3D bioprinting is defined as “the construction of tissue constructs using a set of techniques that transfer biologically important materials onto a substrate with computer-aided, specialized 3D printers.”
The arena of bioprinting, even though young and evolving, has established a niche for itself across various branches of science and technology, including but not limited to materials sciences, tissue engineering, biomedicine, regenerative therapeutics, prosthetics, dentistry, microfluidics, and space technology to name a few.
So, is bioprinting different from 3D printing?
The answer is yes and no! The principle involved in bioprinting is like that of 3D printing. For example, in the case of 3D printing, we design a model that takes physical shape and is printed layer by layer using a polymer/resin/thermoplastic material. When we investigate bioprinting, we replace this resin/polymer with a living cell suspension which gets printed. To ensure that the printed model serves its purpose (in the field of regenerative/reparative/restorative therapy) certain conditions such as maintenance of sterile printing and post-printing environment, temperature control, etc., must be ensured and enforced.
There are three main stages of bioprinting that are employed across multiple fields listed above1. In the context of organ/tissue printing, these stages can be divided into substages as shown in figure 1.
- Preprocessing – to create a display model of the desired tissue to be printed.
- Processing/Printing – Printing process with the help of bio-inks.
- Post-processing – Ensuring the stability of the printed biological material through chemical and mechanical stimulation.
During the preprocessing stage, the role and contribution of computer-aided systems (design and manufacturing—CAD/CAM) cannot be undervalued. The history of CAM dates to the 1950’s when the first commercial numeric control programming system was developed named PRONTO (Program for Numerical Tooling Operations) was developed. The credit for the development of CAD goes to Dr. Ivan Sutherland from the Massachusetts Institute of Technology (MIT), and the first-ever CAD software was known as Sketchpad. The impact of these inventions laid the foundations of modern-day CAD/CAM technology that makes 3D printing (bioprinting) a reality. CAD/CAM technologies have greatly impacted and benefitted the manufacturing industries, which further paved the way for its expansion into Additive Manufacturing (AM)/ 3D Printing (3DP) technologies. Today, AM encompasses various forms such as fused deposition modeling (FDM), stereolithography (SLA), laser sintering (SLS), electron beam melting (EBM), and material jetting (MJ) to name a few2. This further manifested into the field of bioprinting focused on on-body applications. The early 1990’s saw the first successful research output which involved the use of CAD technology to bio print 3D scaffolds3. This research by Langer and Vacanti, was a breakthrough in the field of regenerative tissue engineering and despite the cons of the scaffolds in terms of porosity and lack of intricate nutrient infiltration networks, served as the inspiration for a decade long such endeavors within the scientific community. Such tremendous progress due to advancements in 3DP has made precise control of bio-printed scaffolds a reality today in addition to creating a flourishing market for a wide spectrum of bio-inks to print them4. Throughout this journey, CAD/CAM technologies provided a supporting platform to bring about extensive and exhaustive improvements to the design and development processes5.
As the field of bio printing evolved, the need to visualize and capture the models created through CAD/CAM in 3D rose steadily. This led to development and fine tuning of multiple technologies in the arena of medical imaging, such as, computed tomography (CT), positron emission tomography (PET), sonography, magnetic resonance imaging (MRI), to name a few. By utilizing 3D imaging modules, these techniques paved way for us to visualize broken bones and observe blood vessels for adequate blood flow patterns6. Thus, patient specific 3D geometry data is generated for better understanding of the complexities of the human body. In the direct context of bio printing, the relationship of 3D printing and biomedical imaging can be described in a fourfold manner (figure 2) as published by Squelch (2018)7.
Today, there are still substantial challenges to overcome with regards to establishing ideal data processing methodologies, establishing model accuracies and in mimicking the scanning processes at a cellular level8.
The actual bio printing process is made possible with the help of bio inks. The origin of the term bio ink dates to early 2000’s where it was used as a complementary term with bio paper. Bio paper was mainly a hydrogel material that required the insertion of living cells or tissue constructs as the ‘bio ink’ during the printing process. The definition of bio-ink could be stated as the cellular component that was deposited within the 3D space of the design model tissue to be printed9. Bio inks could thus be aptly called the foundation of the bioprinting process. Careful considerations need to be taken into account while choosing the appropriate bio-ink material, which drastically influences the cell viability, lifespan of the printed construct and its mechanical stability post-implantation. However, till date, there is no single bio ink that could be universally adapted for versatile applications as the mechanical strength and requirements vary drastically between our biological tissues. A wide spectrum of natural and synthetic materials have been investigated to serve as bio inks4,10. Some of them are mentioned below.
Table 1 : A brief overview of biomaterials that have been extensively investigated as bio inks for bioprinting.
There are some properties that these bio ink candidates need to fulfil to be accepted for commercialization. These properties can be classified under four broad disciplines namely: chemical, rheological, mechanical and biological11. In the next few articles, we aim to provide our readers with more insights on the most desirable properties, studies showing current applications of these bio inks and present a few commercial bio ink materials that are out in the market to this date.
