Embedded three-dimensional (EMB3D) printing is an emerging technique that enables free-form fabrication of complex architectures. In this approach, a nozzle is translated omnidirectionally within a soft matrix that surrounds and supports the patterned material. To optimize print fidelity, we have investigated the effects of matrix viscoplasticity on the EMB3D printing process. Specifically, we determine how matrix composition, print path and speed, and nozzle diameter affect the yielded region within the matrix. By characterizing the velocity and strain fields and analyzing the dimensions of the yielded regions, we determine that scaling relationships based on the Oldroyd number, Od, exist between these dimensions and the rheological properties of the matrix materials and printing parameters. Finally, we use EMB3D printing to create complex architectures within an elastomeric silicone matrix. Our methods and findings will both facilitate future characterization of viscoplastic matrices and motivate the development of new materials for EMB3D printing.

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In the published communication, the author lists of several of the references were presented incorrectly, with the first name of some of the authors given as the family name.These references are corrected here:[3] M. G. Mazza,

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The flow behavior of fiber suspensions has been studied extensively, especially in the limit of dilute concentrations and rigid fibers; at the other extreme, however, where the suspensions are concentrated and the fibers are highly flexible, much less is understood about the flow properties. We use a microfluidic method to produce uniform concentrated suspensions of high aspect ratio, flexible microfibers, and we demonstrate the shear thickening and gelling behavior of such microfiber suspensions, which, to the best of our knowledge, has not been reported previously. By rheological means, we show that flowing the suspension triggers the irreversible formation of topological entanglements of the fibers resulting in an entangled water-filled network. This phenomenon suggests that flexible fiber suspensions can be exploited to produce a new family of flow-induced gelled materials, such as porous hydrogels. A significant consequence of these flow properties is that the microfiber suspension is injectable through a needle, from which it can be extruded directly as a hydrogel without any chemical reactions or further treatments. Additionally, we show that this fiber hydrogel is a soft, viscoelastic, yield-stress material.