Printing Organs

Yes, literally,organs are being printed into its 3D replica. Why? In the United States, each patient is listed for an organ, every 15 minutes (Mandrycky et. al., 2016) and such increasing demand can’t be fulfilled.

3D bioprinting is an additive manufacturing technique, requiring  cells and biomaterials to construct a three dimensional structure of an organ or tissue with increased reproducibility ( meeting mechanistic and functionality) to native tissue. On the contrary, the conventional method has its limits in  reproducibility (Xia et. al.,2018). The  bioprinter comprises a computer attached to a machine.

Knowing that a cell not only responds to hormones or nutrients or harmful molecules, but it also responds to its microenvironment. The structure of an extracellular environment, comprising different molecules, such as collagen and hyaluronic acid, thereby, maintaining structure of tissue. The adherence of a cell with its environment, signals a cell to maintain its state or if changes, it may alter its functionality.

Some approaches of 3D bioprinting, includes:

 

1.     Biomimicry: The construction of a tissue or an organ through bioprinter, making it identical to its native tissue or organ (Murphy & Atala, 2014). The organ is constructed, layer by layer, maintaining the pattern of each part, as it is inside our body (Murphy & Atala, 2014).

2.     Autonomous Self Assembly: Knowing  how humans develop and within him or her, how cells develop, and with these,  assembling cells to develop and create their microenvironment and thereby, forming an organ (Murphy & Atala, 2014).

3.     Mini-Tissues: Some organs, like Liver and Kidneys, having microstructures, which combine to form an organ (Murphy & Atala, 2014). This approach designs microstructures through 3D bioprinting and later on, combining them to form an organ (Murphy & Atala, 2014).

So, some few steps of how an organ is created.

1.     Computer-aided Design: So, unlike an ordinary printer, the bioprinter has an extra feature to add layer over layer, to create a 3D construct.  Apart from moving in x and y axis, it moves along z axis, layering each blueprint  obtained from medical data . The data are gathered from CT scan and MRI (Murphy & Atala, 2014). The latter being  more advantageous  than the former, having higher resolution and creating a clear picture of the cross section (Murphy & Atala, 2014). Each data is then sequentially arranged,  providing instructions to software. Also, it can differentiate medical data for support material, to construct a tissue (Lee et. al., 2020).

2.     Preparing Bioink: Studies are being conducted on this aspect. Bioink is somewhat similar to an ink, used in ordinary printers. Instead of an ink, living cells and biomaterials are considered as bioink. Cells are extracted from humans and further cultured to gain enough quantity of cell suspension. Cells and biomaterial can be used as  separate, or in specific composition. The proportion of biomaterials and cells , depends on the type of 3D bioprinter used, the type of cells incorporated, as well the type of  biomaterials. The latter  may be natural, synthetic or hybrid. Natural biomaterials are biopolymers  found among living organisms. For instance, Silk, Collagen, Gelatin, Hyaluronic acid and Cellulose (Gungor-Ozkerim et. al., 2018). Such substances are biocompatible, but are biodegradable (Gungor-Ozkerim et. al., 2018). Material like Collagen, have been highlighted in many studies, regarding its biocompatibility upon forming a skin (Gungor-Ozkerim et. al., 2018).  And due to its  biodegradability and low mechanical strength, other biomolecules are added, creating a network between collagens, to strengthen the structure (Gungor-Ozkerim et. al., 2018). Synthetic materials have been reported for its strength in tissue construction but it might cause allergy. And  of hybrid material, as mentioned, adding biomolecules to collagen can help strengthen the tissue construct. A biomaterial should have high viscosity to establish a tissue structure, as well as, have sheer thinning property to avoid cells from damage. Overall, the role of biomaterial is to create an environment for a cell to adhere, proliferate, differentiate and migrate for biological function, similar to an organ (Wtodarczyk-Biegun & del Campo, 2017). The porosity and the mechanical strength of biomaterials helps cells to form a reproducible organ (Wtodarczyk-Biegun & del Campo, 2017). In  fact, the biodegradable biomaterial can be utilized for 3D tissue construction, if the cells inside produce components for Extracellular Matrix (ECM) and sustain tissue architecture, after removal of biomaterial. (Chawla et. al., 2018).

