Review Reports - Melanin-Inspired Biomimetic Strategy for Preserving Adhesion of Lubricants via Thiol-Quinone Addition

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In the study entitled "Melanin-Inspired Biomimetic Strategy for Preserving Adhesion of Lubricants via Thiol-quinone Addition," researchers reported that catechol-based lubricants, inspired by mussel adhesion, provide enhanced lubrication performance through the formation of coordination bonds, resulting in strong adhesion capabilities. A biomimetic method was developed to synthesize a lubricant with high adhesion properties from mussels and melanin biosynthesis by adding thiol-quinone to recover and stabilize the catechol portion. This biomimetic thiol-quinone addition was studied to overcome the instability of traditional catechol-based lubricants. The study is based on original scientific approaches and findings and presents significant and noteworthy results. However, minor revisions are needed.

On page 5, line 193, the molar ratio of metal ions should be corrected from "BCA-O" to "BCA-ODT".
Figures S1A and S1B on page 4 ??
On page 15, the magnification for the wear surface in Figure 6D for the BCA-ODT in the friction test is too small. Additionally, information about the chemical analysis of the surface could have been included.
Please add the parameters for tribological studies. The parameters are currently limited.

Author Response

Dear Ms. Claire Yuan and reviewers:

Our manuscript, Melanin-Inspired Biomimetic Strategy for Preserving Adhesion of Lubricants via Thiol-quinone Addition (biomimetics-4249819), was revised according to the comments of the reviewers. All the suggested changes have been incorporated in the revised manuscript. The itemized response to comments of each reviewer is attached, including the changes and the explanations. The original manuscript, in which the changes were highlighted in colored type through the track changes version, was also uploaded separately to clearly show the changes made in detail.

Thank you for your suggestions and we apologize for our carelessness while preparing the original manuscript.

Thank you very much again for your attentive review of our manuscript.

Best wishes for you!

Sincerely yours

Wenbin Liu

For your guidance, the itemized response to each reviewers’ comment is appended below.

A list of changes

All the suggested changes have been made. Here are the majors of changes:

Figure 6 was rearranged, and its caption and citations were updated accordingly.
The relevant descriptions and citation positions for Figures S1A and S2B were revised.
Details were provided in the Method Section.
The Conclusion Section was rewritten to highlight its advantages and novelty.
The graphical abstract was revised.

Response to each comment to explain the reasons for changes (shadings indicate comments of reviewers).

Reviewer #1

Comments 1: On page 5, line 193, the molar ratio of metal ions should be corrected from "BCA-O" to "BCA-ODT".

Response 1: We thank the reviewer for this careful reading and helpful comment. The molar ratio of metal ions on page 5, line 193 has been corrected from “BCA-O” to “BCA-ODT” in the revised manuscript.

Comments 2: Figures S1A and S1B on page 4 ??

Response 2: Since these figures provide important supporting information for the experimental description, we agree that they are more appropriately presented in the main text rather than cited from the Supporting Information in the Methods section. Therefore, in the revised manuscript, the content related Figures S1A and S1B have been moved from the Methods Section to the corresponding Results Section to improve the clarity and overall structure of the manuscript. The order of the supplementary material figures has also been adjusted accordingly.

Comments 3: On page 15, the magnification for the wear surface in Figure 6D for the BCA-ODT in the friction test is too small.

Response 3: We thank the reviewer for this valuable comment. We agree that the wear surface image of BCA-ODT in Figure 6D was presented at insufficient magnification in the original manuscript, which may have limited the clear observation of the wear features. Accordingly, in the revised manuscript, this image has been extracted and presented as a standalone figure with a larger display size, so that the morphology of the worn surface can be examined more clearly. We believe this revision improves the clarity and readability of tribological characterization.

Comments 4: Additionally, information about the chemical analysis of the surface could have been included.

Response 4: We appreciate the reviewer’s constructive suggestion on conducting chemical analysis of the surface. XPS is a powerful and effective technique for the chemical analysis of the surface. Unfortunately, due to unavailability of XPS facilities at the current stage, we are unable to perform this characterization within the revision period. Our study aims to develop biomimetic lubricants with resistance against autoxidation, a fully quantitative analysis of the surface of the samples involved in one of the experiments is beyond its scope. We sincerely apologize for this limitation and will consider conducting XPS in our future follow‑up work to further investigate the surface chemical composition.

