Design and Mechanical Characterization of Auxetic 2D Scaffolds and Application to Native Tissues

The selection of biomaterials and the design of the scaffold is crucial, as it directly influences the mechanical properties, which in turn affect cell behavior and tissue integration. This study investigates how scaffold geometry impacts mechanical characteristics, with the aim of replicating the properties of natural tissues. Auxetic geometries, characterized by negative Poisson’s ratios, were investigated. These structures exhibit unique mechanical behavior, expanding laterally when stretched, in contrast to conventional materials that contract. The Fused Deposition Modeling (FDM) technique was used to 3D print scaffolds with a single filament of polycaprolactone (PCL). Two geometries, wavy and sinusoidal, were analyzed by varying the amplitude of the curve within each structural cell. Tensile tests were performed to measure mechanical properties, including Young’s Modulus (E), Poisson’s ratio (ν), and porosity-properties critical for understanding the interaction of scaffolds with cells and tissues. The wavy geometry exhibited a higher E than the sinusoidal geometry at the same amplitude. At a minimum amplitude of 0.3 mm, the wavy structure had E = 6.8 MPa, while the sinusoidal structure had E = 3.8 MPa. At the maximum amplitude of 1.2 mm, the wavy structure had E = 0.6 MPa, and the sinusoidal structure had E = 0.2 MPa. All Poisson’s ratios were negative, with the lowest value (-1.56) observed in the sinusoidal structure at the largest amplitude. The detected negative Poisson’s ratio suggests auxetic behavior, which could enhance scaffold flexibility, improve its ability to deform, promote cell attachment, and facilitate tissue integration. Although the two auxetic structures shared the same undulation angle, the analysis revealed differences in their mechanical properties. Specifically, the wavy structure exhibited a lower Young’s Modulus. To improve cell interaction and attachment by reducing pore size, a correction factor was calculated based on stiffness values and pore area measurements. By adjusting the scaffold geometry, its mechanical properties can be fine-tuned to more closely align with the characteristics of native tissues, potentially enhancing cell attachment and proliferation. This study highlights the potential of modifying scaffold geometry, particularly through the use of auxetic structures, to significantly influence mechanical properties. This approach shows promise in optimizing scaffolds for tissue engineering applications.