Processing of Porous-Core Materials for Bone Implant Applications: A Permeability and Mechanical Strength Analysis

Round 1

Reviewer 1 Report (New Reviewer)

   Old references are usually cited in this work. There are very few references to current references after 2020. Although it is a current topic, there are insufficient references to current studies

      The authors cited some studies on Ti6Al4V foams. They express: “From this study, it was shown that the elastic modulus depends linearly on the thickness of the porous core.” However, the lacks at the literature are not clear. Thus, the originality/novelty of this work must be clearly emphasized compared to other literature studies.

In order to observe phase structure, XRD analysis must be performed

In addition to SEM analysis, to observe elemental distribution, EDX-mapping analysis must be performed

    The English level is not enough to publish in its present form. There are many grammatical errors through the whole text. Thus, the manuscript must be edited by professional grammar editing service.

Author Response

Old references are usually cited in this work. There are very few references to current references after 2020. Although it is a current topic, there are insufficient references to current studies

Additional works that deals with the same subject were added in the reference’s list.

      The authors cited some studies on Ti6Al4V foams. They express: “From this study, it was shown that the elastic modulus depends linearly on the thickness of the porous core.” However, the lacks at the literature are not clear. Thus, the originality/novelty of this work must be clearly emphasized compared to other literature studies.

The novelty is the fabrication bilayer material, since it is difficult to obtain materials with different shrinkage gradients by sintering. The introduction was modified according to the suggestions reviewer.

In order to observe phase structure, XRD analysis must be performed

A SEM image and the x ray pattern of sintered samples was added, however, as samples are sintered in the same conditions it is assume that microstructure is similar for all samples. Therefore, the analysis is more focus on the porosity and layer thickness.

The manuscript was edited by the MDPI services as recommended by the Editor.

In addition to SEM analysis, to observe elemental distribution, EDX-mapping analysis must be performed

EDS was not included because no relevant information could be extracted from this images.

Reviewer 2 Report (New Reviewer)

November, 4th, 2023

Dear authors

Thank you for an interesting report.

In this study, you examined the permeability and mechanical strength of Ti-6Al-4V alloy with mimicking bone’s microstructure. Since biomaterials that mimic the living body play an important role in improving the in vivo compatibility of artificial materials after implantation, the titanium alloy body fabricated in this study, which mimicked bone’s microstructure, is expected to make a significant contribution to medicine. For these reasons, I believe that this study will be of great benefit to surgical care and will be an interesting report for the readers of the journal.

I agree with many parts of your claims. However, I think that several revisions are required as follows:

2. Materials and Methods

1. To make it easier for the reader to read this article, I think you should insert a pictures of the samples.

2. It is not stated how many samples of the same conditions were made and measured for mechanical strength. I think you need to be specific.

3. Results and discussion

1. In mechanical strength analysis, multiple samples are usually prepared under the same conditions, and similar tests are performed to calculate the mean and standard deviation. In addition, statistical analysis is performed based on those data to make comparisons between groups, but it is unclear how this was done in this study. I believe that statistical analysis is necessary to discuss the large/small relationship between groups, and you should add their methods in the previous section and describe their results in this section.

Author Response

The manuscript was edited by the MDPI services as recommended by the Editor

Thank you for an interesting report.

In this study, you examined the permeability and mechanical strength of Ti-6Al-4V alloy with mimicking bone’s microstructure. Since biomaterials that mimic the living body play an important role in improving the in vivo compatibility of artificial materials after implantation, the titanium alloy body fabricated in this study, which mimicked bone’s microstructure, is expected to make a significant contribution to medicine. For these reasons, I believe that this study will be of great benefit to surgical care and will be an interesting report for the readers of the journal.

I agree with many parts of your claims. However, I think that several revisions are required as follows:

2. Materials and Methods
3. To make it easier for the reader to read this article, I think you should insert a picture of the samples.

Thanks for suggestion additional figure was added with photos of the samples.

2. It is not stated how many samples of the same conditions were made and measured for mechanical strength. I think you need to be specific.

We prepared 3 samples for each condition and the average values are reported, this is also included in the materials and methods section

3. Results and discussion
4. In mechanical strength analysis, multiple samples are usually prepared under the same conditions, and similar tests are performed to calculate the mean and standard deviation. In addition, statistical analysis is performed based on those data to make comparisons between groups, but it is unclear how this was done in this study. I believe that statistical analysis is necessary to discuss the large/small relationship between groups, and you should add their methods in the previous section and describe their results in this section.

