3-D printed LED is embedded in contact lens
The lens is not designed for actual use because it requires an external power supply but the device demonstrates the ability to 3-D print electronics into complex shapes and materials.
"This shows that we can use 3-D printing to create complex electronics including semiconductors," said Michael McAlpine, an assistant professor of mechanical and aerospace engineering at Princeton. "We were able to 3-D print an entire device, in this case an LED."
The hard contact lens is made of plastic. The researchers used quantum dots to create the LEDs that generated the colored light. Different size dots can be used to generate various colors.
"We used the quantum dots [also known as nanoparticles] as an ink," McAlpine said. "We were able to generate two different colors, orange and green."
The contact lens is also part of an ongoing effort to use 3-D printing to assemble diverse, and often hard-to-combine, materials into functioning devices. In the recent past, a team of Princeton professors including McAlpine created a bionic ear out of living cells with an embedded antenna that could receive radio signals.
Yong Lin Kong, the lead author of the article describing the current work in the journal Nano Letters, said that the contact lens project involved the printing of active electronics using diverse materials. The materials were often mechanically, chemically or thermally incompatible — for example, using heat to shape one material could inadvertently destroy another material in close proximity. The team had to find ways to handle these incompatibilities and also had to develop new methods to print electronics, rather than use the techniques commonly used in the electronics industry.
"For example, it is not trivial to pattern a thin and uniform coating of nanoparticles and polymers without the involvement of conventional microfabrication techniques, yet the thickness and uniformity of the printed films are two of the critical parameters that determine the performance and yield of the printed active device," Kong said.
McAlpine said that one of 3-D printing’s greatest strengths is its ability to create electronics in complex forms. Unlike traditional electronics manufacturing, which builds circuits in flat assemblies and then stacks them into three dimensions, 3-D printers can create vertical structures as easily as horizontal ones.
"In this case, we had a cube of LEDs," explained McAlpine. "Some of the wiring was vertical and some was horizontal."
The researchers were able to custom 3-D print electronics on a contact lens by first scanning the lens, and feeding the geometric information back into the printer. This allowed for conformal 3-D printing of an LED on the contact lens.
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