# Control of Corrosion Resistance and Osteoclastic Resorbability of Bioresorbable Carbonate Apatite Coating for Biodegradable Mg Alloys through Carbonate Content

## TL;DR

This study shows how adjusting carbonate content in a coating on biodegradable magnesium alloys can control their corrosion and how quickly they are broken down by bone cells.

## Contribution

The study introduces a method to tailor the degradation of biodegradable Mg alloys by controlling carbonate content in their coatings.

## Key findings

- Higher carbonate content in CAp coatings increased polarization resistance in both NaCl and Hanks’ solutions.
- Osteoclasts only survived on CAp coatings with higher carbonate content.
- Higher carbonate content led to faster resorption of the coating by osteoclasts.

## Abstract

To investigate the effect of carbonate content on the
corrosion
resistance and osteoclastic resorbability of carbonate apatite (CAp)
coatings for biodegradable Mg alloys, polarization, electrochemical
impedance, and osteoclast precursor cell culture tests were conducted
for CAp-coated pure Mg (Mg) and Mg–4Y-3RE (WE43) containing
approximately 11, 17, and 18 wt % carbonate. In Hanks’ solution,
the polarization resistance (R
p) was higher
than in a 0.9% NaCl solution, and the CAp coatings improved the R
p of Mg by 7 to 15 times. The R
p of CAp-coated Mg increased by approximately 1.5 times
in a 0.9% NaCl solution and 2 times in Hanks’ solution with
increasing carbonate content, indicating a reduction in coating defects.
For CAp-coated Mg, osteoclasts only survived on the higher carbonate
content coating. For WE43, the coating with a higher carbonate content
exhibited a higher number of mature osteoclasts and approximately
a 1.5-fold increase in the resorbed area by osteoclasts. These findings
demonstrate that the carbonate content in the CAp coating allows for
adjustment of the corrosion rate of biodegradable Mg alloys to suit
the affected part of the body. It was also found that once osteoclasts
are induced, the CAp coating with a higher carbonate content is resorbed
more quickly by the osteoclasts.