1. Fix the requirements first
Where the catheter goes and what it must pass sets every dimension. Write down the access route, the length to the lesion, the size of the guidewire or device it must pass, and the maximum allowed outer diameter. OD is usually given in French; 1 Fr is 0.33 mm.
- Access route — femoral, radial, ureteral, endoscope channel
- Working length and the tightest bend along the path
- Minimum ID — guidewire 0.014″, 0.018″, 0.035″ or the device to pass
- Maximum OD — clearance to the sheath or guiding catheter ID
2. Choose the three layers
Most interventional catheters consist of an inner liner, a middle reinforcement layer and an outer jacket, fused into one by reflow. Each layer has a clear job, so decide the job first and then pick the material.
A PTFE liner will not bond to other materials as is, so its outer surface is etched. If PFAS regulation is a concern, a UHMWPE liner in the same size range is an alternative.
3. Braid or coil
A braid interlaces strands and excels at torque transmission and holding the lumen open; a coil is wound in one direction and excels at flexibility, kink resistance and crush resistance. Braid stiffness is tuned by carrier count (16, 24, 32) and picks per inch (PPI); coil stiffness by wire size and pitch.
Mixed builds are common too: a braid in the proximal section to transmit push and twist, and a coil in the distal section for flexibility.
4. Design stiffness by section
The proximal section must push and the distal section must track. Step the jacket hardness down from 72D proximally to 25–35D distally, and blend the joints by reflow so there is no abrupt change in stiffness — an abrupt change is where kinks start.
5. Stack the tolerances
Total wall thickness is liner plus reinforcement plus jacket, and the OD tolerance is the stack of each layer's tolerance. Specifying a tight tolerance for every layer separately often makes the sum overshoot. Fix the dimensions that drive function, such as OD and ID, first, then allocate layer thicknesses within them.
We produce reinforced tubing from 1.7 to 39 Fr with tolerances of ±0.0127–0.0254 mm.
6. The distal end and finishing
The distal tip is formed soft to reduce vessel injury, and a marker band such as Pt-Ir is added so the position shows on fluoroscopy. Add hydrophilic coating to cut outer friction, and printed scales if length must be read during use. The more of these finishing steps are done where the tube is made, the less dimensional error accumulates.
Common mistakes
- Fixing only the maximum OD and deciding the ID later
- Tightening each layer's tolerance so the total wall overshoots
- Skipping PTFE liner etching so layers separate after reflow
- Choosing the sterilization method late and having to reselect materials
Octudex handles everything from liner to braid and coil reinforcement, tip forming, marker bands and coating in a single order. Send just your requirements and we will propose a three-layer build first.