Bio-Inspired 3D-Printed Polymeric Sheets for Orthoses: Predictive Modeling of Mechanical Integrity and Moisture Absorption

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript offers a significant contribution to the field of additive manufacturing applied to custom-made orthopaedic devices, evaluating the durability of 3D-printed polymers under saline conditions that simulate human sweat via a Box-Behnken design to predict hardness and moisture absorption. The topic is timely and the experimental approach is robust. However, the following points must be addressed prior to acceptance:

Comment 1. The stated aim in the Introduction (lines 135–136) includes a comparison between the Box-Behnken and Taguchi predictive models, which is sought through the analysis of moisture adsorption and hardness; however, this objective is not explicitly reflected in the Abstract. Furthermore, throughout the manuscript, it remains unclear whether the analysis of moisture adsorption and hardness is a means or an end in itself. The authors are encouraged to align the Abstract with the full scope of the study or revise the Introduction accordingly to avoid confusing the reader regarding the primary objective(s) and the methodology.

Comment 2. In Table 4, the caption indicates that only statistically significant effects (p < 0.05) are shown. Nevertheless, a value of 0.486 is reported for source AA regarding the hardness of white PLA, which clearly does not meet the established significance threshold. The authors should verify whether this entry was included in error or clarify the justification for its inclusion.

Comment 3 (Lines 175 - 183). Although the authors provide a general physiological justification for using saline conditions in the Introduction (lines 114 - 118), no bibliographic support is provided for the specific numerical ranges selected for NaCl concentration (0.1 - 5%) and exposure time (1 - 6 days). The authors are encouraged to cite references justifying these particular values in relation to human sweat composition or standardised disinfection protocols.

Comment 4. The authors include a brief discussion of limitations between lines 449 and 451, which is geared towards future work rather than a critical reflection on the constraints of the findings. It would be beneficial to develop the limitations into a dedicated paragraph.

In its current form, the manuscript presents an experimental approach relevant to the field of personalised orthotic devices, with a well-structured design and results that contribute to the knowledge of 3D-printed polymer durability under simulated physiological conditions. Addressing the points raised will substantially enhance the scientific rigour and transparency of the manuscript.

Author Response

Response to Reviewers of Manuscript Biomimetics-4322616 entitled

“Bio-Inspired 3D-Printed Polymeric Sheets for Orthoses: Predictive Modeling of Mechanical Integrity and Moisture Absorption”

The manuscript specified in the title has been revised incorporating the remarks of the referees. We highly appreciate the effort of the editor and the reviewers, and we believe their suggestions have allowed us to improve the quality of the paper. Please find our replies to the reviewer’s comments in the following sections. Please find enclosed with this answer document:

• The revised manuscript with changes highlighted
• The revised manuscript and supplementary material fully ready to be published

 

Kindest regards,

The authors of the manuscript

 

Legend to the layout of this document: Comments of the editor/reviewers are shown in plain text. Author’s replies to the reviewers’ comments are shown in italics. Changes in the revised manuscript are referred to with the line number (referred to the Manuscript with revision changes marked) and marked in blue.

 

 

 

RESPONSE TO REVIEWER #1

The manuscript offers a significant contribution to the field of additive manufacturing applied to custom-made orthopaedic devices, evaluating the durability of 3D-printed polymers under saline conditions that simulate human sweat via a Box-Behnken design to predict hardness and moisture absorption. The topic is timely and the experimental approach is robust. However, the following points must be addressed prior to acceptance:

 

The stated aim in the Introduction (lines 135–136) includes a comparison between the Box-Behnken and Taguchi predictive models, which is sought through the analysis of moisture adsorption and hardness; however, this objective is not explicitly reflected in the Abstract. Furthermore, throughout the manuscript, it remains unclear whether the analysis of moisture adsorption and hardness is a means or an end in itself. The authors are encouraged to align the Abstract with the full scope of the study or revise the Introduction accordingly to avoid confusing the reader regarding the primary objective(s) and the methodology.

 

Answer: Thank you for this observation. We agree that the previous version of the manuscript created confusion by mentioning the Taguchi approach in the Introduction. However, Taguchi was not finally applied in this study. The experimental design, modelling, and optimization were carried out using the Box-Behnken design within the response surface methodology framework. Therefore, the reference to Taguchi in the Introduction was an inadvertent error and has now been removed to ensure consistency between the Abstract, Introduction, methodology, and results (page 3, lines 141-142).

 

Also, moisture absorption and Shore A hardness were analyzed as response variables to evaluate the performance of the selected 3D-printed polymers under saline exposure conditions. The Abstract has also been revised to clarify this point and to better reflect the actual methodological approach used in the study (page 1, lines 21-23 and 25).

 

In Table 4, the caption indicates that only statistically significant effects (p < 0.05) are shown. Nevertheless, a value of 0.486 is reported for source AA regarding the hardness of white PLA, which clearly does not meet the established significance threshold. The authors should verify whether this entry was included in error or clarify the justification for its inclusion.

