3D-Printed Plantar Orthoses and the Conditional Viability of Recycled PLA

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. According to the iThenticate report, the article's similarity rate being around 7% indicates that the authors have largely conveyed the literature using original expressions. However, during a careful examination of the text, serious repetitions have been detected in some sections. For example, the first two sentences of the paragraph starting at line 89 are repeated verbatim from line 92 onward; similarly, the paragraph starting at line 100 begins with the same sentences. What is more striking is that the sources cited in these repeated sentences differ. While references 14 and 15 are cited in the first instance, references 16 and 17 are shown in the subsequent repetitions. This situation both undermines the integrity of the text and raises serious doubts about the accuracy and appropriateness of the sources used. Therefore, the authors need to eliminate the repetitions in the text, restructure the relevant sentences, and carefully review all citations to ensure they are fully consistent with the content. Otherwise, in its current state, the study may create a credibility problem for the reader.
2. It is recommended that the authors carefully review the text from start to finish. A high level of familiarity with the text may have made it difficult to spot certain repetitions and linguistic errors. For this reason, it would be beneficial for the article to be reviewed by someone outside the author team who possesses advanced proficiency in English, particularly with regard to language, fluency and consistency. Such a linguistic review will significantly enhance the overall quality and readability of the text.
3. It is unclear whether the range of nozzle temperatures given in Table 2 is consistent with the relevant temperature ranges mentioned in the text. The authors are advised to ensure consistency by comparing the temperature values in the table and the text, and to make the necessary corrections where required.
4. The authors have provided indicative ranges of characteristics in Table 4; however, as this is a review article, it is necessary to know which sources in the literature these ranges were taken from; in other words, it appears that citations are missing.
5. Consistent with the points stated in item 1, upon examining the reference list, it seems that some studies may have been included more than once. When citation management software (e.g. EndNote or Mendeley) is not used, the same source may be given a different number in different places and presented as a different study. This can particularly occur in studies containing a large number of references. As it is difficult for reviewers to check the reference list in detail from beginning to end, authors are recommended to carefully review all references and eliminate possible repetitions and inconsistencies. Using citation management software can help minimize such errors.

Author Response

According to the iThenticate report, the article's similarity rate being around 7% indicates that the authors have largely conveyed the literature using original expressions. However, during a careful examination of the text, serious repetitions have been detected in some sections. For example, the first two sentences of the paragraph starting at line 89 are repeated verbatim from line 92 onward; similarly, the paragraph starting at line 100 begins with the same sentences. What is more striking is that the sources cited in these repeated sentences differ. While references 14 and 15 are cited in the first instance, references 16 and 17 are shown in the subsequent repetitions. This situation both undermines the integrity of the text and raises serious doubts about the accuracy and appropriateness of the sources used. Therefore, the authors need to eliminate the repetitions in the text, restructure the relevant sentences, and carefully review all citations to ensure they are fully consistent with the content. Otherwise, in its current state, the study may create a credibility problem for the reader.

Response:

We thank the reviewer for this observation. We fully agree that the repeated sentences and the inconsistent citation assignment reduced the clarity of the manuscript. In the revised version, we removed the duplicated information, restructured the affected paragraphs, and carefully reviewed the corresponding citations to ensure that each statement is now supported by the appropriate references. In particular, the repeated introductory text regarding 3D-printing waste, sustainability, and recycled PLA was consolidated into a single coherent passage. We also conducted a broader revision of the manuscript to identify and correct similar cases of redundancy, wording imprecision, and citation inconsistency.

Changes in the manuscript:

Repeated text in the Introduction was removed and rewritten for conciseness and consistency (throughout the Introduction section). Associated citations were reviewed and corrected throughout the affected sections (Lines xx–xx). Additional wording improvements were introduced across the manuscript to improve clarity and avoid redundancy (Lines 66–70).

It is recommended that the authors carefully review the text from start to finish. A high level of familiarity with the text may have made it difficult to spot certain repetitions and linguistic errors. For this reason, it would be beneficial for the article to be reviewed by someone outside the author team who possesses advanced proficiency in English, particularly with regard to language, fluency and consistency. Such a linguistic review will significantly enhance the overall quality and readability of the text.

Response:

Thank you for this recommendation. We have carefully reviewed the entire manuscript from start to finish, with particular attention to language quality, fluency, consistency, and readability. During this revision, repeated expressions were removed or rephrased, grammatical and typographical errors were corrected, and terminology was standardized throughout the text. We also revised sentence structure and paragraph transitions to improve the overall flow of the manuscript. We believe that these changes have substantially improved the clarity, coherence, and readability of the revised version.

