Application Note | Medical Tubing Inspection
Dimensional and Surface Finish Analysis of Polymeric Tubes
Radius and Surface Roughness of TPE and PVC Medical Catheters from One Non-Contact Scan
Research & Experimental Testing
NANOVEA Laboratory
Visual Design & Editorial
Andrew Shore
Introduction
Tubes made from polymeric material are commonly used in many industries ranging from automotive, medical, electrical, and many other categories. In this study, medical catheters made of different polymeric materials were studied using the NANOVEA 3D Non-Contact Profilometer to measure surface roughness, morphology, and dimensions. Surface roughness is crucial for catheters as many problems with catheters, including infection, physical trauma, and inflammation can be linked with the catheter surface. Mechanical properties, such as coefficient of friction, can also be studied by observing surface properties. These quantifiable data can be obtained to ensure the catheter can be used for medical applications.
Why 3D Non-Contact Profilometry Matters for Polymeric Tubes
Compared to optical microscopy and electron microscopy, 3D Non-Contact Profilometry using axial chromatism is highly preferable for characterizing catheter surfaces due to its ability to measure angles/curvature, ability to measure material surfaces despite transparency or reflectivity, minimal sample preparation, and non-invasive nature. Unlike conventional optical microscopy, the height of the surface can be obtained and used for computational analysis; e.g. finding dimensions and removing form to find surface roughness. Having little sample preparation, in contrast to electron microscopy, and non-contact nature also allows for quick data collection without fearing contamination and error from sample preparation.
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Measurement Objective
In this application, the NANOVEA 3D Non-Contact Profilometer is used to scan the surface of two catheters: one made of TPE (Thermoplastic Elastomer) and the other made of PVC (Polyvinyl Chloride). The morphology, radial dimension, and height parameters of the two catheters will be obtained and compared.
NANOVEA ST400 Standard
Optical 3D Profilometer
Samples
Results and Discussion
3D Surface
Despite the curvature on polymeric tubes, the NANOVEA 3D Non-contact profilometer can scan the surface of the catheters. From the scan done, a 3D image can be obtained for quick, direct visual inspection of the surface.
Fig. 1: False color view and 3D view of the catheters.
2D Dimensional Analysis
The outer radial dimension was obtained by extracting a profile from the original scan and fitting an arc to the profile. This shows the ability of the 3D Non-contact profilometer in conducting quick dimensional analysis for quality control applications. Multiple profiles can easily be obtained along the catheter’s length as well.
Surface Roughness Analysis
Fig. 3: Surface roughness of the extracted areas (false color view and 3D view).
| ISO 25178 parameter | TPE catheter | PVC catheter |
|---|---|---|
| Sa (µm) | 0.9740 | 0.1791 |
| Sq (µm) | 1.260 | 0.2765 |
| Sp (µm) | 10.32 | 2.769 |
| Sv (µm) | 12.12 | 2.211 |
| Sz (µm) | 22.44 | 4.979 |
| Ssk | −0.09686 | 0.8676 |
| Sku | 4.498 | 14.65 |
| Spar (µm²) | 998001 | 251001 |
| Sdar (µm²) | 1139760 | 251589 |
Table 1: Height parameters and areas of the two catheter surfaces.
Conclusion
In this application, we have shown how the NANOVEA 3D Non-contact profilometer can be used to characterize polymeric tubes. Specifically, surface metrology, radial dimensions, and surface roughness were obtained for medical catheters. The outer radius of the TPE catheter was found to be 2.40 mm while the PVC catheter was 1.27 mm. The surface of the TPE catheter was found to be rougher than the PVC catheter. The Sa of TPE was 0.9740 µm compared to 0.1791 µm of PVC. While medical catheters were used for this application, 3D Non-Contact Profilometry can be applied to a large variety of surfaces as well. Obtainable data and calculations are not limited to what is shown.
Frequently Asked Questions About Polymeric Tube and Catheter Measurement
Why does catheter surface roughness matter?
Many problems with catheters, including infection, physical trauma and inflammation, can be linked with the catheter surface. Surface properties also relate to mechanical behavior such as the coefficient of friction, so quantifiable surface data helps ensure a catheter is fit for medical use.
Why use 3D non-contact profilometry instead of microscopy?
Profilometry using axial chromatism measures angles and curvature, works on transparent or reflective materials, needs minimal sample preparation and is non-invasive. Unlike optical microscopy it measures height for computational analysis, and unlike electron microscopy it avoids contamination and error from sample preparation.
Can a curved tube surface be measured?
Yes. Despite the curvature, the profilometer scans the catheter surface and produces a 3D image for direct visual inspection; form is then removed to calculate surface roughness.
How is the outer radius of a tube measured?
A profile is extracted across the scan and an arc is fitted to it. The TPE catheter had an outer radius of 2.40 mm and the PVC catheter 1.27 mm, and multiple profiles can be taken along the length for quality control.
Which catheter material was rougher?
The TPE (thermoplastic elastomer) catheter, with Sa 0.9740 µm, against 0.1791 µm for the PVC (polyvinyl chloride) catheter.
Where else are polymeric tubes measured?
Polymer tubes are used across automotive, medical, electrical and many other industries, and the same scan gives surface metrology, dimensions and roughness for any of them.
