1、Designation: F 1854 09Standard Test Method forStereological Evaluation of Porous Coatings on MedicalImplants1This standard is issued under the fixed designation F 1854; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of la
2、st 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 test method covers stereological test methods forcharacterizing the coating thickness, void content, and meaninterc
3、ept length of various porous coatings adhering to nonpo-rous substrates.1.2 A method to measure void content and intercept lengthat distinct levels (“tissue interface gradients”) through theporous coating thickness is outlined in 9.4.1.3 The alternate sample orientation method in 8.2 is notsuitable
4、for the tissue interface gradients method in 9.4.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibili
5、ty 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 Documents2.1 ASTM Standards:2E3 Guide for Preparation of Metallographic SpecimensE 883 Guide for ReflectedLight Photomicrography
6、3. Terminology3.1 Definitions:3.1.1 fieldthe portion of image of a part of the workingsurface upon which measurements are performed.3.1.2 interceptthe point on a measurement grid line pro-jected on a field where the line crosses from solid to void orvice versa.3.1.3 measurement grid linesa evenly sp
7、aced grid ofparallel lines all of the same length.3.1.4 porous coatingcoating on an implant deliberatelyapplied to contain void regions with the intent of enhancing thefixation of the implant.3.1.5 substratethe solid material to which the porouscoating is attached.3.1.6 substrate interfacethe region
8、 where the porous coat-ing is attached to the substrate.3.1.7 working surfacethe ground and polished face of themetallographic mount where the measurements are made.3.1.8 tissue interfacethe surface of the coating that shallhave first contact with biological tissue (that is, the top of thecoating).4
9、. Summary of Test Method4.1 Mean Coating ThicknessEvenly spaced parallel gridlines are oriented perpendicular to the coating-substrate inter-face. For each gridline, the distance from the coating-substrateinterface to the last contact with the porous coating material ismeasured as the coating thickn
10、ess. The average of all of thecoating thickness measurements obtained on a working surfaceis the mean coating thickness for that working surface.4.2 Volume Percent VoidA regular grid of points issuperimposed on a field from the working surface. Thepercentage of points that are in contact with void a
11、reas in thecoating correlates with the volume percent of void present.4.3 Mean Void Intercept LengthMeasurement grid linesare oriented parallel to the substrate interface. The averagelength of the line segments overlaying the void space is themean void intercept length. This is a representative meas
12、ure ofthe scale, or size, of the pores in a porous structure.4.4 Tissue Interface GradientsThe volume percent voidand the mean void intercept length are characterized in three200-m-thick zones below the tissue interface.1This test method is under the jurisdiction ofASTM Committee F04 on Medicaland S
13、urgical Materials and Devices and is the direct responsibility of SubcommitteeF04.15 on Material Test Methods.Current edition approved June 15, 2009. Published August 2009. Originallyapproved in 1998. Last previous edition approved in 2001 as F 1854 01.2For referenced ASTM standards, visit the ASTM
14、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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United
15、States.5. Significance and Use5.1 All of these test methods are recommended for elemen-tary quantification of the morphological properties of porouscoatings bonded to solid substrates.5.2 These test methods may be useful for comparativeevaluations of different coatings or different lots of the samec
16、oating.5.3 With the exception of using the alternate mountingmethod, all the methods should be performed on the sameworking surfaces. The alternate mounting method can only beused for 9.2 and 9.3.5.4 Astatistical estimate can be made of the distributions ofthe mean coating thickness and the volume p
17、ercent void. Noestimate can be made of the distribution of intercept lengths.5.5 There are limits to the accurate characterization ofporosity, depending on spacing between the lines in the linegrid (or points in the point grid) and the individual andcumulative fields used for the measurements. Incre
18、asing thesize of the fields, increasing the number of fields, or decreasingthe grid spacing will increase the accuracy of the measure-ments obtained.5.6 This method is not suitable for ceramic coatings forwhich accurate coating cross sections cannot be producedusing metallographic techniques.5.7 Thi
