## 3 Results
### Antibacterialativity of Selective Plated Copper Coatings against S. aureus and E. coli  
Figure 5 illustrates the inhibition zones (ZOI) formed around the selective plated copper coatings on stainless steel 1.4021 and nickel alloy Ni200 substrates after 24 h of incubation at 37 \({}^{\circ}\)C. The ZOI represents the area surrounding the copper-plated region where bacterial growth is inhibited. It is evident that the ZOI is formed around the copper-plated area but not on the substrate material itself. This suggests that the copper coatings exhibit antibacterial activity, preventing the growth of bacteria in the vicinity of the coated regions.  
Furthermore, Figure 6 highlights that the visible ZOI formed after the incubation period are more pronounced in the samples exposed to Gram-positive (_S. aureus_) versus Gram-negative (_E. coli_) bacteria. This indicates that the copper coatings have a stronger inhibitory effect on the growth of Gram-positive bacteria compared to Gram-negative bacteria.  
Figure 5: Antibacterial activity of selective plated copper coatings using either acidic (Cu acid) or alkaline (Cu alkaline) electrolyte solutions on medical-grade stainless steel (SS 1.4021) and nickel alloy (Ni200) samples against _S. aureus_ (**top row**) and _E. coli_ (**bottom row**) after 24 h incubation at 37 \({}^{\circ}\)C.  
Figure 6: Highlighted extents of the inhibition zones (green) surround the selective plated samples using either acidic (Cu acid) or alkaline (Cu alkaline) electrolyte solutions on medical-grade stainless steel (SS 1.4021) and nickel alloy (Ni200) samples against _S. aureus_ (**top row**) and _E. coli_ (**bottom row**) after 24 h incubation at 37 \({}^{\circ}\)C.  
The formation of inhibition zones around the copper-plated areas confirms the antibacterial properties of the selective plated copper coatings. This observation supports the potential of these coatings as effective measures to reduce bacterial colonization and prevent infections associated with medical devices or other applications where antibacterial properties are desired.  
The average area of the inhibition zones formed around the copper coatings deposited from the alkaline solution and tested with _S. aureus_ and _E. coli_ was approximately 1250 mm\({}^{2}\) and 1050 mm\({}^{2}\), respectively. On the other hand, the inhibition zones formed around the coatings deposited from the acidic copper solution were slightly smaller, with an average area of 1050 mm\({}^{2}\) and 950 mm\({}^{2}\) when tested with _S. aureus_ and _E. coli_, respectively. These results indicate that the selective plated copper coatings demonstrated biocidal activity against both _S. aureus_ and _E. coli_.  
Interestingly, the surface roughness of the copper coatings did not significantly affect their antibacterial activity against both tested strains of bacteria. Regardless of the different surface roughness of the selective plated copper coatings on stainless steel 1.4021 and nickel alloy Ni200 substrates, the coatings retained their bioactive resistance against both Gram-positive _S. aureus_ and Gram-negative _E. coli_. This suggests that the antibacterial properties of the copper coatings are not heavily influenced by surface roughness.  
Figure 6 further demonstrates that the area of the inhibition zones formed around the copper coatings is relatively similar for both tested bacteria, irrespective of the variations in surface roughness. This indicates that the selective plated copper coatings maintain consistent antibacterial efficacy against different types of bacteria, regardless of the surface characteristics.  
Overall, these findings highlight the promising antibacterial activity of the selective plated copper coatings and their potential as effective measures for inhibiting bacterial growth and preventing infections. The coatings demonstrated biocidal effects against both Gram-positive and Gram-negative bacteria, and the surface roughness did not considerably impact their antibacterial performance.