People with chronic conditions need to monitor their bodies around the clock. One way to manage diseases such as diabetes and Parkinson’s is to inject medication directly under the skin. This can be done very conveniently, safely and quickly with insulin pens or other portable medical devices.

The next step forward here is an automated dosing system that can be attached directly to the patient’s skin. At the point of skin contact, an extremely fine needle extends automatically to inject a preprogrammed dose of medicine. Thus, it is possible to administer as little as a few microliters of active ingredient steadily over a period of minutes, hours or even several days.

To keep the medical device small and compact, the micro-injection pump cannot be much larger than a fingernail. This posed a challenge for the developers as regards friction, sealing and bonding to the pump. But these are precisely the areas in which liquid silicone rubber (LSR) excels. What was needed was a primer-less silicone grade that would bond securely to the body of the tiny pump cylinder during two-component (2K) injection molding. But the rubber also had to allow the pump to operate smoothly, without jerking. From a physical point of view, high adhesion and low sliding friction are seemingly irreconcilable. However, it was possible to combine these properties using chemical means.

WACKER already had liquid silicones with self-adhesive properties in its portfolio, as well as products with low coefficients of friction. However, it did not have a product for use in sensitive applications that offered both properties together. The micropump thus provided the perfect opportunity to combine these two properties in one silicone.

SILPURAN^® 6760/50 was chosen as the soft silicone component for injection molding the sealing elements directly onto the cylinder of the micro-injection pump. It ensures that the plunger glides smoothly along the inside surface of the cylinder as the medication is being injected into the patient. This is the only way to achieve the extreme precision dosing that can prove life-saving when the case arises. Were the surface to be rubbery and dull, the plunger movement would be jerky, creating pressure surges and affecting dosing accuracy. The product’s intrinsic sliding property renders lubricant unnecessary; and the silicone surface does not bleed. Thus, there is no risk that the medicine will be contaminated.