ASTM F2038-18

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.  
4.2 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, or 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 guide 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 guide.  
1.2 Fabrication and properties of elastomers is covered in the companion document, F2042. 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 Biological and physical properties tend to be more reproducible when materials are manufactured in accordance with accepted quality standards such as ISO 9001 and current FDA Quality System Regulations/Good Manufacturing Practice Regulations (21CFR, Parts 210, 211, and 820).  
1.5 The values stated in SI units are to be regarded as standard. The values given in parentheses are mathematical conversions to inch-pound units that are provided for information only and are not considered standard.  
1.6 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, health, and environmental 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.  
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Nov-2018
• ICS: 11.040.40 - Implants for surgery, prosthetics and orthotics
• Technical Committee: F04 - Medical and Surgical Materials and Devices
• Drafting Committee: F04.11 - Polymeric Materials

Relations

• Refers: ASTM F2042-18 - Standard Guide for Silicone Elastomers, Gels, and Foams Used in Medical Applications Part II—Crosslinking and Fabrication
• Effective Date: 01-Dec-2018
• Refers: ASTM F2042-00(2011) - Standard Guide for Silicone Elastomers, Gels, and Foams Used in Medical Applications Part II—Crosslinking and Fabrication
• Effective Date: 01-Dec-2011
• Refers: ASTM F2042-00(2005) - Standard Guide for Silicone Elastomers, Gels, and Foams Used in Medical Applications Part II - Crosslinking and Fabrication
• Effective Date: 01-Mar-2005
• Refers: ASTM F2042-00e1 - Standard Guide for Silicone Elastomers, Gels, and Foams Used in Medical Applications Part II - Crosslinking and Fabrication
• Effective Date: 10-Jul-2000
• Refers: ASTM F2042-00 - Standard Guide for Silicone Elastomers, Gels, and Foams Used in Medical Applications Part II - Crosslinking and Fabrication
• Effective Date: 10-Jul-2000

Overview

ASTM F2038-18 is the Standard Guide for Silicone Elastomers, Gels, and Foams Used in Medical Applications – Part I: Formulations and Uncured Materials. Developed by ASTM International, this guide provides essential guidance for selecting, formulating, and handling silicone materials intended for medical device applications. It focuses specifically on uncured silicone elastomers, gels, and foams, delineating key considerations in material selection, safety, biocompatibility, and quality standards relevant to the medical device industry. This guide does not cover silicone powders or fluids, nor does it address finished device fabrication methods (which are covered in companion guides).

Key Topics

• Material Selection: Offers comprehensive information to assist users in choosing silicone elastomers, gels, and foams based on chemical, physical, and toxicological properties.
• Formulation Components: Outlines typical components, including silicone polymers, catalysts, crosslinkers, fillers, additives, inhibitors, and solvents. Both high consistency rubber (HCR) and liquid silicone rubber (LSR) are discussed.
• Types of Cure: Describes condensation cure, peroxide cure, and addition cure silicones, emphasizing how cure chemistry impacts material properties.
• Packaging and Labeling: Defines requirements for packaging and labeling of uncured materials to prevent contamination and ensure traceability.
• Quality Control: Stresses the importance of quality management systems, such as ISO 9001 and compliance with FDA Good Manufacturing Practices (GMP), for ensuring product consistency and reproducibility.
• Health and Safety: Addresses safe handling of uncured silicones, emphasizing the need to consult Material Safety Data Sheets and to implement appropriate workplace practices.
• Sterilization: Details considerations and limitations related to sterilizing uncured silicone materials, including specific reference to ethylene oxide, steam, and radiation sterilization.
• Biocompatibility: Recommends that device manufacturers assess biological suitability based on intended use and in compliance with recognized quality standards.

Applications

ASTM F2038-18 is invaluable to manufacturers, developers, and quality professionals in the medical device industry who rely on silicone elastomers, gels, and foams for products such as:

• Medical Implants: Including pacemaker leads, catheters, and prosthetics.
• Healthcare Consumables: Such as tubing, seals, masks, and cushions.
• Wound Care and Adhesives: Gels and foams for contact with skin and soft tissue.
• Protective Coatings: Applications where uncured materials are used for in-situ curing on devices.

By following this guide, organizations ensure the selection of medical-grade silicone materials aligns with health, safety, and regulatory requirements, and supports the ultimate biocompatibility of finished medical devices.

