PEO-coated bioresorbable Mg-alloy based Screw Implant for Orthopedic Application

Ashutosh Tiwari1, Joerg Zerrer1, Anna Buling1*

1 ELB - Eloxalwerk Ludwigsburg Helmut Zerrer GmbH, Neckartalstrasse 33, DE-71642 Ludwigsburg – Neckarweihingen, Germany,

*buling@ceranod.de

Biomedical implants failure is one of the most common challenge arising during orthopedic surgery, which can lead to improper bone healing, inflammation, and toxicity (infection). These problems instigated due to many reasons such as peri-implant infection, excessive inflammation which causes discomfort and aseptic loosening. Thus, an additional or alternative surgical procedure is required to remove these implants from the body after complete healing process, which is too painstaking.[1]

Magnesium (Mg) and its alloys have shown great potential as promising bioresorbable, biodegradable, and bioactive implantation materials owing good biocompatibility. These materials will dissolve with time without causing any toxicity and avoid cause of another surgical procedure after bone healing. It can be anticipated from Mg-alloys to avoid bacterial infection during healing process. Additionally, Magnesium alloys help to stimulate the healing responses of injured tissues at the molecular level due to osteoinductivity/osteoconductivity properties. Apart from their biocompatible properties, they also illustrate great mechanical properties like low density and an elastic modulus in the range compatible to bone structures [2]. Though, the rapid corrosion rate and degradation of Mg and its alloys in in-vivo atmosphere may induce loss of mechanical integrity before complete bone healing and, hence, restrict its application as implant material [1,2]. To overcome such corrosive behaviour of Mg-alloys, we are developing a ceramic coating on Mg-based screw implants by PEO (Plasma Electrolytic Oxidation) process which helps to protect it against in-vivo corrosive environment leading to 2 months of dimensional stability.

PEO process is a novel environmentally friendly surface modification technique forming crystalline ceramic surfaces on Mg, Al and Ti and their-alloys, which exhibit great hardness and are suitable for both: corrosion and wear protection without any post-process treatment. The corrosion resistance behaviour of PEO-coatings mainly depends on thin barrier layer formed adjacent to substrate/coating interface. The electrolyte composition, the applied energy, and the appearance of micro-discharging events etc. are several parameters which play a crucial role in the properties of coating performance. [3]

The current work was performed under special PEO regime with new process parameters to obtained desired coating thickness and properties best suited for Mg-alloy based screw implants. The microstructural, chemical composition and corrosion resistance of the PEO coatings were studied via of SEM, EDX and electrochemical analysis such as electrochemical impedance spectroscopy and potentiodynamic polarization. Surface roughness, hardness and tribological properties were also investigated to support the mechanical performance of coatings.

References

[1] Saha, Soumya, et al. "Corrosion in Mg-alloy biomedical implants-the strategies to reduce the impact of the corrosion inflammatory reaction and microbial activity." Journal of Magnesium and Alloys (2022).

[2] Wan, Peng, Lili Tan, and Ke Yang. "Surface modification on biodegradable magnesium alloys as orthopedic implant materials to improve the bio-adaptability: a review." Journal of Materials Science & Technology 32, no. 9, (2016), 827-834.

[3] Buling, Anna, and Joerg Zerrer. "Increasing the application fields of magnesium by ultraceramic®: Corrosion and wear protection by plasma electrolytical oxidation (PEO) of Mg alloys." Surface and Coatings Technology 369 (2019): 142-155.