BS-ISO-5834-4-2005.pdf

BRITISH STANDARD BS ISO 5834-4:2005 Implants for surgery Ultra-high molecular weight polyethylene Part 4: Oxidation index measurement method ICS 11.040.40 ? Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 02:52:56 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 5834-4:2005 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 28 October 2005 © BSI 28 October 2005 ISBN 0 580 46381 8 National foreword This British Standard reproduces verbatim ISO 5834-4:2005 and implements it as the UK national standard. The UK participation in its preparation was entrusted by Technical Committee CH/150, Implants for surgery, to Subcommittee CH/150/1, Materials (for surgical implants), which has the responsibility to: A list of organizations represented on this subcommittee can be obtained on request to its secretary. Cross-references The British Standards which implement international publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the ISO title page, pages ii to iv, pages 1 to 7 and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. DateComments Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 02:52:56 GMT+00:00 2006, Uncontrolled Copy, (c) BSI Reference number ISO 5834-4:2005(E) INTERNATIONAL STANDARD ISO 5834-4 First edition 2005-05-01 Implants for surgery Ultra-high molecular weight polyethylene Part 4: Oxidation index measurement method Implants chirurgicaux Polyéthylène à très haute masse moléculaire Partie 4: Méthode de mesurage de l'indice d'oxydation BS ISO 5834-4:2005 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 02:52:56 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 02:52:56 GMT+00:00 2006, Uncontrolled Copy, (c) BSI iii Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 5834-4 was prepared by Technical Committee ISO/TC 150, Implants for surgery, Subcommittee SC 1, Materials. ISO 5834 consists of the following parts, under the general title Implants for surgery Ultra-high molecular weight polyethylene: Part 1: Powder form Part 2: Moulded forms Part 3: Accelerated ageing methods Part 4: Oxidation index measurement method Part 5: Morphology assessment method BS ISO 5834-4:2005 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 02:52:56 GMT+00:00 2006, Uncontrolled Copy, (c) BSI iv Introduction This part of ISO 5834 describes a method for the measurement of the relative extent of oxidation present in ultra-high molecular weight polyethylene (UHMWPE) intended for use in surgical implants. The material is analysed by infrared spectroscopy. The intensity of the carbonyl absorptions (C=O) centred near 1 720 cm1 is related to the amount of chemically bound oxygen present in the material. Other forms of chemically bound oxygen (R1OR2, R1OOR2, ROH, etc.) are not detected by this method. Although this method might give the investigator a means to compare the relative extent of carbonyl oxidation present in various UHMWPE samples, it is recognized that other forms of chemically bound oxygen can be important contributors to characteristics of these materials. The applicability of the infrared method has been demonstrated by many literature reports. This particular method, using the intensity (area) of the C-H absorption centred near 1 370 cm1 to normalize for the samples thickness, has been validated by an interlaboratory study (ILS). BS ISO 5834-4:2005 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 02:52:56 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 1 Implants for surgery Ultra-high molecular weight polyethylene Part 4: Oxidation index measurement method 1 Scope This part of ISO 5834 specifies a method for the measurement of the relative extent of oxidation present in ultra-high molecular weight polyethylene (UHMWPE). It is applicable to ultra-high molecular weight polyethylene (UHMWPE) intended for use in surgical implants. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 5834-2, Implants for surgery Ultra-high molecular weight polyethylene Part 2: Moulded forms ISO 11542-1, Plastics Ultra-high-molecular-weight polyethylene (PE-UHMW) moulding and extrusion materials Part 1: Designation system and basis for specifications ISO 11542-2, Plastics Ultra-high-molecular-weight polyethylene (PE-UHMW) moulding and extrusion materials Part 2: Preparation of test specimens and determination of properties 3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO 11542-1 and ISO 11542-2 and the following apply. 3.1 aperture size La length and width of a rectangular aperture, or the diameter of a circular aperture used by an infrared spectrometer to make spectral measurements 3.2 bulk oxidation index Iox,b sample mean of the oxidation indices collected over a range of about 1,5 mm near the centre of the samples oxidation index profile NOTE Typically this is a plateau region with the smallest oxidation indices. For samples less than about 8 mm to 10 mm thick, this central region might display the samples highest oxidation indices, depending on its state of oxidation. BS ISO 5834-4:2005 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 02:52:56 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 2 3.3 depth locator dl measurement of the mean distance from the articular surface, or surface of interest, from which a spectrum was collected and a corresponding Iox calculated 3.4 increment size Li distance between two adjacent locations on a test film where sequential infrared spectra are collected NOTE This distance is typically a constant for a given test specimen. 3.5 normalization peak area Anorm total area of the normalization peak(s) between 1 330 cm1 and 1 396 cm1 NOTE This area is computed as the area between the baseline and the spectral trace, as shown in Figure 1. 3.6 oxidation incorporation of oxygen into another molecule (e.g. UHMWPE) by means of a chemical covalent bond 3.7 oxidation index Iox ratio of the area of the absorption peak(s) between 1 650 cm1 and 1 850 cm1 (Aox) to the area of the absorption peak(s) between 1 330 cm1 and 1 396 cm1 (Anorm) See Figure 1. 3.8 oxidation index profile graphical representation of variation of the samples oxidation index with distance from its articular surface or the surface of interest NOTE This is a plot of Iox against dl. Typically the graph will show the profile through the entire thickness of the sample. 