Related Standards

To fully address the lifecycle of medical silicone materials, ASTM F2038-18 references and aligns with several key standards and regulations:

• ASTM F2042: Standard Guide for Silicone Elastomers, Gels, and Foams Used in Medical Applications – Part II: Crosslinking and Fabrication.
• ISO 9001: Quality management systems – requirements for manufacturing consistency.
• FDA GMP: US FDA Quality System Regulation (21 CFR Parts 210, 211, 820).
• ISO 10993-7: Biological evaluation of medical devices – requirements for ethylene oxide sterilant residues.
• ANSI/AAMI ST41, ST50, ST79: Standards for sterilization of medical devices using ethylene oxide, dry heat, and steam methods.

Adherence to these related benchmarks ensures material safety and performance from raw formulation through device manufacturing and final use.

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Keywords: silicone elastomer, medical device material, silicone gel, silicone foam, HCR, LSR, platinum cure, peroxide cure, condensation cure, medical silicone, biocompatibility, uncured silicone, ASTM standards, ISO 9001, medical device manufacturing.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: F2038 − 18
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 ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.1 This guide is intended to educate potential users of
mendations issued by the World Trade Organization Technical
silicone elastomers, gels, and foams relative to their formula-
Barriers to Trade (TBT) Committee.
tionanduse.Itdoesnotprovideinformationrelativetosilicone
powders, fluids, or other silicones.The information provided is
2. Referenced Documents
offered to guide users in the selection of appropriate materials,
2.1 ASTM Standards:
after consideration of the chemical, physical, and toxicological
D1566 Terminology Relating to Rubber
properties of individual ingredients or by-products. This guide
F2042 GuideforSiliconeElastomers,Gels,andFoamsUsed
offers general information about silicone materials typically
in Medical Applications Part II—Crosslinking and Fabri-
used for medical applications. Detail on the crosslinking and
cation
fabricationofsiliconematerialsisfoundinPartIIofthisguide.
2.2 Sterility Standards:
1.2 Fabrication and properties of elastomers is covered in
ANSI/AAMI ST41 Ethylene oxide sterilization in health
the companion document, F2042. This monograph addresses
care facilities: Safety and effectiveness
only components of uncured elastomers, gels, and foams.
ANSI/AAMI ST50 Dry Heat (Heated Air) Sterilizers
1.3 Silicone biocompatibility issues can be addressed at
ANSI/AAMI ST79 Comprehensive guide to steam steriliza-
several levels, but ultimately the device manufacturer must
tion and sterility assurance in health care facilities
assess biological suitability relative to intended use.
ANSI/AAM1 ST30 Determining Residual Ethylene Chlo-
1.4 Biological and physical properties tend to be more rohydrin and Ethylene Glycol in Medical Devices
reproducible when materials are manufactured in accordance ISO 10993-7 Biological evaluation of medical devices—
with accepted quality standards such as ISO 9001 and current Part 7: Ethylene oxide sterilization residuals
FDA Quality System Regulations/Good Manufacturing Prac-
2.3 Quality Standards:
tice Regulations (21CFR, Parts 210, 211, and 820).
ISO 9001 Quality Management Systems—Requirements
21 CFR 820 Quality System Regulation
1.5 The values stated in SI units are to be regarded as
21 CFR 210 Current Good Manufacturing Practice in
standard. The values given in parentheses are mathematical
Manufacturing, Processing, Packing or Holding of Drugs;
conversions to inch-pound units that are provided for informa-
General
tion only and are not considered standard.
21 CFR 211 Current Good Manufacturing Practice for Fin-
1.6 This standard does not purport to address all of the
ished Pharmaceuticals
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3. Terminology
priate safety, health, and environmental practices and deter-
3.1 Additional pertinent definitions can be found in Termi-
mine the applicability of regulatory limitations prior to use.
nology D1566.
Users are also advised to refer to Material Safety Data Sheets
provided with uncured silicone components.
1.7 This international standard was developed in accor-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
dance with internationally recognized principles on standard-
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
This specification is under the jurisdiction of ASTM Committee F04 on the ASTM website.
Medical and Surgical Materials and Devices and is the direct responsibility of Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
Subcommittee F04.11 on Polymeric Materials. 4th Floor, New York, NY 10036, http://www.ansi.org.
Current edition approved Dec. 1, 2018. Published February 2019. Originally AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,
