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Medical Plastics
Tubing: Applications, Quality, & Extrusion Process
Challenges
Medical Tubing Configurations
Medical Tubes are categorized mainly by
following types according to Different Configurations:
a. According to the structure :
Single-Lumen, Double-Lumen, Multi-Lumen, Two-Row,
Multi-Row etc.
b. According to the performance : High-Pressure Tube, UV
Protection Tube, Flame Retardant Tube Antimicrobial Tube,
Gamma Ray Protection Tube.
c. According to the usage : High-Transparent Tube, Tube
With Color Line (One Or Multi-Lines), Radiopaque Tube (One
Of Multi-Lines Or Whole), Micro-Flow Tube, Intravascular
Tube, Balloon Tube, High-Pressure Tube.
Single and Multi-lumen tubes
No longer will a single-lumen micro bore
tube suffice for medical applications. What often works
best is a multi-lumen tube, one with passages for several
tasks. Of course, tubes need to stay the same
micro-diameter but now require multiple lumens (more than
one hole). Multiple lumens are designed to achieve a
desired performance in the smallest space possible. Two to
12 lumens can be designed into a single tube to provide
multiple activities through a single access port. ”Lumens
often carry fluids, wires for steering a catheter, and
devices to grasp tissue for a biopsy and doctors want to
monitor their progress during a surgical procedure, so
there could also be a fiber optic line in another lumen,”
So the tube has become a delivery system. For example,
with neurovascular devices designed to reach the brain for
treatment, the catheter and delivery system require
microdiameter extrusions with precisely controlled walls.
Also, Lumens are no longer expected to be round, and
eccentric shapes (oblong or crescent for example) are
becoming more common.
 Tubes and Catheters Sizing
Problems can arise when the customer and
catheter or tubing supplier are not using the same scale
when discussing catheter tubing sizes.
French scale and gauge scale are the
measures used to refer to the diameter of catheters and
tubing. While each have certain advantages,
misinterpreting these standards can lead to confusion .
“OD” and “ID” are abbreviations for outer diameter and
inner diameter, respectively, and are generally measured
in inches or millimeters.
The catheter sizing classification most
commonly used in the medical industry is the French (Fr)
scale, also known as the “Charrière’s system.” The French
scale is an easy method to use to describe the basic size
of a catheter, because it specifies the most obvious
component, the outer diameter. The French size = 3 times
the diameter in millimeters. The disadvantage of the
French scale is that it does not specify the inner
diameter of the catheter or tubing. Thus, the French
sizing used alone, is not specific enough to adequately
describe small catheters, where internal diameter is
critical. This scale is much more useful to specify larger
catheter sizes.
A second method of sizing catheters is the
gauge measurement. Gauge is a descending scale, opposite
the French scale of measurement which ascends with
corresponding size. The higher the gauge size the smaller
the tubing.
Another less common method for sizing
catheter tubing is the “PE” scale. It is specific to
polyethylene and is an ascending scale used by some
manufacturers to represent the OD and ID of the tubing,
similar to French sizing.
The most definitive method to describe a
catheter’s dimension is simply to state the exact
measurements of both the outer and inner diameters. While
it may seem a little more difficult
to communicate, this method will actually give all the
details necessary to the researcher or catheter
manufacturer to properly size your specific catheter and
catheter connections.
Extrusion Technology
Advances in extrusion technology are
aiding the evolution of plastic tubing with the latest
developments that include special formulations offering
unique combinations of desired properties such as
strength, flexibility, a high gas-barrier rating and
lubricity. The extrusion process is only as good as the
manufacturer’s ability to control it.
Tubing quality is affected by a number of
factors, including raw material selection, material
handling, and the many parameters of the tubing extrusion
process. All of these materials
have their pros and cons . One drawback is that many of
them contain gels, requiring that tubing manufacturers
have proper understanding of the process technology and
know how to either minimize or eliminate the gels in the
tubing. Another drawback is residence time in the barrel.
Because these materials have complex
chemistries, they tend to be very
sensitive to excess heat, shear, and process times.
Because they degrade quickly, well
established processes, highly trained technicians, and
well - maintained equipment are key to successfully
extruding precision medical device tubing repeatedly and
reproducibly.
A tube’s dimensions can affect the
performance characteristics of extruded medical tubing.
However, process parameters, equipment, and material
characteristics also play an important role in determining
the end properties of an extruded tube. Tubes have also
shrunk dramatically in recent years, to the point where a
human hair is thick compared with some tube walls.
Manufacturing such products poses considerable challenges,
requiring special extrusion equipment, precise process
control, and painstaking inspections.
Advances & Limitations
Advances in Medical polymeric tubing
science and extrusion technology directly correlate to the
evolution from surgical-based intervention to minimally
invasive approaches and associated medical device design.
The goal of reducing procedure and hospitalization times,
and patient trauma, while improving outcomes has created a
dependency on tubing and extrusion science to keep pace
with clinical demands.
Precision Extrusion makes tubing with
walls about a quarter as thick as a human hair. And some
of Advanced Polymers’ tubes have such thin walls that they
can take the place of coatings. While reducing the outside
diameter (OD) of their products, tubing manufacturers want
to maintain as large an inside diameter (ID) as possible.
Larger IDs give doctors more room to insert tools or
deliver drugs into the body. Multilayer tubes are
sometimes made in a series of steps. “It’s an extrusion
process combined with an assembly process. Although
multilayer tubes offer valuable combinations of
properties, they’re “astronomically expensive” compared
with conventional tubes.
Medical device engineers must understand
the advances and limitations of tubing technology as
defined by both the extrusion process and post-extrusion
technology in order to take advantage of the best designs
and ensure the success of their products. Medical device
manufacturers are being challenged by strong market demand
for tubing that delivers increased functionality, lower
profiles, and lower costs - pushing the limits of material behavior and manufacturing science. Nextgeneration balloon
catheters are expected to deliver significantly higher
burst pressures and better puncture resistance. They are
also being designed to transport target-specific drug
polymer payloads or flexible microelectronic packages to
various parts of the human body. Designs are calling for
ever smaller and more capable medical devices, and many
are made to last only one operation. Smaller tubes
accommodate the trend to less invasive procedures because
less traumatic procedures shorten patient recovery times.
The challenge is to make them tight enough for a reliable
design in terms of how the product will be used, yet loose
enough to facilitate assembly and
avoid unneeded features and costs. |
