It's a wire application that would be best if it was never needed, but a carbon fiber wire that is jacketed by Minnesota Wire and Cable Co. has enabled doctors to better care for prematurely born babies.

The problem with monitoring such babies is that the wire that helps monitor their vital signs can be a hindrance if an X-ray or MRI is needed. The wires obstruct the effectiveness of those processes, but removing them for even a short period poses a risk.

Minnesota Wire and Cable Co., however, has marketed a carbon fiber wire for a number of years that has become extensively used because it eliminates that dilemma. The company starts with Thermal carbon fiber wire and jackets it with a unique coating that allows electricity to be conducted yet remains radio translucent, meaning that it will not show up in X-rays or MRI's. Three lead wires are generally used for monitoring.

"The carbon fiber, which comes from Amoco Performance Products, actually is a standard strength membrane product, used mostly for the aerospace industry," explained Eric Wagner, manufacturing manager for Minnesota Wire and Cable Co., St.Paul, Minnesota, USA.

"The biggest challenge was processing the jacket so that it left intact the integrity of the carbon fibers' properties," Wagner said. "It took two years to develop a jacketing that worked, and R&D continues to find variations needed for different end users," he noted. The carbon fibers range in size from 1,000 filaments to 12,000 filaments per conductor. A 3,000 filament bundle has a normal diameter of .015 in. The finished wires have an OD ranging from .035 in. to .5 in. for multi-conductors.

The smaller size wall monitoring wires are disposable, meant to be used by just one patient.

"Minnesota Wire and Cable Co. follows a standard manufacturing process control used on any electrical wire," Wagner said. It sells the finished product either in bulk, to customers who terminate the wire and put in the electrode, or in finished form, already cut, stripped and terminated. The finished lead wires, 24 in. long, come in kit form, three to a kit.

Minnesota Wire and Cable Co. typically extrudes the wire jacketing five days a month, including about 500,000 feet for the most basic size and smaller runs for the diameters. The company also offers them in ribbon cable form.
In a given week, Minnesota Wire and Cable Co. may cut, strip and crimp 45,000 wire ends for termination. The company also developed special tooling for the metal stamping process because carbon fiber is prone to shearing.
"The handling of the carbon fiber is the biggest challenge," Wagner said. The carbon fiber has very low shearing resistance, and can shear like glass fiber," he warned. Every time the carbon fiber is handled, there is a risk of shearing thousands of carbon filaments.

Standard copper handling equipment, it was decided, was too rough, so the company modified its handling equipment to uphold the integrity of the product.

"Minnesota Wire and Cable Co. has tried other approaches, such as tinsel and small conductors, but carbon fiber has proven to be the most effective to date," Wagner said. "The company, however, continues with its R&D efforts, trying to further enhance its coating's properties and attributes. Characteristics like sterilization, stripability and ability to be worked with automatic processes are typical goals," he said.

"We're always tweaking the coating, trying to make it better," Wagner said.

"The actual process that Minnesota Wire and Cable Co. uses depends on the end user's needs, which can and does vary," Wagner noted. All told, the company's total production of the extruded wire is about nine million feet per year, he estimated.

The monitor wires are a product that in a perfect world would not have to be used at all, but since they are needed - and uses now may soon extend beyond pre and neo-natal care - it is good to know they are there to be used.