Bending Deformation Behavior of Eggshell and Eggshell–Polymer Composites

Round 1

Reviewer 1 Report

The quality of the English needs substantial improvement. In the abstract, what are "wide limits for brittle structure"?

Introduction:

“treated tooth”?

Ethic – ethical or ethics

By the scheme of 3 points bending? 3 point bending

Ethical problems – such as?

What is the governmental guarantee – surely there must be some sort of a reference to quality assurance in legislation?

No idea what is being conveyed by the term – brittle material – viscous coating – the two are mutually exclusive.

“international clinical practice including Russia? Is this not for an international journal?

Materials and methods

“we used” – are personal pronouns used? What are the recommended conditions of the manufacturer?

“during one day at room temperature” – very vague

“The eggshell was fixed on the substrate from a polyurethane foam before the cutting of procedure” – very confusing.

“traverse rate was 0.1 mm/min” – was this the cross-head displacement rate? What international standard was employed to undertake the 3 point bending? Was the distance between support points and their radii in accordance with accepted and defined values?

Our earlier findings on the deformation behavior of the samples cut from hen's eggshell under 3-points 70 bending in air and water are presented in [9]. A summary should be presented – who has access to reference 9? I do not.

The preparation of the composite samples "hen's eggshell - polymer restorative material" for the 3-points bending was realized according to the procedure of tooth plumbing from some manufacturers accepted by the Russian Federation Government for the clinical application.” Completely vague and should be explicitly detailed. “some” and “accepted”?

Please give some details of the cements used!

Deformation behavior of the samples was estimated based on analysis of their deformation (bending) curves. Effective elastic moduli calculated from the inclination of the bending curve, maximal deformation of the sample and ultimate bending strength were used as the mechanical characteristics of the samples in addition to the deformation curve under bending. Please clarify with quantitative details. Inclination – do you mean slope and between what strains?

Figure 1. Preparation of samples from hen’s eggshell: (1) – eggshell on the substrate; (2) – eggshell after cut off procedure; (3) samples for bending, working surface and end surface. There are not numbers 1, 2 and 3 in the figure.

Results:

Is differ?

Figures 1 to 5 – related to which set as they refer? All plots/graphs should have the same axis maximum values and major units for easy comparison. How are the stresses and deformation % calculated – from displacement of the machine cross-head? Surely not? Is stress bending stress? No legends so what does each colour represent?

What are “lower prisms of the bending device”?

No image of the test set up is included – major deficiency for a mechanical type manuscript – the reader cannot attest to the veracity of the results.

Table 1: any statistical analysis of the data? How many repeats of each type of coupon of each set?

How were the deformation and ultimate strength determined – are these maximum values and surely there is some scatter?

Metallographic examination? Microscopic and/or fractographic

Trajectory of a dangerous crack – what is that? Fast growing to catastrophic?  

What is meant by loading “plugged off” and “be braked”? no idea.

“al-ways”?

What is the capacity of the load-cell used and its calibration level – what loads are experienced and are these consistent with the accuracy of the load cell?

No images of fractured surfaces which would indicate to the authors and the reader the type of failure incurred.

Additional argument is the course of the “de-formation” – “deformation” curves for majority of samples, which could approximate by a linear dependence – please clarify.

“hen's eggshell is a natural inorganic biomaterial” - The eggshell is structurally composed by organic and inorganic components. The organic component of the shell consists of the shell membranes, mammillary buttons or tips, the matrix of the shell, and the cuticle (Solomon, 1991). The inorganic component of the eggshell consists of calcium carbonate crystals. The eggshell layers, the inside to the outside, are composed by mammillary buttons layer (internal), palisade layer (intermediate), and crystal surface layer (external; Roberts, 2004). Reference: C. Stefanello, T.C. Santos, A.E. Murakami, E.N. Martins, T.C. Carneiro, Poultry Science, Volume 93, Issue 1, 1 January 2014, Pages 104-113

“mechanical characteristics that varied in wide limits, but always inside the brittle behavior” – completely vague and indeed baffling.

“surface by a blue laser” – can you describe in detail? Wavelength and power?

What are the major conclusion based on the evidenced data?

The quality of the English needs substantial improvement.

Author Response

The first of all the authors would like to express sincerely gratitude to the reviewers for detail analysis of the manuscript and helpful criticism and suggestions. Their analysis served the start of the detail discussions the findings with colleagues that allows understanding better their place in the knowledge on biocomposites. Many questions that were asked by the reviewers having important meaning for the composite science and its application to the dental materials science.

The quality of the English needs substantial improvement. In the abstract, what are "wide limits for brittle structure"?

Introduction:

“treated tooth”?

The term “treated tooth” means a damaged tooth after procedure of dental healing.

Ethic – ethical or ethics

Thank you for the correction: ethics

By the scheme of 3 points bending? 3 point bending

Thanks for the query. The loading scheme sometimes named as 3-points bending, while 3 point bending is also appropriate. We prefer using the first version because in the past the reviewer recommended us namely "3-points bending". However, please, let us know and we will use the second version in the manuscript.

Ethical problems – such as?

Thank you for very important question! According to the Ethical protocol of the Ural state medical university at Yekaterinburg (Russia) a researcher having diploma in dentistry have the right to use as an experimental materials extracted teeth in the university dental clinic and dental clinics connected with the University by the contracts for clinical researches. However, the list of the researches is limited. For example, an experimental material should not use in art performances etc. In particularly, we need the special permission for the usage of the hard tissues tahen from extracted teeth for commercially oriented studies such as the examination of cohesive strength in the join "human tooth enamel - polymer plomb". Of course, it is not a big barrier for a worldwide manufacturer like 3M, but local manufacturers in Yekaterinburg consider this procedure as a "dead deal".

