Out-of-plane auxetic nonwoven as a designer meta-biomaterial

Out-of-Plane Auxetic Behavior in Cellulose Nanofibril Films

While auxeticity has been established in cellulose-based paper and paperboards and computational studies suggest auxetic behavior should occur within cellulose structures, the auxetic response of neat cellulose nanofibril (CNF) films has not yet been experimentally established. Here, we show that an out-of-plane auxetic response does occur in CNF films and that the magnitude of the response is dependent on the film density, microstructure, and sample geometry. CNF films are fabricated using vacuum filtration, followed by conditioning at 23 °C and 50% relative humidity. The CNF aqueous suspension amount is varied from 90 to 450 mL, which progressively increases the film density until reaching a plateau of 1.05 ± 0.02 g/cm3 for films with suspension volumes equal to or greater than 270 mL. Aside from varying the film densities, the aspect ratio of the film is varied from 1.5 to 5 (ratio of rectangular CNF film length to width) to determine how the sample dimensions contribute to the auxetic response, specifically if stress fields associated with gripping of the sample constrain the fiber network. From these studies, CNF films with a density of 1.05 g/cm3 and a film aspect ratio of 5 exhibit the highest auxetic response in the elastic region with a negative Poisson's ratio of -5.3 as determined by linear fitting and the largest instantaneous Poisson' ratio value of -7.99 at 0.4% strain. Overall, this work provides insight into the processing-structure-property relationships that define auxeticity in CNF films, which can enable the use of CNFs as auxetic metamaterials in a broad range of applications such as sensing, protective gears, composites, and structural materials.

Sustainable Nonwoven Scaffolds Engineered with Recycled Carbon Fiber for Enhanced Biocompatibility and Cell Interaction: From Waste to Health

Carbon fibers, driven by ever-increasing demand, are contributing to a continuous rise in the generation of waste and byproducts destined for landfills or incineration. Recycling carbon fibers presents a promising strategy for reducing carbon emissions and conserving resources, thus contributing to more sustainable waste management practices. Discovering applications of recycled carbon fibers (rCFs) would inevitably accelerate the targeted integration of sustainable materials, fostering a circular economy. Herein, we have engineered rCF-based needlepunched nonwoven scaffolds and their blends with polypropylene (PP) fibers, providing the first example of investigating their interactions with human lung epithelial cells (Calu-3) and murine fibroblast cells (NIH/3T3). To promote the adsorption of extracellular matrix proteins such as laminin, these three-dimensional (3D) nonwoven scaffolds are designed and developed to feature tunable porous characteristics and wetting properties. Although cell adhesion and laminin adsorption are minimal on PP fibers, cells are preferentially organized on the rCFs. These nonwovens, composed exclusively of rCFs or their blends with PP fibers, exhibit no cytotoxic effects, with both cell types showing proliferation on the scaffolds and a progressive increase in cell numbers over time. Cell viability and apoptosis assays are also employed to comprehensively evaluate biocompatibility. Thus, our study proves rCF-based nonwoven scaffolds as potential candidates for artificial lung tissue scaffolds.

Superhydrophobic self-similar nonwoven-titanate nanostructured materials

HYPOTHESIS

Self-similarity is a scale-invariant irregularity that can assist in designing a robust superhydrophobic material. A combinatorial design strategy involving self-similarity and dual-length scale can be employed to create a new library of a doubly re-entrant, disordered, and porous network of superhydrophobic materials. Asymmetric wettability can be engineered in nonwoven materials by rendering them with superhydrophobic characteristics on one side.

EXPERIMENTS

A facile, scalable, and inexpensive spray-coating technique was used to decorate the weakly hydrophobicstearate-treatedtitanate nanowires (TiONWs)over the self-similar nonwoven material. Laser scanning confocal microscopy was employed to image the impalement dynamics in three dimensions. With the aid of X-ray microcomputed tomography analysis, the three-dimensional (3D) nonwoven structural parameters were obtained and analyzed. The underwater superhydrophobic behavior of the prepared samples was investigated.

FINDINGS

A classic 'lotus effect' has been successfully endowed in self-similar nonwoven-titanate nanostructured materials (SS-Ti-NMs) from a nonwoven material that housed the air pockets in bulk and water repellent TiONWs on the surface. The finer fiber-based SS-Ti-NMs exhibited lower roll-off angles and a thinner layer of water on its surface. An asymmetric wettability and the unusual display of underwater superhydrophobic behavior of SS-Ti-NMs have been uncovered.

Additive Manufacture of 3D Auxetic Structures by Laser Powder Bed Fusion—Design Influence on Manufacturing Accuracy and Mechanical Properties

The mechanical response of steel auxetic structures manufactured using laser-powder bed fusion was explored. The level of control exerted by the key design parameters of vertical strut length (H), re-entrant strut length (L), strut thickness (t) and re-entrant angle (ϴ) on the mechanical response was examined through a design of experiment approach with ANOVA statistical analysis methods applied. The elastic modulus in directions normal to (Ex) and parallel to (Ey) the vertical strut was found to be primarily dependent upon t and L, respectively, whereas yield strength in both test directions (σx and σy) was strongly dependent on t and L. A large variation in modulus was found between the two test directions (Ex / Ey – 1.02 ± 0.07 GPa/ 4.4 ± 0.1 GPa), whereas, yield strength showed little anisotropy (σx / σy–45 ± 6 MPa/ 45 ± 9 MPa). Poisson’s ratio parallel to the vertical strut varied considerably with geometry but not in a direction normal to the vertical strut. Deformation mechanisms were found to be different of compression in the x and y directions, being a combination of stretching of the vertical strut; compression, bending and hinging of the re-entrant strut (x); and vertical strut compression and re-entrant strut stretching and bending (y).