Self-Healable Biocomposites Crosslinked with a Combination of Silica and Quercetin

Round 1

Reviewer 1 Report

This paper reports the preparation of epoxidized natural rubber functionalized with natural ingredients such as quercetin and silica, and investigates their self-healable properties. A wide range of characterization of the epoxidized natural rubber materials has been carried out, and they systematically study the properties including the rheometric measurements, mechanical tests and crosslinking density, and they further investigate the self-healing properties by the optical and SEM methods. I think these results are interesting and I recommend acceptance, subject to the following, minor corrections:

1 In the materials preparation section (2.1. Materials and Processing), the authors report the use of different DCP, silica and quercetin molar ratio. Are there any reasons why the authors decide to use such a range of ratios? If yes, can they provide more literature for this?

2 In the rheometric properties section (section 3.1 and Figure 1), the ENR and ENR/silica 15 show much lower torque values compared to the other systems, can the author provide some explanation for this result?

Author Response

Institute of Polymer and Dye Technology

Technical University of Lodz

90-924 Lodz, ul Stefanowskiego 12/16, Poland

Tel.: +48 42 631 32 23, Fax: +48 42 636 25 43

June 27, 2021

Materials

Dear Professor,

We are resubmitting our revised paper entitled Self-healable biocomposites crosslinked with combination of silica and quercetin by Olga Olejnik, Anna Masek and Małgorzata Szynkowska-Jóźwik with a request to reconsider it for publication in Materials.

We have carefully considered the Editor and Reviewers' comments. The manuscript was revised exactly according to these comments. The list of responses to the reviewers’ comments and corrections made in the manuscript is attached.

The manuscript has not been previously published, is not currently submitted for review to any other journal, and will not be submitted elsewhere before a decision is made by this journal.

For correspondence please use the following information:

corresponding author: Anna Masek

Institute of Polymer and Dye Technology

Technical University of Lodz

90-924 Lodz, ul Stefanowskiego 12/16, Poland

Tel.: +48 42 631 32 93

Fax: +48 42 636 25 43

e-mail: [email protected]

Yours sincerely,

Ph. D., D.Sc. Anna Masek

Revewer #1:

Comments and Suggestions for Authors

This paper reports the preparation of epoxidized natural rubber functionalized with natural ingredients such as quercetin and silica, and investigates their self-healable properties. A wide range of characterization of the epoxidized natural rubber materials has been carried out, and they systematically study the properties including the rheometric measurements, mechanical tests and crosslinking density, and they further investigate the self-healing properties by the optical and SEM methods. I think these results are interesting and I recommend acceptance, subject to the following, minor corrections:

Revewer #1:

1 In the materials preparation section (2.1. Materials and Processing), the authors report the use of different DCP, silica and quercetin molar ratio. Are there any reasons why the authors decide to use such a range of ratios? If yes, can they provide more literature for this?

Answer 1:

We thank Reviewer for paying attention to this issue. In our research we were focused on finding out a proper mass ratio of components, not molar ratio, because mass ratio is more often used in elastomer technology [phr – parts per hundred rubber]. We wanted to use the same mass ratio of DCP and quercetin (2 phr) to check the possibility of replacing a popular synthetic curing agent with a natural one. According to the results, the same mass ratio of and quercetin is not so efficient and effective in comparison to DCP but silica, which is a popular active and low-cost filler, usually used in much higher ratios, is able to improve the curing effect, which is visible in rheometric results, mechanical properties and crosslinking density. We present the lowest mass ratio of selected components, where visible curing effect, as well as noticeable self-healing properties have been revealed.

Revewer #1:

2 In the rheometric properties section (section 3.1 and Figure 1), the ENR and ENR/silica 15 show much lower torque values compared to the other systems, can the author provide some explanation for this result?

Answer 2:

We are thankful for the Reviewer’s comment. In our opinion, the low values of maximal torque and torque changing of ENR/silica15 is a result of unstable crosslinks and weak forces formation between Si- OH groups of silica aggregates and oxirane rings of ENR. In the case of pure ENR it is a result of crosslinks formation absence. We added an explanation to the article as follows: “. The low values of maximal torque and changing of torque in comparison to other systems can be a result of too low an amount of silica addition. Therefore too little bonds and only unstable crosslinks and weak forces between Si- OH groups of silica aggregates and oxirane rings of ENR were formed, which appear and disappear at the same time during a rheometric measurement. Unlike in ENR/silica15, pure ENR is not a self-crosslinkable material and the crosslinks do not appear at all.”

