Hydrophilic Coating Friction Test – Lubricity/Pinch Test
The purpose of this test is to assess the lubricity and the durability of hydrophilic coatings (on balloons, catheters etc). The most common test used for finding friction at a surface is a pinch test, where test samples are pinched between two plates (pads) with a known amount of force or a defined distance, while using a motor to pull and/or push the test article through the plates. The force it takes to pull and/or push the device through can be measured. Passing the device through the pinch test multiple times will eventually cause the coating to fail and friction readings to increase.
The sample is placed in a defined fluid at a defined temperature. The sample is positioned between two pads covered with defined material. Initial distance between the pad and the distal tip of the sample is defined. A normal pinch force or a pinch distance between pads is applied to the sample. The sample is pulled or pushed through the pads at a defined speed over a defined length. The force it takes to pull or push the sample can be measured. Durability is assessed by passing the sample through the pinch test multiple times.
- Pinch force or distance remained applied; sample is then pushed and pulled several times through pads
- Pinch force or distance is removed, sample is manually pushed back to its original position, pinch force or distance is applied again then sample is pulled through the pads again.
The choice between the two cases depends on the device ability to be pushed through the pads which is defined by 2 parameters:
- Distance of friction
- Pinching force or distance
- Endovascular test bench including:
- Constant flow pump
- Tank with temperature regulation system (capable of controlling fluid temperature to 37 ± 2°C)
- Single roller system with 1 kg load cell, measurement uncertainty ± 3g and encoder, measurement uncertainty ± 0.5mm
- Computer with IDTE1000 software
- Force gauge (Capacity: 30N or 10N), measurement uncertainty ± 1%FS
- Stepper motor linear actuator and associated stepper motor drive
- Data acquisition system with software
- Analog input module
- Bidirectional digital I/O Module
- Excel macro for data post-processing
- Pads and fixture to pinch the sample
- Calibrated gauge block measurement uncertainty ± 0.2µm
- Water tank
Several parameters can be calculated from the results
- Static friction = initial force required to start the test article moving through the pad (Pull force through the pad, push force through the pad)
- Dynamic friction = drop off in force seen after movement begins through the pad (Pull force through the pad, push force through the pad)
- Coefficient of friction (COF) = calculated by dividing the tracking force by the applied pinch load
- Durability = number of cycles to failure (failure can be set arbitrarily for example percentage increase in friction).
- PTA, PTCA, coronary and peripheral stent delivery systems – coated or non-coated
- TAVI and TMVR delivery systems – coated or non-coated
- Thrombectomy devices – coated or non-coated
- Guidewires – coated or non-coated
- Guiding catheters – coated or non-coated
- Endoscopic devices – coated or non-coated
- RF ablation catheters testing – coated or non-coated
- Any interventional coated or non-coated delivery systems
Biocoating Technical White Paper: “Effect of Testing Parameters on Pinch Test Results for Hydrophilic Coatings” by J. Li, J. Simon, W. Work, 2012
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