3D Bioprinting: Process, Types, and Applications

In this hectic era of fast revolution, our average life span has decreased to 60 years. Today’s unhealthy and unorganized lifestyle is also a reason for deteriorating health and malfunctioning of organs. These all result in a decrease in immunity and we are becoming more prone to diseases. As a result, we need good research in the medical field. These require cadavers and organs of human beings and even animals that are useful in biological laboratory research. Nowadays, to fulfil these needs many people are engaged in illegal practices. To overcome this problem we use 3D bioprinting or bioprinting to create artificial organs for research or transplants and cadavers for study purposes.

Image source: Mason, J., Visintini, S., & Quay, T. (2019). An overview of clinical applications of 3-D printing and bioprinting. CADTH issues in emerging health technologies.

3D Printing

3D printing technology is an innovative way to create objects like tools toys, clothing, and even body parts, etc. This is basically the process of additive manufacturing where the object is created by adding material layer by layer. However, it is contradictory to the subtractive manufacturing technique thus reducing the wastage of materials. Also, this technique reduces the cost and helps in producing complex parts in minutes. Moreover, it has already been useful in building houses as in China. 3D printing has its approach to major innovations in areas, such as engineering, manufacturing, art, education, and medicine.

The first step in 3D printing is to particularly create a blueprint of the object you want to print. This uses modeling software to create designs, then these models are sent to the printers to be printed. Thus, if we use biomaterials in the printer to create biological parts then the process is called 3D bioprinting or simply bioprinting.

Also read- Cardiovascular diseases: Types, Symptoms & Tests (mybiologydictionary.com)

3D Bioprinting

To begin with, it is one of the applications of 3D printing which uses the same additive manufacturing technique to produce biological parts, organs, tissues, and cells. It even has the potential to produce complex composite tissue construct through the layer-by-layer fusion or placement of biomaterials and living cells. 3D bioprinting is an emerging technology that is expected to revolutionize the field of tissue engineering and regenerative medicine.

In other words, it can be said that it is the branch of regenerative medicine. It works in integration with tissue engineering and molecular biology to replace, engineer, or process organs, tissues, etc. to restore or establish normal function. Due to the use of materials like cells, bio-inks, controlling factors like growth, temperature, etc. 3D bioprinting is complex. Also, it involves certain technical challenges related to the sensitivities of living cells and the construction of tissues. Hence to overcome these complexities, we require the interdisciplinary field of work to integrate technologies like engineering, biomaterial science, tissue engineering, cell biology, physics, and medicine.

Process of 3D Bioprinting

Bioprinted human tissues involve several stages namely pre-processing, processing, and post-processing to tissues.

1. Pre-processing:

In this step, cells are isolated from the human body. These cells are mainly stem cells that have the property of being totipotent. As result, they can regenerate and differentiate. And most importantly, when these are used in transplants, it prevents graft rejection problems. These isolated cells are now cultured in-vitro for cell expansion. In parallel, the blueprint design of the 3D scaffold model is created that is to be fed into the software to get printed.

2. Processing:

In this process, the bio-ink is prepared, it is basically a biomaterial that is printed. Its preparation is done by mixing cultured cells with hydrogel, in addition to growth factors and optimum conditions. The selection of proper boi-ink is very crucial as it provides the required properties for adequate printing fidelity and mechanical properties. Then the model is printed using appropriate biomaterial and injecting technique as per the requirement.

3. Post-processing:

It particularly involves bioreactor culture systems for stabilization and in vitro scaffold maturation. This is done particularly under optimum conditions, nutritional levels, oxygen delivery, and waste removal.

Types of bioprinting techniques

Bioprinting techniques are mainly divided into three categories. Each technique has its advantages and limitations which we are going to discuss further:

 1. Inkjet-based 3D bioprinting:

Image source: Zheng, Z., Eglin, D., Alini, M., Richards, G. R., Qin, L., & Lai, Y. (2021). Visible light-induced 3D bioprinting technologies and corresponding bioink materials for tissue engineering: A review. Engineering, 7(7), 966-978.

It is very similar to the conventional 2D inject printing process that uses desktop inkjet printers and is also the first bioprinting technology. In this method, the biomaterial is made to directly dispense out of the print head. It works either on the continuous mode or the drop-on-demand mode. In continuous mode, the bio-ink comes out in the continuous column, thus also called continuous inkjet or continuous stream. Whereas, in drop-on-demand mode, bio-ink comes out in the form of discrete droplets.

