1、Designation: F2791 15Standard Guide forAssessment of Surface Texture of Non-Porous Biomaterialsin Two Dimensions1This standard is issued under the fixed designation F2791; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、 last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide describes some of the more common meth-ods that are available for measuring the topographical featuresof a
3、 surface and provides an overview of the parameters thatare used to quantify them. Being able to reliably derive a set ofparameters that describe the texture of biomaterial surfaces isa key aspect in the manufacture of safe and effective implant-able medical devices that have the potential to trigge
4、r anadverse biological reaction in situ.1.2 This guide is not intended to apply to porous structureswith average pore dimensions in excess of approximately 50nm (0.05 m).1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 Th
5、is standard does not purport to address 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.2. Referenced Documen
6、ts2.1 ASTM Standards:2C813 Test Method for Hydrophobic Contamination on Glassby Contact Angle MeasurementF2312 Terminology Relating to Tissue Engineered MedicalProductsF2450 Guide for Assessing Microstructure of PolymericScaffolds for Use in Tissue-Engineered Medical ProductsF2664 Guide for Assessin
7、g the Attachment of Cells toBiomaterial Surfaces by Physical Methods2.2 Other Standards:3ISO 3274 Geometrical Product Specifications (GPS)Surface Texture: Profile MethodNominal Characteris-tics of Contact (Stylus) InstrumentsISO 4287 Geometrical Product Specifications (GPS)Surface Texture: Profile M
8、ethodTerms, Definitions andSurface Texture ParametersISO 4288 Geometrical Product Specifications (GPS)Surface Texture: Profile MethodRules and Proceduresfor the Assessment of Surface TextureISO 135651 Geometrical Product Specifications (GPS)Surface Texture: Profile MethodSurfaces Having Strati-fied
9、Functional Properties; Filtering and General Measure-ment Conditions3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 biomaterial, nany substance (other than a drug),synthetic or natural, that can be used as a system or part of asystem that treats, augments, or replaces any tiss
10、ue, organ, orfunction of the body. F26643.1.2 evaluation length, ln, nlength in the direction of thex-axis used to assess the profile under evaluation.3.1.2.1 DiscussionThe evaluation length may contain oneor more sampling lengths. ISO 42873.1.3 hydrophilic, adjhaving a strong affinity for water;wet
11、table.3.1.3.1 DiscussionHydrophilic surfaces exhibit zero con-tact angles. C8133.1.4 hydrophobic, adjhaving little affinity for water;nonwettable.3.1.4.1 DiscussionHydrophobic surfaces exhibit contactangles appreciably greater than zero: generally greater than 45for the advancing angle. C8133.1.5 im
12、plant, na substance or object that is put in thebody as a prosthesis, or for treatment or diagnosis. F26643.1.6 lay, nthe direction of the predominant surfacepattern. ISO 1356511This guide is under the jurisdiction of ASTM Committee F04 on Medical andSurgical Materials and Devices and is the direct
13、responsibility of SubcommitteeF04.42 on Biomaterials and Biomolecules for TEMPs.Current edition approved May 1, 2015. Published June 2015. Originallyapproved in 2009. Last previous edition approved in 2014 as F2791 14. DOI:10.1520/F2791-15.2For referenced ASTM standards, visit the ASTM website, www.