It is unclear whether the range of nozzle temperatures given in Table 2 is consistent with the relevant temperature ranges mentioned in the text. The authors are advised to ensure consistency by comparing the temperature values in the table and the text, and to make the necessary corrections where required.

Response:

We thank the reviewer for identifying this inconsistency. We carefully rechecked the temperature values reported in the text and in Table 2 and found that the original wording could lead to confusion. In the revised manuscript, the text and Table 2 have been harmonized so that both now present a consistent and more cautious description of nozzle-temperature requirements in recycled PLA processing. Rather than presenting a broad temperature interval as a fixed recommendation, we now clarify that several publications report that recycled PLA may require higher printing temperatures than virgin PLA to achieve stable extrusion and satisfactory mechanical performance, whereas virgin PLA is typically processed within a lower range. This wording better reflects the variability of the literature and avoids overgeneralization.

Changes in the manuscript:

The relevant discussion in the text was revised and aligned with Table 2, and the temperature description was reformulated to improve consistency and accuracy (Lines 318–324; Table 2).The authors have provided indicative ranges of characteristics in Table 4; however, as this is a review article, it is necessary to know which sources in the literature these ranges were taken from; in other words, it appears that citations are missing. In addition, the sources supporting Table 4 were explicitly added, and the table was revised to better reflect its role as a comparative synthesis of heterogeneous literature rather than as a set of fixed standardized values (Lines 469-471; Table 4).

The authors have provided indicative ranges of characteristics in Table 4; however, as this is a review article, it is necessary to know which sources in the literature these ranges were taken from; in other words, it appears that citations are missing.

Response:

We thank the reviewer for this comment. The sources corresponding to the indicative ranges reported in Table 4 have been included in the revised manuscript. We have added the appopiate citations to ensure transparency and traceability of the reported data.

Consistent with the points stated in item 1, upon examining the reference list, it seems that some studies may have been included more than once. When citation management software (e.g. EndNote or Mendeley) is not used, the same source may be given a different number in different places and presented as a different study. This can particularly occur in studies containing a large number of references. As it is difficult for reviewers to check the reference list in detail from beginning to end, authors are recommended to carefully review all references and eliminate possible repetitions and inconsistencies. Using citation management software can help minimize such errors.

Response:

We thank the reviewer for this valuable recommendation. We carefully re-examined the full reference list and all in-text citations in order to detect and correct any duplicated, inconsistent, or misassigned entries. The bibliography has now been cleaned and cross-checked so that each cited source appears only once and is consistently referred to throughout the manuscript. This revision also helped us detect and correct minor citation mismatches associated with repeated text in earlier sections.

Changes in the manuscript:

The full reference list and all in-text citations were reviewed and corrected where necessary to eliminate duplicate or inconsistent entries.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript presents a structured and interdisciplinary review of the feasibility of using recycled polylactic acid (PLA) in 3D-printed plantar orthoses. It integrates clinical, engineering, and materials science perspectives to address a relevant and timely question at the intersection of digital manufacturing and sustainable healthcare. Overall, the review is conceptually well framed, but there are important methodological, analytical, and presentation issues that should be addressed to strengthen its scientific rigor and clarity.
1. The criteria for inclusion and exclusion are broadly defined and lack the transparency expected in high-quality review articles. There is no description of databases searched, search terms, or screening procedures, which makes it difficult to assess the completeness of the evidence base.
2. A second limitation is the heterogeneity of the included studies and the absence of a quantitative synthesis. The review combines clinical trials, engineering studies, and material characterization reports, but does not attempt to standardize outcomes or compare results systematically. As acknowledged by the authors, this prevents formal meta-analysis and weakens the strength of the conclusions . While the narrative synthesis is informative, it would benefit from clearer categorization of evidence levels and more explicit weighting of findings.
3. The manuscript also exhibits an imbalance between technical detail and clinical validation. A substantial portion of the review is devoted to material properties, processing parameters, and design innovations, whereas clinical outcomes such as pressure redistribution, patient comfort, and long-term use are discussed more briefly and are supported by limited data. This imbalance reflects the underlying literature but is not sufficiently critiqued in the analysis. The review could be strengthened by a more critical appraisal of the clinical evidence and by explicitly distinguishing between proof-of-concept studies and clinically validated applications.
4. In terms of interpretation, the concept of “conditional viability” is appropriate but could be more rigorously defined. The authors identify key conditions such as feedstock traceability, process control, and clinical validation, but these are presented qualitatively rather than as measurable criteria. Providing clearer thresholds or benchmarks for material performance and clinical acceptability would improve the practical relevance of the conclusions.
5. Another issue concerns clarity and language. The manuscript contains grammatical inconsistencies, repetition, and occasional ambiguity in phrasing. For example, certain sections repeat similar statements about the growth of 3D printing waste and the interest in recycled PLA, which reduces conciseness. Technical descriptions are sometimes imprecise or difficult to follow, particularly in sections describing recycling workflows and degradation mechanisms. These issues do not invalidate the scientific content but reduce readability and should be addressed through careful editing.

