May
2005
Professor Lisa Pruitt also conducts research on artificial polymers and grafts for damaged cartilage. |
From garage doors to auto shocks, mechanical parts fail from repeated use. The same holds true for artificial hips, shoulders, and knees. Swapping the natural joint for an artificial one the first time is traumatic enough, but eventually the implants wear out as well. UC Berkeley mechanical engineer Lisa Pruitt leads an effort to lengthen the lifetime of artificial parts in the human body shop.
"Everybody seems to either be afflicted with some pain in the knees, hips, or shoulders, or knows someone who has had a joint replacement due to arthritis," says Pruitt. "So our laboratory develops materials technology to improve fatigue and wear resistance and mechanical integrity in the artificial joints."
If the cartilage that allows the bone ends of a joint to move freely and painlessly becomes seriously damaged or diseased, the joint may need to be replaced. Currently, replacement joints often consist of titanium, cobalt chrome alloy and a polymer called polyethylene. For example, in an artificial hip, the stem of the implant that connects to the bone may be titanium while the articulating "ball" at the end is fabricated from cobalt chrome alloy. A polymer cup is substituted for the socket.
"The polymer gives us the best lubricity and mimic of cartilage in the joint," Pruitt says. "But as the joint moves from walking or other load-bearing activities, the hard metal will eventually scratch the plastic or rub off polymer debris that ends up in the joint space."
Over time, this debris can loosen the joint from the bone, causing intense pain. At that point, the patient must undergo "revision" surgery to either repair the artificial joint or replace it with a new one.
"Today's artificial joints are designed to last 15 to 20 years," Pruitt says. "That's OK if you get the replacement when you're 70, but not ideal if you're a lot younger. Revisions never last as long as the primary replacement, so the goal is to get 30 years or more out of these devices."
Artificial hip from Exactech, Inc. |
In Pruitt's medical polymers group, an interdisciplinary team of researchers from mechanical engineering, materials science, biology, and medicine, and a surgeon from UC San Francisco, are developing new techniques to optimize the polymer. The aim is to prevent the plastic from flaking off due to abrasion or crack from repeated cyclic motion. The trick, she explains, is making changes to the microstructure of the material that improves one, or possibly both, characteristics without any sacrifice.
In a recent collaboration with the Harvard Medical School and Brigham and Women's Hospital, the researchers treated a polymer with gamma radiation to produce a material called a highly crosslinked polyethylene with impressive wear resistance. Then they applied a high pressure process to the new material, increasing the crystallinity and thereby the fatigue resistance as well. Once samples are created, they're mechanically tested in Pruitt's lab, put under the microscope, and x-rayed "to correlate the ideal mechanical properties with the specific microstructures."
In the last year, Pruitt and her colleagues have presented preliminary data suggesting that some of their experimental materials not only provide the same phenomenal level of wear resistance of highly crosslinked polyethylene but also show up to 20 percent improvement in fatigue properties.
"They could give us the best of both worlds--fatigue resistance and wear resistance," Pruitt says.
Of course, the new materials still must undergo intense testing and characterization before they will be considered for clinical use. To that end, Pruitt's laboratory is building a custom test system that enables the joints to be subjected to millions of cycles of use while the researchers adjust the kinematics, for example how much an artificial knee rolls in the joint versus sliding.
"In our laboratory, we hope for clinical outcomes in the near future," Pruitt says. "And that's what I like most about this research. We take an interdisciplinary approach to solving a real problem for humanity."
Trafficking in Roadway Sensors
by David Pescovitz
Professor Pravin Varaiya is a researcher with the California Partners for Advanced Transit and Highways. |
We drive over them constantly but may have never noticed the octagonal shapes in the freeway. Buried below the surface of many roadways every third of a mile are wire sensors called loop detectors that, when they're working, count how many cars pass over them and the average time a car is on top of the loop. California alone has more than 25,000 loop detectors. In recent years, UC Berkeley researchers used the loop detectors as a traffic monitoring system to make commuters aware of congestion hotspots before they get on the road. The next step, says professor Pravin Varaiya, is to replace the troublesome and costly loop detector with wireless studs that not only count the vehicles but also distinguish between cars, SUVs, and trucks as they zoom past.
