ASTM F2791-24

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Designation: F2791 − 15 F2791 − 24
Standard Guide for
Assessment of Surface Texture of Non-Porous Biomaterials
in Two Dimensions
This standard is issued under the fixed designation F2791; 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 describes some of the more common methods that are available for measuring the topographical features of a
surface and provides an overview of the parameters that are used to quantify them. Being able to reliably derive a set of parameters
that describe the texture of biomaterial surfaces is a key aspect in the manufacture of safe and effective implantable medical devices
that have the potential to trigger an adverse biological reaction in situ.
1.2 This guide is not intended to apply to porous structures with average pore dimensions in excess of approximately 50 nm 50 nm
(0.05 μm).
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 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.
1.5 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:
C813 Test Method for Hydrophobic Contamination on Glass by Contact Angle Measurement
F2312 Terminology Relating to Tissue Engineered Medical Products
F2450 Guide for Assessing Microstructure of Polymeric Scaffolds for Use in Tissue-Engineered Medical Products
F2664 Guide for Assessing the Attachment of Cells to Biomaterial Surfaces by Physical Methods
2.2 Other Standards:
ISO 3274 Geometrical Product Specifications (GPS)—Surface Texture: Profile Method—Nominal Characteristics of Contact
(Stylus) Instruments
ISO 4287 Geometrical Product Specifications (GPS)—Surface Texture: Profile Method—Terms, Definitions and Surface
Texture Parameters
This guide is under the jurisdiction of ASTM Committee F04 on Medical and Surgical Materials and Devices and is the direct responsibility of Subcommittee F04.42
on Biomaterials and Biomolecules for TEMPs.
Current edition approved May 1, 2015March 15, 2024. Published June 2015March 2024. Originally approved in 2009. Last previous edition approved in 20142015 as
F2791F2791 – 15.– 14. DOI: 10.1520/F2791-15. DOI: 10.1520/F2791-24.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. 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
F2791 − 24
ISO 4288 Geometrical Product Specifications (GPS)—Surface Texture: Profile Method—Rules and Procedures for the
Assessment of Surface Texture
ISO 5436-2 Geometrical Product Specifications (GPS)—Surface Texture: Profile Method; Measurement Standards—Part 2:
Software Measurement Standards
ISO 10993-19 Biological Evaluation of Medical Devices—Part 19: Physico-chemical, Morphological and Topographical
Characterization of Materials
ISO 12179 Geometrical Product Specifications (GPS)—Surface Texture: Profile Method—Calibration of Contact (Stylus)
Instruments
ISO 13565–1ISO 13565-1 Geometrical Product Specifications (GPS)—Surface Texture: Profile Method—Surfaces Having
Stratified Functional Properties; Filtering and General Measurement Conditions
ISO 19606 Fine Ceramics (Advanced Ceramics, Advanced Technical Ceramics)—Test Method for Surface Roughness of Fine
Ceramic Films by Atomic Force Microscopy
ISO 21920-1 Geometrical Product Specifications (GPS)—Surface Texture: Profile—Part 1: Indication of Surface Texture
ISO 21920-2 Geometrical Product Specifications (GPS)—Surface Texture: Profile—Part 2: Terms, Definitions and Surface
Texture Parameters
ISO 21920-3 Geometrical Product Specifications (GPS)—Surface Texture: Profile—Part 3: Specification Operators
ISO 25178-1 Geometrical Product Specifications (GPS)—Surface Texture: Areal—Part 1: Indication of Surface Texture
ISO 25178-2 Geometrical Product Specifications (GPS)—Surface Texture: Areal—Part 2: Terms, Definitions and Surface
Texture Parameters
ISO 25178-3 Geometrical Product Specifications (GPS)—Surface Texture: Areal—Part 3: Specification Operators
ISO 25178-6 Geometrical Product Specifications (GPS)—Surface Texture: Areal—Part 6: Classification of Methods for
Measuring Surface Texture
ISO 25178-70 Geometrical Product Specification (GPS)—Surface Texture: Areal—Part 70: Material Measures
ISO 25178-71 Geometrical Product Specifications (GPS)—Surface Texture: Areal—Part 71: Software Measurement Standards
ISO 25178-72 Geometrical Product Specifications (GPS)—Surface Texture: Areal—Part 72: XML File Format x3p
