Experience with an implantable glucose sensor as a prerequisite of an artificial beta cell

A modification of a Clark-type glucose electrode which proved suitable for implantation and for connection to a glucose-controlled insulin infusion system is presented. It involves a third hydrophilic or perforated hydrophobic membrane and is based upon measurement of the H2O2 generated by the glucose oxidase reaction. The linear calibration range is greater than 40 mmol/l glucose concentration with a tau 95 of 360 or 600 s, respectively (different sandwich prototypes). There is reliable glucose-dependent sensor output up to a 15 mmol/l concentration when the pO2 is as low as 2 to 5 kPa as monitored in subcutaneous tissue. One prototype series of the sensor was employed for paracorporal (ex vivo) glucose monitoring in undiluted blood and for insulin infusions in diabetic dogs, which were feedback-controlled by the sensor's output. Another prototype was designed and applied for subcutaneous implantation. Tissue glucose concentration amounts to 30 to 50% of the simultaneously measured blood plasma glucose level which is mirrored in a total lag time (i.e. tau 95 of sensor and physiological delay in interstitial fluid) of 15-20 min. The glucose sensor presented provides a transient step towards a long-term functioning implantable instrument.