Answer: We have reviewed Table 4 and the p-value reported for the AA term regarding the hardness of PLA_W was incorrectly typed as 0.486. The correct value is 0.0486, which is below the significance threshold of p < 0.05. Therefore, this term was correctly included in the table, and the p-value has now been corrected accordingly (Table 4).

 

Although the authors provide a general physiological justification for using saline conditions in the Introduction (lines 114 - 118), no bibliographic support is provided for the specific numerical ranges selected for NaCl concentration (0.1 - 5%) and exposure time (1 - 6 days). The authors are encouraged to cite references justifying these particular values in relation to human sweat composition or standardised disinfection protocols.

Answer: According to the reviewer comments we have improved justification for the selected NaCl concentration range and exposure time as well as stronger bibliographic support. Accordingly, we have revised the manuscript to include additional references supporting the selected experimental range.

The lower and intermediate NaCl concentrations were selected to cover values commonly reported for human sweat and artificial sweat formulations, whereas the upper value of 5% NaCl was included as an accelerated saline-stress condition rather than as a direct physiological sweat concentration. This point has now been clarified in the manuscript. In addition, the exposure time range of 1–6 days was selected to represent short-term and cumulative exposure conditions, remaining within the order of magnitude of standardized artificial-sweat immersion tests, which commonly use exposure periods of up to one week.

So, the following text has been added to the manuscript in the methodology section (page 5, lines 205-219):

The NaCl concentration range was selected to cover both physiologically relevant and accelerated saline-stress conditions. Human sweat composition is highly variable, with reported sweat sodium concentrations typically ranging from approximately 10 to 90 mmol/L, depending on individual, environmental, and activity-related factors. Standardized and commonly used artificial sweat formulations also include NaCl as a major ionic component, with concentrations varying from 0,5% to 1% NaCl (AATCC pH 4.3; ISO 105-E04; Kulthong et al., 2010; Li et al., 2021) in  artificial perspiration solutions. Therefore, the lower and intermediate levels used in this study were selected to represent sweat-related exposure, whereas the 5% NaCl level was included as an accelerated saline challenge, consistent with the concentration commonly used in neutral salt-spray corrosion testing. The exposure time range of 1–6 days was selected to evaluate both short-term and cumulative exposure (ASTM D570).

References included:

ISO 105-E04 INTERNATIONAL STANDARD Sixth edition 2013-03-15 Textiles — Tests for colour fastness — Part E04: Colour fastness to perspiration

Li J., Yang X., Zhang Z., Xiao H., Sun W., Huang W., Li Y., Chen C., Sun Y. (2021). Aggregation kinetics of diesel soot nanoparticles in artificial and human sweat solutions: Effects of sweat constituents, pH, and temperature. Journal of Hazardous Materials, 403, art. no. 123614. DOI: 10.1016/j.jhazmat.2020.123614.

Artificial sweat standards included American Association of Textile Chemists and Colorists (AATCC Test Method 15-2002).

Kulthong K., Srisung S., Boonpavanitchakul K., Kangwansupamonkon W., Maniratanachote R. (2010). Determination of silver nanoparticle release from antibacterial fabrics into artificial sweat. Particle and Fibre Toxicology, 7, art. no. 8. DOI: 10.1186/1743-8977-7-8.

ASTM International. (2018). Standard test method for water absorption of plastics (ASTM D570-18). https://doi.org/10.1520/D0570-18.

 

The authors include a brief discussion of limitations between lines 449 and 451, which is geared towards future work rather than a critical reflection on the constraints of the findings. It would be beneficial to develop the limitations into a dedicated paragraph.

Answer: To address this issue, we have expanded this section and included a dedicated paragraph specifically discussing the main limitations of the study. The revised paragraph now clarifies that the experiments were conducted under controlled in vitro saline exposure conditions and therefore do not fully reproduce the complexity of real use, where orthoses may be exposed to variable sweat composition, pH, temperature, mechanical loading, cleaning routines, and repeated wear cycles. We have also acknowledged that the analysis focused on moisture absorption and Shore A hardness, while other relevant properties such as fatigue resistance, dimensional stability, surface degradation, long-term ageing, and biocompatibility were not evaluated. This revision provides a more balanced interpretation of the findings and better defines the scope of the conclusions.

So, the following text has been added to the manuscript in the discussion section (pages 14-15, lines 507-516):

Despite the relevance of the results, this study has some limitations. The experiments were conducted under controlled in vitro saline conditions and therefore do not fully reproduce real orthosis use, where variable sweat composition, pH, temperature, mechanical loading, cleaning procedures, friction, and wet–dry cycles may occur. Moreover, only moisture absorption and Shore A hardness were evaluated, while fatigue resistance, dimensional stability, surface degradation, ageing behaviour, and biocompatibility were not assessed. Thus, the findings should be interpreted as an initial comparative assessment under defined saline conditions. Future studies should include more realistic sweat formulations, cyclic loading, longer ageing periods, and user-simulated or in vivo validation.

