Fort Wayne Metals - Technical Blog

The assessment of magnesium wire coatings: Paving the path for absorbable implants

Mon, 05 Feb 2024 15:16:00 Z

Advancing biodegradable medical devices with coated magnesium wire

In recent years, the medical field has witnessed significant innovation in developing absorbable materials for permanent implants. These advances promise to revolutionize devices like stents, staples, and sutures by eliminating the need for permanent materials that may cause long-term complications or additional surgeries to remove them. Among these developments, magnesium (Mg) alloys have emerged as a frontrunner due to their biocompatibility and ability to degrade harmlessly within the body.

Challenges of magnesium in medical applications

Despite its appeal, magnesium's relatively rapid degradation rate poses challenges, particularly for fine diameter wires required in certain medical applications. These wires must maintain their mechanical integrity throughout the healing process to provide sufficient support. This dilemma has driven researchers from our Research and Development team to explore coating techniques that slow the degradation rate while preserving the absorbable magnesium wire’s flexibility and strength.

Innovative coatings for magnesium wire

For this study, Fort Wayne Metals’ patented magnesium alloy LZ21 wire, designed for ductility and moderate strength, was processed into wires with a final diameter of 0.3 mm and subjected to three conditions: bare, anodized, and polymer-coated. The polymer layer, made from polycaprolactone (PCL), was applied over the anodized wire to create a dual-layer system.

Key findings from in vitro and in vivo testing

In vitro testing revealed substantial differences in degradation rates between the coated and bare wires. Bare wires lost 82% of their mechanical strength within seven days. In contrast, anodized wires retained 60% of their strength, and PCL-coated wires maintained over 90% of their strength even after 14 days. These results highlight the significant protective benefits of both anodization and polymer coatings.

In vivo testing, conducted via subcutaneous implantation in mice, showed slower degradation rates compared to in vitro conditions. Bare wires retained 84% of their structure after seven days and 60% after 33 days. The PCL-coated wires exhibited almost no signs of degradation at either time point, underscoring their effectiveness as a corrosion barrier.

Implications for medical device development

These findings offer promising implications for the future of absorbable medical devices. The dual-layer coating system delays corrosion, preserving the mechanical properties through the critical tissue healing period. The study also established an in vitro-in vivo correlation (IVIVC) factor of 8.1, which provides a foundation for predicting real-world performance based on accelerated laboratory testing.

Future directions

While these coatings are promising, further research is needed to fine-tune their performance. For instance, modifying the thickness or composition of the polymer layer could optimize the balance between protection and timely degradation. Additionally, studying the effects of plastic deformation during implantation on corrosion rates is needed to ensure real-world applicability.

Conclusion

The use of coated magnesium wire marks a significant step forward in creating safer, more effective absorbable medical devices. By addressing magnesium's rapid degradation, these innovative coatings pave the way for a new generation of implants that support healing while seamlessly integrating into the body's natural processes.

Magnetic susceptibility of medical metals: New insights for MR conditional devices

Tue, 16 May 2023 15:13:00 Z

A recent study, coauthored by Fort Wayne Metals and MED Institute researchers, provides valuable insights into the magnetic susceptibility of 45 metallic materials commonly used in medical devices. This research offers critical data for selecting materials in applications where MR safety is a concern.

Why magnetic susceptibility matters in medical devices

Magnetic susceptibility refers to a material’s degree of magnetization in response to an external magnetic field. In the medical field, this property is essential for devices that may be used in magnetic resonance (MR) environments. Materials with high magnetic susceptibility can:

Cause image distortion in MRI scans
Generate dangerous forces and torques within strong magnetic fields
Impact the safety of implanted or external medical devices

To achieve an MR Conditional label, a device must be designed with materials that minimize these effects.

Key findings

The study measured the magnetic susceptibility of a wide range of metals and alloys, presenting results in ascending order. Key takeaways include:

Titanium and Nitinol alloys: Extremely low magnetic susceptibility, making them ideal for MR-compatible implants
Cobalt-chromium (CoCr) alloys: Moderate susceptibility but often acceptable for certain applications
Stainless steel: Vary widely depending on composition and cold working, with some grades exhibiting significantly higher susceptibility
Nickel-based alloys: Generally higher susceptibility, which can limit MR compatibility

Material selection for MR Conditional devices

For medical device manufacturers, this data supports informed material selection

Best choices for MR compatibility: Titanium and Nitinol alloys
Moderate risk materials: Certain CoCr alloys and austenitic stainless steels
High susceptibility materials to avoid: Cold-worked stainless steels and some nickel-based alloys

Conclusion

This study provides a comprehensive reference for selecting medical metals based on magnetic susceptibility. By considering this factor early in the design process, manufacturers can enhance MR safety, improve imaging quality, and ensure compliance with MR Conditional labeling standards.