Author Response

The manuscript presents a structured and interdisciplinary review of the feasibility of using recycled polylactic acid (PLA) in 3D-printed plantar orthoses. It integrates clinical, engineering, and materials science perspectives to address a relevant and timely question at the intersection of digital manufacturing and sustainable healthcare. Overall, the review is conceptually well framed, but there are important methodological, analytical, and presentation issues that should be addressed to strengthen its scientific rigor and clarity.

Response:

We appreciate the reviewer’s valuable insights regarding the scientific rigor of our manuscript and have updated the text to address these methodological and analytical points, with detailed responses and justifications provided below.

The criteria for inclusion and exclusion are broadly defined and lack the transparency expected in high-quality review articles. There is no description of databases searched, search terms, or screening procedures, which makes it difficult to assess the completeness of the evidence base.

Response:

We thank the reviewer for this valuable comment. To improve the transparency of the review methodology, we have expanded the manuscript by including a more detailed description of the literature search strategy, including the databases consulted and the search terms employed. This information has been added in the Methods section (lines 172 to 179) of the revised manuscript. 

A second limitation is the heterogeneity of the included studies and the absence of a quantitative synthesis. The review combines clinical trials, engineering studies, and material characterization reports, but does not attempt to standardize outcomes or compare results systematically. As acknowledged by the authors, this prevents formal meta-analysis and weakens the strength of the conclusions . While the narrative synthesis is informative, it would benefit from clearer categorization of evidence levels and more explicit weighting of findings.

Response:

We thank the reviewer fot this important observation. Although the combination of heterogeneous information is a limitation to obtain results with clinical evidence, these studies provided a comprenhensive  overview of the current state of research, the diversity in methodologies and reported outcomes limited the possibility of conducting to a quantitative analysis or making direct comparisions concerning recycled PLA foot orthoses.

The manuscript also exhibits an imbalance between technical detail and clinical validation. A substantial portion of the review is devoted to material properties, processing parameters, and design innovations, whereas clinical outcomes such as pressure redistribution, patient comfort, and long-term use are discussed more briefly and are supported by limited data. This imbalance reflects the underlying literature but is not sufficiently critiqued in the analysis. The review could be strengthened by a more critical appraisal of the clinical evidence and by explicitly distinguishing between proof-of-concept studies and clinically validated applications.

Response:

We agree that there was an imbalance between the technical and clinical aspects of the review. To address this, we have thoroughly revised the manuscript to include a more critical appraisal of the available clinical evidence. Furthermore, we have expanded our discussion on pressure redistribution, patient comfort, and long-term durability, while explicitly distinguishing between preliminary proof-of-concept studies and clinically validated applications.

To address this issue, the manuscript has been revised to distinguish more clearly between direct clinical evidence and indirect technical evidence. In the Materials and Methods section, we now define direct clinical evidence as studies involving orthosis-level assessment, users, plantar-pressure redistribution, gait-related outcomes, comfort, usability, adherence, or functional performance. In contrast, indirect technical evidence is defined as evidence derived from material characterization, recycling cycles, printability, degradation, viscosity, crystallinity, interlayer adhesion, and mechanical testing of specimens.

We have also revised the Results and Discussion sections to avoid overgeneralizing findings from recycled-PLA material studies to clinical orthotic performance. In particular, we now clarify that most orthosis-level studies involve virgin PLA, soft PLA, TPU, or engineered multimaterial systems, while recycled-PLA evidence remains predominantly technical and indirect. The revised manuscript therefore presents recycled PLA as a promising but conditionally viable material whose use in plantar orthoses requires further clinical validation under real-use conditions.

