# 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
This process utilizes a donor layer made of a laser-energy-absorbing material (such as gold or titanium) supported on glass and coated with the biological material (bioink, hydrogel, or cells). When a high-energy pulsed laser is focused on the absorbing layer, it vaporizes a small amount of the donor layer, transferring energy to the substrate where the bioink is present. This generates a high-pressure bubble and creates a small droplet, which is transferred toward the collector substrate [70]. This technology enables precise deposition of materials and high cell densities in relatively small three-dimensional structures without negatively affecting cell viability or function. It is a nozzle-free method, thus not affected by clogging issues and compatible with a range of viscosities. However, the high resolution of this process complicates the uniform distribution of cells in ejected droplets, requires rapid gelation kinetics for high shape fidelity, and results in relatively low overall throughput. Consequently, generating larger, clinically relevant three-dimensional constructs using this method is time-consuming, limiting its widespread application [71]. In evaluating these technologies, it is essential to consider the relative merits and limitations of each, taking into account the specific material and intended application. Inkjet and microextrusion bioprinters offer distinctive advantages in terms of simplicity, flexibility, and relatively low cost. However, these technologies also have inherent limitations. For instance, inkjet bioprinting is susceptible to cell sedimentation due to the low viscosity of bioinks, while microextrusion bioprinting often results in reduced cell viability, which can be attributed to bioink viscosity and shear stress during deposition [72]. Laser-assisted bioprinting offers a number of advantages, including high spatial resolution and the capacity to fabricate three-dimensional biomimetic structures with intricate architectures. However, it requires the use of bioinks with particular gelation properties and typically entails elevated manufacturing costs [70]. Contributions from the chemical engineering research field have improved all these three main technologies for bioprinting. For instance, an improved inkjet bioprinting approach was developed to create mechanically strong bone and cartilage tissue constructs using poly(ethylene glycol) dimethacrylate, gelatin methacrylate, and human mesenchymal stem cells [73]. The adequate design of a simultaneous instant photopolymerization process during the bioprinting was critical to obtain constructs with improved properties. Moreover, a sonochemical treatment was developed to control the viscoelasticity of a gelatin methacryloly-based bioink to be applied by inkjet bioprinting by shortening the length of polymer chains without causing chemical destruction of the methacryloyl groups [74]. This approach effectively increased the maximum printable polymer concentration from 3% to 10% and the control of the mechanical properties resulted in fibroblasts with higher spreading on the hydrogels. Microextrusion bioprinting also can be improved by chemical engineering contributions. Scaffolds produced by traditional microextrusion bioprinting lack collagen anisotropy, which provides essential topographical cues to guide tissue-specific cell function. When extrusion-based bioprinting was combined with a magnetic alignment approach in an innovative 4D printing scheme, tridimensional collagen scaffolds with a high degree of collagen anisotropy were obtained, where human mesenchymal stem cells orient uniformly [75]. More importantly, the obtained collagen anisotropy was found to trigger tendon- or ligament-like differentiation. In another example, the production by the microextrusion-based bioprinting of core/shell constructs to develop millimeter-thick scaffolds with embedded microvasculature for potential soft tissue repair was proposed [76].