Researchers from North Carolina State University recently developed a technique that uses ultrasound to align cells in 3D bioprinted gels. Using this method, the team aims to bolster the quality of these tissues compared to the structures they are designed to replace. Ultimately, the goal is for these 3D printed tissues to treat common injuries.
“We’ve reached the point where we are able to create medical products, such as knee implants, by printing living cells,” said corresponding author Rohan Shirwaiker, associate professor in NC State’s Edward P. Fitts Department of Industrial & Systems Engineering. “But one challenge has been organizing the cells that are being printed, so that the engineered tissue more closely mimics natural tissues.”
The scientists built an ultrasound chamber that imposes ultrasound waves through the 3D printing area containing living cells. These waves travel through the printing region and are reflected back to their source to create a “standing ultrasound wave”. This process herds the cells into rows that align with the ultrasound wave path.
One current limitation of putting cells into a 3D printed structure is that they end up aligning in a random orientation. Being that these structures are often designed to replicate specific structures of optimal strength, it is best for the cells to line up in a specific direction. By using an ultrasound device, these researchers have found a way to align these cells in such a manner.
One limitation of simply dumping cells into a 3D printed structure is that their orientation ends up random. It’s usually best for cells to line up in a certain direction, as that optimizes the strength, flexibility, and other characteristics of the resulting tissues.
“We’ve now developed a technique, called ultrasound-assisted biofabrication (UAB), which allows us to align cells in a three-dimensional matrix during the bioprinting process,” said Shirwaiker. “This allows us to create a knee meniscus, for example, that is more similar to a patient’s original meniscus. To date, we’ve been able to align cells for a range of engineered musculoskeletal tissues.”
To demonstrate their UAB technique, the researchers successfully printed a knee meniscus in the same semilunar arc shape seen in the natural structure.
“We were able to control the alignment of the cells as they were printed, layer by layer, throughout the tissue,” Shirwaiker explained. “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.”
Touching on one of the technique’s shortcomings, Shirwaiker noted that some combinations of ultrasound parameters resulted in cell death. He claims that this finding is of importance, being that it gave them an understanding of what can be done to improve tissue performance and what must be avoided as well. To address this, the researchers have generated computational models that let users predict the performance of ultrasound parameters prior to initiating the biofabrication process.
The researchers note that a big advantage of the technique is it’s cost efficiency.
“There’s a one-time cost for setting up the ultrasound equipment – which can use off-the-shelf technology” he said. “After that, the operating costs for the ultrasound components are negligible. And the UAB technique can be used in conjunction with most existing bioprinting technologies.”
— 3D Printing News (@3DPrintMaven) April 11, 2019