Acoustics in additive manufacturing: A path toward contactless, scalable, and high-precision manufacturing

Acoustic techniques have emerged as a transformative approach in additive manufacturing, enabling contactless, high-precision manipulation of particles, droplets, and cells through acoustic wavefields. While acoustic patterning has demonstrated remarkable control over microscale spatial configurations, its scalability into three-dimensional (3D) fabrication has remained constrained by challenges in bonding limitations and vertical stacking. To solve this challenge, hybrid acoustic-assisted 3D printing integrates acoustophoresis with established methods, such as direct ink writing and stereolithography, enhancing material deposition accuracy, microstructure alignment, and porous structuring of 3D printed products. However, these hybrid systems remain tethered to layer-by-layer architectures, limiting the full potential of acoustic techniques. Recent breakthroughs in standalone acoustic 3D fabrication, leveraging levitation, focusing, and ejection, have unlocked potential in contactless, layerless, and flexible multi-material assembly. Acoustic levitation systems enable mid-air construction on non-planar surfaces, and focused ultrasound techniques facilitate deep-penetration polymerization and acoustic droplet ejection advances nozzle-free droplet-based bioprinting. This review systematically evaluates the evolution of acoustics in additive manufacturing, addressing critical challenges in material compatibility, resolution, and scalability, while outlining the future of acoustics in additive manufacturing technology.