Stent manufacturing is an art that requires expertise in many areas, starting from the selection of the optimal raw material, through high-precision laser cutting of complex geometries, to perfect finishing that includes both surface treatments and heat treatments to ensure the highest quality of the desired product.
The first step entails selecting the optimal material for the intended application. Then, the quality of incoming raw materials must be inspected and verified to ensure consistent production at tight tolerances across and within production lots. Metal stents are typically made of implantable grade metals, such as: Stainless Steel (316LVM), Nickel Titanium (Nitinol), Titanium or Cobalt Chromium (CoCr) alloys (L605, MP35N).
Stent fabrication methods include: Wire braiding or knitting, laser sheet cutting, and especially laser tube cutting. Today, stents are being fabricated mostly by laser cutting metal tubes of various diameters, lengths and wall thickness.
Balloon-expandable stents made of stainless steel and cobalt chrome alloys undergo annealing to: Relieve internal stresses, soften the metal, improve elongation rate, lower the risk of strut breakage, and improve fatigue resistance. Self-expanding stents utilize the elastic properties of Nitinol and require a different process called shape-setting to fix the final shape of the stent and the transition temperature.
Post laser processing steps include: honing, micro-blasting, pickling, electropolishing, passivation and ultrasonic cleaning. These steps result in a high-quality biocompatible product having a bright, shiny surface, free of defects, and improved corrosion resistance.
Improving x-ray visibility
Advances in imaging technology and stent design lead to smaller delivery systems and thinner stent profiles. Fluoroscopic visibility of smaller stents decreases with their size and therefore requires the integration of radiopaque markers into the stent design. Markers are made of precious metals, such as: Gold, Tantalum and Platinum-Iridium. Laser welding of dissimilar materials introduce galvanic corrosion challenges that must be addressed.
Visual and dimensional inspections undertaken throughout the manufacturing process, using high-resolution optical microscopes and video inspection systems, ensure that the final product meets the customer’s specifications. STI’s stent manufacturing and assembling processes adhere to ISO 13485 and ISO 9001 quality standards.