ISO 25178-73 Geometrical Product Specifications (GPS)—Surface Texture: Areal—Part 73: Terms and Definitions for Surface
Defects on Material Measures
ISO 25178-600 Geometrical Product Specifications (GPS)—Surface Texture: Areal—Part 600: Metrological Characteristics for
Areal Topography Measuring Methods
ISO 25178-601 Geometrical Product Specifications (GPS)—Surface Texture: Areal—Part 601: Nominal Characteristics of
Contact (Stylus) Instruments
ISO 25178-602 Geometrical Product Specifications (GPS)—Surface Texture: Areal—Part 602: Nominal Characteristics of
Non-Contact (Confocal Chromatic Probe) Instruments
ISO 25178-603 Geometrical Product Specifications (GPS)—Surface Texture: Areal—Part 603: Nominal Characteristics of
Non-Contact (Phase-Shifting Interferometric Microscopy) Instruments
ISO 25178-604 Geometrical Product Specifications (GPS)—Surface Texture: Areal—Part 604: Nominal Characteristics of
Non-Contact (Coherence Scanning Interferometry) Instruments
ISO 25178-605 Geometrical Product Specifications (GPS)—Surface Texture: Areal—Part 605: Nominal Characteristics of
Non-Contact (Point Autofocus Probe) Instruments
ISO 25178-606 Geometrical Product Specification (GPS)—Surface Texture: Areal—Part 606: Nominal Characteristics of
Non-Contact (Focus Variation) Instruments
ISO 25178-607 Geometrical Product Specifications (GPS)—Surface Texture: Areal—Part 607: Nominal Characteristics of
Non-Contact (Confocal Microscopy) Instruments
ISO 25178-700 Geometrical Product Specifications (GPS)—Surface Texture: Areal—Part 700: Calibration, Adjustment and
Verification of Areal Topography Measuring Instruments
ISO 25178-701 Geometrical Product Specifications (GPS)—Surface Texture: Areal—Part 701: Calibration and Measurement
Standards for Contact (Stylus) Instruments
3. Terminology
3.1 Definitions of Terms Specific to This Standard:Definitions:
3.1.1 biomaterial, n—any substance (other than a drug), synthetic or natural, that can be used as a system or part of a system that
treats, augments, or replaces any tissue, organ, or function of the body. F2664F2312
3.1.2 evaluation length, ln, n—length in the direction of the x-axis used to assessfor assessing the profile under evaluation.
3.1.2.1 Discussion—
The evaluation length may contain one or more sampling lengths. ISO 4287
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3.1.3 hydrophilic, adj—having a strong affinity for water; wettable.
3.1.3.1 Discussion—
Hydrophilic surfaces exhibit zero contact angles. C813
3.1.4 hydrophobic, adj—having little affinity for water; nonwettable.
3.1.4.1 Discussion—
Hydrophobic surfaces exhibit contact angles appreciably greater than zero: generally greater than 45° for the advancing angle.
C813
3.1.5 implant, n—a substancein medicine, or object that is put in the body as a prosthesis, or for treatment or diagnosis.an object,
structure, or device intended to reside within the body for diagnostic, prosthetic, or other therapeutic purposes. F2664
3.1.6 lay, n—the direction of the predominant surface pattern. ISO 13565–1
3.1.6 primary profile, n—thetotal profile after application of the short wavelength filters. ISO 3274
3.1.7 profile peak, n—an outwardly directed (from the material to the surrounding medium) portion of the assessed profile
connecting two adjacent points of the intersection of the profile with the x-axis. ISO 4287
3.1.8 profile valley, n—an inwardly directed (from surrounding medium to material) portion of the assessed profile connecting two
adjacent points of the intersection of the assessed profile with the x-axis. ISO 4287
3.1.9 real surface, n—surface limiting theof a workpiece, body and separating it a set of features which physically exist and
separate the entire workpiece from the surrounding medium. ISO 4287ISO 25178-600
3.1.10 sampling length, lr, n—length in the direction of the x-axis used for identifying the irregularities characterizing the profile
under evaluation. ISO 4287
3.1.11 scaffold, n—a support, delivery vehicle or metricvehicle, or matrix for facilitating the migration, binding, or transport of
cells or bioactive molecules used to replace, repair, or regenerate tissues. F2450F2312
3.1.12 surface profile, n—profile that results from the intersection of the real surface by a specified plane. ISO 4287
3.1.12.1 Discussion—
In practice, it is usual to choose a plane with a normal that nominally lies parallel to the real surface and in a suitable direction.