Changes in the manuscript:

Abstract: revised to clarify the distinction between direct clinical evidence and indirect technical evidence (lines 26–29 and 37–39).

Section 2, Materials and Methods: added a methodological explanation defining direct clinical evidence and indirect technical evidence (lines 216–222).

Section 2.2, Data extraction and synthesis: added a closing statement distinguishing material-level variables from orthosis-level performance variables (lines 248–254).

Section 2.3, Limitations of the review design: added a final clarification acknowledging the limited availability of direct clinical studies on recycled PLA orthoses (lines 259–262).

Section 3.1: expanded the classification of the reviewed study groups and clarified the type of evidence provided by each group (lines 280–285 and 294–297).

Section 3.3 / Table 1: added a new column indicating the level/type of evidence available for each material or system, together with an explanatory statement (lines 366–370).

In terms of interpretation, the concept of “conditional viability” is appropriate but could be more rigorously defined. The authors identify key conditions such as feedstock traceability, process control, and clinical validation, but these are presented qualitatively rather than as measurable criteria. Providing clearer thresholds or benchmarks for material performance and clinical acceptability would improve the practical relevance of the conclusions.

Response:

We appreciate the reviewer’s positive evaluation of the 'conditional viability' concept and agree that establishing measurable criteria enhances its practical value. Some of these parameters, e.g., temperature range for recycled PLA, linear velocity of nozzle movement, melt viscosity of solidification rate already are listed in Table 2. In the revised manuscript (Section 4.2), we have introduced quantitative benchmarks for viscosity, changes in crystallinity and other mechanical properties (Table 4). This numerical framework significantly strengthens the practical relevance of our conclusions.

Changes in the manuscript:

Table 2: includes relevant data for extrusion temperature, nozzle temperature, printing speed, melt flow index and cooling rate.

Page 13, section 4.2.1: information about viscosity changes.

Page 14, section 4.3: inromation about mechanical properties related to recycling.

Another issue concerns clarity and language. The manuscript contains grammatical inconsistencies, repetition, and occasional ambiguity in phrasing. For example, certain sections repeat similar statements about the growth of 3D printing waste and the interest in recycled PLA, which reduces conciseness. Technical descriptions are sometimes imprecise or difficult to follow, particularly in sections describing recycling workflows and degradation mechanisms. These issues do not invalidate the scientific content but reduce readability and should be addressed through careful editing.

Response:

To address the concerns regarding clarity, conciseness, and language, we have thoroughly revised the entire manuscript. Specifically, we have implemented the following changes:

• Removed redundancies: we eliminated repetitive statements concerning the growth of waste and the general interest in recycled PLA, ensuring a more direct and concise narrative.
• Improved technical clarity: we carefully rephrased the technical descriptions within the sections detailing the recycling workflows and degradation mechanisms to ensure they are precise and easy to follow.
• Professional proofreading: the manuscript has undergone a comprehensive grammatical and linguistic review to correct any inconsistencies and eliminate phrasing ambiguities.

Changes in the manuscript:

Removal of redundancies, improved technical clarity and grammatical and linguistic review has been carried out throughout the text.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript addresses an emerging and interdisciplinary topic at the intersection of clinical podiatry, additive manufacturing, biomaterials, and circular economy. The integration of plantar orthosis design with recycled PLA-based additive manufacturing is timely and potentially relevant for both biomedical engineering and sustainable healthcare manufacturing. The manuscript presents a broad synthesis of clinical, engineering, and material science literature.

Comments:

1. Review methodology lacks scientific rigor (Pages 5–6)

   • The manuscript does not clearly describe the literature search strategy, databases used, keywords, or study selection criteria.

   • The review methodology should be better defined to ensure reproducibility and scientific transparency.

2. Repetition and structural redundancy in Introduction (Pages 2–3)

   • Several concepts related to 3D printing waste, sustainability, and recycled PLA are repeated multiple times, affecting the flow and clarity of the introduction.

   • The introduction should be condensed and better organized.

3. Language and grammatical issues throughout the manuscript (Pages 11–15 and other sections)

   • Multiple grammatical errors, awkward sentence constructions, and typographical inconsistencies reduce readability and scientific quality.

   • Thorough language editing is strongly recommended.

4. Limited direct clinical evidence supporting recycled PLA use (Pages 8–10, 15–16)

   • Most conclusions regarding recycled PLA are based on material-level or process-level studies rather than direct orthosis-based clinical validation.

   • The manuscript should more clearly distinguish direct clinical evidence from indirect technical evidence.

