Volumetric printing is a technique that creates 3D objects by projecting 2D images into a photosensitive material, allowing for faster and potentially more detailed printing than traditional layer-by-layer 3D printing. However, light penetration depth is limited, which affects the uniformity of curing and restricts object size and material choices. Now, writing in Science, Junjie Yao, Yu Shrike Zhang and colleagues present a technique to improve the penetration depth of volumetric printing using ultrasound and specifically designed inks.
For this purpose, the team developed a multi-component viscoelastic ink promoting quick heat generation through sound for swift and precise polymerization. There is typically a trade-off between acoustic penetration depth and acoustic streaming; to achieve deeper penetration of ultrasound waves, the medium should be less viscous, but this lower viscosity can exacerbate acoustic streaming, leading to unwanted fluid movement. The designed ink, however, can be temporarily thinned — via shear thinning — when ultrasound is applied, allowing for deep ultrasound penetration. The resulting sonothermal heating then triggers the ink’s phase transition, increasing its viscosity and reducing undesired acoustic streaming.
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