Implant Testing

Sprachauswahl/Language selection

Dieser Artikel ist auch auf Deutsch verfügbar Implantatprüfung

A service provided by
Polymer Service GmbH Merseburg
Tel.: +49 3461 30889-50 E-Mail: info@psm-merseburg.de Web: https://www.psm-merseburg.de
Our further education offers: https://www.psm-merseburg.de/weiterbildung
PSM on Wikipedia: https://de.wikipedia.org/wiki/Polymer Service Merseburg

Implant testing

Material selection for medical implants

The testing of implants (from the Latin *in-* ‘into’ and *plantare* ‘to plant’) and, in particular, implanted prostheses has become increasingly important. Well-known examples include artificial hearts, hip joint prostheses, plastic implants and dental implants. Plastics have a wide range of applications in medicine and medical technology due to their broad spectrum of properties [1]. The increasing use of this group of materials is due to the possibility of medical approval, the excellent adaptability of their property profile, and the possibility of combining them with or substituting them for metallic biomaterials, such as titanium and steel alloys (CrNi, CoCrMo, etc.) or ceramic materials.

In medical technology and the packaging sector, elastomers and thermoplastics are very commonly used, for example, in packaging for pharmaceuticals, syringes (PE, PP), disposable items (PVC, PP), tubing (PET, PC, PA), catheters (polysiloxanes, rubber) or endoscopes (PE, PP), although the sterilisation sometimes required often poses a problem from the perspective of the biofunctionality and biocompatibility of such thermolabile instruments and devices. On the other hand, thermoplastic materials such as PMMA are used as bone cement, for example in joint endoprosthetics or dental surgery, whilst in some cases resorbable short-fibre reinforced plastics are already being used as temporary implants for bone fractures. Plastics based on thermoplastics are used, for example, as replacements for hip sockets in orthopaedics (PE-UHMW), in vascular surgery (PTFE, PET, PUR or polysiloxanes) and in ophthalmology (PMMA, polysiloxanes). In the ear, nose and throat sector, as well as in vascular and reconstructive surgery, silicone or PUR elastomers are frequently used alongside thermoplastic materials such as polyethylene (abbreviation: PE), although this list of applications is by no means exhaustive.

Requirements for medical implants

Medical implants are defined as components or systems of components inserted into the body to support or replace cell or tissue systems; they are classified as ultra-short-term, short-term or long-term implants depending on the intended duration of implantation. Depending on the type of implant and the tissue to be replaced, as well as its function within the body, the aim is to create either a fixed, load-bearing (endoprosthesis) or a movable, removable connection (e.g. a hip socket or bone screw). This means that, to ensure effective load transfer, the material must guarantee sufficient stiffness, strength and toughness, and the design must not feature any notches or impermissibly high stress concentrations (see: fracture mechanics). When combining different materials, friction and changes to the structure of the implant’s surface should also be kept to a minimum. With regard to the desired surface compatibility, the effects of biocorrosion or the formation of biofilms should be minimal in order to achieve the desired clinical interaction. In line with this objective, the materials used are therefore classified as bio-inert, bioactive and biocompatible materials. The optimal implant is therefore designed in such a way that its physical and chemical properties (biocompatibility) and its functionality correspond as closely as possible to those of the recipient tissue [2–4].

The use of plastics as implants offers advantages in terms of the cost-effective manufacture of complex and geometrically intricate components, e.g. using laser sintering or stereolithography techniques [5, 6], but it also has disadvantages that stem from the specific strength and deformation behaviour of these materials (see, for example: deformation behaviour of human cartilage). This applies in particular to viscoelasticity and the creep and relaxation behaviour, as well as the pronounced temperature dependence of the material properties, which make it considerably more difficult to reliably predict long-term behaviour under in vivo conditions. Furthermore, during implantation, adequate sterility—i.e. the absence of all viable organisms, including their endospores or spores—must be ensured. For this reason, the choice of sterilisation method is of crucial importance, particularly for plastics, as both high temperatures and radiation doses can lead to damage or degradation and thus to significant changes in the material’s properties. Further detailed information on the application, selection and characterisation of biomedical materials based on plastics can be found in [7–9].

