Fabrication of a Novel Ta(Zn)O Thin Film on Titanium by Magnetron Sputtering and Plasma Electrolytic Oxidation for Cell Biocompatibilities and Antibacterial Applications

Round 1

Reviewer 1 Report

The conclusion should be presented in more detail.

Author Response

Comments of Reviewer 1

The conclusion should be presented in more detail.

Response:

Thanks a lot for the Reviewer’s suggestion. We have revised the conclusion in more detail as shown in the revised manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report

The present manuscript reports the fabrication of antibacterial coatings on titanium and their biological evaluation. The coatings were based on tantalum oxide and tantalum mixed with zinc oxide. Each formulation was analyzed in terms of surface topography and chemical structure. Biological results showed that the performance of both coatings is almost comparable, even better than titanium itself.

I do not recommend the publication in Metals Journal, except that after the revision of the following points:

Major revision:

• Recommend of a careful revision of English. Some parts of the manuscript are unclear due to the reader.
• It is not so clear the distinction between the two categories of surface treatment. Could the authors expand more the discussion, highlighting advantages and disadvantages with some explicative examples?

Did the authors investigate a mixed approach? Like a first surface modification and a subsequent coating deposition? This part must be enriched with more details.

• Section 2.1. In my opinion, it is very difficult to obtain Ti samples with a surface roughness of 0.5 um using abrasive papers. The authors must consider the repeatability of the experiments. Even the role of sandblasting is not clear.
• Please the authors describe in a clearer manner the biological experiments. It is not clear the time points for the biocompatibility assay (cell seeded on the samples), and when the MTT test has been applied to both biocompatibility and cytotoxic assays.

Another point is related to the cell density used for both experiments since from Figure 6 and 7 different values from the MTT tests were detected.

• The statistical analysis must be reviewed. A Student’s test is not enough when more than 2 groups must be compared. I suggest adopting the ANOVA as statistical model.
• Figure 1. The authors should add the analysis of the untreated titanium as comparison, useful also for the subsequent discussion. Furthermore, an analysis of the average roughness could help to quantitatively define the differences among the tested samples (Ti, Ta2O5, and Ta(Zn)O), for example measuring the cited Ra value. In the manuscript is only reported a range of Ra and Rz, and it is not clear the difference among these groups. Please the authors add more details for this analysis.
• Not only the morphology plays an important role in the wettability, but also the chemical structure of the coating. Please the authors highlight this aspect in the discussion. For example, how the authors judge the very low contact angle value achieved by Ta2O5?
• Figure 6. Please revise the statistical analysis. It seems strange that everything is different.
• Figure 7. Please the authors consider introducing a control group, as for the cytotoxicity test.
• The discussion of the biological results, especially those related to MTT, must be improved. At this purpose, the authors could refer to the following references:

Tantalum:

Vaidulych, M., Pleskunov, P., Kratochvíl, J., Mašková, H., Kočová, P., Nikitin, D., ... & Choukourov, A. (2020). Convex vs concave surface nano-curvature of Ta2O5 thin films for tailoring the osteoblast adhesion. Surface and Coatings Technology, 125805.

Zinc oxide:

Vannozzi, L., Gouveia, P. J., Pingue, P., Canale, C., & Ricotti, L. (2020). Novel ultra-thin films based on a blend of PEG-b-PCL and PLLA and doped with ZnO nanoparticles. ACS Applied Materials & Interfaces.

Minor revision:

• The list of authors misses the last one.
• Section 2.1: “ Greczynski et. al. [27] showed that in reactive processes of HiPIMS, metal reactivity, which controlled the rate of compound formation at the target, was expected to be a decisive parameter, as it affected the target sputtering conditions and the extent of gas rarefaction.” This part must be moved in the Discussion section
• Section 2.2. Which is the meaning of “soft” in line 132? It is correlated to the implant material
• Section 2.2. Which is the meaning of “departures” in line 136? Please the authors use a more appropriate term, as for example “differences”.
• Line 175. Correct the typo “from the standard of ISO 10993-5, Each kind of the samples”
• Figure 2. The statistical analysis is not clear.
• Figure 5. The statistical analysis is not clear.
• Line 300. I would avoid the use of “great” to describe the biomaterial
• Line 316. Correct the typo “issue”

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

The paper concerns complex Ti surface treatment to achieve biocompatibility and antibacterial properties of future implants. However, the treatment itself and the style of report is non-structured and confusing. The paper is too large, and no state-of-the-art is clearly presented.

1. The title is misleading due to the absence of the PEO and problems with English grammar
2. The technological processing route is too complex; therefore, it must be drawn as Fig. 1. Also, the assays must be indicated there.
3. No research goal was formulated in the Introduction
4. What Ti grade was used?
5. Why the initial surface roughness was 0.5 μm? How did you produce the cross-sections of the coatings with so rough substrate? Where are the cross-sections? What is the coating thickness for the both PEO and HiPIMS stages?
6. For the PEO coating, what are the voltage, current pulse magnitudes? Is the treatment unipolar or bipolar? What is the operating electrolyte temperature? How wide the temperature variation is? This all makes the coatings and the results absolutely unreproducible even by the authors.
7. The authors completely misunderstand the concept of the electrochemical treatments, because having growing coating with increasing thickness, and, therefore, resistance, absolutely cannot be achieved under constant voltage and current simultaneously as indicated in lines 102-108.
8. No corrosion studies are shown to characterize the suitability and durability of the coatings for the implant applications.
9. The input of the PEO and HiPIMS processes into the coating morphology is unclear. Neither XPS, nor XRD gives the idea how the coating is generated through the technology.
10. In Fig. 5, 6, 7 only the significant differences must be indicated with the stars.
11. The conclusions are either trivial or unreadable due to the problems with the word choice.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors replied to all my comments.

The only exception regards the statistical analysis. I would suggest to not show in Figure 6-8 cases with p>0.05. And in the case of statistical difference, the use of stars may help to identify the differences among the sample types

Author Response

Thanks a lot for the Reviewer’s suggestion. 

We have revised the Fig. 3 and Fig. 6-8, which do not show with p>0.05. Only use of stars to identify the differences among the sample types. 

Reviewer 3 Report

The authors did a great job on the article correction and improvement. However, some minor points should be completed.
1. The sample codes and photo of Calo test crater should be added to Figure 1.

Author Response

Thanks a lot for the Reviewer’s suggestion. We have revised the Fig. 1 to add sample codes and photo of Calo test crater as shown in the revised manuscript.