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Lighting the way to skin cancer cures
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18/08/2008
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A breakthrough in inkjet-printable lights could soon see the technology applied to the treatment of skin cancer. Tom Shelley reports
A breakthrough in organic chemistry has resulted in extremely bright, inkjet-printable red lights – lasting up to 50 hours! The first intended application is for light bandages for treating skin cancer, where the tumour area alone is treated.
While the technology is of no use for domestic lighting, it is more than adequate for applications in which the light source is disposable. And a number of applications in smart labelling are already envisaged and doubtless it will not be too long before such printed lights are also seen in greetings cards and night-legible reading matter.
This particular set of breakthroughs comes not from the usual OLED (Organic Light Emitting Diode) teams in Cambridge and Enfield, but from a rival company near Oxford called Polymertronics.
OLEDs are carbon-based polymers made by placing a series of organic polymer thin films between two conductors. When a low voltage is applied across the conductors, a light is emitted from the polymer.
For some time, Polymertronics has been selling liquids that can be inkjet-printed, briefly cured by ultra violet light and then, when between electrodes – usually indium tin oxide – made to emit light. While the effect is electroluminescent, CEO Stephen Clemmet does not care to describe it as such. Why? Because what are generally understood to be electroluminescent materials require 50 to 250V, whereas his company’s materials only require 8 to 18V DC, at a current density of 23 mA/square cm.
Up until now, his products have had a light intensity that was “about the brightness of the screen of a laptop” – some 3 micro watts per sq cm, cm – but that has changed.
“About two weeks ago we reformulated our Red Diamond product to make it much brighter,” he reveals.
Bu what about their longevity, since this has been a challenge in the past and the main reason OLEDs have not been more widely used.
“Driven by DC, you would be lucky to get five minutes life”, he concedes, but adds: “We have developed a voltage waveform that gives the material an operational life of 50 hours.”
The waveform uses an electronic driver circuit – for which the company is filing a patent – and will be enshrined in a new chip set. Button cells normally power the OLEDs and one of the functions of the chip sets is to increase the voltage to a level that can drive them.
The other challenge for OLED users – and this has always been true – is to keep water out during manufacture, and encapsulate it to prevent any moisture getting back in.
So what markets would be appropriate for a 50-hour operational life? According to Clemmet, there are two main ones. One is what he describes as disposable medical electronics, especially for photodynamic therapy. This would make practicable a technique that has been around for some 30 years, which is to use drugs that are initiated by light to treat skin cancer and other ailments. The colour produced by Red Diamond is appropriate, but, being ink-jet printable, could be printed to the shape of the area of skin that needed to be addressed, with the treatment device taking the form of a ‘Light bandage’.
The other area of application concerns smart labels that light up with an important message when activated – and this is the one exciting most interest. Applied to pharmaceutical products, 75% of problems associated with wrongly taken medication arises from misreading the label. This could be overcome by using an OLED label, argues Clemmet, which would make the most important parts of its message so obvious, they could not be easily ignored. Furthermore, a medical or other package of goods that failed to light up might indicate it has already been opened and the label activated, so it should not now be used.
Another possible application, which Clemmet regards as “slightly niche”, might be to use the OLEDs for oximetry, a technique in which the absorption of red and infrared light by haemoglobin is used to measure the amount of oxygen being carried by the blood. This is usually done at present via the ear lobe. However, if the device were to use an OLED light source, it could be made very much smaller and perhaps placed within the body.
Might it be possible to use the light bandage idea to cure adhesives? Clemmet points out that this requires UV light, as given out by typical blue LEDs and, while it was possible to produce blue/UV materials, he is not aiming at this market.
There have been a number of UK government-led seminars on the possibility of using OLEDs for lighting, due to their greater efficiency over conventional forms of lighting. This may well come to pass, although the materials being developed by Professor Kathirgamanathan and his colleagues at ELAM-T (previously covered in Eureka), look more appropriate for that purpose.
Ultimately, the problem with all OLEDs is that developing them into commercial products is taking longer than expected and, while improvements are being made all the time, there is a need to find commercial applications that can yield profits now.
Polymertonics has reached the point of offering its products as development kits, and as liquid. It is not cheap as yet, costing from about £50 per ml to slightly more than £100 per ml, but that is not excessively expensive either. Printed thickness is 100 to 200nm, so a ml can, in theory, would cover 5 to 10 square metres. In time, as production processes improve and are scaled up, prices are likely to drop.
It is not inconceivable that greetings card that light up with suitable endearing messages, as well as playing tunes, will one day be on sale. And our evening newspapers may even become objects that can be read in the dark. But these are still some way off as yet.
Pointers
* Inkjet-printable OLED liquids are commercially available that can be cured by ultra violet let in about 4s
* Emitted waveband is 620nm +/- 50nm. Operating voltage 8 to 18V. A new driving waveform greatly improves life.
* Current density is 23mA/sq cm and a new development is somewhat brighter than a laptop screen. Printed thickness is 100 to 200nm
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Author
Tom Shelley
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