Calendar
News
First Annual
Senior Dinner
April 18, 2008
Faculty Update
Effective Fall 2007
Professor Frederick
Nelson has retired from the ME Department after 52 years at
Tufts.
Professor
Benjamin Perlman has retired from the ME Department after 40
years at Tufts.
Professor Jason Rife
joins our faculty from Stanford University.
Professor Chris
Rogers returns from a year sabbatical in Switzerland.
ME Summer Scholars, Aaron Gerratt, Diana Mark, and Jennifer
Nichols, work on summer research
This summer, students in mechanical
engineering spent their summers researching topics including:
designing machines to braid silk for biomedical application;
engineering flow chambers to understand cell growth in bone; and
creating a device piggy-backed onto existing dialysis machines
to gain medical information. ME students Aaron Gerratt (’08),
Diana Mark (’08) and Jennifer Nichols (ME/BME ’08)
are three of many engineering students expanding their knowledge
as part of the Tufts Summer Scholars Program. The Tufts Summer
Scholars Program is a university-wide initiative that offers
research apprenticeships with faculty or clinical mentors to
motivated Tufts undergraduates. With a $3,500 scholarship, the
program gives students a chance to be on the front line of
discovery and scholarship at Tufts.
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Dial-up your dialysis knowledge with Aaron |
Get tubular (braiding) with Diana |
Bone-up on bone fluid mechanics with Jen |
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Name: Aaron Gerratt, ME’08
Project title: Applications of Ultrasound in Dialysis
Monitoring
Advisor: Professor Robert Greif
What it’s all about: When dialysis takes the place of normal
kidney function, patients are dependent upon machines to clean
their blood of contaminants, such as salts and urea. In Aaron’s
design, he sends ultrasonic waves through the medical tubing to
determine the fluid’s sound speed. The wave’s sound speed, in
turn, can be used to indicate blood protein levels and blood
water concentrations. “There’s been research done showing
correlations between sound-speed in blood to total protein
concentration,” said Gerratt.
How it works: In the system, water flows through medical
tubing held in place between two transducers that send the
ultrasonic waves. By recording the time it takes for the wave to
pass between the transducers and then calculating the space
between them, he calculates a velocity.
Aaron takes a “through”-transmission measurement by sending a
wave directly through the tube from one transducer to another.
He then takes a “pulse-echo” measurement which records a wave
echoing from bouncing off the tubing wall back to the transducer
that sent the pulse. “Then the process is repeated with the
other transducer because we can’t be sure that the tube walls
have the same thickness,” he said. These time measurements are
subtracted from the entire through transmission measurement to
get the time the wave actually spends in the fluid, not the
tube.
Then to obtain the distance the waves travel between the
transducers, the equation should be straightforward—the tube’s
outside diameter minus the inside. But the pressure of the clamp
holding the transducers deforms the tubing. “We ran compression
tests on the Instron machine,” said Gerratt. “As we compress the
tube as a whole, we want to know how much one wall would
compress in addition to the water.”
Once Gerratt has perfected the design, he can move from a
water-based system to something more like blood—milk, for
example.
Design changes: In his design, Aaron sent ultrasonic waves
through tubing with running water, as opposed to blood to ensure
he could obtain velocity measurements accurate within 0.1%. In
the initial design, he created the setup holding his transducers
in place with the rapid prototyping machine, which produces
plastic parts. “When you’re trying to get a very accurate
distance measurement, it’s not the best to have so much play in
it,” said Aaron. The second-generation design included machined,
metal parts that rigidly held the transducers in place. Aaron
also replaced the thermocouplers that measured the water
temperature within the tubing to increase the accuracy from ±2
degrees to within ±0.1°C.
Bonus: A look through the scientific literature turned up
some interesting connections between ultrasound and milk, a
substance that may be substituted for blood in future testing of
the device. Food-quality monitoring “actually uses ultrasound to
see if milk’s gone bad,” said Aaron. “You can do it without
opening the carton.”
