Antibacterial Efficacy and Biocompatibility of HiPIMS-Ag Films for Prosthetic Application

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Review

In this manuscript, the authors demonstrated the successful deposition of ultrathin, highly adherent silver thin films onto commercially pure titanium using HiPIMS, achieving significant antibacterial activity with minimal silver ion release and no observable cytotoxicity to osteoblasts. The study is highly relevant and interesting, addressing a critical need in preventing implant-associated infections, but the authors should consider the following comments and questions.

Comments:

Section 2. Materials and Methods

• The manuscript mentions using “commercially pure Ti substrate (50 mm × 50 mm × 1 mm for antibacterial test and 25 mm × 25 mm × 1 mm for osteoblast compatibility test)”. It would be beneficial to specify if the exact same cleaning procedure was applied to both sets of substrates, or if any differences in cleaning for the smaller Ti substrates might have occurred.

Section 3. Results

• In subsection 3.1, the text states, “the thickness of the Ag film deposited for 5 s using HiPIMS was estimated to be 7 nm, as calculated from Figure 2.”. The authors should clarify how the 7 nm thickness for the 5s deposition was determined. Is it from a separate, unshown measurement, or inferred from the growth rate of 1.4 nm/s calculated from thicker films?
• In subsection 3.2, the VDI 3198 test description mentions “favorable VDI 3198 classifications.”. This would be more quantitative to state the specificclassification obtained (g., HF1, HF2, etc.) if it was assessed.
• In subsection 3.3, the authors should improve Figure 6, specifically Figure 6(b), by mirroring the image to present it in the correct orientation.
• In subsection 3.5, Figure 10 shows quantitative proliferation results. The text states, “although the quantified proliferation values on the HiPIMS-Ag films were slightly lower than those on the titanium substrate, they all remained above 80% of the titanium baseline.”. This is a strong claim. To support it, it would be helpful to provide the actual percentage values for each deposition time at 48 hours, or at least the minimum percentage observed, to confirm it’s indeed above 80%.

Section 4. Discussion

• The text mentions “the incidence of columnar porosity commonly observed in low-energy sputter growth [8].”. This would be useful to briefly explain whyHiPIMS’s higher energy leads to less columnar porosity compared to low-energy sputtering.
• The “Goldilocks” regime mentioned in Section 4 (line 301) is a good analogy. However, it would be beneficial to quantitatively define what constitutes this “safe operating window” in terms of Ag+ concentration, linking it back to the measured release rates and the accepted cytotoxic levels.
• The discussion on protein adsorption and conditioning film formation (lines 309–311) is relevant for future work. It would be insightful to hypothesize how these phenomena might interact with the HiPIMS-Ag surface and affect its antibacterial efficacy and biocompatibility, even if this is beyond the scope of the current study.
• The comparison to nanoparticle-based approaches (line 312) is valid. It would be stronger to briefly elaborate on why thin-film Ag avoids particle detachment and limits burst-release behavior, perhaps by referencing the mechanism of film deposition and integrity.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper proposes a study on thin silver coatings deposited by HiPIMS for the antibacterial protection of titanium implants. The study needs to be integrated and improved according to the following observations.

1. How did the authors position the HiPIMS-Ag films in relation to integrated electronic monitoring systems for biomedical devices? Recent studies have analysed monitoring systems based on smart electronic devices for SAR and temperature variations in interaction with human tissues indoors. The authors should integrate the Introduction with these studies, which demonstrate the need to combine coatings with monitoring strategies to emphasise interdisciplinary integration.

2. Why didn't the authors use predictive modelling to analyse the coating's behaviour under stress? The authors should integrate the Discussion section with study 10.3390/electronics14112268, which shows how FEM improves reliability predictions.

3. Should the authors explain how the method accounts for subsurface defects or microcracks that could compromise long-term adhesion?

4. Did the authors consider artificial intelligence or soft computing methods to classify coating degradation?

5. How do electrically conductive coatings interact with the surrounding tissues?

6. Can the authors compare their antibacterial strategy with impedance/tomography-based diagnostic systems? Recent studies have investigated tomographic impedance approaches in biomedical engineering problems for cancer detection. The authors should integrate the Discussion with these studies to delve deeper into parallel technology for biomedical monitoring.

7. The authors did not investigate integration with real-time monitoring systems. Why? Could their system accommodate this integration?

8. How do the authors intend to address the uncertainties in the adhesion or biocompatibility results?

9. Why didn't the authors discuss the broader role of sensor-based monitoring of coatings under extreme conditions?

10. Did the authors consider applying optimisation techniques to their deposition parameters? Recent studies have implemented parametric optimisation models of a mechanical ventilator using the Taguchi method. As an illustration of methodical optimisation that could be used for HiPIMS deposition, these studies ought to be referenced in the Methods section.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

I thank the authors for their replies to the comments. I have no further comments to make.