Insulin MiniMed implantable pump

In the MiniMed implantable pump, a piston pump drives insulin through the delivery catheter. A patented solenoid motor controls the piston movement, to aspirate insulin from the reservoir chamber into the piston chamber and then push it through the insulin delivery catheter. 

Problems with insulin delivery in implanted pumps are difficult to correct. A change in Hoechst 21 pH-neutral semisynthetic insulin 400 U/ml in accordance with regulations of the European Pharmacopoeia (SEDA-20, 397) resulted in more frequent clogging when this insulin was used in the Minimed 2001 implantable pump (MIP 2001). From October 1995 to October 1996, 17 pumps were implanted (241). The refilling period was reduced from 90 to 30-45 days and the reservoirs were washed with insulin-free buffer before each refill. Backflow was seen in 13 pumps after a mean period of 7.2 months. Modification of the manufacturing process produced 21PH ETP insulin (human semisynthetic insulin, Genapol-stabilized) 400 U/ml, Hoechst, with improved stability since July 1997. All pumps were specifically cleaned before the new insulin was used for refill. The refill period was increased from 38 to 78 days. In 16 pumps, only one backflow was seen after 14 months. 

The primary limitation currently facing the development and use of these implantable micropumps is the precipitation of insulin on the pump components (7,11,14,31), although bicarbonate (33), certain serum components (25), or amino acides (32) may minimize or prevent insulin aggregation. These precipitates, if they accumulate, tend to occlude the flow channels in the pump and particularly the fine bore tubing or valves that are integral parts of these devices. Additional concern is related to the reliability and inherent safety of these devices and to their ability to use small, concentrated insulin reservoirs. 

---