Medical Design Briefs: 2021 Technology Leaders - 44

TECHNOLOGY LEADERS Materials/Coatings/Adhesives
Mechanical
stresses
Absorption
of solvents
in plastic
* Softening
* Swelling
* Permeation
* Dissolution
Reduction in
physical
properties
* Oxidation
* Depolymerization
* Reaction of
functional groups
in or on the chain
Fig. 2 - Sequence of events induced in the polymer
material upon chemical attack. Chemical resistance
enables endurance to the polymer against chemical
attack.
tors and handling devices, IV disposable
luer lock connectors and accessories ,
blood plasma oxygenators, drainage sets
for the thorax, medical filter housings,
and disposable luer lock connectors
(see Figure 1).7,8
Polymer Mechanical Behavior: What Is
Chemical Resistance in Medical
Plastics?
The mechanical properties measure
the material's response to a finite strain
by an applied stress. The intermolecular
arrangement of a polymer, among other
attributes, largely governs its mechanical
behavior. However, chemical resistance
measures the ability of a polymeric material
to retain its original properties post
exposure to a chemical agent for a specified
time period.9 Smart design of the
polymer backbone, polymer blending,
CYROLITE®
Performance attributes
BPA free
Transparency
Color stability post EtO/Gamma/E-beam
Bonding with PVC tubing
Flow - Multicavity tools/Thin walls
Lipid Resistance
Alcohol Resistance
(tensile, impact,
flexural)
A stress cracking
agent as in
IPA, lipids,
disinfectants,
drugs, and/or
carrier solvents
The inherent
susceptibility of
the plastic to
stress crack
Fig. 3 - Simultaneous presence of these three factors results in the surface embrittlement of plastic parts
by ESC.
and formulating with specialty additives
to alter the degree of crystallinity,
crosslinking, or molecular weight are
critical factors that influence the chemical
resistance of the blend.10-12
The inability of a polymer to resist
chemical attack could impair physical
and/or chemical properties such as surface
aesthetics, or color, of polymer to
modulus, ductility, impact toughness,
and dimensional stability depending on
the chemical agent and the duration of
exposure. The extent of these detriments
depends on the polymer design
and the degradation pathway. Common
agents leading to chemical attack are
detergents, surfaces active or oxidizing
chemicals such as disinfectants, alcohols,
lipids, processing aids, lubricants,
contaminants, or even ultra-pure water
(see Figure 2).13
Furthermore, crazing and environmental
stress cracking (ESC) are distinct
types of failure phenomena in plastics.
The material under critical external
(mechanical) or residual molded-in
stresses, when exposed to a stress
cracking agent, can experience localized
weakening at the surface of the
material, permitting crack propagation.
G-20 G-20 HiFLO GS-90 CG-97 Med 2
✓
+
✓
++ ++
+
+++ +++
++
+++
++ ++
+
+
✓
+++
✓
+++ ++
++
✓
+
++
+++ +++ +++
++
++
++
+
+
+++ ++
++
+++
Table 1. Roehm America's product portfolio offering CYROLITE® in eight grades designed for performance in
healthcare applications. Performance rating: Good (+), Very Good (++), Excellent (+++).
44
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Depending on the material, macroscopic
crazing occurs, sometimes visible as
stress whitening in the region of maximum
stress. Crazing is physical em -
brittle ment that is induced by the simultaneous
presence of critical stress and a
chemical agent that can lower the cohesive
bond energies of the polymer surface
layers (see Figure 3).9 Strategies to
incorporate functional moieties such as
block, graft, or amphiphilic block co -
polymers, or impact modifiers, in the
polymer design can mitigate crack formation
and crack propagation yielding
environmental stress crack resistance
(ESCR).11,12
Conclusion
Foremost, patient safety from diseasecausing
pathogens is propelling the
industry to design for ESCR utility in
medical assemblies. Designing for ESCR
begins with understanding the chemical
exposure environment before the polymer
material selection. The mechanical
behavior of the polymeric material
drives the subsequent ESCR performance.
Herein, we showcase CYROLITE®
's
product portfolio, for example,
offering performance attributes for
applications in healthcare and medical
devices. The design process for CYROLITE®
involves
understanding the market
landscape, customer input, and cognizance
for potential indications for use.
Furthermore, it combines a methodical
assessment of design factors, such as
material selection and processing, providing
value-added solutions in terms of
optical transparency, mechanical performance,
chemical resistance, sterilizability,
and large-volume processability.
Moreover, the application of aggressive
disinfectants is interfering with the
structural integrity of medical device
assemblies and causing premature failures.
It is essential to integrate an objective
screening matrix to enable medical
Medical Design Briefs 2021 Technology Leaders
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Medical Design Briefs: 2021 Technology Leaders

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