In its current form, the manuscript presents an experimental approach relevant to the field of personalised orthotic devices, with a well-structured design and results that contribute to the knowledge of 3D-printed polymer durability under simulated physiological conditions. Addressing the points raised will substantially enhance the scientific rigour and transparency of the manuscript.

Answer: We appreciate the reviewer’s constructive feedback, which has helped us to strengthen the final version of the work.

 

Kind regards :)

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Prof.,

The authors have written the manuscript in a planned manner

In introduction part the author can add recent publications

The authors have compared with blue white PLA, Eco resin, standard resin with dependent and independent variable

The role of hardness and moisture obtained by the quadratic models, shows the response of the materials. The authors can explain the durability of the specimen for usages with the reference to standard data that is exsist

The response was reported only by the quadratic effects. what is the significance of second order derivative

RSM visualizations relates the non-linear effects. The authors can give an explanation only with linear effects. Comparison with linear and non-linear data.

The authors has mentioned the variation of thickness effects alone, is there any role of other dimensions 

The manuscript reveals the selection of new materials for orthotic devices.

 

 

 

Author Response

Response to Reviewers of Manuscript Biomimetics-4322616 entitled

“Bio-Inspired 3D-Printed Polymeric Sheets for Orthoses: Predictive Modeling of Mechanical Integrity and Moisture Absorption”

The manuscript specified in the title has been revised incorporating the remarks of the referees. We highly appreciate the effort of the editor and the reviewers, and we believe their suggestions have allowed us to improve the quality of the paper. Please find our replies to the reviewer’s comments in the following sections. Please find enclosed with this answer document:

• The revised manuscript with changes highlighted
• The revised manuscript and supplementary material fully ready to be published

 

Kindest regards,

The authors of the manuscript

 

Legend to the layout of this document: Comments of the editor/reviewers are shown in plain text. Author’s replies to the reviewers’ comments are shown in italics. Changes in the revised manuscript are referred to with the line number (referred to the Manuscript with revision changes marked) and marked in blue.

RESPONSE TO REVIEWER #2

The authors have written the manuscript in a planned manner

Answer: We thank you very much for your positive assessment.

In introduction part the author can add recent publications.

Answer: We have revised the introduction and added 9 recent publications, which have included in the introduction and in the reference section.

The authors have compared with blue white PLA, Eco resin, standard resin with dependent and independent variable.

Answer: The independent variables were membrane thickness, NaCl concentration, and immersion time, while the dependent response variables were moisture absorption and Shore A hardness. The comparison among Blue PLA, White PLA, Eco Resin, and Standard Resin was performed to evaluate how each material responds to these controlled experimental factors.

The role of hardness and moisture obtained by the quadratic models, shows the response of the materials. The authors can explain the durability of the specimen for usages with the reference to standard data that is exsist.

Answer: We have expanded the Discussion to better relate the predicted hardness and moisture responses to the practical durability of the specimens for orthotic use. The revised text now explains that low moisture absorption is associated with lower risk of swelling, plasticization, dimensional instability, and discomfort, while stable Shore A hardness indicates better retention of mechanical support. We have also contextualized these interpretations with the standard testing approaches used in the study for hardness and moisture assessment. This revision clarifies that Std-Resin showed the most favourable durability profile under the tested saline conditions, whereas PLA-based materials and Eco-Resin may require optimized thickness, protective coatings, or controlled cleaning protocols for long-term orthotic applications.

So, the following text has been added to the manuscript in the discussion section (page 14, lines 471-482):

In practical terms, low moisture uptake is desirable because it reduces the risk of swelling, plasticization, dimensional changes, and loss of comfort during prolonged contact with sweat or cleaning solutions. Similarly, the retention of Shore A hardness indicates that the material preserves its resistance to indentation and its ability to provide mechanical support. Materials showing both low moisture absorption and stable hardness values can be considered more suitable for long-term orthotic applications. In this sense, Std-Resin exhibited the most favourable durability profile, as it maintained relatively high hardness and limited moisture uptake under the tested saline conditions. By contrast, PLA-based materials and Eco-Resin showed greater sensitivity to saline exposure and immersion time, suggesting that their use in orthotic devices may require optimized thickness, protective coatings, or controlled cleaning protocols.

The response was reported only by the quadratic effects. what is the significance of second order derivative.

Answer: We have clarified in the revised manuscript that the quadratic terms in the Box-Behnken response surface models are important because they allow the detection of curvature in the material response. The second-order terms therefore help to identify non-linear behaviour, possible maxima or minima, and optimum experimental conditions for each material response.

So, the following text has been added to the manuscript in the discussion section (page 8, lines 314-317):

In this context, the second-order terms are relevant because they describe curvature in the response surface and make it possible to detect nonlinear trends, local maxima or minima, and material-specific optimum conditions.

RSM visualizations relates the non-linear effects. The authors can give an explanation only with linear effects. Comparison with linear and non-linear data.

