6. Organ printing
6.1. Heart
Printing a fully functional heart is something that could revolutionize medicine and solve the problem of organ availability for patients in need of transplantation. For a very long time, however, scientists have been able to print at best only a simple tissue, including aortic valves and cartilage tissue. A significant concern was the creation of blood vessels, otherwise known as capillaries. They are necessary for the artificially created organs to perform functions analogous to real organs. In addition, the production of the heart should be carried out with special care because of its important function in the human body and how complex it is.

Breakthroughs were made by scientists from Tel Aviv University. Prof. Tal Dvir, Dr. Assaf Shapira and Nadav Noor created a heart that has blood vessels, cells and chambers. Although this heart is not capable of functioning on its own, nor is it yet suitable for incorporation into the living organism, this project represents a huge step forward in organ printing.
The heart they created had the measurements of a rabbit’s heart, but the technology used to make it is possible to use it to print a heart corresponding to human size.
For this to be possible, it is necessary to produce cells that will not only have the ability to shrink as they have managed to do, but will also be able to pump blood and cooperate with the entire body into which the heart will be implanted.

To print out the heart, the scientists from TAU used a specific ink made of cell-free materials, protein and collagen. Ingredients for its formulation were obtained by obtaining fatty tissue from humans. Then the ingredients were divided into extracellular and cellular. The next step was to adapt the cells so that they could turn into undifferentiated stem cells, and then into endothelial and cardiac cells. Printed organs have one major advantage over organs obtained from donors - as the personal molecules of the person for whom the organ is printed are used, there is a very low probability of not accepting the transplant.[1]
6.2. Liver
For several years there have been attempts to use biodruk technology to produce tissues that would meet those naturally occurring in the human body and could gradually replace them in the future. One of the leaders in this field is the San Diego-based Organovo company. So far it has produced, among other things, tissue similar to smaller liver cells, and its most recent development is liver tissue. Their „patches” of liver have passed tests on mice and the company is gradually trying to implant them into people. The same type of technology used to produce these two tissues is expected to be used to create other types of tissue.

A cell sample is needed to print out the tissue. Usually animal cells are used for this purpose, but sometimes a small sample of human tissue is used as well. The cell sample must then be placed on a petri dish specially adapted for this purpose.
The first step in the creation process is to build a suitable cell tissue and a capillary network of blood cells belonging to it, which can reproduce the blood flow analogous to that of the living organism.
The layers of these cells are arranged in the right order and their thickness is about 500 microns. The process of creating that kind of tissue seems to be quite simple on the surface, but the procedure is very complicated.
The main challenge not only for Organovo but also for other companies trying to print transplantable organs is to create vascular systems that could effectively perform their functions.
However, before it is possible to produce a whole, fully functioning liver, the company is currently focusing on improving their latest innovation - liver patches. According to the scientists’ announcements, they are to be put into use much sooner than one might expect, in 2020. Although at the beginning only patients whose health condition is very serious, such as people with acute liver failure or children, will be able to benefit from them, the spreading of the patches is planned in the future.

