3D Printing of Polyvinyl Alcohol for Meniscus Implant Fabrication

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Guerra, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6609618/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 10 Jul, 2025 Read the published version in The International Journal of Advanced Manufacturing Technology → Version 1 posted 5 You are reading this latest preprint version Abstract Meniscectomy is a common surgical procedure to treat meniscal injuries, but it often leads to long-term complications such as osteoarthritis. Polyvinyl alcohol (PVA) hydrogel implants offer a promising alternative due to their viscoelastic properties, which closely mimic the natural meniscus. However, conventional manufacturing methods rely on manual shaping, which limits precision and customization. This study explores the feasibility of 3D printing PVA hydrogels by direct ink writing (DIW) for patient-specific meniscus implants. A syringe-based extrusion system was developed and printing parameters were optimized using a factorial design experiment, evaluating the effects of speed and flow rate on dimensional accuracy and layer scaling. In addition, tensile tests and post-treatments, including autoclaving, demonstrated that the printed PVA structures could achieve mechanical properties comparable to those of native meniscus. In addition, a molding method validated the formation of meniscus-shaped structures with shock absorption capabilities. Future research should focus on refining printing methods that provide structural support during fabrication to achieve reliable 3D architectures. This work demonstrates the potential of 3D printed PVA hydrogels for meniscal replacement, offering a possible approach for the manufacture of customized implants. Polyvinyl alcohol Direct Ink Write Meniscus Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction Meniscectomy is the most common surgical procedure for treating meniscal injuries in hospitals, as it currently provides the best clinical outcomes. However, despite its effectiveness, meniscectomy often leads to long-term complications such as osteoarthritis and joint degeneration [ 1 ]. Recent studies suggest that replacing the meniscus with a PVA hydrogel implant may lead to improved long-term results. This has been demonstrated in a two-year in vivo study using a rabbit model, where PVA implants showed potential in preserving joint function and delaying osteoarthritis progression [ 2 ]. Given these results, research has focused on modifying the mechanical properties of PVA to enhance its suitability for meniscal replacement. Several strategies have been investigated, including annealing treatments, which enhance polymer stability and mechanical strength, freeze-thaw cycles, which induce physical crosslinking [ 2 ], [ 3 ], salt treatments, which modify the hydrogel's thermal and structural properties to enhance load-bearing capacity etc. [ 3 ]. These conclude that PVA is a promising candidate for meniscal implants, as it closely mimics the viscoelastic and mechanical properties of the natural meniscus if subjected to a certain post-treatment [ 1 ]. However, current manufacturing methods involve first synthesizing the material and then manually shaping it. For example, in previous studies, PVA menisci were prepared by dissolving the PVA in a solvent, subjecting it to controlled freezing and thawing, and then annealing it to optimize mechanical performance [ 2 ]. They were then manually cut with a scalpel. Since meniscectomy remains the standard surgical procedure, the in situ cutting of the implants is not an effective method to create patient-specific prostheses. Also considering that implant misalignment is one of the leading causes of failure in meniscal replacement. To address these challenges, 3D printing of PVA hydrogels has gained interest, enabling the creation of customized implants that may reduce failure rates and improve surgical outcomes. Direct ink 3D printing of PVA-based meniscal implants would be a promising solution that has not yet been achieved. The most advanced approach involving additive manufacturing, so far involves printing a polycaprolactone and graphene scaffold, which is then filled with a PVA and glycerol solution [ 4 ]. This method has demonstrated significant improvements in cartilage protection, the formation of fibrocartilage containing type I and II collagen and reduced synovial inflammation. So far, the most successful approach to 3D printing PVA was conducted by Jiang et al., who utilized DIW to fabricate physically crosslinked hydrogels. However, to achieve printable formulations, they mixed PVA with κ-carrageenan, which resulted in good printing resolution but mechanical properties far from those required for a meniscal implant [ 5 ]. Other attempts to DIW PVA have also required composite formulations to improve printability and mechanical integrity. For instance, PVA has been combined with microfibrillated cellulose to enhance rheology and extrusion properties [ 6 ]. Similarly, another study used multiwalled carbon nanotubes blended with PVA to develop conductive printed structures [ 7 ]. For this reason, this study aims to develop a DIW method to 3D print PVA hydrogels without the need for composite materials. By optimizing printing parameters such as extrusion rate, printing speed and post-processing treatments, this research aims to achieve reliable printing accuracy and demonstrate that PVA can be employed for this type of application. In addition, a mold-based approach is explored to demonstrate that it is feasible to fabricate meniscus-shaped implants with the ink proposed by the study, evaluating its ability to absorb impacts and recover its shape. Methodology 3D printing system. The printing system used in this study was based on a modified Artillery Sidewinder 3D printer, adapted with a custom ink extruder replacing the original fused deposition modelling (FDM) setup, Fig. 1 . The custom extruder was specifically designed for controlled extrusion using a 2,5 mL Hamilton syringe Serie 1000 Gaslight (Sigma, USA), ensuring accurate ink delivery. Ink extrusion was precisely controlled by a mechanical piston, which regulated the volume within the syringe reservoir. The ink was then dispensed through a precision G25 gauge needle (Nordson EFF, USA) with an inner diameter of 0.35 mm, ensuring accurate deposition. The printing surface was heated at 75 ºC throughout the entire procedure. Preparation of the ink. PVA powder (Sigma Aldrich, USA) was mixed with Milli-Q water at a concentration of 23% (w/v). The mixture was heated to 135 ºC and stirred overnight to ensure complete dissolution. After preparation, the ink was stored at room temperature