Answer: The curved surfaces indicate that the material responses cannot be fully explained by simple linear relationships alone. Therefore, the quadratic model was used because it provides a more accurate description of the combined and non-linear effects of thickness, NaCl concentration, and immersion time on moisture absorption and hardness. This explanation has now been added to improve the interpretation of the graphical results.

So, text regarding the need to employ non-linear data has been added to the manuscript in the discussion section (pages 10-11, lines 369-372, 373-377).

The authors has mentioned the variation of thickness effects alone, is there any role of other dimensions.

Answer: In this study, thickness was selected as the main geometrical variable because it directly affects moisture diffusion and mechanical response in thin orthotic membranes. However, we agree that other dimensions, such as specimen length, width, surface area, and overall geometry, may also influence long-term performance, especially in real orthotic devices. These dimensions were kept constant in the present experimental design to isolate the effect of thickness. This point has now been clarified in the manuscript, and the role of other geometrical parameters has been included as a limitation and as a recommendation for future studies.

So, the following text has been added to the manuscript in the discussion section (page 4, lines 186-189):

Thickness was selected as the main geometrical variable as it affects moisture diffusion and mechanical response in thin orthotic membranes. Other variables such as specimen length, surface area or geometry were kept constant to isolate the effect of thickness.

The manuscript reveals the selection of new materials for orthotic devices.

Answer: Thank you for this positive comment. We appreciate the reviewer’s recognition of the relevance of the study for material selection in orthotic devices.

 

 

Reviewer 3 Report

Comments and Suggestions for Authors

The article entitled “Bio-Inspired 3D-Printed Membranes for Orthoses: Predictive Modeling of Mechanical Integrity and Moisture Absorption” is a good scientific effort by Rosa Devesa-Rey and co-workers and have reported some interesting findings regarding biomimetics, additive manufacturing, orthotic materials, and statistical optimization. The study is good, however, some modifications regarding the experimental realism,             mechanical characterization, statistical rigor, interpretation of degradation behavior, and scientific overstatements are required in order to enhance manuscript quality.

1. For the correct terminology and better understanding the concept wordings of layer-by-layer deposition approach needs to be modify to layer-by-layer photopolymerization process.
2. The authors need to justify the use of Shore A or repeat measurements using Shore D hardness scale.
3. The authors are encouraged to modify and include some more references in the introduction section for better insights into biomimetic material design (doi: https://doi.org/10.1016/j.colcom.2025.100818), microporous functional materials (doi: https://doi.org/10.1002/adma.202410650), and additive manufacturing approaches for advanced biomedical applications (doi: https://doi.org/10.1007/s12598-024-03205-7). To study and include these recent studies will would strengthen the scientific background of the manuscript by providing recent advances in biomimetic material design, mechanically adaptive microporous systems, and additive manufacturing-based biomedical materials, thus will improve the novelty, context, and relevance of the study.
4. In the current study, the authors have used only NaCl solutions (0.1–5%) to simulate sweat but in fact NaCl do not realistically represent the physiological sweat conditions. The authors are suggested to use standardized artificial sweat formulations or clearly acknowledge this limitation.
5. According to the manuscript, the exposure times are only 1–6 days, but the authors have claimed as “long-term functional performance” and degradation behavior. A proper justification is required.
6. The authors need to justify the 12.7 × 12.7 cm samples as they claimed as “membranes”, although, these specifications are not truly considered as membranes in biomaterials terminology.
7. The mechanical integrity cannot be adequately assessed using hardness alone, it may be accompanied with missing tests, tensile strength, flexural strength, impact resistance, or fatigue behavior for better support of the claim. Proper justification is required.
8. According to the authors “saline conditions may enhance intermolecular interactions or reduce free volume”, but without providing the DSC, FTIR, XRD, DMA, or microstructural analysis to support this mechanism.
9. According to the manuscript, “longer exposure times minimize moisture absorption”. The authors need to verify calculations, explain desorption or densification experimentally, or reconsider model interpretation.
10. The mathematical equations need to be cross checked.
11. The authors need to include the comprehensive statistical validation.
12. The authors have mentioned the hardness measurements triplicates, but the moisture absorption replication are unclear and need proper justification.