Comments on the Quality of English Language

Author Response

This manuscript addresses an emerging and interdisciplinary topic at the intersection of clinical podiatry, additive manufacturing, biomaterials, and circular economy. The integration of plantar orthosis design with recycled PLA-based additive manufacturing is timely and potentially relevant for both biomedical engineering and sustainable healthcare manufacturing. The manuscript presents a broad synthesis of clinical, engineering, and material science literature.

Response:

We thank the reviewer for the positive assessment of our paper. We appreciate the recognition of its interdisciplinary nature and its relevance to clinical podiatry, additive manufacturing, biomaterials, and circular economy. We have revised the manuscript to further clarify these contributions and improve overall coherence. 

Review methodology lacks scientific rigor (Pages 5–6)

o         The manuscript does not clearly describe the literature search strategy, databases used, keywords, or study selection criteria.

o         The review methodology should be better defined to ensure reproducibility and scientific transparency.

Response:

We thank the reviewer for this valuable comment. In response to this observation, we have revised the  methodology  section in order to clarify the  literature search strategy including the databases consulted and the keywords employed. These modifications have been incorporated into line 207 of the revised manuscript.

Repetition and structural redundancy in Introduction (Pages 2–3)

o         Several concepts related to 3D printing waste, sustainability, and recycled PLA are repeated multiple times, affecting the flow and clarity of the introduction.

o         The introduction should be condensed and better organized.

Response:

Thank you for this comment. The Introduction has been revised to reduce repetition and improve its structure. Redundant statements regarding 3D printing waste, sustainability, and recycled PLA have been removed or merged. The section has been reorganized into a more concise sequence: clinical relevance of plantar orthoses, conventional and digital manufacturing methods, additive manufacturing and sustainability, recent PLA-based orthotic developments, and the specific knowledge gap addressed by this review.

Changes in the manuscript:

Introduction section has been rewritten, reducing redundancies and improving technical description. Also, it has been condensed and re-organized.

Language and grammatical issues throughout the manuscript (Pages 11–15 and other sections)

• Multiple grammatical errors, awkward sentence constructions, and typographical inconsistencies reduce readability and scientific quality.
• Thorough language editing is strongly recommended.

Response:

To address the concerns regarding clarity, conciseness, and language, we have thoroughly revised the entire manuscript. Specifically, we have implemented the following changes:

• Removed redundancies: we eliminated repetitive statements concerning the growth of waste and the general interest in recycled PLA, ensuring a more direct and concise narrative.
• Improved technical clarity: we carefully rephrased the technical descriptions within the sections detailing the recycling workflows and degradation mechanisms to ensure they are precise and easy to follow.
• Professional proofreading: the manuscript has undergone a comprehensive grammatical and linguistic review to correct any inconsistencies and eliminate phrasing ambiguities.

Changes in the manuscript:

Removal of redundancies, improved technical clarity and grammatical and linguistic review has been carried out throughout the text.

Limited direct clinical evidence supporting recycled PLA use (Pages 8–10, 15–16)

o         Most conclusions regarding recycled PLA are based on material-level or process-level studies rather than direct orthosis-based clinical validation.

o         The manuscript should more clearly distinguish direct clinical evidence from indirect technical evidence.

Response:

We thank the reviewer for this valuable comment. We agree that the current evidence supporting recycled PLA in plantar orthoses is mainly indirect and derives largely from material-level, filament-level, specimen-level, or process-level studies rather than from direct clinical validation of complete orthotic devices.

To address this issue, the manuscript has been revised to distinguish more clearly between direct clinical evidence and indirect technical evidence. In the Materials and Methods section, we now define direct clinical evidence as studies involving orthosis-level assessment, users, plantar-pressure redistribution, gait-related outcomes, comfort, usability, adherence, or functional performance. In contrast, indirect technical evidence is defined as evidence derived from material characterization, recycling cycles, printability, degradation, viscosity, crystallinity, interlayer adhesion, and mechanical testing of specimens.

We have also revised the Results and Discussion sections to avoid overgeneralizing findings from recycled-PLA material studies to clinical orthotic performance. In particular, we now clarify that most orthosis-level studies involve virgin PLA, soft PLA, TPU, or engineered multimaterial systems, while recycled-PLA evidence remains predominantly technical and indirect. The revised manuscript therefore presents recycled PLA as a promising but conditionally viable material whose use in plantar orthoses requires further clinical validation under real-use conditions.

