The reliability of medical device actuation can directly impact patient safety and compliance with stringent pharmaceutical regulations. One of the most persistent engineering challenges in this respect is wire form fatigue, which is the gradual weakening of a material under cyclic loading. This results in an eventual loss of force and/or deformation, which can impact how a medical device operates; an inhaler that doesn’t actuate properly can be a big problem.
Achieving long-term reliability with medical-grade wire forms requires careful consideration of material selection and manufacturing processes. Shape-memory alloys like Nitinol offer unique fatigue resistance properties, but other high-performance metals can also deliver robust results when engineered correctly.
Choosing the right wire form material is one of the first and most important steps in combating fatigue to ensure consistent actuation in drug delivery devices. The selected alloy needs to balance strength, corrosion resistance, manufacturability and cost, all whilst meeting stringent medical compliance standards. Each material brings its own performance advantages and trade-offs, meaning the best choice depends on the device’s functional requirements and operating environment.
Stainless steel is a leading choice for medical wire forms due to its excellent corrosion resistance, high strength and cost-effectiveness. Grades such as 302 stainless steel provide a balance between durability and flexibility whereas 304 and 316 grades have enhanced corrosion protection for devices facing bodily fluids or sterilisation. Hard stainless steels can also “kill” springiness to maintain form stability over time for applications where static positioning is required.
Nitronic (a nitrogen-strengthened stainless steel) delivers a higher stress limit and superior corrosion resistance compared to conventional stainless steels. It maintains ductility for complex bends, making it suitable for intricate wire forms that need to resist fatigue under multi-axis loading.
Nitinol is well known for its shape-memory and superelastic properties, making it attractive for components that require repeated flexing without permanent deformation. Its high fatigue resistance is ideal for drug delivery devices that need to endure thousands of cycles over their operational lifespan. However, nitinol can be difficult to machine properly, requiring specialist forming techniques and a trusted partner.
The surface condition of a wire form is important when it comes to fatigue resistance. Micro-scratches, burrs and roughness become stress concentrators that accelerate the formation of cracks. To combat this, appropriate surface finishing techniques can significantly extend component life.
Design for Pharmaceutical Manufacture (DfPM) principles emphasise that fatigue resistance is as much a manufacturing outcome as it is a material property. There are key design steps that can be taken to optimise wire forms for long-term actuation.
Minimising wire form fatigue in drug delivery demands a holistic approach from selecting the right material for the specific device to manufacturing with precision and design in mind from the outset. By addressing each of these factors, manufacturers can significantly extend component life and meet the demanding standards of the pharmaceutical industry.
Advanex Medical is a trusted partner to the world’s leading medical device manufacturers, with proven expertise in designing and producing wire forms that combine durability and compliance with the most stringent international medical trials. Our specialised forming, finishing and quality control processes ensure every component performs flawlessly from the first cycle to the last.
If you want to explore how the right material choice, design approach and finishing techniques can optimise your device’s reliability, download our guide below.