Evaluation of Bond Strength in Multi-Material Specimens Using a Consumer-Grade LCD 3D Printer^†

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Author,

I have provided comments aimed at further highlighting and strengthening the presentation of the project. Please find the document attached.

Best regards

Comments for author File: Comments.pdf

Author Response

Comment (A1): Introduction

• The introduction outlines general trends in additive manufacturing and multi-material

3D printing. What technical or scientific gap is being filled? For instance, is the

contribution in demonstrating the feasibility of low-cost resins, in quantifying bond

strength vs. curing parameters, or in benchmarking adhesive vs. co-printed joints?

• Prior studies on DLP and SLA multi-material printing are cited. Since ABS-like and

Tough resins are widely studied, what makes this work unique beyond being

performed on a personal LCD printer?

• The objective is presented as “demonstrating sufficient bond strength for practical 

use”.? Could the authors reformulate the aim toward providing design

guidelines, critical parameter thresholds, or scalability for consumer-level

applications?

Response (A1): We agree that research gaps and unique contributions needed to be more clearly articulated. In the revised introduction, we clarify that this study addresses the lack of systematic guidelines for multi-material LCD printing using unmodified consumer printers and commercially available photopolymer resins. Our contributions include:

 

Demonstrating that a consumer LCD printer and commercially available 405 nm resin can achieve adhesive strengths comparable to those of single-material parts without machine modifications.

 

Providing quantitative relationships between exposure time, post-cure time, and mechanical properties such as ultimate tensile strength and elongation, thereby identifying critical thresholds for reliable interfacial adhesion (e.g., multi-material printing requires 8 seconds or more of exposure and 30 minutes or more of post-cure to reach 90% or more of the strength of weaker resins).

 

Comparing co-printed joints and adhesive bonds on identical geometries, we find that co-printed joints outperform cyanoacrylate adhesive specimens.

 

We provide design guidance for hobbyists and engineers (including recommendations for selecting exposure/post-cure parameters and predicting the strength-ductility trade-off) to support scalability to consumer applications.

 

We clarified that ABS-like and tough resins were selected because they encompass the typical range of stiffness and ductility for hobbyist LCD resins. This allows us to investigate the interfacial bonding of commercially popular materials with contrasting cure rates. The safety data sheets for these resins provide their chemical properties and tensile strength, allowing for reproducible benchmarking. We plan to expand our research to include flexible and high-strength resins in the future.

Revisions made: Introduction (P3L101–L125): We added a paragraph explicitly comparing prior DLP/SLA studies to our approach and stating that those works relied on industrial equipment or special resins, whereas our study uses a consumer‑grade LCD printer and widely available resins (ABS‑Like and Tough). We also clarified that we evaluate bond strength and tensile properties across different exposure and curing times, which has not been reported previously.

 

Comment (A2): Materials and Methods

• Were specimens oriented in a consistent build direction? Orientation strongly affects

mechanical properties.

• Was resin stirring or homogenization performed between material switches to avoid

phase separation or sedimentation?

• How were surface contaminants removed between resin changes to ensure reliable

interfacial bonding?

• The study uses only two resin types (ABS-like and Tough). The authors should justify

why these materials were chosen as representative. Are they chemically compatible,

or do they have contrasting curing kinetics?

Response (A2):

Build Orientation: All test specimens (single-material and multi-material) were printed in the same vertical direction to minimize mechanical property variations due to layer-to-layer anisotropy. The build orientation and support strategy were selected based on software recommendations and kept constant for all groups.

 

Resin Mixing/Homogenization: Before each print, the resin was mixed to ensure uniformity and prevent settling or phase separation. When switching materials, the resin tank was replaced, and the second resin was mixed immediately before use.

 

Surface Cleaning: To minimize interface contamination, residual resin from the first material was removed with 70% isopropyl alcohol and a lint-free wipe. The second resin was then filled. This procedure is now clearly described in the Methods section.

 

Resin Selection: As mentioned in Comment 1, ABS-like and Tough resins were selected for their contrasting mechanical properties and availability. We note that these resins provide a representative test case due to slightly different photoinitiator compositions and curing rates. We also recognize that using only two materials limits generalizability. Future research will explore flexibility, toughness, and bio-based resins.

