Flexural Strength and Vickers Microhardness of Graphene-Doped SnO2 Thin-Film-Coated Polymethylmethacrylate after Thermocycling
, Gülce Çakmak 3, Mustafa Borga Donmez 3,4,*, Samir Abou-Ayash 3, Emre Mumcu 1,5, Suat Pat 2,5,6 and Burak Yilmaz 3,7,8Round 1
Reviewer 1 Report (New Reviewer)
Dear professor Theeranon Tankam, Editor of coatings,
Thank you very much for invite me to review the manuscript under the title of “Flexural strength and Vickers microhardness of graphene doped SnO2 thin film coated polymethylmethacrylate after thermocycling”
I studied this manuscript very well. The quality, the novelty and the discussion in this work are very low and cannot be accepted in this journal
- The quality of all Figures is very bad.
- In page 2, the authors stated that Graphene flakes were mixed with SnO2 powder, what are quantity of graphene and the quantity of SnO2 that used?
- The authors should add real photo for the TVA system.
- The authors should add XRD patterns and TEM images for the prepared samples.
- Table 1, should be removed.
- The authors stated that the peak at 3400.18 cm–1 confirmed deposition of graphene on specimen surfaces. The FTIR results is not enough for confirming the deposition of graphene on the samples, so, it is recommended to analyze the samples by Raman or XRD.
- The authors should add the FTIR spectrum for the no-coat sample.
- The order and the captions of Fig. 2 and Fig. 3 are reversed.
- The authors added the AFM of the samples without discussion.
- In Fig. 5, what are (a), (b), and so on?
- In comparison the results obtained in this study and that obtained in the literature this work is meaningless.
- The authors should add the antibacterial activity for the prepared samples.
Author Response
Dear professor Theeranon Tankam, Editor of coatings,
Thank you very much for invite me to review the manuscript under the title of “Flexural strength and Vickers microhardness of graphene doped SnO2 thin film coated polymethylmethacrylate after thermocycling”
I studied this manuscript very well. The quality, the novelty and the discussion in this work are very low and cannot be accepted in this journal
Response: The authors would like to thank Reviewer #1 for their comments and contributions to the improvement of the manuscript.
- The quality of all Figures is very bad.
Response: All figures are now revised to improve quality.
In page 2, the authors stated that Graphene flakes were mixed with SnO2 powder, what are quantity of graphene and the quantity of SnO2 that used?
Response: The percentage of the graphene and SnO2 used during the TVA procedure is now mentioned in the first paragraph of Material and Methods, which reads “Graphene flakes were mixed with SnO2 powder with a ratio of 5% to 95%, and pressed into pellets prior to deposition, which prevented flakes to be vacuumed during the TVA process.”
- The authors should add real photo for the TVA system.
Response: A photo of the TVA system is now added (Figure 1).
- The authors should add XRD patterns and TEM images for the prepared samples.
Response: XRD and TEM analyses are not possible given that layers are deposited on PMMA surfaces. However, Raman spectra of the specimens is now added to further elaborate the results.
- Table 1, should be removed.
Response: Table 1 is now omitted.
- The authors stated that the peak at 3400.18 cm–1 confirmed deposition of graphene on specimen surfaces. The FTIR results is not enough for confirming the deposition of graphene on the samples, so, it is recommended to analyze the samples by Raman or XRD.
Response: Raman spectra of each group is now given in Figure 6.
- The authors should add the FTIR spectrum for the no-coat sample.
Response: Representative FTIR spectrum of the No-coat group is now given in Figure 2.
- The order and the captions of Fig. 2 and Fig. 3 are reversed.
Response: The authors would like to thank Reviewer #1 for pointing to this mistake. It is now revised.
- The authors added the AFM of the samples without discussion.
