Exploring the Many Layers
of Tubing Selection
By Bob Donohue, General Manager, Natvar,
a Tekni-Plex company
Medical device manufacturers continue to push the enve- lope regarding the capabilities
their products can offer physicians and
patients. To enable those products to
do their job, manufacturers of individual
components—such as tubing—also have
to invest in the latest technology to be
able to provide desired deliverables.
A broad variety of devices use tubing
to deliver soluble pharmaceuticals.
These include chemotherapy, pain
management, insulin, blood therapy,
and unstable medications. Typical
medical-grade tubing sizes range from
.016 inner diameter (ID) and .060 outer
diameter (OD) to .125 ID and .188 OD
Four- and five-layer tubing is coming
on stream that can provide enhanced
performance attributes, at up to 50 percent
lower cost than traditional monolayer and
some two- and three-layer structures.
First, let’s take a look at desired properties and traditional tubing structures
so that we can better understand the
catalyst for the evolution toward additional layers and what benefits the latest
technology can offer.
Desired Tubing Properties
Key tubing attributes include flexibility,
clarity, and ability to be solvent and UV
adhesive bondable. Additional desired
characteristics could include UV protection and moisture/oxygen barrier.
Both medical device manufacturers
and patients benefit from a flexible line.
A good example of this is a patient receiving IV drug therapy. Flexible tubing
enables a more comfortable experience.
It also facilitates mobility when a patient
is ambulatory while receiving treatment
and minimizes the chance of inadvertent
removal. When packaged, tubing needs
to curl to fit into the medical tray and
easily uncurl when removed.
To assist in assembling the medical
device, tubing also needs to be solvent
and UV adhesive bondable. This enables
the tube to permanently adhere to the
desired surface—such as a port, needle
assembly or spike.
Clarity is another desirable physical attribute so that the fluid traveling
through the internal diameter can be
In many instances, the medical device
manufacturer may also need to specify
additional protection from UV light, as
well as oxygen and moisture migration,
all of which have a negative impact on
shelf life and efficacy.
Traditional Multilayer Tubing
Two- and three-layer coextruded tubes
were first commercialized more than
three decades ago for insulin delivery
devices. The objective was to provide
a fluid path that did not negatively
interact with the medication. This
includes not allowing polymer molecule migration into the medication as
well as not allowing the medication
to migrate through the tubing wall.
As previously mentioned, flexibility
and the ability to bond to the delivery
system were two additional require-
Typical structures have a polyethylene (PE) inner layer of high,
medium, or low density. PE is chemically-resistant and inert; and therefore
does a good job of delivering uncontaminated medication. However, in
a monolayer form, PE tubing is thick
and rigid. It doesn’t have the desired
flexibility to enable it to bend and
stretch to facilitate device use and drug
delivery comfort. Further, PE does not
offer desired transparency, is challenging
to bond to and can kink.
Coextruded tubing was developed to
address some of those issues. Using PE
as the inner layer of a structure which
also includes polyurethane or polyvinyl
chloride, gave medical device companies the desired fluid path attributes
Five-, three- and two-layer coextruded