Medical Device Material Durability Testing

How Fatigue Testing Makes More Reliable Devices

Troy Nickel | Morgan Ulrich
February 03, 2023

Do your patients worry about their replacement hip breaking when they run? Or how long their prosthetic leg will last before needing a new one? Are your regulatory submissions requiring increasingly more lifetime testing?

What is medical device durability testing?

Also known as fatigue or stress testing, durability testing validates device lifetimes by subjecting them to physiological loading. It can also be used to understand device failures and design margins using fatigue-to-fracture methods and hyper-physiologic loading levels. Durability tests serve a critical purpose in helping prevent unintentional product failure, which could have severe consequences.

Durability testing includes physically and repetitively loading implantable medical devices in a very similar way to the loading encountered in the human body over time. Testing typically includes applying broad and targeted loading to devices or specific components using force, torque, rotation, strain, displacement, and/or pressure. Sometimes this loading is applied to an entire device and other times on subcomponents or materials of a device.

What are durability test methods?

Test loading is often repetitively applied through two test methodologies:

Testing to success

Testing to success methodologies help assess that devices do not fail under physiologically representative loading levels. Testing to success has classically been one of the final safeguards that the device will be safe for its intended lifetime. This method has been used for decades as part of the supporting evidence to regulatory approvers that a device is durable.
For example, testing to success can confirm that implants do not fail when subjected to physiological levels for 10 million cycles, approximating 10 years of lifetime of walking and running.

Fatigue to fracture

Fatigue to fracture (FtF) involves understanding where a device’s weakest component lies by pushing it past its failure limits with a larger loading magnitude. This approach is often used earlier during device development because the insights it provides contribute to refining the device’s final design. Fatigue to fracture results are increasingly leveraged in regulatory submissions because they provide even stronger evidence of reliability and a more rigorous assessment of safety margins.
For example, perhaps you’d test implants at 2x physiological levels to determine how and when they fail, then 2.5x or 1.5x to understand how the lifetime decreases or increases with a change in loading levels. This method is repeated at many levels with many samples to obtain higher and higher confidence in the relationship between load levels and lifetime of implants.

Medical Device Fatigue Testing Systems

As explained above, designing new medical device materials and products requires a thorough assessment of material properties and complete performance evaluation within, and sometimes beyond, the intended end-use. Flexible and robust instruments enable accurate and timely execution of device-specific testing standards and rigorous performance evaluation for orthopedic device testing.

ElectroForce technologies have revolutionized the way material testing is performed. Proven for ultra-reliable fatigue and durability testing, these instruments are a staple in medical device labs around the world.

Which instrument is right for my lab?

Choosing an instrument for your medical device testing requires you first get clear on your needs:

Am I testing to success or fatigue to fracture? Or both?
What force will my materials or devices have to withstand? What displacement?
What environment will my devices perform in? I.e., in air, in fluid, at temperature, etc.

The ElectroForce family of load frame test instruments include a full range of force and performance capabilities for various applications. The most common models for medical device testing include the ElectroForce 3200, ElectroForce 3300, ElectroForce 3500, and Multi Specimen Fatigue Instruments. See which one aligns with your needs in the chart below.

	ElectroForce 3200	ElectroForce 3300	ElectroForce 3500	MSF 6	MSF 16
Number of Specimens	1	1	1	6	16
Force range (per sample)	0.002 to 450 N	0.02 to 3000 N	1 to 15,000 N	0.005 to 225 N	0.005 to 100 N
Displacement	0.002 to 13 mm 163mm optional	0.005 to 25 mm, 175 mm optional	0.005 to 50 mm	0.005 to 25 mm, 175 mm optional	0.005 to 25 mm
Maximum Fatigue Frequency	300 Hz	100 Hz	100 Hz	100 Hz	100 Hz

ElectroForce Load Frame Instruments

TA ElectroForce® test instruments feature proprietary ElectroForce linear motion technologies coupled with advanced controls and analysis software. Driven by friction-free electromagnetic motors, they provide a revolutionary approach to mechanical fatigue and dynamic characterization. They are also very lab-friendly thanks to their clean and maintenance-free operation. As a result, they have set a new standard for performance, reliability, and versatility in a single test instrument.

ElectroForce 3200, 3300 and 3500 Load Frames

This family of load frames is highly flexible, offering multiple loading ranges and frame configurations. They each leverage a high-performance friction motor specific for its force range, HADS sensors, plus flexible and convenient frame features that make them perfectly suitable instruments for accelerated testing of many materials, components, and devices.

Electroforce™ Multi-Specimen Fatigue Instruments

The MSF instruments are built from the powerful and dynamic 3300 load frame to increase fatigue throughput by testing multiple specimens simultaneously. Each sample experiences the same applied displacement, e.g. 1mm at 30Hz, but have individual force sensors to monitor the force decay or failure of each specimen. These instruments are especially useful in high cycle fatigue programs of flexible materials or devices, where each specimen can take days, weeks, or even months to fail. This approach can substantially increase your throughput and improve time to market.

ElectroForce 3300 6-Specimen MSF Instrument

MSF6 increases sample throughput by simultaneously testing 6 samples at up to 225N each. It is popular for flexible polymers, elastomers or more flexible metals or structures. MSF6 can also be mounted and operated within an oven to give you a greater understanding of how devices or device materials perform at various temperatures, such as your prosthetic foot in the Minnesota winter or Texas summer.

ElectroForce 3300 16-Specimen MSF Instrument

MSF16 provides an unmatched capacity of 16 specimens with up to 100N each. The optimized design provides greater sample access and visibility for simplified sample loading and viewing. It includes a 37 °C Fluid Bath and is widely used for small device or fatigue of metals such as Nitinol and other tailored Shape Memory Alloys (SMAs).

ElectroForce Load Frames and Multi-Specimen Fatigue are industry-leading medical device durability testing instruments.

Find out more about TA Instruments’ industry-leading medical device durability testing. TA Instruments also offers a number of other test instruments that are useful in characterizing materials and processes used to deliver medical devices.

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