Material selection in catheter development rarely comes down to the properties of one polymer alone. The materials within the assembly, the manufacturing process and the temperatures involved all need to work together.
This becomes particularly important when working with PEBA materials such as Pebax®, which are available in a range of grades for medical applications, including catheter manufacture. Different grades provide different levels of flexibility and have different thermal properties, so processing conditions need to be considered alongside the finished performance of the device.
One factor to consider during catheter development is the heat shrink’s recovery temperature during processing.
Why consider FEP heat shrink?
Adtech’s FEP heat shrink sleeving has an approximate shrink temperature of 110°C and a continuous working-temperature range of -200°C to +200°C.
Its relatively low recovery temperature is one of the characteristics that makes FEP useful where the materials underneath the sleeve may be temperature-sensitive. FEP also provides chemical resistance, a low-friction, non-stick surface and transparency.
For catheter development, the important point is the temperature required to make the heat shrink itself recover around the assembly.
Where a process uses materials with different thermal limits, avoiding unnecessary additional heat from the shrink sleeve can give engineers another variable to consider when developing the manufacturing process.
Why does the PEBA/Pebax® grade matter?
Pebax is a family of polyether block amide thermoplastic elastomers rather than a single material with one set of thermal properties.
Arkema’s published data shows that properties vary between grades. Selected Pebax grades have published melting temperatures ranging from approximately 133.5°C to 174°C, while medical grades are available specifically for catheter applications.
This is why it would be incorrect to specify one heat-shrink or reflow process simply because an assembly contains “Pebax”.
The individual grade, wall thickness, other materials in the assembly and required finished geometry all need to be considered.
What does the 110°C shrink temperature actually mean?
This distinction is important.
110°C is the approximate shrink temperature of Adtech FEP heat shrink. It is not a recommended catheter reflow temperature.
It tells us when the FEP sleeve begins to recover. It does not tell us the temperature required to process a particular PEBA jacket, form the complete catheter shaft or achieve the required bond between layers.
Those parameters depend on the materials and construction being processed.
The benefit of the lower FEP shrink temperature is therefore more specific: the sleeve can begin recovering without requiring a very high temperature simply to activate the heat shrink.
Whether that allows the overall catheter process to operate at a lower temperature must be established through development and testing.
What should be considered when developing the process?
When evaluating FEP heat shrink for an assembly containing PEBA or Pebax, the complete construction should be reviewed rather than selecting the sleeve from diameter alone.
Important considerations include:
- the exact PEBA or Pebax grade;
- the thermal limits and processing requirements of every material within the assembly;
- the supplied and recovered diameter of the FEP heat shrink;
- the required recovered wall thickness;
- the amount of recovery needed around the assembly;
- heating method, temperature and exposure time;
- dimensional tolerances and required surface finish; and
- any application-specific medical or validation requirements.
The process therefore needs to be established for the individual assembly rather than applying a universal temperature profile.
Where could FEP heat shrink be worth evaluating?
FEP heat shrink is worth considering where an engineer needs fluoropolymer performance but also wants to minimise the temperature required to recover the sleeve itself.
This could be relevant during the development of assemblies incorporating temperature-sensitive components or thermoplastic materials such as PEBA, provided the complete process is tested and validated for the particular construction.
Adtech supplies FEP heat shrink in a wide range of standard diameters and wall thicknesses and can also manufacture custom sizes for application-specific requirements. Its standard FEP range currently extends from 1.5 mm to 150 mm ID.
Developing the complete catheter assembly
There is no substitute for application-specific testing when different materials are being brought together.
Through Adtech’s medical fluoroplastics capabilities, products can be processed within a dedicated clean production area, with full resin data traceability and certificates of conformity. Adtech can also offer suitable FDA 21 CFR regulatory raw polymers from stock, with USP Class VI compliant raw polymers available to order.
For applications still at the development stage, Adtech’s fluoropolymer product development service includes sample production, support from its in-house R&D team and development of bespoke processing and assembly methods.
For engineers investigating PEBA/Pebax catheter constructions, FEP heat shrink’s approximately 110°C recovery temperature makes it a material worth evaluating as part of that development process. The final suitability, process temperature and performance should always be established against the specific materials and finished device requirements.
