Low-Temperature Synthesis Approach for Calcium Hydroxyapatite Coatings on Titanium Substrate
, Skirmante Tutliene 2, Aleksej Zarkov 1 and Aivaras Kareiva 1,*
Round 1
Reviewer 1 Report
This article applied a low-temperature synthesis approach for the fabrication of calcium phosphate coatings on titanium substrates by using sol-gel and dissolution-precipitation methods. The authors analyzed and assessed the phase composition, structure, and surface characterization. Though this article has shown some innovations, there are still some suggestions for better improvements. I believed that this article can be considered for publication after revision:
1. Page 2, Line 19 – the introduction section
“All these methods are high-temperature methods, required elevated temperatures to obtain CHAp crystalline phase. However, the high temperatures do not support the formation of nanocrystalline materials.”
It is suggested that the author introduced the influence of the high temperature specifically, which would be more logically flowing and connected with the temperature mentioned in the following section.
Also, in the last paragraph of the introduction, it would be better if the authors address the advantage of the spin-coating technique compared with the previously-mentioned approaches.
2. Page 6, Line 16– the results section
“The results deduced from the FTIR spectra of the formed CHAp coating are in good agreement of XRD and Raman spectroscopy results confirming the formation and origin of intermediate and end products.”
It is suggested that the authors discussed the formation process and the substances formed during this process.
3. Page 8, Line 7– the results section
Please clarify the purpose of heating the coated substrate at 900℃.
4. Page 8, Line 11– the results section
Please give more explanation in Fig.9 and Fig.10.
5. Page 12, Line 19– the results section
“The difference in Eocp values between the tested samples is negligible indicating, that the formed calcium hydroxyapatite coatings are porous.”
It is recommended that you explain the relationship between the differences in Eocp values and the porous structure of calcium hydroxyapatite coatings so that it would be more logically flowing.
6. Page 14, Line 1– the results section
Please concluded the result you obtained, such as comparing the heated Ti substrate and CHAp coating, and 3-CHAp coating after heating at 900℃ when studying the corrosion feature.
7. Please pay attention to the format of Table 1. and turn it into a three-line table.
8. It is recommended that the authors reread the manuscript and adjust some expressions so that the article can be more logically flowing and better understood by the readers.
Author Response
29 December 2022
Editor-in-Chief
Inorganics
In this my letter I enclosed the revised according to the Reviewer 1 comments our manuscript ”Low-Temperature Synthesis Approach for Calcium Hydroxyapatite Coatings on Titanium Substrate” by R. Karalkeviciene, G. Briedyte, A. Popov, S. Tutliene, A. Zarkov, A. Kareiva. (Manuscript No.: inorganics-2131853).
These are changes and answers to the Reviewer comments:
Comment 1. Page 2, Line 19 – the introduction section
“All these methods are high-temperature methods, required elevated temperatures to obtain CHAp crystalline phase. However, the high temperatures do not support the formation of nanocrystalline materials.”
It is suggested that the author introduced the influence of the high temperature specifically, which would be more logically flowing and connected with the temperature mentioned in the following section.
Also, in the last paragraph of the introduction, it would be better if the authors address the advantage of the spin-coating technique compared with the previously-mentioned approaches.
Answer:
Additional sentences are added to the manuscript “The CHAp coatings obtained at 1000 oC could be inhomogeneous, for example consisted of two distinct regions: with small grains, approximately 200 nm in size and with larger grains, approximately 800 nm in diameter [15]. Besides, the formation of TiO2 phase at high temperature reduces adhesion of CHAp films on Ti substrate [16]”.
“The spin-coating method offers great promise for the fabrication of thin films with desirable properties [19]. For example, the spin-coating technique allows to fabricate very homogeneous samples which composed of nano-scaled particles [13].”
Comment 2. Page 6, Line 16– the results section
“The results deduced from the FTIR spectra of the formed CHAp coating are in good agreement of XRD and Raman spectroscopy results confirming the formation and origin of intermediate and end products.”
It is suggested that the authors discussed the formation process and the substances formed during this process.
Answer:
The formation process and the substances formed during this process are discussed in the manuscript, as Reviewer suggested.
Comment 3. Page 8, Line 7– the results section
Please clarify the purpose of heating the coated substrate at 900℃.
Answer:
The obtained CHAp coatings were additionally heated at 900 ℃ to investigate the influence of temperature on the morphological properties and the corrosion behaviour of CHAp thin films obtained at lower and higher temperatures.
