The shrinking scale of engineering is today approaching the proportions of living cells. And scientists have come to realize that the cell faces many, if not most, of the same challenges that we do - to make materials, to harness, convert and transmit energy, to store and process information and to generate motion. But the solutions that cells find are often quite different to those that we use in the macroscopic world.
In particular, the "machinery" of the cell - mostly protein molecules such as enzymes - constitutes a range of "soft machines" with floppy parts, very different from our hard gears, levers and engines. The fuels that cells use are typically energy-rich molecules that drive changes in molecular shape. And yet we can still recognize among these biomolecular machines some of the devices and principles from the world of engineering, such as rotary motors, propellers, electrical circuits and digital information storage, such as that in computers.
Moreover, life's machinery has to work under mild and benign conditions: no high temperatures, no high vacuums, no organic solvents. Yet it is capable of making some astonishing things: super-strong fabrics, such as silk; and tough and resilient hard materials, such as shell, bone and wood. Leaves are essentially cheap and reasonably efficient solar cells. Nature's catalysts - enzymes - can carry out chemical reactions of a delicacy that far exceeds that of synthetic industrial catalysts.
There are plenty of good reasons, then, to conclude that we have a lot to learn from the natural nano- and molecular technologies of the cell. In my article, I look at how biology does things and how chemists and technologists are seeking to mimic them in processes ranging from catalysis to mechanical motion, energy conversion, information processing and materials synthesis.
In catalysis, for example, chemists have long attempted to make "artificial enzymes" that emulate the way that real enzymes have tailor-made cavities for binding and transforming specific molecules. They have had to understand how to use weak bonds between molecules, which can lock them together but also allow them to part again.
From the photosynthetic apparatus that plants and bacteria use to harvest the energy of sunlight, molecular engineers have learned tricks, such as how to capture light over a wide area and channel it to a single location where it is converted into stored chemical energy. They are making artificial molecular motors that, like the so-called motor proteins in muscle, convert the making and breaking of chemical bonds and the bending and straightening of molecules into movement in a single direction.
I think that this is one area where researchers might ultimately prefer not to try to mimic biomolecular machines with "scratchbuilt" artificial versions, but instead to explore a hybridization of the two - adapting nature's existing machinery for technological ends.
But we should beware of always imagining that nature knows best. The cell does not necessarily share the same objectives as the engineer. For genetic information processing, accuracy is more important than speed. Cells have a limited range of materials to work with, and there is no reason to believe that nature always does things in the most efficient way. Nature is encumbered with the accidents of evolution, such as the back-to-front ways in which our retinas are wired up, giving us a blind spot. So the molecular engineer needs to adopt a selective attitude, picking and choosing what is potentially useful from nature's bag of tricks.