and preheated to 50 ºC before printing to facilitate its introduction into the syringe. Further details on the PVA used are provided in Table 1 . Table 1 Material properties. Material density (g/cm 3 ) Melting temperature (ºC) Molecular Weight (Da) Young Modulus (MPa) 1,19 200 89000–98000 707,9 Dimensional Characterization and Parameter Optimization. A two-parameter factorial design of experiments with four levels for the printing speed (P S ) and 3 for the flow rate (F R ) was used to parameterize the printing parameters concerning the dimensions of the printed lines (N = 4). The selected manufacturing parameters were the printing speed (P S : 20–65 mm/s) and the F R at which the material was extruded (FR: 50–100%). The analyzed parameters are detailed in Table 2 . Table 2 Two-parameter factorial design levels. Printing Speed (mm/s) 20-35-50-65 42,5 Flow rate (%) 75 50-75-100 A 20 mm side square was fabricated with no perimeters on the top or bottom layers and an infill of 25%. The slicing process was performed using PrusaSlicer 2.7.1 (Prusa Research, Czech Republic), and the parameter combinations indicated in Table 2 were printed. The dimensional characteristics of cell area (C A ) and strut width (S W ) of each sample were further analyzed using a ZEISS Discovery V12 stereo microscope, coupled with an Invenio 20EIII digital microscope camera (5 Megapixel). Image processing and data collection were performed using Matlab (MathWorks, USA). For each sample, three images of three different squares from the printed grid structures were randomly taken. Scaling on the Z axis. To evaluate the scalability of the printing process along the Z axis, multiple samples of the previously described 20 mm square were fabricated with 1 to 5 layers (N = 5). The thickness of the printed squares was measured at three points (distal, proximal, and middle) using a Micromar 40EWV micrometer (Mahr, Germany). The mean of these measurements was recorded as the sample thickness score. These averaged values were then used to develop a regression model in Matlab (MathWorks, USA) to analyze the scaling behavior. Tensile Testing of Printed Films. Tensile test specimens for the printed films were prepared following the ASTM D882-02 standard. The samples were sliced using optimized parameters with PrusaSlicer to create rectangular specimens of 80 × 10 mm with a thickness of 0.15 mm (3 layers). Prior to post-treatment, all test specimens were dried at 40 ºC for one hour. Three sub-groups were selected for post-treatment; heating at 50 ºC, autoclaving (1 cycle) and autoclaving (2 cycles) After post-treatment, the tensile tests were conducted at room temperature, following the ASTM D882-02 standard. The tests were performed using a universal testing machine equipped with a load cell to measure force and an extensometer to track elongation. The specimens were subjected to unidirectional tensile stress at a constant strain rate, with force and displacement recorded in real time. The key mechanical properties measured included ultimate tensile strength (σ F ), Young’s modulus (E), and yield strength (σ e ). Molding Process. To evaluate the feasibility of constructing a meniscus using PVA-based material, a molding approach was implemented. A two-piece mold was designed using SolidWorks (Dassault Systèmes, France) and fabricated via FDM. The mold was 3D printed in PLA (Ultimaker, Netherlands) using an Ultimaker 3 (Ultimaker, Netherlands), Fig. 3 . The PVA ink was preheated to 60 ºC to enhance its fluidity and then injected into the mold using a 15 mL Discardit syringe (BD, USA). The filled mold was left to cool at room temperature for 4 hours, followed by freezing at -20 ºC to improve the compactness of the structure. After freezing, the mold was brought back to room temperature, disassembled, and the PVA meniscus was carefully extracted. Results and Discussion Optimization of Printing Parameters. As shown in Fig. 4, square structures with infill patterns were printed at different F R and P S to analyze the influence of these parameters on the key characteristics of the printed structures, S W and C A . Microscope images were analyzed to extract both parameters, as depicted in Fig. 4-d. Figure 4 show the regression models for the selected variables. A stepwise regression method was used to determine the final model. At each step, the method evaluated possible terms to be added or deleted based on the statistical criterion. The two variables were fitted into the model, yielding the following equation for the S W estimation (Fig. 4-c): $$\:{S}_{W}=+\text{1,13}-0.02{F}_{R}+\text{0,0001}{F}_{R}^{2}$$ 1 Since the model excludes interaction terms, no significant interactions were found between the analyzed parameters. Consequently, further analysis of these parameters was conducted using only linear and quadratic models (Fig. 4-a and 4-b). This analysis was performed separately for F R and P S . In these figures, it was observed that P S does not have a significant impact on S W and, consequently, on C A . As expected, these parameters are complementary: an increase in S W corresponds to a decrease in C A . Therefore, the lack of a significant contribution from P S to these features suggests that the system correctly synchronizes the extrusion rate with the stepping of the extrusion and displacement motors. On the other hand, when analyzing the effect of F R , a quadratic trend is observed. Initially, at low F R , there is no noticeable increase in S W . It is only when the F R approaches values close to 100 that S W begins to increase, significantly impacting the morphology of the infill pattern. This behavior occurs because, at lower F R , the material is extruded through the same nozzle opening, maintaining a consistent width. However, once the extrusion rate surpasses a certain threshold, excess material is forced to spread laterally, leading to an increase in S W . Additionally, the theoretical S W value, in blue, deviates from the experimental measurements. This discrepancy arises due to the viscoelastic nature of the extruded material. While it has high viscosity, it also exhibits fluid-like behavior, causing it to spread laterally after deposition. It is not until the material consolidates into a hydrogel-like structure that ceases to flow, this issue contributes to the deviation observed between the experimental data to the expected theoretical value. Z-Layering Profile. After modeling the XY coordinates to evaluate the spatial resolution in this plane, it was essential to analyze the relationship between the number of layers and their height to evaluate the scalability of the process. As shown in Fig. 5a, the height of the first printed layer is 0.045 mm. The blue line represents