# Influence of Treated Surface Proportion on the Antibacterial Performance of UV-Activated Hydroxyapatite–Magnesium Phosphate–Zinc Oxide Coating on Magnesium Alloys

## TL;DR

This study shows that partial coating on magnesium alloys can still effectively prevent bacterial growth, even if some surface areas are exposed.

## Contribution

The study introduces a UV-activated coating that maintains antibacterial performance with partial surface coverage.

## Key findings

- Fully coated and UV-activated surfaces achieved over 98% bacterial reduction.
- 60% coating coverage showed antibacterial efficacy similar to fully coated surfaces.
- 30% coverage still provided moderate antibacterial activity against certain bacteria types.

## Abstract

Surface damage occurring during surgery can compromise coating integrity, leaving exposed areas susceptible to bacterial colonization. However, the impact of partial coating loss on antibacterial performance has not yet been investigated. In this work, a multifunctional UV-activated coating composed of hydroxyapatite, magnesium phosphate, and zinc oxide (HMZ) was developed and electrodeposited onto AZ31 and MgCa magnesium alloys. Its antibacterial efficacy against Staphylococcus aureus and Escherichia coli was evaluated under three conditions: adhered bacteria, planktonic cells, and biofilm. In the absence of UV activation, coated surfaces exhibited no significant antibacterial activity. In contrast, fully coated and UV-activated surfaces achieved bacterial reductions above 98% in all scenarios. Surfaces with 60% coverage showed antibacterial efficacy equivalent to that of fully coated surfaces, even against established biofilm. Surfaces with 30% coverage also exhibited moderate activity, particularly against adhered and planktonic bacteria. These results demonstrate that full surface coverage is not required to preserve the coating’s antibacterial effectiveness. This strategy provides a clinically relevant solution to maintain antibacterial protection even when coating integrity is compromised.