Future: The next step is for the machine to have tests run
in an incubator which will more accurately mimic a patient’s
internal temperature and will allow consistent monitoring. Aaron
will be moving from the dialysis project to another mechanical
engineering project working in collaboration with Boston
Engineering Corp. and the U.S. Navy to develop shock-insulation
technology for use in submarines.
Lessons learned: “It got some good design and research
experience,” said Aaron. “I was responsible for everything on my
own. It was up to me to do the work.”
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Name: Diana Mark, ME’08
Project title: Development of Tubular Braiding System for
Tissue Engineering Scaffolds
Advisor: Senior Lecturer Gary Leisk
What it’s all about: Silk is one of the strongest and most
flexible materials available to the biomedical engineering
community. Though currently only in human biomedical use as a
material for stitches, silk has been of interest to engineers
for applications such as ligament repair and the engineering of
scaffolding to mimic the environment where stem cells might
grow. By braiding many strands of silk together, engineers could
weave a sheath to surround biomedical or biological structures
that needed support or form composite structures that
incorporate silk. For example, a silk-braided structure could be
used to surround grafted blood vessels for added strength to
withstand increases in blood pressure, or it might be used to
support discs between the backbone vertebrae. Diana Mark, with
help from lab partner Tony Zhang (MD/BSME), worked on designing
the braiding machine that could generate these structures.
How it works: The machine will be designed to braid silk
“thread” not more than 150 micrometers across, which is the
equivalent of three strands of fine hair. Apart from the thread
thickness and the biomedical applications, the braiding is done
much in the way rope and bungee cords are woven. Thread on
bobbins is carried on carriers that weave in and out along a
track that looks like a daisy-chain of figure eights. The
carriers are passed between gears—called horn gears—which, with
every 180 degree rotation, will shuttle the carrier off to the
next horn gear. In their design, 16 horn gears will pass 32
carriers and draw their silk bobbin strands to the middle of the
machine where they will be braided together to form a tubular
sheath.
Switching (horn) gears: The goal was to base the braiding
machine design on prior work started by other Tufts engineering
students. However, Diana realized that the original braiding
table—with relatively massive 5.2” horn gears—wasn’t going to
meet their needs. For the given application, having a braider
with carriers and horn gears of that size would pull and snap
the silk strands. Putting in a call to Herzog, a German-based
braiding machine manufacturer, alerted them that they needed to
scale-down the original braider design to a more reasonable 3”,
or Type 1, horn gear. “The old table could be great for braiding
something else,” said Diana, “but there’s no way it could be
used for silk” for the intended biological applications. Diana
and Tony also got some good advice from a contact at United
Textile Machinery Corp, in Fall River, Mass., a company that
sells and repairs braiding machines and parts. Here, they
purchased a smaller commercial braider to get a sense of how
everything fit together. “We took it apart and cleaned it to see
how it worked,” said Diana. “The design is really ingenious.”
Bonus: In addition, a similar machine might be used to braid
other materials besides silk, such as “memory wires” made of
titanium-nickel alloy that remember their
original shape when carrying electricity. Co-opting the
silk braider for wire—an idea proposed by Diana’s mentor, Dr.
Gary Leisk—would hold particular relevance for a
multi-disciplinary soft-bodied robot effort, led by Professors
Barry Trimmer and David Kaplan. Trimmer and Kaplan’s robot
design mimics nature—in particular, the tobacco hornworm
caterpillar—to develop flexible robotic technology. “We could
use this machine to wrap this robotic caterpillar in muscle
wires, and when you run current through them could flatten the
body of the robot to squeeze through a hole,” said Tony.
Future: Another design issues Diana will tackle is the
question of how much would they want a particular sample of
material, be it blood vessel or robotic caterpillar, to be
covered by a braided-silk sheath. “We researched equations of
how much the braiding will cover a sample, but the problem is we
don’t know how much we actually want it to cover,” said Diana.