the expected progression of the layer height assuming an ideal proportional model. However, the experimental data deviate from this expected trend. Furthermore, the best regression model for the first three layers is not linear, but logarithmic. This indicates that each additional layer is not simply stacked on top of the previous one, but that the material is dispersed, preventing the layers from maintaining the expected structure. This spreading effect suggests that the ink lacks sufficient mechanical integrity to support the subsequent layers, leading to a deviation from the ideal layering process. It can be observed that after the first three layers, the layer height increases by 2.3 times the increment observed between layers 2 and 3. This is due to the formation of artifacts starting from layer 4, the artifacts can be found in Fig. 5b. These artifacts occur because, as the needle tip moves further away from the intended printing layer, it fails to deposit the ink continuously. Instead, the ink accumulates at the tip of the needle in the form of a droplet, which grows until it becomes large enough to contact the layer below, resulting in a sudden deposition. When measuring layer height with a micrometer, these artifacts were included in the measurements, introducing an error in the recorded values. This measurement error is particularly pronounced between layers 4 and 5, highlighting the impact of the deposition inconsistency. Validating Meniscus Formation in PVA Structures. PVA is a promising material for the fabrication of meniscus implants or meniscus models. To demonstrate that a PVA meniscus could be successfully produced using the proposed ink, a mold was manufactured via FDM printing with PLA. The ink was deposited into the mold and frozen to induce bond formation and enhance crystallinity. After completing the freezing cycle, the molds were removed, and the meniscus-shaped PVA was extracted. Figure 6 confirms that when the material is deposited in a meniscus-shaped mold, the proposed ink formulation is suitable for meniscus fabrication. In addition, to evaluate the impact absorption capacity of the meniscus, it was subjected to an impact using a hammer, as shown in Fig. 7. It can be observed that the hammer not only does not damage the meniscus, but, on the contrary, the structure absorbs the impact, undergoing an elastic deformation. Once the force is released, the meniscus recovers its original shape. This demonstrates that hydrogels made with this ink can form elastic structures capable of absorbing impacts, which makes them promising for applications requiring mechanical strength and flexibility. PVA mechanical properties. To evaluate the mechanical capabilities of the PVA hydrogel printed in ink form, three-layer PVA films were fabricated. According to the literature, the mechanical properties of PVA can be enhanced through various chemical or physical treatments [ 8 ]. For instance, autoclaving has been reported to improve the crystallinity of PVA hydrogels, thereby enhancing their mechanical strength [ 9 ]. To investigate this effect, the tensile test films samples were subjected to three different post-processing treatments. Figure 8 presents a representative sample from each treatment group, demonstrating a noticeable improvement in mechanical properties after one autoclaving cycle. As shown in Fig. 8 and summarized in Table 3 , the E, σ e , and σ F increased significantly in samples subjected to autoclaving, compared to those that were only dried at 50°C. However, this enhancement in mechanical strength was accompanied by a loss in ductility, with the strain at break decreasing by up to three-fold. Furthermore, the second autoclaving cycle further improved the mechanical properties, as seen in both the stress-strain curves and the quantitative data in Table 3 . This suggests that repeated autoclaving cycles continue to influence the structural organization and mechanical behavior of the PVA hydrogel, likely due to increase of the crystallinity. Table 3 PVA film mechanical properties after different post-treatments. Mean values ± standard deviation of E, σ e , and σ F for samples subjected to different thermal and autoclave treatments. Post-treatments E [MPa] σ e [MPa] σ F [MPa] Heating 50 ºC 176,8 ± 106 3,1 ± 1 14,1 ± 9 Autoclaving (1 cycle) 2593,7 ± 967 30,5 ± 11 33,1 ± 13 Autoclaving (2 cycles) 2864,3 ± 411 36,0 ± 6 39,9 ± Tensile data indicate that PVA is a highly tunable material with adjustable mechanical properties. This tunability allows for an order of magnitude variation in properties such as E. Consequently, PVA can be tailored to reproduce the mechanical properties of the meniscus, which, like this ink, is composed of approximately 70% water [ 10 ]. Despite the variability in the literature of meniscal characterization due to the complexity of mechanical testing, the values reported are comparable to those obtained in this study. For example, E values of 156.6 MPa and a σ F of 21.6 MPa have been described [ 11 ]. Other studies on decellularised porcine menisci indicate E values in the range of 113–142 MPa for the native meniscus, and an σ F of 23–33 MPa for the native meniscus, increasing to approximately 35 MPa for decellularised samples [ 12 ]. The meniscus, as part of the knee joint stabilisation system, shares similarities with the fibrous capsule surrounding the knee, including the ligaments. The E of these ligaments ranges from 200 to 700 MPa [ 13 ]. Therefore, our results suggest that PVA can be adjusted to reproduce these mechanical properties, as the range observed in this study encompasses the values found in the literature. Furthermore, our study confirms the feasibility of fabricating impact-absorbing meniscal structures using this technology. However, the main limitation of 3D printing these menisci is scalability in the Z-axis. As seen in Fig. 5, the manufacturing process does not currently allow for reliable scaling beyond three layers. This limitation could be addressed by the application of Freeform Reversible Embedding of Suspended Hydrogels (FRESH) technology, an embedded printing method that extrudes ink into a bath of yield stress support, holding the bioink in place until curing [ 14 ]. Therefore, FRESH technology could be applied to meniscus fabrication using this type of ink. Alternatively, if yield stress-bearing baths are not used, the system could be optimized for printing thin structures such as ligaments. By adjusting parameters such as needle gauge and layer height, structures of around 1–2 mm could be achieved. This could enable the fabrication of medical devices or models of thin ligaments, such as the meniscotibial ligament [ 15 ]. Notably, this ligament is frequently torn together