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.

To date, several methods have been developed to induce alignment in engineered cardiac tissues. [7][8][9][10][11] One common approach is to seed cardiomyocytes onto micro-or nanopatterned surfaces that contain topographical cues, which guide cellular alignment. [12,13] Another approach is to seed cells onto anisotropic polymer scaffolds [14][15][16] or decellularized matrices [17] that guide tissue alignment. In addition, cell-laden hydrogels seeded into molds of varying geometry can self-assemble into aligned cardiac rods, rings, bundles, and sheets. [18][19][20][21][22][23][24] Unfortunately, these methods are typically confined to thin cardiac tissues (≤100 µm thick) with either linear or radial alignment. By contrast, extrusionbased bioprinting offers broad flexibility to control tissue composition and architecture. Recently, we and others have demonstrated that synthetic and biological fibers exhibit shear-induced alignment during printing, opening the possibility to program tissue alignment via cell templating. [25][26][27][28][29][30][31][32][33][34] However, programming the architecture of human tissues by directly aligning anisotropic tissue building blocks has yet to be explored.Here, we report the fabrication of engineered cardiac tissue with programmable alignment via bioprinting of anisotropic organ building blocks (aOBBs) (Figure 1). These aOBBs are elongated microtissues composed of cellular aligned hiPSC-CMs that can be modularly assembled into a printable bioink (Figure 1a). Individual aOBBs within this bioink align along the print path due to the same shear and extensional forces that orient acellular fibers upon extrusion through a tapered nozzle (Figure 1b). [35] Using this method, we fabricated cardiac tissues with high cellular density and programmed alignment across multiple length scales; ranging from individual aOBBs to the sarcomeric machinery that drives their contractile function (Figure 1c). Results and DiscussionThe first step in creating our cardiac bioink is to fabricate scalable micropillar arrays by stereolithography (SLA). These micropillar arrays are used to generate tens of thousands of aOBBs with controlled aspect ratio and cellular composition. After optimizing these parameters, we employed a sequential transfer micromolding process to create a single contiguousThe ability to replicate the 3D myocardial architecture found in human hearts is a grand challenge. Here, the fabrication of aligned cardiac tissues via bioprinting anisotropic organ building blocks (aOBBs) composed of human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) is reported. A bioink composed of contractile cardiac aOBBs is first generated and aligned cardiac tissue sheets with linear, spiral, and chevron features are printed. Next, aligned cardiac macrofilaments are printed, whose contractile force and conduction velocity increase over time and exceed the performance of spheroid-based cardiac tissues. Finally, the ability to spatially control the magnitude and direction of contractile force...

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