# Additive Manufacturing and Chemical Engineering: Looking for Synergies from a Bibliometric Study
## 4 Review of Research Focused on Additive Manufacturing and Chemical Engineering
### Additive Manufacturing and Biofabrication
#### 4.1.1 Bioprinting Technologies  
There are three main technologies for bioprinting: inkjet bioprinting, microextrusion bioprinting, and laser-assisted bioprinting [48]. The selection of these technologies should take into account crucial bioprinting factors such as surface resolution, cell viability, and the choice of biological materials. Inkjet bioprinting is able to generate microscale organization of deposited cells without compromising cell viability or inducing damage. Additionally, this approach offers the possibility of using multiple printheads to simultaneously print various cell types (high throughput), along with bioprinting biomolecules alongside biomaterials, thereby enabling the fabrication of complex multicellular constructs [53]. The two most commonly used methods for cell printing by inkjet are thermal and piezoelectric printing. Printers have been adapted to precisely print picolitre drops of biological materials at a microscale. On the one hand, in thermal bioprinting, the system produces pulses of pressure by vaporization using a heating element, leading to the expulsion of the droplet from the printhead. Despite the demonstration that this localized heating does not have a substantial impact on the stability of biological molecules, the generated heat and resulting evaporation can cause thermal and mechanical stress on the deposited cells and create transient pores in the cell membrane. Nevertheless, the advantages of thermal inkjet printers include high print speed, low cost, and wide availability. On the other hand, in piezoelectric printing, heating is not used; instead, a direct mechanical impulse is applied to the fluid in the nozzle through a piezoelectric actuator, creating an acoustic shockwave that forces the bioink through the nozzle [70]. The advantages of piezoelectric inkjet printers include the ability to generate and control a uniform droplet size and ejection directionality as well as to avoid exposure of the biological molecules to heat and pressure stressors. However, piezoelectric bioprinters are more restricted to material viscosity (ideally below 10 centipoise) due to the excessive force required to eject drops using solutions at higher viscosities. In both inkjet bioprinting cases, after the material is deposited, gelation of the drops must occur immediately through physical or chemical crosslinking to ensure structure stability and preserve shape fidelity, which slows the bioprinting process and involves modification of the bioprinted materials, changing both their chemical and physical properties [71]. Microextrusion bioprinting is the most prevalent technology in this field due to its relatively low cost, accessibility, and adaptability. These systems typically entail the use of multiple syringe-like disposable containers loaded with desired combinations of biomaterials and/or cells, which yield continuous beads of material rather than liquid droplets. Bioinks, hydrogels, biocompatible copolymers, and cell spheroids can be dispensed through a nozzle by the action of pneumatic or mechanical forces (piston-driven or screw-driven) [53]. Pneumatically driven bioprinters have the advantage of having simpler drive-mechanism components. Generally, piston deposition provides more direct control over the flow of bioinks from the nozzle due to the delay of compressed gas volume in pneumatic systems, whereas screw-based systems can offer greater spatial control and are beneficial for -dosing bioinks with higher viscosities [71]. Microextrusion bioprinting technology allows the deposition of higher cell densities than inkjet bioprinting and can manage materials within a very wide range of viscosities. Nevertheless, cell viability after microextrusion bioprinting is lower than that with inkjet-based bioprinting, mainly because of the shear stresses inflicted on cells in more viscous fluids. In laser-assisted bioprinting, a fast-pulsed laser beam is used to selectively propel bioink from a donor layer onto a receiving substrate.