Droplet-based printing methods are widely used in applications ranging from biological microarrays to additive manufacturing. However, common approaches, such as inkjet or electrohydrodynamic printing, are well suited only for materials with low viscosity or specific electromagnetic properties, respectively. While in-air acoustophoretic forces are material-independent, they are typically weak and have yet to be harnessed for printing materials. We introduce an acoustophoretic printing method that enables drop-on-demand patterning of a broad range of soft materials, including Newtonian fluids, whose viscosities span more than four orders of magnitude (0.5 to 25,000 mPa·s) and yield stress fluids (τ₀ > 50 Pa). By exploiting the acoustic properties of a subwavelength Fabry-Perot resonator, we have generated an accurate, highly localized acoustophoretic force that can exceed the gravitational force by two orders of magnitude to eject microliter-to-nanoliter volume droplets. The versatility of acoustophoretic printing is demonstrated by patterning food, optical resins, liquid metals, and cell-laden biological matrices in desired motifs.

Auxetic structures possess a negative Poisson ratio (ν < 0) as a result of their geometrical configuration, which exhibits enhanced indentation resistance, fracture toughness, and impact resistance, as well as exceptional mechanical response advantages for applications in defense, biomedical, automotive, aerospace, sports, consumer goods, and personal protective equipment sectors. With the advent of additive manufacturing, it has become possible to produce complex shapes with auxetic properties, which could not have been possible with traditional manufacturing. Three-dimensional printing enables easy and precise control of the geometry and material composition of the creation of desirable shapes, providing the opportunity to explore different geometric aspects of auxetic structures with a variety of different materials. This study investigated the geometrical and material combinations that can be jointly tailored to optimize the auxetic effects of 2D and 3D complex structures by integrating design, modelling approaches, 3D printing, and mechanical testing. The simulation-driven design methodology allowed for the identification and creation of optimum auxetic prototype samples manufactured by 3D printing with different polymer materials. Compression tests were performed to characterize the auxetic behavior of the different system configurations. The experimental investigation demonstrated a Poisson’s ration reaching a value of ν = −0.6 for certain shape and material combinations, thus providing support for preliminary finite element studies on unit cells. Finally, based on the experimental tests, 3D finite element models with elastic material formulations were generated to replicate the mechanical performance of the auxetic structures by means of simulations. The findings showed a coherent deformation behavior with experimental measurements and image analysis.

Polyetheretherketone (PEEK) has been the focus of substantial additive manufacturing research for two principal reasons: (a) the mechanical performance approaches that of aluminum at relatively high temperatures for thermoplastics and (b) the potential for qualification in both the aerospace and biomedical industries. Although PEEK provides outstanding strength and thermal stability, printing can be difficult due to the high melting point. Recently, high-temperature soluble support has enabled the printing of lattices and stochastic foams with overhanging features in these high-performance carbon fiber thermoplastics, in which density can be optimized to strike a balance between weight and strength to enhance performance in applications such as custom implants or aerospace structures. Although polymer powder bed fusion has long been capable of the combination of these geometries and materials, material extrusion with high-temperature sacrificial support is dramatically less expensive. This research provides a comprehensive mechanical analysis and CT-scan-based dimensional study of carbon fiber PEEK lattice structures enabled with high-temperature support and including model validation.

Powder bed fusion of polymers is becoming increasingly adopted by a variety of industries to tailor the strength, weight and functionality of end-use products. To meet the high standards of the modern manufacturing industry, parts built with powder bed fusion require consistent properties and to be free of defects, which is intrinsically connected to the quality of the powder bed prior to melting. The hypothesis of this work is that the roughness of the top surface of an unmelted powder bed can serve as a proxy for the powder bed density, which is known to correlate with final part density. In this study, a laser line scan profilometer is integrated onto the recoater arm of a custom powder test bench, which is able to automatically create layers of powder. A diverse group of polymers was investigated including polyamide 12 (PA12), polyamide 11 (PA11), polypropylene (PP), and a thermoplastic elastomer (TPU) under different recoating speed in order to increase the variance of the dataset. Data analytics were employed to compare roughness to measured powder bed density and a statically significant correlation was established between them.