19、s test method does not address characterization ofcoatings having a thickness of less than 300 m.6. Apparatus6.1 The procedures outlined in this test method can beperformed manually or using digital image analysis techniques.6.2 Microscope, or other suitable device with a viewingscreen, photomicrogr
20、aphic capability, or digital image capturecapability should be used to image the sample fields of interestfor these test methods.6.3 For manual measurement, a transparent sheet, withmeasurement grid lines or points is superimposed on theviewing screen or photomicrograph for the measurements. Theline
21、 grid (or point grid) and should consist of at least fiveuniformly spaced, parallel lines (or rows).7. Metallography7.1 The procedures outlined in this test method for charac-terizing porous coatings require the preparation of metallo-graphic sections. Good metallographic preparation techniques,in a
22、ccordance with Practice E3and Guide E 883, shall be usedto prevent deformation of the surface of the section or creationof any other artifacts that will alter the morphology of themetallographic section.An example of an unacceptable artifactwould be the absence of a portion of the porous coating, ca
23、usedby its removal, thereby creating an artificial void area.7.2 Care must be taken to ensure that the working surface isperpendicular to the substrate interface. When using thealternative mounting method shown in 8.1.2, extreme caremust be taken to keep the substrate interface parallel to the final
24、working surface.8. Sample Working Surfaces and Fields8.1 Sample Orientation:8.1.1 Normal Section Orientation:8.1.1.1 For accurate coating thickness measurements, theorientation of sample working surfaces should be approxi-mately perpendicular to the plane of the substrate.8.1.1.2 If the angle betwee
25、n the tangent to the coating-substrate interface at one edge of a field and the tangent to thesubstrate interface at the opposite edge of the field is greaterthan 2, the substrate curvature is too large.8.1.1.3 There is a practical limit to the magnification thatcan be used for measurement of the vo
26、id content and meanintercept length. As magnification is increased, the number offields should be increased to obtain a representative sample. Ifthere are too few intercepts in the individual fields, theaccuracy of the measurement could decrease.8.1.2 Alternative Orientation Method:8.1.2.1 An altern
27、ate orientation may be used for the volumepercent void and mean intercept length measurements. Thesection should be prepared such that the working surface isparallel to the substrate interface and the measurements shouldbe taken at a fixed distance from the substrate interface. It isrecommended that
28、 the measurements be made at about 50 % ofthe mean coating thickness.8.1.2.2 At least one additional section immediately adjacentto the fields used on the working surface shall also be preparedperpendicular to the working surface. This shall confirm thatthe substrate interface is parallel to the wor
29、king surface andallow measurement of the distance from the working surface tothe substrate interface.8.1.2.3 This test method is not suitable for substrate inter-faces with a radius of curvature less than 25 mm.8.1.2.4 Since this test method also requires more aggressiveporous surface removal to rea
30、ch 50 % of the mean coatingthickness, it may be more susceptible to creation of metallo-graphic artifacts. Care should be exercised to ensure that themetallographic sections that are used are free of artifacts.8.2 Field Parameters:8.2.1 Resolution:8.2.1.1 The magnification used for the field should
31、be highenough to resolve all the features that need to be measured.8.2.1.2 For most porous coatings, the magnification shouldbe high enough that features as small as 5 m can be easilydistinguished. If digital imaging is used, the pixel size shouldbe less than or equal to 5 m.8.2.2 Field Dimensions:8
32、.2.2.1 The field height must include the full thickness ofthe porous coating for mean coating thickness (9.1).8.2.2.2 A good rule of thumb for an accurate measurementof mean void intercept length is that the minimum field widthshould be greater than or equal to 53 the resulting mean voidintercept le
33、ngth. For example, a mean void intercept lengthvalue of 200 m should have a measurement field width of atleast 1000 m.8.2.2.3 It is possible to measure the mean void interceptlength in a field using a series of shorter non-overlapping gridlines. This does not change the requirement for the number of
34、fields required for the calculation. Care should be exercisedusing multiple short lines in a single field, because it may bepossible to make the grid lines so short that the accuracy of theresult is affected.F18540928.2.2.4 If the magnification used produces an image with aheight or width smaller th