What is the governmental guarantee – surely there must be some sort of a reference to quality assurance in legislation?

This sentence has been rewritten as:

The preparation of the composite samples "hen's eggshell - polymer restorative material" for the 3-points bending was realized according to the procedure of tooth plumbing from some manufacturers accepted by the Russian Federation Government for the clinical application.

No idea what is being conveyed by the term – brittle material – viscous coating – the two are mutually exclusive.

Thank you for the question. You are absolutely right that brittle and viscous/ductile are opposite features. Therefore, a composite, which is a joining a brittle substrate and a viscous coating, has limited application among structural materials. However, the examination of deformation behavior of such composite has some meaning for the composite science. Presented experimental task in dental materials science gives a reader this oppotunity. The following phrase is added to the "Introduction":

This applied task has also some fundamental meaning, since the deformation behavior of the composite "brittle material - viscous coating" under bending is interesting for the composite science, too [11,12].

“international clinical practice including Russia? Is this not for an international journal?

Thank you for the very important question! This is well-known that worldwide manufacturers sometimes use the local trademarks, which could differ from the international trade marks and the local ones in other countries. Therefore, we used only the trademarks that applied around the world in this research. The phrase about this moment was rewritten as:

The aim of this work is the experimental study of the deformation behavior such composites under 3-points bending on example of the joining of hen's eggshell samples with some polymer plomb materials that used in the international clinical practice including Russia.

Materials and methods

“we used” – are personal pronouns used?

You are absolutely right that personal pronouns are not used in scientific texts. However, we do that as exclusion because namely we have purchased a parcel of hen's egg in local Yekaterinburg retail outlet. In other cases we use the passive voice.

What are the recommended conditions of the manufacturer?

They are usual worklwide recommendations for the storage of hen's eggs: (1) eggs should store in a refrigerator at +5C; (2) eggs should store in the darkness; (3) eggs should store in the packaging; (4) the date of eggs storage is one month from the date of supplying to the market.

“during one day at room temperature” – very vague

Experience has shown that no water was detected in the hen's eggshell samples after cutting off procedure. The phrase has been rewritten as:

Further, the eggshell was washed inside by the water and was dried during the couple of days at room temperature.

 “The eggshell was fixed on the substrate from a polyurethane foam before the cutting of procedure” – very confusing.

Thank you for the question. This is our "know-how". The new version contains more detailed description of the procedure:

The fixing of eggshell in the cutting off facility is complicate technical task because eggshell is a brittle material, which additionally possesses the complicated shape. Therefore, eggshell was fixed on the substrate from a polyurethane foam, which was further mounted in the cutting off facility (Figure 1a).

“traverse rate was 0.1 mm/min” – was this the cross-head displacement rate?

Yes, this is the traverse displacement rate.

What international standard was employed to undertake the 3 point bending?

This is 3-points bending that was carried out with a help of the Shimadzu bending device, while the experimental data was processed by the Shimadzu's Trapezium software. Unfortunately, the shape of the hen's eggshell samples does not allow applying any standard for testing.

Was the distance between support points and their radii in accordance with accepted and defined values?

The distance between the lower prisms was minimal for the device (10 mm).

Our earlier findings on the deformation behavior of the samples cut from hen's eggshell under 3-points 70 bending in air and water are presented in [9]. A summary should be presented – who has access to reference 9? I do not.

I am sorry, but we had not opportunity to apply the reprint to the manuscript. You could find full text via https://doi.org/10.1063/5.0084267, while the abstract is below:

Deformation behavior of the chicken eggshell under shearing and bending was examined. An eggshell is a biomineral consisted of more than 90% of calcium carbonate. Samples for mechanical testing were cut from commercial chicken eggs along and perpendicularly to the egg axis. Their average size was 50×3×0.5 mm3. The crack evolution in the samples under bending was studied in situ on the metallographic light microscope. Some samples were exposed to water for 15 min before the testing. The samples exhibit viscoelastic behavior under shearing, while they behave in a brittle manner under bending. The width of the crack in the sample could be grown using the increase of the arrow of bending. It means that some deformation mechanism suppresses fracture in the chicken eggshell and, hence, the crack growth is close to the viscoelastic type. The orientation of the samples and the exposure of them in the water do not qualitatively change the deformation behavior of the chicken eggshell under shearing and bending. The deformation behavior of the chicken eggshell is similar to rock materials and minerals.

The preparation of the composite samples "hen's eggshell - polymer restorative material" for the 3-points bending was realized according to the procedure of tooth plumbing from some manufacturers accepted by the Russian Federation Government for the clinical application.” Completely vague and should be explicitly detailed. “some” and “accepted”?

Agree, we will include detailed description of the procedure in the "Supplementary materials" to the paper.

Please give some details of the cements used!

The plomb materials used in the research are from the worldwide manufacturers (their basis is PMMA polymer): Boston Arkona™, Ceram 1™, Ceram 3M™, DX Flow Composite™. A reader can find some permitted by manufacturer's details of their chemical content and recommendations for clinical applications in the sites of manufacturers and supplier of restorative materials for dentistry.

Deformation behavior of the samples was estimated based on analysis of their deformation (bending) curves. Effective elastic moduli calculated from the inclination of the bending curve, maximal deformation of the sample and ultimate bending strength were used as the mechanical characteristics of the samples in addition to the deformation curve under bending. Please clarify with quantitative details. Inclination – do you mean slope and between what strains?

Thank you for the question. It is very important to know some details of the processing data. Unfortunately, Trapezium is not open software and, hence, we must trust (personally I believe in Shimadzu) this worldwide manufacturer.

Figure 1. Preparation of samples from hen’s eggshell: (1) – eggshell on the substrate; (2) – eggshell after cut off procedure; (3) samples for bending, working surface and end surface. There are not numbers 1, 2 and 3 in the figure.