Advancing neurovascular treatment: FeMnN—Mo composite wires for absorbable flow Diverters

Mon, 06 Feb 2023 14:35:00 Z

The growing demand for innovative solutions to treat intracranial aneurysms has driven advancements in medical materials. Researchers at Fort Wayne Metals have developed FeMnN-Mo composite wires as a foundation for absorbable flow diverters. These devices, designed to treat aneurysms by redirecting blood flow and promoting clot formation, are expected to dissolve after achieving their purpose, reducing long-term complications.

Challenges with existing materialsExisting flow diverters employ permanent metals such as 35N LT® or Nitinol. These devices function well but are unnecessary after aneurysm occlusion and can impede secondary procedures. Absorbable polymers like polyglycolic acid (PGA) and poly-l-lactic acid (PLLA) have been investigated as temporary options but require larger struts for sufficient strength, compromising device profile and flexibility. Absorbable Mg- and Fe-based devices have also been investigated but suffer from rapid degradation and premature fracture.

Innovative FeMnN-Mo composite wiresThe study introduces composite DFT® wires made of:

FeMnN shell: Provides strength, elasticity, and a cell-friendly surface.
Molybdenum (Mo) core: Offers enhanced radiopacity and staged corrosion protection.

These wires, available in diameters as fine as 25 µm, mimic the dimensions of traditional metallic flow diverters while addressing their limitations.

Key findings

Mechanical performance

The composite wires achieved mechanical properties comparable to non-absorbable counterparts, with customizable strength and elasticity by varying Mo content.
Braided prototypes demonstrated crush resistance similar to commercial devices, making them suitable for neurovascular applications.

Enhanced radiopacity

The Mo core significantly improved visibility under fluoroscopic guidance, essential for precise device placement.
Radiopacity increased proportionally with Mo content, ensuring adequate imaging performance without permanent markers.

Corrosion Behavior

In vitro and in vivo tests showed progressive and controlled degradation of the FeMnN shell, while the Mo core remained intact for at least six months.
This staged degradation minimizes the risk of premature fragmentation.

Biocompatibility

Cytotoxicity testing confirmed minimal impact on cellular health, supporting the material's safety for clinical use.

Advantages for Neurovascular Devices

Minimized profile: Comparable to traditional flow diverters, enabling easier navigation in small vessels.
Reduced long-term risks: Absorbability eliminates concerns like chronic inflammation, side branch blockage, and imaging artifacts from permanent implants.
Improved healing: Supports endothelial tissue regeneration over aneurysm necks for effective occlusion.

Future Directions
While these findings highlight the potential of FeMnN-Mo DFT® composite wires, further research is needed to optimize their degradation timeline and assess long-term clinical performance. Exploring additional configurations and alloy combinations could further enhance their functionality.

Conclusion
FeMnN-Mo DFT® composite wires represent a promising step forward in the development of absorbable flow diverters. By addressing critical challenges in material performance and compatibility, this innovation paves the way for safer and more effective neurovascular treatments.

CoNiCr-Nitinol composite wires for guidewire applications

Mon, 17 Feb 2020 12:00:00 Z

Fort Wayne Metals developed a CoNiCr-Nitinol composite wire targeted for use in advanced guidewire applications. This novel material combines the strength and stiffness of CoNiCr alloys with the superelasticity of Nitinol, offering a seamless transition from proximal stiffness to distal flexibility. These properties may enhance physician control, improve tip performance, and facilitate the crossing of chronic total occlusions (CTOs) without requiring a jointed core wire.

Material composition and manufacturingThe composite wire consists of:

Outer Shell: 35N LT® (CoNiCrMo alloy) for high strength and stiffness
Core: Ni50.8Ti49.2 Nitinol for superelasticity and kink resistance

Manufactured using DFT® technology, the wire undergoes co-processing, cold reduction, and heat treatments. This process combines two dissimilar materials into a single wire system, achieving optimal strength, flexibility, and superelastic performance.

Key performance characteristics

Mechanical strength and flexibility

The CoNiCr shell provides an initial elastic modulus of 197 GPa and an ultimate tensile strength of 2600 MPa.
The Nitinol core maintains an elastic modulus of 48 GPa with an ultimate tensile strength of 1170 MPa.
The wire demonstrates a seamless transition from stiffness to flexibility, allowing for precise control.

Torque control and one-to-one response

Rotational testing confirmed minimal lag between proximal and distal ends, providing sufficient torque transmission.
Optical tracking in a whip test showed that the wire exceeded ASTM F2819 standards for straightness.

Bending and kink resistance

The composite wire maintains higher bending stiffness in the proximal section for pushability.
The Nitinol core offers lower bending resistance in the distal end, improving navigation and kink resistance.

Joint-free design

Unlike traditional guidewires that require soldering or adhesives to join different materials, this composite wire integrates high strength and superelasticity into a single, continuous structure.
This composite wire product has the potential to reduce failure points and enhance reliability.