Optical image
(left) and schematic illustration (right) of impeller-based mixing nozzle
MULTIMATERIAL 3D PRINTING VIA ACTIVE MIXING AND SWITCHING
PRINTHEADS
(September 21, 2015) 3D
printing is revolutionizing the production of lightweight structures, soft
robots and flexible electronics, but the technology struggles with complex,
multimaterial integration.
To print a flexible device, including the electronics, a 3D
printer must be able to seamlessly transition from a flexible material that
moves with your joints for wearable applications, to a rigid material that
accommodates the electronic components. It would also need to be able to embed
electrical circuitry using multiple inks of varying conductivity and
resistivity, precisely switching between them. And, it would be ideal to do all
of this without the stopping the printing process.
The ability to integrate disparate materials and properties
within printed objects is the next frontier in 3D printing.
Towards this objective, Harvard researchers have designed
new multimaterial printheads that mix and print concentrated viscoelastic inks
that allow for the simultaneous control of composition and geometry during
printing. Using active mixing and
fast-switching nozzles, these novel printheads change material composition on
the fly and could pave the way for entirely 3D-printed wearable devices, soft
robots, and electronics.
Optical image of
the impeller-based active mixer. 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.
(photo by Thomas
Ober, Harvard SEAS/Wyss Institute)
The research was led by Jennifer A. Lewis, 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 Wyss Institute for Biologically Inspired Engineering at Harvard. The work
was published in The Proceedings of the National Academy of Sciences (PNAS).
Mixing complex fluids is fundamental for printing a broad
range of materials. But most mixing
approaches are passive, wherein two streams of fluids converge into a single
channel where they undergo diffusive mixing. This method works well with
low-viscosity fluids, but is ineffective with high-viscosity fluids, like gels,
especially in small volumes over short timescales.