Changes in the manuscript:

Abstract: revised to clarify the distinction between direct clinical evidence and indirect technical evidence (lines 26–29 and 37–39).

Section 2, Materials and Methods: added a methodological explanation defining direct clinical evidence and indirect technical evidence (lines 216–222).

Section 2.2, Data extraction and synthesis: added a closing statement distinguishing material-level variables from orthosis-level performance variables (lines 248–254).

Section 2.3, Limitations of the review design: added a final clarification acknowledging the limited availability of direct clinical studies on recycled PLA orthoses (lines 259–262).

Section 3.1: expanded the classification of the reviewed study groups and clarified the type of evidence provided by each group (lines 280–285 and 294–297).

Section 3.3 / Table 1: added a new column indicating the level/type of evidence available for each material or system, together with an explanatory statement (lines 366–370).

New Section 6.1, “Direct and indirect evidence supporting recycled PLA”: added a dedicated section distinguishing direct clinical evidence from indirect technical evidence for recycled PLA (lines 694–708).

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have addressed most of the issues satisfactorily. However, to improve the technical soundness, a discussion covering the following points should be incorporated-
1. What is the difference between virgin PLA and recycled PLA in terms of molecular, mechanical, and rheological properties?
2. How the recycling process and number of recycling cycles affect those.
3. Practical implications of mixing virgin and recycled PLA
4. Since there is a growing trend of using glass/ carbon-fiber reinforced materials, how does that affect the recyclability and further usage.

Author Response

Reviewer comments

1. What is the difference between virgin PLA and recycled PLA in terms of molecular, mechanical, and rheological properties?

Response to reviewer: Thank you for this observation. We agree that the distinction between virgin PLA and recycled PLA needed to be made more explicit in the Discussion section. In the revised manuscript, we now clarify that virgin PLA and recycled PLA should not be considered equivalent materials. The new text discusses differences at three levels: molecular, mechanical, and rheological.

Action taken: We expanded the opening part of the Discussion to include a detailed comparison between virgin PLA and recycled PLA in terms of molecular structure, mechanical performance, and rheological behaviour (lines 627-657).

2. How the recycling process and number of recycling cycles affect those.

Response to reviewer: Thank you for pointing this out. We agree that the effect of the recycling process and the number of recycling cycles should be discussed more clearly. In the revised manuscript, we now explain that mechanical recycling generally involves collection, sorting, washing, shredding, drying, extrusion, and either filament production for FDM or direct granule-based fabrication.

Action taken: We added a new paragraph to the Discussion explaining that the recycling history of PLA is a key determinant of material reliability and should not be treated as a secondary variable. The revised text emphasizes that a recycled PLA feedstock subjected to one controlled reprocessing cycle cannot be assumed to behave like material that has undergone several uncontrolled cycles (lines 665-678).

3. Practical implications of mixing virgin and recycled PLA.

Response to reviewer: Thank you for this suggestion. We have expanded the Discussion to address virgin/recycled PLA blends as a practical strategy for balancing sustainability and functional reliability. The revised text explains that adding virgin PLA to recycled PLA can partially compensate for the loss of molecular weight and mechanical performance associated with recycling.

Action taken: We added a paragraph discussing the practical implications of mixing virgin and recycled PLA. The revised manuscript now states that blended materials may be more realistic for near-term orthotic applications than fully recycled PLA, because they reduce some of the risks associated with recycled feedstocks (lines 679-692).

4. Since there is a growing trend of using glass/carbon-fiber reinforced materials, how does that affect the recyclability and further usage.

Response to reviewer: Thank you for raising this point. We agree that the increasing use of glass- and carbon-fiber-reinforced filaments has implications for both mechanical performance and recyclability. The revised Discussion now explains that fiber reinforcement may improve stiffness, dimensional stability, and load-bearing capacity, which can be attractive for selected structural zones of plantar orthoses. However, reinforced PLA should not be treated as equivalent to unfilled PLA from a circular-economy perspective.

Action taken: We added a specific discussion of glass- and carbon-fiber-reinforced PLA systems. The revised text states that repeated recycling may shorten or damage fibers, reduce reinforcement efficiency, increase heterogeneity, and lead to more abrasive feedstock for FDM nozzles. We also clarify that although fiber-reinforced PLA may improve mechanical performance during the first use cycle, it can reduce material circularity and complicate further reuse unless a specific end-of-life and reprocessing route is defined. (Lines 693-705).

Author Response File: Author Response.pdf