Medical Design Briefs - April 2021 - 22

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.

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

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.

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)

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)

22

www.medicaldesignbriefs.com

Cov

ToC

Medical Design Briefs, April 2021


http://www.medicaldesignbriefs.com

Medical Design Briefs - April 2021

Table of Contents for the Digital Edition of Medical Design Briefs - April 2021

Medical Design Briefs - April 2021 - Intro
Medical Design Briefs - April 2021 - Cov4
Medical Design Briefs - April 2021 - Cov1a
Medical Design Briefs - April 2021 - Cov1b
Medical Design Briefs - April 2021 - Cov1
Medical Design Briefs - April 2021 - Cov2
Medical Design Briefs - April 2021 - 1
Medical Design Briefs - April 2021 - 2
Medical Design Briefs - April 2021 - 3
Medical Design Briefs - April 2021 - 4
Medical Design Briefs - April 2021 - 5
Medical Design Briefs - April 2021 - 6
Medical Design Briefs - April 2021 - 7
Medical Design Briefs - April 2021 - 8
Medical Design Briefs - April 2021 - 9
Medical Design Briefs - April 2021 - 10
Medical Design Briefs - April 2021 - 11
Medical Design Briefs - April 2021 - 12
Medical Design Briefs - April 2021 - 13
Medical Design Briefs - April 2021 - 14
Medical Design Briefs - April 2021 - 15
Medical Design Briefs - April 2021 - 16
Medical Design Briefs - April 2021 - 17
Medical Design Briefs - April 2021 - 18
Medical Design Briefs - April 2021 - 19
Medical Design Briefs - April 2021 - 20
Medical Design Briefs - April 2021 - 21
Medical Design Briefs - April 2021 - 22
Medical Design Briefs - April 2021 - 23
Medical Design Briefs - April 2021 - 24
Medical Design Briefs - April 2021 - 25
Medical Design Briefs - April 2021 - 26
Medical Design Briefs - April 2021 - 27
Medical Design Briefs - April 2021 - 28
Medical Design Briefs - April 2021 - 29
Medical Design Briefs - April 2021 - 30
Medical Design Briefs - April 2021 - 31
Medical Design Briefs - April 2021 - 32
Medical Design Briefs - April 2021 - 33
Medical Design Briefs - April 2021 - 34
Medical Design Briefs - April 2021 - 35
Medical Design Briefs - April 2021 - 36
Medical Design Briefs - April 2021 - 37
Medical Design Briefs - April 2021 - 38
Medical Design Briefs - April 2021 - 39
Medical Design Briefs - April 2021 - 40
Medical Design Briefs - April 2021 - 41
Medical Design Briefs - April 2021 - 42
Medical Design Briefs - April 2021 - Cov3
Medical Design Briefs - April 2021 - Cov4
https://www.nxtbook.com/smg/techbriefs/22MDB01
https://www.nxtbook.com/smg/techbriefs/21MDB12
https://www.nxtbook.com/smg/techbriefs/21MDB11
https://www.nxtbook.com/smg/techbriefs/21MDB10
https://www.nxtbook.com/smg/techbriefs/21MDB09
https://www.nxtbook.com/smg/techbriefs/21MDB08
https://www.nxtbook.com/smg/techbriefs/21MDB07
https://www.nxtbook.com/smg/techbriefs/21MDB06
https://www.nxtbook.com/smg/techbriefs/21MDB05
https://www.nxtbook.com/smg/techbriefs/21MDB04
https://www.nxtbook.com/smg/techbriefs/21MDB02
https://www.nxtbookmedia.com