Medical Design Briefs - October 2024 - 40

Design Briefs
Streamlining Medical Device Development and
Manufacturing Using Silicone Elastomers
By Matthew Kihara, NuSil Technology LLC - part of Avantor
S
ilicone elastomers have become a
vital material in the medical device
industry due to their unique
properties, including biocompatibility,
durability and chemical inertness. Silicone
materials are categorized based
on their unvulcanized consistency,
which significantly affects their processability
and their physical properties.
This article compares high consistency
silicone rubbers (HCRs), liquid
silicone rubbers (LSRs), and low consistency
elastomers (LCEs), analyzing
their characteristics and the implications
in selecting each during different
phases in the development of silicone
medical devices.
High Consistency Rubber (HCR). HCR
is a silicone elastomer manufactured with
a blend of fillers and high molecular
weight silicone polymers, which result in
a solid, gum-like consistency in its unvulcanized
state. It is primarily used in extrusion,
calendaring, and compression molding
processes due to its very high viscosity.
The advantages of HCRs include their
high tear strength, resistance to deformation
under stress, and their ability to retain
shape during processing prior to curing
due to their high green-strength. However,
the thick gum-like consistency of HCRs
makes them less suitable for intricate designs,
including complex shapes with thinwalled
sections, and they require the use
of a two-roll mill for mixing the Part A and
Part B components together.
Liquid Silicone Rubber (LSR). LSR
is a silicone elastomer manufactured
with a blend of fillers and medium molecular
weight silicone polymers, which
result in a thick paste consistency in its
unvulcanized state. It is primarily used
in liquid injection molding processes
but may also be used in transfer molding
and knife-coating applications.
The advantages of LSRs include their
ability to mold strong parts with intricate
designs with thin-walled sections
while using high-volume injection
molding processes. However, the thick
paste-like consistency of LSRs make
them less suitable for lab-scale mixing
40
Medical device manufacturers often choose silicone for use in components and devices because of its established
biocompatibility pedigree, broad processing parameter ranges, and excellent physical properties. (Credit: NuSil)
Silicone
Type
Durometer Elongation
HCR 30 sh.A 1050%
LSR
LCE
30 sh.A 750%
27 sh.A 530%
Tensile
Strength
2300 psi
(15.9 MPa)
1350 psi
(9.3 MPa)
685 psi
(4.7 MPa)
and molding during the initial stages of
feasibility and development.
Low Consistency Elastomers (LCE).
LCE is a silicone elastomer manufactured
with a blend of fillers and low
molecular weight silicone polymers,
resulting in a flowable liquid-like
consistency in its unvulcanized state.
It is primarily used in transfer molding
processes but may also be used in
knife-coating and potting applications.
The advantages of LCEs are that their
low viscosity allows them to be easily used
www.medicaldesignbriefs.com
Table 1. A comparison of the types of platinum curable silicone elastomers.
for lab-scale mixing and molding, as well
as for potting and filling applications.
However, the notably lower physical properties
of low consistency elastomers and
the difficulty to use in liquid injection
molding equipment often make them less
suitable for large-scale manufacturing.
Comparison of Long-Term
Implantable Silicone Elastomers
When comparing the types of platinum
curable silicone elastomer options, it is
also critical to understand the differencMedical
Design Briefs, October 2024
Tear Strength
235 ppi
(41.2 kN/m)
150 ppi
(26.5 kN/m)
Specific
Gravity
1.12
1.13
50 ppi (8.3 kN/m) 1.10

https://www.medicaldesignbriefs.com

Medical Design Briefs - October 2024

Table of Contents for the Digital Edition of Medical Design Briefs - October 2024