Reviewer 2 Report

Biobased self-repairing or self-healing materials are important and widely demanded in many fields such as medical, dentistry, pharmaceutical, and biology. The authors here reported that they made a new type of biocompatible self-healing composite by embedding silica and quercetin in the epoxidized natural rubber with 50 mol% of epoxidation polymers. The idea of this article is interesting, but there are several things that the authors should address before the paper is finally published. The questions and comments are as follow:

1. In the abstract, the authors claimed that the self-healing materials that they made did not require any external stimuli, but actually, they heated the materials when they conducted the measurements such as the Rheometric investigation. “The measurements were conducted at the temperature of 160^oC for 60 min”, which is quoted from the article.
2. It seems like the self-healing property of the mixture of ENR/quercetin/silica is not that good. For example, in the rheometric study, the ENR/DCP2 would be expected the best with the fastest torque increase. Also, the ENR/DCP2 has the highest crosslink density compared to the other materials. When it comes to the tensile strength measurements, pure ENR becomes the best with the highest healing efficiency of 80% obtained from tensile strength. It seems that the property of the mixture of ENR/quercetin/silica becomes the highest or the best only in the elongation at break (i.e., Eb in the paper) investigation. However, even in this part, the healing efficiency of the ternary mixture is not much higher than the others. For example, the healing efficiency obtained from Eb of binary mixture ENR/quercetin2 is quite close to the healing efficiency obtained from Eb of the ENR/quercetin4/silica15. Moreover, the authors did not mention why the efficiency obtained from Eb of ENR/quercetin2/silica15 is higher than that of ENR/quercetin4/silica15.
3. The optical microscope photographs do not make any sense as well. In figure 7, at first glance, one would expect Figure7(f) and Figure 7(j) are the best self-healing materials. Because the joint interfaces are the smallest in these two figures. However, these two figures are corresponding to ENR/quercetin2 and ENR/quercetin4. The SEM figures make things even worse, in Figure 8(c), it looks like the two separate parts in ENR/quercetin4/silica15 did not connect or self-repair at all. Instead, these two separate parts look like being put two together. However, on the other hand, the self-healing in Figure 8(a) and (b) are much better than Figure 8(c).
4. There is one more minor thing, all the “et.al.” in this paper should be “et al.”.

Comments for author File: Comments.pdf

Author Response

Institute of Polymer and Dye Technology

Technical University of Lodz

90-924 Lodz, ul Stefanowskiego 12/16, Poland

Tel.: +48 42 631 32 23, Fax: +48 42 636 25 43

June 27, 2021

Materials

Dear Professor,

We are resubmitting our revised paper entitled Self-healable biocomposites crosslinked with combination of silica and quercetin by Olga Olejnik, Anna Masek and Małgorzata Szynkowska-Jóźwik with a request to reconsider it for publication in Materials.

We have carefully considered the Editor and Reviewers' comments. The manuscript was revised exactly according to these comments. The list of responses to the reviewers’ comments and corrections made in the manuscript is attached.

The manuscript has not been previously published, is not currently submitted for review to any other journal, and will not be submitted elsewhere before a decision is made by this journal.

For correspondence please use the following information:

corresponding author: Anna Masek

Institute of Polymer and Dye Technology

Technical University of Lodz

90-924 Lodz, ul Stefanowskiego 12/16, Poland

Tel.: +48 42 631 32 93

Fax: +48 42 636 25 43

e-mail: [email protected]

Yours sincerely,

Ph. D., D.Sc. Anna Masek

Revewer #2:

Comments and Suggestions for Authors

Biobased self-repairing or self-healing materials are important and widely demanded in many fields such as medical, dentistry, pharmaceutical, and biology. The authors here reported that they made a new type of biocompatible self-healing composite by embedding silica and quercetin in the epoxidized natural rubber with 50 mol% of epoxidation polymers. The idea of this article is interesting, but there are several things that the authors should address before the paper is finally published. The questions and comments are as follow:

1. In the abstract, the authors claimed that the self-healing materials that they made did not require any external stimuli, but actually, they heated the materials when they conducted the measurements such as the Rheometric investigation. “The measurements were conducted at the temperature of 160^oC for 60 min”, which is quoted from the article.