"Throughout the world, 90 percent of traffic sensing is done using loop detectors," says Varaiya, a professor of electrical engineering and computer science and researcher with the Center for Information Technology Research in the Interest of Society (CITRIS). "To install each one, you have to saw into the pavement and connect all the wires. Many loop detectors are broken and aren't repaired until roads are repaved."
Each wireless stud contains a sensor, microprocessor, radio, and battery. |
Varaiya became intimately familiar with loop detectors while designing the freeway Performance Measurement System (PeMS) in collaboration with the California Department of Transportation (Caltrans) and California Partners for Advanced Transit and Highways (PATH). The system collects data from the loop detectors and translates it into "news you can use" in the form of real-time traffic reports for commuters. PeMS also provides traffic engineers with historical data to alter operational decisions regarding metering lights or highway closures due to construction. Eventually, strategically-placed electronic message boards informed by PeMS could display constantly-updated travel tips such as: "You're going to spend six minutes on this ramp. Uou should proceed to the next exit instead."
Of course, a system like PeMS is only as accurate as its sensors. Inspired by Berkeley 's wireless sensor innovations like Smart Dust, Varaiya and his colleagues built a new wireless road sensor that's far more accurate and much less expensive than purchasing and installing a new loop detector. Approximately the diameter of a saucer for a teacup, the sensor nodes resemble reflector studs that dot roads. Like the reflectors, the sensors can be glued into place without sawing into the asphalt. Each node contains a small magnetic sensor, computer processor, short-range wireless radio, and battery.
A wireless base station receives data from nearby traffic sensors and transmits via the cellular network to traffic management headquarters. [View larger image] |
"As a vehicle's ferrous structure goes over the sensor, the sensor detects a localized shift in the earth's magnetic field in three dimensions," Varaiya explains. "Buses have different distribution of ferrous material than cars or trucks. So you can use the signature of that distribution to determine the kind of vehicle passing over the sensor."
Data is then transmitted to a base station mounted roadside in range of a handful of the nodes. The base station acts as a midway point for the data, ultimately delivering it via a cellular network to a central traffic management office. It's a two-way channel, enabling the sensor network to be programmed remotely as new software is developed.
Readying a prototype device for the road was no small feat, Varaiya says. From an electrical engineering perspective, it required a very efficient wireless communication system that would run on a single battery for seven years, comparable to the estimated lifetime of loop detectors. Finally, the casing had to be strong enough so "trucks could drive repeatedly over it without cracking it."
Once their design was proven out on real roads in Berkeley, Varaiya and two other Berkeley engineering alums spun out a company, Sensys Networks, to bring the technology to market. Back at the University, Varaiya is exploring variations on the sensor stud design and other real-world applications.
For example, outfitting the studs with tiny accelerometers, devices that sense direction and speed of motion, could measure the vibration of the pavement as a vehicle passes over it. That vibration correlates to the load of the vehicle, Varaiya says. Unlike existing roadside weighing stations, the distributed sensors wouldn't be used to tax trucks based on their load, at least initially. Still, they could be cheaply installed in many locations to gather data that's extremely useful in aggregate.
"When Caltrans considers how fast pavements are wearing, they'd like to know the weight of vehicles and how much load trucks are carrying," Varaiya says. "The studs could be placed right on the road at a cost of a couple thousand dollars each compared to several hundred thousand to build a roadside weigh station."
Recently, Varaiya has considered how the sensor studs may help alleviate the other major headache associated with driving: parking. If simple wireless stud sensors could be produced for just a few hundred dollars each, it would be practical to install them in parking garages to keep tabs on each space. The researchers are just now embarking on experiments of this sort in the campus's student union parking structure. Meanwhile, Emeryville-based start-up ParkingCarma, who has partnered with PATH to test "Smart Parking" systems, is also looking at the Sensys Networks technology for future deployments.
"Parking lots could accurately advertise in real time on a display board how many spaces are open or, of course, say 'sorry, don't even bother, no spots available,'" Varaiya says.
