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3D bioprinting still has a lot of issues that need to be worked out before we can see anything like a 3D printed organ transplant. One issue is figuring out how to grow blood vessels in printed or engineered tissue, but researchers at Penn State have found an alternative to that idea, creating tissues with micropores that allow nutrient and oxygen diffusion into the core.

Ibrahim T. Ozbolat

“One of the problems with fabrication of tissues is that we can’t make them large in size,” said Ibrahim T. Ozbolat, Associate Professor of Engineering Science and Mechanics. “Cells die if nutrients and oxygen can’t get inside.”

Creating tissue building blocks with micropores is an alternative to vascularization, or growing blood vessels inside the tissue, according to the researchers. They refer to the building blocks as “porous tissue strands.” They began with stem cells derived from human fat and mixed them with sodium alginate porogens. Sodium alginate, which is derived from seaweed, can be printed into tiny particles that leave holes, or pores, behind in the fabric of the tissue when dissolved. The researchers used the stem cells and sodium alginate to 3D print strands of undifferentiated tissue, which were then combined, by 3D printing them next to and on top of each other, to form patches of tissue.

The researchers then exposed the tissue to the chemical cocktail that causes stem cells to differentiate, allowing the cells to turn into bone or cartilage. The pores allow the fluid to flow to all of the stem cells. According to the researchers, the strands were able to maintain 25 percent porosity and 85 percent pore connectivity for at least three weeks.

“These patches can be implanted in bone or cartilage, depending on which cells they are,” said Ozbolat. “They can be used for osteoarthritis, patches for plastic surgery such as the cartilage in the nasal septum, knee restoration and other bone or cartilage defects.”

Cartilage tends to be easier to produce than bone because in the human body, cartilage does not have blood vessels running through it. Some bone is naturally porous, however, so porosity in engineered tissue means greater potential for repairing or replacing natural bone. Only tiny patches of tissue can currently be made, but they are still easier to fabricate than growing artificial tissue on scaffolding.

The research was documented in a paper entitled “Porous tissue strands: avascular building blocks for scalable tissue fabrication.” The work has a lot of potential for bone and cartilage regeneration, and the researchers are also considering applying their technique to muscle, fat and other tissues as well.

Authors of the paper include Yang Wu, Monika Hospodiuk, Weijie Peng, Hemanth Gudapati, Thomas Neuberger, Srinivas Koduru, Dino J. Ravnic and Ibrahim T. Ozbolat.

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