A comprehensive review of the challenges in printing with paste-like materials and how understanding the underlying physics could improve manufacturing reliability has been co-authored by a University of Hawaiʻi at Mānoa mechanical engineering researcher. The paper, published in the Annual Review of Fluid Mechanics , brings together decades of research to create a roadmap for printing everything from artificial tissues to buildings.
"Right now, 3D printing leans heavily on experience and rules of thumb, slightly modifying recipes and settings until things work," said Tyler R. Ray , associate professor in the UH Mānoa College of Engineering . "We want to provide engineers the tools needed to complement experience with physics-based predictions."
Direct-ink writing
The printing method examined, called direct-ink writing (DIW), works like decorating a cake. The "frosting" must flow smoothly through the nozzle, then instantly hold its shape without melting or collapsing. The method covers a wide variety of printable "inks" that can be living cells, concrete, ceramics or polymer mixtures, opening possibilities to make objects and forms that regular plastic 3D printing cannot achieve.
"The paste-like materials that are used in direct-ink writing are complex fluids, remarkable materials that display both liquid- and solid-like behavior, depending on their surroundings," said Alban Sauret, associate professor at the University of Maryland and lead author. "Such materials have been studied for decades, but DIW presents new and challenging constraints that require a deeper understanding of how these complex fluids behave during printing."
Make-or-break moments
The review identifies three make-or-break moments where physics determines success or failure. First, the material must flow through the nozzle without clogging, which is a major problem when the ink contains particles or fibers for added strength.
"We've all experienced a clogged pen or ketchup bottle," said Brett G. Compton, associate professor at the University of Tennessee. "If building precise 3D forms using complex fluid weren't challenging enough, imagine the fluid is filled with ceramic particles, cells or fibers, and must be squeezed through a tiny nozzle without clogging the flow or damaging the cells."
Second, as the material exits the nozzle, it can break apart, coil, or develop wobbles that ruin the print. Finally, after deposition, the material must be solid enough to hold its shape but liquid enough to bond with previous layers. To successfully print an object, one must perform a delicate balancing act across these three areas. The fact that DIW asks so much of its ink, and that its ink compositions range so broadly, means many unanswered questions remain, especially for the particle-filled materials that enable stronger, more functional prints.
"We're still in a mode of discovery where each answer provides new questions to ask and new areas to explore, which was what brought the three of us together in the first place," Ray noted.
The review also highlights promising innovations such as materials that harden on command when exposed to light or heat, and cleverly designed nozzles that reduce clogging.
"The fact is, there's excellent DIW research out there, but it has been spread out across fields that don't usually overlap—think medicine, chemistry and civil engineering," Sauret said. "With this review, we're hoping to present a cohesive and fundamental fluid mechanics framework that highlights universal challenges and inspires new interdisciplinary research to make the technology more reliable and accessible, regardless of where it's being used."
The research was supported by the National Science Foundation, Air Force Office of Scientific Research, National Institutes of Health and Honeywell Federal Manufacturing & Technologies, LLC. Read the full report .
The post Building houses and growing tissue: Overcoming physics problems in 3D printing first appeared on University of Hawaiʻi System News .