Comments 5: Please add the parameters for tribological studies. The parameters are currently limited.

Response 5: We thank the reviewer for this helpful comment. In response, we have revised the description of the tribological experiments to provide more complete test parameters. Specifically, the instrument model, test mode, applied load, rotational speed, test duration, and wear-scar observation method have now been clearly stated in the revised manuscript. In addition, the test temperature and ball specification has also been added where applicable to improve the clarity and reproducibility of the tribological study.

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for involving me for the reviewing of the manuscript entitled "Melanin-Inspired Biomimetic Strategy for Preserving Adhesion of Lubricants via Thiol-quinone Addition". There are some detailed suggestions as follows:

1) Keywords: It is recommended to add “drilling fluid” as a keyword.

2) Section 2:
—Line 179: The surface conditions of these substrates should be provided, such as morphology, surface roughness, etc.
—Line 248: Details of the lubrication used during the friction test should be clarified. The shape and dimensions of the specimen, as well as its surface roughness and hardness, all need to be provided.
—Why was such a high load of 300 N applied? What was the corresponding contact stress? What was the configuration of the friction pair?
—Line 261: Equations should be centered, and the font should be consistent with that of the main text.
—Were all tests and labels performed in duplicate?

3) Section 3:
—Fig. 6: What is the physical quantity on the right side of subplot a? Subplot d is unclear; why does the friction coefficient curve exhibit such behavior? Is there no obvious running-in process? Why were photographs of the specimen surface not taken, while only images of the ball surface were provided? Why are there no error bars for the data presented in the figure? Were the experiments not repeated?
—Line 538: Is the friction coefficient in subplot d stable? How was this judged?
—Line 545: How was the WSD value obtained? Why was it not compared with other results?

Author Response

Dear Ms. Claire Yuan and reviewers:

Thank you for your suggestions and we apologize for our carelessness while preparing the original manuscript.

Thank you very much again for your attentive review of our manuscript.

Best wishes for you!

Sincerely yours

Wenbin Liu

For your guidance, the itemized response to each reviewers’ comment is appended below.

A list of changes

All the suggested changes have been made. Here are the majors of changes:

Figure 6 was rearranged, and its caption and citations were updated accordingly.
The relevant descriptions and citation positions for Figures S1A and S2B were revised.
Details were provided in the Method Section.
The Conclusion Section was rewritten to highlight its advantages and novelty.
The graphical abstract was revised.

Response to each comment to explain the reasons for changes (shadings indicate comments of reviewers).

Reviewer #2

Comments and Suggestions for Authors

Comments 1: Keywords: It is recommended to add “drilling fluid” as a keyword.

Response 1: We sincerely thank the reviewer for this helpful suggestion. In accordance with the reviewer’s recommendation, “drilling fluid” has been added to the Keywords section in the revised manuscript.

Comments 2: Line 179: The surface conditions of these substrates should be provided, such as morphology, surface roughness, etc.

Response 2: We thank the reviewer for this helpful comment. We agree that the surface condition of the substrates is important for wettability measurements. The detail of surface conditions of these substrates was provided in Section 2.3, including morphology, size, surface roughness. Accordingly, in the revised manuscript, we have added the relevant information on the substrate dimensions and pretreatment procedure. Specifically, the substrates were 1×1 cm in size and 0.3 mm in thickness, and all plates were cleaned with ethanol, oven-dried prior to use, and had relatively smooth and flat surfaces.

Comments 3: Line 248: Details of the lubrication used during the friction test should be clarified. The shape and dimensions of the specimen, as well as its surface roughness and hardness, all need to be provided.

Response 3: We sincerely thank the reviewer for this valuable comment. We agree that the details of the lubrication conditions and test specimens should be more clearly described. Accordingly, in the revised manuscript, we have specified that the friction tests were performed using sodium bentonite freshwater base mud containing 1 wt% BCA-ODT as the lubricating test fluid. We have also supplemented the description of the friction specimens by providing the material, shape, and dimensions of the steel balls used in the four-ball test, and the relevant surface condition has been clarified in the Methods section. These additions improve the transparency and reproducibility of the tribological experiments. Because no independent roughness or hardness measurements were conducted for the commercially supplied steel balls, we have reported the specimen information that was available and relevant to the present study in the revised manuscript.

