By: Annie Hu
We often hear the word “surgery” and think of medical treatments that mend injuries and treat deadly diseases by stitching up a wound or removing tissue. Dramas like Grey’s Anatomy and The Good Doctor come to mind. Surgery is often thought of as a big operation and a risky last resort. While surgery can be risky, groundbreaking discoveries regarding surgical tools, safe tissue removal, and knowledge of how to alter the human body and assist functioning have made surgery much more safe. In many cases, the operations also save lives! New procedures and safer ways of accomplishing better results are constantly being developed.
Surgical grafting is one of these specific types of surgery that encompasses procedures where tissue is removed from one site of the body to replace damaged tissue from another. For example, skin grafting is a procedure where scarred, deformed, or severely burned tissue from one site can be replaced by healthy tissue skin from a donor site.
There are many challenges to surgical grafting. One of the biggest is that in order to thrive in a new environment, the new tissue graft must have a sufficient blood supply. This is because blood vessels are what nourish graft cells (and the body’s regular cells) and keep them alive. Getting blood to these tissues is hard because blood vessels of the graft need to connect to the patient’s existing circulatory system. This makes surgery especially difficult as the small vessels of the graft need to line up and connect perfectly to the vessels of the graft site. One technique used to supply blood to a skin graft involves adding to the graft cells that can grow new blood vessels. When the tissue becomes detached from its original blood supply, the embedded cells encourage it to grow its own blood supply at the new site instead of trying to meticulously attach existing vessels. Another way to establish a blood supply to grafted tissue is to carefully bioengineer a tissue graft with precisely lined up vessels, much like 3D printing parts of a machine to fit together perfectly. However, pre-assembled tissue grafts seem to be less effective than implanting cells for the graft to naturally build the vessels and result in a successful transfer.
There are four main classifications for grafts. An autograft is a graft taken from the tissue of a donor and grafted in a different site on the same donor. Isografts are taken from someone near identical to the person who will be receiving the graft, like a twin. An allograft (homograft) comes from a member of the same species but with a different genetic code (i.e. human to human). This is what happens in surgeries like organ donation. Taking a kidney from one person and donating it to another is an example of the allograft/homograft type. Lastly, a xenograft (heterograft) is a graft taken from a different species (i.e. an animal donating an organ to a human). The later two classifications run a higher risk of rejection by the recipient’s body, as allografts and xenografts come from genetically different organisms (other humans or other species). Graft rejection occurs because the body recognizes the graft as a foreign substance and produces an immune response to attack and destroy it the same way it would a virus or bacteria. A lot of research is being done to find ways to prevent graft rejection, make transplants more convenient, and lower the risk of complications. One outcome of this research includes matching graft donors and recipients according to similarities in blood and tissue type. Another is giving the recipient immunosuppressant drugs to lower the immune response to the organ. But this comes with the caveat that the recipient may become more susceptible to other illnesses, and falling ill may be much more deadly as their body can’t fight back.
Where do grafts get applied in real life? As mentioned before, skin grafts are a common type of graft surgery. They are used to treat major wounds, burns, infection, and skin cancer. The two main types of skin grafts are “split-thickness” and “full thickness.” Split thickness grafts only remove the epidermis (top layer of skin) and a portion of the dermis (middle layer of skin). Normally skin is harvested from healthy areas like the thighs and back, and are used to treat larger areas that need replacement. Full thickness grafts take all of the epidermis and dermis from a smaller area and use that to graft into a smaller site where they are needed. They can be taken from places like the abdomen and forearms. After being removed from the donor sites, the donor areas are simply stitched back up. Another common type of graft is a bone graft. Teeth implants are one example of bone grafts, and are commonly called dental grafts. For this, sections of bone are taken from the pelvis to replace the missing teeth. Another type of bone graft is called an osteochondral graft. These are used for sports injuries or tissue degenerative diseases like osteoarthritis where the articular (surface) cartilage in joints gets damaged and the bone underneath is exposed. This causes pain when the joint is moved, as there isn’t a cushion of cartilage to smooth the motion. Osteochondral grafts replace both the damaged cartilage and a small portion of the bone underneath. A small hole is made at the site of the graft to remove the damaged cartilage and bone, while a replacement core is secured and fitted into it. Generally this is done just by simply tapping the graft into place.
It is certainly very interesting to see how the common surgery of grafting works. There is also so much yet to learn about how to address the issues of graft acceptance in a recipient’s body, along with the issue of immune response. From organ donation to plastic surgery, grafting has many applications and can be used to improve quality of life.
Image Credit: By Scientific Animations - http://www.scientificanimations.com/wiki-images/, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=74549936
What Did You Learn?
1. What is the importance of blood supply in surgical grafting?
Blood supply is essential in nourishing implanted tissue as it provides nutrients to cells. However, in grafting it is very difficult to line up vessels in such a way that vessels from the graft and from the recipient site are connected to each other and can seamlessly integrate into the circulatory system. The most effective way of encouraging a functional blood supply in the resulting graft is to mix in cells with the graft so they can form vessels on their own.
2. Why might a graft be rejected and what are the implications of this in medicine?
Grafts that are too genetically different and foreign from the recipient will be attacked by the recipient’s immune system. Specifically, allografts and xenografts where the graft is taken from a substantially different donor run the risk of not being accepted by the body. As such, the graft will not be able to fully function as the body tries to fight it off. In terms of medical treatment, the immune system forms a delicate dilemma because of how integral the immune response is to preventing infection, while also making surgeries like grafts much more difficult. Currently, we can only take our best guess as to the donor-recipient match, and if desperately needed, use immunosuppressant drugs that may or may not jeopardize the body’s ability to fight against other illnesses.