Bioprinting: More Than a Futuristic Dream?

3D printing, originally found and developed in the 1980s, has been widely used in commercial and manufacturing applications. However, when it comes to the adoption of 3D printing human cells and organic structures, it is considered a new and intriguing topic for cell biologists, engineers, material scientists, and others due to its promising potential in producing biomaterials for regenerative medicine. Bioprinting is undoubtedly transforming the way that we think about and approach tissue engineering, regenerative medicine, and healthcare, as it presents an innovative and cost-effective means of producing unique human tissues and organs for transplantation and medical needs.

What is Bioprinting and How Does it Work?

Bioprinting is an additive manufacturing process where biomaterials are added up layer-by-layer to create tissue-like structures based on a pre-constructed digital blueprint file. These structures mimic the behaviour of natural living systems and allow living cells to multiply. The process of 3D bioprinting is very similar to that of conventional 3D printing; in both processes, a physical 3D object is created from a digital model, layer-by-layer. However, the difference between bioprinting and traditional 3D printing is that bioprinting creates structures using a material known as bioink, instead of metals and thermoplastic resin. Bioprinting offers the ability to generate patient-specific tissue that is precisely customized to one’s anatomy, physiology and health needs, allowing for the development of accurate, targeted and individualized treatments.

What is Bioink?

Bioink is the material used in bioprinting to create artificial, engineered live tissue. The primary goal of bioinks is to provide an environment where cells can survive, grow, and proliferate after printing. Bioinks are typically composed of a combination of living cells, growth factors, nutrients, and biocompatible carrier materials that envelop the cells. The living cells that are needed (i.e. kidney cells, lung cells, skin cells, etc.) can be obtained from the patient or donors. Since vital organs require a high number of cells, the obtained cells are then cultivated and replicated in the lab. The carrier material is typically an organic or synthetic biopolymer gel which acts as the building blocks of bioprinted tissues - giving cells the essential cues they need to live, grow and produce functional 3D tissue. Cells attach to the biopolymer gel which allows them to spread, grow and stabilize into the correct form.

The Bioprinting Process (Simplified!)

The bioprinting process can be broken down into 3 core stages: pre-bioprinting, bioprinting, and post-bioprinting.

1. Pre-bioprinting: The bioprinting process begins with the pre-bioprinting stage, in which a digital file is generated using modelling software. These digital blueprints are typically based on computer tomography images and CT or MRI scans taken directly from a patient. Once the digital model is completed, the required cells are isolated, multiplied and combined and the bioink is created. During this stage, researchers use a live-cell imaging system to ensure there are enough cells to successfully print the selected tissue structure.

2. Bioprinting: During the second step of the process, the assembled bioink containing the required proteins and specific cells is placed into a cartridge and deposited in very thin layers from precision printer heads, building up the organic object outlined in the digital file. Depending on the structure that is being built, one or multiple printer heads may be used.

3. Post-bioprinting: The post-bioprinting stage is the final step in the process and a critical part of ensuring the printed structure is stable. In order to maintain the form and function of the generated 3D tissue structure, mechanical and chemical stimulation and physical or chemical crosslinking is required. The process of crosslinking strengthens the 3D printed construct by creating new bonds. While there are various crosslinking methods, the method typically used involves treating the printed construct with ionic solution or ultraviolet light. This stage of the bioprinting process is necessary in preserving the shape and mechanical integrity of the structure and maintaining the growth of tissues and cells.

Advances in Bioprinting

Today, as a result of major advances in acquiring and processing biomaterials and successfully generating realistic templates, scientists have been able to produce accurate 3D versions of human organs using donor stem cells. However, these 3D printed organs are only simplified representations or miniature versions of native organs; we have yet to bioprint functional whole organs that fully mimic the complexity of native organs. But, as bioprinting projects continue to advance and the application of bioprinting techniques grows, we are surely becoming closer and closer to printing functional whole organs that are suitable for transplantation and viable long-term solutions. The following list outlines 8 amazing bioprinting projects that demonstrate our progress towards printing organs that are able to perform the necessary and complex functions of native organs.

1. Heart: Did you know that using bioprinting technology, a miniature heart that accurately matches the cellular, physiological and anatomical properties of a human heart can be created in only 3 to 4 hours? In 2019, a team of researchers bioprinted a cherry sized heart consisting of all the complex structures a heart needs to function normally, including cells, blood vessels, ventricles, and chambers. Using fat tissue obtained from the patient, the researchers were able to develop a patient-specific bioink so that the risk of rejection would be reduced when implanted. However, while the cells used to create the 3D printed heart were able to contract, they did not possess the ability pump.

2. Kidney: Professor Anthony Atala, director of the Wake Forest Institute of Regenerative Medicine, successfully bioprinted a kidney in only 7 hours, in 2011. This was a first for the industry. Unfortunately, the kidney did not survive for very long. However, in 2019, researchers at Harvard University successfully bioprinted a vascularized proximal tubule model that mimics the kidney’s reabsorption function to better understand the structure and functions of the kidney. The model successfully remained functional for months.