Three samples of each condition were tested to obtain the mechanical properties of the specimens. The standard deviation is included in the corresponding figures.

Reviewer 3 Report (New Reviewer)

Authors perform a practical work on material with porous core structure which is similar to human bones. This study is meaningful for the development of artificial implants. Before publication, some revisions are needed as follows:

1. For the article title, is the focus on Processing or Mimicking? The entire article may focuses more on the preparation and performance testing of materials. Please modify the title to better reflect the content of this paper.

2. Please move the full name of AM from Line 257 to Line 40.

3. Although titanium alloys have many performance advantages, artificial bone materials are not limited to this type of material. Please supply the performance comparison between titanium alloy and other biological materials.

4. In the part of 2.1, please provide the SEM of original powders.

5. In Fig. 1, how to ensure stability of powder pressed by hand?

6. In Fig. 2, what does the Ti64 mean?

7. In Line 279, the permeability ranges lack “×” in the numerical values?

8. Please provide the testing standards for the compressed samples by citing references or plotting figures.

9. The mechanical performances of human bones are significantly different with the change of gender and age. Please highlight which type (gender and age) of human bone is used as a reference for this study.

Extensive editing of English language is required.

Author Response

The manuscript was edited by the MDPI services as recommended by the Editor

Authors perform a practical work on material with porous core structure which is similar to human bones. This study is meaningful for the development of artificial implants. Before publication, some revisions are needed as follows:

1. For the article title, is the focus on Processing or Mimicking? The entire article may focuses more on the preparation and performance testing of materials. Please modify the title to better reflect the content of this paper.

The paper is focus in the processing; thus the title was modified according to the suggestion.

2. Please move the full name of AM from Line 257 to Line 40.

The was moved at the first time that additive manufacturing is used, thank you.

3. Although titanium alloys have many performance advantages, artificial bone materials are not limited to this type of material. Please supply the performance comparison between titanium alloy and other biological materials.

Thank you for your commentaries, certainly, there are many non-metallic materials that compete to be good options for obtaining biomedical materials. However, they have different uses depending on their nature. Introduction was modified for, included a comparison respect to Ti alloys and another similar material.

In the part of 2.1, please provide the SEM of original powders.

Thanks for suggestion was added SEM of the originals powders

5. In Fig. 1, how to ensure stability of powder pressed by hand?

It is a fairly light pressing that does not affect the physical integrity of the powders, it is carried out to hold the tube and be able to remove the rod from the center for subsequent filling, since the Ti6Al4V powder is bound with PVA, this maintains its provisional shape.

6. In Fig. 2, what does the Ti64 mean?

Ti64 is abbreviation of Ti6Al4V, we change in the whole manuscript for Ti6Al4V.

7. In Line 279, the permeability ranges lack “×” in the numerical values?

Thanks for see the mistake; the "x" will be added to have a more appropriate expression.

8. Please provide the testing standards for the compressed samples by citing references or plotting figures.

Compression tests were performed according to ASTM D695-02 .

Indicated in section 2.4

9. The mechanical performances of human bones are significantly different with the change of gender and age. Please highlight which type (gender and age) of human bone is used as a reference for this study.

It is hard to had only one reference bone or only one age range because the large bones, for example, has a different region with different gradients in itself. But was added references for explaining a compare of that.

Round 2

Reviewer 1 Report (New Reviewer)

The manuscript was dedicated to study entitled “Processing of porous core materials mimicking bone's microstructure: a permeability and mechanical strength analysis” after revision. This paper is acceptable in Coatings in its present form. However, I recommend minor revision for English language.

I recommend minor revision for English language.

Author Response

The manuscript was dedicated to study entitled “Processing of porous core materials mimicking bone's microstructure: a permeability and mechanical strength analysis” after revision. This paper is acceptable in Coatings in its present form. However, I recommend minor revision for English language.

I recommend minor revision for English language.

Thank you. The whole manuscript was revised and minor corrections were made as indicated in the manuscript.

Reviewer 3 Report (New Reviewer)

Although there are significant differences in human bones, it is necessary to point out the sources of human bones used in this study, such as age, gender, and region. Otherwise, it will affect the reference value of the data.

Author Response

Although there are significant differences in human bones, it is necessary to point out the sources of human bones used in this study, such as age, gender, and region. Otherwise, it will affect the reference value of the data.

