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t m c » p u l s e | j u n e 2 0 1 9 20 One Step Closer to printing B y S h a n l e y P i e r c e Bioprinting fully functioning human organs would help address the organ donation shortage in the United States A breakthrough technique developed by a team of bioen- gineers at Rice University and the University of Washington brings 3D-printed organs one step closer to reality. One of the biggest challenges in bioprinting has been recreating the complex architecture of vascular networks that supply blood and nutrients to densely populated tissues. "In biology, you have this idea that form follows function. The form of a biological structure is an evolutionary consequence of its function," said Jordan Miller, Ph.D., assistant professor of bioengineer- ing and founder of the Advanced Manufacturing Research Institute at Rice University. "In bioengineering, we're asking the converse question: Will function follow form? What we're trying to do is build living tissues that can replicate some of the architecture that we observe in the body." To do that, scientists needed to get creative. Developed by a team of bio- engineers led by Miller and Kelly Stevens, Ph.D., assistant pro- fessor of bioengineering at the University of Washington College of Engineering, this new bioprint- ing technique—"stereolithography apparatus for tissue engineering," or SLATE for short—enables scientists to create intricate multivascular networks that mimic those found in the body that are essential to deliv- ering blood, oxygen and nutrients to organs and tissue. "This is a much more accurate representation of human tissue because some of our organs are more complicated in terms of their architecture," Miller explained, citing the lungs, liver, kidney and pancreas. "They don't just have one vessel architecture; they have multiple independent vessel architectures that are occupying the same organ but never touch. It's important that they never touch. If that happened in your lung, you would get blood in your airway or air in your bloodstream. Both of those are fatal." One recent prototype, a lung-mimicking air sac made of a hydrogel material, measures 4.5 mil- limeters at the widest point—smaller than a penny—and contains blood vessels 300 microns in diameter that do not touch. ➟ Rice University bioengineers Bagrat Grigoryan, Jordan Miller, Ph.D., and Daniel Sazer worked with collaborators to create a bioprinting technique that could accelerate technology for 3D-printing replacement organs and tissues. Credit: Left, Jeff Fitlow/Rice University; Right, Bagrat Grigoryan and Jordan Miller b i o p r i n t i n g