Revisions made:Method(P5L167-169)

 

Comment (A3):

• Figures 7–10 show trends in tensile strength and elongation. Could the authors add

error bars, standard deviations, and possibly ANOVA/t-tests to determine

significance between groups?

• The manuscript claims that “rupture can occur outside of the bonding plane,” but then 

states elongation does not represent bond-plane strength. This inconsistency should

be clarified.

• Dimensional shrinkage at the bonding interface is reported but not quantified. Could

microscopy or profilometry be used to support these observations?

• Elongation data are interpreted cautiously, but the lack of fractography (optical or

SEM images) limits understanding of failure modes. A visual characterization of

fracture surfaces would significantly strengthen conclusions.

• Exposure time effects are reported; overcuring and crosslink density are briefly

mentioned; could FTIR or DSC be used to substantiate claims about network

formation and brittleness?

Response (A3): Thank you for your comments regarding the results. I also provided error bars and statistical analysis, as well as observation of the fracture surface and shrinkage values. The chemical analysis was limited due to equipment limitations and my focus on statistical analysis. Regarding the contradiction, some test pieces did not break in the middle. However, since elongation represents the entire piece, it is not believed to represent the strength of a specific surface, so this is not necessarily a contradiction.

Revisions made:
Result: Figure8-11, Add Observation

Result: Figure6-18, Graph revision

Result: P10L268–L289,P11L296-304, P12L325-P13L343, P13L360-P14L399, P14L411-P15L423, P15L434-L447, P16L458-L464, Add statistics

 

Comment (A4):

 Discussion

• Why does ABS strength decrease after 8 s exposure while TOUGH increases? Is this

due to resin chemistry, crosslink density, or printer calibration limits?

• The trade-off between tensile strength and elongation after secondary curing is

observed, but not sufficiently explained in terms of molecular mechanisms.

• Comparisons to prior literature are made, but the discussion does not highlight what

is fundamentally new. Several cited studies already report similar exposure/curing

effects. The authors should emphasize the novelty: is it that consumer-grade LCD

printers can achieve bond strengths comparable to single-material parts?

• Practical implications are missing. Could the authors suggest specific applications or

design recommendations, where these findings are valuable?

Response (A4): Thank you for your questions and comments regarding the discussion.

There is a wide range of results regarding the behavior of each individual material, which is thought to be due to the chemical density of the resin. However, each test often uses specialized tools, making it difficult to reach a unified view.

Regarding trade-offs, there is not much novelty in individual materials, and their molecular mechanisms are likely to be determined by previous research. We decided that making any statements without molecular testing would increase uncertainty.

Statistical correlations indicate that the strength is comparable to that of single materials.

Regarding practical implications, we actually fabricated the materials and reported on the results.

Revisions made: Result: Figure6-18

Revisions made: P18L550-L600

 

Comment (A5):

• The conclusions largely repeat results. They should provide quantitative

takeaways (“bond strength reached >90 of the weaker resin’s strength at 8 s?

exposure”).

• The claim that “there is no problem in using the resin for personal use in terms of 

strength” is too general. Are there limitations in elongation, durability, or

environmental resistance that users should consider?

• A forward-looking statement would add value: potential use of different resin

chemistries, incorporation of interface engineering, or extension to functionally

graded materials.

Response (A5): Under optimized conditions (exposure time ≥ 8 seconds, post-cure time ≥ 30 minutes), multi-material specimens reached 90-114% of the ultimate tensile strength of the weaker resin, indicating that bond strength is not a limiting factor for personal applications.

 

Note that elongation decreased to approximately 40-50% of that of single-resin specimens, and further evaluation of long-term durability (fatigue, UV resistance, etc.) and environmental factors is required.

 

Future research is proposed to investigate different resin chemistries (flexible, bio-resins), interface engineering approaches (surface treatments, interlocking geometries), and functionally graded materials for tailoring mechanical gradients.

 

These were modified, focusing on limitations. Furthermore, actual fabrication and implementation were carried out.