Yes, it is my big fault! This is corrected in the new version of the manuscript.

Results:

Is differ?

Corrected "is differed".

Figures 1 to 5 – related to which set as they refer?

The data on deformation behavior of all samples are given in figures 2, 3, 4, and 5 and in Table 1. Samples in figure 1c are from preliminary testing. The new version of the manuscript sounds:

The data of mechanical testing of the composite samples "hen's eggshell - polymer plomb/coating" under 3-points bending are presented in Figures 2-5 and Table 1.

All plots/graphs should have the same axis maximum values and major units for easy comparison.

Agree, we will send to the editorial the graphs in TIFF format, prepared according your suggestion.

How are the stresses and deformation % calculated – from displacement of the machine cross-head? Surely not? Is stress bending stress?

Mechanical properties were taken from Trapezium. Yes, of course, the processing procedure is closed, but it is the same for all samples. This circumstance allows comparing the data.

No legends so what does each colour represent?

Thank you for query. There are deformation curves of 3 or 4 samples, which were colored differently, in each figure. The legends are corrected as following:

Deformation curves of the hen’s eggshell under 3-points bending in air (each curve is colored differently): (a) – initial state; (b) – after the etching

What are “lower prisms of the bending device”?

They are the prisms on which the sample is laid under 3-points bending.

No image of the test set up is included – major deficiency for a mechanical type manuscript – the reader cannot attest to the veracity of the results.

We can include detail description of the testing facility in the "Supplementary materials" to the paper. I hope that editorial gives permit for this.

Table 1: any statistical analysis of the data? How many repeats of each type of coupon of each set?

The average quantity of the samples for every set is 10-12 pieces. Some important findings we repeated two-three times. Therefore, formally we could add the standard deviations to the average meanings in Table 1. However, the spread of engineering curves for the samples after different stages of the procedure of composite sample preparation is caused by many factors which cannot be correctly described the usual statistics. One of them is the shape of plomb, while another one is the individual profile of each hen's eggshell sample etc. Therefore, we must consider mechanical properties in Table 1 as some qualitative indicators only, which make clear the deformation behavior or the course of curves of the samples. We hope that a reader will understand this disturb of standard for technical papers.

How were the deformation and ultimate strength determined – are these maximum values and surely there is some scatter?

This is average meaning per set of the samples. A reader can understand the level of scatter of mechanical properties from the scatter of the engineering curves in figures 2-5.

Metallographic examination? Microscopic and/or fractographic

Metallographic examination means the study of the samples with a help of optical microscope or SEM under magnification x10-x500. Usually fractorgaphic study, namely examination of fracture surface, does not call metallographic study.

Trajectory of a dangerous crack – what is that? Fast growing to catastrophic?

Dangerous or dominant crack is the crack, whose growth leads to failure of the sample. Usually, this term is used when there are many cracks appear in the sample under loading. Its trajectory means the track / way that the dangerous crack will advance in the sample under loading. 

What is meant by loading “plugged off” and “be braked”? no idea.

Thank you for the question. It is very important for analysis of deformation behavior of macroscopically brittle materials. It is well known that the bend of engineering curve of brittle materials such as silicate glass and some ceramics, means their momentary failure due to the growth of the dangerous/dominant/magistral crack. On the contrary, in ductile metals, the bend of deformation curve points to necking, where dangerous/dominant/magistral crack will appears. The case, described in our work, lays between brittle and ductile behavior. The bend of the engineering curve does not mean the momentary failure of the sample, especially, if the loading is stopped as soon as the bend appears. It means that crack growth in the hen's eggshell samples is braked due to some additional channel for stress accommodation, which is absent in the brittle material.

 “al-ways”?

Corrected. This is MSWord program fault.

What is the capacity of the load-cell used and its calibration level – what loads are experienced and are these consistent with the accuracy of the load cell?

Thank you for the important question. It was our catastrophic fault that we mistakes with the type of our testing facility. In the reviewed version the type was named as Shimadzu™ AG-50K XD, while really we worked with Shimadzu™ AG-S 2kN. This testing machine has appropriative loading diapasone and load cell. Thank you once again! The correction has been done:

We carried out mechanical testing on the Shimadzu™ AG-S 2kN testing machine (traverse rate was 0.1 mm/min).

No images of fractured surfaces which would indicate to the authors and the reader the type of failure incurred.

Following materials science tradition, the fracture surfaces of many samples were documented with SEM facility. Their morphology was examined as brittle fracture in all cases and it was described in details in many papers including cited in our manuscript. No differences in fracture surface morphology were detected between samples from different sets. Therefore we did not include this mater in the manuscript.

Additional argument is the course of the “de-formation” – “deformation” curves for majority of samples, which could approximate by a linear dependence – please clarify.

There are two basic macroscopic features of the brittle fracture. The first is small/tiny deformation prior the failure, which experimentally estimated as - less than 1%. This condition meets our experimental data. The second feature is the function described the deformation behavior should be the line function / line dependence or the deformation curve of a brittle solid should be rectilinear. The second condition meets for the middle and final areas of the engineering curves of the samples tested, while the initial stage does not meet it. The cause of this fault we see in the complicate profile of the samples. Therefore, we consider the second feature as the additional argument only.

 “hen's eggshell is a natural inorganic biomaterial” - The eggshell is structurally composed by organic and inorganic components. The organic component of the shell consists of the shell membranes, mammillary buttons or tips, the matrix of the shell, and the cuticle (Solomon, 1991). The inorganic component of the eggshell consists of calcium carbonate crystals. The eggshell layers, the inside to the outside, are composed by mammillary buttons layer (internal), palisade layer (intermediate), and crystal surface layer (external; Roberts, 2004). Reference: C. Stefanello, T.C. Santos, A.E. Murakami, E.N. Martins, T.C. Carneiro, Poultry Science, Volume 93, Issue 1, 1 January 2014, Pages 104-113

Thank you for important suggestion. We add this work in references under number [8]:

This is expected result because hen's eggshell is a natural inorganic biomaterial/biomineral with covalent chemical bonding [6-8] and, hence, it should not exhibit any other behavior than the brittle fracture behavior [17].

