Plastic fantastic

Here’s the initial version of a leader I wrote for last week’s Nature.

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The transition from basic science to practical technology is rarely linear. The common view – that promising discoveries need only patience, hard work and money to shape them into commercial products – obtains only rarely. Often there are more factors at play: all kinds of technical, economic and social drivers must coincide for the time to be right. So dazzling forecasts fail and fade, but might then re-emerge when the climate is more clement.

That seems to be happening for organic electronics: the use of polymers and other organic molecules as the active materials in information processing. That traditionally insulating plastics could be made to conduct electricity was discovered serendipitously in the late 1960s by Hideki Shirakawa in Tokyo, in the form of silvery films of polyacetylene. Chemists Alan Heeger and Alan MacDiarmid collaborated with Shirakawa in 1976 to boost the conductivity of this material by doping with iodine, and went on to make a ‘polymer battery’. Other conducting polymers, especially polyaniline, were mooted for all manner of uses, such as antistatic coatings and loudspeaker membranes.

This early work was greeted enthusiastically by some industrial companies, but soon seemed to be leading nowhere fast – the polymers were too unstable and difficult to process, and their properties hard to control and reproduce reliably. That changed in the late 1980s when Richard Friend and coworkers in Cambridge found that poly(para-phenylene vinylene) not only would conduct without doping but could be electrically stimulated to emit light, enabling the fabrication of polymer light-emitting diodes. The attraction was partly that a polymer’s properties, such as emission colour and solubility, can be fine-tuned by altering its chemistry. Using such substances for making lightweight, flexible devices and circuits, via simple printing and coating techniques rather than the high-tech methods needed for inorganic semiconductor electronics, began to seem possible. The genuine potential of the field was acknowledged when the 2000 Nobel prize for chemistry went to Shirakawa, Heeger and MacDiarmid.

The synthesis of gossamer-thin organic electronic circuits reported by Martin Kaltenbrunner in Tokyo and colleagues (Nature 499, 458-463; 2013) is the latest example of the ingenuity driving this field. Their devices elegantly blend new and old materials and techniques. The substrate is a one-micron-thick plastic foil, while organic small molecules provide the semiconductor for the transistors, other organic molecules and alumina constitute the insulating layers, and the electrodes are ultrathin aluminium. The featherweight plastic films, 27 times lighter than office paper, can be crumpled like paper, and on an elastomeric substrate the circuits can be stretched more than twofold, all without impairing the device performance. Adding a pressure-sensitive rubber layer produces a touch-sensing foil which could serve as an electronic skin for robotics, medical protheses and sports applications.

Wearable and flexible electronics and optoelectronics have recently taken great strides, propelled in particular by the work of John Rogers’ group at Illinois (D.-H. Kim et al., Ann. Rev. Biomed. Eng. 14, 113-128 (2012)). Such devices can now be printed on or attached directly to human skin, and can be made from materials that biodegrade safely. Especially when coupled to wireless capability, both for powering the devices and for reporting their sensor activity, the possibilities for in situ monitoring of wound care and tissue repair, brain and heart function, and drug delivery are phenomenal; the challenge will be for medical procedures to keep pace with what the technology can offer. At any event, such applications reinforce the fact that organic electronics should not be seen as a competitor to silicon logic but as complementary, taking information processing into areas that silicon will never reach.

At the risk of inflating another premature bubble, these technologies look potentially transformative – more so, on current showing, than the much heralded graphene. The remark by Kaltenbrunner et al. that their circuits are “both virtually unbreakable and imperceptible” says more than perhaps they might have intended. In this regard the new work continues the trend towards the emergence of a smart environment in which all kinds of functionality are invisibly embedded. What happens when packing film (one possible use of the new foldable circuitry), clothing, money, even flesh and blood, is imbued with the ability to receive, process and send information – when more or less any fabric of daily life can be turned, unseen, into a computing and sensing device? Most narratives currently dwell on fears of surveillance or benefits of round-the-clock medical checks and diagnoses. Both might turn out to be warranted, but past experience (with information technology in particular) should teach us that technologies don’t simply get superimposed on the quotidian, but both shape and are shaped by human behaviour. Whether or not we’ll get what’s good for us, it probably won’t be what we expect.