Sep 23, 2014 by Mike Williams Three images reveal the details of heart-defect patches created at Rice University and Texas Childrens Hospital. At top, three otherwise identical patches darken with greater concentrations of carbon nanotubes, which improve electrical signaling between immature heart cells. At center, a scanning electron microscope image shows a patchs bioscaffold, with pores big enough for heart cells to invade. At bottom, a near-infrared microscopy image shows the presence of individually dispersed single-walled nanotubes. Credit: Jacot Lab/Rice University

(Phys.org) Carbon nanotubes serve as bridges that allow electrical signals to pass unhindered through new pediatric heart-defect patches invented at Rice University and Texas Children's Hospital.

A team led by bioengineer Jeffrey Jacot and chemical engineer and chemist Matteo Pasquali created the patches infused with conductive single-walled carbon nanotubes. The patches are made of a sponge-like bioscaffold that contains microscopic pores and mimics the body's extracellular matrix.

The nanotubes overcome a limitation of current patches in which pore walls hinder the transfer of electrical signals between cardiomyocytes, the heart muscle's beating cells, which take up residence in the patch and eventually replace it with new muscle.

The work appears this month in the American Chemical Society journal ACS Nano. The researchers said their invention could serve as a full-thickness patch to repair defects due to Tetralogy of Fallot, atrial and ventricular septal defects and other defects without the risk of inducing abnormal cardiac rhythms.

The original patches created by Jacot's lab consist primarily of hydrogel and chitosan, a widely used material made from the shells of shrimp and other crustaceans. The patch is attached to a polymer backbone that can hold a stitch and keep it in place to cover a hole in the heart. The pores allow natural cells to invade the patch, which degrades as the cells form networks of their own. The patch, including the backbone, degrades in weeks or months as it is replaced by natural tissue.

Researchers at Rice and elsewhere have found that once cells take their place in the patches, they have difficulty synchronizing with the rest of the beating heart because the scaffold mutes electrical signals that pass from cell to cell. That temporary loss of signal transduction results in arrhythmias.

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Nanotubes can fix that, and Jacot, who has a joint appointment at Rice and Texas Children's, took advantage of the surrounding collaborative research environment.

"This stemmed from talking with Dr. Pasquali's lab as well as interventional cardiologists in the Texas Medical Center," Jacot said. "We've been looking for a way to get better cell-to-cell communications and were concentrating on the speed of electrical conduction through the patch. We thought nanotubes could be easily integrated."

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