is a co-founder of Voxel8, Inc. and Mark Skylar-Scott owns stock in Formlabs. A patent has been filed by Harvard University on this research.

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The programmable assembly of innervated LCE actuators (iLCEs) with prescribed contractile actuation, self‐sensing, and closed loop control via core–shell 3D printing is reported. This extrusion‐based direct ink writing method enables coaxial filamentary features composed of pure LM core surrounded by an LCE shell, whose director is aligned along the print path. Specifically, the thermal response of the iLCE fiber‐type actuators is programmed, measured, and modeled during Joule heating, including quantifying the concomitant changes in fiber length and resistance that arise during simultaneous heating and self‐sensing. Due to their reversible, high‐energy actuation and their resistive feedback, it is also demonstrated that iLCEs can be regulated with closed loop control even when perturbed with large bias loads. Finally, iLCE architectures capable of programmed, self‐sensing 3D shape change with closed loop control are fabricated.

SignificanceNatural composites exhibit hierarchical and spatially varying structural features that give rise to high stiffness and strength as well as damage tolerance. Here, we report a rotational 3D printing method that enables exquisite control of fiber orientation within engineered composites. Our approach broadens their design, microstructural complexity, and performance space by enabling site-specific optimization of fiber arrangements within short carbon fiber–epoxy composites. Using this approach, we have created composites with programmable strain distribution and failure as well as enhanced damage tolerance.

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Transition fronts, moving through solids and fluids in the form of propagating domain or phase boundaries, have recently been mimicked at the structural level in bistable architectures. What has been limited to simple one-dimensional (1D) examples is here cast into a blueprint for higher dimensions, demonstrated through 2D experiments and described by a continuum mechanical model that draws inspiration from phase transition theory in crystalline solids. Unlike materials, the presented structural analogs admit precise control of the transition wave’s direction, shape, and velocity through spatially tailoring the underlying periodic network architecture (locally varying the shape or stiffness of the fundamental building blocks, and exploiting interactions of transition fronts with lattice defects such as point defects and free surfaces). The outcome is a predictable and programmable strongly nonlinear metamaterial motion with potential for, for example, propulsion in soft robotics, morphing surfaces, reconfigurable devices, mechanical logic, and controlled energy absorption.

Polymer foams are cellular solids composed of solid and gas phases, whose mechanical, thermal, and acoustic properties are determined by the composition, volume fraction, and connectivity of both phases. A new high‐throughput additive manufacturing method, referred to as direct bubble writing, for creating polymer foams with locally programmed bubble size, volume fraction, and connectivity is reported. Direct bubble writing relies on rapid generation and patterning of liquid shell–gas core droplets produced using a core–shell nozzle. The printed polymer foams are able to retain their overall shape, since the outer shell of these bubble droplets consist of a low‐viscosity monomer that is rapidly polymerized during the printing process. The transition between open‐ and closed‐cell foams is independently controlled by the gas used, while the foam can be tailored on‐the‐fly by adjusting the gas pressure used to produce the bubble droplets. As exemplars, homogeneous and graded polymer foams in several motifs, including 3D lattices, shells, and out‐of‐plane pillars are fabricated. Conductive composite foams with controlled stiffness for use as soft pressure sensors are also produced.

The ability to create architected materials that possess both high stiffness and toughness remains an elusive goal, since these properties are often mutually exclusive. Natural materials, such as bone, overcome such limitations by combining different toughening mechanisms across multiple length scales. Here, a new method for creating architected lattices composed of core-shell struts that are both stiff and tough is reported. Specifically, these lattices contain orthotropic struts with flexible epoxy core-brittle epoxy shell motifs in the absence and presence of an elastomeric silicone interfacial layer, which are fabricated by a multicore-shell, 3D printing technique. It is found that architected lattices produced with a flexible core-elastomeric interface-brittle shell motif exhibit both high stiffness and toughness.