Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Although the PECVD method is described in sufficient detail, there are no details regarding substrate temperature control during multilayer coating deposition. While the temperature was stated to be maintained at 65 ^oC, no explanation is provided regarding how temperature stability was ensured during the transition between layers, particularly given changes in the reactive gas flow. The possible influence of plasma parameters (e.g., plasma density, degree of ionization) on layer stoichiometry and adhesion, which is important for process reproducibility, is also not discussed.

The stated goal of the study is to improve osseointegration; however, the article lacks direct biological tests (cytocompatibility, osteoblast adhesion, and proliferation, in vitro or in vivo models). Conclusions regarding biological efficacy are drawn primarily from indirect data: surface hydrophilicity and comparisons with literature. To substantiate the claimed advantages of a multilayer coating, it is necessary to include the results of at least preliminary biological experiments, such as assessment of protein adsorption or cellular viability.

The decrease in the O/Ti ratio is quite significant, but it is not evident in the XPS spectra. There is also no evidence of the formation of Ti-C bonds. Some clarification would be appreciated.

Therefore, I believe that the article requires major revision.

Author Response

Please refer to the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This study conducted a materials evaluation of a novel coating formed by PECVD of a TiOxCy organometallic multilayer on a Ti6Al4V substrate, where the carbon gradient was designed by varying the O₂ flow rate. The approach of continuously varying chemical composition from inorganic to organic using a TiOₓCᵧ gradient structure is novel. The background of enhancing dental implant performance through surface modification of materials is also clear. However, the current manuscript shows insufficient data to support the claims regarding biological effects. To make the paper more robust, the following concerns should be addressed.

 

・This paper does not present any data on biological performance, such as cell tests (in vitro) or protein adsorption tests (in vivo). Therefore, in sections such as the Abstract, Introduction, and Discussion, assertive statements should be rephrased as speculative ones (e.g., enhanced, promote, improve).

・The authors should discuss the effects of contact angle differences on protein adsorption based on literature and strengthen the scientific rationale.

・Numerous studies exist on TiC and TiOC-based coatings. The novelty of this paper lies in the fact that it achieves a continuous carbon gradient multilayer structure through O₂ flow rate control. However, the thickness of each layer in the multilayer coating, the evaluation method for the continuity of the gradient, and the clarification of differences from existing TiC/TiOC coatings remain unclear. The author should explain these points.

・Presenting the XPS depth profile comparison between multilayer and individual films in a diagram enhances the persuasiveness of the argument.

・The authors should clearly review whether TiOC/TiC multilayers exist in prior research and explicitly state the originality of this study.

・Creating new diagrams for the following items will make it easier for readers to understand.

 

Schematic Diagram of Multilayer

XPS depth profile

Comparison of contact angles for each layer

High O₂ vs Low O₂ XPS spectrum overlay

 

Results

・The actual measured values for the substrate bias voltage and substrate temperature should be clearly specified.

・The XPS atomic % vs. Depth line graph should be displayed as a multilayer graph.

・Adding statistical analysis of the contact angle (ANOVA or t-test) will make it easier for readers to understand.

Discussion

・To provide a more detailed explanation of Veronesi et al. (lines 98–101), which demonstrated improved cell affinity of TiC, the reference should be cited.

・Please provide further explanation regarding the potential for gradient structures to suppress crack propagation (from a materials mechanics perspective).

Author Response

Please refer to the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors point by point answered my questions. However, I would recommend some changes before accepting the manuscript.

I would recommend revising the abstract and introduction, taking into account that no biological experiments were performed, and discussing the coating efficiency more cautiously.

I would also recommend expanding the discussion of XPS in accordance with the authors' answer to my question.

Author Response

Dear Reviewer,

We would like to sincerely thank you for your careful evaluation of our manuscript and for your constructive comments, which have helped us to significantly improve its clarity and scientific rigor. Below, we provide a detailed response to your comments and summarize the modifications introduced in the revised version.

We believe that these revisions have significantly improved the clarity, accuracy, and scientific rigor of the manuscript. We are grateful for your insightful comments, which have strengthened the overall quality of the work.

 

Comment 1: I would recommend revising the abstract and introduction, taking into account that no biological experiments were performed yet, and discussing the coating efficiency more cautiously.

