Researchers to Disrupt & Boost Bioprinting with Suspension Bath Techniques

February 18, 2020 by Bridget O'Neal 3D Printing Bioprinting

Share this Article

Researchers from the US and the UK have been working together on complex and unique bioprinting techniques, outlining their findings in the recently published ‘3D Printing in Suspension Baths: Keeping the Promises of Bioprinting Afloat.’ Focusing on the use of suspension in extrusion-based 3D printing, the researchers develop a strategy for creating ‘water-rich’ and self-supporting parts; however, one of their main goals is to disrupt the current status quo of bioprinting.

While bioprinting continues to progress at an impressive pace with many incredible results, the researchers point out that there are still ongoing questions regarding the ability to fabricate truly functional tissue—leading to the pinnacle of success in 3D printing organs for viable transplant. Because 3D printing puts such minor strain on cells during production processes, the technology is viewed as ‘an attractive candidate’ for taking tissue and organ engineering to the next level. Here though, the authors suspect that greater change is necessary within bioprinting to reach that goal of 3D printing entirely functional organs.

Researchers around the world today tend to be involved either in 3D printing that involves extrusion of filament, creating parts and prototypes that are self-supporting (medical devices are a good example), while others, however, are heavily involved in fabrication related to biomimicry, focusing on tissue engineering—usually with the use of bioinks:

“Such structures are more permissive to tissue maturation than is the printing of the previously mentioned polymer-rich constructs. However, bioinks are less suited for use as fabrication materials, due to their innate weak mechanical properties, and thus they are generally avoided for printing structures that are greater than several millimeters in size or require a high structural fidelity,” explain the researchers.

As 3D printing in suspension media has become more viable as a platform, so has the idea of using it as a combination of the two avenues—using extrusion-based 3D printing that deposits materials into a bath. Because objects are suspended within the security of liquid, there is less chance of collapse. Microstructures also quickly recover their shape, transforming back to a solid state. 3D printing of soft materials is possible including those with a high water content, meaning that many more materials become available for use.

Schematic Representation of the 3D Bioprinting in a Suspension Medium Strategy. (A) Writing of bioink material in a self-healing suspension medium[2,6]. The moving extruder nozzle fluidizes the medium to permit the deposition of printed material. The medium then rapidly resolidifies around the printed filament, providing structural support. Yielding of the media occurs at a localized point of injection, with minimal disturbance to the bulk of the medium. Reproduced from the indicated references, licensed under Creative Commons 4.0 (CC 4.0) series. (B) Computer-aided design of intricate, non–self-supporting arterial tree [3]. Adapted from the original, licensed under Creative Commons Attribution 4.0 International (CC BY 4.0). (C) Example of a printed arterial tree that has been printed in a gelatin slurry suspension medium [3]. Reproduced from the original, licensed under CC BY 4.0.

Potential benefits of 3D printing with in suspension media include:

Prevention of collapse of structures
Improved continuous extrusion
Rapid material deposition
Elimination of dehydrated materials and cells
Availability of omnidirectional printing
Printing in arbitrary locations

Suspension media can be retained after the printing process also:

“The inclusion of cells throughout a suspension medium conjures up the idea of the medium acting as a platform to position cells in 3D space, as well as providing a bulk matrix fulfilling some of the functions of a native ECM. The noticeable advantage of suspension media being leveraged in this manner is linked to the opportunity to fabricate larger 3D tissue constructs in a shorter time, increasing the throughput of 3D bioprinting.”

Bioprinting could receive a real boost also as suspension media can act as a support system for low-viscosity bio-inks—assisting in achieving greater viability and sustainability of cells as well as fabricating shapes that are not in need of ‘persistent scaffolding material.’

