ASTM F2038-00(2005)
(Guide)Standard Guide for Silicone Elastomers, Gels and Foams Used in Medical Applications Part I - Formulations and Uncured Materials
Standard Guide for Silicone Elastomers, Gels and Foams Used in Medical Applications Part I - Formulations and Uncured Materials
SIGNIFICANCE AND USE
4.1 This guide is intended to provide guidance for the specification and selection of silicone materials for medical device applications.
Silicone manufacturers supplying materials to the medical device industry should readily provide information regarding non-proprietary product formulation to their customers either directly, or through the US FDA master file program.
SCOPE
1.1 This guide is intended to educate potential users of silicone elastomers, gels and foams relative to their formulation and use. It does not provide information relative to silicone powders, fluids, and other silicones. The information provided is offered to guide users in the selection of appropriate materials, after consideration of the chemical, physical and toxicological properties of individual ingredients or by-products. This standard offers general information about silicone materials typically used for medical applications. Detail on the crosslinking and fabrication of silicone materials is found in Part II of this standard.
1.2 Fabrication and properties of elastomers is covered in the companion document, F604, Part II. This monograph addresses only components of uncured elastomers, gels and foams.
1.3 Silicone biocompatibility issues can be addressed at several levels, but ultimately the device manufacturer must assess biological suitability relative to intended use.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Users are also advised to refer to Material Safety Data Sheets provided with uncured silicone components.
1.5 Biological and physical properties tend to be more reproducible when materials are manufactured in accordance with accepted quality standards such as ANSI ISO 9001 and current FDA Quality System Regulations/Good Manufacturing Practice Regulations.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:F2038–00 (Reapproved 2005)
Standard Guide for
Silicone Elastomers, Gels, and Foams Used in Medical
Applications Part I—Formulations and Uncured Materials
This standard is issued under the fixed designation F2038; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 This guide is intended to educate potential users of 2.1 ASTM Standards:
silicone elastomers, gels, and foams relative to their formula- D1566 Terminology Relating to Rubber
tionanduse.Itdoesnotprovideinformationrelativetosilicone F813 Practice for Direct Contact Cell Culture Evaluation of
powders, fluids, and other silicones. The information provided Materials for Medical Devices
is offered to guide users in the selection of appropriate 2.2 Sterility Standards:
materials, after consideration of the chemical, physical, and ANSI/AAMIST41 GoodHospitalPractice:EthyleneOxide
toxicological properties of individual ingredients or by- Sterilization and Sterility Assurance
products. This guide offers general information about silicone ANSI/AAMI ST50 Dry Heat (Heated Air) Sterilizers
materials typically used for medical applications. Detail on the ANSI/AAMI ST29 Recommended Practice for Determin-
crosslinking and fabrication of silicone materials is found in ing Ethylene Oxide in Medical Devices
Part II of this guide. ANSI/AAM1 ST30 Determining Residual Ethylene Chlo-
1.2 Fabrication and properties of elastomers is covered in rohydrin and Ethylene Glycol in Medical Devices
the companion document, F604, Part II. This monograph AAMI 13409-251 Sterilization of Health Care Products—
addresses only components of uncured elastomers, gels, and Radiation Sterilization—Substantiation of 25kGy as a
foams. Sterilization Dose for Small or Infrequent Production
1.3 Silicone biocompatibility issues can be addressed at Batches
several levels, but ultimately the device manufacturer must AAMI TIRS-251 Microbiological Methods for Gamma Ir-
assess biological suitability relative to intended use. radiation Sterilization of Medical Devices
1.4 Biological and physical properties tend to be more 2.3 Quality Standards :
reproducible when materials are manufactured in accordance ANSI/ASQC Q9001 Quality Systems—Model for Quality
with accepted quality standards such as ANSI ISO 9001 and Assurance in Design, Development Production, Installa-
current FDAQuality System Regulations/Good Manufacturing tion, and Servicing
Practice Regulations. 21 CFR 820 Quality System Regulation (current revision)
1.5 This standard does not purport to address all of the 21 CFR 210 Current Good Manufacturing Practice in
safety concerns, if any, associated with its use. It is the Manufacturing, Processing, Packing or Holding of Drugs;
responsibility of the user of this standard to establish appro- General (current revision)
priate safety and health practices and determine the applica- 21 CFR 211 Current Good Manufacturing Practice for
bility of regulatory limitations prior to use. Users are also Finished Pharmaceuticals (current revision)
advised to refer to Material Safety Data Sheets provided with
3. Terminology
uncured silicone components.
3.1 Additional pertinent definitions can be found in Termi-
nology D1566.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
This specification is under the jurisdiction of ASTM Committee F04 on Standards volume information, refer to the standard’s Document Summary page on
Medical and Surgical Materials and Devices and is the direct responsibility of the ASTM website.
