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 Faculty Spotlight: Prof. Chen's Implantable Ultrasound Transducer Array Is World's First

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Fast. That's how Prof. Jingkuang Chen runs along La Luz Trail in the Sandias. Fast and thinking. Running provides a form of contemplation for Chen, who trains his mind on some conundrum in his research and then lets it work in pace with the tracks he plants on the trail as he speeds along. There isn't a lot of time to work through the many puzzles of his research--not when you consider the lives Prof. Chen wants to improve, or save, by solving them. Or when you consider that his wife and three children wait for him in Rochester, New York, for the decision about whether to stay 2,000 miles away or to join him here.

Prof. Jingkuang Chen joined ECE in July 2004.

So Prof. Chen works seven days a week. And even his passtimes serve his goal.

Since joining ECE as associate professor in July 2004, Prof. Chen has been working on tiny devices that can deliver life-saving drugs on a cell-by-cell basis, take ultrasound images from inside living tissue, and freeze targeted areas of tissue less than half the diameter of a human hair.

Micro-electro-mechanical systems (MEMS) integrate minute sensors, electronics and mechanical elements on a silicon substrate. When Prof. Chen heard about the MEMS technology developed at UC Berkeley in the mid-1980s, he was hooked. So after receiving his bachelor's and master's degrees in Taipei, Taiwan, he went to the University of Michigan at Ann Arbor, reknowned for its MEMS research, for his doctoral work.

After completing his doctoral dissertation on a "Multifunction Neuroprobe and Related Devices Using Buried Silicon Microchannels," Dr. Chen spent eight years working for Xerox Research. His initial work included research on a small chip used by inkjet printers and on an optical-control switch for routing telephones. Once he had developed the idea for a novel ultrasonic transducer array, however, he sought an environment where he could make it happen. Which brought him to UNM.

The implantable ultrasound transducer is half the diameter of a human hair, less than 100 microns wide.

His current research interests include MEMS-based ultrasonic transducers and smart microfluidic systems for biomedical applications. Early in December, Prof. Chen travels to the ICBME International Conference on Biomedical Engineering (www.icbme.org) in Singapore to talk about his implantable ultrasound transducer array. This miniaturized probe can, at the cellular level, create ultrasound images, freeze or heat cells, sense temperature, and deliver drugs or electrical stimulation.

The device is a micromachined, ultrasonic transducer/imager array that lies along a silicon probe half the diameter of a human hair (less than 100 microns) that can be implanted into neural tissue and fine vessels. It can generate high-frequency (>25MHz) acoustic signals at a driving voltage of less than 40 volts.

By comparison, conventional ultrasound systems are bulky and have comparatively poor image resolution. "Those devices operate outside of the body," Prof. Chen said, "so to penetrate the tissue, you need a long wavelength. Because we can put this silicon probe directly on tissue inside the body, we can use a shorter wave length." And that means a higher-resolution image.

The only currently available device that comes close to offering the benefits of Prof. Chen's probe is an intravascular ultrasound device that is inserted via a catheter to examine vessels inside the body and arteries in the heart. However, its 3 to 4 mm diameter limits its use to large cardiovascular vessels.

The potential uses for Prof. Chen's transducer are many. The tiny silicon probe is able to reach cells and tumors deep inside of tissue without significant disruption. In medical diagnosis, besides its higher-resolution medical imaging it can be used to monitor tissue temperature, measure blood-flow rate in fine vessels, introduce high-frequency acoustic waves, and serve as a visual aid on a microsurgery tool.

The implantable ultrasound transducer array uses a silicon probe that's half the diameter of a human hair.

In medical treatment, the device can be used to heat tissue locally using high-power ultrasound waves, clear plaque when inserted into blood vessels, heal wounded cells using acoustic waves, change cell activities, and trigger neurons. Because of its relatively noninvasive size, it can be used to perform surgery in delicate organs such as the liver and brain and to freeze or heat single, targeted cells.

In cryosurgery, which uses extreme cold to kill cells, the device can cool an area 30 microns in diameter. "So it has very high precision," Chen said. "We integrate three functions on that one chip: the ultrasound array, the freezer, and the temperature sensor."

When the device is used for targeted drug delivery, it can also use ultrasound to increase the cell membrane's permeability, thereby increasing the efficiency of drug-delivery into the cell. Neuroscience applications include inserting an array of the hair-like probes to monitor and control epilepsy.

Not yet being tested on humans, the implantable ultrasound transducer is under patent review. Meanwhile, Prof. Chen continues working seven days a week on his research.

"My research is quite interesting to me," he explained. "because it has practical application. It's not some basic theory; it's a real device. I know it can be used in surgery and in saving lives."

This fall he is also teaching two ECE classes, MEMS Transducer Devices & Technology and Analog Circuit Design.

And he continues to run.

He noticed right away that New Mexico's humidity levels are far below New York's, which is a big plus. Also, "there are many people in New York; it's very crowded," he said. "I don't like crowds."

What he does like are Albuquerque's mountains and hiking. There were no mountains in Michigan or New York. At first, New Mexico's altitude put a crimp in Prof. Chen's running. But now he smiles, saying that during his Rochester visits he must now run twice as long to get a benefit similar to his jaunts in the Sandias.

Prof. Chen's doctoral student, Xiaoyang Cheng, is spending most of his time at his mentor's alma mater in Ann Arbor. This is because the University of Michigan has a silicon fabrication facility there. That's something Prof. Chen is counting on having here at UNM by 2007. Access to such a facility would speed up his work.

Which is the whole idea.

To reach Prof. Chen at ECE, call 277-5490 or e-mail jingchen@ece.unm.edu. To read the story in ECE's 2004 newsletter introducing Prof. Chen, download a PDF of the newsletter here.