To operate on the heart, surgeons usually cut through
the breastbone to expose the organ. After correcting the
heart problem, they reconnect the sternum by piercing it
with steel wires, pulling the bone segments together and
twisting the wires tight. Because this half-century-old
technique poses some risks to both the surgeon and the
patient, a team of undergraduates at Johns Hopkins has
invented a less intrusive and potentially safer chest
closure system that threads locking polymer clasps through
The 11-member team's prototype won first-place honors
in the university's recent Biomedical Engineering Design
Day competition. The project's sponsor, Surgical
Transformations, has obtained a provisional patent covering
the system. If the idea appeals to enough surgeons, the
firm plans to support further research and development to
produce a commercial model.
Malcolm Lloyd, a physician and co-owner of the
company, said he and his partner, heart surgeon Mark
Sumeray, challenged the students last year to devise a
better way to close the chest after surgery. "The premise
was based on an unmet need identified by cardiothoracic
surgeons," Lloyd said. "The students came up with a working
prototype that hit all of the engineering requirements we
proposed. The end result was better than my partner and I
expected, particularly given the limitations they had in
terms of resources."
The students produced their prototype, which resembles
a stapler and uses standard locking cable ties, for about
$1,500. Much of this went to a private prototyping shop
that built the device according to the students' detailed
design drawings. A roughly 8-inch curved piece extends from
the handheld tool to guide the tie between and under the
ribs, enabling a surgeon to connect both ends and pull the
severed sternum parts toward one another. When one end of
the tie is reinserted into the tool and the handles are
squeezed, the device operates like a ratchet, tightening
the clasp and bringing the pieces of the breastbone firmly
together so that the healing process can begin.
The challenge came out of a class called Biomedical
Engineering Design Teams, taught by Robert Allen, an
associate research professor and senior lecturer in
Engineering. The project was selected by a group led by
Chris Weier, a 23-year-old senior from Sterling Heights,
Mich., and Neha Malhotra, a 20-year-old junior from Dubai,
United Arab Emirates.
As part of their research over two semesters, team
members visited a human cadaver lab to study chest anatomy.
They conducted tests in a hospital biomechanics lab to see
how the polymer ties compared to the steel wires. Members
of the team, which included six freshmen, three juniors and
two seniors, also worked with a model chest skeleton.
"Everyone was really involved, and everyone made a
contribution to the project," Malhotra said. "Getting a
provisional patent made the team feel like we really
Weier added: "This was not just a textbook problem.
This was like a real-life industrial project with deadlines
and patent searches."
If the prototype advances through further development
and testing, many patients could benefit, the student
inventors said. According to their research, the vertical
cut in the breastbone, called a median sternotomy, was done
in more than 700,000 operations worldwide in 2002 alone.
The students also learned that the traditional method of
reconnecting the sternum can cause injury because of the
significant force needed to pierce the breastbone in order
to accommodate the steel wires. They learned that these
wires can sometimes cut through the bone if they are pulled
too tight or can lead to poor bone reconnection if they are
left too loose.
"We talked to doctors and asked them what would be an
ideal system," Weier said. "They said it would be a band
that they could tighten. It needed to be very rigid, as
tight as possible without cutting into the bone, the
flatter the better so that it could lay flat against the
The team members concluded that their system was a
safer approach. "We think it will reduce potential injuries
to both the patients and the surgeons because the surgeon
isn't physically pushing a needle through a bone," Malhotra
Although the students used commercial cable ties for
their prototype, they said patients would best be served by
a biocompatible polymer clasp that would dissolve
harmlessly in the body after two years, when the sternum is
Lloyd, the project's sponsor, watched a demonstration
of the finished prototype and walked away impressed. "I
think it was a great learning experience for the students,"
said Lloyd, who earned a bachelor's degree in biomedical
engineering at Johns Hopkins in 1994.
Along with Weier and Malhotra, the design team members
were Matt David, Win Pin Ng, Paromita Chatterjee, Mikhail
"Mike" Basilyan, Eric Kim, Alex King, Barbara Ma, Taylor
Reese and Injeoung "Kate" Shim.