“mechanical characteristics that varied in wide limits, but always inside the brittle behavior” – completely vague and indeed baffling.

You are absolutely right! The experimental data are sometimes "indeed baffling". The viscous polymer coating does not change the brittle deformation behavior of the biomineral, but allows changing its mechanical properties, namely, the elastic modulus and the ultimate strength in the wide limits. It was shown that viscoelastic polymer coatings (for example, the polymer plombs used in dentistry) do not change the deformation behavior of samples cut from hen's eggshell under 3-points bending, which continues to be brittle (the deformation prior the failure always continues to be less than 1%). In spite of this their mechanical characteristics, such as the elastic modulus and the ultimate stress could vary in the wide limits (6-14GPa and 30-180MPa, respectively). Joining "hen's eggshell - plomb" never crack and, hence, it exhibits quite powerful cohesion strength under bending. It seems the composites "hen's eggshell - polymer plomb" under bending could serve as the substitution of the joining "tooth enamel - polymer plomb" under elaboration and examination of novel restorative materials for dentistry, namely, for estimation of their mechanical properties including cohesive strength.

This idea is reflected in the first paragraphs of "Discussion":

Mechanical testing has shown that deformation behavior of the samples cut from hen’s eggshell with polymer coatings under bending continues to be brittle in spite of the different properties of the coatings because in all cases the total deformation prior the failure was less than 1% [14]. Additional argument for this conclusion is the course of the deformation curves for majority of tested samples, which could approximate by a linear dependence [15,16]. This is expected result because hen's eggshell is a natural inorganic biomaterial/biomineral with covalent chemical bonding [6-8] and, hence, it should not exhibit any other behavior than the brittle fracture behavior [17]. At that the composites "hen's eggshell - polymer plomb" possess mechanical characteristics, which varied in wide limits, but always inside the brittle behavior. This finding seems important because it was obtained on the samples possesses the native surfaces and, hence, the influence of such random factor as the preparation of samples on experimental data is minor.

 “surface by a blue laser” – can you describe in detail? Wavelength and power?

We will add the detail information about it in the "Supplementary materials".

What are the major conclusion based on the evidenced data?

We believe that the new version of the manuscript contains the main conclusion:

"…viscoelastic polymer coatings (for example, the polymer plombs used in dentistry) do not change the deformation behavior of samples cut from hen's eggshell under 3-points bending, which continues to be brittle despite their mechanical characteristics could vary in the wide limits."

Comments on the Quality of English Language

The quality of the English needs substantial improvement.

The manuscript was re-written and carefully checked.

Reviewer 2 Report

This article investigates the bending deformation behavior of eggshells and related composite materials, which is very interesting. However, there are some issues that need to be clarified in this work, and additional experiments should be conducted. Please consider the following modification suggestions:

1、 For the title, the standard notation for composite materials should be used to further simplify it, such as: Bending deformation behavior of egg-shell and egg-shell/polyer composites.

2、 The processing defects of brittle materials usually have a significant impact on mechanical behavior. How do you ensure the smoothness of as-cut eggshell samples? Is there an evaluation for it?

3、 Standard deviation should be given for each parameter in Table 1.

4、 The fracture morphology analysis of typical samples in the text should be supplemented, especially the samples corresponding to Figure 5a, whose deformation behavior shows a toughening transition trend.

5、 The discussion of the manuscript is not in-depth enough and further revisions are needed. The discussion should not be a literature review, but rather a complete explanation of the deformation, strengthening, or toughening mechanisms of relevant composite materials.

6、 The cut eggshells clearly cannot be directly used for actual products. The author should point out the preparation methods and structural design strategies for future products.

7、 The conclusion should include information on the mechanical properties of the sample and the main viewpoints. The reviewer suggests that the author supplement relevant content.

8、 What is the microstructure of eggshells and related composite materials? What is the correlation between this structure and mechanical behavior? This article should provide XRD and SEM detection results, or at least provide references as a basis.

There are many syntax error in the manuscript, which should be carefully corrected by the author.

Author Response

The first of all the authors would like to express sincerely gratitude to the reviewers for detail analysis of the manuscript and helpful criticism and suggestions. Their analysis served the start of the detail discussions the findings with colleagues that allows understanding better their place in the knowledge on biocomposites. Many questions that were asked by the reviewers having important meaning for the composite science and its application to the dental materials science.

This article investigates the bending deformation behavior of eggshells and related composite materials, which is very interesting. However, there are some issues that need to be clarified in this work, and additional experiments should be conducted. Please consider the following modification suggestions:

1、 For the title, the standard notation for composite materials should be used to further simplify it, such as: Bending deformation behavior of egg-shell and egg-shell/polyer composites.

Agree! The title of the manuscript was changed as "Bending deformation behavior of egg-shell and egg-shell/polymer composites". Thank you very much for suggestion!

2、 The processing defects of brittle materials usually have a significant impact on mechanical behavior. How do you ensure the smoothness of as-cut eggshell samples? Is there an evaluation for it?

