3D Printing in Suspension Baths: Keeping the Promises of Bioprinting Afloat

Abstract

Extrusion-based 3D printers have been adopted in pursuit of engineering functional tissues through 3D bioprinting. However, we are still a long way from the promise of fabricating constructs approaching the complexity and function of native tissues. A major challenge is presented by the competing requirements of biomimicry and manufacturability. This opinion article discusses 3D printing in suspension baths as a novel strategy capable of disrupting the current bioprinting landscape. Suspension baths provide a semisolid medium to print into, voiding many of the inherent flaws of printing onto a flat surface in air. We review the state-of-the-art of this approach and extrapolate toward future possibilities that this technology might bring, including the fabrication of vascularized tissue constructs. Current Limitations in the Evolution of 3D BioprintingWill we ever be able to engineer functional tissues and organs suitable for in vivo transplantation? Will 3D printing have a role in helping to achieve this? These questions have come to the forefront of research in the tissue engineering (TE) field over the past few decades, fueled by the demonstration that conventional 3D-printing technologies can be adapted to control the deposition of high-density cellular populations in 3D space. Of the different technologies, extrusion-based 3D printing has been identified as the most likely technique to realize the TE vision. Specifically, the mild processing conditions, which have a limited impact on cell viability, in conjunction with their flexibility in processing materials with a broad range of properties make this technology an attractive candidate. Although extrusion printers have been used extensively in the 3D-bioprinting (see Glossary) field, we are a long way from developing whole functional organs. Therefore, it could be hypothesized that a step change is required to harness the full potential of extrusion-based 3D printing in TE.Looking at the plethora of 3D-bioprinting-related publications, there are currently two predominant, distinct perspectives. The first prioritizes ease of fabrication, leveraging materials that can be extruded into filaments with high shape fidelity to create self-supporting structures. This approach has been extrapolated from 3D printing with stiff plastics for medical devices [1], where extruded filaments will immediately hold their shape. Regarding TE, this perspective is related to printing polymer-rich constructs that either are initially acellular or restrict encapsulated cells in their ability to develop tissue.

Design and Characterization of Sheet-Based Gyroid Porous Structures with Bioinspired Functional Gradients

“…Gyroid, one of the most popular TPMS, was utilized here due to its excellent mechanical integrity and porous morphology. Branched structures that are commonly seen in human body, such as coronary arterial tree [ 35 ] and pulmonary trachea [ 36 ], are essential for efficient vascular transport and tissue specific functions [ 37 ]. Inspired by this bionic structure, the TPMS-based scaffold was designed into a branched topology to achieve complex, multi-scale and grading porous structures.…”

Recent progress in extrusion 3D bioprinting of hydrogel biomaterials for tissue regeneration: a comprehensive review with focus on advanced fabrication techniques

“…Recent progress in the application of the jamming transition of granular hydrogels for supporting baths and bioinks expresses a potential paradigm shift in the EBB. They have appeared as a powerful platform for the 3D bioprinting because of the dynamic structures, unique shear-thinning, and self-healing characteristics [336,337].…”

Extrusion and Microfluidic‐Based Bioprinting to Fabricate Biomimetic Tissues and Organs

“…Modulating the shear stress can directly change the cell environment and facilitate high cell viability. [249,250] Desirable shear stress can be achieved by manipulating parameters such as nozzle diameter, the viscosity of the bioink and applied pressure. In microfluidic-based bioprinters which normally work with lower viscosity bioinks, the flow rate plays a crucial role in shear stress applied during bioprinting process.…”