Performances of potentially implantable rechargeable glucose sensors in vitro at body temperature

The authors developed a glucose sensor that operates in vitro at 37 degrees C for at least three months without recharging. The use of fine carbon particles upon which to immobilize the glucose oxidase makes it possible to recharge the sensor when enzymatic activity diminishes. This may enable the sensor to perform for at least a year when implanted, and thus reduce the frequency of surgical replacement. Recharging is accomplished by inserting a hypodermic needle into the septum of an implanted reservoir. Three types of carbon were investigated: graphite powder, carbon lamp black, and low-temperature isotropic carbon powder (ULTI). Two cross-linking procedures were tested. The sensor that remained operational for the longest time used the ULTI and the cross-linking procedure that mixed the enzyme, immobilized on carbon powder, with albumin and glutaraldehyde. This sensor operated continuously at 37 degrees C for at least three months. Further, it was put through four recharge cycles with ten days of successful operation after each without change. The sensor is very stable and the results obtained with it are reproducible.