Comment 4. Page 8, Line 11– the results section
Please give more explanation in Fig.9 and Fig.10.
Answer:
Additional sentences are added to the manuscript ”As seen from Figure 9, the surface roughness of the Ti substrate increases with formation of CaCO3 coating. The results presented in Figure 10 shows that the formed CHAp coatings are not evenly distributed on the Ti substrate. Moreover, the observed surface roughness for CHAp coatings is higher than for CaCO3 coating”.
Comment 5. Page 12, Line 19– the results section
“The difference in Eocp values between the tested samples is negligible indicating, that the formed calcium hydroxyapatite coatings are porous.”
It is recommended that you explain the relationship between the differences in Eocp values and the porous structure of calcium hydroxyapatite coatings so that it would be more logically flowing.
Answer:
Thank you very much for your comment. The sentence was slightly changed to “The difference in Eocp values between the tested samples is negligible indicating, that the surface properties of formed calcium hydroxyapatite coatings are similar”.
Comment 6. Page 14, Line 1– the results section
Please concluded the result you obtained, such as comparing the heated Ti substrate and CHAp coating, and 3-CHAp coating after heating at 900℃ when studying the corrosion feature.
Answer:
In our opinion these results are sufficiently compared and discussed: “The polarization curves for the CHAp coating are shifted towards more positive values indicating a less active corrosion process… From the calculated values, it can be seen that the CHAp coatings are characterized by higher bk values than the uncoated Ti substrate. The anodic tendency of the Tafel dependence of the obtained coatings decreased compared to that of the titanium substrate. The largest positive boost was determined for the just obtained CHAp coatings. Interestingly, the electrode Eocp of the additionally heated at 900 °C CHAp coating was lower...”.
Comment 7. Please pay attention to the format of Table 1. and turn it into a three-line table.
Answer:
The format of Table 1 is changed.
Comment 8. It is recommended that the authors reread the manuscript and adjust some expressions so that the article can be more logically flowing and better understood by the readers.
Answer:
The manuscript is re-checked by native speaker.
First of all, we would like to thank Reviewer for the valuable remarks. We made almost all changes suggested by Reviewer. The changes made are outlined in the revised manuscript.
Yours sincerely,
Prof. Aivaras Kareiva
Reviewer 2 Report
Hydroxyapatite, by definition, is a calcium phosphate mineral with the chemical formula described in the Introduction. Hence, it is unnecessary and unusual to use „Calcium Hydroxyapatite”. Please correct or justify your option.
In the Introduction the authors should focus on presenting the state-of-the-art and setting out the rationale behind the design of this work. In this case, the information is difficult to follow and poorly presented, jumping from HAp to gas sensors, deposition methods, etc. An introduction should be a cohesive section to describe the topic, followed by a brief review of the most recent bibliography, the rationale, the description of the actual work with a focus on its novelty and significance, and finally the outline of the paper’s contents. In my opinion, it should be enlarged and revised accordingly (for the spin-coating deposition and deposition of calcium phosphates in general please cite Nanomaterials 2019, 9(5), 692).
Materials and methods:
„The resulting solution was mixed with PVA ([-CH2CHOH-]n, 99,5 %, Aldrich) in a ratio of 5:3„ – please specify if mass/volume/molar ratio
Starting from the definitions of sol, gel, and solution, it is again unfortunate to use „sol-gel solution”, please correct (suggestion: sol-gel precursor mixture).
The innovation of this manuscript was declared to be the synthesis at low-temperature, yet the samples were treated at 600°C; please justify. Moreover, in the Results, after figure 7, the heating of obtained CHAp coatings is mentioned at 900 °C.
Please give information regarding the deposition parameters (rpm, time per cycle, etc.)
Results and Conclusion:
The results are merely presented and not adequately discussed. Please add a discussion, connecting the results with previous literature studies.
Nothing from the morphology images indicates the nanometric scale, please remove from the entire manuscript any reference to nano-Hap.
Nothing from the results indicates the prospective application of this coating in bone regeneration, real-time sensing of bone pH in vivo and other assumptions the authors made throughout the entire manuscript.
The reference list is too short, given the enormous subject discussed in this paper, and enforces the superficial manner in which the authors chose to write and present the manuscript.
Author Response
29 December 2022
Editor-in-Chief
Inorganics
In this my letter I enclosed the revised according to the Reviewer 1 comments our manuscript ”Low-Temperature Synthesis Approach for Calcium Hydroxyapatite Coatings on Titanium Substrate” by R. Karalkeviciene, G. Briedyte, A. Popov, S. Tutliene, A. Zarkov, A. Kareiva. (Manuscript No.: inorganics-2131853).