Performance in service and testing of materials and components

The performance characteristics of implants, the simulation of their functionality and the prediction of their service life can be assessed, for example, using biomechanical models and approaches [10–12]. The crucial prerequisite in this context, however, is precise knowledge of the properties of the materials used in their initial state and in interaction with the biomedical environment (in vitro testing). The testing and approval of materials for orthopaedic, traumatological and maxillofacial surgical implants is generally carried out in accordance with the relevant EU directives and the Medical Devices Act, as well as the relevant international standards, by accredited testing laboratories (see: accreditation and certification). In line with the degree of use and significance in surgery and orthopaedics, these testing standards primarily relate to biocompatibility, the biomechanics of the lower extremities—such as knee or hip joints—as well as intervertebral disc implants under static and dynamic loads, and wear testing. However, there are no specific standards for plastics with their specific mechanical deformation and strength behaviour. Implant testing for plastic components therefore relies on technological test procedures or application-oriented component tests, which are often unique solutions, and requires a high degree of creativity in the development of test methods and the evaluation of results, which are mostly aimed at characterising the behaviour in use. To simulate critical limit values for load or deformation, such static or dynamic tests are often carried out in a test medium that closely resembles the in-service environment (37 °C, isotonic solution). The encyclopaedia contains numerous examples of the investigation of in-service behaviour and the testing of implants, prostheses and human tissue.

See also

• Push-out test
• Lid-opening test
• Lid-Opening test, voice prosthesis
• Prosthesis pull-trough test
• Prosthesis pull-trough test, voice prosthesis

References

[1]	Bierögel, C.: Implant testing. In: Grellmann, W., Seidler, S. (Eds.): Polymer Testing. Carl Hanser, Munich (2025) 4th Edition, pp. 624–634 (ISBN 978-1-56990-806-8; E-Book: ISBN 978-1-56990-807-5; see AMK-Library under A 22)
[2]	Wintermantel, E., Ha, S.-W.: Biokompatible Werkstoffe und Bauweisen. Implantate für Medizin und Umwelt. Springer, Berlin Heidelberg (2008) (ISBN 978-3-540-74924-0)
[3]	Stallforth, H., Revell, P.: Materials for Medical Engineering. Volume 2, Wiley-VCH, Weinheim (2005) (ISBN 978-3-527-30123-2)
[4]	Bronzino, J. D., Peterson, D. R.: The Biomedical Engineering Handbook. Fourth Edition CRC Press (2015) (ISBN 978-1-439-82533-4)
[5]	Poprawe, R.: Lasertechnik für die Fertigung. Springer, Berlin Heidelberg (2005) (ISBN 978-3-540-21406-9)
[6]	Grießbach, S., Lach, R., Grellmann, W.: Einsatz des Lasersinterns für Kleinserienfertigung hochfester Kunststoffbauteile/ Small series production of high-strength plastic parts. Kunststoffe 5 (2008) pp. 29–32 und Kunststoff International 5 (2008) 11–14 (ISBN 978-3-540-21406-9)
[7]	Planck, H.: Kunststoffe und Elastomere in der Medizin. Kohlhammer Publishing House, Stuttgart (1993) (ISBN 978-3-170-09602-8)
[8]	Eastmond, G. C, Höcker, H., Klee, D.: Biomedical Applications / Polymer Blends. Springer, Berlin Heidelberg (1999) (ISBN 978-3-540-65933-4; e-Book ISBN 978-3-540-48838-5)
[9]	Chiellini, E.; Sunamto, J.; Migliaresi, C.; Ottenbrite, R. M.; Cohn, D.: Biomedical Polymers and Polymer Therapeutics. Springer, Berlin Heidelberg (2001) (ISBN 978-0-3064-6472-0)
[10]	Nachtigall, W.: Biomechanik. Vieweg+Teubner Publishing House, Wiesbaden (2001) (ISBN 978-3-5281-3926-1)
[11]	Morecki, A.: Biomechanics of Engineering, Modelling, Simulation, Control. Springer, Berlin Heidelberg (1998) (ISBN 978-3-2118-1974-6)
[12]	Holweg, K.: Bestimmung der Eigenschaften der Grenzfläche zwischen Knochen und Implantaten. PhD Thesis, Martin-Luther-Universität Halle-Wittenberg (2010) (ISBN 978-3-86948-065-7; see AMK-Library under B 1–22)