Auxetic Structures for Tissue Engineering Scaffolds and Biomedical Devices

Abstract

An auxetic structure utilizing a negative Poisson's ratio, which can expand transversally when axially expanded under tensional force, has not yet been studied in the tissue engineering and biomedical area. However, the recent advent of new technologies, such as additive manufacturing or 3D printing, has showed prospective results aimed at producing three-dimensional structures. Auxetic structures are fabricated by additive manufacturing, soft lithography, machining technology, compressed foaming, and textile fabrication using various biomaterials, including poly(ethylene glycol diacrylate), polyurethane, poly(lactic-glycolic acid), chitosan, hydroxyapatite, and using a hard material such as a silicon wafer. After fabricating the scaffold with an auxetic effect, researchers have cultured fibroblasts, osteoblasts, chondrocytes, myoblasts, and various stem cells, including mesenchymal stem cells, bone marrow stem cells, and embryonic stem cells. Additionally, they have shown new possibilities as scaffolds through tissue engineering by cell proliferation, migration, alignment, differentiation, and target tissue regeneration. In addition, auxetic structures and their unique deformation characteristics have been explored in several biomedical devices, including implants, stents, and surgical screws. Although still in the early stages, the auxetic structure, which can create mechanical properties tailored to natural tissue by changing the internal architecture of the structure, is expected to show an improved tissue reconstruction ability. In addition, continuous research at the cellular level using the auxetic micro and nano-environment could provide a breakthrough for tissue reconstruction.

Keywords: auxetic; biomedical; device; scaffold; tissue engineering.

Figure 1

Behaviors of (a) conventional material and (b) auxetic (negative Poisson’s ratio) material.

Figure 2

Re-entrant structures. (a) Re-entrant honeycomb, (b) double arrowhead, (c) star honeycomb, (d) structurally hexagonal re-entrant honeycomb, (e) lozenge grids, (f) sinusoidal ligaments [9].

Figure 3

Chiral structures. (a) chiral structure with same units, (b) chiral structure with symmetrical units [9].

Figure 4

Rotating unit structures. (a) Triangle unit cells, (b) square unit cells, (c) rectangle unit cells [26,35,36,37]. (A figure was reproduced with permission from John Wiley and Sons [35]).

Figure 5

Fabrication results of the 3D meta-materials with auxetic unit cells. (a–c): 3D auxetic structure with a four-fold axis, (d): 3D auxetic structure with a six-fold axis. (A figure was reproduced with permission from John Wiley and Sons [46]).

Figure 6

Fabrication results of tubular structures with unit cells. (a–c) Non-auxetic structure with intact ribs. (d–f) Auextic (NPR) structure with cut-missing ribs (scale: 1 mm) [65].

Figure 7

Auxetic cardiac patch for the myocardial infarction treatment. (a) Dimension of the re-entrant unit cell. (b) Schematic of the treatment using the auxetic cardiac patch (AuxCP). (c) Auxetic behavior by the re-entrant unit cells. (d) Shape change of the AuxCPs from 0.8% strain to 12.6% strain (scale bar: 1mm), (e) (i) AuxCP-treated heart (scale: 2 mm), (ii) Activation time maps before and after AuxCP (two weeks after treatment), (iii) conduction velocity maps before and after AuxCP (two weeks after treatment) [13].