• To answer the reviewer:
  • Thank you to the reviewer for this interesting comment. The authors have modified several sections of the manuscript to emphasize that no biological tests were performed and that, therefore, our work focuses on the surface and physicochemical characterization of the developed coating. The following details of all the changes made to the abstract, introduction, results, and conclusions.
• Modifications carried out in the revised manuscript:
  • Abstract

OLD Version:

Titanium alloys are widely used in biomedical applications, especially in dental im-plants. While their biological performances are generally satisfactory, surface optimization is crucial to enhance adhesion between the implant screw and the surrounding environment, thus promoting osseointegration and improving clinical success. In this work, individual TiOxCy thin films, and a novel multilayer coating approach, have been investigated to prevent early implant failure through surface properties optimization. The research focuses on designing innovative TiOxCy organometallic multilayer coating, varying from mineral (low C) to organic (high C), on Ti6Al4V substrates. These coatings were prepared using PECVD technique, varying parameters as the re-active gas flow to modify the chemical composition, hydrophilicity, and layer thick-ness. Comprehensive characterization of the surface was conducted using XPS, and by contact angle to evaluate wettability. To further understand the chemical composition within each layer, XPS depth profiling analyses are performed. The results revealed that the newly designed multilayer coating with a decreasing reactive gas flow clearly exhibited a gradient in its composition. Near the upper substrate surface, the layers display a mineral-like, low-carbon structure, transitioning to an organic-like, high-carbon composition at the outermost surface, engineered to interact with organic tissue.

 NEW Version:

Titanium alloys are widely used in biomedical applications, especially in dental implants. In this work, individual TiO_xCy thin films, and a novel multilayer coating approach, have been investigated to prevent early implant failure through surface properties optimization. The research focuses on designing innovative TiOxCy organometallic multilayer coating, varying from mineral (low C) to organic (high C), on Ti6Al4V substrates. These coatings were prepared using PECVD technique, varying parameters as the re-active gas flow to modify the chemical composition, hydrophilicity, and layer thickness. Comprehensive characterization of the surface was conducted using XPS, and by contact angle to evaluate wettability. To further understand the chemical composition within each layer, XPS depth profiling analyses are performed. The results revealed that the newly designed multilayer coating with a decreasing reactive gas flow clearly exhibited a gradient in its composition. Near the upper substrate surface, the layers display a mineral-like, low-carbon structure, transitioning to an organic-like, high-carbon composition at the outermost surface.

• Introduction Line 114:

OLD Version:

Altogether, in this work a TiOₓCᵧ organometallic multilayer with varying compo-sitions was developed and studied to optimize both interfacial adhesion and surface bioactivity

NEW Version:

Altogether, in this work a TiOₓCᵧ organometallic multilayer with varying compo-sitions was developed and studied to optimize the chemical properties of the dental implant interface.

• Introduction Line 129:

OLD Version:

leading to a more organic-like character that could promote osteointegration [34].

NEW Version:

leading to a more organic-like character that could be favorable for interface interactions with biological tissue [34].

• Introduction:

NEW Version:

This work provides a deep chemical characterization of the surface and the carbon gradient multilayer architecture. No biological test has been carried out at this stage; therefore, the results are limited to chemical and wettability analyses. The biological effects have been discussed in base to the literature correlations between surface chemistry and wettability with the biological response. 

• Results and discussion Line 200:

OLD Version:

 The organometallic TiOxCy multilayer coating is proposed for two key purposes: (i) to enhance osteointegration by optimizing the physicochemical properties of the in-terface between the substrate and the organic tissue [35], [36], and (ii) to prevent direct contact between the biological environment and metallic elements such as aluminum and vanadium [8], [37], [38].

NEW Version:

The organometallic TiOxCy multilayer coating is proposed for two key purposes: (i) to modify the physicochemical properties of the interface between the Ti6Al4V and the organic tissue [35], [36], and (ii) to prevent direct contact between the biological environment and metallic elements such as aluminum and vanadium [8], [37], [38].

• Conclusions Line 500

OLD Version:

 These findings highlight that the properties of the multilayer could be favorable for protein adsorption and osteointegration particularly in dental applications.

NEW Version:

These findings indicate that the physicochemical properties of the multilayer could promote protein adsorption, particularly in the context of dental applications..

 

 

Comment 2: I would also recommend expanding the discussion of XPS in accordance with the authors' answer to my question.

• To answer the reviewer:
  • O/Ti ratio:

We thank the reviewer for this comment.  Figures 2, 4, and 6 show the O/Ti, C/Ti, and C/O ratios.

