Carbon nanotubes make it possible to grow human hearts

• By Graham Templeton on February 15, 2013 at 2:40 pm
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One of the most fundamental problems with growing organs in a petri dish (metaphorically speaking) is that organs don’t grow in petri dishes. That is to say, the naturally grown organs we’d like to replace were themselves grown in and amongst organs, which were themselves grown in and amongst others.
This nature-nurture dichotomy highlights how much our genes rely on environmental constants for their mechanisms of action; all the fancy collagens in the world can’t anchor a cell to a basement membrane that isn’t there. Time and again we’ve seen admirable work in cell biology undone by the simple fact that these meticulously engineered cells are without the proper world in which to grow, and some organs have posed more problems than others. A bladder is a relatively simple thing, just a balloon with a couple of special openings. A heart, on the other hand, needs significantly more nurturing to grow up big and strong, precise enough to replace the body-grown version from which it was cloned. This week, the American Chemical Society’s journal Nano printed an article detailing the use of carbon nanotubes in a growth scaffold for rat heart cells. The result? The closest we’ve come to creating a beating heart on demand.
Heart cells share many of the problems of neurons, from a research perspective; they are woefully inept at directing their own growth through space, requiring virtually every effort be made on their behalf, and even when led to the right place require all sorts of special genetic and chemical allowances. It was once thought impossible to regrow neurons, but lately we’ve come to realize that it’s just very, very finicky. Not the least of the reasons for this is conductivity; neurons cannot work unless they somehow come to meet one another such that an electrical signal can propagate between them. Heart cells are much the same — a cluster of so-called pacemaker cells keeps the whole thing contracting as one. This requires not just that the pacemaker signal pass between the cells, but that it happens fast enough for the heart to act seemingly as one coordinated unit.
In pursuit of this, the heart has a class of myocytes that form Purkinje Fibers, long cords that ferry pacemaker signals at a rate unsurpassed in the body. When a contraction signal leaves the pacemaking cells, its order reaches the furthest cells in the heart at an imperceptibly short time after it reaches the closest ones, and so the heart cells seem to beat as one. This ability is absolutely essential to a working heart, and has proven very difficult for organ transplant researchers to overcome.
Enter carbon nanotubes. As anyone familiar with the little critters will know, their important feature is a combination of strength, flexibility, and conductivity. Some combination of these virtues has made them of import to virtually every advanced research and manufacturing sector, from space elevators to flexible computers. Now, we must add conductive tissue development to that quickly growing list. By laying the conductive carbon nanotubes coated with a growth medium, researchers were able to create a scaffold that mimicked the utility of the Purkinje Fibers. By coating the scaffold in rat cardiomyocytes, they were able to create a colony of heart cells capable of contracting properly.
This isn’t the first time science has taken on such a problem in recent times. We’ve already used heart cells to power a small and rather clumsy 3D printed biorobot, and elsewhere used 3D printing to create the sugar scaffold needed by liver cells. We’ve also made smaller steps toward printing conductive materials. As a result, it seems like only a matter of time before this innovation can even be handed off to the Next Big Thing in manufacturing — and in fact, that’s already happened. As with so much of modern research, the sheer volume of work being done has already furnished us with the next step in the series. This paper recently proved that printing gel structures with inlaid carbon nanotubes might not be necessary — predicting and possibly preempting the needs of studies such as this.
As our understanding of cell development continues to advance, it’s increasingly going to be the more mundane concerns that limit our abilities. Providing the physical scaffold for growth might seem like a trivial challenge compared to the nuances of metabolism, but it is no less vital for that. This study produced a small patch of working tissue which contracted spontaneously and as a unit, coordinated enough to swim through a growth medium. See a video here.