10-01 Rice University carbon nanotube fiber

[Image above] Rice University professor Matteo Pasquali (left) and cardiologist Mehdi Razavi of the Texas Heart Institute check a thread of carbon nanotube fiber invented in Pasquali’s lab. They are collaborating on a method to use the fibers as electrical bridges to restore conductivity to damaged hearts. Credit: Texas Heart Institute; Rice University

When I was 27 years old, my heart decided that the average 115,000 beats per day just wasn’t going to cut it anymore.

After a few months of being assessed by doctors and hooked up to countless electrodes, leads, wires, and devices, I was diagnosed with premature ventricular contractions (PVCs). Cardiologists couldn’t find any underlying reason why my heart was drumming out an extra 60,000 beats per day—a whopping ~175,000 total beats daily—it just was, consistently and constantly. 

Those PVCs felt like my heart was constantly skipping a beat. Yet they are actually extra beats that disturb the heart’s normal “thump-thump…thump-thump…” rhythm.

Those extra beats trace back to cardiac cells that suddenly decide they want to march to their own drum—the cells go rogue and fire their own electrical signals, a function normally relegated to only a select set of cells located in your heart’s sinoatrial node.

PVCs are relatively common, and in isolated instances they can be completely benign. But in my case, they were happening so frequently and so consistently that they would have eventually worn out my heart over time.

So my cardiologist suggested that I undergo cardiac ablation, a procedure that uses a catheter snaked up into the heart to kill, or ablate, those rogue cells. 

During the procedure, my cardiologist used a magnetic field to carefully guide the catheter—inserted into a large blood vessel in my thigh—up into my heart. There, he steered the catheter tip to my rogue heart cells, where it used radiofrequency to deliver enough energy to destroy the cells—eliminating the extra beats and locally scarring my cardiac tissue. 

Luckily for me, the procedure was a success, returning my heart to a normal daily rhythm.

Today my heart is still steadily drumming along, only intermittently interrupted by an isolated PVC here or there. But sometimes I think about that small patch of scar tissue, wondering if it will ever negatively impact my heart’s function.

Scar tissue on the heart is certainly a concern because heart tissue, unlike many other tissues in your body, largely does not repair itself. So if a damaged area is large enough, it can impede the heart’s ability to conduct an electrical signal and thus beat properly.

And once cardiac tissue is damaged, there is little that can be done clinically to restore its function. 

New potential for action potentials

But researchers at Rice University and their international colleagues have an interesting new solution—unlike other therapeutic approaches to restore or fix the damaged cardiac tissue itself, the team developed a novel material solution to bypass a damaged area altogether.

The approach uses bundles of aligned carbon nanotubes (CNTs) spun into a thread-like fiber, called CNT fibers (CNTfs). 

CNTs, single-walled hollow cylinders made of carbon atoms, are a familiar material here on Ceramic Tech Today—we’ve written about CNT-coated fibers that keep their coolsupercapacitors made out of CNT yarn, and methods to cook up CNTs from common household products, for just a few examples.

But CNTfs are different. In previous work, the Rice researchers developed an industrially scalable process to spin CNTs into long, robust, yet flexible fibers called CNTfs. This wet-spinning technique combines both high-quality CNT precursors dissolved in liquid and a process to better align the CNTs as they are spun into fibers, resulting in a stronger and more flexible form.

Flexible, conductive fibers made of carbon nanotubes. Credit: Texas Heart Institute, Rice University

“We finally have a nanotube fiber with properties that don’t exist in any other material,” lead researcher Matteo Pasquali, professor of chemical and biomolecular engineering and chemistry at Rice, said in the original press release. “It looks like black cotton thread but behaves like both metal wires and strong carbon fibers.” 

You can see the fibers in action in this video.

Pasquali says this CNTf fabrication process provides a way to translate the nanoscale properties of CNTs into a macroscopic, engineered form with real-world applications.

Those potential applications include as electrical interfaces with the braincochlear implants, and flexible antennas, as well as automotive and aerospace applications. 

But another interesting application is the potential to restore electrical conduction to damaged heart tissue. In an email, Pasquali explains CNTfs are particularly suited for this application because of their unique combination of properties, which include

  • Good electrical conductivity—on par with platinum-iridium—so they transmit the signal well along their length,
  • High mechanical strength, so they do not break under peak load,
  • High flexibility, so they can be sutured on tissue and will not scar the tissue as it moves,
  • High resistance to flexural fatigue, so they do not break under cyclic load, and
  • Low interfacial impedance, so they can capture and effectively deliver electrical signals.

“In the past, multiple materials had to be combined to attain both electrical conductivity and effective contacts,” Pasquali notes in a new Rice press release. “These fibers have both properties built in by design, which greatly simplifies device construction and lowers risks of long-term failure due to delamination of multiple layers or coatings.” 

Putting CNTfs to the test

New research from the Rice team as well as scientists at the Texas Heart Institute tested the ability of these flexible, conductive CNTfs to directly affix to cardiac tissue to determine their biocompatibility as well as their ability to restore electrical function to damaged tissue. Using CNTfs insulated with a layer of polymer and with the ends stripped to function as electrodes, the team tested the materials in animal studies with sheep and rodent hearts.

The results are promising—surgically sewing CNTfs across areas of damaged, non-conductive heart tissue can restore conduction from one side of the tissue to the other. The CNTfs function as a conductive bridge, helping electrical signals span across damaged areas of tissue.

“Instead of shocking and defibrillating, we are actually correcting diseased conduction of the largest major pumping chamber of the heart by creating a bridge to bypass and conduct over a scarred area of a damaged heart,” Mehdi Razavi, cardiologist at Texas Heart Institute who co-led the study with Pasquali, says in the release.

Credit: Illustration by James Philpot/Texas Heart Institute; Rice University

Importantly, the CNTfs implanted on heart tissue also developed good interfacial contact with the tissue itself, which is critical to ensure that the materials continue to conduct and propagate electrical signals through the tissue over time. 

“Carbon nanotube fibers have the conductive properties of metal but are flexible enough to allow us to navigate and deliver energy to a very specific area of a delicate, damaged heart,” Razavi adds in the release.

The team’s recent work also demonstrated that CNTfs are biocompatible (up to a few months). The research represents a first step to exploring the possibility of CNTfs to repair conduction defects in human hearts, although several questions will need to be answered first. 

For instance, what is the optimal length and width of the fibers and how much electricity do they need to conduct? Are the fibers strong enough to keep a heart beating across a lifetime? And, importantly, are they biocompatible in humans, especially long-term?

Even if CNTfs do not offer a perfect solution for human hearts, the overall strategy could potentially be adapted for alternate materials. “Other recently developed fibers with high surface area (such as fibers of graphene or other conductive nanomaterials) can also potentially achieve the mechanical and electrical properties needed as implantable materials for electrical bridging of tissues,” the authors write in the paper.

And from someone who’s experienced electrical conduction abnormalities in the past, that possibility is one I will take to heart.

The open-access paper, published in Circulation: Arrhythmia and Electrophysiology, is “In vivo restoration of myocardial conduction with carbon nanotube fibers” (DOI: 10.1161/CIRCEP.119.007256).