A shortage of organs represents a huge current major health crisis. We currently have an ageing population, and as we age, our organs are proven to fail more and, thus, there aren’t enough organs to go around. In the last ten years, the number of people requiring organs has doubled, whilst the number of transplants has barely increased. Furthermore, in the United States, 20 people die every hour waiting for kidneys. Therefore, there is a need for methods of developing organs that do not require organ donation.
Regenerative medicine is one approach which could alleviate the problem of donation shortages. It is defined as ‘a branch of translational research in tissue engineering and molecular biology which deals with the process of replacing, engineering or regenerating human or animal cells, tissues or organs to restore or establish normal function’. This field holds the promise of engineering damaged tissues and organs by stimulating the body’s own repair mechanisms to functionally heal previously irreparable tissues or organs. Regenerative medicine also includes the possibility of growing tissues and organs in the laboratory and implanting them when the body cannot heal itself. What’s more, when the cell source for a regenerated organ is derived from the patient’s own tissue or cells, we are able to circumvent the challenge of organ transplant rejection. Examples of regenerative medicine include cell therapy using stem cells, utilizing biomaterials as scaffolds, combining these scaffolds with cells taken from the patient, and transplantation of in vitro grown organs and tissues (tissue engineering).
But what I am going to look at in this article is something that aims to solve the biggest challenge of all in regenerative medicine: solid organs. 90% of all patients on the transplant list are waiting for a kidney. It is a large, vascular organ with a large blood supply and a lot of cells; therefore, it poses a big challenge for regenerative medicine.
The first 3D printer was developed in the late 1980s. It could print small objects designed using computer-aided design (CAD) software. A design would be virtually sliced into layers only three-thousandths of a millimetre thick. Then, the printer would piece that design into the complete product.
Now they are looking at printing solid organs using the following method: first, a CT scan of the patient’s kidney is taken. The printer then prints layer by layer, slowly analysing the patient’s kidney to make it as accurate as possible. They print a biocompatible plastic scaffold, and then cells from the patients (or sometimes stem cells) are printed onto and into the scaffold, which is then left in an incubator to multiply, before being implanted into the patient so that the organ is as much a part of the patient’s body as the organs that they were born with. Take for example, wound transformation: there is a printer that can print directly onto the patient. This printer first scans the wound, then sends the information and prints accurately to correct the wound.
The concept of bioprinting was first demonstrated in 1988. At this time, a researcher used a modified HP inkjet printer to deposit cells using cytoscribing (cells positioned in precise, predetermined patterns in which cell adhesion proteins are deposited on a substratum under computer control). Progress continued in 1999 when the first artificial organ, a bladder, made using bioprinting was printed at the Wake Forest Institute for Regenerative Medicine. Using this method, they were able to grow a functioning organ and ten years after implantation, the patient had no serious complications.
In addition, these printed organs can be used for more than just donations. They might be used for physician and surgical training, pharmaceutical training (allowing precise control of droplet size and dose, personalized medicine, and the production of complex drug-release profiles, and implantable drug delivery devices, in which the drug is injected into the 3D printed organ and is released once in vivo), and drug testing (they can display realistic responses to drugs).
There are many challenges, however, such as recreating the vasculature (vascular system of the organ) required to keep these organs alive. Designing a correct vasculature is necessary for the transport of nutrients, oxygen, and waste. Blood vessels, especially capillaries, are difficult due to their small diameter. It is difficult to replicate the entangled networks of airways, blood vessels, and bile ducts and complex geometry of organs. Furthermore, sustainable cell sources must be found, and large-scale manufacturing processes need to be developed. Other challenges include designing clinical trials to test the long-term viability and the complexities in tissue-specific extracellular matrices (ECM) and tissue maturation process (the lack of suitable co-culture medium to support multiple types of cells and the need for further tissue conditioning prior to implantation).
To end this in a wonderful quote from Professor Chua Chee Kai: “While 3D bioprinting is still in its early stages, the remarkable leap it has made in recent years points to the eventual reality of lab-grown, functional organs. However, to push the frontiers of medicine we must overcome the technical challenges in creating tissue-specific bio-inks and optimizing the tissue maturation process. This will ultimately have a huge impact on patients’ lives, many of whom may be reliant on the future of 3D bioprinting,”