with the anterior cruciate ligament (ACL), highlighting its potential as an implantable structure to improve ACL reconstruction procedures. Conclusions This study explored the feasibility of 3D printing PVA hydrogels for the fabrication of meniscus implants using a modified DIW approach. The proposed ink formulation demonstrated promising printability, with dimensional accuracy influenced the F R . However, scalability in the Z-axis remains a limitation, as deviations in layer height and inconsistencies in deposition beyond three layers were observed. Mechanical characterization of the printed PVA structures showed that post-process treatments, in particular autoclaving, significantly improved E, σ F and overall mechanical stability. Tuning the properties of PVA allows the fabrication of structures with mechanical characteristics comparable to those of the native meniscus, reinforcing its potential as a biomaterial for meniscal replacement. Furthermore, the molding method validated the ability of PVA hydrogels to form meniscus-like structures with shock-absorbing properties. Future work should focus on overcoming Z-axis scalability limitations using advanced techniques such as FRESH printing. This method could provide structural support during fabrication, enabling the production of fully three-dimensional meniscus implants. Furthermore, optimization of printing parameters for the fabrication of thinner ligament-like structures could open up new possibilities for soft tissue engineering, including applications in ligament and cartilage repair. In conclusion, this research highlights the potential of DIW-printed PVA hydrogels as a customizable and mechanically tunable solution for meniscus implants. With further technological advances, 3D printing could become a viable alternative for patient-specific meniscal prostheses, improving surgical outcomes and reducing postoperative complications. Declarations Funding This work was supported by the Generalitat de Catalunya through the Ayudas SGR-Cat 2021 program. Conflicts of interest/Competing interests The authors declare no conflicts of interest regarding the publication of this work. The authors have no relevant financial or non-financial interests to disclose. Authors' contributions All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Enric Casanova-Batlle, Pau Escutia, and Aniol Bosch. The first draft of the manuscript was written by Enric Casanova-Batlle and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Enric Casanova-Batlle: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Writing - Original Draft, and Visualization. Pau Escutia: Methodology, Investigation, Writing - Review & Editing. Aniol Bosch: Methodology, Investigation, Writing - Review & Editing. Antonio Guerra: Conceptualization, Writing - Review & Editing, Supervision, and Project administration. Joaquim Ciurana: Conceptualization, Resources, Writing - Review & Editing, Supervision, Project administration, and Funding acquisition. 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Rev Bras Ortop (Sao Paulo) 58(2):206–210. 10.1055/S-0042-1749199 Cite Share Download PDF Status: Published Journal Publication published 10 Jul, 2025 Read the published version in The International Journal of Advanced Manufacturing Technology → Version 1 posted Editorial decision: Minor Revisions Needed 08 Jun, 2025 Reviewers agreed at journal 28 May, 2025 Reviewers invited by journal 15 May, 2025 Editor assigned by journal 14 May, 2025 First submitted to journal 12 May, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6609618","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":457019999,"identity":"94c3bb5e-e82f-4d6b-b7e2-92127eaac608","order_by":0,"name":"Enric Casanova-Batlle","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA6ElEQVRIiWNgGAWjYJCCA0hsGwiXhwQtacRpQQaHCWvhl+59eOAHg528fPvZg495as4n9p1fwPjgbRtuLZJzjhsc7GFINtxwJi/ZmOfY7cSZNx4wG87Fo8XgRhrYMYwbGHLMJGew3U7ccOMAmzQvHi32UC328/vfALX8OwfSwv4bnxYDCYiWxIYbOWYSH9sOJG4438DGjE+LBNCWgz0GyckbbrwxNvjYl2w88wZjs+Scc7i18M9IY/7wo8LOdn5/juGDhG92sn3nDx/88KYMtxao81AsTmwgpB7D4gOk6hgFo2AUjIJhDgAog1idaANhdAAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-2358-3099","institution":"University of Girona: Universitat de Girona","correspondingAuthor":true,"prefix":"","firstName":"Enric","middleName":"","lastName":"Casanova-Batlle","suffix":""},{"id":457020000,"identity":"d76f8669-bcfd-43ce-af01-ff5a46be97f3","order_by":1,"name":"Pau Escutia","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Pau","middleName":"","lastName":"Escutia","suffix":""},{"id":457020001,"identity":"d5675a75-4ca5-4491-bbd2-50ed34c2d038","order_by":2,"name":"Aniol Bosch","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Aniol","middleName":"","lastName":"Bosch","suffix":""},{"id":457020002,"identity":"50d48dae-7a67-4898-99ba-37a1bcd607d8","order_by":3,"name":"Antonio J. Guerra","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Antonio","middleName":"J.","lastName":"Guerra","suffix":""},{"id":457020003,"identity":"8d46dd43-3ff8-4001-a076-8683b90731ff","order_by":4,"name":"Joaquim Ciurana","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Joaquim","middleName":"","lastName":"Ciurana","suffix":""}],"badges":[],"createdAt":"2025-05-07 08:09:42","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6609618/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6609618/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00170-025-16014-8","type":"published","date":"2025-07-10T15:57:11+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":83129191,"identity":"6ce2e1ef-7422-4adc-92f5-4af8b8ece7b8","added_by":"auto","created_at":"2025-05-20 10:03:31","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":128713,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic and operation of the modified 3D printing system. a) Close-up view of the syringe tip extruding PVA to form a tensile test specimen for mechanical testing. b) Grid structure printed for parameter optimization.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6609618/v1/17431490d3cd22cc422de497.png"},{"id":83128443,"identity":"d78d50b9-1e88-4be4-a87b-d98bafd82184","added_by":"auto","created_at":"2025-05-20 09:55:31","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":64631,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentative ASTM D882-02 tensile test setup.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6609618/v1/f2bb58360eba069371ff41fb.png"},{"id":83130299,"identity":"c949595e-a828-4e9a-b4e4-e12f3a1949c0","added_by":"auto","created_at":"2025-05-20 10:11:31","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":31114,"visible":true,"origin":"","legend":"\u003cp\u003e3D-printed mold for meniscus fabrication. The mold is designed for PVA casting. The bottom part is shown on the left, while the top part is displayed on the right.