Materials are critical in medical cables

When specifying cables for machines or systems to be used in a medical application, it is critical to consider the jacketing material covering the cable. Not only must they be durable and flexible, they must also protect from current leakage and also be suitable for use with human and chemical contact.

The cable jacket acts as an isolating agent, protecting insulation, filler, strength member and conductors. Because they are the only material that may touch the patient and prevent the conducting wires and other elements from coming into contact with a patient, they must meet biocompatibility requirements.

First, you must consider some governmental regulations, said Hank Mancini, Business Development Manager, Affinity Medical, a Molex Co. “Medical device makers typically want any cables that come into contact with a patient to meet both ISO 10993 and FDA biocompatibility and cytotoxicity requirements,” Mancini said.

Biocompatibility is key

Silicone is the most compatible material used in cable jacketing and also the most durable in terms of sterilization, disinfection and cleaning, said Mancini. It is the only one that will withstand hundreds of steam autoclave sterilization cycles.

In addition, medical grade thermoplastic elastomers (TPEs), medical grade thermoplastic polyurethanes (TPUs) and medical grade polyvinyl chlorides (PVCs) fully meet ISO and FDA biocompatibility requirements.

Thermoplastic elastomers withstand common cleaning agents and can withstand 50 to 100 autoclave sterilization cycles. Polyurethane and PVC stand up well to most cleaning agents, but cannot be steam sterilized. None of the common jacket materials withstands cleaning agents containing quaternary ammonium compounds such as dimethylammonium chloride, which is intended for use on hard surfaces such as stainless steel and tile.

Other considerations
Although not as critical, the look and feel of a cable jacketing material should be considered during selection. For example, color might be a deciding factor in matching the cable to the equipment or just in keeping it looking new. For example, white cables show wear and debris much sooner than a darker colored jacketing material.

While silicone is soft and flexible, uncoated silicone cables can become tacky, attracting and retaining dirt, said Mancini. To combat this, you could select a cable jacket made of thermoplastic elastomers.

For a more durable option, you may want to go with polyurethane. It offers excellent abrasion resistance, tensile strength, and high tear resistance. Because of this, it is not as flexible as the other options.

Take care with other materials
Mancini cautions against using any other material for medical cable jacketing. “Flame retardants, added to resins to meet UL 94 Flame Classifications, will cause the material not to meet ISO 10993 FDA biocompatibility and cytotoxicity requirements,” he said, adding, “When a device maker requires a UL rating, the common method is to use conductors with a UL rating and enclose them in a cable jacket extruded from medical grade resin.”

Affinity Medical, a Molex Co.
www.affinitymed.com