The outer skin that holds the cable components together is called the “jacket.”
Wire jacketing is a critical aspect of the cable as it protects the inner components and creates the final look-and-feel of the cable itself (i.e., it’s the part of the cable that people actually see).
In this post, we’ll discuss the basics of wire jacketing and information about how you can select the best jacket for your minimally invasive application.
What is a “jacket”?
As mentioned above, the jacket is the exterior layer that pulls the interior components together.
Proper wire jacketing protects the cable components from the outside environment which can damage or deteriorate the conductors, insulation, or shielding.
The jacket is also the part of the cable that people see and interact with, which means it’s the part of the cable that is used for branding and differentiation purposes.
Which materials can you use to make wire jacketing?
As with most plastic products, wire jacketing materials typically fall into two high-level categories: thermoplastics and thermosets.
Thermoplastic Wire Jacketing
According to Merriam-Webster, thermoplastics include plastics “capable of softening or fusing when heated and of hardening again when cooled.”
In other words, thermoplastics can be melted, cooled, hardened, and then re-melted, re-cooled, and re-hardened—the plastic can be used over-and-over again.
These characteristics make thermoplastic wire jacketing easier to manufacture.
Thermoplastic wire jacketing is easier to color and can be produced at a lighter weight than thermoset wire jacketing.
The ease of manufacturability combined with the wide use of thermoplastics throughout the medical device (and other) industries typically make thermoplastic wire jacketing less expensive.
Common types of thermoplastic wire jacketing include:
- Polyvinyl chloride (“PVC”). Due to its relatively low cost, PVC wire jacketing is commonly used for cables on disposable medical devices. For PVC to be used on medical devices it must meet certain criteria, such as using a medical-grade or DEHP-free plasticizer.
- Thermoplastic elastomer (“TPE”). TPEs are a type of copolymer created by mixing a thermoplastic with an elastomer (e.g., rubber). This combination adds some of the durability of a thermoset to the manufacturability of a thermoplastic. TPE wire jacketing is commonly found in re-usable device applications.
- Thermoplastic polyurethane (“TPU”). Similar to TPEs, TPUS are a copolymer. TPUs, however, are composed of thermoplastic and polyurethane (a thermoset). The biocompatibility, durability, and resistance properties of TPUs make them a great choice for both disposable and re-usable application.
Thermoset Wire Jacketing
Thermosets, opposed to thermoplastics, become “permanently rigid when heated or cured.”
Once a thermoset is cured, it cannot be melted down and re-used for another product.
Though thermosets do not offer the manufacturability or cost properties of thermoplastics, they do typically offer longer lifecycles and higher durability.
In the medical device world, the most common type of thermoset wire jacketing is silicone as it offers natural thermal stability, UV resistance, and low toxicity.
Silicone is a viable option in re-useable applications that must undergo many sterilization (i.e., autoclave) cycles.
Selecting the right jacket for your minimally invasive application.
The material you choose for your wire jacketing will impact your cable performance, customization abilities, and cost.
Unfortunately, there is no on-size-fits-all jacket material—each comes with its own set of benefits and trade-offs.
Silicone’s natural durability and flexibility make it an attractive choice for high-cycle use application.
But the difficulty in coloring silicone (i.e., customization) and its higher cost may not be viable for low-margin applications where brand differentiation matters.
Though we recommend speaking with an expert to find the ideal wire jacketing for your minimally invasive device, below are some questions to consider as you move down your path.
- What is the environment the wire will be used in? Does it need to be tough and abrasion resistant?
- How flexible does the wire need to be?
- What is the range of temperatures the wire will be exposed to?
- What is the life expectancy of the wire?
- How resistant does it need to be to various elements: Flame, Heat, Cold, Oil and other Chemicals, Light and Weather?