Subcommittee F04.11 on Polymeric Materials. Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
Current edition approved Mar. 1, 2005. Published March 2005. Originally 4th Floor, New York, NY 10036.
´1 4
published in 2000. Last previous edition approved in 2000 as F2038 – 00 . DOI: AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,
10.1520/F2038-00R05. 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F2038–00 (2005)
3.2 Definitions: such as a two-roll mill and parts are typically fabricated using
compression or transfer molding techniques.
3.2.1 silicone polymer—polymer chains having a backbone
3.2.10.2 low consistency rubbers or liquid silicone rubbers
consisting of repeating silicon-oxygen atoms where each
silicon atom bears two organic groups. The organic groups are (LSRS)—are normally flowable materials which can be readily
pumped. They can be mixed by pumping through static mixers
typically methyl, but can be vinyl, phenyl, fluorine, or other
organic groups. and parts can be fabricated using injection molding techniques.
3.2.2 cyclics and linears—low molecular weight volatile 3.2.10.3 RTVs (room temperature vulcanization)— are one-
part elastomers which cure in the presence of atmospheric
cyclic siloxane species are referred to using the “D” nomen-
clature which designates the number of Si-O linkages in the moisture. Little, if any, acceleration of cure rate is realized by
increasing temperature. Because cure is dependent upon diffu-
material (usually D -D ); species from D to D (or more)
4 20 7 40
sion of water into the elastomer, cure in depths greater than
may be called “macrocyclics”. Linears are straight chain
0.25 in. (0.635 cm) is not recommended.
oligomers that may be volatile or of higher molecular weight,
depending on chain length; they are designated by “M” and
3.2.10.4 gels—are lightly crosslinked materials having no
“D”combinations,where“M”isR Si-O,andDisasexplained or relatively low levels of reinforcement beyond that provided
above; “R” is usually methyl. (For example, MDM is (CH )
by the crosslinked polymer. They are usually two-part formu-
3SiOSiOSi(CH ) ). Low molecular weight species are present lationsutilizingaplatinumcatalyzedadditioncuresystem.The
3 3
in silicone components to varying degrees depending on
hardness of the gel can be adjusted within wide limits. The
process and storage. The levels of macrocyclics that can be material is not usually designed to bear heavy loads but rather
removed from silicone polymers by vacuum, high temperature to conform to an irregular surface providing intimate contact.
stripping, or oven post-cure is dependent on the conditions As a result, loads are distributed over a wider area. These
used. materials may also be used to provide protection from envi-
ronmental contaminants.
3.2.3 catalyst—a component of a silicone elastomer formu-
lation that initiates the crosslinking reaction when the material 3.2.10.5 foams—are crosslinked materials which have a
is vulcanized. component added to them that generates a volatile gas as the
material is being vulcanized. This results in a material with a
3.2.4 crosslinker or crosslinking agent—a component of a
very low density. These are usually two-part formulations
silicone elastomer that is a reactant in the crosslinking reaction
utilizing a platinum catalyzed addition cure system. They
that occurs when an elastomer is vulcanized.
conform to an irregular surface as they expand to provide
3.2.5 inhibitor—a component of a silicone elastomer added
intimate contact and protection from the environment but are
to moderate the rate of the crosslinking reaction.
more rigid and provide more strength than gels. Since foams
3.2.6 filler—a finely divided solid that is intimately mixed
are expanded elastomers, on a weight basis they are highly
with silicone polymers during manufacture to achieve specific
crosslinked relative to gels. Most cure conditions will result in
properties. The fillers used in silicone elastomers are one of
a closed cell foam.
two types:
3.2.11 lot or batch—a quantity of material made with a
3.2.6.1 reinforcing fillers—usually have high surface areas
fixed, specified formulation in a single, manufacturing run
and are amorphous in nature such as fumed or precipitated
carried out under specific processing techniques and condi-
silica. Such fillers impart high strength and elastomeric physi-
tions.
cal properties to the elastomer.
3.2.12 vulcanization—an irreversible process in which co-
3.2.6.2 extending fillers—typically have lower surface area
valent chemical bonds are formed between silicone polymer
and lower cost than reinforcing fillers.They include crystalline
chains. During vulcanization, the material changes from a
forms of silica and diatomaceous earths. While they provide
flowable or moldable compound to an elastomeric material
some reinforcement, because they are relatively inexpensive,
which cannot be reshaped except by its physical destruction.
they are used primarily to extend the bulk of the silicone.
3.2.13 types of cure—based upon the cure chemistry em-
3.2.7 additives—a component of a silicone elastomer used
ployed, silicone elastomers used in medical applications fall
in relatively small amounts to perform functions such as
into one of three categories: condensation cure, peroxide cure,
marking, coloring, or providing opacity to the elastomer.
and addition cure.
