Jay Tourigny, senior vice president at MicroCare Medical, explains why silicone swelling fluids help medical designers to make a connection.

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blue gloved hand holding six surgical introducers

Silicone has been widely used in the medical sector for decades. Thanks to its unique chemical and physical properties, highly-versatile medical-grade silicone can be found in everything from diagnostic and monitoring implements to surgical implants and device tubing.

With developing countries undergoing rapid changes and rising ageing populations, the need for silicone medical tubing in the healthcare and medical device industries is increasing. However, as medical devices become smaller and more complex, the use of this biocompatible material becomes more problematic.

Advanced swelling fluids assist with this challenge by providing greater design flexibility. They are an effective way to easily and successfully incorporate silicone tubing in today’s cutting-edge devices.

Medical device manufacturers require small, light and flexible tubing that meets tight tolerances. This often means reduced inner and outer diameters, thinner wall thickness, and multi-lumen tube construction.

Although medical-grade silicone is a popular material choice for tubing, due to its high level of biocompatibility, durability and flexible structure, it generally does not expand or stretch without assistance.

Silicone also has a high coefficient of friction, or a tacky surface. Therefore, sliding a silicone tube onto a barbed or textured fitting often requires some force which can result in stress-cracks, splitting and ultimately scrapped materials.

Assisting medical device manufacturers in this assembly challenge are fluids that allow silicone tubes to slide and fit more quickly and easily. Oil, alcohol, and elastomer swelling agents are the three most common types.

Ultra-pure isopropyl alcohol (IPA) is another popular fluid when assembling devices that use silicone tubing. Although IPA is cost-effective and easy to obtain, it does have problems.

Because IPA dries very slowly, the assembly cycle time increases while manufacturers wait to move to the next stage of production. Just like oil, IPA can negatively affect the rigidity of thin-structured tubing, making it difficult to work with.

A better option is an engineered silicone swelling fluid. It quickly and evenly swells tubing simply by soaking one end of the tube in the fluid. Depending on how much expansion is required, the longer tubing stays immersed in the fluid allowing it to increase to the desired dimension. For example, if the tubing only needs to expand by 1–2% for assembly, the entire swelling process is often completed in less than a minute.

After the tube is fitted to the connector, the engineered swelling fluid evaporates quickly. The tubing returns to its original size, shape, durometer, compression and strength to form a tight, sealed fit over the fixture, regardless of its geometry. This makes it particularly useful when using multi-lumen tubes.

Unlike hexane or toluene, swelling fluids are specifically engineered for the job. They do not change the physical properties of the tubing. It is not aggressive, so it has excellent materials capability and is safe to use on most elastomers and plastics including neoprene, EDPM, polyethylene and polypropylene. It is especially useful for swelling tubing with thin, soft walls or those with larger diameters.

The swelling fluid does not cause long-term change to the mechanical properties of the tubing material. Furthermore, it will not weld or bond the tubing onto the fitting, so it can be easily removed later, if needed.

Engineered silicone-based swelling fluids are helping advance the design and production of complex medical devices. Tubing that was once difficult or impossible to join to other components can now be securely fitted with ease to ensure the safety and reliability of the medical device. Thanks to their specific properties, swelling agents make medical device assembly efficient and effective and do so in the safest, most sustainable way.

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