Many thanks for the question! It is very important for better understanding of the finding obtained. The first of all, despite some difference of the shape of hen's eggshell samples including profile (figure 1c), the engineering bending curves lay by a dense bunch (figure 2a). We carried our many experiments with samples from different eggshells, but no differences in their behavior and mechanical properties were obtained. We believe that some small difference in the course of the curves is caused sooner by the complicate profile of the surfaces of samples than the defects on their edges. However, this conclusion contradicts with experience of community including our for the brittle materials. It seems that behavior of eggshell samples in the microscopic scale (the level of microcracks etc) is not so brittle as glass or some kinds of oxide ceramics. Indeed, we have shown in ref. 10 that the width of the dangerous crack in the hen's eggshell samples could be increased under additional bending in both air and water. Perhaps, it is a contribution of the bioorganic component of eggshell or something else, but it is clear that this is not feature of brittle fracture.

3、 Standard deviation should be given for each parameter in Table 1.

The average quantity of the samples for every set is 10-12 pieces. Some important findings we repeated two-three times. Therefore, formally we could add the standard deviations to the average meanings in Table 1. However, the spread of engineering curves for the samples after different stages of the procedure of composite sample preparation is caused by many factors which cannot be correctly described the usual statistics. One of them is the shape of plomb, while another one is the individual profile of each hen's eggshell sample etc. Therefore, we must consider mechanical properties in Table 1 as some qualitative indicators only, which make clear the deformation behavior or the course of curves of the samples. We hope that a reader will understand this disturb of standard for technical papers.

4、 The fracture morphology analysis of typical samples in the text should be supplemented, especially the samples corresponding to Figure 5a, whose deformation behavior shows a toughening transition trend.

Thank you for the question. We have some experimental data on the morphology of fracture surface of hen's eggshell samples. Despite the loading scheme (bending or shearing) it is the brittle fracture, which described in details by many workers, including in works referred in the manuscript. It seems that SEM study under magnifications over 10K could be helpful for examination of the thin structure of fracture surfaces of the hen's eggshell samples, including them whose behavior is given in Figure 5a, but the carbon film hidden some features of fracture morphology. We plan to carry out this study in far future. Thank you for the idea!

5、 The discussion of the manuscript is not in-depth enough and further revisions are needed. The discussion should not be a literature review, but rather a complete explanation of the deformation, strengthening, or toughening mechanisms of relevant composite materials.

We are agree with the reviewer's statement. However, in our case we only point to an opportunity to use the hen's eggshell samples as the substitution of the human tooth enamel for some local application. Naturally, questions arise concerning with adhesion mechanisms, stress accommodation channels, the procedure of mechanical testing and the processing of the experimental data. Currently, we cannot give detailed answers and, hence, in discussion we should limit by trivial conclusion, which sooner direct a reader to roots of experience than the direct and clear answers.

6、 The cut eggshells clearly cannot be directly used for actual products. The author should point out the preparation methods and structural design strategies for future products.

Thank you for the question! You are absolutely right. The new version of manuscript states more clearly about the applications of the finding (see paragraph 2 of Introduction).

According to chemical content and genesis, human tooth enamel is the mineral of biological genesis or biomineral, whose mechanical properties should be close to some rocks [5]. Hen's eggshell is also a biomineral [6,7], whose properties including mechanical ones are close to human dentin and enamel under the stress conditions that takes place under the chewing of normal food [8,9]. Eggshell has two natural surfaces, whose morphology is similar to the prism structure of tooth enamel [5], and which do not need in additional preparation before the testing. Its thickness is almost constant value, and it is easily cut into samples for mechanical testing, for example, by the scheme of 3-points bending [10]. Besides, there are many sources of hen's eggs for a legal supply including food markets, farms, and city supermarkets all of them given the government guarantee of the quality. These features allow carrying out mechanical testing of the eggshell samples on the 3-points bending scheme without any engineering and ethical problems. Therefore, samples cut from hen's eggshell and covered by a polymer plomb material, which has been glued on their convex surface, could be used for the experimental estimation of the deformation behavior of composites "tooth hard tissues – polymer plomb", including the cohesive strength between them. Indeed, 3-points bending allows effectively examining the mechanical properties of such composites. This applied task has also some fundamental meaning, since the deformation behavior of the composite "brittle material - viscous coating" under bending is interesting for the composite science, too [11,12].

7、 The conclusion should include information on the mechanical properties of the sample and the main viewpoints. The reviewer suggests that the author supplement relevant content.

Thank you for the important suggestion! Brief information on mechanical properties was included to "Conclusion" chapter of the re-written manuscript.

It was shown that viscoelastic polymer coatings (for example, the polymer plombs used in dentistry) do not change the deformation behavior of samples cut from hen's eggshell under 3-points bending, which continues to be brittle (the deformation prior the failure always continues to be less than 1%). In spite of this their mechanical characteristics, such as the elastic modulus and the ultimate stress could vary in the wide limits (6-14GPa and 30-180MPa, respectively). Joining "hen's eggshell - plomb" never crack and, hence, it exhibits quite powerful cohesion strength under bending. It seems the composites "hen's eggshell - polymer plomb" under bending could serve as the substitution of the joining "tooth enamel - polymer plomb" under elaboration and examination of novel restorative materials for dentistry, namely, for estimation of their mechanical properties including cohesive strength.

8、 What is the microstructure of eggshells and related composite materials? What is the correlation between this structure and mechanical behavior? This article should provide XRD and SEM detection results, or at least provide references as a basis.

There is a lot of research and review papers on structure of eggshell in the literature. Some of them were cited as work 6 and work 7. We believe that a reader who interested in the structure and chemical content of hen's eggshell could find the information in these reviews. Mechanical properties of eggshell were also examined by many researchers. However, we met with a strange situation when begun searching for papers on mechanical properties of samples cut from an eggshell. They were absent in the literature that was opened for us and our colleagues abroad. Currently, we are trying to prepare thin foils for TEM from hen's eggshell that could open new horizons for study of structure and stress accommodation mechanisms of this biomineral.

