Cable Materials for Medical Device Applications

Share this post:
Posted On:
February 04, 2020

When designing a medical device, there are special considerations that come into play. This is also true when designing a cable and wire connectivity solution for a medical device.

There are a lot of different component options as well as material choices that can be selected or avoided depending on the end use and environment of the device. In order to get started down the right path, cable design engineers will ask a series of questions that will help them ensure your cable solution will meet the exact requirements of your project. Below are a few examples of typical questions that would be asked when working on a cable design for a healthcare application.

Questions to Ask:

  • What is the end application? What type of device?
  • What is the expected life span of the cable?
  • Is the product implantable?
    • Yes, over 30 days
    • Yes, 29 days or less
    • No
  • Is sterilization required?
    • Gamma
    • Autoclave
    • ETO
    • Wipe Down
  • Is this a single use cable?
  • Will it come into contact with a patient’s skin?
    • If so, for how long?

Once these questions are answered and the cable designer or application engineer has a better understanding of the requirements that the cable will need to fulfill, he or she will begin to consider the various material options which will result in a design best suited for your project. It will be helpful to note any specific regulatory compliance expectations as well such as biocompatibility standards that the cable will need to meet. Knowing those requirements will quickly narrow down the list of possible material options.

Popular Medical Material Options:

BioCompatic®

First developed by Northwire as a thermoplastic alternative to silicone to meet customer demands where biocompatibility and resilience are vital. Just as flexible and soft to the touch as silicone cables, BioCompatic is much more resistant to environmental factors such as exposure to various chemicals, sterilization, abrasion, cut, and crush. However, unlike silicone, BioCompatic does not require a curing step, making it market-ready much faster than silicone.  To offer customers the best in safe and dependable medical cables, BioCompatic meets some of the strictest standards including optimal biocompatibility under USP Class VI and compliance to ISO 10993-5 cytotoxicity and to ISO 10993-10 irritation and skin sensitization requirements. Free of phthalates, halogens, and latex, BioCompatic is also compatible with steam, H2O2, gamma, and ETO sterilization.

BioCompatic I

  • With a durometer of 69 Shore A, this version of the material was the first to hit the market.

BioCompatic II

  • The softest of the three versions with a durometer of 55 Shore A, BioCompatic II is highly flexible while maintaining good mechanical resistance to cut and crush

BioCompatic III

  • Featuring the hardest durometer of 85 Shore A, BioCompatic III is well suited as an insulation material. This version also features the best gurney wheel crush resistance of >2 million cycles, 150lbs. of cut resistance, and is an excellent option for retractile applications

Download the BioCompatic® Data sheet, which compares the material to silicone and Santoprene™ on various values by clicking here!

Santoprene

A medical grade TPE (thermoplastic elastomer), Santoprene is a rubber-like material with the high-performance characteristics of rubber, but the ease of processing of plastics. With a soft to the touch feel, this material also has superior chemical resistance and is compatible with various sterilization techniques.

Northwire’s PTFE

Northwire PTFE, another new material well-suited for medical applications was recently released by the company. Customers benefit from a more advanced way to process the PTFE conductor insulation and overall jacket material because unlike traditional PTFE, this option from Northwire is well-suited for high volume production, will not suffer from length restrictions, features the thinnest wall on the market, and could even offer a cost savings vs. the original processing technology. Northwire’s PTFE also features a high temperature rating up to 300°C and a high dielectric strength resulting in weight and space reduction. It’s compatibility with steam, H2O2, and ETO sterilization techniques make it a great option for multiple use connectivity solutions within medical devices. Additionally, this material is well-suited for clean room applications as it does not release any volatile components.

Download the data sheet, which compares Northwire’s PTFE to the most popular fluoropolymers on several values by clicking here!

Other Fluoropolymers

PFA

  • PFA is the closest to PTFE in terms of superior performance characteristics
  • One trade-off for the high-performance characteristics is the price

FEP

  • The first melt processable fluoropolymer to be released
  • FEP does not have the almost universal chemical resistance featured by PTFE and PFA, but does offer a more cost-effective alternative to PFA where these two characteristics are not as imperative

ETFE

  • Features improved cold flow resistance, higher tensile strengths, and increased abrasion resistance
  • Although not fully fluorinated like PTFE, PFA, and FEP, ETFE maintains high temperature performance, very good electrical properties, and chemical inertness

Click here to download the Northwire Fluoropolymer data sheet including a comparison of the most common material options.

Cable Components:

There are various internal components that can be cabled together with the conductors such as tubing, strength members, or shielding. Each of these come with their own set of qualifying questions to ensure the correct materials are selected.

1 | What is the primary purpose of the component?

For example, if designing in a tube, it will be important to know if the tube needs to supply, vacuum, or vent. If shielding is required, is it to reduce interference or provide structural integrity and protect the cable from wear and tear?

2 | What are the desired cable features?

If flexibility is determined to be a desired feature, then different durometers or ‘hardness’ will be specified accordingly when it comes to tubing. Or when considering a braid shield, a box weave braid will offer a higher flex life, but a spiral shield will be more flexible.

3 | What type of environment will the cable be exposed to during the lifecycle of the application?

The environment has a significant influence on materials chosen to ensure they will hold up to the demands or stressors being put on the cable.

Flex Requirements:

Flexibility or suppleness characteristics are requests that cable design engineers encounter often when designing for healthcare applications. Within the world of “flex,” flexibility and flex life may sound equivalent, but there are key differences. In fact, some high flex cables can have short flex lives, and other wires and cables with high flex life may not be particularly flexible.

Flexibility

Simply put, flexibility is a measure of how much movement a cable can tolerate at a given time. Flexibility comes in many types; torsional, rolling, bending, and variable all describe different kinds of flexibility. When a cable is bent, twisted, or pulled into positions other than its original state, its flexibility is tested. Flexible cable can bend significantly and stay bent for a large amount of time without being damaged.

Another way that people might refer to a flexible cable is by using the term ‘supple’. Often times when someone is looking for a very flexible cable, they want it to be very soft and supple because they want it to be easy to manipulate or bend back and forth. Think of a surgeon using an electrosurgical tool. In this type of application, the surgeon must be able to effortlessly manipulate the tool without the cable kinking or back twisting and ultimately pulling on the surgeon’s hand, resulting in fatigue.

Flex Life

Flex life deals less with how the cable moves, and more with how often it can move in these ways without taking serious damage. Many cables can bend to some degree for limited use (e.g., installation). High flex life cable can bend repeatedly and regularly without disrupting the cable’s intended use, such as power supply or data transfer.

Will your cable be subject to repeated movement such as is needed in surgical applications? If so, you may need cable with a high flex life.

Ultimately, the distinction comes down to use and application. If your cable needs to move well, it must be flexible. If your cable needs to move often, it must have a high flex life. In many applications, such as electrophysiology or laparoscopic surgery, both flexibility and high flex life are required.

From a cable design perspective, we at Northwire always recommend that you start your connectivity considerations earlier on in your device design to save you time and possible frustration at the end of your project! However, we understand that sometimes that just isn’t reality for our customers, so that is why our cable designers are available and ready to partner with you no matter where you are in your project timeline. Whether you have a napkin sketch and are a newbie at cable design or if you have fully identified specifications and are a seasoned vet, Northwire engineers will provide the level of assistance that you need to design and manufacture a quality cable connectivity solution specific to your end application.  

Get in touch with a NWI Cable Specialist today to start your Cable Design