Answer 1:

We thank the Reviewer for paying attention to the fact that our research is not clearly explained. We have changed a sequence of sentences in the abstract and it seems to be more understandable: “The obtained materials, partially cured with a totally environmentally friendly crosslinking system consisting of natural ingredients, including quercetin and silica, exhibit a self-healing ability resulting from a self-adhesion of ENR-50 and reversible physical forces between curatives and the matrix. The impact of natural components on crosslinking effect in uncured ENR-50 matrix was analyzed based on rheometric measurements, mechanical tests and crosslinking density. The partially crosslinked samples were next cut into two separate pieces, which were instantly contacted together under a slight manual press, then left for healing process occurrence at room temperature for a few days and finally retested. The healing efficiency was estimated by measuring mechanical properties before and after healing process and was also confirmed by photos taken using optical and a scanning electron microscope (SEM).”

It means that at the rheometric measurements were conducted in order to investigate a crosslinking ability of uncured (unvulcanized) semi-finished material but not to assess the self-healing properties of the ready composite. This study was useful to estimate the curing time at 160°C using an electrically heated hydraulic laboratory press to obtain partially-cured final composites with a compromise between mechanical properties and self-healing ability. The self-healing properties of the final composites were investigated later by mechanical properties as follows: “The partially crosslinked samples were cut into two separate pieces, which were instantly contacted together under a slight manual press, then left for healing process occurrence at room temperature for a few days and finally retested. The healing efficiency was estimated by measuring mechanical properties before and after healing process. According to our results, the final composite is able to regain its mechanical properties to 45% of efficiency without any external stimuli, including temperature. We also checked the impact of temperature on the self-healing ability of our composites but according to the results heating is not necessary to obtain 45% of healing efficiency.

Revewer #2:

2. It seems like the self-healing property of the mixture of ENR/quercetin/silica is not that good. For example, in the rheometric study, the ENR/DCP2 would be expected the best with the fastest torque increase. Also, the ENR/DCP2 has the highest crosslink density compared to the other materials. When it comes to the tensile strength measurements, pure ENR becomes the best with the highest healing efficiency of 80% obtained from tensile strength. It seems that the property of the mixture of ENR/quercetin/silica becomes the highest or the best only in the elongation at break (i.e., Eb in the paper) investigation. However, even in this part, the healing efficiency of the ternary mixture is not much higher than the others. For example, the healing efficiency obtained from Eb of binary mixture ENR/quercetin2 is quite close to the healing efficiency obtained from Eb of the ENR/quercetin4/silica15. Moreover, the authors did not mention why the efficiency obtained from Eb of ENR/quercetin2/silica15 is higher than that of ENR/quercetin4/silica15.

Answer 2:

We are thankful for the Reviewer’s comment. In our research it is important to obtain the best mechanical properties in combination with the best self-healing properties of the material. Analysing tensile strength results of pure uncured (unvulcanized) ENR reveals the best healing efficiency but its mechanical properties are poor and useless. On the other hand, ENR cured with DCP reveals the best mechanical properties but its self-healing ability is unsatisfactory. The best compromise between mechanical properties, including good tensile strength (TS) and acceptable elongation at break (Eb), and self-healing efficiency was obtained for ternary composites. We have still been working on obtaining higher mechanical properties in combination with higher self-healing ability.

We thank the Reviewer for paying attention to the issue of mechanical tests results discussion. We added an explanation of higher Eb of ENR/quercetin2/silica15 than ENR/quercetin4/silica15 as follows: “ENR/quercetin4/silica15 composite is characterized by higher elongation at break results (Eb) than ENR/quercetin2/silica15. A higher amount of quercetin containing an aromatic ring in its structure causes an increase in the rigidity of the material. Moreover, more hydroxyl groups entail more crosslinks, thus increase in tensile strength and also decrease in elongation at break.”

Revewer #2:

3. The optical microscope photographs do not make any sense as well. In figure 7, at first glance, one would expect Figure7(f) and Figure 7(j) are the best self-healing materials. Because the joint interfaces are the smallest in these two figures. However, these two figures are corresponding to ENR/quercetin2 and ENR/quercetin4. The SEM figures make things even worse, in Figure 8(c), it looks like the two separate parts in ENR/quercetin4/silica15 did not connect or self-repair at all. Instead, these two separate parts look like being put two together. However, on the other hand, the self-healing in Figure 8(a) and (b) are much better than Figure 8(c).

