Temperature-Responsive Rheology Modifiers from Cellulose to Enable Acoustic Additive Manufacturing of Hydrogels

While photopolymerization is a widely adopted method for additive manufacturing, its versatility is limited by high attenuation by the polymerization medium, which leads to anisotropic parts and slow printing times. Ultrasound bypasses these depth limitations, but challenges of acoustic streaming and heat localization remain. Here, we investigated a single-phase system that integrates temperature-responsive rheology modifiers to enhance ultrasound-based additive manufacturing. We employed cellulose derivatives with lower critical solution temperatures (LCST) to restrict acoustic streaming and localize heat within the focal zone. Our findings show that these rheology modifiers effectively contain heat, minimizing bulk polymerization and enhancing printing precision. Hydroxypropyl cellulose (HPC)-based sono-inks enable rapid printing speeds of up to 60 mm/min with sub-5 mm resolution. Furthermore, HPC inks demonstrated the capability to print at a distance and through optically opaque tissues. Conversely, methylcellulose (MC) formulations improved printing resolution but reduced speed, likely because the LCST could not be reached during the printing process. The developed sono-ink holds promise for future applications such as in vivo 3D printing, volumetric fabrication, and composite material synthesis.