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Material Gains: Why Silicone Fits The Bill For Precise Dosing
Sep 14, 2017

They are vitally important, make therapy possible, and they have become an integral part in hospitals or home-care settings: medication and feeding pumps supply patients with essential medication and nutrition.  It is not only the right electronic and mechanical components that are crucial factors, but also the choice of materials for the pump segment. As in so many other areas of medical engineering, silicone plays a prominent role here.

What properties must a product have in order to find a lasting place in the healthcare sector? What are the specifications? It must be biocompatible, and in many cases skin- and blood-compatible as well. Compatibility with common sterilisation processes is usually a key requirement. It should be resistant to heat and cold and display excellent storage stability while maintaining a consistent pump performance. It is also important that the product works reliably and provides precise pumping over long periods of time. For the use in hospitals and in the home-care domain this means always administering the right dose, whether with drugs or in feeding applications. Obviously, no substances should be released from the processed material. So-called ‘extractables’ can have a negative impact on drug formulations.

It all adds up to quite a long list of product-specific requirements, which must in turn be met by the chosen material and its processing methods.  

Silicone – an exceptional material

Silicone is a perfect fit for the requirements of precise dosing and integrity when in contact with medications. Its physical/mechanical properties and the high degree of chemical purity in its formulation are decisive factors in this respect.

Among its mechanical properties, the exceptional resilience of silicone plays a significant role. It has a direct influence on the tubing segment’s pump performance over the entire period of use. The developer can be sure that his pump will always precisely dose and deliver the prescribed and programmed quantity of medication or nutritional solution. To ensure this functionality, the pump segments are subjected to a qualification and validation process as part of the development phase. Upon customer request, each lot or batch manufactured can also be tested during the production phase. The segments are tested for their adherence to pump performance specifications on a custom-built test stand that has the corresponding production pump built in.

To ensure that medications maintain the greatest possible purity, platinum-cured silicone is often preferred over the use of a peroxide catalyst, due to its excellent extractables profile.

Silicone injection moulding vs extrusion

The pump segments available on today’s market are manufactured in two differently manufactured ways. In terms of ‘pure’ production costs for fixed lengths, extruded tubing is generally more economical. However, customer and product requirements with respect to improved precision in delivery rates are becoming ever more demanding. Injection-moulded variants are therefore beginning to draw increased attention. The reason for this is that the diameter tolerance of tubing segments (for both inside and outside diameter) can be reduced by almost half, depending on dimensions and geometry. This fact has a direct positive influence on the dosing accuracy of individual pump segments in the range of 1%. Combined with the development of the appropriate silicone material formulation, in terms of Shore hardness and the type and degree of crosslinking, extremely high dosing accuracies can be achieved for the pump system as a whole over the course of the product lifecycle.

Silicone injection moulding provides added value

The intelligent use of silicone injection moulding technology allows for a range of features to be integrated in a single part. Previously these had to be provided by a more complex component. The advantages include:

  • no component-internal assembly costs

  • · finishing work such as cutting and stamping processes are no longer necessary

  • · precision-shaped edges of the component--> no sharp corners

  • · material is highly particle-free

  • · very narrow tolerances --> very high dosing accuracy

  • · section for air bubble detection

  • · integrated connectors – poka-yoke principle

  • · high degree of design freedom

  • · improved anti-counterfeiting

  • · maximum patient safety

When it comes to pump segments, the extrusion and injection moulding approaches each have their advantages and disadvantages.