If you've ever watched the space shuttle go up, you've already seen over 4000 Greene, Tweed & Co. (Kulpsville, PA) products in action. Last time you filled your car's gas tank, parts made by the company's Oilfield group probably played a part in getting gasoline from the ground to you.
But if you're lucky, you'll never see anything made of Orthtek™medical composites. And even if you do get an uncomfortably close look at medical devices made of that composite, X-rays will hardly see them at all.
The material is a continuous carbon fiber matrix combined with a thermoplastic resin that creates very strong, light, and chemical- and steam-resistant structures. Currently, the material is being used in a variety of surgical tools and orthopedic fixators for use during and after surgery. Orthtek is an outgrowth of the company's extensive work in oil production: Greene, Tweed was formed in 1863, just four years after Edwin Drake built his first oil well, near Titusville at the other end of the state of Pennsylvania. Among the company's first products were the leather seals used in early oil pumps, as well as buggy whips and uniforms for Union soldiers in the Civil War.
Stock shapes and prototypes of Orthtek and its oilfield predecessor, WR525.
Orthtek had its beginnings in two descendants of those leather pump seals. Composites made by Greene, Tweed called WR525 and WR300 have been used for five years in oil fields, refineries, and chemical plants, and had performed particularly well in so-called "huff and puff" wells, in which steam is forced into underground oil deposits to make the oil flow to the surface. This quality turned out to have a parallel application in the medical field, where surgical instruments must withstand multiple trips to the autoclave for steam sterilization after being used in operating rooms.
"We had a lot of experience with thermoplastic materials, and the properties they exhibit after exposure to steam," says Mike Brewer, an oil industry veteran, Greene, Tweed vice president, and general manager of the Medical and Biotechnology Group. "A lot of materials become brittle upon impact, or they just dissipate and they're gone. A lot of times when you autoclave thermoplastic materials for 20 to 30 cycles they become so brittle that they'll crack."
But it was another, less obvious quality—radiolucency—which opened up new windows in the medical field. The term refers to a material's ability to let X-rays pass through while absorbing only part of their energy, so that the inner structure of parts made of the material becomes visible.
"We knew about it, but as far as applying it to the medical field, that's new," says Chris Toto, the group's engineering manager. "We X-ray our parts for quality control—we look for defects, for voids—so we knew it was radiolucent, we've known that for a long time."
As is often the case, it took an outsider to see how these qualities might apply to other fields. This time, the outsider was German medical device manufacturer Aesculap (Tuttlingen, Germany), which had read about the unique qualities of Greene, Tweed's WR composites in an engineering trade publication. Aesculap made contact with Greene, Tweed's German office and spoke with engineering manager Joachim Bartusch and product manager Erwin Birk about an application which required a thermally stable, radiolucent, stiff material.
"Surgeons have a lot of problems when they're locating pins or plates," says Barry Chadwick, product manager for the group. "They have to move the patient around during surgery to get the right X-ray, to see if it's aligned, and the bones or the plates are in the right position. So to make it easier on the patient and make the operation go quicker, if you have a material that you can see through on the outside to see where the plate is, it's going to help the surgeon in his surgery process."
The first products made in this partnership are external fixators for use during and after surgery, which are noticeably lighter than the steel and aluminum parts they replace. This can be a boon to patients who may wear a device for an extended period, or surgeons who handle the same instrument for several hours at a time.
The radiolucency of the material also comes into play over the long-term healing process. Chadwick cites "halos," the often-painful devices worn by people who have suffered neck injuries, as one example. "The benefit is that when you go back in for monthly X-rays during the healing of the fracture, you don't have to disassemble the fixator and then take the X-ray," he says.
When it comes to design issues, engineering manager Toto says there were several. "The first big problem that I was involved with is that composites, unlike metals, are not isotropic—they don't have the same structure in every direction. They're what we call transverse isotropic or orthotropic, so they have different properties in different directions, and the thickness, it just so happens, is the weakest direction. Especially when you try to interface with metals, there's a weak point where it causes a lot of problems."
How did they get over this barrier? Toto says that there was no magic solution—just lots and lots of testing, both on computers and in the real world. "Trying to control tolerances, putting a reinforcing insert into an area where the fibers aren't oriented in a certain area. There's a science to molding it properly, there's a lot of trial and error."
Toto also recommends that customers leave that trial and error to them. "I would say the majority of people don't know what to do with it," says Toto. "They have no idea how to machine it, there's a big learning curve. You can't just start cutting composites if you've never done it before."
This also puts a large amount of responsibility on the company's shoulders, but the difficulties of the material can translate into advantages. "You can align the fibers any way you want, and you can also affect thermal expansion by the way fibers are aligned," says Brewer. "So if you don't want any expansion in the X and Y, you can align the fibers to make sure that won't happen."
In addition to the high-end, compression-molded version of the material, the company also offers parts made by injection molding, extrusion, or machining.
This sacrifices certain characteristics—some of the tensile strength, for example, or steam and temperature resistance—but results in a lower-cost product. All of the materials in the product matrix retain radiolucency, and all still contain carbon fibers of various lengths.
As for your own close encounter with the product, it might not be that far off. It hasn't been approved for sale in this country yet, but the company is currently seeking approval for use in Europe, and is field testing it in hospitals near its Pennsylvania headquarters.
"It's exciting for Greene, Tweed, for us to be moving forward," says Chadwick. "We're going to be able to develop our materials and stay ahead of our competition, and anybody else that wants to get into this business they're more than welcome. Bring it on!"
Orthtek Medical Composites from Greene, Tweed & Co., visit www.gtweed.com/fluidhandling/fhorthtek.htm.