Medical Design Briefs - July 2022 - 19

surfaces caused by cell formation that creates
the lower density foam.
Tubing Materials
Depending on the application, medical
hoses and tubing are produced in a variety
of materials, including plastics such as fluorinated
ethylene propylene (FEP), Nylon,
PVC, polyetheretherketone (PEEK),
polytetrafluoroethylene (PTFE); thermoplastic
elastomers (TPE); and elastomers,
in particular, silicone.
Silicone. Silicone is a key tubing material
for medical devices, especially for
implants. The unique characteristics of
high-consistency rubber (HCR) silicones
offer an uncured, green strength that allows
for a variety of custom and complex
processing techniques. Additional advantages
include the following:
* It is proven to be inert and biostable,
making it the gold standard in terms of
biocompatibility.
* It is nonreactive with other elements.
* It can be platinum-cured for the highest
degree of purity.
* Durometers can be easily altered.
* It allows for extended post-cure for lowest
level extractables.
* It does not utilize leaching plasticizers.
* Certain formulations are suitable for
long-term surgical implant.
* It is odorless, tasteless, and nontoxic.
* It possesses favorable physical and haptic
attributes.
* It can be manufactured with a variety
of textures.
* It can be sterilized by radiation, EtO,
steam: 30 psi/2 bar at +123 °C/+253 °F.
* It resists temperature extremes with flexibility
retention: from -54 ° to +204 °C/
from -65 ° to +400 °F; brittle point: -73
°C/-100 °F.
* It is processable in numerous ways, including
molding, overmolding, sheeting,
dipping, and extrusion, as well as
in combination with other materials
and substrates.
* It can include different fillers for specific
applications.
* It offers exceptional permeability, allowing
absorption of APIs.
Drug eluting. Silicone is often used for
catheters, respirators, and implants due to
its biocompatibility and biostability benefits;
however, silicone is not immune to
bacterial colonization.
One option to prevent tubing from
transmitting bacteria is to impregnate vulcanized
silicone with APIs. The silicone is
immersed in the drug solutions, which can
be absorbed into the material.
The APIs do not interfere with the cure
chemistry of the silicone and are uniformly
impregnated through the matrix
of the silicone. Customizing the API concentration
and adding
release membranes
enables a drug to be released at a
constant rate. APIs can also be used to
release a variety of drugs slowly, over longer
periods, and focused at the site of
need. For example, hormones and cancer
treatments can elute through silicone.
Platinum-cured silicone. Platinumcured
silicones can eliminate the need
for a secondary post-cure process, which
is required for older peroxide-cured silicone
systems. Platinum-cured silicone
contains fewer volatile organic compounds
and can be formulated to have
faster cure times at lower temperatures.
Medical Design Briefs, July 2022
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Medical Design Briefs - July 2022

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