Jun 27, 2016 | By Alec

Numerous 3D bioprinting studies are ongoing at the moment, and most are working on their own unique ways to 3D print cell structures, which might one day be used to make transplantable organs and tissue. But all are faced with one significant obstacle: how do you 3D print a scaffolding in which the cells can live and grow? While most solutions revolve around embedding stem cells in a hydrogel structure, a team of researchers from Penn State University might have found a superior solution to 3D print cartilage. Involving the injection of cells into alginate to form 3D printable strands of cartilage, it produces tissue with far more desirable mechanical properties.

This new technique was developed by a team of engineers led by Ibrahim T. Ozbolat, associate professor of engineering science and mechanics. It also involved PhD graduate Yin Yu, graduate student Kazim K Moncal, visiting scholar in engineering science and mechanics Weijie Peng and associate professors Iris Rivero and James A. Martin. Funding was secured from The National Science Foundation, Grow Iowa Value Funds and the China Scholarship Fund.

As Ozbolat explained, cartilage is a prime target for 3D bioprinting efforts, because it only consists of one cell type and has no blood vessels within the tissue. This makes it very easy to scale up, once you get the basics right. What’s more, it’s also a tissue that is causing a lot of problems for patients, as it cannot repair itself – it simply remains damaged for the rest of your life. “Those who have osteoarthritis in their joints suffer a lot. We need a new alternative treatment for this,” he says.

But as the professor argues, there’s a fundamental problem with how most cartilage 3D printing efforts are being conducted. Almost universally, this is done by embedding the cartilage cells in a hydrogel scaffolding. The material itself is made from polymer chains and water (90 percent of it). “Hydrogels don't allow cells to grow as normal,” said Ozbolat. “The hydrogel confines the cells and doesn't allow them to communicate as they do in native tissues.” These limitations affect the tissue’s mechanical integrity, while the hydrogel can also degrade and produce compounds that are detrimental to cell growth.

Another solution was therefore needed, which Ozbolat and his research team found in alginate. The material itself is an algae extract, and is shaped into tubes of 3 to 5 one hundredths of an inch in diameter. Cartilage cells are injected into those tubes, and serve as the scaffolding for about a week of growing. During that period, the cells adhere to each other, but not to the alginate – meaning they’re easy to remove as a strand of cartilage cells. The cells itself are derived from cartilage or stem cells differentiated into cartilage cells, and can come from each and every patient. This technique is also detailed in the latest edition of Scientific Reports.

These strands of cartilage are perfect for 3D printing, replacing any bio-inks that might be used. With a special type of nozzle that can feed the strand, a 3D bioprinter can create layered structures of the material in any pattern. After about half an hour, the cartilage patch that is formed self-adheres enough for it to be moved to a petri-dish, in which the cartilage can grow with the help of nutrients. Theoretically, this then grows into full cartilage tissue.

The great thing about this technique is that the unwieldly scaffolds are completely removed from the equation. “We can manufacture the strands in any length we want,” said Ozbolat. “Because there is no scaffolding, the process of printing the cartilage is scalable, so the patches can be made bigger as well. We can mimic real articular cartilage by printing strands vertically and then horizontally to mimic the natural architecture.”

While the 3D printed cartilage is not as strong as natural cartilage, its mechanical properties are far superior to that of hydrogel-based prints or damaged cartilage. It also somewhat resembles native cow cartilage. But Ozbolat believes that, over time, they can begin to rival natural cartilage. That natural cartilage is formed under pressure from the joints, and exposing 3D printed cartilage to mechanical pressure could improve the material’s properties. Could this be the 3D bioprinting breakthrough we’ve been waiting for?



Posted in 3D Printing Technology



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