The dawn of commercial bioprinting is rapidly advancing the tissue engineering field. In the past few years, new bioprinting approaches as well as novel bioinks formulations have emerged, enabling biological research groups to demonstrate the use of such technology to fabricate functional and relevant tissue models. In recent years, several companies have launched bioprinters pushing for early adoption and democratisation of bioprinting. This article reviews the progress in commercial bioprinting since the inception, with a particular focus on the comparison of different available printing technologies and important features of the individual technologies as well as various existing applications. Various challenges and potential design considerations for next generations of bioprinters are also discussed.

Drop-on-demand (DOD) bioprinting has attracted huge attention for numerous biological applications due to its precise control over material volume and deposition pattern in a contactless printing approach. 3D bioprinting is still an emerging field and more work is required to improve the viability and homogeneity of printed cells during the printing process. Here, a general purpose bio-ink was developed using polyvinylpyrrolidone (PVP) macromolecules. Different PVP-based bio-inks (0%–3% w/v) were prepared and evaluated for their printability; the short-term and long-term viability of the printed cells were first investigated. The Z value of a bio-ink determines its printability; it is the inverse of the Ohnesorge number (Oh), which is the ratio between the Reynolds number and a square root of the Weber number, and is independent of the bio-ink velocity. The viability of printed cells is dependent on the Z values of the bio-inks; the results indicated that the cells can be printed without any significant impairment using a bio-ink with a threshold Z value of ≤9.30 (2% and 2.5% w/v). Next, the cell output was evaluated over a period of 30 min. The results indicated that PVP molecules mitigate the cell adhesion and sedimentation during the printing process; the 2.5% w/v PVP bio-ink demonstrated the most consistent cell output over a period of 30 min. Hence, PVP macromolecules can play a critical role in improving the cell viability and homogeneity during the bioprinting process.

Collagen, which is often used in healthcare materials and biomedical research, is largely extracted from animal sources. Recombinant human collagen has the potential to be a promising alternative to animal collagen which has many shortcomings, including immunogenicity and lack of biocompatibility. Currently, recombinant human collagen has been expressed in both eukaryotic and prokaryotic hosts with varying degrees of success. One issue with recombinant collagen across all hosts is the inability to achieve full length collagen with native amounts of post‐translational modifications, prompting much exciting research in this direction. There has also been much effort in improving yield and biomimicry of recombinant collagen. This review discusses collagen structure and current methods for extracting animal collagen, before introducing current research in synthesising recombinant human collagen in various hosts, and finally highlighting challenges in the field.

3D bioprinting of hierarchical porous structures for tissue engineering.