Comments on the Quality of English Language

There are many syntax error in the manuscript, which should be carefully corrected by the author.

The manuscript was re-written and carefully checked.

Reviewer 3 Report

The paper contains the experiment study of the deformation behavior of the composite “hen’s eggshell-polymer plomb” under bending. However, there are still some questions that the authors may need to answer:

1. The description of the research background needs to be strengthened. In the introduction part, the analysis of the probably substitute materials in the dental field is not sufficient, and the paper should cite an appropriate range of literature sources in the field.

2. Page2-Line 56, Which standard was used to extract liquid organisms from eggshells? Please cite it. Line 60-64, ‘Figure 1a’ is used in the text, however, the numbers 1-3 are used in Figure 1, and the pictures are not marked one by one.

3. In Figure 1. The sample cut from the eggshell is not a regular shape. Please describe in detail whether the loading point is convex or concave. Can the mechanical properties measured by this method represent the real bending behavior?

4. The clarity of the picture in the text is very poor, please check carefully.

5. Page6-Line 173. ‘Cohesive strength of the joining between hen’s egg-shell and polymer plomb is homogeneous…’, The cohesive strength between the polymer coating and the eggshell was not quantified. It seems impossible to draw the ‘powerful strength’ conclusion only through the phenomenon of no cracks during the bending test. The test of the cohesive strength through experiments would make the conclusion more convincing.

6. The writing of the manuscript needs to be further improved.

Moderate editing of English language required

Author Response

The first of all the authors would like to express sincerely gratitude to the reviewers for detail analysis of the manuscript and helpful criticism and suggestions. Their analysis served the start of the detail discussions the findings with colleagues that allows understanding better their place in the knowledge on biocomposites. Many questions that were asked by the reviewers having important meaning for the composite science and its application to the dental materials science.

Many thanks for the helpful comments and suggestions! I tried responding them.

1. The description of the research background needs to be strengthened. In the introduction part, the analysis of the probably substitute materials in the dental field is not sufficient, and the paper should cite an appropriate range of literature sources in the field.

Thank you very much for very important suggestion. The modern polymer plomb / restorative materials and their properties is extremely interesting topic for the composite science. Many review and research papers have been published in dental literature. However, it seems that subject our brief study is limited by the influence of the polymer coating / plomb on the deformation behavior of hen's eggshell and, therefore, we use the brief description of polymer plomb materials used in modern dentistry including some references. If need, we could give some properties of these materials, however, a reader has a wide opportunity to find needed data in dental literature or in the manufacturer's website directly.

2. Page2-Line 56, Which standard was used to extract liquid organisms from eggshells? Please cite it.

Thanks! Good note! I asked for this colleagues from Institute of Ecology of Plants and Animals at Yekaterinburg. They could not give the direct answer because "this is the theme from a basic biological education". Therefore, I rewrite the sentence as:

Liquid biomass was extracted from eggshells by the following procedure. Holes of 2 mm in diameter were drilled in sharp and blunt ends of an egg. A warm water from the schpritz for injections diluted biomass inside the egg through these holes. Diluted biomass was pumped from the egg by the schpritz for injections. Further, the eggshell was washed inside by the water and was dried during the couple of days at room temperature.

Line 60-64, ‘Figure 1a’ is used in the text, however, the numbers 1-3 are used in Figure 1, and the pictures are not marked one by one.

Sorry for the fault! The Figure 1 with the correct legend is included in the revised version.

3. In Figure 1. The sample cut from the eggshell is not a regular shape. Please describe in detail whether the loading point is convex or concave. Can the mechanical properties measured by this method represent the real bending behavior?

The sample cut from the eggshell is not a regular shape.

You absolutely right that every sample cut from hen's eggshell possesses the individual shape. Of cause, we try to diminish this "irregularity". Therefore, the samples for testing always cut from the middle part of eggshell along its main axis, as it is shown in figure 1b. Despite this the shape of hen's eggshell samples is not the same, however, the difference between the shapes of the samples is minimal from possible.

Please describe in detail whether the loading point is convex or concave.

The loading prism contacts with the concave surface of the sample, while the polymer coating has been glued on its convex surface.

Can the mechanical properties measured by this method represent the real bending behavior?

Thank you for the question! This is almost philosophical question. I would like to answer as following. Concerning an eggshell as a construction: the answer is no, because our samples and an eggshell have different shapes and the loading conditions are different, as well. On the other hand, our experiments give some information of mechanical properties of hen's eggshell, which can be helpful for the modelling of the behavior of an eggshell under loading.

4. The clarity of the picture in the text is very poor, please check carefully.

Yes, this is our fault. The graphs will be send in the professional format. The problem with the digital images of the samples is connected with a small focus distance of the light microscope. Indeed, we need in the image of the sample in whole, but with satisfactory resolution. Therefore, for documenting of the samples prior and after processing and testing, we use the optical scanner with the resolution at least 4800dpi. This technique does not damaged the samples, gives economy of time and allows comparing all our samples between themselves. However, low clarity of some small details is its accompanying feature.

5. Page6-Line 173. ‘Cohesive strength of the joining between hen’s egg-shell and polymer plomb is homogeneous…’, The cohesive strength between the polymer coating and the eggshell was not quantified. It seems impossible to draw the ‘powerful strength’ conclusion only through the phenomenon of no cracks during the bending test. The test of the cohesive strength through experiments would make the conclusion more convincing.

