Over the years, the field of bioprinting has attracted attention for its highly automated fabrication system that enables the precise patterning of living cells and biomaterials at pre-defined positions for enhanced cell-matrix and cell–cell interactions. Notably, vat polymerization (VP)-based bioprinting is an emerging bioprinting technique for various tissue engineering applications due to its high fabrication accuracy. Particularly, different photo-initiators (PIs) are utilized during the bioprinting process to facilitate the crosslinking mechanism for fabrication of high-resolution complex tissue constructs. The advancements in VP-based printing have led to a paradigm shift in fabrication of tissue constructs from cell-seeding of tissue scaffolds (non-biocompatible fabrication process) to direct bioprinting of cell-laden tissue constructs (biocompatible fabrication process). This paper, presenting a first-time comprehensive review of the VP-based bioprinting process, provides an in-depth analysis and comparison of the various biocompatible PIs and highlights the important considerations and bioprinting requirements. This review paper reports a detailed analysis of its printing process and the influence of light-based curing modality and PIs on living cells. Lastly, this review also highlights the significance of VP-based bioprinting, the regulatory challenges and presents future directions to transform the VP-based printing technology into imperative tools in the field of tissue engineering and regenerative medicine. The readers will be informed on the current limitations and achievements of the VP-based bioprinting techniques. Notably, the readers will realize the importance and value of highly-automated platforms for tissue engineering applications and be able to develop objective viewpoints towards this field.

In recent years, there has been widespread adoption of machine learning (ML) technologies to unravel intricate relationships among diverse parameters in various additive manufacturing (AM) techniques. These ML models excel at recognizing complex patterns from extensive, well‐curated datasets, thereby unveiling latent knowledge crucial for informed decision‐making during the AM process. The collaborative synergy between ML and AM holds the potential to revolutionize the design and production of AM‐printed parts. This review delves into the challenges and opportunities emerging at the intersection of these two dynamic fields. It provides a comprehensive analysis of the publication landscape for ML‐related research in the field of AM, explores common ML applications in AM research (such as quality control, process optimization, design optimization, microstructure analysis, and material formulation), and concludes by presenting an outlook that underscores the utilization of advanced ML models, the development of emerging sensors, and ML applications in emerging AM‐related fields. Notably, ML has garnered increased attention in AM due to its superior performance across various AM‐related applications. It is envisioned that the integration of ML into AM processes will significantly enhance 3D printing capabilities across diverse AM‐related research areas.

Bioprinting is a promising automated platform that enables the simultaneous deposition of multiple types of cells and biomaterials to fabricate complex three-dimensional (3D) tissue constructs. Collagen-based biomaterial used in most of the previous works on skin bioprinting has poor printability and long crosslinking time. This posed an immense challenge to create 3D constructs with pre-determined shape and configuration at high throughput. Recently, the use of chitosan for wound healing applications has attracted huge attention due to its attractive traits such as its antimicrobial properties and ability to trigger hemostasis. In this paper, we optimized polyelectrolyte gelatin-chitosan hydrogel for 3D bioprinting. Modification to the chitosan was carried out via the oppositely charged functional groups from chitosan and gelatin at a specific pH of ~pH 6.5 to form polyelectrolyte complexes. The polyelectrolyte hydrogels were evaluated in terms of physical interactions within polymer blend, rheological properties (viscosities, storage and loss modulus), printing resolution at varying pressures and feed rates and biocompatibility. The polyelectrolyte gelatin-chitosan hydrogels formulated in this work was optimized for 3D bioprinting at room temperature to achieve high shape fidelity of the printed 3D constructs and good biocompatibility with fibroblast skin cells.

Three-dimensional (3D) pigmented human skin constructs have been fabricated using a 3D bioprinting approach. The 3D pigmented human skin constructs are obtained from using three different types of skin cells (keratinocytes, melanocytes and fibroblasts from three different skin donors) and they exhibit similar constitutive pigmentation (pale pigmentation) as the skin donors. A two-step drop-on-demand bioprinting strategy facilitates the deposition of cell droplets to emulate the epidermal melanin units (pre-defined patterning of keratinocytes and melanocytes at the desired positions) and manipulation of the microenvironment to fabricate 3D biomimetic hierarchical porous structures found in native skin tissue. The 3D bioprinted pigmented skin constructs are compared to the pigmented skin constructs fabricated by conventional a manual-casting approach; in-depth characterization of both the 3D pigmented skin constructs has indicated that the 3D bioprinted skin constructs have a higher degree of resemblance to native skin tissue in term of the presence of well-developed stratified epidermal layers and the presence of a continuous layer of basement membrane proteins as compared to the manually-cast samples. The 3D bioprinting approach facilitates the development of 3D in vitro pigmented human skin constructs for potential toxicology testing and fundamental cell biology research.

Bioprinting is an emerging research field that has attracted tremendous attention for various applications; it offers a highly automated, advanced manufacturing platform for the fabrication of complex bioengineered constructs. Different bio-inks comprising multiple types of printable biomaterials and cells are utilized during the bioprinting process to improve the homology to native tissues and/or organs in a highly reproducible manner. This paper, presenting a first-time comprehensive yet succinct review of microvalve-based bioprinting, provides an in-depth analysis and comparison of different drop-on-demand bioprinting systems and highlights the important considerations for microvalve-based bioprinting systems. This review paper reports a detailed analysis of its printing process, bio-ink properties and cellular components on the printing outcomes. Lastly, this review highlights the significance of drop-on-demand bioprinting for various applications such as high-throughput screening, fundamental cell biology research, in situ bioprinting and fabrication of in vitro tissue constructs and also presents future directions to transform the microvalve-based bioprinting technology into imperative tools for tissue engineering and regenerative medicine.