published in 2000. Last previous edition approved in 2011 as F2038 – 00 (2011). 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401, http://
DOI: 10.1520/F2038-18. www.access.gpo.gov.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2038 − 18
3.2 Definitions: 3.3.10 silicone elastomer—an uncured elastomer that has
been subjected to conditions which cause it to become cross-
3.2.1 lot or batch—a quantity of material made with a fixed,
linked.Elastomersmaybeeitherhighconsistencyrubbers,low
specifiedformulationinasingle,manufacturingruncarriedout
consistency rubbers, or RTVs (see 3.3.10.3).
under specific processing techniques and conditions.
3.3.10.1 high consistency rubber (HCR)—an elastomer hav-
3.3 Definitions of Terms Specific to This Standard:
ing a viscosity such that it cannot be moved or transferred by
3.3.1 silicone polymer—polymer chain having a backbone
readily available pumping equipment. These elastomers are
consisting of repeating silicon-oxygen atoms where each
fabricated using high shear equipment such as a two-roll mill
silicon atom bears two organic groups. The organic groups are
and cannot be injection molded. They are typically used in
typically methyl, but can be vinyl, phenyl, fluorine, or other
compression or transfer molding and extrusion processes.
organic groups.
3.3.10.2 low consistency rubber or liquid silicone rubber
3.3.2 cyclics and linears—low molecular weight volatile
(LSR)—an elastomer having a viscosity such that it can be
cyclic siloxane species are referred to using the “D” nomen-
moved or transferred by readily available pumping equipment.
clature which designates the number of Si-O linkages in the
LSRs are typically used in injection molding operations.
material (usually D -D ); species from D to D (or more)
4 20 7 40
may be called “macrocyclics”. Linears are straight chain
3.3.10.3 room temperature vulcanization (RTV)—a one-part
oligomers that may be volatile or of higher molecular weight,
elastomerwhichcuresinthepresenceofatmosphericmoisture.
depending on chain length; they are designated by “M” and
Little, if any, acceleration of cure rate is realized by increasing
“D”combinations,where“M”isR Si-O,andDisasexplained
temperature. Because cure is dependent upon diffusion of
above; “R” is usually methyl. (For example, MDM is
water into the elastomer, cure in depths greater than 0.64 cm
(CH ) SiOSiOSi(CH ) ). Low molecular weight species are
3 3 3 3
(0.25 inches) is not recommended.
present in silicone components to varying degrees depending
3.3.10.4 gels—lightly crosslinked materials having no or
on processing and storage. The levels of macrocyclics that can
relatively low levels of reinforcement beyond that provided by
be removed from silicone polymers by vacuum, high tempera-
the crosslinked polymer. They are usually two-part formula-
ture stripping, or oven post-cure is dependent on the conditions
tions utilizing a platinum-catalyzed addition cure system. The
used.
hardness of the gel can be adjusted within wide limits. The
3.3.3 catalyst—a component of a silicone elastomer formu-
material is not usually designed to bear heavy loads but rather
lation that initiates the crosslinking reaction when the material
to conform to an irregular surface providing intimate contact.
is vulcanized.
As a result, loads are distributed over a wider area. These
materials may also be used to provide protection from envi-
3.3.4 crosslinker or crosslinking agent—a component of a
ronmental contaminants.
silicone elastomer that is a reactant in the crosslinking reaction
that occurs when an elastomer is vulcanized.
3.3.10.5 foams—crosslinked materials which have a com-
ponent added to them that generates a volatile gas, creating
3.3.5 inhibiter (aka retarder)—a component of a silicone
elastomer added to moderate the rate of the crosslinking gas-filled cells as the material is being vulcanized. This results
in a material with a very low density. These are usually
reaction.
two-part formulations utilizing a platinum-catalyzed addition
3.3.6 filler—a finely divided solid that is intimately mixed
cure system. They conform to an irregular surface as they
with silicone polymers during manufacture to achieve specific
expand to provide intimate contact and protection from the
properties. The fillers used in silicone elastomers are one of
environment but are more rigid and provide more strength than
two types:
gels. Since foams are expanded elastomers, on a weight basis
3.3.6.1 reinforcing fillers—usually have high surface areas
they are highly crosslinked relative to gels. Most cure condi-
and are amorphous in nature such as fumed or precipitated
tions will result in a closed cell foam.
silica. Such fillers impart high strength and elastomeric physi-
3.3.11 vulcanization—an irreversible process in which co-
cal properties to the elastomer.
