Out‐of‐Plane 3D‐Printed Microfibers Improve the Shear Properties of Hydrogel Composites

Abstract

Melt electrowriting (MEW) is an additive manufacturing technique that directwrites ultrafine fibers onto a surface using molten fluid columns that are stabilized with an applied voltage. [1][2][3] The process is different to polymer melt, [4] hydrogel, [5] and colloidal ink [6,7] extrusion through nozzles which all operate with direct-contact deposition for each layer. In this study, the electrified molten jet is periodically written back and forth across a wall-like structure with remarkable consistency, with minimal variation in structural dimensions. When embedded within a hydrogel, these "out-of-plane fibers" distinctly increase the shear modulus of the composite, even though they partake in a small fraction of the total composite volume.Previously MEW has been used for "inplane" printing, meaning that the fiber is aligned along a single plane for cartesian coordinates, [1] or a single curvature for rotating collectors. [8] The technique is capable of producing micrometer-scale dia meter fibers, ranging from 45 µm [1] to as small as 820 nm. [9] In addition, MEW results in a narrow fiber diameter distribution (3-5% coefficient of variation), emphasizing the reproducibility of this technique. [10] The accurate and reproducible fiber deposition is a crucial characteristic for the use of such a technology in biomedicine, filtration, and energy applications. [11][12][13][14][15] The mechanical advantage of accurate control over fiber placement was shown in a recent study, where a weak hydrogel matrix was reinforced with either small-diameter MEW (2-7 vol%) fibers or with thicker (16 vol%) fused deposition modeling (FDM) fibers. [16] The MEW-reinforced constructs were able to recapitulate the compressive properties of native articular cartilage, whereas the FDM fibers-containing structures were significantly stiffer than the native tissue and failed at comparatively low deformations (less than 10% strain). [16] The implications for tissue engineering (TE) applications is that such fiber/hydrogel composites enable the use of a mechanically weak hydrogel for cell differentiation and matrix formation, while still providing a structural support required for high compressive loading conditions. [17] Other methods to reinforce hydrogels include using random solution electrospun meshes, [18] interpenetrating polymer networks, [19] or the inclusion of carbon nanofiber tubes. [20] However, the restricted control over the fiber meshes architectures limits their reinforcing potential of soft hydrogels by One challenge in biofabrication is to fabricate a matrix that is soft enough to elicit optimal cell behavior while possessing the strength required to withstand the mechanical load that the matrix is subjected to once implanted in the body. Here, melt electrowriting (MEW) is used to direct-write poly(ε-caprolactone) fibers "outof-plane" by design. These out-of-plane fibers are specifically intended to stabilize an existing structure and subsequently improve the shear modulus of hydrogelfiber composites. The stabilizing fiber...

Biologically Inspired Scaffolds for Heart Valve Tissue Engineering via Melt Electrowriting

“…tailored mechanical properties and biomimetic microarchitecture provided by the fiber phase, and enhanced ECM production typically observed for cell‐laden fibrin . Soft network composites combining MEW fibers and a soft hydrogel have shown to be a promising way to achieve desirable cell behavior while withstanding the required mechanical loading conditions . The molding process resulted in homogenously‐embedded MEW scaffolds with no exposed PCL fibers ( Figure A,B) and no negative effect on HUVSMC viability (Figure C).…”

Melt Electrowriting of Thermoplastic Elastomers

“…A custom‐built MEW device was used, described elsewhere . Briefly, a 24 G flat‐tipped cannula printing nozzle was positioned above a 26 × 76 mm 2 glass microscope slide and a positive high voltage was applied.…”

“…A custom-built MEW device was used, described elsewhere. [8,15] Briefly, a 24 G flat-tipped cannula printing nozzle was positioned above a 26 × 76 mm 2 glass microscope slide and a positive high voltage was applied. The microscope slide was moved under the charged nozzle using two computer-controlled linear axis (x and y).…”

Melt electrowriting of electroactive poly(vinylidene difluoride) fibers

“…15 Electrospun fibers from melts tend to have (but not always) larger diameters than those obtained from a polymer solution, 16 but have a significantly smaller diameter than most direct-written, extruded polymer melts. 17 Such well-placed micron-diameter fibers provide mechanical and biological properties not seen with solution electrospun meshes 18,19 and bridge the gap in a size regime that is relevant for numerous applications.…”