ISO/DTR 4234

ISO/TC 150/WG 12
Secretariat: DIN
Date: 2025-09-0211-21
First edition
Non-active surgical implants - — Implant coating –— Best
practices for Coating System Assessmentcoating system
assessment
WD/CD/DIS/FDIS stage
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iii
Contents
Foreword . v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Guidance for coating system assessment . 3
4.1 General . 3
4.2 Foundational considerations . 3
4.3 Coating assessment guide . 6
Annex A (informative) Example flowcharts . 9
Bibliography . 12

iv
Foreword
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This document was prepared by Technical Committee ISO/TC 150, Implants for surgery.
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.
v
Introduction
Coatings for surgical implants are widely used in the medical device industry. These coatings are sophisticated
systems involving the coating, the coating interface, and substrate(s) to the coating. Due to this increasing
complexity and variability of coating systems, tools for the consistent assessment of their performance and
suitability to their application (i.e. their service environment) are increasingly necessary. Specifically, herein
the assessment of coating systems is described from design, functional, and manufacturing perspectives.
As described in ISO 17327-1, an implant coating is a layer of material with any different property than the
natural surface of the substrate that it is intentionally added [upon] and it is designed to have specific physical
features such as dimension, phase, and coverage as well as mechanical, physical, optical, electrical, bonding
and perhaps other properties such as elution. A coating also can have specific interactions with the contacting
tissues, that can lead to the tissue’s biological reactions to the coating and the tissue’s impact on the coating.
A coating has multiple intended functions; e. g.,, such as allowing easier delivery, achieve optimal tissue
integration iandand support the proper functioning of the device. The functions of a coating are supported by
a coating’s characteristics and intended use conditions in the patient. This drives the coating evaluation work
into two areas:
a) i) coating characterization per design; and
b) ii) functional evaluation in context of the finished products for the patients.
Although these two areas can overlap, e.g.,. lubricity of the lubricious coating where both the designer and
user see the same thing from the patient’s function perspective, these two perspectives can also diverge
significantly from a coating characteristic testing perspective.
A coating and the substrate upon which the coating is placed make up a system that is intimately connected
through the interface such that the coating can have an effect on the substrate and the substrate can have an
effect on the coating. Some coatings are multi-layered, and as such, they can have multiple coating-substrate
and coating-coating interfaces to consider. The substrate and intermediate surface can require pre-treatment
such as roughening and cleaning, the use of process and post coating finishing can be necessary. Due to this
complexity, it is possible that some unintended chemicals, physical structures, or properties can be present in
the final product. Therefore, the process is not only considered for producing the coating but couldcan also
impart characteristics to the coating. For this reason it is necessary to evaluate, both the pre- and post-coating
processes are evaluated when determining the necessary biological functions and safety of a coating system.
A coating is usually made with a validated manufacturing process, that can involve one or more steps or
technologies. It is common that multiple parties are involved in designing and manufacturing finished devices
for medical uses. It is important that all theAll parties arehave to be aware of the intended use of the materials,
components, and product that they produce and be properly compliant to the quality control regulations.
Blind use of materials, components, and processes to make finished products can notcannot only add risks to
the quality control but also add burden to be compliant to regulations.
vi
Non-active surgical implants - — Implant coating –— Best practices for
Coating System Assessmentcoating system assessment
1 Scope
This document specifies a systematic approach for the development of an assessment plan for coating systems
for potential use for implants. The goal of thisThis document is to provideprovides a brief introductory guidance
for a “Coating System”the coating system and “intended functions”. This document describes the assessment
process from the context of product design, manufacturing (including sterilization), product aging, and clinical
intended use. This assessment process is intended to help evaluate coating properties that are pertinent to the
performance of the coated devices and uses relevant examples to illustrate the process. ISO 17327-1 defines a
set of coating properties that can be pertinent for any specific coating.
NOTE ISO 17327-1 defines a set of coating properties that can be pertinent for any specific coating.
This document is intended to be a useful tool in the development of an assessment plan of coating systems
and is meant to support communication, e.g. among coatings manufacturer, OEM,original equipment
manufacturer and regulatory bodies (through direct interaction or master files).
This document does not address the clinical safety and performance of the surgical implant for which the
coating system is a part.
This document also does not cover specific tests for coating systems, as it is intended asto be a structure for
determining important properties and tests that can be appropriate for any given coating system.
NOTE ISO/TR 17327-2 provides several tables listing standards related to coatings including some known test
methods.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements 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 14630, Non-active surgical implants -— General requirements
ISO 17327-1:, Non-active surgical implants -— Implant coating -— Part 1: General requirements
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 14630, ISO 17327-1 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
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— IEC Electropedia: available at https://www.electropedia.org/
Field Code Changed
3.1 3.1
implant coating
surface coating (3.2(3.2)) or surface modification (3.3(3.3))
Note 1 to entry: Implant coating is considered a constituent of an implant.
Note 2 to entry: A laminate, i.e. a composite material made of multiple layers of the same or different materials with the
same or different internal structures assembled sandwich-like and bonded by heat, pressure, welding, soldering or
adhesives, is not in itself considered an implant coating. But the exposed surface of the laminate can be an implant coating.
Note 3 to entry: A covering is not considered an implant coating. For example, additional material (e.g. a graft) added to
a structure (e.g. a stent) specifically to bridge elements of the structure for the sole purpose of reducing the permeability
of the structure.
[SOURCE: ISO 17327-1:2018, 3.1]
3.2 3.2
surface coating
layer of material with any different property than the natural surface of the substrate that is intentionally
added to the substrate
Note 1 to entry: The coating can partially or fully cover the substrate surface.
Note 2 to entry: The term includes surface coatings created as a result of additive manufacturing.
[SOURCE: ISO 17327-1:2018, 3.2]
3.3 3.3
surface modification
intentional conversion or reconstruction of the surface of the original substrate to form a new surface material
consisting of components of the substrate´ssubstrate’s own material and possibly foreign material and
forming a surface layer with different properties
[SOURCE: ISO 17327-1:2018, 3.3]
3.4 3.4
coating system
region starting from the outer surface of the coating and ending within the substrate where the coating no
longer affects substrate prop
...