Ultrasound single droplet generation and deposition of a nanocellulose bioink*

Drop-on-demand devices and bioinks are critical components of state-of-the-art platforms for bioprinting applications. Commercial nanocellulose bioinks have recently attracted much attention due to their biocompatibility, excellent mixing and rheological properties. In this research, we construct two compact acoustic droplet ejectors using 3D printed Fresnel acoustic lenses. Liquid ejectors with ultrasound frequencies at 2.3 MHz and 4.0 MHz are studied. For droplet generation, we use aqueous suspensions of cellulose nanofibers (CNF), which present remarkably stable shear-thinning and elastic properties. We vary the solid content concentration of our liquid CNF suspension to identify a regime of single droplet ejection. We find that CNF suspensions at concentrations between 0.5% w/v – 0.6% w/v and pH of 8.5 are ideal for single droplet generation. Our acoustic ejectors produce 1.0 mm (4.0 MHz) and 1.5 mm (2.3 MHz) droplet diameters with high reproducibility of greater than 95% accuracy.