The technology used by Organovo is very complex, so only pharmaceutical companies working on a small number of drugs at the same time use it.
Nevertheless, according to predictions, part of properly functioning, man-made and safe liver tissue can be expected to be implanted into the patient in about 3 years.
This is particularly important information for people waiting for a liver transplant, as this technology can help to add years to life. According to scientists, it is only a matter of time before the entire liver can be created, functioning in a similar way to the one naturally occurring in the human body, but due to the complexity of this organ and its important function, it will certainly take much longer to wait for it.[2]
6.3. Kidney
It is estimated that even about 10% of the population has kidney disease. In the United States alone, about 16,000 kidney transplants are performed every year, and more than 100,000 people are still in line for surgery, waiting for a donor to arrive. 3D printing technology is used in many scientific fields, but particular attention is paid to its development in the context of healthcare, especially organ printing. Not only can 3D printing support the treatment of kidney diseases, but it is expected that it will be possible to produce transplantable kidneys for patients in the future.
At the moment, the technology is not yet organised enough to create a fully functioning kidney, but it is already possible to print certain parts of the kidney and a 3D model of the patient’s organ showing changes in the organ, which is also very useful for both kidney treatment and transplantation.
One of the main advantages of being able to print a properly functioning transplantable kidney is to ensure that the organ is accessible to those who are still waiting for it.
The difference between the number of patients who need a kidney and the number of donors is enormous.
In addition, the treatment of kidney diseases and the printing of their parts can be specifically tailored to the individual needs of the patient. When a kidney is created specifically for a particular person, all the most important factors are taken into account to ensure that the artificial kidney can bring maximum benefit. Thanks to the possibility of printing out a 3D model of a person’s kidney, it is easy to trace the location of a tumour. This helps significantly during the operation, as surgeons are able to perform the procedure faster once they know the exact location of the tumor. It is estimated that it allows to reduce the duration of the surgery by up to one hour. The printed 3D model of the kidney can also be used for educational purposes. One can easily show the patient the condition of his kidney and what is the source of the problem, or use the model for teaching purposes. It makes it easier to visualize the actions on the kidney and the whole surgical process.
Because of the very complicated structure of the real kidney, it may still take time to create a whole artificial organ which would be safe for medical use, but scientists are definitely on the right track to achieve this goal.
3D printing enables the medicine to take a big step forward. It is already possible to create prostheses and 3D models that significantly help in performing treatments, treating and improving patients’ lives. Printing organs and tissues that can be implanted into the living organism will make the medical care rise to a completely different, higher level. Although the complexity of many organs can take quite a long time to design and create, scientists predict that this will be possible in a relatively short period of time for a printed kidney transplant. The possibility of obtaining an artificial kidney will significantly reduce the problems associated with kidney diseases and the unavailability of an organ for transplantation. [3]
6.4. Skin
Plastic surgery is an area that focuses on the repair of skin fragments that have been damaged or reconstruction in places where the skin is lacking. Alongside aesthetic considerations, the aim is also to ensure that the skin and tissues subjected to plastic surgery perform their functions properly. The achievements of scientists from the Rensselaer Polytechnic Institute can significantly revolutionize skin grafts in many fields. By using 3D printing, they have succeeded in creating skin that corresponds to living skin and contains blood vessels. Apart from the fact that the printed skin has mechanisms similar to natural skin, it is also very similar in appearance.
The design is already being extensively tested and improved in order to enable transplants to be performed as quickly as possible using printed skin.
The skin grafting procedure performed by plastic surgeons is to fill in the place where the skin is missing or damaged with healthy skin, which is previously taken from another part of the body. The thickness of the skin used in the treatment depends on where exactly the skin will be obtained. In the case of the former, three layers of skin are required to perform the surgery, which is why it is usually removed from such places as the upper arm, groin or neck. For a split-thickness skin graft, the skin is taken from parts of the body such as the calf, buttock or thigh, because the skin must be thin for the transfer. The transplantation results in more wounds on the body, only in other places.
Besides, there is always a risk that the transplant will not be accepted.
This is a problem especially for people who suffer from circulation problems and smoking tobacco. The solution to these problems may be 3D skin printing. By producing live skin, there will be no need to take it from other parts of the body for transplantation. Researchers at the Rensselaer Polytechnic Institute in New York aren’t the first to do so - there have been attempts to produce skin using 3D printing before, but only they’ve been able to produce a working vascular system for transplantation. In order to start transplantation using 3D printed skin, the skin needs to be modified so that the implanted skin can properly integrate with the rest of the patient’s body and perform its intended functions together. The project is currently being tested on mice. Tests are carried out by means of transplanting a 3D printed skin onto their backs.
The first results turned out to be positive, the printed skin worked perfectly with the blood vessels already present in the mice. This allows us to be optimistic about the future in terms of improving skin grafting.
Although skin grafts are not one of the most complicated treatments, however, due to the fact that it is some kind of interference with the human body, a dangerous infection may occur. Another issue is that the transplanted skin does not always match the skin that naturally occurs in a given place. They may vary in colour, hair appearance, and the transplanted skin may also look reticular. 3D printed skin significantly reduces the likelihood of rejecting the transplant, and there is still an ongoing effort to make it look as realistic as possible and fit the transplant site as much as possible. For these reasons, the actions of Rensselaer Polytechnic scientists are closely followed and many are looking forward to further innovations in this field.[4]
6.5. Corneas
The cornea is the outer layer of the eye. It is quite thin, transparent and elastic, it covers the pupil by moving with it and is the first place where light reaches the pupil. Its main task is to protect the eye from any harmful elements. In case of significant corneal damage, it is often the last resort to perform a graft, but it is not easily accessible.
The average waiting time for a cornea transplant is about 6 years and in many cases it is even longer.
This situation has motivated many scientists to focus on the problem of creating an artificial cornea that could be used for transplantation, but so far all attempts have been fruitless or have had numerous flaws.

