## 4 Discussion  
This study introduces a novel approach to the selective plating of copper coatings on medical-grade stainless steel 1.4021 and nickel alloy Ni200 substrate materials. These materials are commonly used for production of surgical instruments, e.g., forceps/tweezers. Selective plating offers several distinct advantages over traditional plating methods [25]. First, it provides a highly targeted and localized plating approach, allowing for precise and controlled deposition of coatings on specific areas or components of a workpiece. This selective nature eliminates the need for extensive masking or complex setups typically required for other plating methods, thereby saving time and reducing material waste. Furthermore, the selective plating allows for easy control and adjustment of the plating parameters such as current density and solution composition, facilitating customization of coating thickness, composition, and other characteristics according to specific requirements [25; 26].  
For the purpose of this study, a precalculated selective plating regime was set to achieve a copper coating with a targeted thickness of 40 \(\upmu\)m. This precalculated value served as a guideline to achieve the desired thickness during the plating process. The actual thickness of the coatings obtained in the study was 40 \(\pm\) 2 \(\upmu\)m. The close agreement between the targeted and actual coating thickness confirms the accuracy and precision of the selective plating method employed in this work. The ability to consistently obtain a desired coating thickness is crucial for ensuring the functional and protective characteristics of the coatings. In applications where a specific coating thickness is required for optimal performance, the ability to accurately control the plating process and achieve a desired thickness is of great importance [27; 28]. Overall, the close agreement between the targeted and measured coating thickness affirms the effectiveness of the precalculated selective plating regime, providing confidence in the reproducibility and reliability of the plating process.  
These XRD analysis and the corresponding evaluated peak parameter provide valuable insights into the crystallographic properties and phase composition of the selective plated copper coatings. The consistent identification of a single-phase pure copper solid solution confirms the successful formation of the desired coatings.  
The results related to surface roughness indicate similar patterns observed for its alterations when using both substrate materials this study. Although the initial surface roughness was different for the SS 1.4021 and Ni200 substrates, the surface roughness of the selective plated copper coatings was approximately 80% of the corresponding substrate value when acidic copper solution was used, and nearly 60% when alkaline copper was used for plating on both metallic substrates. Surface roughness is presumably important for the antibacterial properties of the biocidal surfaces as it may increase considerably the active exposure area.  
The analysis of the inhibition zones formed around the selective plated copper coatings provides valuable insights into their antibacterial activity. The average area of the inhibition zones varied depending on the type of used copper solution and tested bacteria. However, these results highlight the potential of the selective plated copper coatings as effective antibacterial agents against both Gram-positive and Gram-negative bacteria. The ability of the coatings to exhibit biocidal activity while maintaining their performance across different surface roughness conditions is advantageous for various applications where surface hygiene and bacterial resistance are critical. Further research could delve into the underlying mechanisms responsible for the antibacterial activity of the coatings and explore potential optimizations to enhance their performance even further.