Polyphenol-based coatings to control the degradation of magnesium alloys

Sara Ferraris; Jacopo Barberi; Francesca Gamna; Muhammad Saqib; Anna Dmitruk; Joerg Opitz; Krzysztof Naplocha; Natalia Beshchasna; Aldo Boccaccini; Silvia Spriano

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Polyphenol-based coatings to control the degradation of magnesium alloys

^{*

1},

¹,

¹,

²,

³,

²,

Krzysztof Naplocha

³,

Natalia Beshchasna

²,

Aldo R. Boccaccini

⁴,

Silvia Spriano

¹ Department of Applied Science and Technology, Politecnico di Torino, 10129 Turin, Italy;
² Fraunhofer Institute for Ceramic Technologies and Systems IKTS, 01109 Dresden, Germany
³ Department of Lightweight Elements Engineering, Foundry and Automation, Faculty of Mechanical Engineering, Wroclaw University of Science and Technology, 50-370 Wroclaw, Poland
⁴ Department of Materials Science and Engineering, University of Erlangen-Nuremberg, Erlangen, Germany

Academic Editor: Pankaj Vadgama

Published: 08 July 2024 by MDPI in The 1st International Online Conference on Functional Biomaterials session Bone Biomaterials

Abstract:

Introduction: magnesium alloys are promising for implants because of their biocompatibility and biodegradability. However, they are still poorly applied in clinics due to too rapid degradation, which does not match with tissue regeneration and is often associated with inflammation due to a pH rise and hydrogen development. The aim of this work is the development of natural organic coatings that can modulate the degradation rate of the substrates.

Methods: Plane samples (AZ31-AZ91) and porous 3D structures (AZ91) obtained by 3D printing combined with investment casting were considered as substrates. Natural organic coatings, tannic acid (TA) or polyphenols extracted from green tea leaves (TPH) were obtained by immersion in aqueous solutions of the selected molecules without the addition of toxic chemicals. The functionalization conditions were optimized in order to obtain homogeneous coatings that were free of cracks.

Results: Coating formation by soaking allowed for the treatment of complex geometries and porous structures. TA uniformly covered the surface of magnesium alloys, maintaining its redox activity after grafting, as well as the micro-topography, but it presented several micro-cracks (more evident in AZ31). The TA coating allowed us to keep the pH at the physiological level during AZ91 soaking in PBS. The result was less effective on AZ31. TA-coated AZ91 was poorly corroded after 14 days of soaking in PBS, and TA was still present on it. However, electrochemical tests did not evidence the effects of the coating improvements in terms of corrosion potential and rate. This effect was probably due to the presence of cracks. The use of TPH and surface pre-treatment allowed for the development of more homogeneous and crack-free coatings on both AZ91 and AZ31 surfaces. These coatings presented improved corrosion resistance (electrochemical tests) and biocompatibility.

Conclusion: Natural organic coatings represent a promising green and sustainable strategy for the modulation of the degradation rate of magnesium alloys for biomedical applications.

Keywords: Mg-alloys, polyphenols, degradation

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