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6609618/v1/686a1f9ed0a5710c196c5dbe.jpg"},{"id":83130301,"identity":"42275a59-7032-43d3-b5fc-1c41d93cb3f2","added_by":"auto","created_at":"2025-05-20 10:11:32","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":334058,"visible":true,"origin":"","legend":"\u003cp\u003ea, b) Fitted response plots of the regression model for the area of the square. The dashed line represents the regression equation describing the data. Gray markers indicate the experimental results, plotted according to their respective flow and speed values. The blue dashed line represents the theoretical expected values under ideal system performance. c) Surface plot of the interpolated values for the two variables (speed and flow) with respect to the S\u003csub\u003eW\u003c/sub\u003e. Colormap units: mm. d) Representation of the calculated values of S\u003csub\u003eW\u003c/sub\u003e and C\u003csub\u003eA\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6609618/v1/d8623050095b695be610fa01.png"},{"id":83128449,"identity":"3ca09559-7018-4dd9-b612-38bfcb4add9f","added_by":"auto","created_at":"2025-05-20 09:55:31","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":527144,"visible":true,"origin":"","legend":"\u003cp\u003ea) Thickness of the fabricated films as a function of the number of layers. The blue line represents the expected thickness assuming a proportional increase relative to the first layer. A dashed line highlights that the first three values do not follow a linear trend but rather a logarithmic one. b) Stereoscopic microscope image showing artifacts that appear after the third layer due to the reduced thickness increment per layer.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6609618/v1/5de91b66c669d6e4ea7105ab.png"},{"id":83129192,"identity":"f6c21d00-1d02-4d71-b987-3b083304375f","added_by":"auto","created_at":"2025-05-20 10:03:31","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":60080,"visible":true,"origin":"","legend":"\u003cp\u003ePVA meniscus model fabricated using the 3D-printed mold after the complete fabrication process.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6609618/v1/248a22c3f5e2d6f1ca44bdae.png"},{"id":83128453,"identity":"07e84e42-feb0-41e2-88af-4e8bc5e80291","added_by":"auto","created_at":"2025-05-20 09:55:32","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":553722,"visible":true,"origin":"","legend":"\u003cp\u003eSequence of images showing a PVA meniscus subjected to impact by a hammer. The sequence illustrates the meniscus absorbing the impact and subsequently recovering its original shape once the force is released.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6609618/v1/43ab593075a0c35c278e137b.png"},{"id":83128451,"identity":"14f92897-03e9-435f-a2cf-b1ef008582eb","added_by":"auto","created_at":"2025-05-20 09:55:31","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":4339,"visible":true,"origin":"","legend":"\u003cp\u003eStress-strain curves from tensile tests on samples subjected to Autoclaving (1 cycle) (black), Autoclaving (2 cycles) (light gray), and Heating 50 ºC (dark gray).\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-6609618/v1/5e53a05b307997ae0afe3b69.png"},{"id":86699284,"identity":"89dddeb6-0276-48d7-bcba-f6683f2b359f","added_by":"auto","created_at":"2025-07-14 16:07:43","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2587833,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6609618/v1/d4a69e92-ed88-4382-836c-28363341485f.pdf"}],"financialInterests":"","formattedTitle":"3D Printing of Polyvinyl Alcohol for Meniscus Implant Fabrication","fulltext":[{"header":"Introduction","content":"\u003cp\u003eMeniscectomy is the most common surgical procedure for treating meniscal injuries in hospitals, as it currently provides the best clinical outcomes. However, despite its effectiveness, meniscectomy often leads to long-term complications such as osteoarthritis and joint degeneration [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Recent studies suggest that replacing the meniscus with a PVA hydrogel implant may lead to improved long-term results. This has been demonstrated in a two-year in vivo study using a rabbit model, where PVA implants showed potential in preserving joint function and delaying osteoarthritis progression [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Given these results, research has focused on modifying the mechanical properties of PVA to enhance its suitability for meniscal replacement. Several strategies have been investigated, including annealing treatments, which enhance polymer stability and mechanical strength, freeze-thaw cycles, which induce physical crosslinking [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], salt treatments, which modify the hydrogel's thermal and structural properties to enhance load-bearing capacity etc. [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. These conclude that PVA is a promising candidate for meniscal implants, as it closely mimics the viscoelastic and mechanical properties of the natural meniscus if subjected to a certain post-treatment [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHowever, current manufacturing methods involve first synthesizing the material and then manually shaping it. For example, in previous studies, PVA menisci were prepared by dissolving the PVA in a solvent, subjecting it to controlled freezing and thawing, and then annealing it to optimize mechanical performance [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. They were then manually cut with a scalpel. Since meniscectomy remains the standard surgical procedure, the in situ cutting of the implants is not an effective method to create patient-specific prostheses. Also considering that implant misalignment is one of the leading causes of failure in meniscal replacement. To address these challenges, 3D printing of PVA hydrogels has gained interest, enabling the creation of customized implants that may reduce failure rates and improve surgical outcomes. Direct ink 3D printing of PVA-based meniscal implants would be a promising solution that has not yet been achieved. The most advanced approach involving additive manufacturing, so far involves printing a polycaprolactone and graphene scaffold, which is then filled with a PVA and glycerol solution [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. This method has demonstrated significant improvements in cartilage protection, the formation of fibrocartilage containing type I and II collagen and reduced synovial inflammation. So far, the most successful approach to 3D printing PVA was conducted by Jiang