Sep 22, 2015 | By Kira

A team of researchers has invented a method for integrating disparate materials and properties—including flexible and rigid materials, and conductive and resistive inks—into a single 3D printed object, opening up new possibilities for entirely 3D printed wearable devices, soft robots and electronics. These new multi-material printerheads are based on active mixing technology, wherein a range of complex fluids are combined by using a rotating impeller inside a microscale nozzle.

While we have seen a rise PCB 3D printer technology, as well as some very recent 3D printed wearables that embed electronic components, current 3D printing technology struggles with multi-material integration—that is, the seamless and precise transition between flexible materials, rigid materials, and electrical circuitry without stopping the printing process. This is because most approaches to mixing complex fluids are passive: two streams of fluids converge into a single channel where they undergo diffusive mixing. This method works well enough for low-viscosity fluids, but is ineffective with high-viscosity liquids such as gels.

The new research, led by Professor Jennifer A. Lewis, instead uses active mixing and fast-switching nozzles, allowing for the printing of concentrated viscoelastic inks and the simultaneous control of composition and geometry during printing. With this method, rather than the fluids converging in a single stream, each fluid enters the mixing chamber through a separate inlet and is mixed in a narrow gap by an impeller rotating at a constant rate.

Lewis is the Hansjörg Wyss Professor of Biologically Inspired Engineering at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and a Core Faculty Member at the Ywss Institute for Biologically Inspired Engineering at Harvard. She designed the active mixing technology alongside Thomas Ober, postdoctoral research scholar at the Wyss Institute, and Daniele Foresti, the Society in Science Branco Weiss postdoctoral fellow.

Prof. Jennifer A. Lewis

"Passive mixtures don't guarantee perfectly mixed materials, especially highly viscous inks," said Ober. "We developed a rational framework -- and verified it experimentally -- for designing active microfluidic mixers that can mix a wide variety of materials."

The applications of active mixing technology within 3D printing are significant. The team demonstrated that silicone elastomers can be seamlessly printed into gradient architectures composed of soft and rigid regions (meaning that for wearable devices, flexible materials that move with our bodies and joints can be combined to rigid materials that house electrical components). Reactive materials can also be printed, and conductive and resistive inks can be mixed on demand.

 Previously, the idea of mixing material systems on the fly in 3D printing was merely a concept, however Lewis’ team has made it realistic and achievable with today’s technology. The same lab also recently designed a printhead that can switch between multiple inks within a single nozzle, eliminating the need to align multiple nozzles and start and stop ink flow during the printing process.

“Together, these acting mixing and switching printheads provide an important advance for multi-material 3D printing,” said Lewis. “They allow one to programmably control both materials composition and structure at the microscale, opening new avenues for creating materials by design.”

 The research was supported by the Department of Energy Frontier Research Center on Light Material Interactions in Energy Conversion, and published in the Proceedings of the National Academy of Sciences (PNAS).



Posted in 3D Printing Technology



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