Revisions made: P18L550-L600

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript explores bond strength in LCD-SLA multi-material prints using consumer resins , testing exposure time and post-cure on tensile performance of single- and bi-material coupons. The work is timely, but as written it falls short on novelty framing and experimental controls at the resin–resin interface as detailed below:

1. The paper claims practicality of multi-material LCD printing, but prior DLP/LCD multimaterial studies (and even consumer modifications) are already cited by the authors; the manuscript doesn’t clearly articulate what is "new" beyond using two shelf resins on a consumer LCD printer. Spell out the unique contribution.
2. Ultimate tensile tests on dog-bones mostly probe bulk and Z-anisotropy, not interfacial adhesion. Without dedicated interfacial tests (single-lap shear, peel/T-peel, butt-joint fracture, or notched interface specimens), it’s difficult to support claims about bond strength. Add interfacial-geometry tests and report cohesive vs adhesive failure with fractography (optical/SEM) at the resin–resin plane.
3. Reporting only layer exposure time (s) is insufficient; irradiance (mW·cm⁻²) and thus dose (mJ·cm⁻²) determine conversion and crosslink density. Provide a radiometric calibration (e.g., 405 nm power at the vat floor) and compute dose per layer; otherwise, the process window cannot be reproduced or generalized to other LCD engines.
4. Fig. 5 caption reads like a “conceptual diagram” but appears to show print outcomes; ensure the image and caption match. Several figures lack error bars and axis units/labels with sufficient font size.

Author Response

Comment (A1): The paper claims practicality of multi-material LCD printing, but prior DLP/LCD multimaterial studies (and even consumer modifications) are already cited by the authors; the manuscript doesn’t clearly articulate what is "new" beyond using two shelf resins on a consumer LCD printer. Spell out the unique contribution..

Response (A1): Thank you for pointing out the need to state our contribution more clearly. We agree that early versions of the manuscript focused more on summarising existing work than on highlighting the gap we address. Our study is the first, to our knowledge, to systematically evaluate the feasibility of multi‑material printing with commercially available photopolymer resins on a consumer‑grade LCD printer, and to quantify how exposure time and post‑curing conditions affect tensile properties and bond strength between dissimilar materials. Previous studies using DLP or SLA platforms generally involved proprietary machines or specialised resins, whereas our work uses low‑cost materials and equipment accessible to hobbyists. This advances the field by demonstrating the practicality of multi‑material LCD printing for personal use and by analysing the effects of process parameters on both strength and elongation.

Revisions made: Introduction (P3L101–L125): We added a paragraph explicitly comparing prior DLP/SLA studies to our approach and stating that those works relied on industrial equipment or special resins, whereas our study uses a consumer‑grade LCD printer and widely available resins (ABS‑Like and Tough). We also clarified that we evaluate bond strength and tensile properties across different exposure and curing times, which has not been reported previously.

 

Comment (A2): Ultimate tensile tests on dog-bones mostly probe bulk and Z-anisotropy, not interfacial adhesion. Without dedicated interfacial tests (single-lap shear, peel/T-peel, butt-joint fracture, or notched interface specimens), it’s difficult to support claims about bond strength. Add interfacial-geometry tests and report cohesive vs adhesive failure with fractography (optical/SEM) at the resin–resin plane.

Response (A2): Thank you for underscoring the importance of dedicated interfacial testing. We fully agree that single-lap shear, peel/T-peel, butt-joint, or notched-interface geometries are more specific to resin–resin adhesion than dog-bone tension tests.

 

For this revision, however, adding those additional test modes proved impractical. On desktop LCD printers the measured strength is strongly affected by build orientation, support strategy, and local dose heterogeneity; moreover, forcing fracture to initiate precisely at the printed interface without introducing new geometric notches is non-trivial. Given these sources of variability, we were concerned that a small, quickly added set of interfacial-geometry tests would be under-powered and potentially misleading within the current timeline.

 

To address your concern without over-extending the experimental scope, we have taken the following steps and toned down claims accordingly:

 

Justification of the chosen metric. We retained tensile test because it is the predominant approach in recent multi-material stereolithography studies, enabling direct comparability across papers.

 

Fracture-mode documentation. We added representative fracture photographs (optical) to classify cohesive vs. adhesive outcomes at the resin–resin plane. These images are annotated in the Results, and we discuss how low-dose or no post-cure conditions more often show interfacial indications, whereas adequately cured conditions tend to fail in the weaker matrix.

