Development of remotely controlled implantable devices for programmed insulin infusion

Broadbased clinical research during recent years has shown that programme controlled insulin infusion with externally portable devices is an excellent means for improving glucose control of labile diabetics. On the basis of this experience we concentrated on the development of implantable units, which would allow the potentialities of the method to become available for long-term therapy. Implantable devices have to be small, lightweight, long-lived, biocompatible, reliable, safe and externally controllable if they are to be used in humans. We have developed such a device with a volume of 94 cm3, a weight of 180 g and a refillable insulin reservoir of 10 ml. Using an insulin concentration of 100 units per ml, the reservoir has to be refilled through the skin about every three weeks. Energy is provided for more than one year by a lithium battery. Insulin infusion is controlled by a roller pump driven by a stepping motor. Twelve different basal rates and 12 different prandial doses can be programmed by an external programmer. One hour after programming, the high prandial infusion rates return automatically to the basal rate. The telecontrol system includes circuits for acknowledgement of programme transmission, monitoring of the stepping frequency and checking of the catheter pressure. Emphasis has been placed on making the implant safe against overdosing. All the components including the insulin reservoir are encapsulated in a titanium housing. In this way, the whole insulin tract is well protected against damage, and even in the case of a leak no insulin could be released into the body because an underpressure is maintained in the interior of the titanium capsule. Overdosing due to electronic defects is prevented with additional safety circuitry, the function of which can be checked at any time, even after implantation. Research prototypes of the devices have been tested widely in dogs and have been implanted in humans recently.