1、Designation: F 2038 00 (Reapproved 2005)Standard Guide forSilicone Elastomers, Gels, and Foams Used in MedicalApplications Part IFormulations and Uncured Materials1This standard is issued under the fixed designation F 2038; the number immediately following the designation indicates the year oforigin
2、al adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide is intended to educate potential users ofsilicone ela
3、stomers, gels, and foams relative to their formula-tion and use. It does not provide information relative to siliconepowders, fluids, and other silicones. The information providedis offered to guide users in the selection of appropriatematerials, after consideration of the chemical, physical, andtox
4、icological properties of individual ingredients or by-products. This guide offers general information about siliconematerials typically used for medical applications. Detail on thecrosslinking and fabrication of silicone materials is found inPart II of this guide.1.2 Fabrication and properties of el
5、astomers is covered inthe companion document, F 604, Part II. This monographaddresses only components of uncured elastomers, gels, andfoams.1.3 Silicone biocompatibility issues can be addressed atseveral levels, but ultimately the device manufacturer mustassess biological suitability relative to int
6、ended use.1.4 Biological and physical properties tend to be morereproducible when materials are manufactured in accordancewith accepted quality standards such as ANSI ISO 9001 andcurrent FDA Quality System Regulations/Good ManufacturingPractice Regulations.1.5 This standard does not purport to addre
7、ss all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. Users are alsoadvised to refer to Material Safety Data Sh
8、eets provided withuncured silicone components.2. Referenced Documents2.1 ASTM Standards:2D 1566 Terminology Relating to RubberF 813 Practice for Direct Contact Cell Culture Evaluation ofMaterials for Medical Devices2.2 Sterility Standards:3ANSI/AAMI ST41 Good Hospital Practice: Ethylene OxideSterili
9、zation and Sterility AssuranceANSI/AAMI ST50 Dry Heat (Heated Air) SterilizersANSI/AAMI ST29 Recommended Practice for Determin-ing Ethylene Oxide in Medical DevicesANSI/AAM1 ST30 Determining Residual Ethylene Chlo-rohydrin and Ethylene Glycol in Medical DevicesAAMI 13409-251 Sterilization of Health
10、Care ProductsRadiation SterilizationSubstantiation of 25kGy as aSterilization Dose for Small or Infrequent ProductionBatchesAAMI TIRS-251 Microbiological Methods for Gamma Ir-radiation Sterilization of Medical Devices2.3 Quality Standards4:ANSI/ASQC Q9001 Quality SystemsModel for QualityAssurance in
11、 Design, Development Production, Installa-tion, and Servicing21 CFR 820 Quality System Regulation (current revision)21 CFR 210 Current Good Manufacturing Practice inManufacturing, Processing, Packing or Holding of Drugs;General (current revision)21 CFR 211 Current Good Manufacturing Practice forFini
12、shed Pharmaceuticals (current revision)1This specification is under the jurisdiction of ASTM Committee F04 onMedical and Surgical Materials and Devices and is the direct responsibility ofSubcommittee F04.11 on Polymeric Materials.Current edition approved Mar. 1, 2005. Published March 2005. Originall
13、ypublished in 2000. Last previous edition approved in 2000 as F 2038 00e1.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe
14、ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.4Available from U.S. Government Printing Office Superintendent of Documents,732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401.1Copyright ASTM International, 100 Barr Har
15、bor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3. Terminology3.1 Additional pertinent definitions can be found in Termi-nology D 1566.3.2 Definitions:3.2.1 silicone polymerpolymer chains having a backboneconsisting of repeating silicon-oxygen atoms where eachsilicon atom bea
16、rs two organic groups. The organic groups aretypically methyl, but can be vinyl, phenyl, fluorine, or otherorganic groups.3.2.2 cyclics and linearslow molecular weight volatilecyclic siloxane species are referred to using the “D” nomen-clature which designates the number of Si-O linkages in themater
17、ial (usually D4-D20); species from D7to D40(or more)may be called “macrocyclics”. Linears are straight chainoligomers that may be volatile or of higher molecular weight,depending on chain length; they are designated by “M” and“D” combinations, where “M” is R3Si-O, and D is as explainedabove; “R” is
18、usually methyl. (For example, MDM is (CH3)3SiOSiOSi(CH3)3). Low molecular weight species are presentin silicone components to varying degrees depending onprocess and storage. The levels of macrocyclics that can beremoved from silicone polymers by vacuum, high temperaturestripping, or oven post-cure
