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Article
Peer-Review Record

Influence of Post-Deposition Thermal Treatments on the Morpho-Structural, and Bonding Strength Characteristics of Lithium-Doped Biological-Derived Hydroxyapatite Coatings

Coatings 2022, 12(12), 1883; https://doi.org/10.3390/coatings12121883
by L. Duta 1,*, G. E. Stan 2, G. Popescu-Pelin 1, I. Zgura 2, M. Anastasescu 3 and F. N. Oktar 4,5
Reviewer 1: Anonymous
Reviewer 2:
Coatings 2022, 12(12), 1883; https://doi.org/10.3390/coatings12121883
Submission received: 4 November 2022 / Revised: 25 November 2022 / Accepted: 29 November 2022 / Published: 4 December 2022
(This article belongs to the Special Issue Synthetic and Biological-Derived Hydroxyapatite Implant Coatings)

Round 1

Reviewer 1 Report

Thank you for the opportunity to review this paper. This is an interesting piece of work considering that it aims to survey if a fine tuning of the physical-chemical and surface energy characteristics, as well as of the bonding strength of Li-doped BHA coatings could be further made possible via post-deposition annealing treatments performed at different temperatures and ambient. Despite the hard work collecting data in this manuscript,  I do not think this present version is good enough to be published in COATINGS.

·         The Introduction section is too long and sometimes vague (e.g: HA paragraphs); it must be rewritten to be better understood by a broad audience.

·         M&M, section 2.3: Did the powder receive any mixing with reused powder, or were they virgin?

·         Section 2.6: how the amount of Carbon from contamination was measured? What was the rationale for using Contact Angle on a rough surface?  

 

·          Please provide the implications of your results for the clinical level (primarily related to Lithium biocompatibility), the limitations of your project, and recommendations for future works.

Author Response

In response to the recommendations and suggestions of your first Reviewer:

 

Thank you for the opportunity to review this paper. This is an interesting piece of work considering that it aims to survey if a fine tuning of the physical-chemical and surface energy characteristics, as well as of the bonding strength of Li-doped BHA coatings could be further made possible via post-deposition annealing treatments performed at different temperatures and ambient.

Response (R): First of all, the authors would like to thank very much to this Reviewer for her/his appreciative words regarding our study. We are also grateful for the constructive suggestions which helped us improve the quality of the manuscript. Our responses are listed in the order they appear in the report.

 

  1. The Introduction section is too long and sometimes vague (e.g: HA paragraphs); it must be rewritten to be better understood by a broad audience.

R1: The authors took into consideration the Reviewer’s suggestion and rewrote the Introduction section. Its length was initialy reduced, by eliminating any possible vague pharagraphs. To respond to one of the recommendations of the second Reviewer, the authors had to introduce suplementary information, but paid attention also to the overall length of the text. We do hope now that, the current version of this section is easier to be read and understood by a broader audience.

 

  1. M&M, section 2.3: Did the powder receive any mixing with reused powder, or were they virgin?

R2: When fabricating the targets, to avoid any possible mixing with reused powders, the authors paid extra attention to (i) always use virgin powders, and (ii) assure a careful cleaning of the stainless-steel matrix (used to press the powders), mortar and pestle. This information was introduced in the revised version of the manuscript (please see page 3, lines 131 to 132).   

 

  1. Section 2.6: how the amount of Carbon from contamination was measured? What was the rationale for using Contact Angle on a rough surface?

R3: The possible Carbon (C) contamination of our source materials and targets did not pose any problem because these were sintered at high temperatures, where C is eliminated. In the case of films, C was indeed present. Its origin can be partly due to atmospheric pollution during various sample manipulations after deposition. But the authors would like to stress upon that, HA containing C was demonstrated to be more osseoconductive and more resorbable than stoichiometric HA. In the case of animal origin materials, C was shown to be an ubiquitous element, the mineral component of bone being, in fact, a non-stoichiometric carbonated HA.

Keeping in mind the case of a liquid droplet on an ideal solid surface (which is flat, rigid, smooth and chemically homogeneous), one should emphasize that, in reality, there are only few solid surfaces which are actually flat. In this respect, the roughness is one of the important parameters that should be considered when investigating the wetting behavior of a certain solid surface. Moreover, it was demonstrated that, the roughness influence can prove significant for dynamic or static wetting. Also, it is important to mention that, the CA is not influenced by the topological aspects only, but also by the physical-chemical, and mechanical characteristics.

A summary of this information, along with the corresponding references, was included in the revised version of the manuscript (please see page 14, lines 477 to 480, page 16, lines 531 to 538, page 20, lines 610 to 614).  

 

  1. Please provide the implications of your results for the clinical level (primarily related to Lithium biocompatibility), the limitations of your project, and recommendations for future works.

R4: The possible implications of our current results in medicine, along with recommendation for future work were introduced in the Conclusions section (please see page 23, lines 687 to 699).

