Abstract
Three-dimensional (3D) printing is used to fabricate tissue scaffolds. Polymer chains in these objects are typically unoriented. The mechanical properties of these scaffolds can be significantly enhanced by proper alignment of polymer chains. However, post-processing routes to increase orientation can be limited by the geometry of the printed object. Here, we show that it is possible to orient polymer chains during printing by optimizing printing parameters to take advantage of the flow characteristics of the polymer. This is demonstrated by printing a polymeric scaffold for meniscus regeneration using poly(desaminotyrosyl-tyrosine dodecyl dodecanedioate), poly(DTD DD). Alignment of polymer chains was achieved by translating the printhead at sufficiently high speeds when the polymer was still in a semi-solid state as it cooled from the fluid state at the tip of the nozzle using a critical combination of nozzle diameter, extrusion pressure, and temperature. The degree of orientation as evaluated by x-ray diffraction and thermal shrinkage, was greater than that of drawn fibers. Significant orientation and defect-free printing was achieved even for scaffolds with complex geometries. The ability to orient polymers during 3D printing has the potential to combine the advantages of 3D printing with the superior mechanical performance of more conventional polymer processing methods, such as drawing.
Highlights
The term “orientation” in 3D printing often refers to the relative physical orientation of the fibers in successive layers, e.g., at 0°and 90° (Farzadi et al, 2014; Moroni et al, 2006; Zein et al, 2002)
The temperature range within which this drawing can be done efficiently is rather narrow: at temperatures far below the melting point of the polymer, the force required for mechanical deformation is too high, and at temperatures closer to the melting temperature, the polymer molecules can quickly relax to a randomly oriented state
We show that high degree of molecular orientation comparable to drawn fibers can be obtained in the bulk of the polymer in 3D printing by translating the printhead at sufficiently high speeds
Summary
The term “orientation” in 3D printing often refers to the relative physical orientation of the fibers in successive layers, e.g., at 0°and 90° (Farzadi et al, 2014; Moroni et al, 2006; Zein et al, 2002). The temperature range within which this drawing can be done efficiently is rather narrow: at temperatures far below the melting point of the polymer, the force required for mechanical deformation is too high, and at temperatures closer to the melting temperature, the polymer molecules can quickly relax to a randomly oriented state. Such molecular orientation is difficult to achieve in 3D printing. We here demonstrate polymer chain orientation in the bulk and demonstrate that we can 3D print a meniscus with performance similar to that made with fibers
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