3.9 oxidation peak area Aox total area of the absorption peak(s) between 1 650 cm1 and 1 850 cm1 NOTE This area is computed as the area between the baseline and the spectral trace, as shown in Figure 1. 3.10 surface oxidation index Iox,s sample mean of the oxidation indices from the samples articular surface, or the surface of interest, to a depth of 3 mm subsurface 4 Test articles The test articles shall be made from UHMWPE moulded material and classified as Type 1, Type 2 or Type 3 in accordance with ISO 5834-2. NOTE The UHMWPE finished products for this application are not equipped with light stabilizers and therefore need to be protected against UV influence. BS ISO 5834-4:2005 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 02:52:56 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 3 5 Materials and apparatus 5.1 Materials The test articles for oxidation index measurements shall be made from UHMWPE moulded forms complying with the requirements of ISO 5834-2. 5.2 Apparatus 5.2.1 Infrared spectrometer, calibrated, capable of recording a transmission absorption spectrum over the range of about 1 200 cm1 to about 2 000 cm1, using 0,15 mm to 0,25 mm thick films at a resolution of 4 cm1 and an aperture of about 0,2 mm × 0,2 mm. An increment size of 0,2 mm is recommended. Other modes of collection i.e. percent reflection, attenuated total reflection (ATR), etc., and aperture and increment sizes may be used to generate the samples absorption spectrum provided they can be demonstrated to produce equivalent results. Too large an aperture can result in a loss of profile accuracy. When a Fourier transform infrared (FTIR) spectrometer is used, a minimum of 32 scans shall be collected per spectrum. The FTIR instrument and sample compartment should be purged with a moisture- and carbon- dioxide-free inert gas (e.g. nitrogen, helium, or argon) to minimize spectral interference from these components. 5.2.2 Specimen holder, consisting of equipment capable of accurately positioning the sample under the aperture. 5.2.3 Microtome, consisting of equipment capable of producing 0,15 mm to 0,25 mm thick slices (films) of a sample perpendicular to the articular surface or the surface of interest. 6 Significance and use The methods described in this part of ISO 5834 may be used to measure the oxidation indices of UHMWPE components under real-time conditions such as shelf ageing and after implantation and accelerated oxidative challenges. 7 Procedure 7.1 Preparation of test specimens Using a microtome, or other appropriate device, prepare a thin slice of the sample 0,15 mm to 0,25 mm thick. The slice shall typically be taken near the centre of the samples articular surface or the surface of interest. The orientation of the slice shall typically be perpendicular to the articular surface or the surface of interest. 7.2 Configuration of test specimen in the spectrometer The test film (slice) shall be first configured in the spectrometer (after an appropriate background spectrum has been collected) so that the aperture is positioned over the first 0,2 mm of the film starting at the articular surface. Subsequent spectra shall be collected sequentially at about 0,2 mm increments from the articular surface across the width of the film to the opposite surface. Larger increment sizes may be used, however too large an increment size can result in a loss of profile accuracy. 7.3 Preparation of the infrared spectrometer Prepare the infrared spectrometer for collection of a transmission absorption spectrum from a thin film of the UHMWPE sample, according to the manufacturers recommendations and the conditions described in 7.1. Collect the sequence of spectra according to 7.2. BS ISO 5834-4:2005 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 02:52:56 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 4 8 Calculations 8.1 General The results obtained from the following calculations can be useful for describing the oxidation characteristics of a sample or comparing the oxidation characteristics of one sample with another. 8.2 Oxidation peak area For each absorbance spectrum, calculate the total area of the peak absorptions between 1 650 cm1 and 1 850 cm1 (Figure 1, Aox). This is the area below the samples absorption curve and above the straight baseline drawn between the same starting and ending points, namely: 1 650 cm1 and 1 850 cm1. 8.3 Normalization peak area For each absorbance spectrum, calculate the total area of the peak absorptions between 1 330 cm1 and 1 396 cm1 (Figure 1, Anorm). This is the area below the samples absorption curve and above the straight baseline drawn between the same starting and ending points, namely: 1 330 cm1 and 1 396 cm1. 8.4 Oxidation index For each absorbance spectrum, calculate its Iox by dividing the area of its oxidation peak (8.1) by the area of its normalization peak (8.2), as shown in Figure 1. 8.5 Depth locator Calculate the mean distance from the articular surface (dl) for each spectrum and its corresponding Iox from the following equation: dl = 0,5La + nLi where La is the size of the aperture in micrometers in the step direction; n is the number of steps (increments) by which the aperture is moved from its initial location at the articular surface; Li is the step (increment) size in micrometers. NOTE The absorbance recorded by the instrument corresponds to the area of the sample (aperture) being illuminated by the IR beam. The 0,5La factor in the equation allows for the calculation of the position of the centre of the aperture relative to the starting point or edge of the sample film. 8.6 Sample's surface oxidation index Calculate a samples Iox,s by calculating the mean average of the samples oxidation indices (Iox) with depth locator (dl) values between 0 mm and 3 mm. NOTE The first 3 mm of material subsurface to an articular surface typically experiences the greatest degree of real time oxidation and the greatest stresses during real time use. The Iox,s is one way of representing the samples oxidative state in this important region. 8.7 Sample's bulk oxidation index