# 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
#### 4.1.3 Bioprinting Applications  
The field of bioprinting for organ transplantation and regeneration has witnessed considerable advancement in the creation of thick living cellular structures, which are regarded as an intermediate phase towards organ-level complexity. Despite intrinsic biological and technical constraints, additive manufacturing holds considerable promise in printing complete organs, thanks to its ability to arrange cells hierarchically and build tissue blocks within a three-dimensional microenvironment [69]. In recent years, notable progress has been made in constructing various types of thick tissues with diverse shapes, ultimately aiming to print complete organs or body parts for transplant use. Harvesting a patient's stem cells and printing them into a replacement organ offers the potential to circumvent the complications associated with transplants, such as long donor waiting periods or the risk of immunological rejection of the transplanted organ. Multiple recent advancements have demonstrated the successful 3D bioprinting of tissues, leading to the creation of organ-level structures, including bones [53; 93], cartilage [94], heart [95], and skin [96]. While the fabrication of fully developed vascularized organs would facilitate the production of fully functional human organs suitable for surgical implantation, the realization of this objective still confronts a multitude of challenges, particularly with regard to post-processing remodeling associated with tissue fusion, shrinkage, and compaction of the printed soft tissue [69]. The bioprinting of organs lies far beyond the traditional scope of chemical engineering, yet significant contributions have been made in the preliminary stages toward achieving this goal, providing useful scaffolds or improved bioinks. Despite the high demand for hexagonal scaffolds in liver lobule regeneration, traditional fabrication methods are inadequate to produce their intricate three-dimensional design, making additive manufacturinga better choice. Different hexagonal scaffolds were developed for liver lobule regeneration via bioprinting using biodegradable and photocurable polymeric materials: poly(glycerol sebacate) acrylate (PGSA) and poly(ethylene glycol) diacrylate (PEGDA) [97]. The scaffolds were fabricated with diverse structures, varying surface areas, and three-dimensional designs to optimize cell seeding density and improve culture medium diffusivity. A biocompatible and printable instant gelation hydrogel system was developed based on a designed hyperbranched poly(ethylene glycol)-based multihydrazide macro-crosslinker and an aldehyde-functionalized hyaluronic acid [98]. The reversible crosslinking mechanism between the hydrazide and aldehyde groups provided shear-thinning and self-healing properties to the hydrogel. Moreover, the fast sol-to-gel transition of the hydrogel protected the cells during the bioprinting procedure, avoided their damage during extrusion, and improved the transplanted cell survival, demonstrating great potential to be applied to organ bioprinting. The creation of biomimetic structures within adequate environments for interactions between cells and extracellular matrix can be achieved by bioprinting, thereby mimicking in vivo conditions with high-resolution vascularized tissue. These bioprinted tissues could serve as valuable tools for generating physiologically relevant in vitro models of human organs, useful for drug toxicity testing and disease modeling, and accurately replicating key physiological aspects of the human body. Combining bioprinting with microfluidic technology opens up the possibility of developing miniature in vitro tissue models known as organs-on-chips, which surpass the limitations of traditional models [99; 100]. These tissue models circumvent the ethical challenges associated with animal models, making them an appealing option for various industries. However, they have not yet been systematically validated for reliably predicting toxicity.