14、astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ans
15、i.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.7 primary profile, nthe profile after application of theshort wavelength filters. ISO 32743.1.8 profile peak, nan outwardly directed (from thematerial to the surrounding medium
16、) portion of the assessedprofile connecting two adjacent points of the intersection of theprofile with the x-axis. ISO 42873.1.9 profile valley, nan inwardly directed (from surround-ing medium to material) portion of the assessed profileconnecting two adjacent points of the intersection of theassess
17、ed profile with the x-axis. ISO 42873.1.10 real surface, nsurface limiting the body and sepa-rating it from the surrounding medium. ISO 42873.1.11 sampling length, lr, n length in the direction of thex-axis used for identifying the irregularities characterizing theprofile under evaluation. ISO 42873
18、.1.12 scaffold, na support, delivery vehicle or metric forfacilitating the migration, binding, or transport of cells orbioactive molecules used to replace, repair, or regeneratetissues. F24503.1.13 surface profile, nprofile that results from the inter-section of the real surface by a specified plane
19、.3.1.13.1 DiscussionIn practice, it is usual to choose aplane with a normal that nominally lies parallel to the realsurface and in a suitable direction. ISO 42873.1.14 surface texture, nirregularities on a surface (peaksand valleys) produced by the forming process.4. Significance and Use4.1 The term
20、 “surface texture” is used to describe the localdeviations of a surface from an ideal shape. Surface textureusually consists of long wavelength repetitive features thatoccur as results of chatter, vibration, or heat treatments duringthe manufacture of implants. Short wavelength features super-impose
21、d on the long wavelength features of the surface, whicharise from polishing or etching of the implant, are referred to asroughness.4.2 This guide provides an overview of techniques that areavailable for measuring the surface in terms of Cartesiancoordinates and the parameters used to describe surfac
22、e tex-ture. It is important to appreciate that it is not possible tomeasure surface texture per se, but to derive values forparameters that can be used to describe it.5. The Relationship Between Surface Texture, SurfaceChemistry, Surface Energy, and Biocompatibility5.1 The biocompatibility of materi
23、als is influenced by manyfactors such as size, shape, material bulk, and surface chemicalcomposition, surface energy, and surface topography. Chang-ing any one of these related characteristics of a biocompatiblematerial can have a significant effect on cell behavior. Theresponse of a cell to a bioma
24、terial can be assessed bymeasuring the adhesive strength between it and the underlyingsurface, monitoring changes in its shape or in the expression ofbiomarkers.5.2 The chemical species present on a surface can bemapped in detail using surface sensitive analysis techniques(for example, X-ray photoel
25、ectron spectroscopy where thepenetration depth is 10 nm or below (1).4The chemicalspecies present on the surface together with the surfacetopography determine how hydrophilic the surface is. Measur-ing the contact angle between the surface and a fluid, usuallywater, can assess the degree of hydrophi
26、licity of a surface. Careshould be taken when comparing contact angle measurementsmade on different surfaces, as the relative contributions fromthe surface chemistry and texture are unlikely to be the same.6. Surfaces and Surface Profiles6.1 Conventionally surfaces are described in Cartesian co-ordi
27、nates where the x-axis is defined as being perpendicular tothe lay direction. The y-axis is in-plane and is perpendicular tothe x-axis direction. The z-axis is out of plane. The profile of asurface that has a uniform, non-directional texture can bemeasured at any in-plane orientation (see Fig. 1(A);
28、 however,several profiles at different orientations should be measured to4The boldface numbers in parentheses refer to a list of references at the end ofthis standard.NOTE 1The surface shown in (A) has no directionality or lay, therefore profiles can be oriented at any angle. Profiles (dashed line a
29、rrow) are drawnperpendicular to the lay (solid line arrow) in surfaces that have directionality (B).FIG. 1 Profile Orientation and Surface FeaturesF2791 152find the maximum amplitude (see Fig. 1(A). For patternedsurfaces that have periodic features, a lay, the orientation of theprofile is at right a
30、ngles to it (see Fig. 1(B).6.2 The measured surface is composed of three components:form, waviness and roughness. The form corresponds to theunderlying shape and tilt of the surface with respect to themeasuring platform. The software packages used for surfacetexture analysis all have a methodology f
31、or removing the formfrom the surface. The “corrected” surface can then be used toobtain a 2-D profile that describes the surface texture. Thisprofile after removal of form is defined according to ISO 3274as the primary profile. The stages involved in the analysis ofthe measured profile through prima
32、ry profile to the roughnessprofile are shown in Fig. 2.7. Filtering and the Cut-Off Wavelength7.1 Surface data can be filtered to remove unwanted noise orto remove texture information at unwanted wavelengths. Fil-ters are classified according to the spatial periodicity that theyallow to pass through
