ISO/TS 20721:2025
(Main)Implants for surgery — Absorbable implants — General guidelines and requirements for assessment of absorbable metallic implants
Implants for surgery — Absorbable implants — General guidelines and requirements for assessment of absorbable metallic implants
This document establishes the currently recognized approaches and special considerations needed when evaluating the in vitro and in vivo performance of absorbable metals and implants fabricated, in whole or in part, from them. This document describes how the evaluation of these metals can differ from those utilized for permanent non-absorbable implantable implants (or subcomponents), in that absorbable metal implants (or subcomponents) are – by design – intended to be absorbed in their entirety by the host. This document provides guidance regarding the materials considerations, in vitro degradation/fatigue characterization, and biological evaluation of medical implants made of absorbable metals. The provided content is intended to deliver added clarity to the evaluation of these materials and implants to increase awareness of critical factors and reduce potential for generation of erroneous or misleading test results. While this document and the herein described referenced standards contain many suggested alterations or modifications to currently practiced procedures or specifications, the provided content is intended to complement, and not replace, current conventions regarding the assessment of implantable implants. This document covers the evaluation of absorbable metal specific attributes in general and is not intended to cover application or implant specific considerations. Thus, it is important to consult relevant implant and/or application specific standards. This document does not apply to non-absorbable or non-metallic components (e.g. polymeric coatings, pharmaceuticals, non-absorbable metals) used in conjunction with absorbable metal implants.
Implants chirurgicaux — Implants absorbables — Lignes directrices et exigences générales pour l'évaluation des implants métalliques absorbables
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Standards Content (Sample)
Technical
Specification
ISO/TS 20721
Second edition
Implants for surgery — Absorbable
2025-05
implants — General guidelines and
requirements for assessment of
absorbable metallic implants
Implants chirurgicaux — Implants absorbables — Lignes
directrices et exigences générales pour l'évaluation des implants
métalliques absorbables
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Absorbable metal considerations . 2
4.1 General .2
4.2 Design considerations .3
4.2.1 Composition .3
4.2.2 Coatings .4
4.2.3 Non-absorbable subcomponents .4
4.2.4 Microstructure .4
4.2.5 Implant design and functional performance .4
4.3 Absorption process . .5
4.3.1 General outline .5
4.3.2 Metallic conversion .5
4.3.3 Subsequent degradation reactions .6
4.3.4 Elemental impact on absorption .6
4.3.5 Biological absorption . .6
4.3.6 Mechanical loss .6
5 Metallurgical and manufacturing considerations . 7
5.1 General .7
5.2 Composition .8
5.3 Production process .8
5.3.1 General .8
5.3.2 Raw material purity .8
5.3.3 Metal melting practice .8
5.3.4 Metal casting . .8
5.3.5 Metal thermo-mechanical processing .8
5.3.6 Surface considerations .9
5.3.7 Implant cleaning, sterilization, packaging, storage and handling .9
6 Evaluation of in vitro degradation characteristics . 9
6.1 General .9
6.2 Additional considerations .9
7 Biological evaluation . 10
7.1 General .10
7.2 Biocompatibility of degradation products .10
7.3 In vitro biological evaluation .10
7.4 In vivo biological evaluation .10
7.4.1 Biocompatibility end point studies .10
7.4.2 Animal safety and implant performance studies .11
Annex A (informative) Nomenclature of absorb, degrade and related terms .12
Bibliography .13
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.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 150, Implants for surgery.
This second edition cancels and replaces the first edition (ISO/TS 20721:2020), which has been technically
revised.
The main change is as follows: references have been updated.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
This document provides general information regarding implantable absorbable metals, a detailed description
of their absorption processes and an outline of the design considerations which differ significantly from
non-absorbable metals.
This document discusses:
— the metallurgical evaluation of absorbable metals with reference to ASTM F3160, with a commentary on
the impact of composition and production processes on the final performance;
— in vitro degradation corrosion testing with reference to ASTM F3268, with a commentary on the
importance of environmental conditions in the tests;
— in vitro and in vivo biological assessments, with reference to several parts of the ISO 10993 series and
ISO/TS 37137-1.
NOTE ISO/TS 37137-1 applies to all absorbable materials, including metals and polymers.
The interrelation of this document with various absorbable-specific reference documents is shown in
Figure 1.
Figure 1 — Interrelation of this document with standards specific to absorbable metallic implants
This document can be useful to both material suppliers and implant manufacturers.
Absorbable polymers used in conjunction with absorbable metals, either for performance modification
or drug delivery, are not addressed. However, it is expected that a polymer coating, absorbable or non-
[23]
absorbable, can influence absorption and performance of the underlying absorbable metal. ASTM F2902
addresses absorbable polymers.
Some existing standards address specific absorbable implants (e.g. ISO/TS 17137 addresses absorbable
cardiovascular implants) made of either polymer or metal.
v
Technical Specification ISO/TS 20721:2025(en)
Implants for surgery — Absorbable implants — General
guidelines and requirements for assessment of absorbable
metallic implants
1 Scope
This document establishes the currently recognized approaches and special considerations needed when
evaluating the in vitro and in vivo performance of absorbable metals and implants fabricated, in whole or in
part, from them. This document describes how the evaluation of these metals can differ from those utilized
for permanent non-absorbable implantable implants (or subcomponents), in that absorbable metal implants
(or subcomponents) are – by design – intended to be absorbed in the
...
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