Author Response

Response to Reviewers of Manuscript Biomimetics-4322616 entitled

“Bio-Inspired 3D-Printed Polymeric Sheets for Orthoses: Predictive Modeling of Mechanical Integrity and Moisture Absorption”

The manuscript specified in the title has been revised incorporating the remarks of the referees. We highly appreciate the effort of the editor and the reviewers, and we believe their suggestions have allowed us to improve the quality of the paper. Please find our replies to the reviewer’s comments in the following sections. Please find enclosed with this answer document:

• The revised manuscript with changes highlighted
• The revised manuscript and supplementary material fully ready to be published

 

Kindest regards,

The authors of the manuscript

 

Legend to the layout of this document: Comments of the editor/reviewers are shown in plain text. Author’s replies to the reviewers’ comments are shown in italics. Changes in the revised manuscript are referred to with the line number (referred to the Manuscript with revision changes marked) and marked in blue. RESPONSE TO REVIEWER #3 The article entitled “Bio-Inspired 3D-Printed Membranes for Orthoses: Predictive Modeling of Mechanical Integrity and Moisture Absorption” is a good scientific effort by Rosa Devesa-Rey and co-workers and have reported some interesting findings regarding biomimetics, additive manufacturing, orthotic materials, and statistical optimization. The study is good, however, some modifications regarding the experimental realism, mechanical characterization, statistical rigor, interpretation of degradation behavior, and scientific overstatements are required in order to enhance manuscript quality. Answer: Thank you very much for your detailed and constructive evaluation of the manuscript. We appreciate your positive assessment of the scientific effort and the relevance of the study. We have carefully revised the manuscript to address the comments related to terminology, experimental justification, statistical interpretation, and the scope of the conclusions. The revised version now provides a clearer and more cautious interpretation of the results and better defines the limitations of the study. For the correct terminology and better understanding the concept wordings of layer-by-layer deposition approach needs to be modify to layer-by-layer photopolymerization process. Answer: The manuscript has been revised to distinguish between the manufacturing mechanisms used for the different materials. For PLA specimens, the term “material extrusion/FDM layer-by-layer deposition” is used, whereas for resin specimens the text now refers to “layer-by-layer photopolymerization” or “vat photopolymerization”. This correction improves the technical accuracy of the manufacturing description. So, the following text has been added to the manuscript in the discussion section (page 4, lines 179-181): Two additive manufacturing techniques were used according to the material type. PLA specimens were manufactured by Fused Deposition Modeling (FDM) and resin specimens were manufactured by VAT photopolymerization. The authors need to justify the use of Shore A or repeat measurements using Shore D hardness scale. Answer: Shore A was selected because the tested specimens were intended to represent orthotic membranes in contact with the body, where indentation resistance, comfort, and surface compliance are significant. The objective was to compare changes in surface hardness under the same controlled conditions rather than to fully characterize bulk mechanical strength. Also, Shore A hardness was considered appropriate for this comparative study because it provided measurable and reproducible values within the tested material range, enabling the assessment of relative surface hardness changes after saline exposure. So, the following text has been added to the manuscript in the discussion section (page 5, lines 221-223): Shore A hardness provided measurable and reproducible values within the tested material range, enabling the assessment of relative surface hardness changes after saline exposure. The authors are encouraged to modify and include some more references in the introduction section for better insights into biomimetic material design (doi: https://doi.org/10.1016/j.colcom.2025.100818), microporous functional materials (doi: https://doi.org/10.1002/adma.202410650), and additive manufacturing approaches for advanced biomedical applications (doi: https://doi.org/10.1007/s12598-024-03205-7). To study and include these recent studies will would strengthen the scientific background of the manuscript by providing recent advances in biomimetic material design, mechanically adaptive microporous systems, and additive manufacturing-based biomedical materials, thus will improve the novelty, context, and relevance of the study. Answer: We have revised the Introduction and incorporated recent publications related to biomimetic material design, mechanically adaptive microporous systems, and additive manufacturing approaches for biomedical applications, including the references suggested by the reviewer. So, the following text has been added to the manuscript in the discussion section (pages 2-3, lines 138-148): Recent advances in biomimetic and additively manufactured biomaterials further support the need to combine material selection, structural design, and durability assessment in biomedical devices. For example, additive manufacturing has been increasingly explored for biodegradable metallic biomaterials, where material composition, manufacturing quality, degradation behaviour, and biocompatibility are key research challenges. In parallel, bio-inspired strategies based on microporous architectures and natural interfaces, such as insect cuticles, have shown how structural design can improve toughness, elasticity, adaptability, and durability. These recent studies highlight the importance of integrating biomimetic design principles with predictive material evaluation when developing 3D-printed orthotic components. References that will be include in the reference section: Yuan K.-S., Deng C.-C., Wang X.-X., Li Y.-C., Zhou C., Zhao C.-R., Dai X.-Z., Khan A.-R., Zhang Z., Guidoin R., Zhang H.-J., Zheng Y.-F., Wang G.