19、is dependent on the conditionsused.3.2.3 catalysta component of a silicone elastomer formu-lation that initiates the crosslinking reaction when the materialis vulcanized.3.2.4 crosslinker or crosslinking agenta component of asilicone elastomer that is a reactant in the crosslinking reactionthat occu
20、rs when an elastomer is vulcanized.3.2.5 inhibitora component of a silicone elastomer addedto moderate the rate of the crosslinking reaction.3.2.6 fillera finely divided solid that is intimately mixedwith silicone polymers during manufacture to achieve specificproperties. The fillers used in silicon
21、e elastomers are one oftwo types:3.2.6.1 reinforcing fillersusually have high surface areasand are amorphous in nature such as fumed or precipitatedsilica. Such fillers impart high strength and elastomeric physi-cal properties to the elastomer.3.2.6.2 extending fillerstypically have lower surface ar
22、eaand lower cost than reinforcing fillers. They include crystallineforms of silica and diatomaceous earths. While they providesome reinforcement, because they are relatively inexpensive,they are used primarily to extend the bulk of the silicone.3.2.7 additivesa component of a silicone elastomer used
23、in relatively small amounts to perform functions such asmarking, coloring, or providing opacity to the elastomer.3.2.8 silicone basea uniformly blended mixture of sili-cone polymers, fillers, and additives which does not containcrosslinkers or catalyst.3.2.9 uncured elastomera silicone base which co
24、ntainscrosslinker and/or catalyst but has not been vulcanized.3.2.10 silicone elastomeran uncured elastomer that hasbeen subjected to conditions which cause it to becomecrosslinked. Elastomers may be either high consistency rub-bers, low consistency rubbers, or RTVs (see below).3.2.10.1 high consist
25、ency rubbers (HCRS)are materialswhich cannot be pumped by conventional pumping equipment.They normally must be processed using high shear equipmentsuch as a two-roll mill and parts are typically fabricated usingcompression or transfer molding techniques.3.2.10.2 low consistency rubbers or liquid sil
26、icone rubbers(LSRS)are normally flowable materials which can be readilypumped. They can be mixed by pumping through static mixersand parts can be fabricated using injection molding techniques.3.2.10.3 RTVs (room temperature vulcanization) are one-part elastomers which cure in the presence of atmosph
27、ericmoisture. Little, if any, acceleration of cure rate is realized byincreasing temperature. Because cure is dependent upon diffu-sion of water into the elastomer, cure in depths greater than0.25 in. (0.635 cm) is not recommended.3.2.10.4 gelsare lightly crosslinked materials having noor relatively
28、 low levels of reinforcement beyond that providedby the crosslinked polymer. They are usually two-part formu-lations utilizing a platinum catalyzed addition cure system. Thehardness of the gel can be adjusted within wide limits. Thematerial is not usually designed to bear heavy loads but ratherto co
29、nform to an irregular surface providing intimate contact.As a result, loads are distributed over a wider area. Thesematerials may also be used to provide protection from envi-ronmental contaminants.3.2.10.5 foamsare crosslinked materials which have acomponent added to them that generates a volatile
30、gas as thematerial is being vulcanized. This results in a material with avery low density. These are usually two-part formulationsutilizing a platinum catalyzed addition cure system. Theyconform to an irregular surface as they expand to provideintimate contact and protection from the environment but
31、 aremore rigid and provide more strength than gels. Since foamsare expanded elastomers, on a weight basis they are highlycrosslinked relative to gels. Most cure conditions will result ina closed cell foam.3.2.11 lot or batcha quantity of material made with afixed, specified formulation in a single,
32、manufacturing runcarried out under specific processing techniques and condi-tions.3.2.12 vulcanizationan irreversible process in which co-valent chemical bonds are formed between silicone polymerchains. During vulcanization, the material changes from aflowable or moldable compound to an elastomeric
33、materialwhich cannot be reshaped except by its physical destruction.3.2.13 types of curebased upon the cure chemistry em-ployed, silicone elastomers used in medical applications fallinto one of three categories: condensation cure, peroxide cure,and addition cure.3.2.13.1 condensation curethese mater
34、ials liberate an or-ganic leaving group during curing and are normally catalyzedby an organometallic compound.one-partmaterial supplied ready to use in an air tightcontainer which cures upon exposure to atmospheric moisture.The material cures from the surface down and cure depths ofgreater than abou