Response: AFM results are now discussed in the penultimate paragraph of Discussion. The section reads “Trends in the surface roughness of tested groups also support this hypothesis as Coat-20s and Coat-30s had smoother surfaces after thermocycling than before thermocycling, whereas thermocycling led to rougher surfaces for the other groups (Fig. 4). However, it should also be noted that Coat-20s and Coat-30s had rougher surfaces than other groups before thermocycling. Even though the average roughness of the specimens ranged between 40 nm and 160 nm in the present study, which is lower than the previously reported threshold of 0.2 µm for plaque accumulation [5], future in vivo studies on the surface roughness and bacterial plaque accumulation of SnO2-graphene coated denture base materials are needed to substantiate this hypothesis.”
- In Fig. 5, what are (a), (b), and so on?
Response: Figure 5 is now revised for clarity.
- In comparison, the results obtained in this study and that obtained in the literature this work is meaningless.
Response: Given that the present study was the first on how SnO2-graphene coating affected the mechanical properties of a denture base material, comparisons with previous similar studies were not possible. However, the authors think that comparing the results of the present study with those of previous studies that involved graphene reinforced denture base materials, without making definitive conclusions, is important to broaden the knowledge on the applicability of this method to improve the properties of tested denture base material. Therefore, no revisions were made.
- The authors should add the antibacterial activity for the prepared samples.
Response: The present study aimed to evaluate how mechanical properties of a denture base material are affected by SnO2-graphene coating. Thus, antibacterial activity was not involved in the present study. However, the penultimate paragraph of Discussion highlights the need for future studies that focus on this aspect. The section reads “In the present study, denture base resins were coated by using SnO2-graphene. Graphene was the essential component of coating for the parameters tested in the present study due to its high mechanical stability along with its low cost [35]. However, the other component, SnO2, which has already been tested in dental studies [23,36], has an antibacterial effect that may be particularly efficient considering that denture base materials are prone to deterioration and increased surface roughness due to intraoral stresses [16]. Because increased surface roughness might lead to denture stomatitis, one of the most commonly encountered complications for denture wearers [37], coating the denture bases with SnO2-graphene by using the TVS method may be a suitable alternative to increase the longevity of removable dentures as graphene was also reported to have antibacterial activity [38]. Trends in the surface roughness of tested groups also support this hypothesis as Coat-20s and Coat-30s had smoother surfaces after thermocycling than before thermocycling, whereas thermocycling led to rougher surfaces for the other groups (Fig. 4). However, it should also be noted that Coat-20s and Coat-30s had rougher surfaces than other groups before thermocycling. Therefore, future in vivo studies on the surface roughness and bacterial plaque accumulation of SnO2-graphene coated denture base materials are needed to substantiate this hypothesis.”
Reviewer 2 Report (New Reviewer)
The work is interesting and is relevant to the journal scope. I suggest the following minor corrections.
1 The idea of this work needs to be reflected in the Abstract section.
2 Relevant and recent references needs to be added not older than 2019.
3 The equations need to be cited where required.
4 Graphs may be explained more physically. Adjust the captions and figure sizes as per journal format.
5 add nomenclature.
Looks good
Author Response
The work is interesting and is relevant to the journal scope. I suggest the following minor corrections.
Response: The authors would like to thank Reviewer #2 for their comments and contributions to the improvement of the manuscript.
1 The idea of this work needs to be reflected in the Abstract section.
Response: The first sentence of the Abstract is now revised as “Removable dental prostheses are commonly fabricated by using polymethylmethacrylate, a material that does not have favorable mechanical properties and needs reinforcement with particles such as graphene.” to highlight the reasoning behind this study.
2 Relevant and recent references need to be added not older than 2019.
Response: Given that the present study was the first on the mechanical properties of SnO2-graphene coated denture base materials, similar previous studies could not be cited. However, studies older than 2019, which can be omitted, are now removed.
3 The equations need to be cited where required.
Response: The equation used for the calculation of flexural strength is now cited under the “Microhardness and 3-point flexural strength tests” subheading of Material and Methods. The section reads “Figure 3 illustrates the 3-point bending test and the formula used for calculations [8].”
4 Graphs may be explained more physically. Adjust the captions and figure sizes as per journal format.
Response: All figures are now revised and the legends are elaborated for clarification.