valent chemical bonds are formed between silicone polymer
3.3.6.2 extending fillers—typically have lower surface area
chains. During vulcanization, the material changes from a
and lower cost than reinforcing fillers.They include crystalline
flowable or moldable compound to an elastomeric material
forms of silica and diatomaceous earths. While they provide
which cannot be reshaped except by its physical destruction.
some reinforcement, because they are relatively inexpensive,
3.3.12 types of cure—based upon the cure chemistry
they are used primarily to extend the bulk of the silicone.
employed,siliconeelastomersusedinmedicalapplicationsfall
3.3.7 additive—a component of a silicone elastomer used in
into one of three categories: condensation cure, peroxide cure,
relativelysmallamountstoperformfunctionssuchasmarking,
and addition cure.
coloring, or providing opacity to the elastomer.
3.3.12.1 condensation cure—these materials liberate an or-
3.3.8 silicone base—a uniformly blended mixture of sili-
ganic leaving group during curing and are normally catalyzed
cone polymers, fillers, and additives which does not contain
by an organometallic compound.
crosslinkers or catalysts.
one-part—material supplied ready to use in an air-tight
3.3.9 uncured elastomer—a silicone base which contains container which cures upon exposure to atmospheric moisture.
crosslinker and/or catalyst but has not been vulcanized. The material cures from the surface down and cure depths of
F2038 − 18
greater than about 0.64 cm (0.25 inches) are not practical. pourable. Platinumcatalysts can be used in the rangeof5to20
two-part—material supplied in two separate containers ppm of active platinum but typically are present at about 7.5
which must be intimately mixed in the prescribed proportions ppm.
shortly before use. Because they do not rely upon dispersion of 5.1.2.2 tin—one-part condensation cure formulations will
atmospheric moisture into the silicone, the cure depth is not typically contain from 0.1 to 0.5 % by weight of an organotin
limited. compound.Two-part condensation cure formulations will typi-
cally contain from 0.5 to 2.0 % by weight of an organotin
3.3.12.2 peroxide cure—one-part formulations vulcanized
compound. The ligands attached to tin will be some combina-
by free radicals generated by the decomposition of an organic
tion of alkyl groups, alkoxy groups, or the anions of a
peroxide.
carboxylic acid.
3.3.12.3 addition cure—two-part elastomers which must
5.1.3 crosslinker or crosslinking agent:
first be mixed together and then cured by addition of a
5.1.3.1 two-part, addition cure formulation—the crosslinker
silylhydride to a vinyl silane in the presence of a platinum
is a polymer of the structure shown in Fig. 2 where R is
catalyst.
generally a methyl or a hydrogen group such as to provide at
3.3.13 dispersion—an uncured silicone elastomer dispersed
least 2.0 SiH groups per chain and x and y are integers greater
in a suitable solvent to allow application of a thin layer of
than or equal to zero. In order to avoid chain extension, the
elastomer to a substrate by either dipping or spraying.
functionality of either the v
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: F2038 − 00 (Reapproved 2011) F2038 − 18
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
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, andor 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 guide 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 guide.
1.2 Fabrication and properties of elastomers is covered in the companion document, F604F2042, 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 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.Regulations (21CFR, Parts 210, 211, and 820).
1.5 The values stated in inch-poundSI units are to be regarded as standard. The values given in parentheses are mathematical
conversions to SIinch-pound units that are provided for information only and are not considered standard.
1.6 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 safety, health, and healthenvironmental 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.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D1566 Terminology Relating to Rubber
F813F2042 Practice for Direct Contact Cell Culture Evaluation of Materials for Medical DevicesGuide for Silicone Elastomers,
Gels, and Foams Used in Medical Applications Part II—Crosslinking and Fabrication
2.2 Sterility Standards:
ANSI/AAMI ST41 Good Hospital Practice: Ethylene Oxide Sterilization and Sterility AssuranceEthylene oxide sterilization in
health care facilities: Safety and effectiveness
ANSI/AAMI ST50 Dry Heat (Heated Air) Sterilizers
ANSI/AAMI ST29ST79 Recommended Practice for Determining Ethylene Oxide in Medical DevicesComprehensive guide to
steam sterilization and sterility assurance in health care facilities
