Choosing The Right Manufacturing Process For Your Silicone Medical Balloon

By Vesta

Compliant medical balloons are often produced from silicone due to its biocompatibility and because its tensile and elongation properties allow balloons to expand as internal pressure increases. There are three processes used to manufacture compliant silicone medical balloons: extrusion, molding and dip casting. Process and material choice will depend on your design and application requirements. Which one is right for your medical balloon? Read on for answers.

Extrusion
Extrusion is a good process choice for producing low-profile silicone medical balloons that are round when inflated and are used to fixate a device. The walls of extruded balloons generally fall in the range of 0.015" to 0.020".

The medical balloon extrusion process limits your material choices to high-consistency silicone rubbers. Poor concentricity and cosmetic issues can result in asymmetrical expansion or reduced burst pressure. To ensure uniform quality of your extruded balloons, choose a manufacturing partner that precisely controls concentricity and cosmetics in silicone extrusion.

Molding
Molding allows for greater design flexibility than other silicone medical balloon manufacturing processes. Liquid silicone rubbers (also known as LSRs or LIM materials) are preferable to other types of silicone, as their viscosity allows them to be molded into thin cross sections.

In the molding process, balloons are formed around cores in the center of mold cavities. The balloon is removed from its core after molding. The tensile properties and elongation of the material, as well as the thickness of the wall, limit the minimum vs. maximum diameter. A typical rule of thumb is 4:1. The shape of amolded balloon is virtually limitless, but the size is limited by the distance uncured silicone can be injected into the thin cross section of a hot mold. Molding under vacuum provides improved quality control, especially when molding balloons with unique profiles or convoluted cross sections. Choosing a supplier with experience in mold design and molding process control is critical for producing consistent wall thickness with high production capability.

Dip Casting
Dip casting is the preferred method for thin walled or large balloons and produces balloons without parting lines or flash. In the dip casting process, a mandrel is submerged into a dispersion of silicone rubber, so there’s no limit to how far material needs to be pumped. Like molded balloons, dip-cast balloons need to be removed from a mandrel. The physical properties of cured silicone dispersions allow for greater minimum vs. maximum diameters of 5:1 or more. The desired thickness or thinness of the balloon wall is achieved by controlling dispersion viscosity and the number of coats, and can reach 0.08" (2.0mm) if required. Understanding the nuances of dip casting and how to control this process are critical to achieving consistent wall thickness and expansion performance so choose a supplier with extensive experience in this technique.

Ask an Engineer

Question:
What types of requirements do I need to call out on my specification or drawing to ensure regulatory compliance?

Answer:
Thanks for asking such an important and timely question! Over the past couple of years, we’ve seen a sharp increase in regulatory oversight in the medical device industry. If your manufacturing requirements aren’t specific enough, your contract manufacturer might unknowingly make a problematic substitution. Of course, the types of requirements you should call out will vary based on your manufacturing process — so how do you know which ones are most important for your product? We’ll review some of the most critical requirements in our next few e-newsletters to help you avoid costly mistakes. We'll start here with material type.

Specifying Material Requirements
Clearly defining your material requirements helps eliminate variability in your manufacturing process because it ensures that the same raw material — from the same manufacturer, using the same formulation and manufacturing specifications — is always used to produce your part. Specifying the exact material also allows for traceability back to the raw material lots of both the base material and any additives you specify, and prevents misinterpretations and substitutions of raw materials or additives.

Consider specifying the following:

• Material manufacturer or trade name
• Material designation
• Formulation, including pigments, radiopacifiers, additives and actives

It’s always best to work closely with your contract manufacturer to ensure that your design requirements are properly documented in your specification or drawing.