This technique has various advantages like high-throughput capability, high resolution, inexpensiveness, reproducibility, relatively high cell viability, etc. Moreover, it helps in depositing multiple cells or proteins to the targeted place with multiple print heads. For this, the most crucial part is the choice of bio-ink material.

2. Laser-assisted 3D bioprinting:

Image source: Keriquel, V., Oliveira, H., Rémy, M., Ziane, S., Delmond, S., Rousseau, B., … & Fricain, J. C. (2017). In situ printing of mesenchymal stromal cells, by laser-assisted bioprinting, for in vivo bone regeneration applications. Scientific reports, 7(1), 1-10.

Laser-assisted bioprinters mainly consist of five parts, namely, a pulsed laser beam, a focusing system, a print ribbon ( contains the energy-absorbing layer that responds to laser stimulation, a layer of bio-ink solution, and a receiving substrate for patterning and crosslinking bio-ink.

In this technique, the laser pulse is made to fall on the inclined mirror at an angle, which on reflection passes through the lens. This indirect laser beam now reaches the print ribbon that consists of the energy-absorbing layer just above the bio-ink-containing layer. This melts the bio-ink and it starts to fall in the form of droplets on the tissue culture plate. These drops are up to 50 micrometres in diameter. This is basically developed to transfer biological material such as DNA, peptides, and cells.

The lack of direct contact between the dispenser and the bio-ink prevents cell damage and stress and leads to high cell viability. It has certain limitations like high equipment cost, the complexity of the laser printing control system, etc.

3. Extrusion-based 3D bioprinting:

Image source: Derakhshanfar, S., Mbeleck, R., Xu, K., Zhang, X., Zhong, W., & Xing, M. (2018). 3D bioprinting for biomedical devices and tissue engineering: A review of recent trends and advances. Bioactive materials, 3(2), 144-156.

The extrusion-based bioprinting uses the fluid dispensing system for extrusion in combination with an automated robotic system for printing. The fluid dispensing system is controlled by the power source. With the use of the automated robotic system, we can fabricate the desired 3D designs. It does print in the form of droplets rather it uses continuous force or pressure for the bio-ink to print uninterrupted cylindrical lines.

The main advantage is that it particularly has the ability to print a wide range of biomaterials of different viscosities. One of the limitations of this technique is that it can cause a reduction in the viability of cells due to the continuous force applied.

Applications of 3D bioprinting

To begin with, there are various applications of bioprinting. It is useful in:

1. Biomimicry, creating identical tissue or organs.

2. Reconstruction of damaged body tissues.

3. Making transplantable organs that are made with the use of a person’s own stem cells so that there is no graft rejection. Even with such a high population, it is very difficult to get organs for transplants. If it is available, it may lead to graft rejection or generate an immune response. However, 3D bioprinting eliminates such possibilities to a certain extent.

4. In making organs for research purposes. Nowadays, there are many illegal practices for obtaining organs for transplants or for research purposes. So, to overcome this problem and cater to the need this technology can be very useful.

5. Making cadavers for medical studies.

In conclusion, in the present era of revolution, 3D bioprinting emerge as a beneficial alternative in many cases as mentioned above. And it will soon be the in-use technology and provide us with better transplants, and research technologies.

Thanks for reading!

Team MBD

Further reading- 3D Bioprinting of Living Tissues (harvard.edu)

References:

1. Zheng, Z., Eglin, D., Alini, M., Richards, G. R., Qin, L., & Lai, Y. (2021). Visible light-induced 3D bioprinting technologies and corresponding bioink materials for tissue engineering: A review. Engineering, 7(7), 966-978.
2. Keriquel, V., Oliveira, H., Rémy, M., Ziane, S., Delmond, S., Rousseau, B., … & Fricain, J. C. (2017). In situ printing of mesenchymal stromal cells, by laser-assisted bioprinting, for in vivo bone regeneration applications. Scientific reports, 7(1), 1-10.
3. Derakhshanfar, S., Mbeleck, R., Xu, K., Zhang, X., Zhong, W., & Xing, M. (2018). 3D bioprinting for biomedical devices and tissue engineering: A review of recent trends and advances. Bioactive materials, 3(2), 144-156.