Harvard John A. Paulson School of Engineering and Applied Sciences
A new rotational, multi-material 3D printing process has been developed by a team of researchers across different institutes at Harvard University.
The team was looking to mimic the helical structures that constitute biological systems, and create a method of 3D printing that would allow for the design of structures that are able to contract.
The team consisted of researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Wyss Institute for Biologically Inspired Engineering at Harvard University.
In the human body, proteins assemble into helical filaments to allow for the contraction of muscles. Plants can change shape due to the helical cellulose fibres within the cell walls. Materials in nature are rarely straight.
The team of researchers developed a 3D printing process to mimic this and used it to design and fabricate artificial muscles and springy lattices for use in soft robotics and structural applications.
“Our additive manufacturing platform opens new avenues to generating multifunctional architected matter in bio-inspired motifs,” said Jennifer Lewis, the Hansjorg Wyss Professor of Biologically Inspired Engineering at SEAS and senior author of the study, and Core Faculty member of the Wyss Institute.
The printhead created by the team consists of four cartridges, each containing different materials. The inks are fed through a nozzle that allows multiple materials to be printed at once. The nozzle rotates which makes the extruded inks form the filament with embedded helical features.
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“Rotational multi-material printing allows us to generate functional helical filaments and structural lattices with precisely controlled architecture, and ultimately, performance,” said Natalie Larson, postdoctoral fellow at SEAS and first author of the study.
The team printed artificial muscles in the form of helical ‘dielectric elastomer actuator filaments’ that can contract under an applied voltage, in collaboration with David Clarke, the Extended Tarr Family Professor of Materials. The conductive electrodes form intertwining helices encapsulated in a soft elastomer matrix.
According to the team, by tuning how tightly the helical electrodes are coiled, a contractile response of the actuators can be programmed.
Structural lattices with varying stiffness were also designed, by embedding stiff helical springs within a soft, compliant matrix, similar to how springs work in a soft mattress. The team says that the overall stiffness of the material can be tuned by tuning the tightness of the springs in the matrix.
Potential applications for the structural lattices include joints or hinges in soft robotic systems, according to the team.
Larson added: “By designing and building nozzles with more extreme internal features, the resolution, complexity, and performance of these hierarchical bio-inspired structures could be further enhanced.”
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