These are changes and answers to the Reviewer comments:
Comment 1. Hydroxyapatite, by definition, is a calcium phosphate mineral with the chemical formula described in the Introduction. Hence, it is unnecessary and unusual to use „Calcium Hydroxyapatite”. Please correct or justify your option.
Answer:
The „Hydroxyapatite” is used instead of „Calcium Hydroxyapatite”, as Reviewer suggested.
Comment 2. In the Introduction the authors should focus on presenting the state-of-the-art and setting out the rationale behind the design of this work. In this case, the information is difficult to follow and poorly presented, jumping from HAp to gas sensors, deposition methods, etc. An introduction should be a cohesive section to describe the topic, followed by a brief review of the most recent bibliography, the rationale, the description of the actual work with a focus on its novelty and significance, and finally the outline of the paper’s contents. In my opinion, it should be enlarged and revised accordingly (for the spin-coating deposition and deposition of calcium phosphates in general please cite Nanomaterials 2019, 9(5), 692).
Answer:
In the Introduction part we summarized:
- The most important application of CHAp as implant materials in medicine and as sensor for different analytes.
- The state-of-the-art in the field of preparation of CHAp thin films and coatings.
- The possibilities and advantages of low-temperature synthesis methods for CHAp.
- The aim of this study
New references are cited and discussed in the Introduction part, as Reviewer suggested.
Materials and methods:
Comment 3. „The resulting solution was mixed with PVA ([-CH2CHOH-]n, 99,5 %, Aldrich) in a ratio of 5:3„ – please specify if mass/volume/molar ratio
Answer:
Specified in the text.
Comment 4. Starting from the definitions of sol, gel, and solution, it is again unfortunate to use „sol-gel solution”, please correct (suggestion: sol-gel precursor mixture).
Answer:
„Sol-gel solution” or „sol-gel precursor” is colloidal solution, therefore the term „sol-gel solution” is correct and is used for many people in the sol-gel society.
Comment 4. The innovation of this manuscript was declared to be the synthesis at low-temperature, yet the samples were treated at 600°C; please justify. Moreover, in the Results, after figure 7, the heating of obtained CHAp coatings is mentioned at 900 °C.
Answer:
The synthesis of CHAp was performed for 28 days at 80 °C. The 600°C was used only for fabrication of CaCO3 coatings.
The obtained CHAp coatings were additionally heated at 900 ℃ just to investigate the influence of temperature on the morphological properties and the corrosion behaviour of CHAp thin films obtained at lower and higher temperatures.
Comment 5. Please give information regarding the deposition parameters (rpm, time per cycle, etc.)
Answer:
Several drops of the precursor solution were placed onto the substrates and spin coated for 30 s @ 3000 rpm (acceleration was 1000 rpm/s).
Results and Conclusion:
Comment 6. The results are merely presented and not adequately discussed. Please add a discussion, connecting the results with previous literature studies.
Answer:
The results obtained for CHAp coatings are discussed with previously obtained.
Comment 7. Nothing from the morphology images indicates the nanometric scale, please remove from the entire manuscript any reference to nano-Hap.
Answer:
Only in the introductory part, it was briefly emphasized that nano CHAp remains a very important research object.
Comment 7. Nothing from the results indicates the prospective application of this coating in bone regeneration, real-time sensing of bone pH in vivo and other assumptions the authors made throughout the entire manuscript.
Answer:
The results summarized show that the developed synthesis method is suitable for the fabrication sufficient quality CHAp coatings on Ti substrate. Therefore, theoretically these coatings are potential candidates for various applications, including biosensors, sensors and as bone implants. In our opinion, the last simple sentence “These CHAp thin films obtained by suggested synthesis method may be potential candidates in the development of bone implants and different sensors for various analytes” is supported by obtained results.
Comment 8. The reference list is too short, given the enormous subject discussed in this paper, and enforces the superficial manner in which the authors chose to write and present the manuscript.
Answer:
The Ref. list now is much longer.
First of all, we would like to thank Reviewer for the valuable remarks. We made most of changes suggested by Reviewer. The changes made are outlined in the revised manuscript.
Yours sincerely,
Prof. Aivaras Kareiva
Round 2
Reviewer 1 Report
I don not have any more questions or/and suggestions,
Reviewer 2 Report
I appreciate the authors response to my comments. I would further suggest to abreviate hydroxyapatite as HAp instead of CHAp.
