Recent progress in acoustic field-assisted 3D-printing of functional composite materials

Research advances of acoustic particle manipulation techniques in field-assisted manufacturing

Field-assisted manufacturing (FAM) technology, which employs external fields to transport and manipulate micro/nanoparticles for tailored arrangements and structures, can produce novel materials with specific properties and functions. Acoustic particle manipulation has attracted increasing attention in FAM due to its various advantages, such as a wide range of materials, ease of fabrication, rapid actuation, non-invasive operation and high biocompatibility. The present review summarizes the recent progress of acoustic particle manipulation in the FAM area, with respect to operation principles, fabrication and control of particles, and particle cluster patterning. The emphasis is placed on the recent innovative applications of microparticle manipulation realized by acoustic fields in different advanced manufacturing technologies. Finally, we provide our perspective on the current challenges and potential prospects of acoustic particle manipulation technology in FAM.

SonoPrint: Acoustically Assisted Volumetric 3D Printing for Composites

Advances in additive manufacturing in composites have transformed aerospace, medical devices, tissue engineering, and electronics. A key aspect of enhancing properties of 3D-printed objects involves fine-tuning the material by embedding and orienting reinforcement within the structure. Existing methods for orienting these reinforcements are limited by pattern types, alignment, and particle characteristics. Acoustics offers a versatile method to control the particles independent of their size, geometry, and charge, enabling intricate pattern formations. However, integrating acoustics into 3D printing has been challenging due to the scattering of the acoustic field between polymerized layers and unpolymerized resin, resulting in unwanted patterns. To address this challenge, SonoPrint, an innovative acoustically assisted volumetric 3D printer is developed that enables simultaneous reinforcement patterning and printing of the entire structure. SonoPrint generates mechanically tunable composite geometries by embedding reinforcement particles, such as microscopic glass, metal, and polystyrene, within the fabricated structure. This printer employs a standing wave field to create targeted particle motifs-including parallel lines, radial lines, circles, rhombuses, hexagons, and polygons-directly in the photosensitive resin, completing the print in just a few minutes. SonoPrint enhances structural properties and promises to advance volumetric printing, unlocking applications in tissue engineering, biohybrid robots, and composite fabrication.

Projection Stereolithography 3D-Printed Bio-Polymer with Thermal Assistance

A stereolithography process with thermal assistance is proposed in this work to address the tradeoff between the flowability and the high concentration of solute loadings at room temperature, through which the improved performance of polymers prepared using stereolithography 3D printing can be achieved. For the experiment, polyethylene glycol diacrylate (PEGDA) with a high molecular weight of 4000 is adopted to improve the mechanical properties of 2-Hydroxyethyl methacrylate (HEMA). For the polymer of HEMA, the highest soluble concentration of PEGDA is about 20 wt% at 25 °C (room temperature) while the concentration could be raised up to 40 wt% as the temperature increases to 60 °C. The 3D printing tests showed that the objects could be easily fabricated with the HEMA polymer loaded with 40 wt% of PEGDA through the thermally assisted projection stereolithography technology. By adding the 40 wt% of PEGDA, the Young's modulus has been enhanced by nearly 390% compared to the HEMA resin without solute, of which the Young's modulus is 63.31 ± 2.72 MPa. The results of the cell proliferation test proved that the HEMA resin loaded with PEGDA led to a better biocompatibility compared to the HEMA resin without the loading of the PEGDA solute. All of the results demonstrate that the polymer loaded with high solute is feasible to be precisely 3D-printed using the projection stereolithography process with thermal assistance, and the improved mechanical properties are beneficial for biomedical applications.

Ultrasound Manipulation and Extrusion of Active Nanorods

Synthetic self-propelled nano and microparticles have a growing appeal for targeted drug delivery, collective functionality, and manipulation at the nanoscale. However, it is challenging to control their positions and orientations under confinement, e.g., in microchannels, nozzles, and microcapillaries. This study reports on the synergistic effect of acoustic and flow-induced focusing in microfluidic nozzles. In a microchannel with a nozzle, the balance between the acoustophoretic forces and the fluid drag due to streaming flows generated by the acoustic field controls the microparticle's dynamics. This study manipulates the positions and orientations of dispersed particles and dense clusters inside the channel at a fixed frequency by tuning the acoustic intensity. The main findings are: first, this study successfully manipulates the positions and orientations of individual particles and dense clusters inside the channel at a fixed frequency by tuning the acoustic intensity. Second, when an external flow is applied, the acoustic field separates and selectively extrudes shape-anisotropic passive particles and self-propelled active nanorods. Finally, the observed phenomena are explained by multiphysics finite-element modeling. The results shed light on the control and extrusion of active particles in confined geometries and enable applications for acoustic cargo (e.g., drug) delivery, particle injection, and additive manufacturing via printed self-propelled active particles.