- The values reported in this paper were obtained from the following paper https://doi.org/10.1016/j.biomaterials.2016.01.012, which is the reference [1] in the manuscript, in where there are listed the compression resistance of different bones, although as it is well establish, this values will vary from different parameters like age, gender and region. The reference values agree with the average of values of bones reported and the processing route proposed in this work will be able to tune the mechanical strength as needed for a specific patient by controlling the porosity and the sintering cycle.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

This study presents a method for the preparation of Ti6Al4V cylindrical compacts with highly porous cores and dense shells with the aim of simulating the microstructure of bone. Compacted blanks with different core diameters were obtained using conventional pressing and sintering methods. The pore characteristics were investigated using X-ray microchromatography imaging at different resolutions and permeability values were deduced from the 3D images by numerical simulations. The permeability and mechanical strength were evaluated by 3D microstructure and compression tests. The results show that the different densification rates of the porous and dense layers limit the sintering process. However, defect-free densification was obtained due to neck bonding between Ti6Al4V particles. The design cores all have large pores within them with similar pore size distributions. The permeability increases in a power law with the pore volume fraction. The stiffness of the bilayer members is mainly driven by the porous core and the strength is mainly driven by the two-layer composite. The mechanical properties and allowable strain (σy /E) were similar to those of human bone. Although this study presents a method to prepare materials that can mimic the microstructure of bone, which is expected to provide ideas for the industrial-scale preparation of Ti6Al4V cylindrical compacts, further experiments are needed to provide more reliable support for this system. The following key comments may help to improve the quality of the manuscript.

PCR-1: Note the writing of the upper and lower corner signs of the chemical formulae of the substances in the text, please check them carefully.

PCR-2: 2.1 Sample preparation is proposed to be reformulated so that raw materials and sample preparation can be presented separately.

PCR-3: 2.2. Microstructural characterisation, 2.3. Compression testing and 2.4. Numerical penetration simulation are recommended to be united under 2.2 Analytical methods.

PCR-4: Note that the description of the physical quantities of equations in lines 197, 296, 312 and 332 should be consistent with the format of the equation.

PCR-5: Note that the dimensions of the diagram and the upper left corner corner labels a) and b) should be in a uniform format.

PCR-6: Authors are encouraged to include some recent relevant references to support this description. It is recommended that some recent publications are included in the references section.：Microstructure and phase transformation behavior of Al₂O₃–ZrO₂ under microwave sintering. Ceramics International. 2023, 49(3): 4855-4862. DOI:10.1016/j.ceramint.2022.09.376.

PCR-7: English of the manuscript is poor and some sentences are grammatically wrong. The manuscript should be subjected to a thorough English grammar and spell check.

I hope you can carefully modify the above suggestions to make your article more recognized.

This study presents a method for the preparation of Ti6Al4V cylindrical compacts with highly porous cores and dense shells with the aim of simulating the microstructure of bone. Compacted blanks with different core diameters were obtained using conventional pressing and sintering methods. The pore characteristics were investigated using X-ray microchromatography imaging at different resolutions and permeability values were deduced from the 3D images by numerical simulations. The permeability and mechanical strength were evaluated by 3D microstructure and compression tests. The results show that the different densification rates of the porous and dense layers limit the sintering process. However, defect-free densification was obtained due to neck bonding between Ti6Al4V particles. The design cores all have large pores within them with similar pore size distributions. The permeability increases in a power law with the pore volume fraction. The stiffness of the bilayer members is mainly driven by the porous core and the strength is mainly driven by the two-layer composite. The mechanical properties and allowable strain (σy /E) were similar to those of human bone. Although this study presents a method to prepare materials that can mimic the microstructure of bone, which is expected to provide ideas for the industrial-scale preparation of Ti6Al4V cylindrical compacts, further experiments are needed to provide more reliable support for this system. The following key comments may help to improve the quality of the manuscript.

PCR-1: Note the writing of the upper and lower corner signs of the chemical formulae of the substances in the text, please check them carefully.

PCR-2: 2.1 Sample preparation is proposed to be reformulated so that raw materials and sample preparation can be presented separately.

PCR-3: 2.2. Microstructural characterisation, 2.3. Compression testing and 2.4. Numerical penetration simulation are recommended to be united under 2.2 Analytical methods.