Answer 3:

We thank the Reviewer for the suggestion. We added some explanations as follows: “Self-healing phenomenon was also observed using two types of microscope: an optical microscope and a scanning electron one. The optical microscope photos have been taken to show the sudden self-adhesion after the connection of the damaged sides together under a slight manual press. Photos of composites after the damage and after healing as a result of self-adhesion are presented below in Figure 7. As shown in the photos, the damaged surfaces of all tested composites were able to join to themselves. The faulty part of the samples were observable as a scar but in the case of pure ENR and ENR with quercetin such a defect was least visible. Based on the photos, ENR/quercetin2 and ENR/quercetin4 are materials with the best self-adhesion. It is also confirmed by mechanical tests results, where healing efficiency was calculated but other data shows that the mechanical properties of these materials are not sufficient. To the improve mechanical properties, including tensile strength, silica was added but this compound caused also a slight decrease in healing efficiency, which is visible in the pictures as well. To obtain the compromise between acceptable mechanical properties and satisfactory self-healing ability, the silica must be added. The pure ENR and ENR/silica15 materials are transparent, thus it is hard to show its self-adhesion in comparison to other samples in the same conditions. The self-adhesion of tested materials is also confirmed by SEM photos introduced in Figure 8.

The best self-adhesion effect of material is visible in pure ENR and ENR/quercetin materials. The totally mobile polymer chains are able to move and create new interactions between the cut surfaces. On the other hand, samples made of ENR, quercetin and silica also reveal self-adhesion, where the polymer chains are partially mobile and are able to permeate surfaces and form new bondings. It must also be highlighted that the proper match is important and affects healing efficiency. According to Figure 8 (c), the broken parts of the samples were not ideally aligned, which can give the impression of poor self-adhesion and can affect self-healing efficiency. Nevertheless, such a material reveals the compromise between acceptable mechanical properties and satisfactory self-healing ability. In the case of ENR/DCP2 composite, there are a lot of free spaces, where surfaces are not connected to themselves. This material has the best mechanical properties but the self-adhesion phenomenon is not acceptable.”

Revewer #2:

4. There is one more minor thing, all the “et.al.” in this paper should be “et al.”.

Answer 4:

We are grateful for Reviewer’s comment and we have changed presented mistake into correct form.

Reviewer 3 Report

The article focuses mainly on the physical and chemical composition of the material, and not enough on the mechanical behavior (strength and stiffness).

Issues to be significantly improved:

2.4 The tensile test should be adequately described:

- "dumbbell-shaped specimens" is not quite rigorous, a sketch with the precise shape and dimensions of the specimens should be provided.

- According to which standard have the tests been carried out?

- The features of the testing machine should also be indicated.

3.3

- Tables with the results should be added, or at least indicate the number of tests performed in each case and the statistical treatment applied.

- It is necessary to comment on the meaning of the data shown:

ENR material presents low TS and high elongation, how does this mean in terms of strength and stiffness?

It is not sufficiently emphasized, in my opinion, that self-healing negatively affects the mechanical behavior of the material, both in strength and deformability; although the best situation is found for the ENR/quercetin/silica material.

Conclusions

They are lacking.

A strength value above 3 MPa is, however, low. Mention should be made of values achieved in other similar materials.

The stiffening experienced by the material is not analyzed either.

In summary, a more detailed discussion of results is necessary, as far as the mechanical properties of the material are concerned.

Author Response

Institute of Polymer and Dye Technology

Technical University of Lodz

90-924 Lodz, ul Stefanowskiego 12/16, Poland

Tel.: +48 42 631 32 23, Fax: +48 42 636 25 43

June 27, 2021

Materials

Dear Professor,

We are resubmitting our revised paper entitled Self-healable biocomposites crosslinked with combination of silica and quercetin by Olga Olejnik, Anna Masek and Małgorzata Szynkowska-Jóźwik with a request to reconsider it for publication in Materials.

We have carefully considered the Editor and Reviewers' comments. The manuscript was revised exactly according to these comments. The list of responses to the reviewers’ comments and corrections made in the manuscript is attached.

The manuscript has not been previously published, is not currently submitted for review to any other journal, and will not be submitted elsewhere before a decision is made by this journal.

For correspondence please use the following information:

corresponding author: Anna Masek

Institute of Polymer and Dye Technology

Technical University of Lodz

90-924 Lodz, ul Stefanowskiego 12/16, Poland

Tel.: +48 42 631 32 93

Fax: +48 42 636 25 43

e-mail: [email protected]

Yours sincerely,

Ph. D., D.Sc. Anna Masek

#Revewer3:

Comments and Suggestions for Authors

The article focuses mainly on the physical and chemical composition of the material, and not enough on the mechanical behavior (strength and stiffness).

