How the microcatheter tube will be measured, how to specify material and layers by behavior, and what the quality section has to say before a quality team asks. From a precision micro extrusion team that has been in Jaffrey, NH for over 50 years. Part two of two.
The geometry was the easy half
Part 1 covered the dimensions: design intent, the tolerance arithmetic that binds OD, ID, and wall together, concentricity, and what a tighter tolerance actually costs. If wall thickness is your constraint, our Thin Wall Extrusions Guide covers it in more depth.
Get all of that right and the print is still incomplete. The sections that follow are the ones that decide whether the microcatheter tubing you receive behaves the way the drawing intended, and whether anyone can prove it when a quality team asks.
How will you measure it?
A dimension with no method behind it is not yet a specification.
At the scale of microcatheter tubing, the reading depends on how the tube was supported, whether the feature was read optically or under contact. We can guide the method of measurement and can coordinate measurement correlation with your quality team. So the print should say the method, the feature, the sample plan, and the acceptance. If it does not, your incoming inspection and your supplier’s certificate will eventually disagree, and the disagreement will surface at the point in the program where you have the least time to resolve it.
Reconciling method takes an afternoon at kickoff. It takes weeks at validation.
Name the behavior, not just the durometer
Durometer reads like a single hardness value. In a catheter it is a set of behaviors: how the tube flexes, how it transmits push, how it tolerates a tight bend, how gently it interacts with tissue. Two materials at the same Shore reading can draw differently, relax differently, and behave like different tubes in the device.
So name the material if you know it, and name the behavior regardless. If a lower durometer is the goal but the wall on the drawing will not hold at that durometer, that is a conversation worth having before the print is released rather than after the first lot. The honest version of that conversation sounds like “that durometer will not hold the wall you want, and here is what will.”
Multilayer tubing: say what each layer is for
If the design calls for a multilayer construction, the print should say what each layer is being asked to do.
A slip layer reducing deployment force is a different engineering problem from a structural layer carrying burst pressure, even when the two occupy the same fraction of the wall. A bonding layer exists because two chemistries need to act as one. An ultra soft outer layer exists because the anatomy will not tolerate anything harder.
Layer intent drives material selection, tooling geometry, and process. Every additional layer multiplies the alignment, bonding, and dimensional decisions that have to land precisely, so knowing which layer is carrying the design lets us decide what the process protects first.
Layers are also where the wall gets thinnest. One two-layer construction we run holds each layer to its own precise thickness inside a total wall of 0.003 in (0.076 mm). Having processes that can deliver at production volumes across ID and OD configurations is key. At that scale, a print that gives only the total wall leaves the split between the layers to chance.
For a multilayer tube, the print should state the layer order from inner to outer, the material and purpose of each layer, which layer thickness is critical and which is reference, and how layer thickness will be measured. Individual layers are usually read on a magnified cross section rather than with a gauge, so the method belongs on the print alongside the dimension. Where two dissimilar materials share a wall, as they do in a three layer microcatheter shaft, say what adhesion the interface has to hold and how delamination will be checked.
Fewer extruders work in multilayer at microcatheter scale than in single layer tubing. We extrude constructions of up to three layers, and the programs that go smoothest are the ones that bring layer intent to the first conversation, while there is still room to adjust the split.
Spools, coil set, and the three weeks between our measurement and yours
Prints tend to describe the tube and skip the things that determine what condition it arrives in.
How is it to be supplied: on a spool, in cut lengths, in a specific coil diameter? Is there a straightness or coil set requirement? Does the tubing need to be conditioned before measurement, and if so, for how long? How is it packaged, and what has to travel with it?
These are not administrative details. In materials that creep, the dimension measured at the line is not always the dimension measured three weeks later, and the difference between the two can be larger than the tolerance band being argued about.
Write the quality section before a quality team asks for it
The last section of a good print describes the evidence. What inspection data has to accompany the lot. What certifications and material traceability are required. What is retained, and for how long.
Validation is where programs lose months, usually not because the part was wrong but because the proof was not ready. A lot can look perfect at the line and still create problems at IQ, OQ, and PQ if the process behind it was never characterized, or if the data traveling with it does not answer the questions a quality team is about to ask.
Every order that leaves our floor includes our MC Q-Pack, which contains inspection data, certifications, and full material traceability, so the engineer opening the box already holds the evidence their validation depends on. The best time to define that content is while the print is being written, not while a quality team is waiting on it.
The print is the cheapest place to solve the problem
Every problem in a micro extrusion program can be solved at some stage. The cost of solving it multiplies at every stage it survives.
A material conversation costs an afternoon before release. It costs a change order during development. It costs a lot on hold during validation. It costs a supply interruption after launch. Nothing about the underlying engineering changes. Only the price of addressing it.
The tubing on these prints ends up in devices that restore flow to a threatened limb or clear a clot from the brain. Quality and precision are foundational to the work we do at Microcatheter Components, and the earliest place either one can be built in is the document itself.
If you are writing or revising a microcatheter tubing print, we would welcome the conversation. The earlier, the better. We do our best work alongside design teams at the concept stage, before the first print is drafted.
