Evaluating the Electrochemical and In Vitro Degradation of an HA-Titania Nano-Channeled Coating for Effective Corrosion Resistance of Biodegradable Mg Alloy

Round 1

Reviewer 1 Report

It is a interesting work and the manuscript is clear in logic and thorough in analysis. It is suggested that this article be published  after addressing the following problems.

1. The thickness of the TNC and HA-TNC should be addressed.

2. The morphology of the cross-section of the HA-TNC and TNC  should be studied.

Author Response

Authors are highly thankful to the reviewer for his valuable comments and we have tried our level best to incorporate all the suggestions given by the reviewer. All the amendments in the manuscript have been depicted in red text for the convenience of editors and reviewer.

Reviewer 2 Report

The manuscript by Kamal Kumar et al. describes a study that focused on combining anodization and sol-gel dip coating. In this work, a new and almost defect-free hydroxyapatite (HA)-TiO2 nano-channelled (TNC) coating architecture was made on ZM21 Mg alloy.
The work itself is nice, the study is properly conducted, the data presentation and description are clear, and the authors' claims and conclusions seem well supported. So, I think the manuscript on biomimetic thin films is interesting for coatings and could be published. However, I would suggest a few small changes to the text, some of which are in the pdf file and others are listed below:
Which is the nature of the bonding between the HA-TNC-coated surfaces?
What is the optimal thickness in terms of interface adhesion?
What about the hydrophilicity of the HA-TNC-coated surfaces? Can the author tell us more about the surface's roughness?

A cross-section of the interface would be useful to understand the interface modification before and after the corrosion test..

The captions of Figures 3 and 9 are not clear, and the readability should be improved.
Out of curiosity, in what sense do "the results of this work give a reasonable design for the creation of bioactive ceramic coatings on bioimplants based on magnesium"?

 

Comments for author File: Comments.pdf

Author Response

The authors are highly thankful to the reviewer for his valuable comments, and we have tried our level best to incorporate all the suggestions given by the reviewer. All the amendments in the manuscript have been depicted in red text for the convenience of the editor and reviewer.

Author Response File: Author Response.docx

Reviewer 3 Report

General comments

 

The submitted manuscript reports on the production and characterisation of a hydroxyapatite (HA)-TiO2 nano-channelled (TNC) coating on ZM21 Mg alloy by combining anodization and sol-gel dip coating technique.

The topic is interesting and worthy of investigation, and it matches with the aim and scope of Coatings. However, major revisions have to be applied.

Finally, a deep English grammar and language revision is strongly recommended.

More details and specific remarks and suggestions are reported below point by point.

 

 

Keywords

The chosen keywords (i.e. Corrosion resistance; Hydroxyapatite; Titania nano-channels; Mg alloy, apatite mineralization) have to be reported in a more logical order (i.e. materials, processing, characterisations, properties, applications).

 

Introduction

-        The incipit “Worldwide millions of people suffer bone fractures every year from diseases and accidents. Due to contemporary work culture, the meagre physical routines of humans have resulted in a rising number of skeletal disorders in recent decades..” needs to be supported with suitable references,

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-        The originality has to be better highlighted, at the end of the Introduction section.

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2. Materials and Methods

2.2. Coatings Development

2.2.1. Development of TiO2 nano-channeled (TNC) coating

- The heating and cooling rates for the sintering at 450 °C have to be specified.

2.2.2. Fabrication of Hydroxyapatite - TiO2 nano-channeled (HA-TNC) coating

- For the calcination, the heating and cooling rates have to be specified.

2.3. Analysis of surface morphology

- For FTIR measurements, the number of scans has to be specified.

3. Results and Discussion

As a general consideration, the Authors should more deeply discuss the acquired data, comparing them with the literature.

3.1. Analysis of surface morphology

- Please, correctly rewrite the following phrase “The SEM-EDX analysis of Polished ZM21 Mg alloy shown in Fig. 2 (a).

- How were the tubular nanochannels sizes evaluated? Add details in the related Experimental section, specifying the used software and the numer of nanochannels considered in order to provide an average value.

- The following sentence “However, a few microcracks in the coating that were caused by the evaporation of organic residue from the coating surface during the calcination process.” has to be correctly rewritten.

- It is not possible to use the EDX data to evaluate the Ca/P ratio, sicne it is not a quantitative and chemical analysis. Specific chemical analyses have to be used, such as ICP, XRF…

- All the FTIR peaks assignements have to be supprote dwith proper references. For example, for HAP, the reference “Thermal stability and sintering behaviour of hydroxyapatite nanopowders. Journal of thermal analysis and calorimetry, 88(1) (2007), 237-243” could be used and cited.

3.4. In-vitro apatite mineralization

- The statement “Such substitution caused lattice distortion and compromised the structural stability of HA” needs proper references, including “Mg-substituted hydroxyapatite nanopowders: synthesis, thermal stability and sintering behaviour. Journal of the European Ceramic Society, 29(14) (2009), 2969-2978.”.

- As evidenced before, EDS data cannot be considered quantitative data, but only an estimation.

- All the FTIR assignements have to be supported with appropriate references.

Author Response

The authors are highly thankful to the reviewer for his valuable comments, and we have tried our level best to incorporate all the suggestions given by the reviewer. All the amendments in the manuscript have been depicted in red text for the convenience of the editor and reviewer.

Author Response File: Author Response.pdf

Reviewer 4 Report

The paper is very interesting for the readers. However, there are some items which needs to be revised as follows:

(1) The EDX analysis confirms the uniform distribution of secondary phase particles (i.e. Zn and Mn) in the Mg matrix. How do you confirm these secondary phases? I suppose the microstructure analysis in this paper is not well written. For example, it had better give some interface analysis between the Mg matrix and  HA-TNC or TNC.Even it is necessary ti give some interfacial images. 

(2) The Polished ZM21 Mg samples showed a significantly higher degradation rate than the biosafety limits prescribed for human consumption. How do you know that? Proof or references?

(3) As compared to HA-TNC coated ZM21(28 day) sample, continues decrease in the intensity of PO4 3- peaks and gain in intensity of Mg-O peaks were observed in order of HA-TNC coated ZM21(28 day) sample  < HA-TNC(14 day) sample < TNC coated (28 day) sample < TNC coated (14 day) sample.  For this setence, there exists some English errors. Please check other sentences in this paper again.

Author Response

The authors are highly thankful to the reviewer for his valuable comments, and we have tried our level best to incorporate all the suggestions given by the reviewer. All the amendments in the manuscript have been depicted in red text for the convenience of the editor and reviewer.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Now it can be accepted.

Reviewer 3 Report

The Authors have applied the Reviewers'suggestions and now the paper looks very improved.