Making Strong, X-Ray Visible Cobalt Alloys for Medical Implants

This patent describes a specific heat treatment process to remove unwanted particles from cobalt-based alloys, making them strong and visible on X-rays for use in medical implants like stents.

What it covers

This patent details a method for improving cobalt-based alloys, specifically those containing cobalt, chromium, tungsten, nickel, and a heavy metal like platinum, to make them suitable for implantable structures such as stents. The core mechanism involves a precise heat treatment to remove 'precipitate inclusions,' which are tiny, unwanted particles (like tungsten-rich precipitates) that weaken the alloy. The process requires heating the alloy within a narrow temperature range of about 1225° C. to 1275° C. (specifically around 1250° C.) for a short period, approximately 20 to 40 minutes (specifically around 30 minutes). This treatment results in a 'substantially homogenous structure,' meaning the material becomes uniform and strong enough for medical use, while also being 'radiopaque' (visible on X-rays).

What it doesn't cover

• —Does not cover heat treatments outside the narrow temperature range of 1225° C. to 1275° C. for removing these specific precipitates.
• —Does not cover heat treatment durations significantly longer or shorter than 20 to 40 minutes for the described effect.
• —Does not cover alloys that do not include tungsten or a heavy metal with an atomic number or density greater than cobalt for radiopacity.
• —Does not cover processes for removing precipitate inclusions that are not tungsten-rich or of a different chemical nature.
• —Does not cover the formation of implantable structures from alloys that are not intended to be radiopaque.

The clever bit

The surprising discovery is that only a very specific and narrow window of heat treatment (around 1250° C. for about 30 minutes) effectively removes the unwanted tungsten-rich precipitates. Higher temperatures or longer times, which one might intuitively think would work better, actually fail to resolve these inclusions, making the material unsuitable.

Why it matters

Radiopaque implantable structures, like stents, are crucial in medicine because doctors need to see them clearly using X-ray imaging after they are placed inside a patient. This patent addresses a critical material science challenge: ensuring these alloys are not only visible but also structurally sound and free from defects that could cause failure. By providing a precise method to remove harmful precipitates, it enables the creation of safer and more reliable medical devices, directly impacting patient outcomes and the longevity of implants.

Real-world examples

• 1.Coronary stents
• 2.Peripheral vascular stents
• 3.Other radiopaque implantable structures
• 4.Medical guidewires