The ability to integrate disparate materials and properties within printed objects is the next frontier in 3D printing. Harvard University researchers have designed new multimaterial printheads that mix and print concentrated viscoelastic inks, enabling simultaneous control of composition and geometry during printing. Using active mixing and fast-switching nozzles, the printheads change material composition on the fly and could pave the way for entirely 3D-printed wearable devices, soft robots, and electronics.

Most mixing approaches are passive, wherein two streams of fluids converge into a single channel where they undergo diffusive mixing. Harvard University's active mixer efficiently mixes a wide range of complex fluids by using a rotating impeller inside a microscale nozzle. The active printheads pattern heterogeneous materials in three dimensions.

The researchers demonstrated that silicone elastomers can be seamlessly printed into gradient architectures composed of soft and rigid regions. The structures may find potential application in flexible electronics, wearable devices, and soft robotics. Reactive materials, such as two-part epoxies, were also printed, and conductive and resistive inks could be mixed on demand to embed electrical circuitry.