“We don’t want to overdesign a machine that will cover 90% of
say a 5-cm diameter sample when you only really need 25%.”
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Name: Jennifer Nichols, ME/BME’08
Project title: Fluid Mechanics of
Bone Marrow
Advisor:
Professor Rich Wlezien
What it’s all about: Though we think of bone as a rigid,
static framework for our bodies, bone is a dynamic material.
Most of body’s blood cells are produced inside bone,
specifically in bone marrow. The different types of blood
cells—including oxygen-carrying red blood cells and
immune-system defense white blood cells—all begin as
unspecialized cells. These generalized cells, more commonly
known as adult stem cells, have the ability to grow into
different types of cells. Doctors use adult stem cells in
bone-marrow transplants, in which the donor gives the recipient
a fresh supply of adult stem cells to boost the production of
blood cells. In the future scientists and engineers hope to
utilize adult stem cells for other life-saving procedures. If
engineers like Jen Nichols determine how these adult stem cells
form and migrate through the bone marrow, the discovery could
result in the ability to control and augment the production of
healthy tissue. “Once you’re able to
see where the stem cells want to grow, you can create an
environment that they want to be in,” said Jen. To understand
the fluid mechanics of bone marrow and study stem cell movement,
Jen is designing and building a flow chamber.
How it works: “To study the fluid mechanics of bone marrow,”
said Jen, “I designed the flow chamber to allow fluid to flow
through a piece of silk scaffold, a synthetic bone material
created by the biomedical engineering department.” In her
initial design, Jen will use water, rather than blood, to mimic
blood flow through the silk-based structure created by David
Kaplan’s group. Jen will place an electrified platinum wire, a
hundredth of an inch thick, in the flow, causing hydrogen
bubbles to form from the water. “It’s
like writing lines in the fluid”, Jen’s advisor, Professor
Richard Wlezien, explained. “When you turn on the power, it
almost looks like smoke. You get a fine array of microbubbles.
By using a computer algorithm you can track the patterns.” The
process, known as hydrogen bubble flow visualization, is
a new technique as it relates to bone mechanics. “No
one’s really looked at the fluid flow through bone in this way
before,” said Jen.
Gluing it all together: Moving from drawing to prototype
design meant that Jen had to develop new skills—especially in
Plexiglas gluing techniques. “I put markers here, here and
here,” said Jen pointing to some leaking joints and the seams of
a plastic container that forms the reservoir to supply water to
the flow chamber. In the final design of Jen’s flow chamber, she
used silicone rubber to prevent leaks at the weaker joints.
“The water is going to be pumped through the flow chamber under
pressure, so I didn’t want to take any chances that the chamber
would start leaking during experiments,” Jen said. Besides
perfecting the water-tight seal of the container design, Jen
will also need to make the next prototype able to withstand
intense temperatures for sterilization in an autoclave machine.
“The final design must be autoclavable
so that chamber is sterile for the nutrient solution used to
grow cells and the silk-scaffold,” said Jen.
Lessons learned: “I am enjoying working closely with my
mentor, Professor Richard Wlezien, who is both encouraging and
knowledgeable. He provides me with direction and feedback, yet
at the same time gives me the freedom to make my own decisions
even if they are not the same decisions he would have made,”
said Jen. “Even though the research can be frustrating, it can
also be exhilarating.”
Internships and Programs
There are summer internships and programs available through Tufts University!
Undergraduates should contact Peter Wong if
you are interested in summer research.
Undergraduate female engineers are invited to work with middle school girls in
the area to build their science and technology skills. The final product will be
an interactive science museum exhibit. Please contact or
Peter Wong, for more information.
Last August students participated in an undergraduate research project designed
to be tested in zero gravity. Those four students were admitted to a program run
by NASA to take a ride on their "Vomit Comet", or the KC-135. This year there is
a new team already planning their trip to Houston to experience weightlessness!
If NASA programs are of interest to you, check
out their summer programs, and look for internships there as well. They have
lots of programs available. You could be floating soon!
Useful Resources
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