MATERIALS | MEDICAL TUBING
Finally, the pusher catheter assists in stent deployment. To do this, it needs sufficient column strength. Its overall profile must be minimised so it can move in tandem with the other parts of the delivery system. In each case, polyimide’s ability to retain mechanical performance at low thickness is critical. Teleflex says that – for the same thickness – polyimide gives twice the mechanical performance of polyamide 12, which is the material typically chosen for such applications.
Above: Balloon catheters rely heavily on plastics for correct operation
microscopy. This involves cutting a small sample, embedding it into a resin and examining it under an optical or electron microscope to study features like grain size, phase distribution, inclusions or defects. The company also published several papers on the subject, identifying sources of ‘stress’ that affect performance. “The goal is to create an amorphous structure prior to balloon forming,” they said. “If the tube is more crystalline than amorphous prior to balloon forming, the stress might be the reason for defects in balloon forming.”
Thinner walls Chris Pehoviak, EMEA sales manager at Teleflex Medical, told delegates how his company is developing advanced catheters using polyimides. Medical device designers must reduce the
overall profile and wall thickness of catheter- based devices – and this is where material innovations can help. When the limits of extrusion or hand- assembled catheter fabrication technologies are reached, film casting offers a route to tighter tolerances and thinner walls – with polyimide- based composites, he said. In a prime example, the material can improve the functionality of each layer of a triaxial delivery system, he said – which is used for deployment of synthetic heart valves and vascular stent grafts. For the inner catheter to navigate freely in the
system, it must have a low profile and sufficient crush resistance to withstand the forces that the implant exerts during delivery. It must also have high creep resistance. At the same time, the retention sheath screens
the pre-deployed implant during delivery. It must also be thin, to minimise the overall profile of the triaxial delivery system and needs high radius strength.
14 PIPE & PROFILE EXTRUSION | Summer 2025
Tube control Andrew Traver, CTO of SIS Medical, explained how understanding – and controlling – tubing material helps improve product performance and stability. He cited a real example of a Twin-Wall design of balloon catheter tube. He said that factors such as raw material and
processing conditions cause product variability. Although an identical grade may be coming from the same supplier, analysis shows that there may be a molecular weight difference between batches, meaning a change in viscosity. During production, humidity changes can affect polymers – especially polyamides. Water content in a PA12 can vary between 0% (if stored dry) to around 1.5% if stored in humid conditions. Here, moisture can be characterised before processing, or can be removed post-processing. He said that pre-processing to achieve tube saturation stabilises wall thickness (usability) and reduces scrap. This can be followed by a post-processing study of moisture removal to improve performance. “Have patience because there is always a
solution,” he said. “Don’t go backwards – go forwards – and anticipate changes before they happen.”
Material selection Bryan Mathias, CEO of Mathias Synergy Solutions (MSS) told delegates of several key criteria for selecting a catheter material at the design stage. These include: biocompatibility; mechanical and chemical properties; manufacturability; and surface properties. This applies to all materials, including
polyurethane (strong, flexible and biocompatible), silicone (biocompatible and flexible), PVC (less biocompatible, but lower cost) and polyamide (strong, with high chemical resistance). Emerging materials are also helping to expand
this, he said – with anti-microbial coatings helping to cut infection risk, nanomaterials enhancing mechanical properties and bioabsorbable
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IMAGE: SHUTTERSTOCK
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