Bioengineers Battle Stowaways At Sea
by David Pescovitz
International Research Fellows (from left) Stephanie Yeung, Julien Decot, Nate Beyor, and Erik Douglas |
Three UC Berkeley bioengineering students are developing an approach to sniff out stowaways on cargo ships. But they're not looking not human stowaways. What they're looking for are invasive marine species that hitch a ride in a ship's ballast water before it leaves home port and wreaks havoc on the non-native ecosystems when that ballast is eventually released. According to the International Maritime Organization, the introduction of invasive species is one of the four greatest threats to the world's oceans. The students, recently-named fellows in the University's Management of Technology (MOT) International Research Program, will head to China to conduct a feasibility study of their innovative idea for combating the problem.
Nate Beyor, Stephanie Yeung, and Erik Douglas, PhD students in the UCB/UCSF joint graduate group in bioengineering, work in the laboratory of Richard Mathies. Their theses work focuses on developing lab-on-a-chip technology, chemical analyzers that pack the power of large, expensive instruments into a thumbnail-sized device complete with microscale valves, pumps, and reaction chambers.
Last year, the three students were brainstorming ideas for research projects that would dovetail with the MOT fellowship program's goal of bringing technological solutions to problems in developing countries. Beyor happened to talk with a friend's father who is a marine engineer for shipping companies. The engineer explained to Beyor that when a ship docks at a port and empties its cargo, it takes in millions of gallons of seawater to rebalance the boat. Once it arrives at another port to pick up a new load, it dumps that ballast.
"By doing that, they're transporting all sorts of organisms that can cause health problems, destroy fisheries, and harm ecosystems" Beyor says.
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Inspired by the conversation, Beyor, Douglas, and Yeung teamed up with Haas School of Business student Julien Decot to submit a proposal to the MOT program. In March, the students landed a $17,000 fellowship to conduct preliminary research and connect with key organizations, including the local Port of Oakland , the UK-based Global Ballast Water Management Programme (GloBallast), and, in China , port authority personnel, government officials, and private companies in the shipping industry. Two of the three largest ports in the world are located there.
While writing the proposal, the students quickly learned how serious the danger of invasive species has become. From bacteria and invertebrates to eggs and larvae, 7,000 marine species are carried around the world in ships' ballast tanks, according to GloBallast. While most species die during the journey or shortly after arrival, some do establish a population in their new home. These invasive species may then out-compete native species for food and multiply to the point that the ecosystem is permanently altered.
For example, the commercial fishing industry in the Black Sea collapsed in part because of a displaced species of North American jellyfish's insatiable appetite for native plankton. In the US , the European zebra mussel has infested 40% percent of internal waterways and the Great Lakes causing as much as $1 billion dollars in control measures between 1989 and 2000. In several other locales, microscopic "red-tide" algae introduced in dumped ballast water have been absorbed by oysters and shellfish. Eating the contaminated shellfish can cause paralysis or even death in humans.
Current regulations recommend dumping local ballast water at sea and reballasting with the ocean water. The problem is that the tanks may still harbor some organisms. More recently, other approaches to kill the organisms--from heating the water to chlorinating it--have been applied. However, testing the effectiveness of those treatments is a time-consuming and imprecise process requiring hand-sampling and chemical assays run by trained individuals.
"A lab-on-a-chip could automate the whole thing," Douglas says.
Bulk fabricated the same way integrated circuits are manufactured, a lab-on-a-chip enables biological samples to be mixed and tested much faster and with higher sensitivity than full-size laboratory equipment. Because they're small and inexpensive, a number of the devices could be inexpensively installed in throughout the ship's ballast tank.
"A system of these chips could be operating as the ship moves from port to port without requiring anyone on board to be trained to deal with chemical analysis," Douglas says. "As a ship approaches a shore, a detailed report would automatically be transmitted to port where personnel could determine if further treatment were needed before the boat docks."
Before they can develop the technology, Yeung says they must fully understand both the problem and its context. In August, they'll make a three week trip to China to suss out what it would take to bring such an innovative technology to the shipping industry.
"There are technological and scientific challenges to this, but also many economic factors and regulations in countries around the world that must be taken into consideration," Yeung adds.
