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46 PCB007 MAGAZINE I NOVEMBER 2018 by Trent Knoss, University of Colorado Boulder University of Colorado Boulder engineers have developed a 3D printing technique that allows for localized control of an object's firm- ness, opening up new biomedical avenues that could one day include artificial arteries and or- gan tissue. The study outlines a layer-by-layer printing method that features fine-grain, programma- ble control over rigidity, allowing researchers to mimic the complex geometry of blood ves- sels that are highly structured, yet must remain pliable. The paper was published in the jour- nal Nature Communications. The findings could one day lead to better, more personalized treatments for those suffer- ing from hypertension and other vascular dis- eases. "The idea was to add independent mechan- ical properties to 3D structures that can mim- ic the body's natural tissue," said Xiaobo Yin, an associate professor in CU Boulder's Depart- ment of Mechanical Engineering and the senior author of the study, "This technology allows us to create microstructures that can be custom- ized for disease models." Hardened blood vessels are associated with cardiovascular disease, but engineering a so- lution for viable artery and tissue replacement has historically proven challenging. To over- come these hurdles, the researchers found a unique way to take advantage of oxygen's role in setting the final form of a 3D-printed struc- ture. Yonghui Ding, a postdoctoral researcher in mechanical engineering and the lead author of the study, said oxygen usually causes incom - plete curing. "Here, we utilize a layer that al- lows a fixed rate of oxygen permeation," he said. By keeping tight control over oxygen migra- tion and its subsequent light exposure, the re- searchers have the freedom to control which areas of an object are solidified to be harder or softer all while keeping the overall geome- try the same. "This is a profound development, and an encouraging first step toward our goal of creating structures that function as a healthy cell should," Ding said. As a demonstration, the researchers print - ed three versions of a simple structure: a top beam supported by two rods. The structures were identical in shape, size, and materials, but printed with three variations in rod rigidity: soft-soft, hard-soft, and hard-hard. The hard - er rods supported the top beam while the soft- er rods allowed it to fully or partially collapse. The researchers repeated the feat with a small Chinese warrior figure, printing it so that the outer layers remained hard while the inte - rior remained soft, leaving the warrior with a tough exterior and a tender heart, so to speak. The tabletop-sized printer is currently capa- ble of working with biomaterials down to a size of 10 microns, or about one-tenth the width of a human hair. The researchers are optimistic that future studies will help improve the capa- bilities even further. "The challenge is to create an even fin- er scale for the chemical reactions," said Yin, "But we see tremendous opportunity ahead for this technology and the potential for artificial tissue fabrication." Additional co-authors of the new study in - clude Hang Yin, Yao Zhai, and Associate Pro- fessor Wei Tan of mechanical engineering. The National Science Foundation and the National Institutes of Health provided funding for the re- search. PCB007 3D Bioprinting Artificial Blood Vessels and Organ Tissues Photo: A new 3D printing technique could lead to new biomedical opportunities. (Source: UC Boulder)