**2.3 Laser-based printing**

There are two laser-based techniques used for bioprinting. The first is stereolithography (SLA), which is a nozzle-free technique that depends on photocuring with ultraviolet light (UV). The UV energy is directed at a reservoir of photosensitive polymers to formulate 3D structures in a layer-by-layer fashion. This technique is known to have quick fabrication times as its speed depends on the height of the print rather than on the print complexity [19]. A resolution ranging between 5 and 300 μm can be achieved using SLA [20, 21]. This technique is not limited by the viscosity of the bioink, however, photoinitiators are often added to the bioink to improve polymer photosensitivity, and can affect the viability of the cells. The type and concentration of photoinitiator will influence cell viabilities differently [19]. Another concern is UV-induced damage to the cells, and has led to the development of alternative visible light-based and initiator-free techniques [22, 23]. Collectively, the short fabrication time and the absence of shear stress-induced apoptosis make SLA a good candidate for bioprinting.

 Another laser-based bioprinting technique is laser-assisted bioprinting (LAB), which is a scaffold-free and nozzle-free technique where droplets of biomaterial/ cells/peptides are propelled from a donor material slide onto a receiver material. Laser energy induces a vaporization effect used to transfer material from the donor material slide onto the receiver. This technique can achieve a micro-scale resolution with multicell positioning [24, 25]. The accurate positioning of multiple cell types using this technique has great potential in creating biologically relevant complex designs, yet the main drawbacks of this technique are its low stability and scalability [24].