Until now, artificial corneas have been attempted to be produced using synthetic biocompatible materials, which, however, did not work. The main obstacle was to create a surface that would not only be flexible and thin, but also transparent and allow light to pass through, just the same way as a real human cornea does. The transparency and the extent to which the cornea transmits light are caused by the collagen fibres present in it. Although numerous attempts have been made to reconstruct the pattern of the cornea mesh, the problem has been mainly related to cytotoxic substances.
The breakthrough was the project of professors Jinah Jang, Hong Kyun Kim, Dong-Woo Cho and Hyeonji Kim. They managed to print out a 3D cornea that would allow the eye to penetrate the light as much as a human cornea.
In order to produce this cornea, a bioink consisting of stem cells and a de-cellularized steep cornea was used, which gave a spectacular effect and overcame the problem of the lack of transparency in artificially created corneas. In order to create a properly functioning corneal mesh pattern, a group of scientists decided to adjust the shear stress in 3D printing due to the frictional force generated when the ink comes out of the nozzle in the printer. The stresses were controlled in such a way that the corneal collagen fibre pattern produced allows light to pass through.

According to the team of researchers, they are already pretty close to perfecting their artificial cornea design, not only in terms of transparency but also in terms of ensuring total safety in grafting into the real human eye. It all goes in the right direction, and not much separates people suffering from corneal damage and corneal-related diseases from enjoying good, healthy eyesight.[5]
6.6. Ears
There is no denying the fact that the printing of prostheses and 3D organs, both of certain parts and the attempts to create whole ones, is still moving forward. However, the thing that often remains the same is the way of performing the operation on the patient. The procedure most often involves the introduction of tissue into the body surgically, which may result in damage to the surrounding tissue and the implant. As a result of such actions, patients are often forced to repeat the procedure, spend additional time on a hospital bed and suffer from the pain caused. As it turned out, there is another way.
A team of scientists managed to print a tissue like the human ear on the back of a mouse, using only bioinjection and light, without making a single cut. This achievement can give rise to a medicine that is completely non-invasive.
The technology using 3D biodromechanical and digital light processing is not as new as it might seem. Attempts have already been made to activate light patterns previously placed in the tissue of the bioinjection. In the case of damage to such tissues as nerve fibres, blood vessels and spinal cords, the attempts were successful and resulted in a significant improvement of the tissue condition.
What is the phenomenon of the experiment carried out by the team of scientists is the fact that they used previously designed shapes in a digital micromirroscopic device to create living tissue in the shape of the human ear, which allowed them to generate the desired shape using infrared beams in just 20 seconds.
Surprisingly, within just one month, it was noticed that the ear forms its own supporting structures so that it can maintain its correct shape. However, according to the research team, this is not the only way to use this kind of technology. A similar procedure can be performed when treating severe wounds. It has been proven that fat stem cells have properties that support tissue regeneration. To ensure this, it was decided to carry out a test on mice. Stem cells were placed at the sites of the mouse wounds, i.e. where some kind of injury occurred, and then activated the printed tissues with light. As we observed, after 10 days, the earlier mouse wounds were much more closed compared to mice not tested.

The fact that you don’t need to perform risky operations to repair or create new tissue in your body and stimulate faster wound healing can significantly affect the process of performing various treatments.
However, despite its positive aspects, this technology also has its drawbacks. It is questionable whether it is possible to act in this way on tissues that are really deep, or whether the revolutionary effect of light will be limited only by the skin surface. It is also not yet known whether the resulting tissues will cooperate with the body in the long run.
Despite this, the team of scientists remains in good spirits and believes that further research will find answers to these questions. Even if this discovery will only allow for surface effects, it is still a great success. As it proves, it is possible to quickly create or rebuild even very complicated tissue directly in the desired place, and there is no need to undergo any intervening operations to achieve this.[6]
6.7. Ovaries
Researchers from Northwestern University Feinberg School of Medicine and McCormick School of Engineering have made a breakthrough. They have managed to print 3D ovaries that actually perform their function. Once they were implanted into mice that had previously removed their own ovaries, ovulation was noticed. What is more, after some time, they also allowed the female mice to become pregnant and give birth to healthy offspring.
The main goal of the study was to restore fertility and increase the amount of hormones produced.
This study proved that bioprosthetic ovaries are able to perform identical functions to the ovaries naturally occurring in the female body and can provide a solution to the infertility problem.