ISO 4287
NOTE 1—The surface shown in (A) has no directionality or lay, therefore, profiles can be oriented at any angle. Profiles (dashed line arrow) are drawn
perpendicular to the lay (solid line arrow) in surfaces that have directionality (B).
FIG. 1 Profile Orientation and Surface Features
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3.1.13 surface texture, n—irregularities on a surface (peaks and valleys) produced by the forming process.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 lay, n—the direction of the predominant surface pattern.
4. Significance and Use
4.1 The term “surface texture” is used to describe the local deviations of a surface from an ideal shape. Surface texture usually
consists of long wavelength repetitive features that occur as results of chatter, vibration, or heat treatments during the manufacture
of implants. Short wavelength features superimposed on the long wavelength features of the surface, which may arise from
polishing or etching of the implant, are referred to as roughness.
4.2 This guide provides an overview of techniques that are available for measuring the surface in terms of Cartesian coordinates
and the parameters used to describe surface texture. It is important to appreciate that it is not possible to measure surface texture
per se, but to derive values for parameters that can be used to describe it. ISO has published a series of standards on surface texture
measurements that may be consulted for more information (ISO 3274, ISO 4287, ISO 4288, ISO 5436-2, ISO 10993-19, ISO
12179, ISO 13565-1, ISO 19606, ISO 21920-1, ISO 21920-2, ISO 21920-3, ISO 25178-1, ISO 25178-2, ISO 25178-3, ISO
25178-6, ISO 25178-70, ISO 25178-71, ISO 25178-72, ISO 25178-73, ISO 25178-600, ISO 25178-601, ISO 25178-602, ISO
25178-603, ISO 25178-604, ISO 25178-605, ISO 25178-606, ISO 25178-607, ISO 25178-700, ISO 25178-701).
5. The Relationship Between Surface Texture, Surface Chemistry, Surface Energy, and Biocompatibility
5.1 The biocompatibility of materials is influenced by many factors such as size, shape, material bulk, and surface chemical
composition, surface energy, and surface topography. topography (ISO 10993-19). Changing any one of these related
characteristics of a biocompatible material can have a significant effect on cell behavior. The response of a cell to a biomaterial
can be assessed by measuring the adhesive strength between it and the underlying surface, monitoring changes in its shape or in
the expression of biomarkers.
5.2 The chemical species present on a surface can be mapped in detail using surface sensitive analysis techniques (for example,
X-ray photoelectron spectroscopy where the penetration depth is 10 nm or below (1)). The chemical species present on the surface
together with the surface topography determine how hydrophilic the surface is. Measuring the contact angle between the surface
and a fluid, usually water, can assess the degree of hydrophilicity of a surface. Care should be taken when comparing contact angle
measurements made on different surfaces, as the relative contributions from the surface chemistry and texture are unlikely to be
the same.
6. Surfaces and Surface Profiles
6.1 Conventionally, surfaces are described in Cartesian coordinates where the x-axis is defined as being perpendicular to the lay
direction. The y-axis is in-plane and is perpendicular to the x-axis direction. The z-axis is out of plane. The profile of a surface that
has a uniform, non-directional texture can be measured at any in-plane orientation (see Fig. 1(A)); however, several profiles at
different orientations should be measured to find the maximum amplitude (see Fig. 1(A)). For patterned surfaces that have periodic
features, a lay, the orientation of the profile is at right angles to it (see Fig. 1(B)).
6.2 The measured surface is composed of three components: form, waviness, and roughness. The form corresponds to the
underlying shape and tilt of the surface with respect to the measuring platform. The software packages used for surface texture
analysis all have a methodology for removing the form from the surface. The “corrected” surface can then be used to obtain a
2-D2D profile that describes the surface texture. This profile after removal of form is defined according to ISO 3274 as the primary
profile. The stages involved in the analysis of the measured profile through primary profile to the roughness profile are shown in
Fig. 2.
7. Filtering and the Cut-Off Wavelength
7.1 Surface data can be filtered to remove unwanted noise or to remove texture information at unwanted wavelengths. Filters are
The boldface numbers in parentheses refer to a list of references at the end of this standard.
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FIG. 2 Summary of Stages Involved in Analysis of Measured Profile to Obtain a Roughness Profile
classified according to the spatial periodicity that they allow to pass through; low-pass filters admit long wavelengths and reject
short ones; high-pass filters do the opposite. Band-pass filters, as the name implies, allow a limited range of wavelengths to pass.
