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

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.

A composite material with Poisson’s ratio tunable from positive to negative values: an experimental and numerical study

“…As a result, it is very hard to use traditional manufacturing techniques to fabricate NPR materials, especially in a 3D space. With the fast development of additive-manufacturing methods, some studies were performed to fabricate NPR materials using these techniques [23,24]. Although only a mono-material has been used to fabricate NPR materials based on the well-known NPR structures, the efforts have proven the potential of these techniques to fabricate 2D and 3D NPR materials.…”

“…To date, most of the NPR materials are studied based on certain re-entrant, chiral structures, and rotating units [5,[18][19][20]. These basic units are usually periodically and symmetrically assembled [17,[21][22][23][24], according to their deformation mechanism and orientations to provide the NPR effects. Although these materials could extend the NPR behavior of the basic units to the overall materials, the overall NPR effects are limited to certain directions.…”

Numerical analysis of composite structure with in-plane isotropic negative Poisson’s ratio: Effects of materials properties and geometry features of inclusions

“…This is true, for example, reentrant, chiral, star-shape structures and rotating units [2][3][4][5][6]. These structures, known as skeletal structures, are well studied, and most of them are periodic and often symmetric as well [7][8][9][10][11][12][13][14][15]. In these structures, the NPR effect only occurs along certain in-plane directions, and the concept of NPR is hardly used in 3D space.…”

Nano‐ and Micro‐Auxetic Plasmonic Materials

“…[ 19 ] Soft lithography, [ 12 ] femtosecond laser ablation, [ 13 ] and digital micromirror device projection printing [ 14 ] have allowed the fabrication of negative Poisson's ratio structures with characteristic sizes of hundreds of micrometers. Smaller dielectric auxetics with unit cells on the order of 100 µm have been made by laser micromachining, [ 15 ] while dielectric auxetics with a characteristic size of 10 µm have been realized by direct laser writing.…”

“…In contrast to normal materials, negative Poisson's ratio structures have the peculiar property that, when stretched in one direction, they will expand in the perpendicular direction. Numerous auxetic structures have been demonstrated theoretically [ 3,4,[8][9][10] and experimentally studied at millimeter to submillimeter [11][12][13][14][15][16] and molecular scales.[ 17 ] Suitable fabrication techniques are determined by the characteristic size of the auxetic structure. For example, macroscopic structures with unitcell dimensions larger than 1 mm were fabricated using open cell polymeric or metallic foams, [ 1 ] aramid paper, [ 11 ] mechanical devices made of hinges, springs, and sliding collars, [ 18 ] Adv.…”