Implanted Wireless Glucose Sensor Lasts 520 Days

One of the challenges of developing an effective glucose sensor that sits in tissue just below the surface of the skin is how to overcome the problem of "tissue encapsulation" which causes unpredictable fluctuations in the readings.

Dr. David Gough, first author and bioengineering professor at UCSD told the press that the most important aspect of their paper is how they overcame this problem so their sensor remained insensitive to tissue encapsulation for over 500 days.

"That's a big step from a scientific point of view, and it's due to the sensor's unique oxygen detection scheme," said Gough.

He and his team hope that after human trials and FDA approval, their device may help people with diabetes manage their condition more effectively than methods currently in use such as finger-sticking and short-term, needle-like glucose sensors that have to be replaced every three to seven days.

"If all goes well with the human clinical trials, we anticipate that, in several years, this device could be purchased under prescription from a physician," said Gough.

The problem with many current methods, for example the so-called finger-sticking system where the patient pricks his or her finger to get some blood to test in a portable reader (usually done about four times a day), is that they do not monitor the level of glucose continuously, leaving open the risk of dangerous ups and downs of glucose levels, known as "glucose excursions." The more "glucose excursions" a patient has, the higher the risk of developing long term problems of diabetes, affecting the eyes, kidneys, heart, brain, feet and nerves.

The device that Gough and his team developed and tested in the pigs is about 1.5 inches (3.8 cm) in diameter and about 5/8 ins thick (1.6 cm). It is implanted under the skin and continuously monitors tissue glucose and transmits the information without wires to an external receiver.

The device worked effectively, they said, because of its unique way of producing a reliable reading without being affected by the problem of tissue encapsulation.

It does this by taking in glucose and oxygen from surrounding tissue and using the enzyme glucose oxidase to catalyze a reaction where oxygen is consumed in proportion to the amount of glucose present.

Any oxygen left over is measured and compared to the baseline oxygen recorded by a reference sensor, so the difference indicates how much glucose is present.

The authors said that the effect of exercise and changes in local blood flow to the tissues are also in the main subtracted out in this differential oxygen sensing system, where the two sensors sit side by side in the same device.

The sensors used in the animal trials sent the glucose information to a data recorder the size of a cell phone. Gough said the data could be made useful in many ways, for example it could be sent to cell phones or displayed in other ways.

"There are parents with diabetic children who spend their nights worrying that their child in a nearby bedroom may go into nocturnal hypoglycemia," he said, explaining that a continuous glucose sensor could trigger an alert if the level dropped too low in the night.

A long term implanted monitor would keep measuring glucose day and night.

"Others wouldn't even know if someone is using a glucose sensor. Our goal is to get people off the finger-stick cycle," he added. He said if the device passes human trials, it could be implanted in patients in a simple outpatient procedure.

Source: http://www.diabetesincontrol.com/index.php?option=com_content&view=article&id=9662&catid=53&Itemid=8, "Function of an Implanted Tissue Glucose Sensor for More than 1 Year in Animals." David A. Gough, Lucas S. Kumosa, Timothy L. Routh, Joe T. Lin, and Joseph Y. Lucisano. Sci Transl Med Vol. 2, Issue 42, p. 42ra53, published online 28 July 2010 DOI: 10.1126/scitranslmed.3001148