Transforming medical technology with nitinol

The fabrication of stand-alone nitinol components can be categorized into the following three groups: 

1. Structuring the wrought material: 
   If the product is fabricated from tubes or sheets, the following methods are suitable: laser cutting, wire Electrical Discharge Machining (EDM), waterjet cutting, and chemical etching. On the other hand, if a wire, strip, or ribbon is needed, profiling would most likely involve abrasive techniques such as grinding. In some cases, eroding or chemical etching to be successful. 
   
   
2. Shape setting: 
   The process required to set the shape is similar whether starting with wire, sheet, or tube material. The structured component from step one must be constrained on a fixture, followed by heat treatment. The heat treatment may involve a salt bath, sand bath, air or vacuum furnace, or various heating methods such as inductive heating.
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3. Surface finish: 
   Depending on the heat treatment, the material will have a different surface condition (oxide layer). The resulting surface finish will affect the performance of the instrument. For implants, it will impact durability, corrosion resistance, and other properties.

If the nitinol component is only one part of the assembly, designers must carefully consider the joining methods. Nitinol can be easily welded to itself using a laser or e-beam. However, one must consider that welds do not have super-elastic properties and should be placed in a section of the assembly where only slight deformation occurs. When joining nitinol to other materials like titanium or stainless steel, the process can be quite difficult. Research has shown successful joining using soft soldering with aggressive fluxes, while resistance or diffusion welding can also be applied. Generally, alternative mechanical options like crimping or shrink-fitting are preferred.

A) Deformation resistant applications
Within every process step in processing components in the category of deformation-resistant applications, one must be aware of the effect it has on the properties of the material. The amount of cold work, the heat treatment, the rate of strain, and the number of cycles all impact material properties and therefore change the stress-strain behavior. 

Therefore, the industry is having a hard time converting nitinol fabrication steps into industrial automation. Today, medical products made from nitinol are mainly processed through manual operations, handcrafted with a very low degree of automation. This makes the outcome dependent on the worker, and the process is very difficult to validate. That is also why there has been little demand for serial production from the industry. In the last few decades, the alloy became popular in the treatment of peripheral vascular diseases. Stents were the first medical products with high demand. Unfortunately, the variety of needed versions of these implants is so high that the profitability of installing automated processes is questionable. Therefore, these implants are mainly processed with a low level of automation. 

There has however been mass production of nitinol articles. The first article in this field was the super-elastic, kink-resistant, nitinol guide wire used in surgical procedures. Using these methods the surgeon can reach a point of interest in the body in a minimally or non-invasive way. Due to its elasticity, the ability of the wire to follow a tortuous path in the body and still rotate smoothly led to improved performance.  

B) Shape-restoring applications
Moreover, the largest family in medical instruments is the group of shape-restoring applications. These products are temporarily deformed to be introduced into the body, and when removed, spring back to their original shape without the need to increase the temperature. They are used for various functions such as loops, snares, retractors, and baskets, as well as for removing foreign bodies and blood clots. 

In the urological field, there is already a worldwide yearly need for stone retrieval baskets. The same instrument can also be used to catch various stones that are anywhere from 1-12 millimeters in size. Therefore, the diversity of versions needed in this field is very low. This enables the possibility of installing a certain degree of automation in the manufacturing process. The most common version of stone retrieval baskets is manufactured from wires, which form a basket-like structure. 

When looking into a factory of medical device manufacturers, the quality of the product is certainly the first thing we have to think about. Following this comes the productivity and thereafter, the profitability. These parameters do not have to depend on whether you have an all-hands-on operation or an automated process. You simply have to team up with a partner who is experienced in processing nitinol and knows every process step and what effect it has on the properties of the material. The amount of cold work, the heat treatment, the rate of strain, and the number of cycles, all have an impact on material properties and therefore change the stress-strain behavior.

Alleima is one of those partners with the necessary experience and processing capabilities to bring life-changing medical solutions to life. In my role as Global Technology and Innovation manager I am working with a team of experienced materials specialists, development and mechatronics engineers, quality managers and skilled operators to support our customers realize their ideas and lead them through each stage of the challenging development process, all the way to the market approval. This really sets us apart from the competition.