Their method, referred to as ‘rotational 3D printing’, could have broad ranging applications. Given the modular nature of their ink designs, many different filler and matrix combinations can be implemented to tailor electrical, optical, or thermal properties of the printed objects.
“Being able to locally control fibre orientation within engineered composites has been a grand challenge,” said Jennifer Lewis, professor of biologically inspired engineering at Harvard SEAS. “We can now pattern materials in a hierarchical manner, akin to the way that nature builds.”
The key to the team’s approach is to precisely choreograph the speed and rotation of a 3D printer nozzle to program the arrangement of embedded fibres in polymer matrices. This is achieved by equipping a rotational printhead system with a stepper motor to guide the angular velocity of the rotating nozzle as the ink is extruded.
“Rotational 3D printing can be used to achieve optimal, or near optimal, fibre arrangements at every location in the printed part, resulting in higher strength and stiffness with less material,” said Brett Compton, another member of the researcher team. “Rather than using magnetic or electric fields to orient fibres, we control the flow of the viscous ink itself to impart the desired fibre orientation.”
Compton noted that the team's nozzle concept could be used on any material extrusion printing method, from fused filament fabrication, to direct ink writing, to large-scale thermoplastic additive manufacturing, and with any filler material, from carbon and glass fibres to metallic or ceramic whiskers and platelets.
The technique allows for the 3D printing of engineered materials that can be spatially programmed to achieve specific performance goals. For example, the orientation of the fibres can be locally optimised to increase the damage tolerance at locations that would be expected to undergo the highest stress during loading, hardening potential failure points.
“One of the exciting things about this work is that it offers a new avenue to produce complex microstructures, and to controllably vary the microstructure from region to region,” added researcher, Jordan Raney. “More control over structure means more control over the resulting properties, which vastly expands the design space that can be exploited to optimise properties further.”