A Japanese research group implanted a sensor whose color intensity changes depending on blood glucose level in a mouse's ear, kept it in the ear for more than four months and measured the mouse's blood glucose level.
The group, which consists of members of the Institute of Industrial Science at the University of Tokyo and Beans Laboratory, aims to apply the sensor to humans by using it for blood glucose level monitoring systems for people with diabetes.
The sensor implanted in the mouse's ear is based on the "Hydrogel," which was developed by the research group. Its color intensity changes depending on blood glucose level.
This time, the group succeeded in keeping the sensor in the ear for more than four months by making fiber-shaped Hydrogel to ensure stability (immobility inside a living body) and to make it easier to take out the sensor. In the former method, bead-shaped Hydrogel is used. So, the beads often moved in a living body, and they were difficult to be removed.
Furthermore, by mixing biocompatible polymer (polyethylene glycol) with the Hydrogel, the group reduced skin inflammation caused by the implantation of the sensor and enabled to measure blood glucose level for a longer period of time.
The fiber-shaped sensor has a diameter of about 1mm. It was implanted to a depth of about 100μm from the skin surface. When a 405nm light (excitation light) is directed at the fiber, it emits a 488nm fluorescence. Depending on blood glucose level, the intensity of this light changes. The sensor is used not for measuring an absolute value of blood glucose level but for showing blood glucose level in a relative manner.
To realize a blood glucose level monitoring system using the new fiber-shaped sensor, it is necessary to develop some peripheral systems such as a light source that emits a 405nm light and a device that can measure the fluorescence intensity of the fiber. The research group considers that this is a challenge for the future.
There are some problems that have to be solved to apply the fiber-shaped sensor to human bodies.
"We have to find out whether we can continue to use this material, where we should implant the sensor and so forth," said Shoji Takeuchi, associate professor at the Institute of Industrial Science at the University of Tokyo. He also said that it is necessary to reduce the sizes of the detector, etc.