5 add nomenclature.
Response: It is not clear what Reviewer #2 refers to with nomenclature. Therefore, no revisions were made.
Reviewer 3 Report (New Reviewer)
This work deals with the characterization in terms of microhardness and flexural strength of PMMA structures coated with graphene doped SnO2. The work is interesting as it potrays the possibility to obtain enanched structures that opens many possibility in the framework of dental protheses. However there are some issue that should be addressed:
- In the abstract, can the authors specify better the target of their experiments? The Introduction section specifies that the prostheses analysed are dental prostheses: is it possible to describe it better in the abstract?
-The term "TVA duration" appears inappropriate: it would be more suitable to use "duration of TVA process" or "coating time" as the authors correctly state in the "materials and methods" section.
- It would be preferable to use SI units for the measures (e.g. torr, gf etc are NOT preferable). Moreover, the authors should be consistent with the use of units of measurement.
- In Table 2 the thickness of the coatings should be presented.
- I suggest the authors to show more clearly the grains of SnO2 and the plates of graphene in Figure 5
-Further hardness analyses should be taken into consideration to understand better the decrease in hardness of the Coat-20s specimens. A coating time superior to 30s should be taken into consideration in order to furtherly prove the improvement of characteristics of the samples in terms of microhardness.
- Can the authors perform roughness analyses? As stated in the discussion, roughness is a crucial parameter for dental structures. It would be interesting to compare non-coated structures and coated structures in term of roughness. There are no quantitative data in this study about the surface roughness as Figure 3 only portrays the mean surface.
-I encourage the authors to furtherly enhance the conclusions. Some of the future developments presented in the discussion should be moved to the conclusions section.
English grammar should be severely checked, as some sentences appear vague and a little difficult to comprehend.
Author Response
This work deals with the characterization in terms of microhardness and flexural strength of PMMA structures coated with graphene doped SnO2. The work is interesting as it portrays the possibility to obtain enhanced structures that opens many possibilities in the framework of dental prostheses. However, there are some issue that should be addressed:
Response: The authors would like to thank Reviewer #3 for their comments and contributions to the improvement of the manuscript.
- In the abstract, can the authors specify better the target of their experiments? The Introduction section specifies that the prostheses analyzed are dental prostheses: is it possible to describe it better in the abstract?
Response: The authors think that Abstract concisely explains the reason for conducting this study. However, the first sentence of the Abstract is now revised as “Removable dental prostheses are commonly fabricated by using polymethylmethacrylate, a material that does not have favorable mechanical properties and needs reinforcement with particles such as graphene.” to highlight the fact that tested polymethylmethacrylate is indicated for dental use.
-The term "TVA duration" appears inappropriate: it would be more suitable to use "duration of TVA process" or "coating time" as the authors correctly state in the "materials and methods" section.
Response: Entire manuscript is now revised to introduce the term “duration of the TVA process”.
- It would be preferable to use SI units for the measures (e.g. torr, gf etc are NOT preferable). Moreover, the authors should be consistent with the use of units of measurement.
Response: Entire manuscript is now revised considering the request of the reviewer.
- In Table 2 the thickness of the coatings should be presented.
Response: The information on the thickness of the coating is now given under the subheading “TVA application”. The section reads “Both sides of the samples were coated and the thickness of the coating was approximately 20 nm given the short duration of the TVA process.”
- I suggest the authors to show more clearly the grains of SnO2 and the plates of graphene in Figure 5.
Response: Figure 5 and its legend are now revised
-Further hardness analyses should be taken into consideration to understand better the decrease in hardness of the Coat-20s specimens. A coating time superior to 30s should be taken into consideration in order to furtherly prove the improvement of characteristics of the samples in terms of microhardness.
Response: As stated in Material and Methods, duration of the TVA process was limited to 15, 20, and 30 seconds as longer durations may convert graphene into graphite. In addition, it is not possible to conduct other hardness analyses on tested samples given that they were subjected to thermocycling. However, the final paragraph of Discussion is now elaborated to highlight the fact that further analyses by using alternative test methods are needed to corroborate the findings of the present study. The section reads “Therefore, future studies should investigate different properties of SnO2-graphene coated denture base resins in different materials and the same properties by using different tests with broadened TVA parameters to better comprehend the effect of this procedure on the properties of materials it is applied on.”
