In-Depth Jet Dynamics Investigations of Femtosecond Laser Bioprinting

The previously developed femtosecond (fs) laser bioprinting is a direct-printing technique, which applies an ultrashort laser source with a wavelength of 1030 nm. Unlike its predecessors, it no longer requires an absorbing layer. The ultrafast laser pulse steers the non-linear interaction within the volume of the transparent bioink. Optical breakdown allows for the strong absorption of the photons in a focal volume with dimensions of a few micrometres. The high energy density leads to the formation of an expanding cavitation bubble and a liquid jet from the surface. This advanced bioprinting technique allows a single cell transfer precision of approximately 15 μm [1]. Additionally, it shows promising results in terms of the survival rate of transferred mammalian cells. In recent studies, cell survival rates of up to 95% [2] could already be achieved, and since this technology is still considerably new, follow up studies are expected to further exceed these numbers. However, mastering the process in its entirety, requires a profound understanding of its physical background, particularly, the mechanisms involved in the jet formation and propagation. Recent studies already indicate that even slight variations of process parameters, drastically affect the transfer behaviour [1]–[3].