Ultrasound Powers Potential In-Body 3D Printing

A new approach to three-dimensional (3D) printing uses ultrasound waves to create objects from sonically cured inks. The approach enables volumetric 3D printing even in opaque media or at deep penetration depths, including, potentially, inside the body. 3D printing technologies are poised to revolutionize manufacturing processes for a wide range of applications. Volumetric printing, an emerging 3D printing technique, can build objects faster and with better surface quality than printing methods that build objects layer-by-layer. Most existing volumetric printing techniques rely on light to trigger photopolymerization in optically transparent inks. However, light scattering by the inks themselves, the presence of functional additives within the inks, and light-blocking by already cured portions of the build limit the material choices and the build sizes feasible, particularly in configurations that require deep light penetration. Compared to light waves, ultrasound waves can penetrate much deeper into materials and can, in principle, be used to trigger polymerization. Here, Xiao Kuang and colleagues present a new approach to volumetric printing they call deep-penetrating acoustic volumetric printing (DAVP), which uses focused ultrasound waves and "sono-ink." The sono-ink the authors developed overcomes key challenges of acoustic volumetric printing by using a thermally responsive adaptive acoustic absorber to form a viscous gel that prevents streaming flow while simultaneously initiating a heat-triggered polymerization. In tests, DVAP allowed the authors to print objects quickly from various nanocomposite materials at a millimeter scale – and several centimeters deep in opaque media. As a proof of concept, Kuang et al. applied DAVP to high-speed, high-resolution through-tissue manufacturing and minimally invasive medicine. Through experiments in ex vivo tissues infused with sono-ink, the authors demonstrate the in situ fabrication of artificial bone and of a left atrial appendage closure. In a related Perspective, Yuxing Yao and Mikhail Shapiro discuss the DAVP approach, its limitations, and its potential uses, including minimally invasive medical procedures. "It is conceivable that the running shoes of the future could be printed with the same acoustic method that repairs bones," Yao and Shapiro write.