Droplet-Inkjet

The droplet or inkjet-based printing takes place when a bioink solution is forced under pressure and ejected as droplets through a nozzle onto an electronically controlled stage as a result of thermal or acoustic forces [14,43,44]. This heuristic technology favors the precise control of injected cells, growth factors, genes and drugs

The high resolution of the droplet-inkjet construct enables the control of the geometry and scaffold size, whilst the accuracy of cell positioning is an important advantage of the injection method. Moreover, this method is widely used in the case of blood vessels, due to the high-speed printing and the cost-effectiveness construction [14].

Drawbacks of this method include bioink materials with microcarriers, fragments and highly viscous hydrogels that can accumulate within the nozzle and block the flow [45]. Overall, controlling the number of cells to be encapsulated in a single droplet remains the basic challenge of this method [27].

In the Christensen et al. study, vascular-like cellular structures with horizontal and vertical bifurcations were successfully introduced using a liquid support-based inkjet, while the high post-printing fibroblast's cell viability of printed cellular tubes was also reported [46]. Another study introduced a 3D "half-heart" scaffold with connected ventricles printed via an inkjet-based method, where mammalian cardiac cells remained viable with adequate elastic moduli and tensile strength [47].
