Catheter manufactures continually monitor their product and this is done by physically testing the complete units, as well as individually testing the component parts
We all hope it never happens to us but, at some time in our life, we may have to undergo a surgical procedure.
It's a sobering thought but, thankfully, the progress in cardiovascular operating techniques has made these major operations much safer and more routine.
Many of these techniques now involve the use of catheters and some years ago Zwick was contacted by one of its existing customers, a major manufacturer of catheters.
The company works closely with surgeons to develop standard and customized catheters, stents, and guide-wires, and wanted to replicate a patient lying in an operating theatre and a surgeon inserting a catheter.
The result was a horizontal testing machine with a range of special adaptations to enable the simulated operational procedure on the patient.
What is a catheter? The word 'catheter' comes from the Greek word for 'let down', and is generally described as a flexible narrow tube which can be guided into body organs.
This article describes the cardiac catheter which is directed through a tiny incision in the groin and moved through the blood vessels to the heart.
There are many different types of catheters; those used to transport various small instruments, testing materials, or repair devices to the correct site in the body.
Others have small built-in small tools so that a surgeon can repair the patient's problem without having to perform open heart surgery.
Some provide drugs directly to an infected area, whilst some can deploy a stent which will keep an artery open.
Catheter manufactures continually monitor their product and this is done by physically testing the complete units, as well as individually testing the component parts.
'Pull-off' testing is important, as joined parts should not fail as the catheter is inside the patent.
Stents are tested, both in compression and flexure modes, and the frictional behaviour of the complete catheter is measured as it is been pushed through a simulated artery, called a torturous path.
This test could be done on a standard vertical testing machine but more realistic results are achieved if the tests are done in a horizontal direction.
Working together with the customer, Zwick took a standard universal testing machine and customized it to the suit the application.
This step required an in-depth understanding of the customer's application and so Zwick engaged a team, from its special projects division, to ensure that the project ran smoothly and was professionally managed from the beginning.
One of the most important tests is to simulate the action of a surgeon inserting the catheter into a patient in the horizontal direction.
This is achieved by placing a torturous path (or simulated artery) into the test area.
The Zwick project engineers developed a unique solution by using the combination of Testcontrol hardware, and Testxpert software, which controls the test machine crosshead and special automated pneumatic grips.
The testing machine pushes the catheter into the torturous path for a designated distance, then the pneumatic grip then releases the catheter and the crosshead moves back to the original start point.
The pneumatic grips close onto the catheter, and the crosshead moves forwards once again.
This sequence is repeated until the catheter has been fully inserted into the simulated artery.
This test procedure which is fully automated, can easily accommodate different sizes of tortuous path, and the Testxpert software enables the following results to be calculated:.
Track force measures the force needed to advance a catheter, interventional device or guide wire through a torturous path.
Push efficiency uses the proximal and distal load cell to measure the amount of force the distal tip of the product sees when a known force is being applied to the product on the proximal end.
Insertion force measurement measures the force used to advance through the introducer sheath.
Guide wire movement measures the force needed to advance a guide wire though catheter, guide catheter or other interventional device.
Flexibility measure of a catheter tips ability to track over a specified bend in a guide wire, such as 90 degrees.
Guide wire and catheter lubricity track measurement comparative test using the Track test data to determine if coatings have an affect on the force required to advance product through a tortuous path The results can be calculated with extremely high precision due to the technology employed by Zwick.
The extremely stiff load frame with digital control and drive systems is able to ensure that forces measured during the test originate from the sample under test and not from within the machine itself.
The Testcontrol system has such a high accuracy and resolution that it is able to position the crosshead of the machine to less than 1um, and read forces to an accuracy of better than 0.5% down to values of less than 0.1milliNewtons (mN),/0.02lbf.
The Testxpert software platform is able to control all of the test parameters including the safety features of the testing machine.
At the same time, it is able to acquire and process all of the raw test data in real-time and store this data, as individual data points and as calculated result data.
For catheter testing a software module has been created which allows all of the functionality required by the customer, whilst enabling easy future upgrading as new and relevant versions of the software platform are released.
This is often not the case with other customized solutions.
It is extremely important for certain organizations connected with the medical industry to meet the requirements to meet FDA 21 CFR Part 11.
This is totally integrated as an option into the Testxpert software, and customers can take full advantage of this, saving the costs of third party accreditation.
Test results can be automatically stored in the customer's database applications through the standard windows ODBC interface as well as the traditional Ascii format, further improving the data integrity.
The machines are supplied with splash-proof electrical connectors, and an additional emergency stop button for additional safety.
A moveable touch screen can be fitted to the side of the machine to enable much safer operation so that the operator can start, stop, and monitor the test without having to move to a separate PC.
In summary, the customer now has a integrated testing system which is fully compliant with the FDA regulations, and as the software is 'future proof', new requirements can be easily added if test procedures change, or in connection with commercial PC hardware and software evolution.
Zwick has also supplied customers with multi-channel systems consisting of six load cells linked to the Testxpert software and displaying six force / stress versus displacement / strain curves on one screen.
If it is necessary to video record the test sequence, a Testxpert software plug-in is available which enables a standard video camera to be connected to the system.
The incoming video signal is automatically synchronized with the force / displacement data, and allows a more complete record of the test to be saved or transmitted to interested third parties.
