Liquid Silicone with a Vital Function

When people with chronic conditions leave home, their cellphones, keys and wallets are not the only items they must take with them. They often have to remember their medication too, as well as the paraphernalia that goes with it. All the better then that liquid medication can now be injected automatically and conveniently via compact dosing systems – thanks to a new silicone developed specifically for the intricate pump housing.

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.

Humans and Materials Working Together

The centerpiece of these medical devices is a tiny microinjection pump that reliably delivers precise doses of the essential medication. The pump housing, made of thermoplastic and silicone, was developed by Trelleborg, a polymer processor and WACKER customer, on behalf of a world-leading supplier of pharmaceutical and medical products. A new, unique material from WACKER ensures that everything proceeds smoothly on the inside.

Virtually Impossible: Self-Adhesion together with Low Sliding Friction

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.

Strict Production Monitoring Ensures Absolute Purity

The new self-adhesive, intrinsically sliding product from WACKER is called SILPURAN® 6760/50. This liquid silicone rubber consists of two components and, once mixed, cures to form a transparent, mechanically robust elastomer. Unveiled to the public for the first time in 2016, it remains to this day the only market-ready, self-adhesive, friction-modified liquid silicone rubber with biocompatibility certificates. This is made possible by carrying out fine filtration, inspection and dispensing under cleanroom conditions at WACKER.

Precision Dosing Due To Low Friction

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.

The principle of combining sealing with good sliding friction is widely utilized in syringes: given the right silicone material, the sealing element glides uniformly and smoothly along the syringe wall. This enables the liquid to be administered in the correct dosage.

The micro-injection pump is of the piston type, with a small plunger conveying the liquid. The picture shows the pump cylinder, the internal wall of which has an extremely thin lining of SILPURAN® 6760/50.

Do you have a similar application?

If so, find out more about our SILPURAN® 6760/50.

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