Manufacturing has historically followed a mass production approach due to economies of scale and the engineering challenges of large-scale customization, leading to a one-size-fits-all paradigm. This manufacturing-centric approach has forced consumers and patients to adapt to medical devices in terms of anatomical fit and biological performance, often significantly decreasing their quality of life. In order to improve the biological interface with the human body, the materials science and bioengineering communities are rapidly adopting three-dimensional (3D) printing, which promises high precision, automation, and a customized fit. However, numerous design and engineering constraints, many posed by the fragile nature of living cells and soft gels, suggest exciting opportunities for further research in materials synthesis, characterization, and integration. Specifically, materials innovations in bioinks and support materials, coupled with improved 3D bioprinting processes for multiple materials, have the potential to empower the next generation of biology by enabling precision engineered tissues, organoids, and eventually whole organs.

Bioprinting, the three-dimensional (3D) printing of cell-laden inks, will be a truly revolutionary technology for the biomaterials community. The number of bioink studies, especially aimed at functional tissues, remains significantly limited, and furthermore, current bioinks are limited by a narrow window of printability. This can be largely attributed to the fact that the preparation of bioinks and their 3D printing is significantly complicated by the presence of cells, which require strict conditions for their viability. This article discusses how cells should be considered during bioink synthesis, 3D printing, and post-printing processing. We also discuss what has been reported thus far with regard to the relationships between bioink material properties and cells. This underlines the need for next-generation bioinks that simultaneously achieve excellent printability, high cell viability, and a wide range of material properties.

Three-dimensional (3D) printing has expanded beyond the mere patterned deposition of melted solids, moving into areas requiring spatially structured soft matter—typically materials composed of polymers, colloids, surfactants, or living cells. The tunable and dynamically variable rheological properties of soft matter enable the high-resolution manufacture of soft structures. These rheological properties are leveraged in 3D printing techniques that employ sacrificial inks and sacrificial support materials, which go through reversible solid–fluid transitions under modest forces or other small perturbations. Thus, a sacrificial material can be used to shape a second material into a complex 3D structure, and then discarded. Here, we review the sacrificial materials and related methods used to print soft structures. We analyze data from the literature to establish manufacturing principles of soft matter printing, and we explore printing performance within the context of instabilities controlled by the rheology of soft matter materials.

Bioprinting promises to create three-dimensional in vitro models to study pathological states and possible new therapies, and in the future, to produce complex tissue and organ replacements. This article will describe the recent advances in bioprinting technologies to engineer artificial tissues and organs by controlling spatial heterogeneity of chemical and physical properties of scaffolds and, at the same time, the cellular composition and spatial arrangement. Despite significant technological improvements in recent years, the positioning at the micrometric level and the switching of different cell types and biomaterials remain a challenge, which limits the development of resilient vascular, neural, and lymphatic networks for metabolites, signaling, and waste transport, and thus limits the development of thick and clinically relevant engineered vascularized tissues.

Three-dimensional (3D) bioprinting has become a fast-developing research field in the last few years. Many different technical solutions are available, with extrusion-based printing being the most promising and versatile method. In addition, a variety of biomaterials are already available for 3D printing of live cells. The real challenge, however, remains bioprinting of macroscopic, volumetric constructs of well-defined structures since hydrogels used for cell-embedding must consist of rather soft materials. This article describes recent developments to overcome these limitations that prevent clinical applications of bioprinted human tissues. New approaches include technical solutions such as in situ cross-linking or gelation processes that now can be performed during the bioprinting process, modified bioinks that combine suitable viscosity and cytocompatible gelation mechanisms, and utilization of additional materials to provide mechanical strength to the cell-laden constructs.

Multimaterial bioprinting technologies offer promising avenues to create mini-organ models with enhanced tissue heterogeneity and complexity. This article focuses on the application of three-dimensional bioprinting to fabricate organ-on-a-chip systems for in vitro drug testing and screening. We illustrate the capabilities and limitations of a bioprinting approach compared to microfabrication in constructing an organ-on-a-chip device. Further, we propose strategies in multimaterial integration for printing microphysiological tissue models. With these analyses, key challenges and future directions are highlighted.

The holy grail of regenerative technologies is to regrow a limb. This grand challenge requires us to develop truly innovative strategies and toolboxes across advanced materials science, stem cell science, physics, and developmental biology, and converge these advancements to address the limitations of wound healing and harness the regenerative capacity in humans. We discuss the convergence approach put forward by the field of regenerative engineering to develop translational strategies involving electrically conductive and novel polymers, stem cells, high-throughput technologies, and nanotechnology to regenerate the limb.