Printing 3D organs is about the proper location of the fibers, and thus determining the appropriate distance between the individual sections and the degree of opening of angles between them. Thanks to that, many different shapes can be created depending on the purpose. The structure resulting from the printing was called „scaffolding” by Northwestern scientists. They are extremely helpful in supporting the cells responsible for the production of hormones and immature egg cells, they enable the whole process of maturing and ovulation of egg cells.
As a result of the presence of scaffolds, numerous blood vessels are also formed in the area of the implanted tissue to help the hormones to enter the bloodstream, which makes it possible to induce lactation.
It is not only the shape of the scaffolding that differs from other scaffolding tests, but also the components of which the material used for its construction is composed. Scientists from Northwestern University Feinberg School of Medicine and McCormick School of Engineering used gelatin, a human-safe substance created by breaking down collagen. Thanks to this organic material, the scaffolding is sufficiently stiff and porous to have a natural effect on the rest of the adjacent tissue and is suitable for use in surgery. Other such studies used hydrogels, which usually consisted of a major amount of water, so they were not strong enough and collapsed. The use of bioengineering to create fully functioning tissues and organs is a great progress in the context of regenerative medicine. The creation of biopolitical ovaries that allow the production of suitable hormones to restart and the fertility of females gives hope to many infertile people. By carrying out this study, we particularly refer to women who have fought cancer in the past, both in adult and childhood, which often results in problems with both hormone production and infertility. As it appears, their chances of having healthy children are not entirely lost.[7]
6.8. Pancreas
Researchers from the Foundation for the Development of Research and Science, headed by Dr Michał Wszoły, have done something that no one else has done - they have managed to create the first bionic pancreas that contains blood vessels. Admittedly, numerous attempts were made, but they ended without success. The main reason was the complexity of the required vascularization. The method used to place a biodegradable scaffold previously fed with cells in the body worked well for such tissues as bladder, cartilage, trachea or bones, but did not pass the test for others. This method was not suitable for kidneys, liver, lungs or pancreas. The development of bionic pancreas is not the only success of this team. They also include carrying out a pancreatic pulp transplant to treat diabetes. Their next project is to be a bionic pancreas that has a therapeutic effect on diabetes.

The pancreas printed artificially by a team of researchers is composed of pancreatic islets only. It is expected that after further improvements, it will be able to help in the treatment of diabetes by restoring proper insulin production.
At present, a similar effect can only be obtained by placing the hormone in the body using an insulin pump or dispenser.
Similar improvements in pancreatic function may be questionable, but in fact, everything makes sense. Naturally occurring human pancreas has pancreatic islets around it that are responsible for producing glucagon and insulin. The organisms of people who suffer from diabetes lack both because their pancreas islets are damaged. For this purpose, they are forced to use insulin injections. The pancreas that stimulates insulin production can become an alternative for them. To create a bionic pancreas it was necessary to use pancreatic islet cells. These were obtained from animals and then bioinks were added to them to ensure their survival. The substance created in this way was used to print out the designed pancreatic model. No ink used so far in 3D organ printing was suitable for this project, so Polish scientists had to develop their own formula. During the process of tissue creation, it was also necessary to create blood vessels that could ensure the transport of sufficient oxygen and glucose to all cells. According to the scientists, it is possible to print an organ up to 150 mm thick.

The next step in this project is to attempt to place printed pancreatic flakes and pancreatic islets in the mouse. The purpose of this is to test their effect on the living organism. Once this stage is successful, scientists will try to place a small piece of bionic pancreas in a pig’s organism. This is necessary to ensure that the artificially created organ will also function properly in the human body. This whole process is designed to enable the production of pancreas which will be specially adapted to the needs of patients. This way, the risk of rejecting the transplant would be negligible and the number of benefits from it could be maximized.[8]
[1] Efrati, I. ,Israeli Scientists Print World’s First 3-D Heart’, Haaretz.com, Published on 15.04.2019

[2] Mearian, L. ‘3D-printed partial liver transplants targeted for 2020’, COMPUTERWORLD, MAR 27, 2017

[3] Gaget, L. ‘3D printed kidney: What is actually possible?’, Sculpteo, May 31, 2018

[4] Kent, C. ‘3D-printed living skin: the future of skin grafts?’, Verdict, 5 MARCH 2020

[5] Choi, H. ‘3D printed artificial corneas similar to human ones’, EurekAlert!, 28-MAY-2019

[6] Fan, S. ‘Scientists 3D Printed Ears Inside Living Mice Using Light’, Singularity Hub, Jun 09, 2020

[7] Samuelson, K. ‘3-D printed ovaries produce healthy offspring’, NORTHWESTERN NOW, May 16, 2017

[8] Wojtasiński, Z. ‘Polish researchers printed the world`s first bionic pancreas with vessels’, Science in Poland, 20.03.2019