33、; low-pass filters admit long wavelengthsand reject short ones; high-pass filters do the opposite. Band-pass filters, as the name implies, allow a limited range ofwavelengths to pass. In practice, using filters can createproblems in deciding how much of the noise in the measure-ments is “real” and h
34、ow much can be attributed to the surface.It should be noted that some aspects of the surface are notfaithfully reproduced due to limitations of the measurementmethod, for example, an inability to track the sides of steepvalleys that is in essence a form of filtering. This topic isfurther discussed i
35、n Section 11.7.2 Filters used in surface texture measurements do not havea sharp cut-off in spatial frequency above or below whichinformation is rejected. This gradual attenuation of high or lowspatial frequency data helps avoid distortion of the measure-ments that can occur when strong features are
36、 close to thefiltration limits. The point on the transmission curve at whichthe transmitted signal is reduced to 50 % is referred to as thecut-off wavelength, c, of the filter (Fig. 3). For measurementsmade using a stylus instrument (Section 11), the choice of cdepends on the sampling frequency and
37、the speed at which thestylus moves over the surface. For example, measurementsmade at intervals of 0.01 mm from a device moving at 1 mms1will generate data at a frequency of 100 Hz. Increasing thesampling interval to 0.1 mm will reduce the frequency at whichdata are obtained to 10 Hz.Ahigh-pass filt
38、er that suppresses allfrequencies below 10 Hz effectively removes any surfaceirregularities larger than 0.1 mm spacing from the data. Hence,filters can be used to bias the experimental data towardsdetecting profile (surface texture after applying a low-pass tofilter the data), waviness (after applyi
39、ng a band-pass filter), androughness (after applying a high-pass filter). Measurementconditions are set for filters according to the respective valuesof the sampling interval, measurement speed, and filtrationlimits, according to ISO 3274.FIG. 2 Summary of Stages Involved in Analysis of Measured Pro
40、file to Obtain a Roughness ProfileF2791 1537.3 ISO 4287 specifies that 2-D roughness parameters needto be determined over five sequential sampling lengths, lr,unless otherwise specified. This grouping of five serial sam-pling lengths is referred to as the evaluation length, ln. Thesampling length va
41、ries according to the length scale of thetexture being assessed; larger features require a long samplinglength. Guidance as to which sampling length to use for a givenrange of feature sizes is shown in Table 1. It may be necessaryto perform one or more iterations to identify the best value forlr. Th
42、is can be achieved by calculating the mean width of aprofile element, RSm (see Fig. 4), from a measured profilewhere the value for lr is based on a best guess. This initialiteration will enable a new value for RSm to be determined andthat leads to a potential revision of lr according to Table 1.8. Q
43、uantification of Surface Profiles8.1 Parameters that are used to characterize 2-D surfaceprofiles are grouped as:8.1.1 Amplitude parameters, which are measures of varia-tions in profile height. These parameters are split into twosubclasses: averaging parameters, and peak and valley param-eters;8.1.2
44、 Spatial parameters, which describe in-plane variationsof surface texture; and8.1.3 Hybrid parameters, which combine both amplitudeand spatial information (for example, mean slope).8.2 RaThe most widely used parameter to quantify sur-face texture is the arithmetical mean deviation of the absoluteord
45、inate values, Z(x), of the profile from a center line (seeTable 2 and Fig. 5). Despite its common usage, Ra does notprovide a truly accurate representation of a surface profile sinceany information regarding peak heights or valley depths can belost in its derivation. This insensitivity to surface te
46、xture isapparent in Fig. 6, which shows that quite different profiles canhave the same Ra value. The statistical significance of Ra isimproved by averaging the values obtained for each of the fivesampling lengths.8.3 RqThe root-mean-square value of all distances of themeasured profile away from the
47、center line, Rq, althoughsimilar in terms of its derivation to Ra, has a subtle butsignificant difference. The deviations of the peak heights andvalley depths from the midline appear as a squared term in Rq.That increases its sensitivity to high peaks or deep valleys. Thissensitivity can be useful,
48、but it should be noted that thepresence of a foreign body, for example, hair or a scratch in thesurface can have a significant influence on the value of Rq.8.4 RskSkewness, the distribution of peak heights andvalley depths provides valuable information about surfacetexture. A surface that has a rang
49、e of peak heights and valleydepths will have a bell-shaped probability distribution centeredon the mean. The dimensionless skewness parameter, Rsk,isused to quantify bias in the shape of this distribution. Theskewness of a perfectly random surface with a wide range ofpeak heights and valley depths is zero. If the surface has morevalleys than peaks then the distribution will skew away fromFIG. 3 50 % Reduction in Transmission CurveTABLE 1 Guide to Choosing Sampling Lengths for theMeasurement of Periodic ProfilesAMean profile elementwidth, RS
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