Comments 4: Why was such a high load of 300 N applied? What was the corresponding contact stress? What was the configuration of the friction pair?

Response 4: We sincerely thank the reviewer for this helpful comment. The response to this point is provided in two aspects, as follows.

(A) The applied load was selected based on literature precedent and the consideration of assessing the potential extreme-pressure performance of the lubricant.

The applied load of 300 N was selected with reference to a closely related four-ball tribological study on a catechol-based biomimetic lubricant for water-based drilling fluids, in which comparable test conditions were used to evaluate lubricant performance under simulated point-contact friction[1]. Meanwhile, this value also fell within the standard range[2,3]. In addition, the present lubricant was molecularly designed not only to enhance interfacial adhesion through the catechol moiety, but also to introduce a sulfur-containing group, which is generally considered to have potential extreme-pressure and anti-wear functionality. Therefore, a relatively high load was intentionally employed in order to preliminarily assess the lubrication and wear-protection behavior of BCA-ODT under comparatively severe contact conditions.

(B) Friction-pair configuration and corresponding contact stress.

The friction pair used in this study was a conventional steel-on-steel four-ball configuration, consisting of one rotating upper steel ball in contact with three stationary lower steel balls. The contact stress was not directly measured in the present work. However, based on the conventional steel-on-steel four-ball geometry and Hertzian contact estimation, the applied axial load of 300 N corresponds to an approximate mean contact stress of 2.10 GPa and a maximum contact pressure of 3.15 GPa. In addition, the friction torque during the test was about 0.1 N·m, providing a practical indication of the frictional behavior of the tested system.

(C) The answer to this query and the suggested changes in the revised manuscript.

Contact stress was provided in Section 2.7.4.

(D) References to this query.

Xukun, Y.; Guancheng, J.; Fan, L.; Yinbo, H.; Rentong, L.; Tengfei, D. Lubricity and mechanism of catechol-based biomimetic lubricant in water-based drilling fluid. Tribology International 2023, 188.
Deleanu, L.; Georgescu, C.; Cristea, G.; Ionescu, T.; Guglea, D.; Ojoc, G.-G.; Dima, D.; Păduraru Graur, I. Standardization in Tribology. Tribology in Industry 2024, 3, 398-417, doi:10.24874/ti.1615.01.24.01.
Georgescu, C.; Solea, L.; Deleanu, L. The Influence of Degumming Process on Tribological Behaviour of Soybean Oil. Tribology in Industry 2015, 330, 330-335.

Comments 5: Line 261: Equations should be centered, and the font should be consistent with that of the main text.

Response 5: We sincerely thank the reviewer for this careful comment. The formatting of the equations has been corrected throughout the manuscript. Specifically, all equations have been centered, and the font style has been made consistent with that of the main text according to the requirement of journal.

Comments 6: Were all tests and labels performed in duplicate?

Response 6: We thank the reviewer for this valuable comment. In order to clarify the number of experimental replicates, a separate statement has been added to the Materials and Methods section. It is now specified that all experiments and measurements were conducted in triplicate unless otherwise noted for specific tests. We believe this addition improves the clarity and reproducibility of the manuscript.

Comments 7: Fig. 6: What is the physical quantity on the right side of subplot a? Subplot d is unclear;

Response 7: We thank the reviewer for this helpful comment. We recognize that the original Fig. 6 contained some ambiguity in the labeling and presentation. Accordingly, the physical quantity shown on the right side of subplot (a) has now been clearly identified, and subplot (d) has been adjusted to provide a clearer and more legible presentation. These revisions were made to improve the accuracy and readability of the figure.

Comments 8: why does the friction coefficient curve exhibit such behavior? Is there no obvious running-in process?