-X. (2025). Research advances and future perspectives of zinc-based biomaterials for additive manufacturing. Rare Metals, 44 (7), pp. 4376 – 4410. DOI: 10.1007/s12598-024-03205-7. Sun F., Zhang J., Liu T., Yao H., Wang L., Meng H., Gao Y., Cao Y., Yao B., Xu J., Fu J. (2024). A Versatile Microporous Design toward Toughened yet Softened Self-Healing Materials. Advanced Materials, 36 (50), art. no. 2410650. DOI: 10.1002/adma.202410650. Zheng Y., Wang J., Wang J., Li Y., Jiang Z. (2025). Insect cuticle: A source of inspiration for biomimetic Interface material design. Colloids and Interface Science Communications, 64, art. no. 100818. DOI: 10.1016/j.colcom.2025.100818. In the current study, the authors have used only NaCl solutions (0.1–5%) to simulate sweat but in fact NaCl do not realistically represent the physiological sweat conditions. The authors are suggested to use standardized artificial sweat formulations or clearly acknowledge this limitation. Answer: The manuscript has been revised to clarify that the NaCl solutions used in this study do not fully reproduce the complete chemical complexity of physiological sweat. NaCl was selected as a simplified and controlled saline medium because it is one of the main ionic components of sweat and allows the isolated evaluation of salt concentration effects. Comments about salinity, concentrations employed and sweat simulation have been included in the “Materials and Methods” section (page 5, lines 205-219). According to the manuscript, the exposure times are only 1–6 days, but the authors have claimed as “long-term functional performance” and degradation behavior. A proper justification is required. Answer: The exposure time range of 1–6 days was selected to represent short-term and cumulative exposure conditions, remaining within the order of magnitude of standardized artificial-sweat immersion tests, which commonly use exposure periods of up to one week. The manuscript has been revised to avoid claiming complete long-term clinical performance based only on 1–6 days of exposure. The exposure period is now described as a short-term and cumulative saline exposure test intended to provide an initial comparative assessment of material stability. So, the following text has been added to the manuscript in the methodology section (page 5, lines 218-219): The exposure time range of 1–6 days was selected to evaluate both short-term and cumulative exposure (ASTM D570). Also, the “long-term” expression has been moderated when necessary. The authors need to justify the 12.7 × 12.7 cm samples as they claimed as “membranes”, although, these specifications are not truly considered as membranes in biomaterials terminology. Answer: We have revised the terminology to avoid confusion with biomaterial membranes in the strict biological or porous-membrane sense. In this study, the term “membrane” refers to thin, flat polymeric sheets designed to represent simplified orthotic components with variable thickness. To improve clarity, the manuscript now uses the terms “thin polymeric sheets” or “flat specimens” where appropriate. The dimensions were selected to provide sufficient surface area for hardness measurements and moisture absorption testing while maintaining a controlled geometry for comparison among materials. The mechanical integrity cannot be adequately assessed using hardness alone, it may be accompanied with missing tests, tensile strength, flexural strength, impact resistance, or fatigue behavior for better support of the claim. Proper justification is required. Answer: The manuscript has been revised to clarify that Shore A hardness provides information on surface indentation resistance but does not fully describe mechanical integrity. Therefore, the conclusions have been adjusted to avoid overstating the mechanical performance of the materials. We now refer to “surface hardness stability” rather than complete mechanical integrity when discussing the Shore A results. We also acknowledge that tensile strength, flexural strength, impact resistance, fatigue behavior, and dimensional stability should be evaluated in future studies to obtain a more complete assessment of orthotic performance. Changes have been applied throughout the manuscript when appropriate. According to the authors “saline conditions may enhance intermolecular interactions or reduce free volume”, but without providing the DSC, FTIR, XRD, DMA, or microstructural analysis to support this mechanism. Answer: The corresponding statement has been deleted to avoid unsupported mechanistic claims. According to the manuscript, “longer exposure times minimize moisture absorption”. The authors need to verify calculations, explain desorption or densification experimentally, or reconsider model interpretation. Answer: The manuscript has been revised to clarify that the predicted reduction in moisture absorption at longer exposure times is a model-derived response within the studied experimental domain and should not be interpreted as a general material law (pages 12-13, changes within lines 420-423). The mathematical equations need to be cross checked. Answer: The mathematical equations have been carefully reviewed. The notation of the linear, interaction, and quadratic terms has been checked to ensure consistency with the Box–Behnken response surface methodology (page 11, equations 6 to 10). The authors need to include the comprehensive statistical validation. Answer: We have expanded the statistical validation description in the manuscript. The revised text now clarifies that model adequacy was evaluated using R², adjusted R², standard error, Durbin–Watson statistic, and ANOVA-based F-ratio and p-values. We also clarified that center-point replicates were used to estimate experimental error and that only statistically significant terms (p < 0.05) were retained in the reduced predictive equations. In addition, models with lower adjusted R² or Durbin–Watson values far from 2 are now interpreted with caution (page 7, lines 273-280). The authors have mentioned the hardness measurements triplicates, but the moisture absorption replication are unclear and need proper justification. Answer: We have revised the Materials and Methods section to clarify the replication strategy used for moisture absorption measurements. Both hardness and moisture were run in triplicates.   Kind regards :)