PCR-4: Note that the description of the physical quantities of equations in lines 197, 296, 312 and 332 should be consistent with the format of the equation.

PCR-5: Note that the dimensions of the diagram and the upper left corner corner labels a) and b) should be in a uniform format.

PCR-6: Authors are encouraged to include some recent relevant references to support this description. It is recommended that some recent publications are included in the references section.：Microstructure and phase transformation behavior of Al₂O₃–ZrO₂ under microwave sintering. Ceramics International. 2023, 49(3): 4855-4862. DOI:10.1016/j.ceramint.2022.09.376.

PCR-7: English of the manuscript is poor and some sentences are grammatically wrong. The manuscript should be subjected to a thorough English grammar and spell check.

I hope you can carefully modify the above suggestions to make your article more recognized.

Author Response

Reviewer 1

Comments and Suggestions for Authors

This study presents a method for the preparation of Ti6Al4V cylindrical compacts with highly porous cores and dense shells with the aim of simulating the microstructure of bone. Compacted blanks with different core diameters were obtained using conventional pressing and sintering methods. The pore characteristics were investigated using X-ray microchromatography imaging at different resolutions and permeability values were deduced from the 3D images by numerical simulations. The permeability and mechanical strength were evaluated by 3D microstructure and compression tests. The results show that the different densification rates of the porous and dense layers limit the sintering process. However, defect-free densification was obtained due to neck bonding between Ti6Al4V particles. The design cores all have large pores within them with similar pore size distributions. The permeability increases in a power law with the pore volume fraction. The stiffness of the bilayer members is mainly driven by the porous core and the strength is mainly driven by the two-layer composite. The mechanical properties and allowable strain (σy /E) were similar to those of human bone. Although this study presents a method to prepare materials that can mimic the microstructure of bone, which is expected to provide ideas for the industrial-scale preparation of Ti6Al4V cylindrical compacts, further experiments are needed to provide more reliable support for this system. The following key comments may help to improve the quality of the manuscript.

PCR-1: Note the writing of the upper and lower corner signs of the chemical formulae of the substances in the text, please check them carefully.

The chemical formulae were revised and modified according to the suggestion.

PCR-2: 2.1 Sample preparation is proposed to be reformulated so that raw materials and sample preparation can be presented separately.

The manuscript was modified as mentioned.

PCR-3: 2.2. Microstructural characterisation, 2.3. Compression testing and 2.4. Numerical penetration simulation are recommended to be united under 2.2 Analytical methods.

The manuscript was modified according to this suggestion.

PCR-4: Note that the description of the physical quantities of equations in lines 197, 296, 312 and 332 should be consistent with the format of the equation.

The description was revised and modified.

PCR-5: Note that the dimensions of the diagram and the upper left corner labels a) and b) should be in a uniform format.

The labels were updated with uniform format.

PCR-6: Authors are encouraged to include some recent relevant references to support this description. It is recommended that some recent publications are included in the references section.：Microstructure and phase transformation behavior of Al₂O₃–ZrO₂ under microwave sintering. Ceramics International. 2023, 49(3): 4855-4862. DOI:10.1016/j.ceramint.2022.09.376.

Recent relevant references were added however, the reference suggested is quite far from this work. Therefore, it wasn’t included in the manuscript.

PCR-7: English of the manuscript is poor and some sentences are grammatically wrong. The manuscript should be subjected to a thorough English grammar and spell check.

The whole manuscript was revised for an specialist in the English language.

I hope you can carefully modify the above suggestions to make your article more recognized.

Thank you for your suggestions.

Reviewer 2 Report

Abstract is very general, highlight the significance of results obtained and conclusions

On what basis 85/15 and 50/50 alone considered for this study?

For all measurements, how may tests were repeated? in case average, it should be reported

Microscopic findings should be encircled 

Fig 4b, what is the purpose of equation? Whether in all future case, this equation can be used?

Drastic difference in compression strength, but detailed discussion is missing

E value seems to be vary drastically, how ?

Most references are too old, update it

Need revisions

Author Response

Reviewer 2

Comments and Suggestions for Authors

Abstract is very general, highlight the significance of results obtained and conclusions

Abstract was modified highlighting the main findings of the paper.

On what basis 85/15 and 50/50 alone considered for this study?

We used those two ratios because the different equipment used limit us to test larger samples and in order to have more combinations it is necessary to fabricate larger samples. This is possible with the methodology proposed, however, for evaluating the dilatometry and/or mechanical compression is not possible with the equipment available in our laboratories.

