The mechanical artificial pancreas (Medtronic) is made up of the sensor (A) to detect blood sugar levels, a computer programme (B) to determine the amount of insulin required, and an insulin pump (C) to pump insulin into the body. This is a "closed-loop" device. With a perfect computer algorithm, the glucose sensor can literally "talk" to the insulin pump to secrete the required insulin.

The sensor is implanted under the skin of the abdomen or threaded to the large vein of the heart (vena cava). However, there are problems with such a mechanical artificial pancreas:

1. The sensor needs to be recalibrated to correct values and replaced periodically.
2. A "perfect" computer algorithm, which could deliver the correct insulin dose, has not yet been developed.
3. A stable, sensitive, and accurate sensor has not yet been developed.
4. Any kind of error in sensing, computation or delivery of insulin could lead to weight gain or worse, to life-threatening hypoglycemia.
5. There might not be a swift response to changes in blood sugar like the normal pancreas.

In order to address these difficulties, researchers have tried to adopt a less mechanical and more biological approach. The outcome has been the bio-artificial pancreas or biohybrid artificial pancreas (BHAP), composed of both biological and nonbiological components. While the biological component consists of islets of Langerhans that sense glucose levels and secrete appropriate amount of insulin, the nonbiological component (microcapsules fabricated with alginate-based polymers) protects the islets from rejection by the body. A BHAP is implanted into the peritoneal cavity and contains 2-3 million islet cells.

The most encouraging research data have come from such passive diffusion devices that cause no rejection, and allows passive diffusion of oxygen, glucose, and other nutrients in, and insulin and other hormones outside the device.

However, more studies in animal models are required. It can be hoped that an efficient and safe artificial pancreas would be available within a decade.