New medical devices can cause new immune problems

Feb 28 2005

Medical devices are traditionally thought of as fairly simple implants such as stents and hip replacements – pieces of plastic or metal that are placed in the body to handle a very specific function. But biomedical devices now on the drawing board are considerably more sophisticated and represent an unprecedented melding of man and machine.

Combination products, devices that include a combination of drug, biological and device components, are expected to be the next big thing in biomedical devices. An example of a combination product is a tissue-engineered device that combines living cells with a polymer scaffold. When implanted into a patient, the device can replace or restore damaged tissue or organ function. While the response of the body to each component is well known, considerably less is known about how their new union may affect the body’s reaction to a combination device.

According to new research from the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University, the body can have a different – and potentially detrimental – reaction when there’s more than one component involved. Findings from the study headed by Dr. Julia Babensee, an assistant professor in the Department of Biomedical Engineering, were presented Feb. 20 at the annual meeting of the American Association for the Advancement of Science (AAAS).

When a biomedical implant is introduced into a patient’s body, the body’s response is a threat to the acceptance of the implant and could result in device failure. The body responds to biomaterials with an inflammatory reaction and to foreign biological components with an immune reaction. But the two reactions may affect one another when triggered simultaneously, as they would be in a combination device if the combination product contains any foreign biological material.

“If you’re combining a polymer with a biological component, the body may respond differently to that combination than it would to either component by itself. The immune response towards a foreign biological component of the device may be affected by the inflammatory response to the biomaterial component,” Babensee said.

According to Babensee, there is a need to better understand more complex combination products so that as they move into wider use, they can be designed to integrate as smoothly as possible into the patient.

Babensee’s work focuses on strategies for designing biomaterials and devices that can best integrate into the body by controlling host responses. In some combination products, biomaterials (in the form of polymer sponges) are used in the medical device to provide sites for transplanted cells to grow on to help it be better incorporated, strengthening its connection to the body.

Initial in-vivo research findings indicate that the inflammatory response to a biomaterial can affect the immune response to a foreign protein that is delivered at the same time. The presence of the biomaterial (a polymer) enhanced the body’s immune response to a foreign protein. The polymer boosts the immune response by spurring the dendritic cells (cells that direct immune responses) to mature so that they can effectively initiate an immune response.

The finding means that for combination devices, if there was a potential immune response to a biological component, the biomaterial component could further exacerbate the immune response, making it more difficult for the device to integrate smoothly.

To better understand the body’s reaction to biomedical devices that incorporate both biomaterials and biological components, Babensee works with human blood cells, treating them with a variety of biomaterials to see what response is induced from the dendritic cells.

“These cells control which way the immune response will go, so if we can control their phenotype, the idea is that we can control immune responses,” Babensee said.

But there are ways around triggering a response. Babensee’s research has determined that immature dendritic cells don’t cause an immune response, making them a good option for biomaterials used in combination biomedical devices.

“Eventually, this may be a way to integrate the control of immune responses towards a biomedical device through a biomaterial,” Babensee said.

Different materials seem to have varying effects on the dendritic cells. This may indicate which biomaterials will be good for which application. For example, biomaterials that support dendritic cell maturation may be best suited as polymeric carriers for vaccine delivery and those that do not support dendritic cell maturation may be used as sponges in tissue engineering.

“It seems that there may be a way to control the immune response to a biological component through the use of different biomaterials,” Babensee said.

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