As balloon catheters are used in critical therapeutic applications, they simply must work as they are intended. Therefore, testing these devices must ensure that failure will not occur. This article looks at the testing process for balloon catheters and what decisions manufacturers need to consider.
Balloon catheters require rigorous testing and validation to ensure that they perform at their intended use and labeling, such as nominal and rated burst pressures. They must perform the intended task of inflating, without the risk of leaking or burst. It is equally important that the device deflates completely after performing its intended function within a required amount of time. Catheters require leak testing and deployment pressurization of the balloon to its rated inflation rate and then to burst. Measurements of pressure and volume are then recorded and stored. Compliance characteristics and profile are also measured and accumulated. How this is accomplished varies by testing format and can be either contact or non-contact. The tests should remain consistent once determined as variation in pressure or volume, ramp rate, dwell, and hold time may vary the outcomes and deter the reliability of the test results. Market-driven demands, such as high pressure (greater than 50 atm, PTA), larger diameters [20 to 50 mm (e.g., TAVI)] and longer length (more than 300 mm) balloon catheters have required more robust testing equipment with ample volume and pressure capabilities.
Testing equipment must provide precise control of pressure, volume, and flow rates. A variety of high-pressure tests are performed requiring pressure cycles with a specified sequence, magnitude, and number of repetitions. Equipment must measure and plot pressure and volume compliance of balloons, and measure the inflation and deflation times of balloon catheters.
Compliant and Non-Compliant Balloon Catheters
Testing systems need to be evaluated for compatibility with both non-compliant and compliant balloon materials available on the market.
Non-Compliant Balloon Catheters—Stent delivery, PTA and PTCA, dilation, and more. Catheter testing is often performed using positive pressure and/or vacuum decay testing and verification of inflation/deflation. Burst pressures as high as 68 atm.
Compliant Balloon Catheters—Occlusion (vascular/bronchial), esophageal, urinary, and more. Catheter testing is often performed using a combination of pressure and vacuum decay for verification of inflation/deflation, ramp to burst event, and dilation curve information. Volume pressures for diameter for meeting specific compliance characteristics. Burst pressures typically range from 0-30 psi (0-2 atm).
A step test is a standard test for determining the typical burst pressure of a catheter balloon or other component. The test sample starts at an initial pressure and then the pressure is periodically increased over time. The test is ended when the test sample bursts.
In the ramp test, volume is delivered to the test sample at a near constant rate until one of the following occurs.
- The test sample reaches a maximum pressure
- The test sample reaches a maximum diameter
- A maximum volume has been delivered
- A time limit has been reached
Cycle testing allows for balloons or other catheter components to be loaded with a specified number of pressure cycles of the same magnitude and duration, so that the material “creep” and fatigue can be studied. The purpose of this test is to confirm that the balloon can be safely cycled through a defined number of inflations up to its rated pressure (fatigue testing).
The evacuation test determines the inflation and deflation time of a balloon sample. The purpose of the test is to measure how long it takes the balloon to fully inflate to its rated pressure, and then to deflate.
Accessories for Added Testing Capabilities
Interface Catheter Solutions offers several hydraulic pressure testing systems that accommodate the tests described within this article. Pressure testing systems offer either nitrogen gas or compressed air. Companies such as Interface provide accessories to pressure testing equipment to offer broader testing options and more customization.
The water bath is used for pressure testing of devices at elevated temperatures (e.g., at 37° body temperature) to more closely mimic clinical setting use.
An optical micrometer provides accurate non-contact diameter measurements of balloons under test. It allows for accurately measuring the balloon profile.
The multiport manifold pressure tests multiple balloon catheters.
Balloon Compliance Test Fixture
The balloon compliance test fixture allows for the automatic measurement of balloons or tubing while submerged in a water bath. The test fixture simplifies compliance testing, eliminating the need for repeatedly pulling testing components in and out of the water bath.
Finding the Right Pressure Testing System
It is ideal to find a pressure testing system that can accommodate both research and development along with quality manufacture testing. A pressure testing system that offers and can accommodate add-on options as needed for customization of test requirements is preferred.
Pressure testing volume ranges up to 68 bar capacity. Pressure testing can be completed with either nitrogen gas or compressed air so whether to evaluate a system with the capability to offer testing with both or only one option should be determined.
Testing systems on the market today offer options for contact or non-contact compliance and profile testing. Pressure testing systems also should accommodate compliant and non-compliant materials.
All of these options should be considered when finding the right pressure testing system for all balloon and balloon catheter testing requirements.