Gold Nanowires Offer Breakthrough In Cardiac Patches

Researchers at Massachusetts Institute of Technology (MIT) and Children´s Hospital Boston have developed cardiac patches using gold nanowires, which could create parts of tissue whose cells beat in time, mimicking the way the natural heart muscle works, MIT reported on Monday.
The breakthrough, which was published this week in the journal Nature Nanotechnology, could someday help those who have suffered a heart attack.
The research improves on existing cardiac patches, which fall short of achieving the level of conductivity needed to ensure a smooth, continuous “beat” throughout a large tissue, MIT said.
“The heart is an electrically quite sophisticated piece of machinery,” said 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 MIT News Office quoted her as saying.
The innovative 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 said.
The researchers said they believe the technology may ultimately result in implantable patches that would replace tissue that´s been damaged in a heart attack.
The current technique for building new tissue typically involves using miniature scaffolds resembling porous sponges to organize cells into functional shapes as they grow to build new tissue.
However, these scaffolds have usually been made from materials with poor electrical conductivity.  This is significant problem when creating cardiac cells, which rely on electrical signals to coordinate their contraction.
“In the case of cardiac myocytes in particular, you need a good junction between the cells to get signal conduction,” said co-first author Brian Timko, a MIT postdoc student.
But the scaffold acts as an insulator, blocking signals from traveling much beyond a cell´s immediate neighbors, he explained.
This makes it virtually impossible to get all the cells in the tissue to beat together as a unit.
To solve the problem, Timko and co-author Tal Dvor, a former MIT postdoc student now at Tel Aviv University in Israel, designed a 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 said.
“You can grow them to be a couple microns long, which is more than enough to pass through the walls of the scaffold.”
The researchers used alginate — an organic gum-like substance that is often used for tissue scaffolds — as a base material.  Then 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.  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 said.
There, they observed a significant improvement among cells grown on the composite scaffold, finding that he range of signals conduction improved by about three orders of magnitude.
“In healthy, native heart tissue, you´re talking about conduction over centimeters,” Timko said.
This is a significant improvement over conventional methods, in which tissue grown on pure alginate showed conduction over only a few hundred micrometers.
By comparison, the combination of alginate and gold nanowires achieved signal conduction over a scale of “many millimeters,” Timko noted.
“It´s really night and day. The performance that the scaffolds have with these nanomaterials is just much, much better,” Kohane added.
The researchers plan to conduct studies in vivo to determine how the composite-grown tissue functions when implanted into live hearts.
In addition to implications for heart-attack patients, the current research “opens up a bunch of doors” for engineering other types of tissues, Kohane said.

Image 1: A scanning electron microscope (SEM) image of nanowire-alginate composite scaffolds. Star-shaped clusters of nanowires can be seen in these images. Image courtesy of the Disease Biophysics Group, Harvard University
Image 2: A wider SEM image of the nanowire-alginate composite scaffolds. Image courtesy of the Disease Biophysics Group, Harvard University

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