Issues to be significantly improved:

2.4 The tensile test should be adequately described:

- "dumbbell-shaped specimens" is not quite rigorous, a sketch with the precise shape and dimensions of the specimens should be provided.

- According to which standard have the tests been carried out?

- The features of the testing machine should also be indicated.

Answer 1:

We are thankful for the Reviewer’s suggestions. We changed description of mechanical tests as follows: “Partially cured plates of ENR-50-based materials were cut into dumbbell-shaped samples type 2 according to ISO 37 standard for smaller preferred size (Figure 1), which are approximately 1 mm thick, 75 mm long and 12.5 mm wide at ends. Five dumbbell-shaped specimens type 2 of every prepared material were tested in terms of mechanical properties using the universal mechanical testing machine Zwick 1435 (Zwick Roell GmbH & Co. KG, Ulm, Germany) equipped with extensometer. The measurement was carried out for prepared samples at a crosshead speed of 500 mm/min according to ISO 37 standard.”

Figure 1. Exemplary ENR/quercetin2/silica15 sample (type 2 according to ISO 37 standard) dedicated to mechanical test.

#Revewer3:

3.3

- Tables with the results should be added, or at least indicate the number of tests performed in each case and the statistical treatment applied.

- It is necessary to comment on the meaning of the data shown:

ENR material presents low TS and high elongation, how does this mean in terms of strength and stiffness?

It is not sufficiently emphasized, in my opinion, that self-healing negatively affects the mechanical behavior of the material, both in strength and deformability; although the best situation is found for the ENR/quercetin/silica material.

Answer 2:

We thank the Reviewer for the suggestions. We have already added tables with the results in supplementary material to not duplicate data in bar chart and in table.

Table S1. Tensile strength (TS) results of pristine ENR-50-based composites and the same materials after 2 days, 4 days of self-healing without any external stimuli and after 4 days of self-healing with extra 20 minutes of heating.

Table S2. Elongation at break (Eb) results of pristine ENR-50-based composites and the same materials after 2 days, 4 days of self-healing without any external stimuli and after 4 days of self-healing with extra 20 minutes of heating.

We have also commented mentioned issues as follows:

“Based on mechanical test results, the uncured ENR-50, similarly to other typical unvulcanized rubbers, is characterized by low tensile strength (TS), thus the crosslinker is an indispensable part of such elastomeric composites to make ENR-50 useful. Crosslinking process using only silica15 or DCP2 resulted in significant increase in strength and slight decrease in elongation of ENR-50 and deterioration in self-healing ability. On the other hand, ENR-50 samples with quercetin become more rigid because of aromatic rings, which are present in the structure, have better self-healing ability but need filler to improve strength of materials. The ENR-50-based composites containing combination of quercetin and silica are stronger but also stiffer than samples cured using only quercetin or only silica because of strong connection between quercetin molecules and silica aggregates. Such materials reveal satisfactory self-healing properties despite silica presence Moreover, elongation at break of pristine ENR/quercetin/silica composites is around 200% lower than highly cured ENR/DCP material, which is also caused by the presence of rigid aromatic structures belonging to quercetin. Furthermore, ENR/quercetin4/silica15 composite is characterized by increased elongation at break results (Eb) than ENR/quercetin2/silica15. A higher amount of quercetin containing aromatic ring in its structure causes increase in rigidity of material. Moreover, more hydroxyl groups entail more crosslinks, thus increase in tensile strength and also decrease in elongation at break occur.”

#Revewer3:

Conclusions

They are lacking.

A strength value above 3 MPa is, however, low. Mention should be made of values achieved in other similar materials.

The stiffening experienced by the material is not analyzed either.

