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22 The PCB Magazine • July 2016 these gray-tones paint a different kind of pic- ture for your investigation, easily showcasing clam shells, striations, coalesced voiding, grain boundaries, and other fracture surface trade- marks. Ultimately, as with just about any testing, having the correct instrumentation is key for obtaining the information needed to solve your problem or answer your question. For this top- ic, fractography, a solid visual inspection/ex- amination is almost all you need to determine the root cause of the fracture and the stereomi- croscope and SEM are key players. Obviously, further testing could be needed after this visual examination depending on what questions are being asked. For example, material proper- ties—such as tensile strength, hardness, impact strength, alloy/material composition, etc.— may need to be investigated to determine if the correct material was called out or even, in some circumstances, if the correct material was used in construction. Nonetheless, a somewhat sim- plistic visual examination, along with a little background study on failure modes, will go a long way in the world of fractography. PCB Keith M. Sellers is operations manager with NTS in Baltimore, Maryland. SEEING IS BELIEVING IN FRACTOGRAPHIC ANALYSIS To study brain cell's operation and test the effect of medication on indi- vidual cells, the con- ventional Petri dish with flat electrodes is not sufficient. For truly realistic studies, cells have to flourish within three-dimen - sional surroundings. Bart Schurink, researcher at University of Twente's MESA+ Institute for Nano- technology, has developed a sieve with 900 open- ings, each of which has the shape of an invert- ed pyramid. On top of this array of pyramids, a micro-reactor takes care of cell growth. Schurink defends his PhD thesis June 23. A brain-on-a-chip demands more than a series of electrodes in 2D, on which brain cells can be cultured. To mimic the brain in a realistic way, you need facilities for fluid flow, and the cells need some freedom for themselves even when they are kept at predefined spaces. Schurink therefore de - veloped a micro sieve structure with hundreds of openings on a 2 by 2 mm surface. Each of these holes has the shape of an inverted pyra- mid. Each pyramid is equipped with an electrode, for measur- ing electrical signals or sending stimuli. At the same time, liquids can flow through tiny holes, needed to cap- ture the cells and for sending nutrients or medication to a single cell. Neuronal Network After neurons have been placed inside all the pyramids, they will start to form a network. This is not just a 2D network between the holes: by plac- ing a micro reactor on top of the sieve, a neuron network can develop in the vertical direction as well. Schurink's new µSEA (micro sieve electrode array) has been tested with living cells, from the brains of laboratory rats. Both the positioning of the cells and neuronal network growth have been tested. The result is a fully new research platform for performing research on the brain, diseases and effects of medication. Brain-on-a-Chip in 3D

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