An 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. Credit: Thomas Ober, Harvard SEAS/Wyss Institute
>>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.
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.
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.
So a new multimaterial printhead based on active mixing was designed. The active mixer efficiently mixes a wide range of complex fluids by using a rotating impeller inside a microscale nozzle.
They showed silicone elastomers can be seamlessly printed into gradient architectures composed of soft and rigid regions >> potential application in flexible electronics, wearable devices, and soft robotics. They also printed reactive materials, such as 2-part epoxies, which typically harden quickly when the two parts are combined. Finally, they showed conductive and resistive inks could be mixed on demand to embed electrical circuitry inside 3D printed objects.
“This printhead design eliminates the need to align multiple nozzles as well as start and stop ink flow on demand,” said James Hardin, “They allow one to programmably control both materials composition and structure at the microscale, opening new avenues for creating materials by design.” http://www.alphagalileo.org/ViewItem.aspx?ItemId=156498&CultureCode=en
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