et al., who utilized DIW to fabricate physically crosslinked hydrogels. However, to achieve printable formulations, they mixed PVA with κ-carrageenan, which resulted in good printing resolution but mechanical properties far from those required for a meniscal implant [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Other attempts to DIW PVA have also required composite formulations to improve printability and mechanical integrity. For instance, PVA has been combined with microfibrillated cellulose to enhance rheology and extrusion properties [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Similarly, another study used multiwalled carbon nanotubes blended with PVA to develop conductive printed structures [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFor this reason, this study aims to develop a DIW method to 3D print PVA hydrogels without the need for composite materials. By optimizing printing parameters such as extrusion rate, printing speed and post-processing treatments, this research aims to achieve reliable printing accuracy and demonstrate that PVA can be employed for this type of application. In addition, a mold-based approach is explored to demonstrate that it is feasible to fabricate meniscus-shaped implants with the ink proposed by the study, evaluating its ability to absorb impacts and recover its shape.\u003c/p\u003e"},{"header":"Methodology","content":"\u003cp\u003e \u003cb\u003e3D printing system.\u003c/b\u003e The printing system used in this study was based on a modified Artillery Sidewinder 3D printer, adapted with a custom ink extruder replacing the original fused deposition modelling (FDM) setup, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The custom extruder was specifically designed for controlled extrusion using a 2,5 mL Hamilton syringe Serie 1000 Gaslight (Sigma, USA), ensuring accurate ink delivery. Ink extrusion was precisely controlled by a mechanical piston, which regulated the volume within the syringe reservoir. The ink was then dispensed through a precision G25 gauge needle (Nordson EFF, USA) with an inner diameter of 0.35 mm, ensuring accurate deposition. The printing surface was heated at 75 \u0026ordm;C throughout the entire procedure.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003ePreparation of the ink.\u003c/b\u003e PVA powder (Sigma Aldrich, USA) was mixed with Milli-Q water at a concentration of 23% (w/v). The mixture was heated to 135 \u0026ordm;C and stirred overnight to ensure complete dissolution. After preparation, the ink was stored at room temperature and preheated to 50 \u0026ordm;C before printing to facilitate its introduction into the syringe. Further details on the PVA used are provided in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMaterial properties.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaterial density (g/cm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMelting temperature (\u0026ordm;C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMolecular Weight (Da)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYoung Modulus (MPa)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1,19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e89000\u0026ndash;98000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e707,9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eDimensional Characterization and Parameter Optimization.\u003c/b\u003e A two-parameter factorial design of experiments with four levels for the printing speed (P\u003csub\u003eS\u003c/sub\u003e) and 3 for the flow rate (F\u003csub\u003eR\u003c/sub\u003e) was used to parameterize the printing parameters concerning the dimensions of the printed lines (N\u0026thinsp;=\u0026thinsp;4). The selected manufacturing parameters were the printing speed (P\u003csub\u003eS\u003c/sub\u003e: 20\u0026ndash;65 mm/s) and the F\u003csub\u003eR\u003c/sub\u003e at which the material was extruded (FR: 50\u0026ndash;100%). The analyzed parameters are detailed in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eTwo-parameter factorial design levels.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePrinting Speed (mm/s)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e20-35-50-65\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e42,5\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFlow rate (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e50-75-100\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eA 20 mm side square was fabricated with no perimeters on the top or bottom layers and an infill of 25%. The slicing process was performed using PrusaSlicer 2.7.1 (Prusa Research, Czech Republic), and the parameter combinations indicated in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e were printed. The dimensional characteristics of cell area (C\u003csub\u003eA\u003c/sub\u003e) and strut width (S\u003csub\u003eW\u003c/sub\u003e) of each sample were further analyzed using a ZEISS Discovery V12 stereo microscope, coupled with an Invenio 20EIII digital microscope camera (5 Megapixel). Image processing and data collection were performed using Matlab (MathWorks, USA). For each sample, three images of three different squares from the printed grid structures were randomly taken.\u003c/p\u003e \u003cp\u003e \u003cb\u003eScaling on the Z axis.\u003c/b\u003e To evaluate the scalability of the printing process along the Z axis, multiple samples of the previously described 20 mm square were fabricated with 1 to 5 layers (N\u0026thinsp;=\u0026thinsp;5). The thickness of the printed squares was measured at three points (distal, proximal, and middle) using a Micromar 40EWV micrometer (Mahr, Germany). The mean of these measurements was recorded as the sample thickness score. These averaged values were then used to develop a regression model in Matlab (MathWorks, USA) to analyze the scaling behavior.\u003c/p\u003e \u003cp\u003e \u003cb\u003eTensile Testing of Printed Films.\u003c/b\u003e Tensile test specimens for the printed films were prepared following the ASTM D882-02 standard. The samples were sliced using optimized parameters with PrusaSlicer to create rectangular specimens of 80 \u0026times; 10 mm with a thickness of 0.15 mm (3 layers). Prior to post-treatment, all test specimens were dried at 40 \u0026ordm;C for one hour. Three sub-groups were selected for post-treatment; heating at 50 \u0026ordm;C, autoclaving (1 cycle) and autoclaving (2 cycles)\u003c/p\u003e \u003cp\u003eAfter post-treatment, the tensile tests were conducted at room temperature, following the ASTM D882-02 standard. The tests were performed using a universal testing machine equipped with a load cell to measure force and an extensometer to track elongation. The specimens were subjected to unidirectional tensile stress at a constant strain rate, with force and displacement recorded in real time. The key mechanical properties measured included ultimate tensile strength (σ\u003csub\u003eF\u003c/sub\u003e), Young\u0026rsquo;s modulus (E), and yield strength (σ\u003csub\u003ee\u003c/sub\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eMolding Process.