PRODUCT UPDATE
Combining Material Forces
for Composite Tubing
Composite tubing affords flexibility in
a multipurpose package for minimally
invasive applications
employed, a composite tube can offer rigidity,
chemical resistance, precise tolerances, and a high
strength-to-weight ratio.
Whereas OEMs repeatedly voice their desire
for tighter tolerances, thinner walls, and
ever-shorter lead times, a new set of
demands for medical tubing is becoming increasingly
more audible. With the increased use of minimally
invasive surgery (MIS) and the emerging field of
natural orifice transluminal endoscopic surgery
(NOTES), the need for minuscule, multifunctional,
problem-solving tubes that offer design flexibility is
on the rise.
“It used to be that you could just have a
homogeneous tube—a tube that was either going to
carry fluid or be a path for a guidewire,” observes
Tim Lynch, operations manager for MicroLumen
Inc. (Tampa, FL; www.microlumen.com). “But
today, the devices are getting more and more
complex. They’re trying to do more and more in
smaller devices, and therefore there’s really not
enough room to have tubes that function only as
a tube—the real estate in there is critical and
tubes have to have multiple features and multiple
purposes.” Aiding in living up to this expectation of
multitasking are multiple materials and geometries
in the form of composite tubing.
Giving Devices the Slip
The materials employed in the tube ultimately
dictate its properties and suitability for particular
applications. For example, Teflon (PTFE),
renowned in the cookware circuit for its nonstick
properties, is also a key component in many
companies’ medical-grade composite tubing.
Frequently used as a liner in composite tubing,
PTFE provides its patented nonstick and lubricious
surface to facilitate device delivery. “Teflon is so
slippery that the product being pushed in the middle
[of the tube]—whether it’s an angioplasty balloon
or stent-type product—can move more freely with
that lubricious surface,” says Michael Badera,
president, Precision Extrusion Inc. (Glens Falls,
NY; www.precisionextrusion.com).
Precision Extrusion, a specialty high-end
extrusion house, is venturing into composite
tubing for the first time in response to customer
demand. A natural outgrowth from its efforts to
expand its value-added capabilities, the company
has developed a PTFE-lined braid-reinforced
catheter. Contributing lubricity for device delivery or
guidance, PTFE lines the catheter shafts. The shafts
PolyMed composite tubing is electrically insulated to
prevent capacitance coupling issues.
Offering Reinforcement
Providing functional flexibility in composite
tubing is the combination not just of several
materials, but geometries as well. Jim Shobert,
chairman of Polygon Co. (Walkerton, IN;
www.polygoncompany.com) likens the design of
composite tubing to that of a bridge. When building
a bridge, there is first laid out a latticework of
metal over which concrete is then poured. The
metal latticework serves to reinforce the concrete,
increasing the structure’s strength.
Like bridges, composite tubing often features
coiling or braiding to reinforce the tube structure,
especially in applications requiring thin walls.
Potential advantages of such a construction can
various applications. For example, Polygon
supplies its PolyMed composite tubing line as an
option for manufacturers that want to move away
from metal tubes without sacrificing strength or
performance.
Engineered to replace stainless steel,
aluminum, or thermoplastics, PolyMed composite
tubing features circumferentially wound or
unidirectional geometries made from continuous
electrical-grade fiberglass encapsulated
within a thermoset resin matrix. Along with
providing rigidity and electrical insulation, this
construction boasts the strength of metal without
the need for a secondary protective sheath,
according to Polygon.
“If you use a stainless-steel or metal tube
in a laparoscopic instrument where you’re
doing any sort of cauterization, you have to be
careful of capacitance coupling,” warns Shobert.
“The real estate in [a tube]
“Typically, you have to put a plastic sheath over
the metal so that [capacitance coupling] doesn’t
is critical and tubes have
happen. With our materials, it’s all electrically
to have multiple features
insulated, so the capacitance coupling issues
cease to be a problem.”
and multiple purposes.”
Available in both single- and multilumen
configurations, PolyMed is also corrosion resistant,
—TIM LYNCH
sterilizable, and radiolucent. It is offered with
inner diameters as small as 0.042 in. and with wall
thicknesses as thin as 0.010 in.
A braid-reinforced catheter from Precision Extrusion
features a PTFE liner to enhance lubricity for device-delivery and guiding applications.
include better tensile and burst strength, as well as
kink reduction in flexible tubes.
“I always use that [bridge] example because
it is very analogous to composites,” Shobert
says. “You take a fiber structure and then put the
polymer around it and you can vary the material
and the mechanics of that structured tube based on
the fiber geometry. Not only can you change the
geometry, but you can also change the material
constituent to change physical characteristics.”
Depending on the materials and geometries
can be braided using round, single- or double-ended,
flat, or ribbon wire with different tensile strengths.
Variable stiffness is achieved along the catheter
shaft from the proximal to the distal end using
nylon, polyurethane, or Pebax jacket materials.
Precision Extrusion’s catheter also features clear
and radiopaque distal tips. “The properties are
variable depending on the type of wire that’s used,
the braid pattern, and the hardness of the materials
that go into the outer jacket,” Badera explains.
This ability to vary properties and hardness
throughout a tube is among the main advantages
of composite tubing, according to Lynch of
MicroLumen. He points out that composite tubing
allows both for stiffness at the proximal end of a
catheter, where the surgeon may be working, and
flexibility within the body at the distal end. Plus, the
addition of other elements can further enhance the
composite product. For example, platinum marker
bands enable the tube to be seen during fluoroscopy.
MicroLumen supplies a variety of tubing
products, including braid- and coil-reinforced
composite tubing engineered with PTFE or polyimide
liners. Claiming to offer the thinnest PTFE liners
in the industry at roughly 0.0005 in., MicroLumen
provides Teflon liners in a range of different
dimensions. Etching the liners on a silver-plated
copper mandrel eliminates the need for additional
labor required to stretch the liners over mandrels,
Lynch says of MicroLumen’s process. He adds
that this offering also helps to keep manufacturing
costs down by enabling processes to be performed
continuously.
Looking into the Future
Owing to its design flexibility and ability to be
tailored to suit an application’s needs, composite
tubing appears to be concurrently on the rise with
MIS procedures. MIS applications dictate the need
for tubing that features such unique characteristics
as variable stiffness and the benefits of combined
material properties working together. And while
composite tubing is helping to meet these demands,
it’s not doing so without challenges.
“For the entry sites where someone might have
formerly used a 7, 8, or 9 French device, people
are now going in with 4, 5, and 6 French devices,
forcing us to do more and more, less invasively to
the patient,” Lynch says. That’s what is pushing
everything to be more specific. “We have to
accomplish more in the same or less space than we
used to,” he adds.
Another challenge is that composite tubing
has been overlooked by many engineers over the
years for applications for which it would have
been ideal, according to Shobert. “Our biggest
issue is education of the engineers that this is the
material of choice,” he muses. “Engineers come
out of college typically educated in metals and
thermoplastics. Engineers have not in the past been
trained in the nuances of composite materials.”
Lynch concurs, adding that a concerted educational
effort by tubing suppliers is necessary so that
engineers are informed about the options available
to them as well as the capabilities of suppliers.
—Shana Leonard
Shedding the Sheath
As is the case with enhancing tube lubricity
through the incorporation of PTFE liners,
composite tubing can serve as a problem solver in
For more articles and
information on tubing for
medical applications, visit
devicelink.com/mpmn/tubing
