Eyeworld

EW NEWS & OPINION 26 November 2017 by EyeWorld Contributing Reporter 3-D printed corneas Dr. Zakaria's lab is working toward full-thickness 3-D prints of the cornea. Source: Bert Van den Bogerd 3-D printed corneas may be the future of corneal transplants. Could they be the answer to the donor cornea shortage? I magine a future without eye banks, where patients need- ing new corneas can have them 3-D printed using their own cells, and the corneas are tailor-made according to their exact geometric specifications so patients can achieve perfect vision without the need for long-term reliance on immunosuppressants. Researchers in Belgium are working to make this a reality. A group at the University of Antwerp in collaboration with the Catholic University of Leuven has been work- ing on creating 3-D printed corneas since 2014. "What we are trying to do is cre- ate a cornea that would mimic what we see in vivo," said Nadia Zakaria, MD, PhD, University of Antwerp. She explained that the cornea is ideal for mimicking ex vivo because "the spatial orientation of its layers and the way the collagen fibers are parallel to each other allow the cor- nea to be biochemically robust and quite tough." The fact that it's without blood vessels and simpler than a lot of the other organ tissues being tissue engineered, like the kidney, helps, she said. "To create something so com- plex and large and for it to be func- tioning is more difficult," Dr. Zakaria said. "But if we look at the cornea, it's a much simpler tissue, and it is at the surface so it would be easier to follow up on whether it functions correctly. It seems to be the ideal tis- sue to start tissue engineering with." Still, the process of creating a 3-D print of a cornea is complex, requiring a multidisciplinary team with different expertise. Two full- time PhD students, Steffi Matthys- sen, University of Antwerp, and Rory Gibney, University of Leuven, are working on this project. The right tools The first consideration for the team was acquiring the appropriate mate- rial for the research. "One of the early problems was sourcing recombinant human colla- gen," Dr. Zakaria said. Each of the recombinant human collagen has pros and cons, she said. "So we've been looking at different types of collagen and how they orient as well." Separate from the project, her team is working to develop collagen mimicking peptides with May Grif- fith, PhD, Department of Ophthal- mology, University of Montreal, and her team. Just as important in the re- search is the technical aspect of 3-D printing. Dr. Zakaria explained that there are extrusion-based 3-D printers, where material "squeezes" through a nozzle and layers are built upon each other. There are also aerosol 3-D jet printers, which are used for printing electronics because of their ability to print with very high resolution. The latter is what the research team is currently using. "We want to go with something that has a very high resolution rather than extrusion-based printers because the resolution is just not there, so it's bulky and the tissue would not mimic anything close to what we want for good vision," she said. When they first started printing with the collagen "bio-ink," their collaborators, Eleonora Ferraris, PhD, Department of Mechanical Engineering, and her team at the Catholic University of Leuven, had to "modify the 3-D printer to be able to print effectively and reproducibly with the collagen," Dr. Zakaria said. It was the first time this had been done. The aerosol 3-D jet print- er was designed to print electronics, not biological samples. "The cornea in itself is only about half a millimeter thick and 9 mm in diameter, but printing with high resolution means that in order to obtain a sample of about 100 mi- crons, approximately 300 layers of bio-ink needs to be deposited, which can take up to 2 hours of machine time," Dr. Zakaria said. "Being able to print is one thing, but the colla- gen also needs to be crosslinked so that it has good mechanical proper- ties and can withstand the intraocu- lar pressure without being too brittle or losing its biocompatibility." The team had to work in close collaboration with biomaterial specialist Jennifer Patterson, PhD, and her team at the Department of Materials Engineering, Catholic

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