Response 8: We appreciate the reviewer’s insightful comment on the friction coefficient (COF) curve. The COF profile fluctuated around 0.06–0.18 throughout the 1200 s test, with no distinct initial running-in stage. That observation can be fully explained by the lubrication mechanism of the 1% BCA-ODT.

(A) Rapid formation of boundary lubrication film

BCA-ODT contains catechol groups that can spontaneously and rapidly adsorb onto the steel surface and form a dense film within the initial 10–30 s of the test. This film immediately establishes a stable boundary lubrication state, eliminating the need for a prolonged running-in period, which is typically characterized by a gradual COF decrease as the surface is smoothed and the film forms. The rapid formation of lubrication film can be attributed to the quick kinetics for the complexation between catechol and iron ions. As a result, the rapid formation of lubrication film contributed to the absence of a distinct running-in process. It demonstrated the advantage of BCA-ODT on rapid formation of lubrication film. It is beneficial to provide effective protection within an extremely short time. BCA-ODT enables immediate low friction without obvious running-in. A stable lubrication state is achieved right from the start, without the need for a running-in stage for friction reduction.

(B) In-situ tribochemical reaction

Under the test load (300 N, 1200 rpm), the BCA-ODT undergoes mild tribochemical reactions with the steel surface, generating a composite protective layer that maintains low and stable friction. The minor fluctuations in COF are attributed to the dynamic equilibrium between film wear and in-situ reassemble, which is a typical characteristic of high-performance boundary lubricants with excellent anti-wear and extreme pressure properties.

(C) Consistency with literature

This COF behavior is consistent with reported catechol-based lubricant additives[1], which are known for their rapid film-forming ability and long-term friction stability, further validating the reliability of our results.

(D) References to this query.

Xukun, Y.; Guancheng, J.; Fan, L.; Yinbo, H.; Rentong, L.; Tengfei, D. Lubricity and mechanism of catechol-based biomimetic lubricant in water-based drilling fluid. Tribology International 2023, 188.

Comments 9: Why were photographs of the specimen surface not taken, while only images of the ball surface were provided?

Response 9: We sincerely apologize for the incomplete surface characterization in the original manuscript. In the standard four-ball friction test, the primary wear evaluation index is the wear scar diameter (WSD) on the three stationary lower balls, as the upper rotating ball is in continuous contact with all three lower balls, and its wear behavior is highly correlated with the lower balls. Therefore, we initially focused on characterizing the ball surface to quantify the anti-wear performance of BCA-ODT.

Comments 10: Why are there no error bars for the data presented in the figure? Were the experiments not repeated?

Response 10: The test was repeated three times, and the mean value of COF was shown. Considering that this figure is a time-dependent curve with acquisition of one data point per second, the dataset is large and densely distributed. If error bars were added, they would overlap and cluster with the data points due to the inherent fluctuations in the data, making visual distinction difficult and obscuring the overall data trend. For this reason, error bars were not included. This presentation method has also been widely adopted in relevant literature[1].

(A) References to this query.

Xukun, Y.; Guancheng, J.; Fan, L.; Yinbo, H.; Rentong, L.; Tengfei, D. Lubricity and mechanism of catechol-based biomimetic lubricant in water-based drilling fluid. Tribology International 2023, 188.

Comments 11: Line 538: Is the friction coefficient in subplot d stable? How was this judged?

Response 11: The friction coefficient curve in subplot d can be regarded as stable in the overall test duration. This judgment is based on the following aspects:

(i) As shown in the violin plot, the mean value is 0.09, and the standard derivation is 0.02. The coefficient of variation (SD/Mean) is 22%, less than the widely accepted criterion 25% for fluctuation level. The median is 0.08. Moreover, the most frequent range is 0.06 to 0.07, which is close to the mean, accounting for 30% of the total data. Therefore, the COF fluctuates only within a narrow and limited range without an obvious upward or downward trend, which indicates that the lubrication state and contact interface have reached a dynamic equilibrium.

(ii) There is no sudden increase in friction coefficient, which would signify lubrication failure, severe wear, or scuffing.

(iii) The small fluctuations observed are normal and commonly seen in four-ball tests, mainly originating from the dynamic formation and removal of the tribo-film on the contact surface.

