1、Designation: F 2791 09Standard Guide forAssessment of Surface Texture of Non-Porous Biomaterialsin Two Dimensions1This standard is issued under the fixed designation F 2791; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、of 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
3、 a 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 trig
4、ger 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
5、This 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 Docum
6、ents2.1 ASTM Standards:2C 813 Test Method for Hydrophobic Contamination onGlass by Contact Angle MeasurementF 2312 Terminology Relating to Tissue Engineered MedicalProductsF 2450 Guide for Assessing Microstructure of PolymericScaffolds for Use in Tissue Engineered Medical ProductsF 2664 Guide for As
7、sessing 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: Pro
8、file MethodTerms, 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
9、-fied Functional Properties; Filtering and General Measure-ment Conditions3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 biocompatible, adja material may be consideredbiocompatible if the materials perform with an appropriate hostresponse in a specific application. F 23123.1.
10、2 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 tissue, organ, orfunction of the body. F 26643.1.3 evaluation length, ln, nlength in the direction of thex-axis used to assess the profile un
11、der evaluation.3.1.3.1 DiscussionThe evaluation length may contain oneor more sampling lengths. ISO 42873.1.4 hydrophilic, adjhaving a strong affinity for water;wettable.3.1.4.1 DiscussionHydrophilic surfaces exhibit zero con-tact angles. C 8133.1.5 hydrophobic, adjhaving little affinity for water;n
12、onwettable.3.1.5.1 DiscussionHydrophobic surfaces exhibit contactangles appreciably greater than zero: generally greater than 45for the advancing angle. C 8133.1.6 implant, na substance or object that is put in thebody as a prosthesis, or for treatment or diagnosis. F 26643.1.7 lay, nthe direction o
13、f the predominant surface pat-tern. ISO 1356511This guide is under the jurisdiction of ASTM Committee F04 on Medical andSurgical Materials and Devices and is the direct responsibility of SubcommitteeF04.42 on Biomaterials and Biomolecules for TEMPs.Current edition approved Aug. 1, 2009. Published Se
14、ptember 2009.2For 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 ASTM website.3Available from American National Standards Inst
15、itute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.8 primary profile, nthe profile after application of theshort wavelength filters. ISO 32743.1.9 profil
16、e peak, nan outwardly directed (from thematerial to the surrounding medium) portion of the assessedprofile connecting two adjacent points of the intersection of theprofile with the x-axis. ISO 42873.1.10 profile valley, nan inwardly directed (from sur-rounding medium to material) portion of the asse
17、ssed profileconnecting two adjacent points of the intersection of theassessed profile with the x-axis. ISO 42873.1.11 real surface, nsurface limiting the body and sepa-rating it from the surrounding medium. ISO 42873.1.12 sampling length, lr, nlength in the direction of thex-axis used for identifyin
18、g the irregularities characterizing theprofile under evaluation. ISO 42873.1.13 scaffold, na support, delivery vehicle or metric forfacilitating the migration, binding, or transport of cells orbioactive molecules used to replace, repair, or regeneratetissues. F 24503.1.14 surface profile, nprofile t
19、hat results from the inter-section of the real surface by a specified plane.3.1.14.1 DiscussionIn practice, it is usual to choose aplane with a normal that nominally lies parallel to the realsurface and in a suitable direction. ISO 42874. Significance and Use4.1 The term “surface texture” is used to
20、 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-imposed on the long wavelength feat
21、ures 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 surface tex-ture. It is important t
22、o 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 materials is influenced by manyfact
23、ors 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 biomaterial can be assessed bymeas
24、uring 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 photoelectron spectroscopy where the
25、penetration 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 hydrophilicity of a surface. Careshou
26、ld 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-ordinates where the x-axis is def
27、ined 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); however,several profiles at
28、different orientations should be measured tofind the maximum amplitude (see Fig. 1(A). For patternedsurfaces that have periodic features, a lay, the orientation of theprofile is at right angles to it (see Fig. 1(B).6.2 The measured surface is composed of three components:form, waviness and roughness
29、. The form corresponds to the4The boldface numbers in parentheses refer to a list of references at the end ofthis standard.NOTEThe surface shown in (A) has no directionality or lay, therefore profiles can be oriented at any angle. Profiles (dashed line arrow) are drawnperpendicular to the lay (solid
30、 line arrow) in surfaces that have directionality (B).FIG. 1 Profile Orientation and Surface FeaturesF2791092underlying shape and tilt of the surface with respect to themeasuring platform. The software packages used for surfacetexture analysis all have a methodology for removing the formfrom the sur
31、face. 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 primary profile to the roughnessprofi
32、le 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; low-pass filters admit long wa
33、velengthsand 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 how much can be attributed to the
34、 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 in Section 11.7.2 Filters used in
35、 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 close to thefiltration limits.
36、The point on the transmission curve at whichthe transmitted signal is reduced to 50 % is referred to as thecut-off wavelength, lc, of the filter, Fig. 3. For measurementsmade using a stylus instrument (Section 11), the choice of lcdepends on the sampling frequency and the speed at which thestylus mo
37、ves 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 filter that suppresses allfrequenci
38、es 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 applying a band-pass filter), androug
39、hness (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 3274.7.3 ISO 4287 specifies that 2-D roughness parameters needto be determined over five sequentia
40、l sampling lengths, lr,unless otherwise specified. This grouping of five serial sam-pling lengths is referred to as the evaluation length, ln. Thesampling length varies according to the length scale of thetexture being assessed; larger features require a long samplinglength. Guidance as to which sam
41、pling length to use for a givenFIG. 2 Summary of Stages Involved in Analysis of Measured Profile to Obtain a Roughness ProfileF2791093range of feature sizes is shown in Table 1. It may be necessaryto perform one or more iterations to identify the best value forlr. This can be achieved by calculating
42、 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. Quantification of Surface Profiles
43、8.1 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 Spatial parameters, which descri
44、be 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 absoluteordinate values, Z(x), of the profile
45、 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 texture isapparent in Fig. 6, which
46、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 center line, Rq, althoughsimilar i
47、n 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, but it should be noted that thepres
48、ence 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 range of peak heights and valleydepths
49、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 fromthe ideal distribution producing negative values of skewness.The converse will be true for a surface that has more peaks thanvalleys.8.5 RkuKurtosis is a statistical measure of the sharpnessof a
