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Three-Dimensional Polymer Constructs Exhibiting a Tunable Negative Poisson's Ratio

Authors

  • David Y. Fozdar,

    1. Department of Mechanical Engineering, The University of Texas at Austin, 204 E. Dean Keaton St., ETC 1.210A, Austin, TX 78712, USA
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  • Pranav Soman,

    1. Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Atkinson Hall, MC-0448, La Jolla, CA 92093, USA
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  • Jin Woo Lee,

    1. Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Atkinson Hall, MC-0448, La Jolla, CA 92093, USA
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  • Li-Hsin Han,

    1. Department of Orthopaedic Surgery, Stanford University School of Medicine, 300 Pasteur Dr., Edwards R132, Stanford, CA 94305, USA
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  • Shaochen Chen

    Corresponding author
    1. Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Atkinson Hall, MC-0448, La Jolla, CA 92093, USA
    • Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Atkinson Hall, MC-0448, La Jolla, CA 92093, USA.
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Abstract

Young's modulus and Poisson's ratio of a porous polymeric construct (scaffold) quantitatively describe how it supports and transmits external stresses to its surroundings. While Young's modulus is always non-negative and highly tunable in magnitude, Poisson's ratio can, indeed, take on negative values despite the fact that it is non-negative for virtually every naturally occurring and artificial material. In some applications, a construct having a tunable negative Poisson's ratio (an auxetic construct) may be more suitable for supporting the external forces imposed upon it by its environment. Here, three-dimensional polyethylene glycol scaffolds with tunable negative Poisson's ratios are fabricated. Digital micromirror device projection printing (DMD-PP) is used to print single-layer constructs composed of cellular structures (pores) with special geometries, arrangements, and deformation mechanisms. The presence of the unit-cellular structures tunes the magnitude and polarity (positive or negative) of Poisson's ratio. Multilayer constructs are fabricated with DMD-PP by stacking the single-layer constructs with alternating layers of vertical connecting posts. The Poisson's ratios of the single- and multilayer constructs are determined from strain experiments, which show (1) that the Poisson's ratios of the constructs are accurately predicted by analytical deformation models and (2) that no slipping occurrs between layers in the multilayer constructs and the addition of new layers does not affect Poisson's ratio.

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