\u003c/b\u003e To evaluate the feasibility of constructing a meniscus using PVA-based material, a molding approach was implemented. A two-piece mold was designed using SolidWorks (Dassault Syst\u0026egrave;mes, France) and fabricated via FDM. The mold was 3D printed in PLA (Ultimaker, Netherlands) using an Ultimaker 3 (Ultimaker, Netherlands), Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The PVA ink was preheated to 60 \u0026ordm;C to enhance its fluidity and then injected into the mold using a 15 mL Discardit syringe (BD, USA). The filled mold was left to cool at room temperature for 4 hours, followed by freezing at -20 \u0026ordm;C to improve the compactness of the structure. After freezing, the mold was brought back to room temperature, disassembled, and the PVA meniscus was carefully extracted.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003e\u003cstrong\u003eOptimization of Printing Parameters.\u003c/strong\u003e As shown in Fig. 4, square structures with infill patterns were printed at different F\u003csub\u003eR\u003c/sub\u003e and P\u003csub\u003eS\u003c/sub\u003e to analyze the influence of these parameters on the key characteristics of the printed structures, S\u003csub\u003eW\u003c/sub\u003e and C\u003csub\u003eA\u003c/sub\u003e. Microscope images were analyzed to extract both parameters, as depicted in Fig.\u0026nbsp;4-d. Figure\u0026nbsp;4 show the regression models for the selected variables. A stepwise regression method was used to determine the final model. At each step, the method evaluated possible terms to be added or deleted based on the statistical criterion. The two variables were fitted into the model, yielding the following equation for the S\u003csub\u003eW\u003c/sub\u003e estimation (Fig. 4-c):\u003c/p\u003e\n\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e$$\\:{S}_{W}=+\\text{1,13}-0.02{F}_{R}+\\text{0,0001}{F}_{R}^{2}$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eSince the model excludes interaction terms, no significant interactions were found between the analyzed parameters. Consequently, further analysis of these parameters was conducted using only linear and quadratic models (Fig. 4-a and 4-b). This analysis was performed separately for F\u003csub\u003eR\u003c/sub\u003e and P\u003csub\u003eS\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003eIn these figures, it was observed that P\u003csub\u003eS\u003c/sub\u003e does not have a significant impact on S\u003csub\u003eW\u003c/sub\u003e and, consequently, on C\u003csub\u003eA\u003c/sub\u003e. As expected, these parameters are complementary: an increase in S\u003csub\u003eW\u003c/sub\u003e corresponds to a decrease in C\u003csub\u003eA\u003c/sub\u003e. Therefore, the lack of a significant contribution from P\u003csub\u003eS\u003c/sub\u003e to these features suggests that the system correctly synchronizes the extrusion rate with the stepping of the extrusion and displacement motors.\u003c/p\u003e\n\u003cp\u003eOn the other hand, when analyzing the effect of F\u003csub\u003eR\u003c/sub\u003e, a quadratic trend is observed. Initially, at low F\u003csub\u003eR\u003c/sub\u003e, there is no noticeable increase in S\u003csub\u003eW\u003c/sub\u003e. It is only when the F\u003csub\u003eR\u003c/sub\u003e approaches values close to 100 that S\u003csub\u003eW\u003c/sub\u003e begins to increase, significantly impacting the morphology of the infill pattern. This behavior occurs because, at lower F\u003csub\u003eR\u003c/sub\u003e, the material is extruded through the same nozzle opening, maintaining a consistent width. However, once the extrusion rate surpasses a certain threshold, excess material is forced to spread laterally, leading to an increase in S\u003csub\u003eW\u003c/sub\u003e. Additionally, the theoretical S\u003csub\u003eW\u003c/sub\u003e value, in blue, deviates from the experimental measurements. This discrepancy arises due to the viscoelastic nature of the extruded material. While it has high viscosity, it also exhibits fluid-like behavior, causing it to spread laterally after deposition. It is not until the material consolidates into a hydrogel-like structure that ceases to flow, this issue contributes to the deviation observed between the experimental data to the expected theoretical value.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eZ-Layering Profile.\u003c/strong\u003e After modeling the XY coordinates to evaluate the spatial resolution in this plane, it was essential to analyze the relationship between the number of layers and their height to evaluate the scalability of the process. As shown in Fig. 5a, the height of the first printed layer is 0.045 mm. The blue line represents the expected progression of the layer height assuming an ideal proportional model. However, the experimental data deviate from this expected trend. Furthermore, the best regression model for the first three layers is not linear, but logarithmic. This indicates that each additional layer is not simply stacked on top of the previous one, but that the material is dispersed, preventing the layers from maintaining the expected structure. This spreading effect suggests that the ink lacks sufficient mechanical integrity to support the subsequent layers, leading to a deviation from the ideal layering process.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003cdiv align=\"left\" class=\"colspec\"\u003eIt can be observed that after the first three layers, the layer height increases by 2.3 times the increment observed between layers 2 and 3. This is due to the formation of artifacts starting from layer 4, the artifacts can be found in Fig. 5b. These artifacts occur because, as the needle tip moves further away from the intended printing layer, it fails to deposit the ink continuously. Instead, the ink accumulates at the tip of the needle in the form of a droplet, which grows until it becomes large enough to contact the layer below, resulting in a sudden deposition. When measuring layer height with a micrometer, these artifacts were included in the measurements, introducing an error in the recorded values. This measurement error is particularly pronounced between layers 4 and 5, highlighting the impact of the deposition inconsistency.\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003eValidating Meniscus Formation in PVA Structures.