recognized no disciplinary boundaries. Perhaps it
was no coincidence that the earlier models of human creativity followed the analogy of
evolution closely (40).
In this context, we extend the notion of reverse-engineering biology to address the ques-
tion of how to make a sensor exhibit the kind of intelligence unique to higher animals.
Artificial intelligence essentially stems from an attempt to imitate the intelligence exhib-
ited by human beings. The enigma of human creativity has defied repeated attempts by
psychologists, psychiatrists, and cognitive scientists over the past century. A century's
worth of research has generated a wealth of detailed information, from the behavioral
level all the way down to the molecular level. Yet, it is now commonly known that detailed
local information does not always lead to the elucidation and understanding of the whole
in a system as complex as the human brain. Here, artificial intelligence research could
actually inspire our understanding of human creativity. It was reverse engineering in the
opposite direction. For example, it is well known in artificial intelligence and in operations