Reviewer 2 Report

The study is mostly focusing on biologically-derived hydroxyapatite (HA) coated with lithium carbonate 19 (LiC) and lithium phosphate (LiP) synthesized by pulsed laser deposition onto Ti6Al4V 20 substrates fabricated by additive manufacturing.

1. Title is too long and should be shortened. 

2. Along the same lines, graphical abstract may also help to draw the readers' attention with a specific paper focus.

3. Also, just as a suggestion, a brief paragraph about the past/current studies in the field may be good to mention.

Author Response

In response to the recommendations and suggestions of your second Reviewer:

The study is mostly focusing on biologically-derived hydroxyapatite (HA) coated with lithium carbonate 19 (LiC) and lithium phosphate (LiP) synthesized by pulsed laser deposition onto Ti6Al4V 20 substrates fabricated by additive manufacturing.

Response (R): The authors are grateful to the Reviewer for her/his careful analysis and recommendations. We considered all of them in the revised version of the manuscript. Our responses are listed in the order they appear in the report.

  1. Title is too long and should be shortened.

R1: Modification done. The new title reads as: “Influence of post-deposition thermal treatments on the morpho-structural, and bonding strength characteristics of lithium-doped biological-derived hydroxyapatite coatings”.

 

  1. Along the same lines, graphical abstract may also help to draw the readers' attention with a specific paper focus.

R2: The authors took into consideration the Reviewer’s recommendation and improved the Graphical Abstract. We hope now that the main idea of the manuscript is better focused.

 

  1. Also, just as a suggestion, a brief paragraph about the past/current studies in the field may be good to mention.

R3: The Introduction section was reconsidered based on the suggestions and recommendations of the three Reviewers. 

Reviewer 3 Report

The authors reviewed research articles dedicated to the influence of post-deposition thermal treatments on the structural, morphological, and bonding strength characteristics of 3 lithium-doped biological-derived hydroxyapatite coatings synthesized by pulsed laser deposition.

There are several problems to be addressed:

The authors should add some more information in introduction regarding the goal of adding lithium to the coating. What is the mechanism of it’s influence on the improvement of cell adhesion and differentiation?

The introduction describes the prospects of titanium using for use as implant material. However, the substrate preparation section describes the TiAlV alloy. It is known that the components of this alloy have a toxic effect. Authors should describe the justification for using such an alloy in the introduction. In the paper indicates that the substrate is titanium. The authors should use term of titanium alloy.

Provide images of the drops in the wettability analysis.

I suggest improve the conclusion section. The authors should outline the most appropriate coatings for biomedical applications. What type of coating and thermal treatment parameters allow to obtain the coating with optimal or best properties.

Author Response

In response to the recommendations and suggestions of your third Reviewer:

 

The authors reviewed research articles dedicated to the influence of post-deposition thermal treatments on the structural, morphological, and bonding strength characteristics of 3 lithium-doped biological-derived hydroxyapatite coatings synthesized by pulsed laser deposition.

Response (R): The authors are grateful to the Reviewer for her/his careful analysis and valuable remarks and recommendations. We considered all of them in the revised version of the manuscript. Our responses are listed in the order they appear in the report.

 

  1. The authors should add some more information in introduction regarding the goal of adding lithium to the coating. What is the mechanism of it’s influence on the improvement of cell adhesion and differentiation?

R1: The authors took into consideration the Reviewer’s suggestion, but kept in mind also the recommendation of the first Reviewer to reduce the length of this section. Thus, the Introduction section was amended with information on lithium incorporation in HA-based structures (please see page 2, lines 89 to 96).  

 

  1. The introduction describes the prospects of titanium using for use as implant material. However, the substrate preparation section describes the TiAlV alloy. It is known that the components of this alloy have a toxic effect. Authors should describe the justification for using such an alloy in the introduction. In the paper indicates that the substrate is titanium. The authors should use term of titanium alloy.

R2: The Introduction section was revised based on the Reviewer’s suggestion. Thus, text containg the justification for using Ti6Al4V as apropriate substrates for the current study was introduced (please see page 2, lines 51 to 64). Moreover, to avoid any possible confusion, the term „Ti substrates” reads now as „Ti6Al4V substrates” (page 4, line 159).

 

  1. Provide images of the drops in the wettability analysis.

R3: Following the Reviewer suggestion, two new figures (Figures 13 and 14, page 19) containing the representative images of the droplets on the sample surfaces, were introduced in the revised version of the manuscript.

 

  1. I suggest improve the conclusion section. The authors should outline the most appropriate coatings for biomedical applications. What type of coating and thermal treatment parameters allow to obtain the coating with optimal or best properties.

R4: The conclusion section was improved based on the Reviewer’s suggestion. The optimal thermal treatment parameters allowing to obtain the most appropriate coatings for medical applications were therefore outlined (please see page 23, lines 684 to 687).

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