Accordingly, we conclude that the friction coefficient is stable on the whole during the test. The minor fluctuations in COF are attributed to the dynamic equilibrium between film wear and in-situ reassemble, which is a typical characteristic of high-performance boundary lubricants with excellent anti-wear and extreme pressure properties.

Comments 12: Line 545: How was the WSD value obtained? Why was it not compared with other results?

Response 12: (A) Our study showed a comparable WSD.

The wear scar diameter (WSD) was obtained by measuring the wear scars on the three stationary steel balls after the four-ball test using an optical microscope. Each wear scar was measured in two mutually perpendicular directions, and the diameter was obtained by the average value of two mutually perpendicular directions. The final WSD was obtained by the average value for three steel balls.

The comparison between current study and previous works was not attempted in the submitted manuscript because the heterogeneity of data in literatures might bring risk of ambiguousness.

In the reference, it is reported the WSD for sample L_2,₅, L_3,5, L_3,4 was 0.96 mm, 0.63 mm, and 0.39 mm, respectively[1]. WSD of Our sample was 0.63 mm, which was equal to that of sample L_3,5 but larger than that of sample L_3,4. The sample L_3,5 has 3,5-dihydroxyl group, while the sample L_3,4 has 3,5-dihydroxyl group. One must keep in mind that the variability of assay conditions should be considered during direct comparison between difference studies in literatures.

(B) Our study showed a comparable COF.

Although the WSD of our sample is larger than the sample containing same catechol moiety in reference, the COF of our sample (0.09) is comparable to that of sample L_3,4 (0.06) but less than that of sample L_3,5(0.16). In addition, our sample exhibits absence of running-in stage, which is consistent with sample L_3,4 reported in that literature. It clearly demonstrates the competitive anti-wear performance of our material.

The primary purpose of our study was to develop biomimetic lubricant with resistance against autoxidation. And we did achieve that aim for the first time. Therefore, the anti-wear performance was not particularly underlined, although the anti-wear performance for our study were excellent. Therefore, in comparison to previous methods, our study exhibited the novelty and advantage on resistance against autoxidation.

(C) The answer to this query and the suggested changes in the revised manuscript.

In the revised version, we have supplemented a comparison with relevant reported additives in Section 3.6.

(D) References to this query.

Xukun, Y.; Guancheng, J.; Fan, L.; Yinbo, H.; Rentong, L.; Tengfei, D. Lubricity and mechanism of catechol-based biomimetic lubricant in water-based drilling fluid. Tribology International 2023, 188.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors present a manuscript which contains a biomimetic molecular design strategy for improving the stability and adhesion of catechol-based lubricants via thiol–quinone Michael addition, which they claimed to be inspired by mussel adhesion and melanin biosynthesis. The manuscript explains the Rational chemical synthesis, Spectroscopic characterization (FTIR, ¹H/¹³C NMR), Physicochemical evaluation (thermal stability, oxidation resistance), and Tribological and adhesion performance tests.

The approach present in manuscript is scientifically sound and relevant, particularly for water-based drilling fluids, where adhesion and stability are critical challenges. The results demonstrate improved thermal stability (~350 °C), adhesion, and lubrication performance, indicating practical potential.

Overall, the manuscript is well organized and suitable for publication, but requires minor revisions to improve clarity, rigor, and presentation.

The authors reported the yield of 108.12% (page ~9) is physically unrealistic. The authors should Recalculate or clarify the yield determination, and explain possible sources (e.g., residual solvent, impurities).
The authors should clearly distinguish between experimental evidence and hypothesis, for example cross-linking network formation via Fe³⁺ coordination) are plausible but not directly proven.
The concept of the presented manuscript is novel and interesting. However, the should also explain that how their concept is better or differ from the existing catechol-based or thiol-modified lubricants. The authors should also notify the main novelty of their approach, either it is chemical stability or application performance.

Author Response

Dear Ms. Claire Yuan and reviewers:

Thank you for your suggestions and we apologize for our carelessness while preparing the original manuscript.

Thank you very much again for your attentive review of our manuscript.

Best wishes for you!

Sincerely yours

Wenbin Liu

For your guidance, the itemized response to each reviewers’ comment is appended below.

