12-03 :: March/April 2012

nanotimes News in Brief

In close collaboration with four industrial partners and Helmholtz-Institute for Biomedical Enginee- ring of RWTH Aachen University, researchers from the Fraunhofer Institute for Manufacturing Engi- neering and Automation IPA in Stuttgart develo- ped an automated production facility that can make venous valve prostheses from polycarbonate-ure- thane (PCU), a plastic. The project was sponsored by the German Federal Ministry of Economics and Technology BMWI.

The centerpiece of the facility is a 3D droplet dis- pensing tool which enables the researchers to pre- cisely apply a particular polymer onto freeform sur- faces and at the same time combine various grades of polymer hardness, called Shore hardnesses.

But how does the PCU become a venous valve prosthesis? Initially, the polymers are dissolved in a solvent and deposited onto a venous valve prosthe- tic mold one droplet at a time, using the dispensing tool. The system is accurate to within 25µm, and can deliver up to 100 droplets per second, each with a volume of 2 to 60 nanoliters. A six-axis kine- matic system positions the piezo feeder precisely above the mold.

Once it is fully coated with droplets, the mold is ba- thed in a warm stream of nitrogen. This causes the solvent to evaporate, leaving the polymer behind. Further layers are applied by repeating the dispen- sing process, and in the end the polymer prosthesis can simply be peeled from the mold. Doctors can take the finished replacement valves and implant them into the veins of the leg via a catheter passed through the skin.

© Fraunhofer IPA

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Dr. rer. nat. Oliver Schwarz, Fraunhofer Institute for Ma- nufacturing Engineering and Automation IPA, Germany, Phone +49 711 970-3754: http://www.ipa.fraunhofer.de/

Doris Keh-Ting Ng at the A*STAR Data Storage Institute and co-workers have now successfully fabricated a laser on top of a silicon chip. The III-V semiconductor materials are bonded to silicon to provide optical gain and the laser has a unique mir- ror design that promises enhanced device operation compared to the conventional feedback mirrors based on device facets.

“Integrated Si/III-V lasers can take advantage of low-loss silicon waveguides, while addressing the problem of low light emission efficiency that silicon devices typically have,” says Ng. Attaching a Si/III-V laser on top of silicon requires challenging fabri-