This specification is under the jurisdiction of ASTM Committee F04 on Medical and Surgical Materials and Devices and is the direct responsibility of Subcommittee
F04.11 on Polymeric Materials.
Current edition approved Dec. 1, 2011Dec. 1, 2018. Published January 2012February 2019. Originally published in 2000. Last previous edition approved in 20052011 as
F2038 – 00 (2005).(2011). DOI: 10.1520/F2038-00R11.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2038 − 18
ANSI/AAM1 ST30 Determining Residual Ethylene Chlorohydrin and Ethylene Glycol in Medical Devices
AAMI 13409-251 Sterilization of Health Care Products—Radiation Sterilization—Substantiation of 25kGy as a Sterilization
Dose for Small or Infrequent Production Batches
AAMI TIRS-251ISO 10993-7 Microbiological Methods for Gamma Irradiation Sterilization of Medical DevicesBiological
evaluation of medical devices—Part 7: Ethylene oxide sterilization residuals
2.3 Quality StandardsStandards::
ANSI/ASQC Q9001ISO 9001 Quality Systems—Model for Management Systems—RequirementsQuality Assurance in
Design, Development Production, Installation, and Servicing
21 CFR 820 Quality System Regulation(current revision)
21 CFR 210 Current Good Manufacturing Practice in Manufacturing, Processing, Packing or Holding of Drugs; General(cur-
rent revision)
21 CFR 211 Current Good Manufacturing Practice for Finished Pharmaceuticals(current revision)
3. Terminology
3.1 Additional pertinent definitions can be found in Terminology D1566.
3.2 Definitions:
3.2.1 lot or batch—a quantity of material made with a fixed, specified formulation in a single, manufacturing run carried out
under specific processing techniques and conditions.
3.3 Definitions:Definitions of Terms Specific to This Standard:
3.3.1 silicone polymer—polymer chainschain having a backbone consisting of repeating silicon-oxygen atoms where each
silicon atom bears two organic groups. The organic groups are typically methyl, but can be vinyl, phenyl, fluorine, or other organic
groups.
3.3.2 cyclics and linears—low molecular weight volatile cyclic siloxane species are referred to using the “D” nomenclature
which designates the number of Si-O linkages in the material (usually D -D ); species from D to D (or more) may be called
4 20 7 40
“macrocyclics”. Linears are straight chain oligomers that may be volatile or of higher molecular weight, depending on chain
length; they are designated by “M” and “D” combinations, where “M” is R Si-O, and D is as explained above; “R” is usually
methyl. (For example, MDM is (CH ) SiOSiOSi(CH ) ). Low molecular weight species are present in silicone components to
3 3 3 3
varying degrees depending on processprocessing and storage. The levels of macrocyclics that can be removed from silicone
polymers by vacuum, high temperature stripping, or oven post-cure is dependent on the conditions used.
3.3.3 catalyst—a component of a silicone elastomer formulation that initiates the crosslinking reaction when the material is
vulcanized.
3.3.4 crosslinker or crosslinking agent—a component of a silicone elastomer that is a reactant in the crosslinking reaction that
occurs when an elastomer is vulcanized.
3.3.5 inhibitor—inhibiter (aka retarder)—a component of a silicone elastomer added to moderate the rate of the crosslinking
reaction.
3.3.6 filler—a finely divided solid that is intimately mixed with silicone polymers during manufacture to achieve specific
properties. The fillers used in silicone elastomers are one of two types:
3.3.6.1 reinforcing fillers—usually have high surface areas and are amorphous in nature such as fumed or precipitated silica.
Such fillers impart high strength and elastomeric physical properties to the elastomer.
3.3.6.2 extending fillers—typically have lower surface area and lower cost than reinforcing fillers. They include crystalline
forms of silica and diatomaceous earths. While they provide some reinforcement, because they are relatively inexpensive, they are
used primarily to extend the bulk of the silicone.
3.3.7 additives—additive—a component of a silicone elastomer used in relatively small amounts to perform functions such as
marking, coloring, or providing opacity to the elastomer.
3.3.8 silicone base—a uniformly blended mixture of silicone polymers, fillers, and additives which does not contain crosslinkers
or catalyst.catalysts.
3.3.9 uncured elastomer—a silicone base which contains crosslinker and/or catalyst but has not been vulcanized.
3.3.10 silicone elastomer—an uncured elastomer that has been subjected to conditions which cause it to become crosslinked.
Elastomers may be either high consistency rubbers, low consistency rubbers, or RTVs (see 3.3.10.3below). ).
3.3.10.1 high consistency rubbers (HCRS)—rubber (HCR)—are materials which cannot be pumped by conventional pumping
equipment. They normally must be processed an elastomer having a viscosity such that it cannot be moved or transferred by readily