A list of changes

All the suggested changes have been made. Here are the majors of changes:

Figure 6 was rearranged, and its caption and citations were updated accordingly.
The relevant descriptions and citation positions for Figures S1A and S2B were revised.
Details were provided in the Method Section.
The Conclusion Section was rewritten to highlight its advantages and novelty.
The graphical abstract was revised.

Response to each comment to explain the reasons for changes (shadings indicate comments of reviewers).

Reviewer #3

Comments and Suggestions for Authors

Overall, the manuscript is well organized and suitable for publication, but requires minor revisions to improve clarity, rigor, and presentation.

Comments 1: The authors reported the yield of 108.12% (page ~9) is physically unrealistic. The authors should Recalculate or clarify the yield determination, and explain possible sources (e.g., residual solvent, impurities).

Response 1: We sincerely thank the reviewer for this careful and important comment. We agree that a yield value of 108.12% is physically unrealistic if interpreted as the true isolated yield of BCA-ODT. In the present work, this value was calculated from the absorbance at 290 nm using the calibration curve of BCA-ODT. Therefore, it should be understood as an apparent yield based on UV-Vis quantification.

One possible reason for this overestimation is that, after the formation of BCA-ODT, a minor portion of the product may further undergo oxidation and/or side reactions, producing species that still absorb at or near 290 nm. As a result, the absorbance-based calculation may slightly overestimate the amount of BCA-ODT. Because the UV-based calculation assumes that the absorbance at this wavelength arises solely from BCA-ODT, the presence of such species may lead to a slight overestimation of the calculated yield. Accordingly, the value of 108.12% most likely reflects spectral interference from minor byproducts, rather than the actual isolated yield of the target product. We have clarified this point in the manuscript to avoid misunderstanding.

Comments 2: The authors should clearly distinguish between experimental evidence and hypothesis, for example cross-linking network formation via Fe³⁺ coordination) are plausible but not directly proven.

Response 2: (A) The results and conclusion were based on the experiments data.

(i) The synthesis of thiol-functionalized lubricant was confirmed by UV spectra, FT-IR, and NMR.

(ii) Adhesion performance of thiol-functionalized lubricant was confirmed by contact angles of substrate sheets.

(iii) Metal ion interactions ability of thiol-functionalized lubricant was confirmed by titration with iron ion. (iv) Autoxidation resistance of thiol-functionalized lubricant was confirmed by UV spectra and adhesion performance under oxygen exposure, and thermal stability of thiol-functionalized lubricant was confirmed by TG and DSC.

(v) Lubrication performance of thiol-functionalized lubricant was confirmed by lubricity test, adhesion coefficient test, four-ball friction test, and rheological analysis. On the basis of these results, we clearly and definitively conclude that the thiol-functionalized lubricant exhibits strong resistance to autoxidation, excellent thermal stability, high adhesion capability, and effective lubrication performance.

(B) The conclusion on bis-coordination was drawn from experiment data.

Job’s plots revealed apparent 1:1 complexation stoichiometry with both iron ion. Because BCA-ODT molecule contains two catechol functional groups, a single metal ion could simultaneously coordinate with two catechol moieties. It suggested an intrinsic 1:2 (metal ion: catechol) binding mode. Bis-coordination indeed occurs between the catechol group in BCA-ODT and iron ion.

(C) The concept on cross-linking network formation via Fe³⁺ coordination was based on a reasonable hypothesis.

Considering the structure and steric hindrance of BCA-ODT, it is unlikely that the two catechol groups from a single BCA-ODT molecule simultaneously coordinate with one iron ion. Instead, it is reasonable to hypothesize that one iron ion separately coordinates with one catechol group from each of two different BCA-ODT molecules, thereby forming a metal-catechol cross-linking structure. Cross-linking network formation via Fe³⁺ coordination are plausible but not directly proven. It is worth to exploring the structure and underlying mechanism cross-linking coordination network in the future research.

(D) Utilization of BPA to generate biscatechol structure is crucial for the formation of cross-linking coordination network.

Such multidentate coordination network is conducive to enhancing the cohesion strength of the lubricant molecules, and improving the adsorption strength and stability of the interfacial film. By contrast, conventional lubricants mainly depend on weak single-point adsorption, which was easily disrupted.

