By: Hannah Lee
Organ failure is a leading cause of death worldwide. In the United States alone, over 100,000 people are on a transplant waiting list; even those who do receive organ transplants face health issues from immune-suppression drugs* to prevent organ incompatibility. To combat this issue, scientists are developing 3D organs through a method most commonly referred to as bioprinting.
Bioprinting is a scientific technique that involves the usage of 3D printing technology that combines several thin layers of stem cells*, natural polymers, synthetic polymers, and other biomaterials to create artificial organs that accurately imitate real working organs. By printing these artificial organs, patients can receive organ transplants more quickly and with improved safety. This technique can also be applied in other areas such as in drug discovery and organ regeneration. Despite the immense progress made on the development of organ printing, scientists still face numerous ethical, financial, and research-related challenges.
Materials and Techniques:
There are four main techniques for bioprinting: inkjet-based, extrusion-based, laser-based, and combinations of the first three methods; each technique has its own strengths and flaws. All techniques involve the usage of both natural and synthetic polymers as well as hydrogels. In general, bioprinting involves the use of a hydrogel solution which is cut up into 2D slices of the particular organ in high resolution. The slices are then stored as data in a file and sent to 3D bioprinters, which follow instructions in the file, for printing. The file contains information about the organ’s geometric shape, optimal temperature, biomaterials used, etc.
Natural polymers usually use proteins, polysaccharides, and glycoproteins. These polymers provide support for cells and other bioactive agents, allow networks to be semipermeable, guide cells to differentiate* and proliferate* into specialized tissue, and, in specific conditions, aid tissue and organ maturation. Semipermeability* is an especially important function as it allows necessary exchanges to be made in the organ systems and protects entrapped cells and bioagents from environmental stresses. However, natural polymers cannot be printed by themselves because they are usually soluble and cannot handle specific temperatures; instead, these polymers are used as additives in hydrogels or other polymers. Natural polymers play a major role in bio-ink, a combination of biomaterials that replicate an extracellular matrix (ECM)* to support adhesion, proliferation, and differentiation of living cells so the cells can create functional tissue. A prominent type of natural polymer is gelatin which is preferred by many scientists to be used in bio-inks.
On the other hand, synthetic polymers, produced through the chemical reactions of different monomers, are more commonly used as support for the organ to function more stably and safely. Some of its functions are to improve management of cells and space assigned to the organ, enhance mechanical properties, and provide extra functions, for example adding protective covers. Despite the stability synthetic polymers provide, they must be used sparingly due to their lack of functional groups. PEG is a hydrophilic synthetic polymer that can be modified to crosslink with other functional groups, giving the polymer adaptable mechanical properties for 3D bioprinting.
Benefits:
Bioprinting is making fast progress and fine-tuning as more information is being discovered every day. Ideally, the synthesis of 3D-printed organs will provide a much safer way to transplant organs that are compatible with the patient, preventing immune system rejection. As a result, this technology has also solved a lot of bottleneck* problems caused by health issues, for example, it helps to construct vascular and nerve networks that will properly function under stress. The construction of biosynthetic organs continues to advance and is becoming more particular in function as well as efficiency. For example, the idea of “off the shelf” tissue was proposed so that patients could receive fast treatment for damaged tissue, however, scientists still face the issue of providing patient-specific organs quickly.
Drawbacks:
Although 3D Organ Printing has been making fast progress, the unknowns and the risks that come with this technique still seem limitless. One particular problem is that biosynthetic organs must be able to replicate anastomosis* in organs so that the vascular systems will be able to properly exchange and transport materials such as blood and nutrients. Scientists are also unsure of how to ensure organs will be compatible with the patient instead of failing or being rejected by the nervous system. Another issue that scientists face is that they are unsure of how safe or ethical it is to use stem cells and other bioactive agents. As a result, there are a lot of potential risks in using 3D organs and more research and testing must be done to truly apply this technique.
Despite the challenges that come with bioprinting, scientists have made impressive progress so far in printing 3D organs and tissue. Recently, a team of bioengineers from Rice University, the University of Washington School of Medicine and the UW College of Engineering tested a scale model of a lung-mimicking structure. They observed that the structure was strong enough not to bust during blood flow and that red blood cells were successful in taking up oxygen and slowing through the blood vessels around the model. There is still a long way to go, but the mass amount of progress made in the synthesis of 3D organs provides huge progress made in science and medicine.
*immune-suppression drugs: drugs that lower the ability of the body to reject transplanted organs
*stem cells: unspecialized cells that can infinitely produce a copy itself as well as another cell that can differentiate into a specialized cell under certain conditions
*differentiation: when a cell becomes committed to developing into a specialized cell
*proliferation: multiplying in number
*semipermeable: allowing certain substances to pass through, but not others
*extracellular matrix (ECM): a large network of proteins and other molecules that surround, support, and give structure to cells and tissues in the body
*bottleneck: when a population drastically reduces in size because of an event or sudden change in environment
*anastomosis: the union of parts or branches (as of streams, blood vessels, or leaf veins) so as to intercommunicate or interconnect
Sources:
“Anastomosis Definition & Meaning.” Merriam-Webster, Merriam-Webster, https://www.merriam-webster.com/dictionary/anastomosis.
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“NCI Dictionary of Cancer Terms.” National Cancer Institute, https://www.cancer.gov/publications/dictionaries/cancer-terms/def/extracellular-matrix.
“3D Organ Bioprinting Gets a Breath of Fresh Air: UW Bioengineering.” UW Bioengineering | University of Washington Department of Bioengineering, 26 Feb. 2021, https://bioe.uw.edu/3d-organ-bioprinting-gets-a-breath-of-fresh-air/.
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