 

Controls and reporting. We clarify in Methods that all bi-material dog-bones were fabricated with the same build orientation and support policy, the interface centered in the gauge and normal to the loading axis, and that visibly defective specimens were excluded a priori.

 

Limitations and future work. The Discussion and Conclusion now explicitly state that our adhesion claims are inferred from tension tests plus fracture-mode inspection, and we outline a plan for single-lap shear and T-peel with dose-calibrated interlayers and SEM fractography in subsequent work.

 

We hope this strikes a balance between acknowledging the limitation and strengthening the evidence base in the current manuscript.

Revisions made:Introduction (P8L232)

 

Comment (A3): Reporting only layer exposure time (s) is insufficient; irradiance (mW·cm⁻²) and thus dose (mJ·cm⁻²) determine conversion and crosslink density. Provide a radiometric calibration (e.g., 405 nm power at the vat floor) and compute dose per layer; otherwise, the process window cannot be reproduced or generalized to other LCD engines.

Response (A3): As you pointed out, the photocuring reaction depends not only on the exposure time but also on the exposure intensity and cumulative dose. In this study, a UV light meter (AH-NUV 405nm/385nm) was installed on the LCD panel of the printer (Elegoo Mars 4 Ultra) used, and the irradiance (mW/cm²) at each exposure point was measured. Similar measurements were also performed on the post-curing device (Form Cure) to determine the irradiance under standard conditions.Revisions made: Discussion (P5L173–L182)

 

Comment (A4): Fig. 5 caption reads like a “conceptual diagram” but appears to show print outcomes; ensure the image and caption match. Several figures lack error bars and axis units/labels with sufficient font size.

Response (A4): Regarding the discrepancy between the caption and the figure content in Figure 5, in the previous version, the caption was not updated after the text and figure were replaced. In the revised version, the figure and caption have been revised to accurately represent the experimental content.

Revisions made: Result: Figure6-18

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

1. The manuscript explores multi-material bond strength using a consumer-grade LCD 3D printer, which is relevant and timely. However, the novelty compared to prior DLP and SLA-based studies should be clarified more explicitly. Currently, the introduction cites prior works but does not sufficiently distinguish how this study advances beyond them.
2. While the abstract and introduction mention verifying bond strength and effects of exposure/curing, the research objectives are scattered. A concise statement of hypotheses or research questions at the end of the introduction would strengthen the framing.
3. Only two commercial resins (ABS-Like and Tough) were used. While this is acceptable as a pilot study, the paper would benefit from a justification of why these two were chosen over other widely available consumer resins (e.g., flexible or high-strength variants). Without this, the generalizability of findings is limited.
4. The manuscript reports average tensile strength and elongation values but lacks statistical analysis (ANOVA, Tukey, or confidence intervals). This omission makes it difficult to judge whether observed differences between exposure times, curing times, or material combinations are statistically significant.
5. Some figures (e.g., Figures 7–10) include bar charts without error bars. Adding standard deviations or error bars would improve scientific rigor. Moreover, figure captions are sometimes too brief and do not provide a clear explanation of what the reader should interpret.
6. The discussion often reiterates results rather than critically interpreting them. For example, the trade-off between tensile strength and elongation after post-curing is acknowledged but not linked to resin chemistry or polymer network behavior in detail. A more mechanistic explanation would enhance impact.
7. The conclusion suggests multi-material LCD printing is “sufficiently practical” for personal use. However, the implications for specific application domains (e.g., medical devices, engineering prototypes) are not well developed. Including case-use scenarios or limitations, such as biocompatibility issues, would make the findings more useful.
8. You can improve it by adding the most recent articles that align with your study, such as https://doi.org/10.1007/s00170-024-14820-0, https://doi.org/10.1007/s40964-024-00684-z, DOI: 10.1007/s40964-025-01257-4, DOI: 10.1007/s40964-025-01201-6
9. While the manuscript is generally understandable, there are several grammatical inconsistencies (e.g., “a ention” instead of “attention,” “bo om” instead of “bottom”) that distract from readability. Careful proofreading and editing are recommended. Also, references [7–13] rely heavily on news articles and web sources; a stronger emphasis on peer-reviewed literature would improve credibility.