Moving on to the post processing stage, bioreactors are essential tools in making organ printing a reality. In simple terms, organ printing is the biomedical application of additive manufacturing processes, enabled largely by “computer-aided robotic layer by layer additive bio fabrication of functional living human tissue constructs”12. The fundamental principle behind organ printing revolves around tissue fusion which is accomplished to a large extent on a small scale with bioreactors and tissue spheroids. Post-processing plays an important part in the whole bioprinting process in conferring stability and ensuring that the printed construct is mechanically viable for the intended application. In this regard, different types of bioreactors dominate tissue and organ regeneration arena today, each applicable for a particular organ of interest, for instance: Cartilage tissues prefer a compression-based bioreactor13.The most commonly used bioreactors in the field of bioprocessing are:
- Stirred Tank Bioreactors
- Bubble Column Bioreactors
- Airlift Bioreactors
- Fluidized Bed Bioreactors
- Packed Bed Bioreactors
Each of these have innate advantages and concerns in context to desired tissue construct that can be grown in it which are beyond the scope of this current article. However, in addition to choosing the right type of bioreactor, finding the optimal parameters to tailor such as hydrostatic pressure, shear stress, growth factor control plays a predominant role in finally defining the outcome of the process14. Moreover, the outcome of bioprinting a tissue in a bioreactor is not always the final product. Accelerated maturation of the bio printed construct with the help of a pre-defined concoction of chemical and physical factors is carried out. These factors are known as maturogens or maturogenic factors. Till date, there are quite a few matrix materials that have been established as maturogenic factors – TGFβ, Serotonin, Periostin, Transglutaminase, Fibronectin to name a few15.
Having understood the basic processes and terminologies involved in various stages of printing an organ/tissue construct, let us continue our discussion on the different types of bioprinters in the upcoming article. Stay Tuned!
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2. Wimpenny, D. I., Pandey, P. M. & Kumar, L. J. Advances in 3D printing & additive manufacturing technologies. (Springer, 2017).
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4. Chopra, H., Kumar, S. & Singh, I. Bioinks for 3D printing of artificial extracellular matrices. in Advanced 3D-Printed Systems and Nanosystems for Drug Delivery and Tissue Engineering 1–37 (Elsevier, 2020).
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6. Abdullah, K. A., McEntee, M. F., Reed, W. & Kench, P. L. Development of an organ‐specific insert phantom generated using a 3D printer for investigations of cardiac computed tomography protocols. J. Med. Radiat. Sci. 65, 175–183 (2018).
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10. Janarthanan, G. & Noh, I. Recent trends in bioinks for 3D printing. Biomater. Res. 22, (2018).
11. Lee, H. J. et al. A new approach for fabricating collagen/ECM‐based bioinks using preosteoblasts and human adipose stem cells. Adv. Healthc. Mater. 4, 1359–1368 (2015).
12. Esmond, R. W. & Sterling, D. Bioprinting: The Intellectual Property Landscape BT – 3D Printing and Biofabrication. in (eds. Ovsianikov, A., Yoo, J. & Mironov, V.) 1–28 (Springer International Publishing, 2016). doi:10.1007/978-3-319-40498-1_18-1.
13. Elitok, M. S., Gunduz, E., Gurses, H. E. & Gunduz, M. Tissue engineering: towards development of regenerative and transplant medicine. in Omics Technologies and Bio-Engineering 471–495 (Elsevier, 2018).
14. Rosser, J. & Thomas-Vazquez, D. Bioreactor processes for maturation of 3D bioprinted tissue. in 3D Bioprinting for Reconstructive Surgery: Techniques and Applications 191–215 (2018). doi:10.1016/B978-0-08-101103-4.00010-7.
15. Hajdu, Z. et al. Tissue spheroid fusion-based in vitro screening assays for analysis of tissue maturation. J. Tissue Eng. Regen. Med. 4, 659–664 (2010).
About the Author:
Dr VIDYA CHAMUNDESWARI NARASIMHAN (Scientist) 3DHEALS COMMUNITY MANAGER SAN FRANCISCO
Dr. Vidya is a Research Scientist at an upcoming cultivated meat company based in Berkeley, California. She received her Ph.D from Nanyang Technological University(NTU), Singapore in 2018. Her research focused on developing bioactive polymeric scaffolds for musculoskeletal tissue regeneration applications.
Over the last two years, Vidya spearheaded various academia-industrial collaborative projects in Singapore. At 3DHEALS, she is our Community Manager of San Francisco Bay Area and is also actively involved in STEM mentor ship as well as in tutoring University and Junior college students for various competitive examinations.
Vidya has been actively involved in research pertaining to sustainability within the agro-food and biomaterials sector, and is passionate about emerging technologies in the field of 3D bioprinting. She hopes to actively share and spread this interest amongst like minded professionals in the field of regenerative medicine and tissue engineering. Currently Vidya has contributed to a couple of expert column blogs on bone tissue engineering and is the co-instructor of an online course on Bioinks used for Bioprinting available on Udemy!