For all measurements, how may tests were repeated? in case average, it should be reported

For the dilatometry and compression tests, the tests were carried out in triplicate. To avoid a severe change in the averages, the data that obtained values that were closest or equal to each other and that were logical with what was reported in the bibliography were taken into account.

Microscopic findings should be encircled

This was modified in the manuscript

Fig 4b, what is the purpose of equation? Whether in all future case, this equation can be used?

This equation could be used to customize the permeability according to the pore volume fraction with similar pores size distribution. This will help to obtain materials with a desired permeability by using this fabrication process.

Drastic difference in compression strength, but detailed discussion is missing

Additional discussion is added in the manuscript, however, the reduction on mechanical properties is highly affected by the pore volume fraction.

E value seems to be vary drastically, how?

The addition of pores brings to materials a larger elastic deformation, which makes that E can be reduced. This phenomenon is mainly due to the voids that allows to absorb some energy before to reach the yielding.

Most references are too old, update it

Additional references were added, in particular, the subject has been investigated by additive manufacturing because is relatively easy to fabricate complex shapes. Nevertheless, the methodology proposed in this work offers an alternative to fabricate this kind of complex materials by conventional powder metallurgy.

Reviewer 3 Report

The manuscript titled "Processing of porous core materials mimicking bone’s microstructure: a permeability and mechanical strength analysis" by L. Olmos and co-workers presents a methodology for crafting Ti6Al4V cylindrical compacts, aiming to replicate the microstructure of natural bone. The study employs conventional pressing and sintering methods, incorporating pore formers to create larger pores within the compacts, resulting in variations in core diameters. Regrettably, this manuscript is marred by several significant issues that severely diminish its quality and scientific rigor.

First and foremost, a glaring omission is the complete lack of integration with existing literature. Despite ample references available, such as https://doi.org/10.1016/j.jmbbm.2020.103673  and https://doi.org/10.1016/j.jmbbm.2022.105275, the authors inexplicably choose to disregard pertinent research that could have provided essential context for their work. This oversight undermines the credibility and relevance of the study and leaves readers questioning the uniqueness and impact of the presented results.

Furthermore, the brevity of the Introduction section is a significant concern. A comprehensive introduction is essential for establishing the background and significance of the study. The authors fail to adequately situate their work within the existing body of research, leaving readers without a clear understanding of the study's place in the field.

Moreover, the manuscript lacks clarity in several places, with convoluted sentence structures and ambiguous phrasing that hinder comprehension. This issue is exacerbated by the absence of clear figures or diagrams to aid in visualizing the experimental setup and results.

The manuscript falls significantly short of the standards expected for publication in the MDPI journal Coatings. The lack of integration with existing literature, insufficiently detailed methodology, and unclear presentation severely hinder the quality and impact of the work. It is recommended that the authors undertake substantial revisions to address these fundamental issues.

Language presentation should be polished.

Author Response

Reviewer 3

Comments and Suggestions for Authors

The manuscript titled "Processing of porous core materials mimicking bone’s microstructure: a permeability and mechanical strength analysis" by L. Olmos and co-workers presents a methodology for crafting Ti6Al4V cylindrical compacts, aiming to replicate the microstructure of natural bone. The study employs conventional pressing and sintering methods, incorporating pore formers to create larger pores within the compacts, resulting in variations in core diameters. Regrettably, this manuscript is marred by several significant issues that severely diminish its quality and scientific rigor.

First and foremost, a glaring omission is the complete lack of integration with existing literature. Despite ample references available, such as https://doi.org/10.1016/j.jmbbm.2020.103673  and https://doi.org/10.1016/j.jmbbm.2022.105275, the authors inexplicably choose to disregard pertinent research that could have provided essential context for their work. This oversight undermines the credibility and relevance of the study and leaves readers questioning the uniqueness and impact of the presented results.

The references were added to the paper. In the first instant, the authors decide to not include them because they make similar materials but using additive manufacturing, which is outstanding but different technique and thus, different properties and microstructure are obtain to compare against each other.

Furthermore, the brevity of the Introduction section is a significant concern. A comprehensive introduction is essential for establishing the background and significance of the study. The authors fail to adequately situate their work within the existing body of research, leaving readers without a clear understanding of the study's place in the field.

Introduction was updated and additional information was added.

