As the name suggests, bifilar and multifilar wire-constructions comprise two or more wires in a single configuration, utilising a polymer coating in medical applications to prevent interference between the different wires. 

Multifilar wires are used to simplify wire handling if a medical device requires multiple signals, such as current that flows in parallel or opposite directions. Multifilar coated wires are commonly used for bifilar pairs in applications such as medical micro-thermocouple, as well as quadfilar goldplated copper leads for sensor signal transmission, and micro cables that need to be strengthened for load bearing or assembly operations.

Thermocouples are comprised of two different metal wires that are coupled at two points. The temperature difference between the two points is recorded in proportion to the corresponding difference of voltage. These devices are able to give extremely precise measurements of tissue temperature during ablation. Sandvik manufactures thermocouple sensor wire and lead wire from multiple alloys in single, bifilar and multi filar configurations. Alloys available include:

  • Ni-Ni leads for PTC, and NTC, thermistors
  • Thermocouple types K, T, E, and N (others on request)
  • Precious metals Pt, Pt10Ir, Pt20Ir

Overall, a multifilar approach makes the assembly of signal or power wires into the final medical device much easier.

Challenges and solutions of multifilar wire-constructions

An immediate challenge of using multifilar wire-constructions is that medical devices are getting smaller, meaning anything that makes components bigger is a disadvantage. Fortunately, medical wire technology has come a long way, and companies such as Sandvik offer ultra-fine wire that doesn’t compromise strength or efficiency. 

Automated manufacturing and machines specifically designed and built for precision cutting means Sandvik can efficiently produce uniform batches of wire suitable for multifilar wire-constructions. The process of manufacturing multifilar wires can be adjusted to accommodate specific requirements for the final product design, such as colour coding individual strands. The bond strength between the strands may also be adjusted to overcome challenging assembly conditions.

Multifilar wire-constructions from Sandvik

Sandvik offers multifilar wire cables in a flat or bundled configuration, with eight different colours in multiple shades for easy identification. 

The company provides continuous lengths of multi-filar ribbon wires, as well as selectively bonded lengths with various bond coatings. Common outer coating options include polyimide, polyester-imide, polyurethane and PTFE.

Working with more than 200 metals and metal alloys, as well as specialising in choosing the best materials and configurations for any given application, Sandvik EXERA® wire-based components can be customised for anything from vascular therapy to biosensing and neurostimulation. So far, they have been used for devices such as cochlear implants, pacemaker leads, continuous glucose monitors, catheters, and guidewires. Innovative design is crucial in an era of continual development, and Sandvik has worked with customers to develop wire-components that are used for remote monitoring devices that can be integrated with machine learning and artificial intelligence software.

For more information about Sandvik metal materials and coatings, download the whitepaper below.