On the one hand, in Figure 2b, where the chemical composition of the surface is analyzed, it can be observed that the O/Ti ratio is stable with a value of 1.6, while the C/Ti and C/O ratios decrease with increasing oxygen flux. Specifically, the C/Ti ratio presents values ​​of 1.3, 1.1, 1.0, and 0.4 for oxygen fluxes of 0, 5, 10, and 15 sccm, respectively.

To better understand these changes, I have overloaded the spectra to analyze how the different chemical states change depending on the oxygen flow

Furthermore, Figure 3d introduces the quantification of chemical states to graphically support the decrease in carbon with increasing oxygen flux and specifically shows the decrease in the C-C contribution.

On the other hand, Figure 4 shows the XPS profiles inside the individual thin films. Specifically, in Figure 4f, one can observe the O/Ti, C/Ti, and C/O ratios obtained inside the individual sheets. Again, the O/Ti ratio is stable, with a value of 0.9, while the C/Ti and C/O ratios decrease as the oxygen flow increases.

 

The reactive gas (oxygen) reacts with the precursor but does not modify the oxidation of the titanium from the precursor and consequently of the layers (O/Ti being stable), but the oxygen introduced into the chamber breaks the carbon bonds of the precursor inducing a reduction of carbon and for that reason the C/O and C/Ti ratios decrease with the increase in the oxygen flow

 

There was an error in line 453; evidently, the O/Ti value is stable at approximately 0.9, while the C/Ti ratio decreases, as can be seen in Figures 2, 4, and 6. This error has already been corrected in the manuscript

 

The difference between the O/Ti ratio values ​​obtained on the surface and inside the layers, which varies from 1.6 to 0.9 respectively, is due to surface contamination and the oxidation that titanium undergoes when exposed to air. This decrease can be seen in the first few seconds of etching in Figure 6b. Despite efforts to minimize exposure time to air, some surface contamination always remains.

• Ti-C bond:

The absence of the Ti-C bond has been explained

• Ar⁺ sputtering:

The depth profiles were performed using argon ion sputtering with an energy of 2000 eV, it may induce slight preferential sputtering or reduction effects in titanium oxides. However, the measurements performed on the surface of the individual films indicate that the carbon gradient behavior is intrinsic to the deposition process rather than an artifact of sputtering.

 

 

• Modifications carried out in the revised manuscript:

 

• Results and discussion O/Ti ratio Line 453:

OLD Version:

 Notably, the sequential reduction in the empirical coefficient y equal to the O/Ti ratio varies from 0.35 to 0.10 across the organometallic TiO0.9Cy multilayer directly correlates with the modulation of oxygen flow during deposition (0 to 15 sccm) and confirms that carbon incorporation can be finely tuned by adjusting the flow of the re-active oxygen plasma environment.

NEW Version:

Notably, the sequential reduction in the empirical coefficient y equal to the C/Ti ratio varies from 0.35 to 0.10 across the organometallic TiO0.9Cy multilayer directly correlates with the modulation of oxygen flow during deposition (0 to 15 sccm) and confirms that carbon incorporation can be finely tuned by adjusting the flow of the re-active oxygen plasma environment.

 

• Results and discussion O/Ti ratio Line 315:

OLD Version:

 Figure 3d shows the atomic percentage of the different contributions. The graph shows that the titanium oxide and O-Ti contributions increase with increasing oxygen flow, while the C-C contribution decreases.

NEW Version:

Figure 3d shows the atomic percentage of the different contributions. The graph shows that the titanium oxide and O-Ti contributions increase with increasing oxygen flow, while the C-C contribution decreases. This behavior indicates that Ti:O is practically stable, while the carbon content can be systematically adjusted by modulating the oxygen flow.

 

• Results and discussion Ti-C bond Line 311:

OLD Version:

Concerning the possible formation of Ti–C bonds, no such contribution is detected in the C 1s spectra. No peak is observed in the 281–282 eV binding energy range characteristic of titanium carbide.

NEW Version:

Concerning the possible formation of Ti–C bonds, no such contribution is detected in the C 1s spectra. No peak is observed in the 281–282 eV binding energy range characteristic of titanium carbide indicating that no titanium carbide bonds were created.

Reviewer 2 Report

Comments and Suggestions for Authors

Congratulations！

All modifications confirmed.

Author Response

We would like to sincerely thank the reviewer for the positive evaluation of our manuscript. We truly appreciate the time and effort devoted to the review process. The constructive comments and suggestions have been very helpful and have significantly contributed to improving the quality and clarity of our manuscript.