Moreover, the manuscript lacks clarity in several places, with convoluted sentence structures and ambiguous phrasing that hinder comprehension. This issue is exacerbated by the absence of clear figures or diagrams to aid in visualizing the experimental setup and results.

The whole manuscript was modified and some phrases were rewritten, with the aim to improve the clarity and understanding.

The manuscript falls significantly short of the standards expected for publication in the MDPI journal Coatings. The lack of integration with existing literature, insufficiently detailed methodology, and unclear presentation severely hinder the quality and impact of the work. It is recommended that the authors undertake substantial revisions to address these fundamental issues.

Additional literature was added; the methodology was improved by adding a schematic figure to make easier the understanding and the English grammar was also revised in the whole manuscript.

Reviewer 4 Report

I have the following questions and comments about the submitted article:

1. line 94 - is it seriously 0 to 45 μm? Perhaps it would be better to write 1-45 μm.

2. line 103 - the quantity (unit) and the end of the sentence are missing after the value 70.

3. line 103 - the designation Ti64 in brackets should also be used above in the text for Ti-6Al-4V so that it is not confusing for the reader. Unify the labeling throughout the article.

4. line 116 - correct the space at the beginning of the sentence.

5. line 117 - fix the gap between 50 and %

6. It would be appropriate to support Chapter 2.1 Sample preparation with some picture or diagram or table. Add an explanation to the labeling of the samples.

7. line 36 and 42 - used references [4-7] and [9-13] more detailed and write specifically

8. line 151, 154 - italics should be used to indicate (E) and (σy), as well as in other parts of the article

9. line 172 - correct Pa*s

10. line 199-202 - Db, Dc, Ds, fc and fs should be formatted with italics and subscript.

11. Figure 1. mark figures a and b below the pictures and move them away from each other - on the left: axis Y - write axial strain as a dimensionless unit [-], units in square brackets, temperature is without °; right: overwrite values on the Y axis.

12. Table 1. - fill in the units in which the quantities are.

13. Figure 2. - use images of the same size - lighten the images because they are too dark, increase the quality of the images.

14. Figure 3. - move away from each other images (a) from (b), (c) from (d) and (e) from (f). What do the color scales represent?

15. line 268, 269 - 3.10−11 to 5.10−10 m2 and 10-8 to 10-9 - fix superscripts

16. Figure 4 and Table 2 - separate captions from each other

17. Figure 4. mark figures a and b below the pictures and move them away from each other - on the left: axis Y - write as a dimensionless unit [-], units in square brackets, right: overwrite values on the Y axis .

18. line 298-300 - Eb, Ec, Es, fc and fs should be formatted with italics and subscript.

19. Figure 5 and 6 - mark figures a and b below the pictures and move them away from each other, axis X - write as a dimensionless unit [-], units in square brackets, x and y axis labels in figure 5a are in bold, use the format as in figure 5b

20. line 313-317 σyb, σyc, σys, and (σy/E) should be formatted with italics and subscript.

21. line 319, 321 and table 3 - you use different number formats, please unify to one format

22. Figure 7 - improve the quality of SEM images or change the contrast + separate the images from each other

23. delete lines 387-397.

24. please write the references according to the MDPI template (names of journals and volume in italics)

+ check spaces between tables and chapter titles according to the template

25. Please add numerical values of the main results to the abstract

26. Insert a discussion chapter in which you discuss the main results and compare them with the already existing results of other authors.

27. Explain sentence 176 - 180 and mark it in Fig. 1a.

28. The conclusion is written only in general terms, it is necessary to process the final part into bullet points and write down the main results of the publication and the specific values achieved in them.

Author Response

Reviewer 4

Comments and Suggestions for Authors

I have the following questions and comments about the submitted article:

1. line 94 - is it seriously 0 to 45 μm? Perhaps it would be better to write 1-45 μm.

This was modified according to the commentaries.

2. line 103 - the quantity (unit) and the end of the sentence are missing after the value 70.

The unit was added.

3. line 103 - the designation Ti64 in brackets should also be used above in the text for Ti-6Al-4V so that it is not confusing for the reader. Unify the labeling throughout the article.

This was modified according to the commentaries.

4. line 116 - correct the space at the beginning of the sentence.

This was modified according to the commentaries.

5. line 117 - fix the gap between 50 and %

This was modified according to the commentaries.