These findings suggested that the enhanced metal ion coordination interaction might be one of the key reasons for the superior lubricating and anti-wear properties of the product in water-based drilling fluids. Utilization of biscatechol A (BCA) derived from BPA is therefore crucial for the formation of cross-linking coordination network. Utilization of BPA can be regarded as one the of the innovative points of this study, providing insight for the design and development of novel biomimetic lubricants.

(E) The answer to this query and the suggested changes in the revised manuscript.

We have carefully revised the relevant description in the manuscript to clearly distinguish experimental evidence from hypotheses. The hypothesis of crossing-linking coordination network is clearly stated in the manuscript to be based on rational assumption on the basis of experimental results. The corresponding expressions have been modified to be more accurate and rigorous.

Comments 3: The concept of the presented manuscript is novel and interesting. However, the should also explain that how their concept is better or differ from the existing catechol-based or thiol-modified lubricants. The authors should also notify the main novelty of their approach, either it is chemical stability or application performance.

Response 3: (A) Our study overcome the instability of catechol-based lubricant.

Thiol-functionalized biomimetic lubricant was developed via thiol-quinone coupling to overcome the instability of catechol. A high-adhesion lubricant containing S-catecholyl functionality was obtained. This strategy effectively preserves the catechol structure and minimizes the risk of autoxidation.

Compared with the existing catechol-based lubricants, this strategy exhibits four distinct advantages.

(i) Autoxidation resistance via thiol functionalization preserves active catechol moiety. S-catecholyl linkage endowed the molecule with enhanced resistance to catechol autoxidation and helped preserve the active catechol functionality.

(ii) Cross-linking coordination network via bis-coordination enhances adhesion strength. The biscatechol groups derived from BPA form coordination network with metal ions.

(iii) Introduction of sulfur as extreme pressure element reduces friction and improve thermal stability.

(iv) Thiol-quinone coupling reaction enables a facile and efficient synthesis.

Compared with the existing thiol-modified lubricants, this strategy exhibits high adhesion capacity.

(B) Our study showed novelty on biomimetics.

Our study embodies bionic concepts in four aspects:

(i) protection of catechol groups from autoxidation through the formation of S-catecholyl functionalities inspired by mussel Mfp-6 protein;

(ii) strong interfacial adhesion derived from catechol groups inspired by mussel adhesive chemistry;

(iii) green synthetic route based on the high reactivity of spontaneous thiol-quinone addition reaction inspired by melanin biosynthesis;

(iv) one-pot oxidation of BPA to o-quinone using IBX inspired by the tyrosinase-catalyzed oxidation involved in melanin biosynthesis.

Thiol-functionalized biomimetic lubricant integrate bioinspiration from both melanin biosynthesis and mussels adhesion. Thiol-functionalized biomimetic lubricant have novel structure analogous to melanin with S-catecholyl linkage.

The resulting lubricant better mimics the mussels adhesion. It not only emulates the adhesion mechanism of Mfp-3 and Mfp-5, which is the traditional approach for mimicry, but also further imitates the protective mechanism of Mfp-6 for the first time. Our study represents a comprehensive mimicry of mussel for adhesion.

(C) ODT is the critical material for our study to achieve the novelty.

ODT is the critical and innovative material that determines the achievement of our goals.

It embodies its bionic concepts in four aspects:

(i) ODT acts as an efficient nucleophile to readily reacts with o-quinone to form the corresponding adduct.

(ii) ODT provides sulfur element as extreme-pressure functionality for anti-wear, friction-reducing, and thermal stability.

(iii) ODT provides a long hydrophobic chain for lubrication due to excellent hydrophobicity.

(iv) ODT contributes to strong adsorption and defoaming on the metal surface.

(D) The answer to this query and the suggested changes in the revised manuscript.

The advantages of our concept compared with existing lubricants, as well as the core novelty of the present approach, were clearly clarified. In the Conclusion Section, we have supplemented a detailed advantages and novelty, highlighting that our strategy not only exhibits superior performance but also possesses unique structural characteristics over traditional lubricants.