Reviewer 4 Report

Comments and Suggestions for Authors

The paper addresses a topic of certain interest by examining the behavior of 3D-printed polymers for long-term use in orthopedics, exposed to salinity and humidity. The combination of biomimicry, biomaterials engineering, and predictive modeling for stainless biomedical devices makes the topic highly interesting.
However, several issues currently limit the scientific robustness and translational impact of the work. In particular, the biological relevance of the experimental model, the interpretation of some statistical findings, and the connection with real orthotic applications demand substantial improvement. Some conclusions also appear stronger than warranted by the presented data.

Major Comments

Limited Clinical and Biomimetic Relevance of the experimental setup: the manuscript repeatedly refers to “simulation of orthotic operating conditions”; however, the environmental model remains relatively simplistic and does not involve many realistic features which may reproduce the complexity of real wearable biomedical conditions. The experimental setup includes NaCl concentration, humidity exposure and time. However, real orthotic environments also involve: 
Cyclic mechanical loading;
Temperature fluctuations;
Sweat composition variabilty;
Microbial exposure;
Frictional wear;
UV exposure;
Repeated cleaning/disinfection cycles.

Therefore, the claim that the study simulates “real orthotic conditions” should be moderated.

Recommendation

Please add:
Explicit acknowledgment of the simplified nature of the environmental simulation;
Discussion of the limitations about saline-only exposure;
Better justify the biomimetic relevance of the chosen conditions.

Hardness alone is insufficient to support Material Suitability claims.
The conclusions regarding material suitability for orthotic applications appear justified by limited mechanical characterization. Orthotic devices are strongly influenced by fatigue resistance, flexural strength, creep behaviour and dimensional stability under cyclic loading. Therefore to support material suitability conclusion, these variables should also be considered.

Recommendation

The authors should:
Moderate the wording of their conclusions;
Clearly state that findings are limited to hardness and moisture behavior;
Avoid generalized statements regarding overall clinical suitability.

Statistical Interpretation
The statistical methodology is generally appropriate, however interpretations regarding molecular mechanisms should be presented more cautiously and explicitly identified as hypotheses rather than demonstrated phenomena.

Minor Comments

English Language
Overall English quality is good and publication-ready.

Discussion Section
The discussion contains repetition, particularly regarding:
Salinity effects;
Hydrolytic degradation;
Exposure time.

Strenghts of the Manuscript
The manuscript has several positive aspects:
Relevant topic in additive manufacturing and biomedical materials;
Appropriate use of experimental design methodology;
Good integration of response surface modeling;
Comparative evaluation of multiple polymer systems;
Translational relevance for orthotic device manufacturing;
Discussion of sustainability-related materials.
The use of Box-Behnken is particularly valuable and provides methodological originality.

Author Response

Response to Reviewers of Manuscript Biomimetics-4322616 entitled

“Bio-Inspired 3D-Printed Polymeric Sheets for Orthoses: Predictive Modeling of Mechanical Integrity and Moisture Absorption”

The manuscript specified in the title has been revised incorporating the remarks of the referees. We highly appreciate the effort of the editor and the reviewers, and we believe their suggestions have allowed us to improve the quality of the paper. Please find our replies to the reviewer’s comments in the following sections. Please find enclosed with this answer document:

• The revised manuscript with changes highlighted
• The revised manuscript and supplementary material fully ready to be published

 

Kindest regards,

The authors of the manuscript

 

Legend to the layout of this document: Comments of the editor/reviewers are shown in plain text. Author’s replies to the reviewers’ comments are shown in italics. Changes in the revised manuscript are referred to with the line number (referred to the Manuscript with revision changes marked) and marked in blue.

 

RESPONSE TO REVIEWER #4

The paper addresses a topic of certain interest by examining the behavior of 3D-printed polymers for long-term use in orthopedics, exposed to salinity and humidity. The combination of biomimicry, biomaterials engineering, and predictive modeling for stainless biomedical devices makes the topic highly interesting.

However, several issues currently limit the scientific robustness and translational impact of the work. In particular, the biological relevance of the experimental model, the interpretation of some statistical findings, and the connection with real orthotic applications demand substantial improvement. Some conclusions also appear stronger than warranted by the presented data.

Answer: Thank you very much for your detailed and constructive evaluation of the manuscript. The manuscript has been revised to clarify the simplified nature of the environmental simulation, to better define the limitations of the study, and to avoid overextending the conclusions beyond the experimental evidence.

Major Comments

Limited Clinical and Biomimetic Relevance of the experimental setup: the manuscript repeatedly refers to “simulation of orthotic operating conditions”; however, the environmental model remains relatively simplistic and does not involve many realistic features which may reproduce the complexity of real wearable biomedical conditions. The experimental setup includes NaCl concentration, humidity exposure and time. However, real orthotic environments also involve: Cyclic mechanical loading; Temperature fluctuations; Sweat composition variabilty; Microbial exposure; Frictional wear; UV exposure; Repeated cleaning/disinfection cycles. Therefore, the claim that the study simulates “real orthotic conditions” should be moderated.

 

Recommendation

 

Please add:

Explicit acknowledgment of the simplified nature of the environmental simulation; Discussion of the limitations about saline-only exposure; Better justify the biomimetic relevance of the chosen conditions.