Advancement of Omnidirectional 3D Printing: From Yield Stress Fluids to Suspension Media. (A) Omnidirectional printing in a non–self-healing yield stress fluid. (Top) Schematic for the 3D-printed vascular network using a removable ink. (Bottom) A fluorescence image of a 3D microvascular network fabricated via omnidirectional printing of a fugitive ink (dyed red) within a photopolymerizable Pluronic F-127–diacrylate matrix. Scale bar, 10 mm. Reproduced from [13]. (B–F)Omnidirectional printing in suspension media. (B) Miniature Russian dolls printed in a granular suspension medium [2]. Reproduced from the indicated reference, licensed under Creative Commons 4.0 (CC 4.0) series. (C) Printedfilament of a fluorescein-labeled ink (in green) surrounded by a continuous spiral structure (in red), printed with a rhodamine-labeled ink [5]. Scale bar, 200μm. (D) Continuous knot written with fluorescent microspheres in a granular suspension medium. Reproduced from [2]. (E and F)Human brain model 3D-printed in an alginate suspension media. Scale bar, 1 cm. [3]. Reproduced from the original, licensed under Creative Commons Attribution 4.0International (CC BY 4.0). Trends in BiotechnologyTrends in Biotechnology, Month 2019, Vol. xx, No. xx5

Suspension Media Used as a Strategy to Aid Better Biomimicry in the 3D-Bioprinting Field. (A) Overview of the 3D-printing pathways that can be followed when printing in a suspension medium. (Top) The pathway is defined by the removal of the medium after printing. Suspension medium provides mechanical stability to printed ink while crosslinking of the ink takes place (e.g., by exposing the embedded ink to ultraviolet light). The medium is subsequently removed in order to extract the printed construct. (Bottom) The pathway is defined by retention of the medium after printing. Following the deposition of a sacrificial ink, the medium is crosslinked to form a single construct. In this crosslinked state, the medium has lost its ability to flow. The sacrificial ink can then be extracted, such as with a syringe needle, leaving behind hollow channels embedded within the construct. (B1) Writing of sacrificial ink within an embryoid body suspension medium [27]. Reproduced from the original, licensed under Creative Commons Attribution 4.0 International (CCBY 4.0). (B2) Row 1: Singular organ building block. Scale bar, 50μm. Row 2: Cross-section of channel printed in an embryoid body suspension medium following removal of the sacrificial printed ink. Scale bar, 500μm[27]. Reproduced from the original, licensed under CC BY 4.0. (C1 and C2) Example of a highly branched tubular network printed in a Carbopol suspension medium where(C2) is the structure freed from the media [2]. Reproduced from the original, licensed under CC BY-NC 4.0. Trends in Biotechnology6Trends in Biotechnology, Month 2019, Vol. xx, No. xx

“We foresee the exploitation of suspension media to double as a bulk matrix providing an enabling technology to engineer large functional tissues. Additionally, we believe there is the potential to embed organoids and print surrounding vascular channels within the suspension medium,” concluded the researchers. “Work by the Lutolf research group in Switzerland showed that separate stages in organoid formation require different mechanical environments. The opportunity to alter the mechanical properties of the suspension medium over time, such as by either the addition of crosslinking chemistries or dilution of a microparticle medium, may be permissive to mimicking the dynamic character of the organoid microenvironment.
“Analogous to the upsurge of research in the biofabrication field within the introduction of the various 3D-printing platforms, we believe suspension media can provide the required technological platform that will support the next level of 3D-bioprinting research.”

Bioprinting continues to encompass a vast area of study as researchers continue to transform the cell culture, innovate with hydrogel microenvironments, create composites for bone regeneration, and so much more.

What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

Suspension Media Used as Technological Aid for 3D Bioprinting of a Human Heart. (A–C) Example of a 3D bioprinted, miniaturized, cell-laden human heart [35]. The figure is reproduced from the indicated references, licensed under Creative Commons Attribution 4.0 International (CC BY 4.0). (D) 3D-printed heart extracted from the medium, then perfused with red and blue dyes to demonstrate hollow chambers within the construct [35]. Scale bar, 1 mm. The figure is reproduced from the indicated references, licensed under CC BY 4.0. (E and F) Gelatin microparticles that comprise FRESH v1.0 and v2.0 suspension media, respectively. From [11]. Reprinted, with permission, from the American Association for the Advancement of Science (AAAS). (G and H) Collagen-printed heart valve, printed within a FRESH v2.0 medium. From [11]. Reprinted, with permission, from AAAS. Trends in BiotechnologyTrends in Biotechnology, Month 2019, Vol. xx, No. xx7

[Source / Images: ‘3D Printing in Suspension Baths: Keeping the Promises of Bioprinting Afloat’]