In summary, a more detailed discussion of results is necessary, as far as the mechanical properties of the material are concerned

Answer 3:

We are grateful for Reviewer’s suggestions and we have completed lacking information as follows:

“The presented composites containing novel bio-based crosslinking system based on pure quercetin and a combination of silica and quercetin reveal self-healing properties. The compromise between satisfactory tensile strength of above 3 MPa and healing efficiency of around 40-45% were reached after adding silica combined with quercetin. The tensile strength of above 3 MPa might be considered to be low but comparing to the results of another self-healable biomaterials, for instance composites of ENR and chitin nano-crystals containing hydrogen bonding supramolecular network with the tensile strength of 1.19 MPa [28] , our materials seem to be promising. The self-healing phenomenon oc-curs as a result of self-adhesion of ENR combined with hydrogen bonding and other physical interactions formed between hydroxyl groups of quercetin and oxirane rings of ENR, hydroxyl moieties of silica and epoxy groups of ENR as well as between hydroxyl groups of quercetin and silica. Such composites after 20 minutes of vulcanizing also revealed a higher crosslink density than ENR/silica or ENR/quercetin materials. It must be mentioned that biocomposites of ENR-50 containing quercetin and quercetin with silica are stiffer that conventionally cured elastomers with elongation at break of about 500-600% because of rigid structure with aromatic rings of quercetin and strong interaction between silica, quercetin and ENR matrix. Nevertheless, obtained results seem to be promising. A further improvement of the created composites is challenging but can result in obtaining self-healable long-term soft denture lining materials, because the selected components are safe for oral cavity.”

Author Response File: Author Response.docx

Reviewer 4 Report

determined from the introduction, I have no clear idea on why the authors did this research. The reduction in crosslinking density to achieve good self-healing can be an approach. However, the mechanical properties were decreased greatly either. And the self-healing efficiency was also bad. To date, many work has been done to create dynamic or reversible crosslinking points. Why physical manner was still used?

The authors must give a more convinced aim for this research.

Author Response

Institute of Polymer and Dye Technology

Technical University of Lodz

90-924 Lodz, ul Stefanowskiego 12/16, Poland

Tel.: +48 42 631 32 23, Fax: +48 42 636 25 43

July 02, 2021

Materials

Dear Professor,

We are resubmitting our revised paper entitled Self-healable biocomposites crosslinked with combination of silica and quercetin by Olga Olejnik, Anna Masek and Małgorzata Szynkowska-Jóźwik with a request to reconsider it for publication in Materials.

We have carefully considered the Editor and Reviewers' comments. The manuscript was revised exactly according to these comments. The list of responses to the reviewers’ comments and corrections made in the manuscript is attached.

The manuscript has not been previously published, is not currently submitted for review to any other journal, and will not be submitted elsewhere before a decision is made by this journal.

For correspondence please use the following information:

corresponding author: Anna Masek

Institute of Polymer and Dye Technology

Technical University of Lodz

90-924 Lodz, ul Stefanowskiego 12/16, Poland

Tel.: +48 42 631 32 93

Fax: +48 42 636 25 43

e-mail: [email protected]

Yours sincerely,

Ph. D., D.Sc. Anna Masek

Comments and Suggestions for Authors

#Revewer4:

determined from the introduction, I have no clear idea on why the authors did this research. The reduction in crosslinking density to achieve good self-healing can be an approach. However, the mechanical properties were decreased greatly either. And the self-healing efficiency was also bad. To date, many work has been done to create dynamic or reversible crosslinking points. Why physical manner was still used?

The authors must give a more convinced aim for this research.

Answer 1:

We thank the Reviewer for the suggestions. We added lacking information as follows:

“In our research, to obtain self-healable biocomposites made of epoxidized natural rubber, it was proposed to reduce crosslinking density in ENR-50 by replacing conventional curing agents, such as dicumyl peroxide (DCP), by combination of more pro-ecological substances, i.e. quercetin and silica. A popular natural antioxidant – quercetin was responsible for low crosslinking density of ENR-50, and silica filler provided enhanced mechanical properties. In the studied self-healing phenomenon, which occurs in ambient conditions, physical forces play a key role. The relationship between the self-healing ability and mechanical properties of prepared materials were studied. Such composites stand a chance of becoming  innovative self-repairable biomaterials.”

We decided to study physical forces of epoxidized natural rubber because such interactions seem to be interesting and do not require external stimuli, including an increased temperature or light. We are still working on obtaining enhanced self-healing ability with improved mechanical properties, but we wanted to show the best self-healing properties in combination with the best mechanical properties which can be achieved only in such s simple way, including self-adhesion. The further research with taking into account dynamic or reversible crosslinking points creation will be studied in the future.

Round 2

Reviewer 2 Report

After a careful reading of the revised paper this time and thorough consideration, I think the paper has been sufficiently improved. Especially the figures have been improved and I indeed suggest the manuscript to be published in Materials.

Reviewer 3 Report

The reviewer thinks that the article is suitable for publication, since his recommendations have been followed.

Reviewer 4 Report

can be accepted