- Can the authors perform roughness analyses? As stated in the discussion, roughness is a crucial parameter for dental structures. It would be interesting to compare non-coated structures and coated structures in term of roughness. There are no quantitative data in this study about the surface roughness as Figure 3 only portrays the mean surface.
Response: The penultimate paragraph of Discussion is now elaborated with the findings of the roughness analyses, even though a statistical analysis was not performed. The section reads “Trends in the surface roughness of tested groups also support this hypothesis as Coat-20s and Coat-30s had smoother surfaces after thermocycling than before thermocycling, whereas thermocycling led to rougher surfaces for the other groups (Fig. 3). However, it should also be noted that Coat-20s and Coat-30s had rougher surfaces than other groups before thermocycling. Even though the average roughness of the specimens ranged between 40 nm and 160 nm in the present study, which is lower than the previously reported threshold of 0.2 µm for plaque accumulation [5], future in vivo studies on the surface roughness and bacterial plaque accumulation of SnO2-graphene coated denture base materials are needed to substantiate this hypothesis.”
-I encourage the authors to furtherly enhance the conclusions. Some of the future developments presented in the discussion should be moved to the conclusions section.
Response: Conclusions section is now revised as “Graphene doped SnO2 coating of heat-polymerizing PMMA by using tested thermionic vacuum arc method may be a suitable alternative to increase the longevity of removable dentures as the surface roughness of the surfaces with this coating is low and graphene has been reported to have antibacterial activity.”
Round 2
Reviewer 1 Report (New Reviewer)
1- Still the quality of Figures is very bad.
2- There are repeating in Figures.
3- Fig. 2, and Fig. 6 should redraw like that presented in these papers 10.1039/D2RA02515A , 10.1007/s00339-020-03762-5
Author Response
Reviewer #1:
1- Still the quality of Figures is very bad.
Response: All figures are now revised to improve their quality.
2- There are repeating in Figures.
Response: Entire manuscript is now revised to omit repetition.
3- Fig. 2, and Fig. 6 should redraw like that presented in these papers 10.1039/D2RA02515A , 10.1007/s00339-020-03762-5
Response: Figures 2 and 6 are now redrawn as suggested by Reviewer #1.
Reviewer 3 Report (New Reviewer)
The authors have followed all the suggestions encouraged. I recommend the publication in the present form.
Author Response
The authors have followed all the suggestions encouraged. I recommend the publication in the present form.
Response: The authors would like to thank Reviewer #3 for their comments.
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 is just the author's draft content, nothing to review, request to add more content to the article and increase the content to analyze the results and clarify the problem.
Author Response
Response: The authors would like to thank Reviewer #1 for their comments, which improved the manuscript. The entire manuscript is now revised to improve readability. Introduction is now revised to better clarify the problem and introduce more information on the topic.
Reviewer 2 Report
Authors have reported “Flexural strength and Vickers microhardness of graphene doped SnO2 thin film coated polymethylmethacrylate after thermocycling” needs minor revision for publication. While the research work appears to be conducted with thoroughness, I would like to bring to your attention some significant shortcomings in the manuscript which are outlined below:
1. The author needs to revise the "INTRODUCTION" section to either provide a brief summary of their findings or highlight the incorporation of novel technologies.
2. The "Schematic design of thermionic vacuum arc system" needs to be improved by the author to provide valuable information to the reader, as it currently appears to have been done carelessly.
3. Figure 3 “the representative atomic force microscopy images provided by the authors for each group before and after thermocycling are not clearly visible. This could potentially affect the interpretation of the results and conclusions drawn from the study. Therefore, it is recommended that the authors make changes to ensure that these images are clearly visible to the readers. This could be done through better resolution images, appropriate labeling, or by including additional images to clearly depict the changes observed before and after thermocycling.