Thank you for the question that point to the hearth of the problem considered! The main idea of our short research work is the looking for the way of estimation of cohesive strength between tooth hard tissues and polymer plomb materials, namely, its quantitative value. The first of all, the appropriative loading scheme should be applied for such task. Uniaxial compression and diametral compression (Brazilian testing) cannot be applied for this purpose, because the problems with analysis of the findings and calculations of the cohesive strength. Bending, namely 3-points bending, is the most appropriative scheme for brittle materials, but the preparation of samples, especially from human tooth enamel, is almost jewelry job and, hence, this scheme cannot be applied to the tooth hard tissue. We suggest to substitute the enamel by another biomineral, because the deformation behavior of the hen's eggshell samples under bending can be realized in every materials science laboratory. Our testing has shown that the joint between biomineral substrate and polymer coating never fails under bending, despite the level of applied stress was about the one that occurs under chewing food. This finding allows stating that the cohesive strength of this joint is quite enough for usage as a plomb in a tooth. Of cause, this is not quantitative estimation in "digitals", but it allows to state that the cohesive strength is powerful for a normal human food. As the future task, we plan to carry out the work for realizing you suggestion.

6. The writing of the manuscript needs to be further improved.

The manuscript was re-written and carefully checked.

Round 2

Reviewer 1 Report

Many of my queries remain. Extensive revision of the English is still required. What is a schpritz? Is it a spray? Traverse is the crosshead displacement or movement rate. In the manuscript - working surface and end surface? Surely: coupon plan view and side view or else give an XYZ co-ordinate system/axes? The procedure for calculating the modulus is hidden behind the "closed" software of the machine - surely the methodology is defined or user defined to give the range of strain for calculating the slope of a curve for modulus values - the hidden excuse is not acceptable to any scholar of mechanics of materials or experimentalist in solids mechanics and if this cannot be explained in detail should be rejected. Again, all plots/graphs should have the same limits on the axes, or else plots can be redrawn on one set of axes so that differences in responses can be easily assessed by the reader (figures 4 and 5). Figure 6 - see comment above on surfaces.  

The quality is still poor from singular to plural to misuse of words and phrases - I'm afraid the lexicon warrants exploration. Vast improvement is required for publication in an English publication.

Author Response

Many of my queries remain.

Extensive revision of the English is still required.

Please, will you excuse me for the low level of our English? We are trying to change this sad feature.

What is a schpritz? Is it a spray?

Sorry, this is my big fault! I took this word from the label of a plastic syringe for injection. The word "schpritz" has been changed on the English word "syringe" in the modified manuscript. The correction is highlighted by blue color.

Traverse is the crosshead displacement or movement rate.

The traverse rate means the rate of a movement of the traverse of testing machine. The term "traverse rate" is frequently used in the technical literature, including our papers, therefore we usually did not explain its meaning. However, we have added some words concerning this term in the modified text: We carried out mechanical testing on the Shimadzu™ AG-S 2kN testing machine (traverse rate that means the rate of a movement of an active traverse of the testing machine was 0.1 mm/min).

In the manuscript - working surface and end surface? Surely: coupon plan view and side view or else give an XYZ co-ordinate system/axes?

The Figure 1 c has been signed by "working surface" and "end surface". If need we could add the arrows pointed to these surfaces of the sample.

The procedure for calculating the modulus is hidden behind the "closed" software of the machine - surely the methodology is defined or user defined to give the range of strain for calculating the slope of a curve for modulus values - the hidden excuse is not acceptable to any scholar of mechanics of materials or experimentalist in solids mechanics and if this cannot be explained in detail should be rejected.

We are completely agree with your argument. It is especially important for the case of detailed examination of the mechanical properties of materials. You are right that we have some opportunity to correct the angle of inclination of the engineering curve under processing of experimental data because software "Trapezium" allows doing that. Moreover, an estimation of an elastic moduli given in the manuscript is sooner the estimation of the angle of inclination of the deformation curves under bending than physical procedure for determination of the elastic properties of the model materials. Indeed, the loading scheme and the shape of the samples are not appropriate for the correct examination of elastic properties of a material. On the initial stage of our research we planned calling this parameter as "the angle of inclination of the engineering curve", but discussion with colleagues has shown that it could disorient some researchers, especially who has a limited experience in such works. Therefore, we used two basic mechanical parameters (the ultimate strength and the deformation prior the failure) in discussion. The elastic modulus or the angle of inclination is only the additional characteristic, which is sooner a "tribute to tradition". Indeed, some readers and other reviewers could be “dazed and confused” a little bit, if "effective elastic moduli" were disappeared from the analysis of deformation behavior of brittle composite materials. In the any case, your arguments are extremely important and we shell consider it in our further work. Thank you very much!

Again, all plots/graphs should have the same limits on the axes, or else plots can be redrawn on one set of axes so that differences in responses can be easily assessed by the reader (figures 4 and 5).

Thank you for the query. Trapezium software allows presenting the processed data according to the publisher request. We can present the curves according to the your suggestion without any problems, but this correction causes to considerable difference in the size of each figure in the manuscript. I would ask you to allows accepting the final decision to a production editor, who could transform the figures with the deformation curves, which will be send to the Editorial office in the professional graphic format (TIFF or any other), according to the template of the Journal issue.

Figure 6 - see comment above on surfaces. 

The surfaces in Figure 6 have been signed.

Comments on the Quality of English Language

The quality is still poor from singular to plural to misuse of words and phrases - I'm afraid the lexicon warrants exploration. Vast improvement is required for publication in an English publication.

The text of manuscript has been rewritten by me and reviewed by colleague from USA. 

Author Response File: Author Response.docx

Reviewer 2 Report

The questions raised by the reviewer seem to have been answered appropriately, and the current status of the manuscript only requires minor modifications to be published. The writing method of noun possessive case "hen's" is not suitable for scientific papers. It is suggested to use nouns as modifiers, which can be changed to: "eggshell".

The writing method of noun possessive case "hen's" is not suitable for scientific papers. It is suggested to use nouns as modifiers, which can be changed to: "eggshell".