3.2.8 silicone base—a uniformly blended mixture of sili-
3.2.13.1 condensation cure—these materials liberate an or-
cone polymers, fillers, and additives which does not contain
ganic leaving group during curing and are normally catalyzed
crosslinkers or catalyst.
by an organometallic compound.
3.2.9 uncured elastomer—a silicone base which contains
one-part—material supplied ready to use in an air tight
crosslinker and/or catalyst but has not been vulcanized.
container which cures upon exposure to atmospheric moisture.
3.2.10 silicone elastomer—an uncured elastomer that has
The material cures from the surface down and cure depths of
been subjected to conditions which cause it to become
greater than about 0.25 inches (0.635 cm) are not practical.
crosslinked. Elastomers may be either high consistency rub-
two-part—material supplied in two separate containers
bers, low consistency rubbers, or RTVs (see below).
which must be intimately mixed in the prescribed proportions
3.2.10.1 high consistency rubbers (HCRS)—are materials shortly before use. Because they do not rely upon dispersion of
which cannot be pumped by conventional pumping equipment. atmospheric moisture into the silicone, the cure depth is not
They normally must be processed using high shear equipment limited.
F2038–00 (2005)
3.2.13.2 peroxide cure—one-part formulations vulcanized 5.1.3 Crosslinker or crosslinking agent:
by free radicals generated by the decomposition of an organic 5.1.3.1 Two-part, addition cure formulation—the
peroxide. crosslinker is a polymer of the structure shown in Fig. 2 where
3.2.13.3 addition cure—two-part elastomers which must R is generally a methyl or a hydrogen group such as to provide
first be mixed together and then cure by addition of a at least 2.0 SiH groups per chain and x and y are integers
silylhydride to a vinyl silane in the presence of a platinum greater than or equal to zero. In order to avoid chain extension,
catalyst. the functionality of either the vinyl-containing polymer or the
3.2.14 dispersion—an uncured silicone elastomer dispersed SiH-containing crosslinker must be at least 3.0.
in a suitable solvent to allow application of a thin layer of Because of the limitless possibilities for the structure of both
elastomer to a substrate by either dipping or spraying. thecrosslinkerandthefunctional(vinylcontaining)polymer,it
would be meaningless to define a weight range for the level of
4. Significance and Use
crosslinker in a formulation. However, the amount of
4.1 This guide is intended to provide guidance for the crosslinker will typically be sufficient to provide a stoichio-
specification and selection of silicone materials for medical
metric excess of SiH groups over the amount of unsaturated
device applications.
alkyl groups when the 2 components (parts) of the addition
4.2 Silicone manufacturers supplying materials to the medi- cure silicone elastomer are mixed together in the manufactur-
cal device industry should readily provide information regard-
er’s recommended ratio.
ing non-proprietary product formulation to their customers 5.1.3.2 One-part RTVs and two-part addition cure
either directly, or through the US FDA master file program.
formulations—the crosslinker may be an organosilane mono-
mer of the general formula:
5. Formulation
R Si~OR’! (1)
x 42x
5.1 Elastomers,gels,andfoamsshallbemanufacturedusing
formulations containing combinations of the following raw where:
materials. R = organic group excluding phenyl
OR’ = hydrolyzable group such as alkoxy, acetoxy, ke-
5.1.1 silicone polymer—any polymer of medium or high
toximo, etc.
molecular weight of the structure shown in Fig. 1 where R is a
5.1.3.3 Peroxide vulcanized elastomers—organic peroxides
methyl, an unsaturated alkyl group or a hydroxy group, R is
comprise a third type of crosslinking agent which participates
generally a methyl or an unsaturated alkyl group but may also
in the crosslinking reaction that does not become directly
be a phenyl, trifuoropropyl, or other hydrocarbon radical, and
incorporated into the crosslinked network. Peroxide levels
x and y are integers greater than or equal to zero. At least 2.0
range from less than a percent to as high as a couple of weight
alkenylgroupsmustexistperchainifRisnotahydroxygroup.
percentinthetotalformulation.Theseperoxidesdecompose,at
5.1.2 catalyst—an organometallic complex of platinum or
a rate which is dependent upon the temperature, to form
tin bonded to ligands made of any suitable combination of
radicals which then abstract hydrogen atoms from some of the
elements such as carbon, hydrogen, oxygen, fluorine and
silicon. alkyl groups attached to the silicone backbone. Recombination
of these radicals results in the formation of a crosslinked
5.1.2.1 platinum—this catalyst may be dispersed in a sili-
cone polymer of the structure shown in Fig. 1 having a silicone network. One commonly used peroxide is 2,4,-
dichlorobenzoyl peroxide. Decomposition of this peroxide
viscosity low enough that the resulting dispersion is easily
results in the formation of small amounts of polychlorinated
pourable.Platinumcatalystscanbeusedintherangeof5to20
biphenyls and other catalyst decomposition by-products which
ppm of active platinum but typically are present at about 7.5
must be, and are, remove
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.