4. To enable a more comprehensive performance comparison, it is recommended to analyze all characteristic parameters of the single coating film material.
5. Manuscript result discussion is very short, there be more result and discussion. Author must show a SEM/TEM image of coated film of different materials.
6. If the author did not provide conformational material characterization, it is unclear how they can claim that the film has been deposited.
7. To enhance the thin film analysis, the author should consider incorporating "Rutherford Backscattering of Thin Films".”
8. Conclusion is also not upto the mark, please change it and put some valuable information
Author Response
Authors have reported “Flexural strength and Vickers microhardness of graphene doped SnO2 thin film coated polymethylmethacrylate after thermocycling” needs minor revision for publication. While the research work appears to be conducted with thoroughness, I would like to bring to your attention some significant shortcomings in the manuscript which are outlined below:
Response: The authors would like to thank Reviewer #2 for their comments and contributions for the improvement of the manuscript.
1. The author needs to revise the "INTRODUCTION" section to either provide a brief summary of their findings or highlight the incorporation of novel technologies.
Response: The authors think that providing a summary of the findings of the any study should be provided in later stages of a manuscript. However, the first paragraph of Introduction is now revised to introduce the new technologies used to fabricate denture bases along with their potential disadvantages and how it might not be easy to implement these technologies into daily clinical practice. The section reads “Advancements in computer-aided design and computer-aided manufacturing (CAD-CAM) technologies have facilitated fabrication of denture bases as an alternative to conventional heat-polymerized PMMA [3]. Subtractively manufactured prepolymerized PMMA disks were shown to have higher mechanical properties compared with conventional heat-polymerized PMMA considering their standardized and controlled polymerization that is performed under high temperature and pressure [4,5]. However, implementation of CAD-CAM technologies might not be suitable for every clinician or dental technician, considering the costs related to milling units, auxiliary equipment, CAD-CAM disks, and maintenance.”
2. The "Schematic design of thermionic vacuum arc system" needs to be improved by the author to provide valuable information to the reader, as it currently appears to have been done carelessly.
Response: Figure 1 is now revised to better display the thermionic vacuum arc system.
3. Figure 3 “the representative atomic force microscopy images provided by the authors for each group before and after thermocycling are not clearly visible. This could potentially affect the interpretation of the results and conclusions drawn from the study. Therefore, it is recommended that the authors make changes to ensure that these images are clearly visible to the readers. This could be done through better resolution images, appropriate labeling, or by including additional images to clearly depict the changes observed before and after thermocycling.
Response: Figure 3 is now revised to improve its resolution.
4. To enable a more comprehensive performance comparison, it is recommended to analyze all characteristic parameters of the single coating film material.
Response: Additional analyses are now performed and results are added to manuscript, including FESEM images. The coating parameters and surface properties are now given in the manuscript.
5. Manuscript result discussion is very short, there be more result and discussion. Author must show a SEM/TEM image of coated film of different materials.
Response: A new figure (Figure #5) is now added and the Results section is now elaborated with the findings of the FESEM analyses, which reads “Grains of SnO2 and plates of graphene were clearly visible in the before thermocycling FESEM images of Coat-15s, Coat-20s, and Coat-30s, which cannot be seen in the images of No-coat. Granules and voids were noticeable in the before thermocycling FESEM images of No-coat along with a rough surface for each group, which could be associated with the fact that no polishing was performed. When after thermocycling FESEM images were evaluated, lines that indicate separation within graphene plates were visible in Coat-15s, Coat-20s, and Coat-30s, while the granules have accumulated into plates with voids between them in No-coat (Figure 5).”. These findings are now also mentioned in Discussion, where appropriate, to further support the interpretations made on the results of the present study.
6. If the author did not provide conformational material characterization, it is unclear how they can claim that the film has been deposited.
Response: The authors think that AFM, FTIR, and now newly added FESEM analyses of both coated and uncoated specimens clearly demonstrate that the thin film has been deposited on coated specimens.