In practice, using filters can create problems in deciding how much of the noise in the measurements is “real” and how much can
be attributed to the surface. It should be noted that some aspects of the surface are not faithfully reproduced due to limitations of
the measurement method, for example, an inability to track the sides of steep valleys that is in essence a form of filtering. This
topic is further discussed in Section 11.
7.2 Filters used in surface texture measurements do not have a sharp cut-off in spatial frequency above or below which information
is rejected. This gradual attenuation of high or low spatial frequency data helps avoid distortion of the measurements that can occur
when strong features are close to the filtration limits. The point on the transmission curve at which the transmitted signal is reduced
to 50 % is referred to as the cut-off wavelength, λc, of the filter (Fig. 3). For measurements made using a stylus instrument (Section
11), the choice of λc depends on the sampling frequency and the speed at which the stylus moves over the surface. For example,
–1
measurements made at intervals of 0.01 mm from a device moving at 1 mms will generate data at a frequency of 100 Hz.
Increasing the sampling interval to 0.1 mm will reduce the frequency at which data are obtained to 10 Hz. A high-pass filter that
suppresses all frequencies below 10 Hz effectively removes any surface irregularities larger than 0.1 mm spacing from the data.
Hence, filters can be used to bias the experimental data towards detecting profile (surface texture after applying a low-pass to filter
the data), waviness (after applying a band-pass filter), and roughness (after applying a high-pass filter). Measurement conditions
are set for filters according to the respective values of the sampling interval, measurement speed, and filtration limits, according
to ISO 3274.
7.3 ISO 4287 specifies that 2D roughness parameters need to be determined over five sequential sampling lengths, lr, unless
otherwise specified. This grouping of five serial sampling lengths is referred to as the evaluation length, ln. The sampling length
varies according to the length scale of the texture being assessed; larger features require a long sampling length. Guidance as to
which sampling length to use for a given range of feature sizes is shown in Table 1.
ISO 4287 specifies that 2-D roughness parameters need to be determined over five sequential sampling lengths, lr, unless
otherwise specified. This grouping of five serial sampling lengths is referred to as the evaluation length, ln. The sampling length
varies according to the length scale of the texture being assessed; larger features require a long sampling length. Guidance as to
which sampling length to use for a given range of feature sizes is shown in Table 1. It may be necessary to perform one or more
F2791 − 24
FIG. 3 50 % Reduction in Transmission Curve
TABLE 1 Guide to Choosing Sampling Lengths for the
A
Measurement of Periodic Profiles
Mean profile element Sampling length,
width, RSm (μm) lr (μm)
13 < RSm # 40 80
40 < RSm # 130 250
130 < RSm # 400 800
400 < RSm # 1300 2500
1300 < RSm # 4000 8000
A
Based on ISO 4288. The evaluation length is usually taken to be five times the
sampling length.
iterations to identify the best value for lr. This can be achieved by calculating the mean width of a profile element, RSm (see Fig.
4), from a measured profile where the value for lr is based on a best guess. This initial iteration will enable a new value for RSm
to be determined and that leads to a potential revision of lr according to Table 1.
NOTE 1—The sum of each peak and adjacent valley, Xs is RSm.
i
FIG. 4 Mean Width of Profile Elements Over the Evaluation Length
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TABLE 2 A Summary of Commonly Used Parameters for Quantifying 2-D2D Roughness Profiles
Type of
Parameter Definition
Parameter
Amplitude Ra Arithmetic mean deviation of the absolute ordinate value from a mean line.
(Average
Rq Root-mean-squared value of the deviation of ordinate values from a midline.
of cordinates) Rsk A measure of the skewness in the distribution of peaks and valleys across a surface.
Rku A measure of the similarity of the distribution of measured peaks and valleys to a Gaussian distribution (kurtosis).
Amplitude Rp Maximum profile height above a mean line.
(Peak and Rv Maximum profile depth below a mean line.
valley) Rz Difference between Rp and Rv.
Rc The mean value of the profile element widths within a sampling length.
Rt The total height of profile.
Spatial RSm The mean value of the profile element widths within a sampling length.
Hybrid RΔq The root mean square slope, dz/dx, over the length of the profile at a location y on the surface.
8. Quantification of Surface Profiles
8.1 Parameters that are used to characterize 2-D2D surface profiles are grouped as:
8.1.1 Amplitude parameters, which are measures of variations in profile height. These parameters are split into two subclasses:
averaging parameters, and peak and valley parameters;
8.1.2 Spatial
...