Author Response

Comment (A1): The manuscript explores multi-material bond strength using a consumer-grade LCD 3D printer, which is relevant and timely. However, the novelty compared to prior DLP and SLA-based studies should be clarified more explicitly. Currently, the introduction cites prior works but does not sufficiently distinguish how this study advances beyond them.

Response (A1): Thank you for pointing out the need to state our contribution more clearly. We agree that early versions of the manuscript focused more on summarising existing work than on highlighting the gap we address. Our study is the first, to our knowledge, to systematically evaluate the feasibility of multi‑material printing with commercially available photopolymer resins on a consumer‑grade LCD printer, and to quantify how exposure time and post‑curing conditions affect tensile properties and bond strength between dissimilar materials. Previous studies using DLP or SLA platforms generally involved proprietary machines or specialised resins, whereas our work uses low‑cost materials and equipment accessible to hobbyists. This advances the field by demonstrating the practicality of multi‑material LCD printing for personal use and by analysing the effects of process parameters on both strength and elongation.

Revisions made: Introduction (P3L101–L125): We added a paragraph explicitly comparing prior DLP/SLA studies to our approach and stating that those works relied on industrial equipment or special resins, whereas our study uses a consumer‑grade LCD printer and widely available resins (ABS‑Like and Tough). We also clarified that we evaluate bond strength and tensile properties across different exposure and curing times, which has not been reported previously.

 

Comment (A2): While the abstract and introduction mention verifying bond strength and effects of exposure/curing, the research objectives are scattered. A concise statement of hypotheses or research questions at the end of the introduction would strengthen the framing.

Response (A2): We appreciate this suggestion and agree that a clearer statement of objectives helps readers follow the study design. (1) What minimum exposure time allows stable multi‑material printing on a consumer LCD printer? (2) How do differences in exposure time and post‑curing duration affect tensile strength and elongation of both single‑material and multi‑material specimens? (3) Can strength and elongation be manipulated by adjusting printing parameters when bonding dissimilar resins? These questions frame our experiments and results.

Revisions made:Introduction (P3L101–L125): Corrections have been made in line with question A1.

 

Comment (A3): Only two commercial resins (ABS-Like and Tough) were used. While this is acceptable as a pilot study, the paper would benefit from a justification of why these two were chosen over other widely available consumer resins (e.g., flexible or high-strength variants). Without this, the generalizability of findings is limited.

Response (A3): Thank you for raising this point. We selected the ABS‑Like and Tough resins because they represent two ends of the stiffness spectrum among common LCD photopolymers: ABS‑Like is relatively rigid with higher tensile strength, while Tough has higher ductility and impact resistance. These contrasting properties make them suitable for studying interfacial bonding in dissimilar materials. We acknowledge that additional resins (e.g., flexible or highly reinforced types) could broaden applicability, but our goal in this pilot study was to establish baseline behaviour with two widely used resins. We note this limitation and propose exploring more resins in future work.

Revisions made:

Revisions made: Discussion (P18L569–L571): We added a sentence recognising that the findings may not generalise to all resin types and suggesting future studies using flexible or high‑strength variants.

 

Comment (A4): The manuscript reports average tensile strength and elongation values but lacks statistical analysis (ANOVA, Tukey, or confidence intervals). This omission makes it difficult to judge whether observed differences between exposure times, curing times, or material combinations are statistically significant.

Response (A4): Thank you for pointing this out. I agree with your comment and have added statistical results to each result.

Revisions made:

Revisions made: Result: P10L268–L289,P11L296-304, P12L325-P13L343, P13L360-P14L399, P14L411-P15L423, P15L434-L447, P16L458-L464

 

Comment (A5): Some figures (e.g., Figures 7–10) include bar charts without error bars. Adding standard deviations or error bars would improve scientific rigor. Moreover, figure captions are sometimes too brief and do not provide a clear explanation of what the reader should interpret.

Response (A5): Thank you for pointing this out. I agree with your comment and have added error bars to each result.

Revisions made: Result: Figure12-18

 

Comment (A6): The discussion often reiterates results rather than critically interpreting them. For example, the trade-off between tensile strength and elongation after post-curing is acknowledged but not linked to resin chemistry or polymer network behavior in detail. A more mechanistic explanation would enhance impact.