3.     3D Bioprinting: To construct a tissue, a substrate is required where the tissue gets constructed. Three types of bioprinter are well known. The most common and inexpensive method of bioprinting is the inkjet method. It’s similar to inkjet printers (like the one we use for our assignments). The cartridge is filled with bioink and the orientation of printing is changed (Holzl et. al., 2016). The method creates droplets of bioink, with cells encapsulated inside, by employing two techniques i.e. of thermal and  piezoelectric. Thermal technique heats nozzles at 300 C for microseconds, vaporizing bioink  near the nozzle, forming droplets (Holzl et. al., 2016). The piezoelectric method employs the pulse to create pressure, forming droplets (Holzl et. al., 2016). Despite its cost, the dense bioink is not applicable for this method  could clog the nozzle and blocks for further release of droplets (Holzl et. al., 2016). Unlike inkjet, extrusion methods have more choices of using different biomaterials and using high cell density bioink for tissue construction (Mandrycky et. al., 2016). The method is also applicable for high dense bioinks, using constant mechanical force  from piston or screw (Mandrycky et. al., 2016). With this technique, cells are prone to getting damaged, unlike inkjets (Mandrycky et. al., 2016). The third method, laser-assisted technique, employs certain lasers, projecting on a gold ribbon, heating the portion and creating a pressure, which causes bubbles on the bioink interface, vaporizing and projected on substrate for tissue construction (Mandrycky et. al., 2016). Similar to the extrusion method, highly viscous bioink is applicable but on contrary, it’s expensive and it’s not developed yet (Mandrycky et. al., 2016). Research is being performed, mainly on its laser, but not on controlling the bubble of bioink (Mandrycky et. al., 2016).

1.     Crosslinking of hydrogel to strengthen tissue architecture: While under process and/or after creating a 3D organ,  cross linking is necessary for shape integrity. Cross linkings are of two types: 1) Physical bonding: Including, Ionic and Hydrogen bonds, which occurs among polar molecules, and, 2) Covalent bonds: Such as Disulfide bonds, which are strong enough to maintain the structure of the organ (Zhang et. al.,2017). Crosslinking biomaterials can be done through light, illuminating a light of certain wavelength and intensity to produce free radicals, which attacks on biopolymers, creating covalent bonds within a polymer and strengthening the tissue (Gu et. al., 2016). This technique can be hazardous, as it could damage proteins and Nucleic acids within cells, affecting the functionality.

As this technique does create a tissue or an organ, it doesn’t mean it’s beneficial for organ transplant only. Other applications have been enlisted in articles.

1.       Cancer Research: It is based on the complexity of its pathogenesis. Not only each type of cancer is different from each other, but are different within cancer subtypes (Ozbolat et. al., 2016). To understand the mechanism of cancer, we should know of how it develops inside humans and due to the reproducibility of 3D bioprinters, it could be much easier to understand more of cancer by studying within a replicated tissue or an organ.  During these past years, cancers were examined under cell cultures, which lacked vasculature and cell to cell interaction (Ozbolat et. al., 2016).

2.       Drug Screening: In order to approve an effective drug, clinical trials take place (which requires months) and out of thousands drugs, only one drug gets approved and sold at market (Ozbolat et. al., 2016). Instead, if a drug is tested on 3D construct of tissue or organ, for the safety and toxicity (Ozbolat et. al., 2016), it could be tested quickly and accurately because the construct mimics the body part.

To sum it up, this field is in its infancy and several research are being performed, especially to formulate bioink for organ development. The method is rapid and could fulfill the needs of patients who require organs.

Written by: Mohammad Irtaza Tafheem

References:

Chawla, S., Midha, S., Sharma, A., & Ghosh, S. (2018). Silk‐based bioinks for 3D bioprinting. Advanced healthcare materials, 7(8), 1701204.

Gu, B. K., Choi, D. J., Park, S. J., Kim, M. S., Kang, C. M., & Kim, C. H. (2016). 3-dimensional bioprinting for tissue engineering applications. Biomaterials research, 20(1), 12.

Gungor-Ozkerim, P. S., Inci, I., Zhang, Y. S., Khademhosseini, A., & Dokmeci, M. R. (2018). Bioinks for 3D bioprinting: an overview. Biomaterials science, 6(5), 915-946.

Hölzl, K., Lin, S., Tytgat, L., Van Vlierberghe, S., Gu, L., & Ovsianikov, A. (2016). Bioink properties before, during and after 3D bioprinting. Biofabrication, 8(3), 032002.

Lee, J. M., Sing, S. L., & Yeong, W. Y. (2020). Bioprinting of multi materials with computer-aided design/computer-aided manufacturing. International Journal of Bioprinting.

Mandrycky, C., Wang, Z., Kim, K., & Kim, D. H. (2016). 3D bioprinting for engineering complex tissues. Biotechnology advances, 34(4), 422-434.

Murphy, S. V., & Atala, A. (2014). 3D bioprinting of tissues and organs. Nature biotechnology, 32(8), 773-785.

Ozbolat, I. T., Peng, W., & Ozbolat, V. (2016). Application areas of 3D bioprinting. Drug discovery today, 21(8), 1257-1271.

Włodarczyk-Biegun, M. K., & del Campo, A. (2017). 3D bioprinting of structural proteins. Biomaterials, 134, 180-201.

Xia, Z., Jin, S., & Ye, K. (2018). Tissue and organ 3D bioprinting. SLAS TECHNOLOGY: Translating Life Sciences Innovation, 23(4), 301-314.

Zhang, Y. S., Yue, K., Aleman, J., Mollazadeh-Moghaddam, K., Bakht, S. M., Yang, J., ... & Dokmeci, M. R. (2017). 3D bioprinting for tissue and organ fabrication. Annals of biomedical engineering, 45(1), 148-163.