Answer: We have expanded the methodology section and included a dedicated paragraph specifically discussing the main limitations of the study. The revised paragraph now clarifies that the experiments were conducted under controlled in vitro saline exposure conditions and therefore do not fully reproduce the complexity of real use, where orthoses may be exposed to variable sweat composition, pH, temperature, mechanical loading, cleaning routines, and repeated wear cycles.

So, the following text has been added to the manuscript in the discussion section (page 14, lines 507-516):

Despite the relevance of the results, this study has some limitations. The experiments were conducted under controlled in vitro saline conditions and therefore do not fully reproduce real orthosis use, where variable sweat composition, pH, temperature, mechanical loading, cleaning procedures, friction, and wet–dry cycles may occur. Moreover, only moisture absorption and Shore A hardness were evaluated, while fatigue resistance, dimensional stability, surface degradation, ageing behaviour, and biocompatibility were not assessed. Thus, the findings should be interpreted as an initial comparative assessment under defined saline conditions. Future studies should include more realistic sweat formulations, cyclic loading, longer ageing periods, and user-simulated or in vivo validation.

Also, a paragraph about the limitations of the study has also been introduced in the Discussion section (pages 14-15, lines 507-516):

Despite the relevance of the results, this study has some limitations. The experiments were conducted under controlled in vitro saline conditions and therefore do not fully reproduce real orthosis use, where variable sweat composition, pH, temperature, mechanical loading, cleaning procedures, friction, and wet–dry cycles may occur. Moreover, only moisture absorption and Shore A hardness were evaluated, while fa-tigue resistance, dimensional stability, surface degradation, ageing behavior, and bi-ocompatibility were not assessed. Thus, the findings should be interpreted as an initial comparative assessment under defined saline conditions. Future studies should include more realistic sweat formulations, cyclic loading, longer ageing periods, and us-er-simulated or in vivo validation.

 

Hardness alone is insufficient to support Material Suitability claims.

The conclusions regarding material suitability for orthotic applications appear justified by limited mechanical characterization. Orthotic devices are strongly influenced by fatigue resistance, flexural strength, creep behaviour and dimensional stability under cyclic loading. Therefore to support material suitability conclusion, these variables should also be considered.

 

Recommendation

 

The authors should:

Moderate the wording of their conclusions; Clearly state that findings are limited to hardness and moisture behavior; Avoid generalized statements regarding overall clinical suitability.

Answer: The manuscript has been revised to avoid presenting Shore A hardness as a complete indicator of mechanical integrity or material stability. Shore A hardness is now described as a measure of surface indentation resistance and hardness stability under the tested conditions.

So, the following text has been added to the manuscript in the discussion section (page 5, lines 221-223):

Shore A hardness provided measurable and reproducible values within the tested material range, enabling the assessment of relative surface hardness changes after saline exposure.

And also the following information in the discussion section (pages 14-15, lines 510-516):

Moreover, only moisture absorption and Shore A hardness were evaluated, while fatigue resistance, dimensional stability, surface degradation, ageing behaviour, and biocompatibility were not assessed. Thus, the findings should be interpreted as an initial comparative assessment under defined saline conditions. Future studies should include more realistic sweat formulations, cyclic loading, longer ageing periods, and user-simulated or in vivo validation.

Finally, wording has been moderate when necessary throughout the manuscript.

 

Statistical Interpretation

The statistical methodology is generally appropriate, however interpretations regarding molecular mechanisms should be presented more cautiously and explicitly identified as hypotheses rather than demonstrated phenomena.

Answer: The Discussion section has been revised to moderate possible molecular explanations. Statements related to hydrolytic degradation, structural rearrangement, reduced diffusivity, or hardening mechanisms have been moderated and are now presented as hypotheses rather than demonstrated phenomena. Wording has been moderated throughout the manuscript when necessary.

 

Minor Comments

 

English Language. Overall English quality is good and publication-ready.

Answer: Thank you for the comment.

 

Discussion Section

The discussion contains repetition, particularly regarding: Salinity effects; Hydrolytic degradation; Exposure time.

Answer: We have revised the Discussion to reduce repetition, particularly in the sections referring to salinity effects, hydrolytic degradation, and exposure time. Similar statements were merged, redundant explanations were removed, and the interpretation was made more concise while maintaining the main findings and limitations of the study.

 

Strenghts of the Manuscript

The manuscript has several positive aspects: Relevant topic in additive manufacturing and biomedical materials; Appropriate use of experimental design methodology; Good integration of response surface modeling; Comparative evaluation of multiple polymer systems; Translational relevance for orthotic device manufacturing; Discussion of sustainability-related materials. The use of Box-Behnken is particularly valuable and provides methodological originality.

Answer: Thank you very much for your positive and constructive comments, which helped us improve the clarity and quality of the manuscript.

 

Kind regards :)

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

I have reviewed the revised manuscript. The authors have adequately addressed most of my previous comments and concerns. The manuscript has been improved and is now methodologically sound and clearly presented. I find the current version acceptable and recommend it for publication.