What Is Accelerated Wear Testing for Prosthetic Heart Valves?

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What Is Accelerated Wear Testing for Prosthetic Heart Valves and How Does It Work?

A prosthetic heart valve may open and close tens of millions of times during its service life. Each cycle exposes its leaflets, frame, hinges, sutures, and connecting structures to repeated pressure and motion. Although the load applied during one heartbeat may appear small, accumulated cyclic stress can eventually cause wear, deformation, tearing, fracture, or loss of function.

Waiting years to observe these effects under real-time conditions is not practical during medical device development. Accelerated wear testing, commonly abbreviated as AWT, addresses this problem by operating a heart valve at a frequency far above the normal human heart rate. It condenses millions of opening and closing cycles into a manageable laboratory period.

The purpose of the test is not simply to make the valve move as fast as possible. A properly designed accelerated wear test must apply controlled cyclic loading while maintaining meaningful valve motion, closing differential pressure, fluid conditions, and inspection procedures. It is therefore both a durability test and a carefully controlled simulation.

What Does Accelerated Wear Testing Evaluate?

Accelerated wear testing evaluates whether a prosthetic valve can continue functioning after prolonged cyclic operation. It may be used for surgical or transcatheter aortic, mitral, pulmonary, and tricuspid valve substitutes.

During testing, engineers look for physical or functional changes such as:

◆ Leaflet tearing, cracking, abrasion, or delamination
◆ Permanent leaflet deformation
◆ Damage near commissures, attachment points, or suture lines
◆ Hinge or occluder wear in mechanical valve designs
◆ Frame, wire, or supporting-component fracture
◆ Changes in opening and closing behavior
◆ Incomplete leaflet excursion
◆ Increased leakage or reduced hydrodynamic performance
◆ Loosening or displacement of connected components

The test is particularly important for designs using biological tissue, polymers, metallic frames, mechanical occluders, or combinations of materials. Each construction may have different fatigue mechanisms, so the test conditions and inspection plan should reflect the device design and its risk analysis.

How Does a Heart Valve Durability Tester Work?

The test valve is mounted inside a fluid-filled test chamber that permits repeated opening and closing. A drive system generates cyclic displacement or pressure, while sensors monitor the pressure difference across the valve.

The system normally uses purified water, saline solution, phosphate-buffered saline, or another validated test medium. Fluid temperature may also be controlled because temperature can influence material behavior, fluid viscosity, and equipment stability.

Once the test begins, the valve operates at an elevated frequency. A system running at 20 Hz produces 20 cycles per second, or approximately 1.73 million cycles per day if operated continuously. Completing 200 million cycles at this rate would require about 116 days before allowing for inspections, maintenance, interruptions, and functional assessments.

Higher frequency reduces the theoretical test duration, but it does not automatically produce a better test. The selected speed must still allow the valve to achieve the required opening and closing motion without introducing unrealistic loading.

Why Is Differential Pressure Important?

When a heart valve closes, it must resist a pressure difference between its upstream and downstream sides. This closing differential pressure contributes significantly to the stress placed on the leaflets, hinges, attachment regions, and supporting structure.

For this reason, counting cycles alone is insufficient. A cycle should meet the loading conditions defined by the applicable test protocol. If the valve completes millions of cycles without receiving the required differential pressure, the cycle count may not represent a valid durability exposure.

Closed-loop control is valuable because specimen behavior can change during a long test. Small variations in fluid level, compliance, temperature, mounting, or material response may alter the pressure waveform. A closed-loop system can use sensor feedback to adjust the drive condition and maintain the target loading more consistently.

Independent control is especially useful in multi-station equipment. Different specimens may not behave identically, even when they have the same nominal design. Controlling every test station separately helps prevent one sample’s behavior from affecting the loading applied to another.

Why Can Excessive Test Frequency Cause Misleading Results?

Accelerated testing creates conditions that are more severe than normal physiological operation. As frequency increases, inertial forces and fluid-dynamic effects can also increase. The valve may experience pressure spikes, abnormal leaflet motion, incomplete opening, unusually high closing velocity, or other effects that would not occur in the body.

These test artifacts matter because they can cause a technically sound valve to fail prematurely. Such a result may reflect the test apparatus or selected frequency rather than a genuine weakness in the device.

Before starting a long-duration test, engineers should determine the maximum frequency at which the sample can still demonstrate the required motion and loading. High-speed imaging or stroboscopic observation can help confirm whether the leaflets or occluders are opening and closing correctly.

