Fig. 2: Examples of bioprinted structures using SLAM A) Collagen hand highlighting the ability to print digitating structures B) bioprinted composite structure with regional variation consisting of a 3mm collagen layer and 7mm alginate layer C) Example of a bioprinted spherical structure containing a collagen core and a alginate shell. Credit to Dr Jessica Senior for Figure 2<\/figcaption><\/figure>\nWhen developing this technology, we needed to find or develop a material with very specific properties. The gel needed to be shear thinning to facilitate the depositing needle of the bioprinter to move freely through the material. But at the same time, it needed to restructure quickly in order to support the deposited bioink. Moreover, it was important that the gel material would not integrate with the deposited bioink and that once the printed structure was solidified and ready to be removed from the suspending media the gel could be easily washed off without damaging the structure. Another desired property was for the gel to be stable at 37\u00b0C so that, if needed, the 3D bioprinted structure could be incubated in situ within the suspending media until required.<\/p>\n
We managed to achieve all of these properties using an agarose particulate fluid gel. Fluid gels (sometimes termed \u2018sheared gels\u2019) can be prepared from many gel-forming polymers by applying shear as the material passes through its sol-gel transition. The resulting material is a suspension of gel particles that can be poured like a liquid but have solid-like behaviour when at rest, which is in stark contrast to the solid bulk gel that would be produced if allowed to gel quiescently.<\/p>\n
Furthermore, these materials are created through a mechanism similar to that of crystallisation and growth, which therefore gives rise to various microstructures that include spherical particles, ellipsoids, elongated structures, and hairy particles. This is distinctly different to the gelled particles that are obtained by mechanically breaking a solid bulk gel into a slurry.<\/p>\n
Importantly, the nature of the fluid gel microstructure produced can be controlled during manufacture and it depends on several environmental parameters such as shear rate, temperature, and those that are intrinsic to the material such as chemical structure and gelation kinetics. When processing agarose in a specific way, it was possible to generate a fluid gel consisting of microscopic hairy particles that entangle at rest, creating solid like behaviour. However, with the addition of a small amount of agitation, they can easily flow and, importantly, once the agitation force has been removed, the particles quickly re-entangle reverting to a solid-like behaviour. This behaviour was deemed ideal for suspending medium.<\/p>\n
In addition, agarose gels have many other favourable properties, including thermal stability at 37\u00b0C, they are biologically compatible, they are from a non-animal origin, are non-toxic, are transparent, and can easily be washed off the printed construct.<\/p>\n
Although it is relatively easy to make an agarose fluid gel, we found that any small deviations in the parameters used during manufacturing can result in different particle sizes, and subsequently, a change in the performance of the fluid gel as a suspending medium. As such, optimising the performance and reproducibility of the fluid gel was initially a significant challenge that was overcome by carefully controlling production conditions.<\/p>\n
What will the main applications of the gel be (osteochondral plugs to repair cartilage defects etc.)?<\/h3>\n The main function of the fluid gel material in bioprinting will be to allow printing of low viscosity bioinks, which will enable the printing of various soft tissues and also facilitate the printing of tissue interfaces between hard and soft tissue. Thus, replicating tissues with natural gradients such as osteochondral region, skin, or neural interfaces.<\/p>\n
We believe there are, however, many additional applications that we are only just beginning to realise. These include developing disease models, developing tissue replicas as in vitro drug screening platforms, and in developing more sophisticated wound dressings.<\/p>\n
There are also wider applications of fluid gel materials beyond bioprinting due to their tuneable multifunctional material behaviour. We have recently explored using fluid gels as drug delivery systems, for instance, and have developed modified release oral liquid medicines, mucoadhesive nasal sprays, and topical gel formulations, while other groups have investigated using these materials to deliver bioactives in ophthalmic formulations and in cell delivery.<\/p>\n
How important is it for the new manufacturing process to allow for the use of a wide range of polymeric materials, including many already approved by regulatory bodies? Are there any yet to be approved materials that you also feel could have added benefits?<\/h3>\n Formulation of a range of bioinks is paramount for the successful development of bioprinted living structures. This technology will facilitate the use of materials that are not compatible with conventional printing techniques. Indeed, we have demonstrated that it is possible to 3D print with bioinks that have viscosities as low as water. We believe this will enable the use of more materials, in particular biopolymers, many of which already have regulatory approval but are currently poorly compatible for bioprinting systems either due to low viscosity or lengthy gelation kinetics. This will subsequently result in a quicker route to clinical trials of bioprinted constructs.<\/p>\n
It is important to note that there are other fluid gels or even gel slurries (mechanically homogenised gels) that can be used as suspending medium for 3D bioprinting that have their own particular advantages and disadvantages depending on the type of tissue to be printed, the bioinks used, and material used to create the suspending medium.<\/p>\nWhen using standard extrusion bioprinting, the low viscosity liquid bioink can spread quickly when deposited onto a planar surface before crosslinking can be initiated, thereby resulting in poor resolution at best, or even completely misshapen and collapsed structures<\/figcaption><\/figure>\nMoving forwards, you also plan to investigate the integration of stem cells into the system. What do you hope to achieve here, and what are your more general hopes for the future?<\/h3>\n We have recently undertaken work with adipose derived mesenchymal stem cells and demonstrated that they can be differentiated following bioprinting using SLAM. This has enabled us to 3D bioprint a full thickness skin model (epidermis, dermis, and hypodermis) containing adipocytes that had differentiated from the loaded stem cells within the hypodermal layer.<\/p>\n
We are currently exploring the use of SLAM to create a range of soft tissue models that include skin to assess topical drug delivery and as potential wound healing solutions, and brain cancer models to test potential drug treatments.<\/p>\n
My hope for the future of this system is for it to be used as an enabling technology to create a bioprinted implant that is functional and ultimately improves the quality of life of the recipient.<\/p>\n
Professor Alan Smith<\/strong> \nDirector, The Biopolymer Research Centre <\/strong> \nUniversity of Huddersfield<\/strong> \na.m.smith@hud.ac.uk <\/strong> \nTweet @profalanmsmith<\/a> @HuddersfieldUni<\/a><\/strong> \n https:\/\/research.hud.ac.uk\/institutes-centres\/centres\/biopolymerresearchcentre\/<\/strong><\/a><\/p>\nPlease note, this article will also appear in the seventh edition of our\u00a0<\/em><\/strong>quarterly publication<\/strong><\/em><\/a>.<\/em><\/strong><\/p>\n","protected":false},"excerpt":{"rendered":"Professor Alan Smith discusses a method of using gel particles as a suspending media for 3D bioprinting replacement soft body tissues.<\/p>\n","protected":false},"author":15,"featured_media":14205,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[766,24429],"tags":[3475,24183,24185],"acf":[],"yoast_head":"\n
Reshaping the landscape of 3D bioprinting replacement soft body tissues<\/title>\n \n \n \n \n \n \n \n \n \n \n \n \n\t \n\t \n\t \n \n \n \n \n \n\t \n\t \n\t \n