Characterisation of TiCN Coatings for Biomedical Applications

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The objective of this work is to analyze the properties of TiCN coatings that are applied over Ti6Al4V via physical vapor deposition. The study presents results on surface morphology, geometric structure, adhesion, instrumental hardness, and tribology. The topic is interesting followed by deep analysis. To improve the manuscript, some minor issues must be addressed by the authors:

1.     In the manuscript, "biomedical application" was the central core of the analysis. However, the biocompatibility of the use of TiCN coatings is not addressed in the Introduction. Please include this information in order to enhance the current state of the research. Also, please add What are the key properties of coatings that make them suitable for biomedical applications?

2.     Line 64. Who are the authors in the citation must be written. Please see the author's guide

3.     Line 122. What is the significance of the acoustic emission in the scratch test in the context of biomedical application? Please elaborate in detail.

4.     Line 212-213. “Based on the results of mechanical tests, it is assumed that the titanium alloy will have lower wear resistance than the titanium nitride coating.” It is recommended that the discussion regarding the implications of low wear resistance in the context of biomedical application be included in accordance with the central topic of the paper, which is biomedical application.

5.     Line 226-2277. “This was most likely due to the high surface roughness of the coating and the running-in stage in the initial phase of the test.” Please explore on what is the main effect of surface roughness on the tribological properties of DLC coatings to create this trend.

6.      Please elaborate in detail what is the exact “high” value of the surface roughness. In Line 98 “The surface roughness (Sq) after mechanical processing was 0.08 μm.” In my opinion. the surface roughness is not so high in the scale system used by the authors.

7.     How do the mechanical properties of TiCN cotaings compare to other commonly used coatings in biomedical applications? Please add it

Author Response

Dear Reviewer,Thank you very much for your time, substantive and editorial assessment of my manuscript, and for your positive opinion and comments. For me, they are valuable tips for future research. I would like to inform that, I have followed your comments.

1. The introduction contains information about the biocompatibility of TiCN coatings and the properties that make it a good material for medical applications.
2.  I corrected it.
3. The most important parameter indicating the suitability of coatings is their adhesion to the substrate. One of the criteria assessing the quality of deposited coatings is acoustic emission. Critical points Lc1-Lc3 by the PN-EN ISO 4624:2016-05 standard describe the moments when the coating was violated: cracking or chipping. In the case of biomaterials, adhesion of coatings is extremely important because their task is to improve mechanical, tribological, and corrosion properties, but also to perform protective functions against bacteria. Lack of adhesion of the coating poses a risk of implant loosening and wear products of the Ti6Al4V alloy entering the blood. The results obtained during the test describe the coating's resistance to scratching and how the material's surface will cooperate with human tissue.
4. Due to the achievement of higher values ​​of the instrumental hardness of the tested coatings (TiCN) in relation to the base material - Ti6Al4V alloy, better tribological properties of biocompatible coatings should be expected.
5. The literature [1] shows that during lapping, the tops of the roughness are sheared, which, when the surface is highly developed, as in the case of the TiCN coating, causes an increase in the friction coefficient in the initial phase of the test. In the case of the titanium alloy Ti6Al4V with Sq equal to 0.08 μm, this phenomenon was not observed.
6. For ground and polished titanium alloy samples, the amplitude parameters were Sq = 0.08 μm, Sv = 0.51 μm, Sp = 1.50 μm, Ssk = -0.04, Sku = 3.34, respectively. However, after applying the TICN coating, these parameters increased and were Sq = 0.13 μm, Sv = 1.55 μm, Sp = 2.12 μm, Ssk = 0.98, Sku = 9.75, respectively. Therefore, as a result of the deposition of the TiCN coating on the Ti6Al4V titanium alloy, all amplitude parameters increased - which indicates that the surface roughness of the Ti6Al4V titanium alloy increased. Depending on the application, different surface development is required. For example, endoprosthesis heads must have a Ra parameter of 0.05 μm. However, in the case of applications for elements, e.g. hip endoprosthesis stems or connectors used in dental implantology, greater surface development is expected due to better osseointegration.
7. Carbon coatings are very popular in medicine. Comes with features: • good tolerance in the tissue environment, • electrical neutrality ensuring good hemocompatibility, • good physicochemical properties, and therefore very good biocompatibility, • low friction coefficient, around 0.08. For this reason, they can be used for heads of endoprostheses where low friction coefficients are required. Hard ceramic coatings are also increasingly used in biomedical engineering. Titanium nitrides and carbonitrides deserve special attention. The great interest in titanium nitride-based coatings results from their mechanical properties - high hardness and adhesion, biocompatibility and surface roughness. On this basis, TiN-based coatings are very often deposited on the surfaces of tools or prosthesis elements made of surgical steel or titanium alloys. Coatings applied to biomaterials may also fulfill additional functions in terms of induced biological reactions. This effect can be achieved by doping these with specific elements. They can perform both antibacterial functions (e.g. silver, copper, silicon) and accelerate the osseointegration process (e.g. titanium, silicon). Additionally, due to its color (pink), the TiCN coating can be used for prosthetic connectors and elements of dental prostheses. The choice of coating depends on the application and what function it will perform. Comparison of the properties of titanium nitride-based coatings will be the subject of the next article, in which I will discuss the following coatings: TiN:Ag, TiCN and TiAlN.
    

[1]. Guegan J., Kadiric A., Gabelli A., Spikes H., The Relationship Between Friction and Film Thickness in EHD Point Contacts in the Presence of Longitudinal Roughness, Tribology Letters, 64(33), 2016

Reviewer 2 Report

Comments and Suggestions for Authors

This is an interesting high-quality paper devoted to the characterization of TiCN coatings for biomedical applications. The coatings of TiCN system on titanium alloys are well known and have been investigated in numerous papers. Despite the rather developed topic, the paper under review obtains some original new results that may be of interests to the readers of the Coatings journal. For example, tribological characteristics of TiCN coating in artificial saliva compared to the original titanium alloy. These results may be of interest both for science and for the development of implantology. The reviewer did not find any serious remarks to the paper, excluding some misprints. The article can be published at present form.

 

Author Response

Dear Reviewer,

Thank you very much for your time, substantive and editorial assessment of my manuscript, and for your positive opinion and comments.

Reviewer 3 Report

Comments and Suggestions for Authors

 The paper entitled “Characterisation of TiCN coatings for biomedical applications” presents a topic of real interest regarding biomaterials and medical devices.

The authors demonstrate a good adhesion of TiCN coating on Ti6Al4V which ensures low-friction and anti-wear properties to the surface of the titanium alloy.

The manuscript is very well structured, and easy to understand, offering valuable data in figures and tables.

In Conclusions section, the authors should highlight the field of application of the obtained results.

This manuscript could be accepted after a minor revision.

Author Response

Dear Reviewer,

Thank you very much for your time, substantive and editorial assessment of my manuscript, and for your positive opinion and comments.