Medical therapeutics have grown leaps and bounds from leaches and bloodletting, ingesting mercury, cocaine, heroin, and chloroform, to replacing joints and keeping hearts beating that have lost their rhythm. With these advances, we of course have run into new obstacles to overcome. When a patient is given a new kidney or a new heart, their body recognizes that it is not theirs and will begin to attack the organ, through the work of our immune system which keeps our bodies safe from harm. That is why these patients are often placed on immunosuppressive drugs to keep the organ safe, but then we lose all of the good things our immune system does including fighting off infections and helping heal wounds. Furthermore, the organ waiting list is growing longer and longer, and researchers are now looking at how to restore function to a broken organ without the need for a transplant. This is where the field of bioengineering comes into play. Here, we can use man-made materials to design devices or implants that keep a heart beating, replace battered and worn knees, deliver life-saving insulin to diabetics, or for cosmetic reasons such as tissue fillers and implants. These all come with their own consequences, mainly something we call the foreign body response.

As mentioned previously, our body’s immune system defends us against all sorts of dangers, and these include what we call “foreign bodies.” If you’ve ever gotten a splinter or had your ears pierced, you have had your immune system respond against a foreign body – in those cases the splinter or the earring is the foreign body. This response is why you begin to have issues with medical device implants, like the glucose monitors and insulin pumps mentioned in the video. Once our immune system detects this threat, it begins the process of trying to break it down. Special immune cells called macrophages come in and begin to try to break down the implant, and in the case of the glucose monitors, even these early actions of the immune system are enough to begin to throw off readings. After macrophages cannot degrade the implant, then our body tries to wall it off my depositing dense scar tissue around the implant. This tissue is made of collagen – the scar that forms around an implant is very similar to the scar that forms when you get a cut on your skin, both are trying to protect you from the outside world and any invading bacteria!

Check out another TED-Ed lesson on how the immune system works by clicking here.

Here is an example video of the foreign body response to implantation of a hernia mesh.

Academic Readings:
Anderson, James M., Analiz Rodriguez, and David T. Chang. "Foreign body reaction to biomaterials." Seminars in immunology. Vol. 20. No. 2. Academic Press, 2008.

Coleman, D. L., R. N. King, and J. D. Andrade. "The foreign body reaction: a chronic inflammatory response." Journal of biomedical materials research 8.5 (1974): 199-211.

Ziats, Nicholas P., Kathleen M. Miller, and James M. Anderson. "In vitro and in vivo interactions of cells with biomaterials." Biomaterials 9.1 (1988): 5-13.

Anderson, James M., et al. "Host reactions to biomaterials and their evaluation." Biomaterials science. Academic press, 1996. 165-214.

Badylak, Stephen F., et al. "Macrophage phenotype as a determinant of biologic scaffold remodeling." Tissue Engineering Part A 14.11 (2008): 1835-1842.

Academic Papers by author of video:
Sadtler, Kaitlyn, et al. "Design, clinical translation and immunological response of biomaterials in regenerative medicine." Nature Reviews Materials 1.7 (2016): 16040.

Sadtler, Kaitlyn, et al. "Divergent immune responses to synthetic and biological scaffolds." Biomaterials 192 (2019): 405-415.