Available from U.S. Government Printing Office Superintendent of Documents, 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401, http://
www.access.gpo.gov.
F2038 − 18
available pumping equipment. These elastomers are fabricated using high shear equipment such as a two-roll mill and parts cannot
be injection molded. They are typically fabricated usingused in compression or transfer molding techniques. and extrusion
processes.
3.3.10.2 low consistency rubbersrubber or liquid silicone rubbers (LSRS)—rubber (LSR)—are normally flowable materials
which can be readily pumped. They can be mixed by pumping through static mixers and parts can be fabricated using injection
molding techniques.an elastomer having a viscosity such that it can be moved or transferred by readily available pumping
equipment. LSRs are typically used in injection molding operations.
3.3.10.3 RTVs (room temperature vulcanization)—room temperature vulcanization (RTV)— are a one-part elastomerselastomer
which curecures in the presence of atmospheric moisture. Little, if any, acceleration of cure rate is realized by increasing
temperature. Because cure is dependent upon diffusion of water into the elastomer, cure in depths greater than 0.25 in. (0.635
cm)0.64 cm (0.25 inches) is not recommended.
3.3.10.4 gels—are lightly crosslinked materials having no or relatively low levels of reinforcement beyond that provided by the
crosslinked polymer. They are usually two-part formulations utilizing a platinum catalyzed platinum-catalyzed addition cure
system. The hardness of the gel can be adjusted within wide limits. The material is not usually designed to bear heavy loads but
rather to conform to an irregular surface providing intimate contact. As a result, loads are distributed over a wider area. These
materials may also be used to provide protection from environmental contaminants.
3.3.10.5 foams—are crosslinked materials which have a component added to them that generates a volatile gas gas, creating
gas-filled cells as the material is being vulcanized. This results in a material with a very low density. These are usually two-part
formulations utilizing a platinum catalyzed platinum-catalyzed addition cure system. They conform to an irregular surface as they
expand to provide intimate contact and protection from the environment but are more rigid and provide more strength than gels.
Since foams are expanded elastomers, on a weight basis they are highly crosslinked relative to gels. Most cure conditions will
result in a closed cell foam.
3.2.11 lot or batch—a quantity of material made with a fixed, specified formulation in a single, manufacturing run carried out
under specific processing techniques and conditions.
3.3.11 vulcanization—an irreversible process in which covalent chemical bonds are formed between silicone polymer chains.
During vulcanization, the material changes from a flowable or moldable compound to an elastomeric material which cannot be
reshaped except by its physical destruction.
3.3.12 types of cure—based upon the cure chemistry employed, silicone elastomers used in medical applications fall into one
of three categories: condensation cure, peroxide cure, and addition cure.
3.3.12.1 condensation cure—these materials liberate an organic leaving group during curing and are normally catalyzed by an
organometallic compound.
one-part—material supplied ready to use in an air tight air-tight container which cures upon exposure to atmospheric moisture.
The material cures from the surface down and cure depths of greater than about 0.25 inches (0.635 cm)0.64 cm (0.25 inches) are
not practical.
two-part—material supplied in two separate containers which must be intimately mixed in the prescribed proportions shortly
before use. Because they do not rely upon dispersion of atmospheric moisture into the silicone, the cure depth is not limited.
3.3.12.2 peroxide cure—one-part formulations vulcanized by free radicals generated by the decomposition of an organic
peroxide.
3.3.12.3 addition cure—two-part elastomers which must first be mixed together and then curecured by addition of a silylhydride
to a vinyl silane in the presence of a platinum catalyst.
3.3.13 dispersion—an uncured silicone elastomer dispersed in a suitable solvent to allow application of a thin layer of elastomer
to a substrate by either dipping or spraying.
4. Significance and Use
4.1 This guide is intended to provide guidance for the specification and selection of silicone materials for medical device
applications.
4.2 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.
5. Formulation
5.1 Elastomers, gels, and foams shall be manufactured using formulations containing combinations of the following raw
materials.
5.1.1 silicone polymer—any polymer of medium or high molecular weight of the structure shown in Fig. 1 where R is a methyl,
an unsaturated alkyl group, o
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