The nickel-and-titanium alloy known as nitinol is a super-elastic shape-memory alloy responsible for major advances in medical technology over the last 15 years. Nitinol is a highly elastic material that can be processed to maintain a desired geometry.
These properties, combined with high fatigue resistance and its ability to provide constant force over a wide range of displacements, makes it ideally suited for use in numerous medical implants and devices, such as:
- Vascular stents (Cardio, AAA, Peripheral, Carotid, Venous and Neuro)
- Transcatheter heart valve frames
- Vascular closure implants
- Neurovascular clot pullers
- Devices and flow diverters
- Vena cava filters
- Atrial fibrillation devices
- Orthopedic anchors
As well-suited as nitinol is for vascular implant applications, few manufacturers are able to produce finished goods with it.
Some barriers to working with Nitinol are:
- Nitinol knowledge: Working with the alloy requires extensive knowledge of its mechanical properties and fatigue characteristics.
- Low machinability: As a raw material, nitinol is difficult to machine with conventional technologies. Multiple proprietary manufacturing processes are required to produce even the most basic nitinol-based device.
- Electropolishing and passivation: To protect against the harmful release of nickel into the human body, electropolishing or passivation are required to create a protective titanium oxide layer.
- Process validation: Nitinol implant manufacturing requires strict process controls and validation to meet the finished material specifications.
When pursuing a manufacturer to produce a new nitinol-based implant or device, it’s important to consider a number of decision factors, some of which are mentioned below.
Raw material sourcing
Before committing to any manufacturer, it’s crucial to know how they will source nitinol for a given project. An OEM’s ability to supply the market with product is directly dependent on the contract manufacturer’s ability to source the raw material required to maintain continuity of supply.
A sustained disruption in supply is often catastrophic for OEMs. At a minimum, ensure the contract manufacturer will qualify and validate two sources of nitinol for production. Any disruption in the material quality from the primary source can be quickly resolved by increasing supply from the second.
Equally important, the quality, type (sheet or tube) and characteristics of the nitinol supplied by any given raw material producer is variable. The manufacturer who regularly sources material from many suppliers is able to best match the raw material to your design requirements and product application.
Design for manufacturability (DFM) and finite element analysis (FEA)
It’s also critical to evaluate product design specifications during the prototyping stage to identify opportunities to reduce cost without compromising the manufactured part’s intended function. Any cost-reducing design changes must be implemented prior to design freeze.
For any prospective new device design, extensive design and testing services should be available to help the design engineer perform FEA. This ability to model and simulate mechanical behavior reduces the time needed between design iterations, a critical step in the race to bring products to market.
Dedicated process engineering
Each manufacturing step requires the contract manufacturer to custom design that operation for any particular product design. This is done by designing, testing and refining the step using the same model and type of equipment and conditions that will be used in production. The capability to design and manufacture all shape-set tooling and fixturing for each process step in-house is essential to ensure the highest level of quality and process control.
It’s important to understand whether the manufacturer does this testing using equipment, experienced engineering personnel and facilities dedicated solely to process development, so it does not compete for time with products already in the production-manufacturing stream.
Manufacturing parts complete
Producing finished nitinol parts is a complex, multi-phase endeavor requiring years of experience and numerous manufacturing and finishing process capabilities. It’s important to understand up front whether your supplier can completely manufacture your part in-house using special nitinol processing techniques. Can they handle all manufacturing and finishing required to produce a marketable product without outsourcing any steps?
By handling all steps in the manufacturing process, the supplier can tune each step based on its knowledge of the upstream or downstream capabilities. This produces the highest level of quality assurance and process control.