7. To enhance the thin film analysis, the author should consider incorporating "Rutherford Backscattering of Thin Films".”
Response: During the time of the experiments, the authors did not have access to tools needed for “Rutherford Backscattering of Thin Films” analysis. Therefore, this analysis was not performed. However, Fourier Transform Infrared Spectroscopy analysis was performed to confirm the presence of graphene on coated specimens and transmittance peaks visible at 3400.18 cm- 1 (Figure 2) corroborates the SnO2-graphene coating. Surface properties of the coatings were analyzed by using AFM and FESEM, which revealed the topography of the surfaces and grains of SnO2 and plates of graphene.
8. Conclusion is also not upto the mark, please change it and put some valuable information
Response: Conclusions section is now revised and reads “Graphene doped SnO2 coating of heat-polymerizing PMMA by using tested thermionic vacuum arc durations did not affect the material’s flexural strength. However, graphene doped SnO2 coating for 30 seconds by using the thermionic vacuum arch method enhanced the Vickers hardness of heat-polymerizing PMMA, which may lead to a more stable and damage-resistant surface in the long-term.”
Reviewer 3 Report
The topic is of interest. However, the study can be improved by addressing carious issues:
1. Standard deviation is fairly high. Does the choice of n as 10 have to do with it?
2. Quality of the coating is not adequately addressed. Perhaps the coating was not uniformly applied.
3. Three point bending equation is taken from classical mechanics of materials where the beam is presented using single material. Would it make sense to include the coating as a second material?
4. No photo of the bending experimental setup was included. Why?
5. Was any post-experiment analysis conducted? It would be useful to provide assessment of the area where the load was applied
Author Response
The topic is of interest. However, the study can be improved by addressing carious issues:
Response: The authors would like to thank Reviewer #3 for their comments and contributions to the improvement of the manuscript.
1. Standard deviation is fairly high. Does the choice of n as 10 have to do with it?
Response: The number of specimens in each group was decided based on a priori power analysis. However, considering that the present study was the first on the mechanical properties of SnO2-graphene coated heat-polymerized PMMA, future studies with highernumber of specimens are needed to corroborate the findings of the present study.
2. Quality of the coating is not adequately addressed. Perhaps the coating was not uniformly applied.
Response: FESEM and AFM analyses were performed to analyze the surface topography of coated groups. However, absence of further surface characterization tests is now elaborated in the final paragraph of Discussion as “Even though the surface topography of all groups wasanalyzed by using FESEM and AFM analyses, structure of the SnO2-graphene thin films was not evaluated by using further analyses such as transmission electron microscopy.”
3. Three point bending equation is taken from classical mechanics of materials where the beam is presented using single material. Would it make sense to include the coating as a second material?
Response: The formula used to calculate flexural strength of a specimen tested by using thethree-point bending test setup, which can be seen in Figure 4, does not have a component related to the inherent properties of the material tested. Thickness of the coated specimens, the only parameter that could change due to coating, was controlled by using a digital caliper and calculation of those specimens were made accordingly. This is now mentioned in subheading “2.3. Microhardness and 3-point flexural strength tests”. However, no furtherrevisions were made.
4. No photo of the bending experimental setup was included. Why?
Response: Three-point bending test is a well-documented method to evaluate the flexural strength of bar-shaped specimens. In addition, the authors think that the schematic design of the test setup illustrated in Figure 4 clearly describes the test. Therefore, no revisions were made.
5. Was any post-experiment analysis conducted? It would be useful to provide assessment of the area where the load was applied
Response: Absence of a qualitative post-experimental analysis is a limitation of the present study, which is now highlighted in the final paragraph of Discussion, which reads “…In addition, no qualitative fractographic analysis was performed after the 3-point bending test and elaborating the fracture pattern of the specimens may broaden the effect of SnO2-graphene coating on heat-polymerized PMMA.”
Round 2
Reviewer 3 Report
I am unconvinced by the response you provided especially to #3. As a result, I am not convinced that the current quality of the work reaches the level of publishing in a technical journal.