Response (A6): Thank you for pointing this out. I have included it in my discussion, but since it is impossible to make a definitive conclusion based on experimental data and previous research, I have noted this in the limitations.

Revisions made: Limitation and future trends:  P19L583-584

 

Comment (A7): The conclusion suggests multi-material LCD printing is “sufficiently practical” for personal use. However, the implications for specific application domains (e.g., medical devices, engineering prototypes) are not well developed. Including case-use scenarios or limitations, such as biocompatibility issues, would make the findings more useful.

Response (A7): We agree that discussing potential applications and limitations adds value. In the revised Conclusion we elaborate on possible uses, such as prototyping functional parts with gradients of stiffness (e.g., splints combining rigid and flexible sections), customised orthotic devices, and educational models. We also caution that our findings relate to mechanical feasibility; issues such as biocompatibility, long‑term environmental stability, and performance of flexible or reinforced resins must be addressed before adoption in medical devices. Additionally, we note that although the bond strength achieved is comparable to single‑material parts, applications requiring very high loads may still require reinforced joints or alternative bonding techniques.

Revisions made: Limitation and future trends:  P19L585-600

 

Comment (A8): You can improve it by adding the most recent articles that align with your study, such as https://doi.org/10.1007/s00170-024-14820-0, https://doi.org/10.1007/s40964-024-00684-z, DOI: 10.1007/s40964-025-01257-4, DOI: 10.1007/s40964-025-01201-

Response (A8): Thank you for directing us to these recent publications. We have incorporated these articles where relevant.

 

Comment (A9): While the manuscript is generally understandable, there are several grammatical inconsistencies (e.g., “a ention” instead of “attention,” “bo om” instead of “bottom”) that distract from readability. Careful proofreading and editing are recommended. Also, references [7–13] rely heavily on news articles and web sources; a stronger emphasis on peer-reviewed literature would improve credibility.

Response (A9): Thank you for this helpful observation. We have conducted a thorough language edit and corrected typographical and grammatical issues throughout. Regarding the specific phrases you noted, we searched the entire manuscript but could not locate those exact instances. If you could kindly indicate the page and line numbers, we will correct them immediately.

With respect to references, we have replaced news- and web-based sources with peer-reviewed literature wherever an equivalent scholarly citation exists. The few remaining web citations are limited to manufacturer technical datasheets and product specifications (e.g., nominal resin composition and tensile properties) for which no archival publications are available. These are necessary to identify the exact materials used and to report baseline specifications for proprietary consumer resins.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Author,

Thank you for addressing the comments provided. I wish you success with this and your future projects.

Best regards.

Author Response

Comment
Dear Author,

Thank you for addressing the comments provided. I wish you success with this and your future projects.

Best regards.

We sincerely appreciate the positive evaluation and the valuable suggestions provided in the previous round. For this final resubmission, we addressed the Academic Editor’s comments and conducted a final check for consistency in figures (graphs), language, formatting, and references, making minor editorial corrections. These changes do not affect the results, analyses, or conclusions in any way.
We are grateful for your guidance, which has helped improve the quality of the manuscript. Thank you again.
—Shunpei Shimizu, on behalf of all authors

Reviewer 2 Report

Comments and Suggestions for Authors

Comments have been addressed. Recommended for acceptance to publication

Author Response

Comment
Comments have been addressed. Recommended for acceptance to publication

We are grateful for the encouraging assessment and the recommendation for acceptance. For this final version, we addressed the Academic Editor’s comments as well and confirmed that all prior reviewer comments have been fully incorporated. We also conducted a final pass to harmonize figure labeling, terminology, language, and reference formatting, making only minor editorial/typographical corrections. These changes do not affect the results, analyses, or conclusions.
Thank you again for your time and support.
—Shunpei Shimizu, on behalf of all authors

Reviewer 3 Report

Comments and Suggestions for Authors

I am not satisfied with the response. 

Author Response

Comment
I am not satisfied with the response. 

We apologize that our previous response did not fully meet your expectations. In this revision—also addressing the Academic Editor’s comments—we improved the figures/tables and statistics, and unified language. These are minor editorial refinements only; the results, analyses, and conclusions remain unchanged. We hope this resolves your concerns.