Medical Design Briefs: 2021 Technology Leaders - 30

TECHNOLOGY LEADERS Tubing/Extrusion
Polyolefin Heat Shrink Tubing for
Tight-Tolerance Medical Applications:
Understanding the Advantages and
Development Process
H
eat shrink tubing benefits medical
devices and applications in
many ways - by serving as a
protective covering, as insulation
for electrical wires, or by aiding with
component bundling and manufacturing.
Of the three major types of heat
shrink tubing materials, only one, polyolefin-
based heat shrink tubing, is capable
of high shrink ratios, excellent fit,
compliance and thin walls. This article
covers the basics of heat shrink tubing
and its use in medical device manufacturing,
focusing on the benefits of
polyolefin- based heat shrink tubing, and
reviewing critical considerations the
medical device design engineer needs to
evaluate in order to choose the best solution
for a specific application.
Understanding Materials
Three main material families are primarily
used in medical-grade heat shrink
tubing applications: polyolefins, polyester
(PET), and fluoropolymers such as
PTFE and FEP. Fluoropolymers are generally
chosen for their high temperature
resistance. They also create a smooth surface
finish on the substrate when the
heat shrink tubing is removed after
reflowing. For example, a device manufacturer
may build up a braided catheter
with an inner layer of a polymer, a middle
layer of a wire braid, and an outer
layer of another polymer, intending to
create a single shaft. The inner and outer
layers would bond together, encapsulating
the braid in the middle.
This is accomplished by applying
either FEP or PTFE heat shrink tubing to
the assembled shaft. The assembly is then
exposed to high temperatures and the heat
shrink tubing shrinks, melting the polymers
beneath it and adding the compressive
force needed to bond the inner and outer
layers together. The heat shrink is then
removed and discarded. Fluoropolymer
heat shrink is very lubricious, and after
removal, the resulting outer skin of the
catheter tubing is very smooth.
Because PET heat shrink tubing has
very high dielectric strength, it's a logical
choice for applications that require insulation
of electrical wires. PET can offer very
thin walls and is known for its high tensile
strength. When specifying a PET heat
shrink for an application, the design engineer
should specify a heat shrink close to
the final diameter of the product, as PET
performs better at lower shrink ratios.
Polyolefin offers the greatest shrink
ratio of the three material options, followed
by fluoropolymers and then PET.
Polyolefin heat shrink ratios vary from
1.5:1 to 10:1, although it is not unusual
to see them in the 4:1 range. In some
applications, the shrink ratio can be in
excess of 10:1. This makes it ideal for
products that require coverage over
varying diameters. For PET, the shrink
ratios will vary from 1.1:1 to 3:1. For fluoropolymers,
the shrink ratio will typically
range from 1.3:1 to 4:1.
In addition to high shrink ratios, polyolefin
shrink tubing exhibits low recovery
temperature, making it suitable for
use in low-temperature applications to
avoid damaging the components (such
as electrodes) beneath the shrink tubing.
It also offers good surface lubricity
and can produce very thin expanded
walls with high compressive strength.
Because polyolefin heat shrink tubing
can have high expansion ratios, it can be
utilized across varying diameters of a
device. An example would be when the
diameter of a device changes from 10 Fr
to 3 Fr along a 4-in. transition, and the
heat shrink tubing must make the same
transition. Polyolefin heat shrink tubing
In the medical industry, heat shrink tubing can be
used as a protective covering, insulation, or a manufacturing
aid, depending on the material family.
(Credit: Lubrizol Life Science)
30
The addition of EVA makes the tubing softer, more supple and easier to expand to high shrink ratios at lower
levels of EVA content. (Credit: Lubrizol Life Science)
www.medicaldesignbriefs.com
Medical Design Briefs 2021 Technology Leaders

https://www.medicaldesignbriefs.com

Medical Design Briefs: 2021 Technology Leaders

Table of Contents for the Digital Edition of Medical Design Briefs: 2021 Technology Leaders