China is an ideal place to begin the research, Beyor says, because it's home to some of the largest ports in the world and also a developing economy where funds for environmental concerns may be limited. While that could make it harder to implement the technology, " regulations and practices must be applied everywhere or it will not work."
The end goal of the fellowship, he adds, is to outline the steps that must occur for the industry to, literally, "buy in." Next year, the students will present their findings at the Bridging the Divide Conference, a collaboration between the Management of Technology Program and the United Nations Industrial Development Organization (UNIDO). If all goes well, Beyor says, a post-graduation startup is always a possibility.
"Public awareness and a push for regulation are key if this idea is to succeed," he says. "Once those things are in place though, the industry can't wait ten years for the right device to be developed. The technology needs to be ready to fit right in."
Francisco Castillo (B.S.'95 M.S.'97 CEE) |
In his Oakland office, Francisco Castillo (B.S.'95 M.S.'97 CEE) talks passionately - and voluminously - about three things. One is family: his wife, Sonia Rocha Castillo (B.S.'02 IEOR, whom he met on campus), his parents, and nieces and nephews. The second is the 49ers, which Castillo insists will make a comeback this year. The third is work. "I do engineering because it's as fun as the first day I was in class," he says. "I don't take it too seriously."
Actually, Castillo takes his contributions to the designs of prominent Bay Area buildings quite seriously. As serious, say, as translating for his Spanish-speaking mother during her cancer operation when he was 14 or getting a degree from Berkeley Engineering against the odds. "I always take pride in the fact that you can open doors if you struggle and work really hard," he explains.
In 1986, Castillo's family emigrated from Nicaragua , settling in the Bay Area. His mother worked as a nurse's aide in people's homes making minimum wage; his father worked for a company that prepared airline meals. Castillo went to the inner-city Mission High School . While he struggled to learn English and adapt to a new culture, he cruised through math and science. Extra-curricular programs like the Mathematics, Engineering, Science Achievement (MESA) and Early Academic Outreach Program (EAOP) challenged him and gave him his first exposure to engineering. He even came to Berkeley as a high school student, taking extra classes in math and science through the EAOP program.
Back in Nicaragua , Castillo's grandfather, a civil engineer himself, predicted that his grandson would go to Berkeley and become a civil engineer. "I didn't want to go anywhere but Berkeley," Castillo remembers.
Castillo applied to the CEE department and was accepted in 1991. He worked incredibly hard, teaching himself the math and science he didn't get in high school as well as staying on top of his regular coursework. The most difficult thing, he says, was the economic challenge. "I couldn't afford a computer so I did everything by hand," he says.
Being an underrepresented minority in the College is a matter of overcoming real barriers as well as barriers you create in your own mind, he explains. He became involved with the Charles Tunstall Multicultural Engineering Program (MEP) and the Hispanic Engineering Society (HES), he says, making friends who were like him. By finding people he was comfortable with and by working hard, he succeeded. When he looks back on it now, Berkeley Engineering "was a real home to me. It helped me realize all my dreams."
Castillo left the College in 1997 with just his master's degree so he could get a job and help his parents financially. The highlight of his first job at Structural Design Engineers (SDE) was to help in the construction administration of the $186 million Moscone West Convention Center in 2002. According to the San Francisco Business Times, the building went on to help stimulate the sluggish San Francisco convention and hotel industry still recovering from the dot.com bust. Castillo holds up the article. "I'm proud we had an impact on the city."
While at SDE, he also worked on an Oakland building now used by the District Attorney's Office, the design of the Lesbian Gay Bisexual Transgender (LGBT) Community Center in San Francisco , and the new dorms for the California College of Arts and Crafts in Oakland .
Castillo now works at OLMM Consulting Engineers in Oakland . He's grateful that engineering not only provides him and his family with a good living, but also keeps him passionate. "That's the thing about engineering. You never stop learning," he says.
Castillo's life has come full circle. He now passes his enthusiasm for engineering on to local high school students, where he introduces them to engineering. He also volunteers with MEP and advises current student engineers.
"If someone gives you a hand, you have to return the favor," he says.