35、an that which is required, multipleimages may be carefully stitched together to produce a field ofsufficient height and width.9. Procedure9.1 Mean Coating Thickness:9.1.1 An array of equally spaced parallel gridlines should besuperimposed on the field perpendicular to the substrateinterface, as show
36、n in Fig. 1. The gridlines should be spaced nomore than 100 m apart.Appendix X2 includes two typical setsof gridlines each with ten equally spaced parallel lines.9.1.2 At each gridline, the distance from the substrateinterface to the last contact with a solid coating feature ismeasured. A measuremen
37、t is only valid if the gridline isoriented 90 6 2 to the substrate interface.9.1.3 Coating thickness measurements should be obtainedover a continuous linear distance of at least 10 mm of poroussurface with no overlap between measurement sites.9.1.4 The average of all the measurements is the meancoat
38、ing thickness for that working surface. The standarddeviation estimator and the 95 % confidence interval should becalculated for each working surface. The equations for calcu-lating these values are as follows:T51M 3 n(i51nti(1)where:ti= the individual magnified thickness line length,n = the number
39、of thickness measurements,M = the magnification, andT= the mean coating thickness.S51n13(i51ntiM T# (2)where:S= the standard deviation estimator, andCI = the confidence interval.CI 5 23S=n(3)9.2 Volume Percent Void:9.2.1 For this measurement, the field should be entirelycontained between the tissue
40、interface (see 9.4.1) and thesubstrate interface.9.2.2 An array containing at least 100 regularly spacedpoints should be superimposed on the field, as shown in Fig. 2.The points should be spaced no more than 50 m apart. If thevoid areas form a regular or periodic pattern, the use of a gridhaving a s
41、imilar pattern should be avoided. The height of thearray should be at least half the distance from the tissueinterface to the substrate interface, thereby producing a valuerepresentative of an average for the entire coating thickness.Appendix X2 includes two typical arrays each with at least 100regu
42、larly spaced points.9.2.3 The number of points overlying void areas (Pa) on theworking surface shall be counted and recorded.When using themanual method, any points falling on a boundary between avoid area and solid features should be counted as one half.Anyquestionable points should be counted as o
43、ne half.9.2.4 The number of contact points in void area (Pa),divided by the total number of points on the grid (PT) times 100gives the percentage of grid points on the void for that field.This should be calculated for each grid application.Pv5PaPT3 100 (4)where:Pa= the total number of counted points
44、,PT= the total number of grid points, andPv= the volume percent void.9.2.5 Volume percent voids should be measured over anarea of the working surface totaling at least 15 mm2with nopart of that area being measured more than once. If the coatingthickness is below 500 m, at least 3 cm of coating lengt
45、h mustbe used for the void measurement.9.2.6 Fields to be analyzed should include as much of thecoating thickness as possible.9.2.7 These measurements may also be made with anappropriate digital image analysis system. This can be done byconsidering each pixel as a regularly spaced point in the array
46、.The volume percent void for each field should be the ratio ofNOTEThe solid line is the measured distance.FIG. 1 Illustration of Coating Thickness MeasurementF1854093the number of pixels representing void space to the totalnumber of pixels in the image of the field.9.2.8 The average percentage of th
47、e grid points on the voidsprovides an unbiased statistical estimator for the void volumepercentage in the three dimensional structure. The mean voidpercentage (Pv) for that working surface, the standard devia-tion estimator (S) and the 95 % confidence interval (CI) shouldbe calculated for each worki
48、ng surface. The equations forcalculating these values are as follows:Pv51n(i51nPvi(5)S51n 13(i51nPvi Pv# (6)CI 5 23S=n(7)9.2.9 The volume percent void estimate is given by thefollowing relationship:Vv5 Pv(8)9.3 Mean Void Intercept Length:9.3.1 For this measurement, the field should be entirelycontai
49、ned between the tissue interface (see 9.4.1) and thesubstrate interface.9.3.2 An array of equally spaced parallel gridlines should besuperimposed on the field parallel to the substrate interface, asshown in Fig. 3. The height of the array should be at least halfthe distance from the tissue interface to the substrate interface,thereby producing a value representative of an average for theentire coating thickness. The gridlines should be spaced nomore than 100 m apart.Appendix X2 includes two typical setsof gridlines each with ten equally
