Picture: Brett Compton, University of Tennessee
Researchers with participation from the University of Hawaiʻi at Mānoa have presented a comprehensive overview of 3D printing processes with paste-like materials. The review in the Annual Review of Fluid Mechanics brings together several decades of research and is intended to serve as a basis for planning direct ink writing processes more reliably, from prototyping through to house and tissue printing.
“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.”
The focus is on direct ink writing (DIW), in which paste-like “inks” are continuously extruded through a nozzle – similar to piping icing. The composites used can contain living cells, ceramic particles, polymers or concrete components.
“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.”
The review identifies three critical phases of the process. First, the ink must flow through the nozzle without clogging – a problem that becomes more severe in fiber- or particle-filled systems.
“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.”“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.
Open questions remain in particular for highly filled pastes, which are needed for load-bearing, functional components. The article discusses approaches such as on-demand curing materials that respond to light or temperature, as well as nozzle designs that optimize shear profiles and pressure losses.
“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.”
Sauret sees the consolidation of previously scattered findings from medicine, chemistry and civil engineering as the basis for a shared fluid-mechanics framework that is intended to make DIW more robust and more widely applicable.
Subscribe to our Newsletter
3DPresso is a weekly newsletter that links to the most exciting global stories from the 3D printing and additive manufacturing industry.
