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Micro biomedical device size plays a role in effectiveness

7/29/15     Micro sized biomedical devices that are implanted into the body for drug delivery, tissue engineering, or sensing helps improve treatment for many diseases. But these devices are susceptible to being attacked by the immune system.

MIT researchers have developed a way to reduce this immune-system rejection. In a study that appeared in the May 18, 2015, issue of Nature Materials, they found that the geometry of these implantable devices has a significant impact on how the body tolerates them.

It was found that larger spherical devices are actually better able to maintain their function and avoid scar-tissue buildup, than smaller ones. All are still micro in size, but the smaller ones couldn’t withstand the immune system attacks as well.

The material it is made out of is still important, but you need to pick the right size and shape to decrease the scar tissue.

The researchers hope to use this insight to further develop an implantable device that could mimic the function of the pancreas, potentially offering a long-term treatment for diabetes patients. It could also be applicable to devices used to treat many other diseases.

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In their studies they tested spheres in two sizes – 0.5mm and 1.5mm 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 larger spheres also evaded the immune response in tests in nonhuman primates. Smaller spheres implanted under the skin were engulfed by scar tissue after only two weeks, while the larger ones remained clear for up to four weeks.

This effect was seen not only with alginate, but also with 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. Optimizing particle size and shape could also help guide scientists in developing other types of implantable cells for treating diseases other than diabetes.