بسم الله الرحمن الرحیم
یک مقاله جالب از نشریه مؤسسه تکنولوژی ماساچوست ( MIT ). تاریخ چاپ: 26 سپتامبر 2011!
A team of researchers at MIT and Children’s Hospital Boston
has built cardiac patches studded with tiny gold wires that could be used to
create pieces of tissue whose cells all beat in time, mimicking the dynamics of
natural heart muscle. The development could someday help people
who have suffered heart attacks. The study, reported this week in Nature
Nanotechnology, promises to improve on existing cardiac patches, which have
difficulty achieving the level of conductivity necessary to ensure a smooth,
continuous “beat” throughout a large piece of tissue. “The heart is an electrically quite sophisticated
piece of machinery,” says Daniel Kohane, a professor in the Harvard-MIT
Division of Health Sciences and Technology (HST) and senior author of the
paper. “It is important that the cells beat together, or the tissue won’t
function properly.” The unique new approach uses gold nanowires
scattered among cardiac cells as they’re grown in vitro, a technique that
“markedly enhances the performance of the cardiac patch,” Kohane says. The
researchers believe the technology may eventually result in implantable patches
to replace tissue that’s been damaged in a heart attack. Co-first authors of the study are MIT postdoc
Brian Timko and former MIT postdoc Tal Dvir, now at Tel Aviv University in
Israel; other authors are their colleagues from HST, Children’s Hospital Boston
and MIT’s Department of Chemical Engineering, including Robert Langer, the
David H. Koch Institute Professor. Ka-thump,
ka-thumpTo build new tissue, biological engineers
typically use miniature scaffolds resembling porous sponges to organize cells
into functional shapes as they grow. Traditionally, however, these scaffolds
have been made from materials with poor electrical conductivity — and for
cardiac cells, which rely on electrical signals to coordinate their
contraction, that’s a big problem. “In the case of cardiac myocytes in particular,
you need a good junction between the cells to get signal conduction,” Timko
says. But the scaffold acts as an insulator, blocking signals from traveling
much beyond a cell’s immediate neighbors, and making it nearly impossible to
get all the cells in the tissue to beat together as a unit. To solve the problem, Timko and Dvir took
advantage of their complementary backgrounds — Timko’s in semiconducting
nanowires, Dvir’s in cardiac-tissue engineering — to design a brand-new
scaffold material that would allow electrical signals to pass through. “We started brainstorming, and it occurred to me
that it’s actually fairly easy to grow gold nanoconductors, which of course are
very conductive,” Timko says. “You can grow them to be a couple microns long,
which is more than enough to pass through the walls of the scaffold.”From
micrometers to millimetersThe team took as their base material alginate, an
organic gum-like substance that is often used for tissue scaffolds. They mixed
the alginate with a solution containing gold nanowires to create a composite
scaffold with billions of the tiny metal structures running through it. Then, they seeded cardiac cells onto the
gold-alginate composite, testing the conductivity of tissue grown on the
composite compared to tissue grown on pure alginate. Because signals are
conducted by calcium ions in and among the cells, the researchers could check
how far signals travel by observing the amount of calcium present in different
areas of the tissue. “Basically, calcium is how cardiac cells talk to
each other, so we labeled the cells with a calcium indicator and put the
scaffold under the microscope,” Timko says. There, they observed a dramatic
improvement among cells grown on the composite scaffold: The range of signals
conduction improved by about three orders of magnitude.“In healthy, native heart tissue, you’re talking
about conduction over centimeters,” Timko says. Previously, tissue grown on
pure alginate showed conduction over only a few hundred micrometers, or
thousandths of a millimeter. But the combination of alginate and gold nanowires
achieved signal conduction over a scale of “many millimeters,” Timko says.“It’s really night and day. The performance that
the scaffolds have with these nanomaterials is just much, much better,” Kohane
says. “It’s very beautiful work,” says Charles Lieber, a
professor of chemistry at Harvard University. “I think the results are quite
unambiguous, and very exciting — both in showing fundamentally that they’ve
improved the conductivity of these scaffolds, and then how that clearly makes a
difference in enhancing the collective firing of the cardiac tissue.”The researchers plan to pursue studies in vivo to
determine how the composite-grown tissue functions when implanted into live
hearts. Aside from implications for heart-attack patients, Kohane adds that the
successful experiment “opens up a bunch of doors” for engineering other types
of tissues; Lieber agrees. “I think other people can take advantage of this
idea for other systems: In other muscle cells, other vascular constructs,
perhaps even in neural systems, this is a simple way to have a big impact on
the collective communication of cells,” Lieber says. “A lot of people are going
to be jumping on this.”