As of March 2022, there are approximately 106,309 people waiting for an organ donation in the US [1]. Out of this number, about 75% will fail to receive a transplant. Organ donation is largely hindered by donor consent, ethics, and general lack of understanding [2]. While many efforts aim to overcome the barriers by increasing the number of donors and maximizing the effectiveness of organ donations, some attention has turned towards alternative methodologies. With the advent of 3D printing, the option of artificial organs made with tissue engineering has become an increasingly viable alternative. This article will cover the technology behind the printing process, the current applications, and the future direction of the field.
Before covering what the technology can do, here are some basics about bioprinting. There are three main approaches to bioprinting: 2D biolayers printed on top of each other, porous scaffolding later filled with cells, and cellular self-assembly in cell aggregates. The three approaches are used in conjunction with current biological 3D printing tools. Among the available tools, the inkjet printer that can perform all aforementioned approaches is most utilized, where layers of cells are applied with minute jets of biological ink [3]. Since the inkjet printer has been considered the most likely technology to become the main method used, one of the current focuses for researchers has been finding better bioinks that can support a variety of cell types and structural stability [4]. However, since the different approaches are suited to different tasks, most bioprinting approaches use a combination of these methods [5].
While 3D organ printing has not been used in vivo for organs that are typically donated, it has been successfully used in printing multiple different types of grafts and full-size bladders. Although the combination of various cell types in an ordered manner is still slightly beyond the limitations of current technology, several cell types and structures have been independently manufactured and transplanted in the form of grafts. Grafts made from the patient’s cells are advantageous for eliminating the risk of organ rejection and building the organ into needed shapes. Some grafts that have already been used are blood vessels, bones, and cartilage [6]. Regarding full organ transplants, Atala et al. (2006) demonstrated the transplantations of bladders made with the patients’ own cells and the scaffolding method. The patients all showed significant improvements, proving the feasibility of using printed organs [7]. However, bladders are one of the simple organs to 3D print, due to the thinness and lack of cell differentiation and structure [3], so it may be a while before other printed organs are viable.
The target for future research is the assembly of complete organs. The current issue is that the current methods and technology are incapable of effectively creating the structure and precise cell differentiation required before the cells need to be introduced into a metabolically sustainable environment [5]. Therefore, currently tissue engineering is not cost-effective or feasible in a clinical setting. In the future, full organ printing will be needed to ensure long-term cell survivability and control stem cell differentiation [8].
One of the promising technologies is the use of nanocomposite bioinks, or tissue printing ink with minuscule components. These inks can help promote differentiation and cell growth [4]. Once these barriers are overcome, it is likely that 3D organ printing will begin to resolve the organ shortage.
Although 3D printing of the majority of organs to be transplanted in vivo is currently not possible, various manufacturing techniques and ongoing developments show that tissue engineering is a very promising field. Several uses of engineered tissues have already been used in the form of grafts and simple organs, such as bladder implants. In the future, it is likely that complex organs will be able to also be printed. Maybe this technology will be the solution to the organ shortage, and people who need an organ transplant will be able to receive the treatment without helplessly waiting years.
References
1. Heath Resources & Service Administration. (2022, March). Organ Donation Statistics. Organdonor.gov. https://www.organdonor.gov/learn/organdonation-statistics.
2. Lewis, A., Koukoura, A., Tsianos, G., Gargavanis, A. A., Nielsen, A. A., Vassiliadis, E. (2021). Organ donation in the US and Europe: The supply vs demand imbalance. Transplantation Reviews, 35(2), 100585. https://doi.org/10.1016/j.trre.2020.100585
3. Ringeisen, B. R., Pirlo, R. K., Wu, P. K. et al. (2013). Cell and organ printing turns 15: Diverse research to commercial transitions. MRS Bulletin, 38, 834– 843. https://doi.org/10.1557/mrs.2013.209
4. Bhattacharyya, A., Janarthanan, G., Noh, I. (2021). Nano-biomaterials for designing functional bioinks towards complex tissue and organ regeneration in 3D bioprinting. Additive Manufacturing, 36, 101639. https://doi.org/10.1016/j.addma.2020.101639
5. Shapira, A., Dvir, T. (2021). 3D Tissue and Organ Printing—Hope and Reality. Adv. Sci., 8, 2003751. https://doi.org/10.1002/advs.202003751
6. Munoz-Abraham, A. S., Rodriguez-Davalos, M. I., Bertacco, A. et al. (2016). 3D Printing of Organs for Transplantation: Where Are We and Where Are We Heading?. Curr Transpl Rep, 3, 93–99. https://doi.org/10.1007/s40472- 016-0089-6
7. Atala, A., Bauer, S. B., Soker, S., Yoo, J. J., Retik, A. B. (2006). Tissueengineered autologous bladders for patients needing cystoplasty. The Lancet, 367(9518), 1241-1246. https://doi.org/10.1016/S0140-6736(06)68438-9
8. Swarnima, A., Shreya, S., Krishna, B. V., Aniruddha, P., Ananya, B., Subhadip, B. (2020). Current Developments in 3D Bioprinting for Tissue and Organ Regeneration–A Review. Frontiers in Mechanical Engineering, 6. https://doi.org/10.3389/fmech.2020.589171