Science

Cell-herding ultrasound developed for better bioprinting

A human meniscus created via ultrasound-assisted biofabrication
A human meniscus created via ultrasound-assisted biofabrication
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A human meniscus created via ultrasound-assisted biofabrication
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A human meniscus created via ultrasound-assisted biofabrication

We've been hearing a lot lately about how living cells can be combined with polymer gels, the mix then being 3D-printed to create biological tissue for use in transplants or experimentation. Such material could soon be getting even more like the real thing, thanks to new ultrasound tech.

In natural biological tissue, the cells are aligned in distinct orientations. So far, however, this hasn't been the case with most bioprinted tissue. Led by Assoc. Prof. Rohan Shirwaiker, a team at North Carolina State University recently set out to change that. The result is a technique known as ultrasound-assisted biofabrication (UAB).

The system incorporates a chamber in which a bioprinter deposits layers of material containing living cells. While it's doing so, ultrasound waves travel from one side of the chamber to the other, then are reflected back in the direction from which they came. This creates standing ultrasound waves, where the emitted and reflected waves meet.

The nearby cells get "herded" along the length of each wave, ending up sitting in a row. By tweaking ultrasound parameters such as frequency and amplitude, it's possible to alter the manner in which the cells in each row are aligned. While this can result in bioprinted tissue that's more like the genuine article, certain ultrasound parameters can also lead to cell death, so it's important to get them right. To that end, computer models have been created, that predict the outcome of given sets of parameters.

In a demonstration of the UAB system, the researchers bioprinted a human meniscus, which is a C-shaped disc within the knee that heals very slowly (if at all) when injured. The cells within that printed meniscus were aligned in a semilunar arc, as is the case in natural menisci.

"We were able to control the alignment of the cells as they were printed, layer by layer, throughout the tissue," says Shirwaiker. "We've also shown the ability to align cells in ways that are particularly important for other orthopedic soft tissues, such as ligaments and tendons."

The university is now looking for industry partners to help commercialize the technology. Once available, it should reportedly be quite inexpensive to use, with most of the cost going into initially adding it to existing bioprinting systems.

A paper on the research was recently published in the journal Biofabrication.

Source: North Carolina State University

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