Using Finite Element Analysis to Evaluate Laser-Cut Hypo Tubes

Introduction

Medical device development is notoriously expensive and time-consuming. Every new design feature—whether in a catheter, stent, or surgical instrument—typically requires multiple cycles of prototyping and bench testing before it can be approved for use. Each cycle consumes materials, labor, and weeks (or even months) of calendar time. Finite element analysis for medical products is a powerful tool for reducing medical product development costs.

Finite element analysis (FEA) offers a way to reduce that burden. By running simulations early in the design process, engineers can evaluate trends, explore multiple design variations, and identify problems before building the first prototype. In this case study, I applied FEA to catheter hypo tubes with different laser-cut patterns to see whether the analysis could capture the stiffness trends observed in lab testing.

Why Hypo Tube Cut Patterns Matter

Catheters rely on carefully balanced stiffness and flexibility. Laser-cut patterns in stainless steel hypo tubes allow engineers to “tune” these properties for specific clinical applications. Small changes in cut angle or spacing can significantly affect how the catheter bends and twists inside the body.

In bench tests, one of our experimental cut patterns behaved unexpectedly. We anticipated that it would be stiffer than the standard design, but it turned out to be noticeably softer. This result raised an important question: could a simple FEA model have predicted this behavior before we cut real parts?

Building the FEA Models

To answer this, I created 3-D finite element models of two laser-cut hypo tubes:

• Nominal design (baseline) – the standard cut pattern used in production

• Test design – an experimental pattern that had shown reduced stiffness in lab testing

Rather than duplicating the exact test loads or stress levels, the goal was to see whether FEA would predict the trend between the two patterns.

Model details:

• Geometry: 3-inch tube length, 0.066-inch diameter, 0.003-inch wall

• Outer layer: 0.003-inch PBAX plastic bonded to the tube

• Materials: stainless steel (tube) and PBAX polymer (outer layer)

• Boundary conditions: both ends fully constrained

• Applied deflection: 0.25 inches

nominal catheter hypo tube – meshed model

 

The models were meshed to capture the cut pattern details, and figures (not shown here) illustrate the geometry, constraints, and deflected shapes.

Note cut pattern perpendicular to tube lung axis

 test  cut pattern – meshed . Note cut angle compared to baseline

Results

Catheter Cut Pattern	FEA         Test  (lb)
Baseline / Nominal	1.20            1.15
Test Pattern	0.67           0.75

The force required to produce the 0.25-inch deflection was measured for both cut patterns, including the PBX reflow material.

The analysis model accurately predicted the stiffness trend observed in catheter testing. While it slightly overestimated the stiffness difference between the two cut patterns, the overall direction matched experimental results. Finite element analysis (FEA) proved valuable in evaluating hypotube cut patterns, which were less stiff than the standard design. By running 3-D FEA models before building prototypes, development teams could reduce physical testing cycles and shorten the design timeline.

If more information is needed, such as

• minimum bend radius
• torque response
• effect of cut pattern spacing/width/angle
• hypo tube wall thickness/diameter/material change
• plastic type/thickness

all this and more can be generated with simple model changes.