6. It would be appropriate to support Chapter 2.1 Sample preparation with some picture or diagram or table. Add an explanation to the labeling of the samples.

A diagram was included in the 2.1 section.

7. line 36 and 42 - used references [4-7] and [9-13] more detailed and write specifically

Additional commentaries were made.

8. line 151, 154 - italics should be used to indicate (E) and (σy), as well as in other parts of the article

This was modified according to the commentaries.

9. line 172 - correct Pa*s

This was modified according to the commentaries.

10. line 199-202 - Db, Dc, Ds, fc and fs should be formatted with italics and subscript.

This was modified according to the commentaries.

11. Figure 1. mark figures a and b below the pictures and move them away from each other - on the left: axis Y - write axial strain as a dimensionless unit [-], units in square brackets, temperature is without °; right: overwrite values on the Y axis.

This was modified according to the commentaries.

12. Table 1. - fill in the units in which the quantities are.

All quantities are dimensionless units.

13. Figure 2. - use images of the same size - lighten the images because they are too dark, increase the quality of the images.

The size cannot be matched due to the resolution obtained by the size of the original samples. The quality of such images was improved.

14. Figure 3. - move away from each other images (a) from (b), (c) from (d) and (e) from (f). What do the color scales represent?

Figure 3 is now Figure 4 in the corrected manuscript. In Figure 4a, 4b, 4c and d, the blue color indicates the interconnected porosity and in Figure 4c and 4d the colored dots visualize the pores not interconnected with the rest of the matrix. In figures 4e and 4f the colors indicate qualitatively the velocity of flow at any point thought the porosity inside the sample according to the numerical simulations.

15. line 268, 269 - 3.10−11 to 5.10−10 m2 and 10-8 to 10-9 - fix superscripts

This was modified according to the commentaries.

16. Figure 4 and Table 2 - separate captions from each other

This was modified according to the commentaries.

17. Figure 4. mark figures a and b below the pictures and move them away from each other - on the left: axis Y - write as a dimensionless unit [-], units in square brackets, right: overwrite values on the Y axis.

This was modified according to the commentaries.

18. line 298-300 - Eb, Ec, Es, fc and fs should be formatted with italics and subscript.

This was modified according to the commentaries.

19. Figure 5 and 6 - mark figures a and b below the pictures and move them away from each other, axis X - write as a dimensionless unit [-], units in square brackets, x and y axis labels in figure 5a are in bold, use the format as in figure 5b

This was modified according to the commentaries.

20. line 313-317 σyb, σyc, σys, and (σy/E) should be formatted with italics and subscript.

This was modified according to the commentaries.

21. line 319, 321 and table 3 - you use different number formats, please unify to one format

This was modified according to the commentaries.

22. Figure 7 - improve the quality of SEM images or change the contrast + separate the images from each other

This was modified according to the commentaries.

23. delete lines 387-397.

This was modified according to the commentaries.

24. please write the references according to the MDPI template (names of journals and volume in italics)

This was modified according to the commentaries.

+ check spaces between tables and chapter titles according to the template

This was modified according to the commentaries.

25. Please add numerical values of the main results to the abstract

The abstract was modifying according to the suggestions.

26. Insert a discussion chapter in which you discuss the main results and compare them with the already existing results of other authors.

Include a discussion chapter will change the whole structure of the paper because we choose to make a results and discussion section with the aim to avoid redundant phrases.

27. Explain sentence 176 - 180 and mark it in Fig. 1a.

This was modified according to the commentaries.

28. The conclusion is written only in general terms; it is necessary to process the final part into bullet points and write down the main results of the publication and the specific values achieved in them.

Conclusion was rewritten to include the suggestions.

Round 2

Reviewer 1 Report

Extensive editing of English language required

Extensive editing of English language required

Reviewer 2 Report

Nil

Minor revisions required

Reviewer 3 Report

The revised manuscript entitled “Processing of porous core materials mimicking bone’s microstructure: a permeability and mechanical strength analysis” submitted by L. Olmos and co-workers for reconsideration for publication in the MDPI journal Coatings presents definitely higher level than the first submission. The Authors have performed all the required corrections and add additional explanations. Therefore, I consider the revised manuscript is suitable for publication in the MDPI journal Coatings. My congratulations to the Authors. I wish You all the best and next good papers.

Minor editing of English language required

Reviewer 4 Report

I thank the authors for incorporating my comments, I recommend the article for publication.