A frequency-ramping study is often useful. The operator can gradually increase the cycling rate while observing pressure waveforms and valve kinematics. When the waveform becomes unstable or valve motion becomes unrepresentative, the test frequency should be reduced.

Industry testing resources also warn that high-frequency AWT can create inertial artifacts and therefore requires close control of closing behavior and differential pressure.

How Many Cycles Are Required?

The number of cycles depends on the valve design, intended use, failure behavior, applicable standard, regulatory strategy, and risk analysis. A frequently referenced durability target is 200 million cycles. Some devices may require 400 million cycles or additional testing when an immediate loss of function is possible, the design lacks an established clinical history, or a regulatory authority requests further evidence.

However, reaching a target cycle count should not be treated as the only measure of success. Engineers must also determine:

◆ How many cycles met the specified loading conditions
◆ Whether the valve maintained its required motion
◆ Whether interruptions or abnormal events occurred
◆ What physical changes appeared during inspection
◆ Whether hydrodynamic performance changed
◆ Whether the observed damage represents a clinically relevant failure mechanism

The test report should document valid cycles, pressure waveforms, equipment settings, temperature, test-medium condition, inspections, photographs, videos, and any deviation from the approved protocol.

What Is the Difference Between AWT and DFM Testing?

Accelerated wear testing and dynamic failure mode testing are related but serve different purposes.

AWT is generally conducted as a durability demonstration. Samples are expected to complete a defined number of cycles under specified conditions without unacceptable deterioration. It is often described as a pass/fail-oriented test.

Dynamic failure mode testing, or DFM testing, intentionally investigates how and where a device may fail. The test conditions may be adjusted or intensified to produce damage and characterize the device’s weak points. The goal is not merely to obtain a passing cycle count but to understand possible failure mechanisms.

For example, an AWT program may show that a valve completes its specified durability exposure. A DFM study may then help identify whether extreme cyclic loading produces leaflet tearing near a commissure, frame fatigue at a particular junction, or damage at a suture attachment.

Using both approaches provides more useful engineering information. AWT demonstrates durability under defined conditions, while DFM helps design teams understand the device’s failure behavior and safety margin.

What Should Be Included in a Reliable Test Plan?

A reliable test program begins before the equipment starts cycling. The protocol should define the device configuration, sample quantity, mounting method, test fluid, fluid temperature, waveform, operating frequency, differential pressure, inspection intervals, acceptance criteria, and response to equipment alarms.

Samples should represent the final device as closely as practical. Depending on the device, this may include manufacturing, sterilization, crimping, tracking, deployment, or other simulated-use conditioning before durability testing.

Baseline documentation is also important. Engineers should record the initial appearance of every sample and assess its functional or hydrodynamic performance. Periodic inspections can then reveal when damage first appeared and how it progressed.

After the cycling program, the samples should receive detailed visual and functional examination. Optical microscopy, high-speed video, dimensional inspection, and hydrodynamic testing may be used to compare post-test performance with baseline results.

Is Accelerated Wear Testing Enough by Itself?

AWT is essential, but it cannot reproduce every biological and mechanical condition inside the human body. A laboratory fluid may not simulate calcification, thrombosis, tissue ingrowth, immune response, or long-term biochemical degradation. High-frequency operation also differs from normal cardiac timing.

Therefore, durability results should be interpreted together with hydrodynamic testing, material characterization, structural fatigue analysis, simulated-use testing, biocompatibility evaluation, animal studies, clinical evidence, and risk management.

ISO 5840 uses a broader risk-based verification and validation framework rather than treating a single durability test as complete proof of safety and performance.

Conclusion

Accelerated wear testing allows engineers to evaluate millions of prosthetic heart valve cycles within a controlled laboratory period. Its value depends not only on speed or total cycle count, but also on accurate differential-pressure control, representative valve motion, stable test conditions, planned inspections, and careful identification of test artifacts.

For laboratories developing artificial valves, valve clips, or occluders, UnitedTest offers the UT1037E Heart Valve Accelerated Durability Tester. The system supports AWT and DFM testing, accommodates up to six independently controlled samples, provides Autopilot Stroke and Fixed Stroke modes, operates at frequencies up to 50 Hz, and supports real-time control, data acquisition, analysis, and recording for ISO 5840-oriented test programs.

We offer customization to meet your specific needs. Our expert team will collaborate with you to develop the perfect product for you