35、t 0.25 inches (0.635 cm) are not practical.two-partmaterial supplied in two separate containerswhich must be intimately mixed in the prescribed proportionsF 2038 00 (2005)2shortly before use. Because they do not rely upon dispersion ofatmospheric moisture into the silicone, the cure depth is notlimi
36、ted.3.2.13.2 peroxide cureone-part formulations vulcanizedby free radicals generated by the decomposition of an organicperoxide.3.2.13.3 addition curetwo-part elastomers which mustfirst be mixed together and then cure by addition of asilylhydride to a vinyl silane in the presence of a platinumcataly
37、st.3.2.14 dispersionan uncured silicone elastomer dispersedin a suitable solvent to allow application of a thin layer ofelastomer to a substrate by either dipping or spraying.4. Significance and Use4.1 This guide is intended to provide guidance for thespecification and selection of silicone material
38、s for medicaldevice applications.4.2 Silicone manufacturers supplying materials to the medi-cal device industry should readily provide information regard-ing non-proprietary product formulation to their customerseither directly, or through the US FDA master file program.5. Formulation5.1 Elastomers,
39、 gels, and foams shall be manufactured usingformulations containing combinations of the following rawmaterials.5.1.1 silicone polymerany polymer of medium or highmolecular weight of the structure shown in Fig. 1 where R is amethyl, an unsaturated alkyl group or a hydroxy group, R isgenerally a methy
40、l or an unsaturated alkyl group but may alsobe a phenyl, trifuoropropyl, or other hydrocarbon radical, andx and y are integers greater than or equal to zero. At least 2.0alkenyl groups must exist per chain if R is not a hydroxy group.5.1.2 catalystan organometallic complex of platinum ortin bonded t
41、o ligands made of any suitable combination ofelements such as carbon, hydrogen, oxygen, fluorine andsilicon.5.1.2.1 platinumthis catalyst may be dispersed in a sili-cone polymer of the structure shown in Fig. 1 having aviscosity low enough that the resulting dispersion is easilypourable. Platinum ca
42、talysts can be used in the range of 5 to 20ppm of active platinum but typically are present at about 7.5ppm.5.1.2.2 tinone-part condensation cure formulations willtypically contain from 0.1 to 0.5 wt percent of an organotincompound. Two-part condensation cure formulations will typi-cally contain fro
43、m 0.5 to 2.0 weight percent organotin com-pound. The ligands attached to tin will be some combination ofalkyl groups, alkoxy groups, or the anions of a carboxylic acid.5.1.3 Crosslinker or crosslinking agent:5.1.3.1 Two-part, addition cure formulationthecrosslinker is a polymer of the structure show
44、n in Fig. 2 whereR is generally a methyl or a hydrogen group such as to provideat least 2.0 SiH groups per chain and x and y are integersgreater than or equal to zero. In order to avoid chain extension,the functionality of either the vinyl-containing polymer or theSiH-containing crosslinker must be
45、at least 3.0.Because of the limitless possibilities for the structure of boththe crosslinker and the functional (vinyl containing) polymer, itwould be meaningless to define a weight range for the level ofcrosslinker in a formulation. However, the amount ofcrosslinker will typically be sufficient to
46、provide a stoichio-metric excess of SiH groups over the amount of unsaturatedalkyl groups when the 2 components (parts) of the additioncure silicone elastomer are mixed together in the manufactur-ers recommended ratio.5.1.3.2 One-part RTVs and two-part addition cureformulationsthe crosslinker may be
47、 an organosilane mono-mer of the general formula:RxSiOR!42x(1)where:R = organic group excluding phenylOR = hydrolyzable group such as alkoxy, acetoxy, ke-toximo, etc.5.1.3.3 Peroxide vulcanized elastomersorganic peroxidescomprise a third type of crosslinking agent which participatesin the crosslinki
48、ng reaction that does not become directlyincorporated into the crosslinked network. Peroxide levelsrange from less than a percent to as high as a couple of weightpercent in the total formulation. These peroxides decompose, ata rate which is dependent upon the temperature, to formradicals which then
49、abstract hydrogen atoms from some of thealkyl groups attached to the silicone backbone. Recombinationof these radicals results in the formation of a crosslinkedsilicone network. One commonly used peroxide is 2,4,-dichlorobenzoyl peroxide. Decomposition of this peroxideresults in the formation of small amounts of polychlorinatedbiphenyls and other catalyst decomposition by-products whichmust be, and are, removed from the cured elastomer duringpost-curing.5.1.4 Fillera high purity amorphous silica commerciallyknown as fumed or precipitated sili
