Implanted biomedical devices used for drug delivery, tissue engineering, or sensing can help improve disease treatment. But, often these devices are susceptible to attack by the immune system. To help reduce that immune-system rejection, a team of scientists at Massachusetts Institute of Technology, Cambridge, has discovered that the geometry of implantable devices has a significant impact on how well the body tolerates them.

While initially, the researchers expected smaller devices to better evade the immune system, they discovered that larger spherical devices maintained their function better and were able to avoid scar-tissue buildup.

The researchers are using this insight to develop an implantable device that could mimic the function of the pancreas, potentially offering a long-term treatment for diabetes patients.

They tested two sizes of spheres, 0.5 and 1.5 millimeters in diameter. In tests of diabetic mice, the spheres were implanted within the abdominal cavity and the researchers tracked their ability to accurately respond to changes in glucose levels. The devices prepared with the smaller spheres were completely surrounded by scar tissue and failed after about a month, while the larger ones were not rejected and continued to function for more than six months.

The same effect was seen with alginate, as well as spheres made of stainless steel, glass, polystyrene, and polycaprolactone, a type of polyester.

The researchers believe this finding could be applicable to any other type of implantable device, including drug-delivery vehicles and sensors for glucose and insulin, which could also help improve diabetes treatment.