3. Corneas: Did you know that as of 2021, approximately 10 million people worldwide require a cornea transplant to prevent corneal blindness? With such a high demand for corneal transplants, there is a significant shortage of corneas available for transplantation. However, in 2018, researchers at Newcastle University made a breakthrough advancement in ophthalmology when they developed the first 3D printed artificial cornea in less than 10 minutes, using a unique bioink that combined alginate and collagen. After scanning, studying, and collecting data on a patient’s eyes, the researchers were able to design a 3D model of a cornea that matches the size, shape and other unique specifications of the patient.

4. Ovaries: In May 2017, Northwestern University researchers successfully implanted a bioprinted ovary in a sterile mouse, allowing the mouse to give birth to a litter. Following this achievement, the researchers went on to create a bioink that could bioprint functional human ovaries. This was achieved by identifying and mapping the location of the structural proteins in a pig ovary, as pig ovaries have the same type of proteins found in humans.

5. Liver: Researchers from São Paulo, Brazil have successfully used blood cells to bioprint fully functioning miniature versions of a human liver in only 90 days. These mini-livers can produce vital proteins, store vitamins, secrete bile, and perform all other typical functions of a native liver.

6. Ears: In 2018, Queensland University of Technology (QUT) and the HearSay Foundation successfully constructed a fully functional ear using 3D bioprinting for Maia Van Mulligan - a two-year old girl who was born with one ear due to a condition known as Microtia. Using Maia’s cartilage cells, researchers were able to bioprint an ear implant to help her hear again.

7. Pancreas: On March 14th, 2019, the Foundation for Research and Development of Science printed the first ever, fully vascularized bionic pancreas. This innovation aims to help eliminate the need for diabetic patients to inject insulin and minimize the development of secondary complications and progression of diabetes in patients.

8. Skin: To date, there have been several studies conducted on the fabrication of human skin using bioprinting technology. By using bioink composed of donor keratinocytes, the primary cell found in the outer layer of skin, and fibroblasts, the primary cell found in connective tissue, researchers have successfully bioprinted skin tissue that is morphologically and biologically representative of human skin tissue. Additionally, the use of melanin-producing cells in the bioprinting process has enabled the creation of bioprinted skin tissue that is similar in pigmentation to the skin cell donors. Skin tissue bioprinting technology plays a huge role in the ability to improve wound healing and wound reconstruction. However, there is still a lot of research to be done in order to bioprint skin tissue that replicates the complete physiology and anatomy of human skin, including the ability to stimulate the regeneration of nerves, hair follicles, and sweat glands.

Applications of Bioprinting

Artificial Organs

Currently, there are thousands of people worldwide who are waiting to receive a critical organ transplant, and unfortunately, the organ donor list is unable to meet the growing demand for organ transplants. One of the ultimate goals of bioprinting is to generate personalized, patient-specific organs for transplantation to meet this demand and eventually eliminate the extensive organ transplant waiting list. Even once a donor organ is received and transplanted, there is a very high risk that the patient’s body will reject the organ if it recognizes it as foreign. With bioprinted organs, the patients’ own cells can be used to print a customized organ - reducing the risk of rejection.

Drug Development and Testing

Bioprinted organ models can also be used to eliminate the use of living subjects for drug testing, offering a more ethical, precise, and cost-effective solution. 3D bioprinting technology allows you to produce patient-specific, disease-relevant tissue models that can be used to evaluate the impacts and side effects of drugs. By using personalized models, researchers can more accurately analyze how potential new treatments may impact a patient’s body. Additionally, using miniaturized models that replicate a patient’s diseased tissue can allow researchers to test and scan the effects of different possible treatments, and determine what treatment would be the best individual choice for that specific case. This personalized approach that bioprinting offers not only saves money and time, but it helps avoid the administration of ineffective or harmful treatments; ultimately increasing the patient’s chance of recovery.

Teaching and Education

As discussed in our previous blog, a major application of 3D printing is the creation of anatomical models for medical education, preoperative planning, and patient-specific care. Accurate bioprinted organ models are often used to help teach and train medical professionals as they can provide a better visualization of a patient’s medical condition; for example, a bioprinted model can provide a better visualization of the disease location relative to adjacent organs. Additionally, bioprinted organ models have been used to help simulate complex surgeries. Researchers at Carnegie Mellon University have successfully bioprinted a full-sized human heart model that allows for visual planning and physical practice. This bioprinted heart model provides medical professionals with realistic practice and training as it can be manipulated and worked on like a real heart, and it will respond like real tissue. 3D bioprinting has also been used to develop patient specific cancer models that contain patient-derived cancer and mimic the behavior of real tumors. Such bioprinted cancer models are used for personalized cancer therapy screening and to investigate the growth of the cancer cells to learn how to better combat them.

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