Component Atlas · Help me decide
Choosing a reinforcement
Braid, coil, both, laser-cut hypotube, or nothing at all. They fail differently, and which failure you can tolerate is a property of the procedure rather than of the catheter.
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How to read this, and what it is not
There are no numbers on this page, on purpose. A filled grid of figures reads as measurement, and any figure we published would be a measurement of somebody else's shaft — different liner, different wall, different anatomy. What generalises is the mechanism, so that is what each cell carries.
Every judgement is tagged with the kind of claim it is:
- mechanics Follows from how the structure carries load.
- geometry Follows from the shape of the construction.
- process Follows from how the part is made and bought.
This is a beta. If the axis you actually choose on is missing, that is the most useful thing you could tell us.
| Construction | Torque transmission Does a turn at the hub become a turn at the tip? | Kink resistance Does it collapse when bent past its limit, or recover? | Flexibility / trackability Will it follow anatomy without pushing it out of the way? | Pressure capacity What holds the lumen open, and what resists bursting it? | Wall penalty How much of your wall budget does the reinforcement itself eat? | Cost and lead time What does it cost to make, and what does it cost to change? |
|---|---|---|---|---|---|---|
| Braid Wire woven into a lattice and laminated into the wall. The default when the shaft has to be steered. | Strong mechanics Twisting the shaft loads the braid wires in tension along their helix. A lattice in tension is stiff, so the angle you apply at the hub is close to the angle you get at the tip. | Moderate mechanics The lattice resists ovalisation up to a point, then the crossings slip past each other and the wall folds. It bends well until it does not. | Moderate geometry Pick count and braid angle set it. A lower angle stiffens torque and costs bending flexibility; the two are traded against each other on the same shaft. | Strong mechanics Hoop load is carried by the wire crossings, so a braided wall holds pressure well for its thickness. | Costly geometry At every crossing the wall has to contain two wire diameters, not one. That is the wall penalty, and it is set by geometry rather than by process. | Moderate process Braiding is a standard operation on standard equipment. Changing pick count or angle is a setup change, not new tooling. |
| Coil A single wire wound helically. The default when the shaft has to stay open through a bend. | Weak mechanics Twisting a helix winds it tighter or unwinds it, so the input is absorbed by the coil changing pitch rather than transmitted along the shaft. This is the trade a coil makes. | Strong mechanics The turns bear against each other and resist the wall collapsing inward, which is what a kink is. It is the construction that holds a lumen open through a tight bend. | Strong geometry Adjacent turns are not tied to each other, so the structure bends by opening the pitch on the outside of the bend. Nothing has to stretch. | Moderate mechanics Hoop strength is good, but there is no axial member, so pressure capacity depends more on the polymer than on the reinforcement. | Moderate geometry One wire diameter, not two — there are no crossings. For the same wire, a coil costs less wall than a braid. | Moderate process Winding is standard. Flat wire buys wall efficiency at a higher material and setup cost than round. |
| Braid over coil Both, stacked. Chosen when neither construction alone survives the anatomy. | Strong mechanics The braid does the torque work; the coil underneath does not interfere with it. | Strong mechanics The coil holds the lumen open exactly where the braid alone would let the wall fold. | Moderate geometry Two structures in the wall are stiffer than either alone, and the distal section usually has to drop the braid to recover flexibility. | Strong mechanics Both structures carry hoop load. | Expensive geometry The penalties add. This is the construction that most often runs a shaft out of wall budget before it runs out of performance. | High process Two reinforcement operations, two sets of parameters, and more ways for a lamination to go wrong. |
| Laser-cut hypotube A metal tube with a cut pattern that grades its stiffness along the length. The proximal shaft of most devices that need 1:1 response. | Strong geometry It is a continuous metal tube. Torque response approaches one-to-one, which is the reason to accept everything else on this row. | Strong mechanics A metal tube does not ovalise easily, and the cut pattern is what sets where it is allowed to bend at all. | Tunable geometry This is the distinguishing property: cut density is a designed variable along the length, so stiffness can be graded continuously rather than stepped at a joint. | Strong mechanics A metal wall, and the cuts are the limiting feature rather than the tube. | Efficient geometry The reinforcement IS the wall rather than something embedded in it, so there is no separate penalty to pay. | High process Cutting is per-part machine time and the pattern is design work. Changing the pattern means re-cutting and re-testing, so it is the slowest of these to iterate. |
| Unreinforced Extruded polymer, nothing in the wall. The right answer more often than it gets picked. | Weak mechanics A polymer tube in torsion winds up. For a device that is pushed rather than steered, this may not matter at all. | Weak mechanics Nothing resists ovalisation but the polymer itself, so the kink radius is a property of the material and the wall. | Strong geometry Nothing in the wall to stiffen it. | Moderate mechanics Set entirely by the polymer and the wall thickness — which does make it straightforward to compute rather than test blind. | Efficient geometry No reinforcement, no penalty. The whole wall is available to the pressure and stiffness requirement. | Low process Extrusion only. The cheapest construction to make and by far the cheapest to change. |
The short version
If the device has to be steered, you need braid or a hypotube, because a coil absorbs torque rather than transmitting it. If it has to stay open through a tight bend, you need a coil, because that is the construction that resists the wall collapsing inward. Needing both is why braid-over-coil exists, and paying for both in wall is why it is not the default.
If the device is pushed rather than turned, unreinforced is a real answer and it gets picked less often than it should. It is the cheapest to make, by far the cheapest to change, and it leaves the whole wall available to the pressure requirement.
A laser-cut hypotube is the only one of these where stiffness is a continuous designed variable along the length rather than something stepped at a joint. That is what you are buying, and the cost is that changing it means re-cutting and re-testing.
What this page cannot tell you
Whether your specific stack closes. Working lumen, wall and OD are a three-way constraint, and a reinforcement choice that is right on every axis here can still be the one that runs you out of wall. That arithmetic is worth doing before the first build rather than after the first bench test.
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