Author Response

Comments and Suggestions for Authors

The questions raised by the reviewer seem to have been answered appropriately, and the current status of the manuscript only requires minor modifications to be published.

Thank you very much. Sure, your and other remarks and suggestions were highly helpful and very important for our work.

The writing method of noun possessive case "hen's" is not suitable for scientific papers. It is suggested to use nouns as modifiers, which can be changed to: "eggshell".

Thanks. Agree. The word "hen's" was cancelled in the modified manuscript. (1) The sentence “Hen eggs were taken as a biological material for experiments.” was added in to the Abstract as #2. (2) The term “eggs of hens” was added to the Keywords. The changings connected with this correction are highlighted by the blue color in the text.

 

Comments on the Quality of English Language

The writing method of noun possessive case "hen's" is not suitable for scientific papers. It is suggested to use nouns as modifiers, which can be changed to: "eggshell".

Need changes have been done

Author Response File: Author Response.docx

Reviewer 3 Report

Here is my feedback on the revised manuscript which I had previously recommended for major revision. 

I appreciate the time and effort the authors have taken to address the concerns raised in my initial review. I can see that the authors have thoroughly responded to the review questions and made the necessary changes to improve the quality of the article.

Upon reviewing the revised manuscript, I am pleased to say that the revisions have correctly answered the possible confusion, and I believe it can now be considered for publication. However, before final acceptance, I would like to suggest a few minor corrections that should be addressed to ensure the polished presentation of this work.

In particular, there are still some issues with the referencing of figures and sets within the text. Please carefully review the manuscript to ensure that all references to figures are accurate and consistent. Especially, I identify the followings:

1. On page 2, line 81: "figure 1c" should be changed to "Figure 1c".

2. On page 4, line 131: "set 2" should be changed to "Set 2".

3. On page 7, line 221: "figure 7" should be changed to  "Figure 7".

Please also double-check all other references to ensure that similar issues have not been overlooked.

Once these minor corrections have been made, I will be happy to recommend the manuscript for publication in Section Biocomposites of journal J. Compos. Sci.. 

 

Based on the quality of the English language writing in the revised manuscript, I would say the writing is generally good, but there is room for improvement in terms of clarity and precision.

Author Response

Comments and Suggestions for Authors

Here is my feedback on the revised manuscript which I had previously recommended for major revision. 

I appreciate the time and effort the authors have taken to address the concerns raised in my initial review. I can see that the authors have thoroughly responded to the review questions and made the necessary changes to improve the quality of the article.

Upon reviewing the revised manuscript, I am pleased to say that the revisions have correctly answered the possible confusion, and I believe it can now be considered for publication. However, before final acceptance, I would like to suggest a few minor corrections that should be addressed to ensure the polished presentation of this work.

In particular, there are still some issues with the referencing of figures and sets within the text. Please carefully review the manuscript to ensure that all references to figures are accurate and consistent. Especially, I identify the followings:

1. On page 2, line 81: "figure 1c" should be changed to "Figure 1c".
2. On page 4, line 131: "set 2" should be changed to "Set 2".
3. On page 7, line 221: "figure 7" should be changed to  "Figure 7".

Please also double-check all other references to ensure that similar issues have not been overlooked.

Once these minor corrections have been made, I will be happy to recommend the manuscript for publication in Section Biocomposites of journal J. Compos. Sci.. 

Many thanks for the help in the work with the manuscript. Your remarks and suggestions are really very important and helpful for both our current and planned researches. All suggestions concerning the manuscript writing have been done. Thank you very much again.

Comments on the Quality of English Language

Based on the quality of the English language writing in the revised manuscript, I would say the writing is generally good, but there is room for improvement in terms of clarity and precision.

Please, sorry that my English is not perfect. My colleagues and I are trying to overcome this flaw.

 

Author Response File: Author Response.docx

Round 3

Reviewer 1 Report

The possessive form of the plural noun hens is hens'. Amend this, AND you should abide by the suggestion of reviewer 3 throughout the complete manuscript or rethink.

P 5 & 6            from Line 144: “The dangerous crack in the sample with non-flowing plomb could be braked when the testing was stopped, whereas the one never braked in the samples with liquid flowing plombs and, therefore, such samples al-ways failed.” What do you mean by braked – is it slow down or arrest, stop? Could you reword to: “The dangerous (or critical) crack in the sample with the non-flowing plomb could be arrested when the testing was stopped, whereas the crack never stopped growing in the samples with liquid flowing plombs and, therefore, such samples always failed.”

Authors’ response from a query: The word "schpritz" has been changed on the English word "syringe" in the modified manuscript. The correction is highlighted by blue color.

It has not, but deleted.

Previous commentary: Again, all plots/graphs should have the same limits on the axes, or else plots can be redrawn on one set of axes so that differences in responses can be easily assessed by the reader (figures 4 and 5).

Response from authors: “Thank you for the query. Trapezium software allows presenting the processed data according to the publisher request. We can present the curves according to the your suggestion without any problems, but this correction causes to considerable difference in the size of each figure in the manuscript. I would ask you to allows accepting the final decision to a production editor, who could transform the figures with the deformation curves, which will be send to the Editorial office in the professional graphic format (TIFF or any other), according to the template of the Journal issue.”

I suggest importing the raw data into Excel and all graphs can be sized to the same outside dimensions, with the same units, major units and axes. The publisher may have further suggestions.

The units for the Y-axes in Figure 5 a and b should be in MPa, not MPA. should be in MPa, not MPA.

 

I commend as English is not their first language. The English is tolerable.

Reviewer 3 Report

I appreciate the time and effort the authors have taken to address the previous comments. The review questions have been adequately answered and the quality of the article has been improved. Thus I will be happy to recommend the manuscript for publication in J. Compos. Sci..