\u003c/strong\u003e PVA is a promising material for the fabrication of meniscus implants or meniscus models. To demonstrate that a PVA meniscus could be successfully produced using the proposed ink, a mold was manufactured via FDM printing with PLA. The ink was deposited into the mold and frozen to induce bond formation and enhance crystallinity. After completing the freezing cycle, the molds were removed, and the meniscus-shaped PVA was extracted. Figure \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e confirms that when the material is deposited in a meniscus-shaped mold, the proposed ink formulation is suitable for meniscus fabrication.\u003c/p\u003e\n\u003cp\u003eIn addition, to evaluate the impact absorption capacity of the meniscus, it was subjected to an impact using a hammer, as shown in Fig. 7. It can be observed that the hammer not only does not damage the meniscus, but, on the contrary, the structure absorbs the impact, undergoing an elastic deformation. Once the force is released, the meniscus recovers its original shape. This demonstrates that hydrogels made with this ink can form elastic structures capable of absorbing impacts, which makes them promising for applications requiring mechanical strength and flexibility.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePVA mechanical properties.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo evaluate the mechanical capabilities of the PVA hydrogel printed in ink form, three-layer PVA films were fabricated. According to the literature, the mechanical properties of PVA can be enhanced through various chemical or physical treatments [\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e]. For instance, autoclaving has been reported to improve the crystallinity of PVA hydrogels, thereby enhancing their mechanical strength [\u003cspan class=\"CitationRef\"\u003e9\u003c/span\u003e]. To investigate this effect, the tensile test films samples were subjected to three different post-processing treatments. Figure \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e presents a representative sample from each treatment group, demonstrating a noticeable improvement in mechanical properties after one autoclaving cycle. As shown in Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e and summarized in Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, the E, \u0026sigma;\u003csub\u003ee\u003c/sub\u003e, and \u0026sigma;\u003csub\u003eF\u003c/sub\u003e increased significantly in samples subjected to autoclaving, compared to those that were only dried at 50\u0026deg;C. However, this enhancement in mechanical strength was accompanied by a loss in ductility, with the strain at break decreasing by up to three-fold. Furthermore, the second autoclaving cycle further improved the mechanical properties, as seen in both the stress-strain curves and the quantitative data in Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. This suggests that repeated autoclaving cycles continue to influence the structural organization and mechanical behavior of the PVA hydrogel, likely due to increase of the crystallinity.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003ePVA film mechanical properties after different post-treatments. Mean values\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation of E, \u0026sigma;\u003csub\u003ee\u003c/sub\u003e, and \u0026sigma;\u003csub\u003eF\u003c/sub\u003e for samples subjected to different thermal and autoclave treatments.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"4\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePost-treatments\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eE [MPa]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u0026sigma;\u003csub\u003ee\u003c/sub\u003e [MPa]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u0026sigma;\u003csub\u003eF\u003c/sub\u003e [MPa]\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHeating 50 \u0026ordm;C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e176,8\u0026thinsp;\u0026plusmn;\u0026thinsp;106\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3,1\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14,1\u0026thinsp;\u0026plusmn;\u0026thinsp;9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAutoclaving\u003c/p\u003e\n \u003cp\u003e(1 cycle)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2593,7\u0026thinsp;\u0026plusmn;\u0026thinsp;967\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30,5\u0026thinsp;\u0026plusmn;\u0026thinsp;11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e33,1\u0026thinsp;\u0026plusmn;\u0026thinsp;13\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAutoclaving\u003c/p\u003e\n \u003cp\u003e(2 cycles)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2864,3\u0026thinsp;\u0026plusmn;\u0026thinsp;411\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e36,0\u0026thinsp;\u0026plusmn;\u0026thinsp;6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e39,9 \u0026plusmn;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eTensile data indicate that PVA is a highly tunable material with adjustable mechanical properties. This tunability allows for an order of magnitude variation in properties such as E. Consequently, PVA can be tailored to reproduce the mechanical properties of the meniscus, which, like this ink, is composed of approximately 70% water [\u003cspan class=\"CitationRef\"\u003e10\u003c/span\u003e]. Despite the variability in the literature of meniscal characterization due to the complexity of mechanical testing, the values reported are comparable to those obtained in this study. For example, E values of 156.6 MPa and a \u0026sigma;\u003csub\u003eF\u003c/sub\u003e of 21.6 MPa have been described [\u003cspan class=\"CitationRef\"\u003e11\u003c/span\u003e]. Other studies on decellularised porcine menisci indicate E values in the range of 113\u0026ndash;142 MPa for the native meniscus, and an \u0026sigma;\u003csub\u003eF\u003c/sub\u003e of 23\u0026ndash;33 MPa for the native meniscus, increasing to approximately 35 MPa for decellularised samples [\u003cspan class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eThe meniscus, as part of the knee joint stabilisation system, shares similarities with the fibrous capsule surrounding the knee, including the ligaments. The E of these ligaments ranges from 200 to 700 MPa [\u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e]. Therefore, our results suggest that PVA can be adjusted to reproduce these mechanical properties, as the range observed in this study encompasses the values found in the literature. Furthermore, our study confirms the feasibility of fabricating impact-absorbing meniscal structures using this technology. However, the main limitation of 3D printing these menisci is scalability in the Z-axis. As seen in Fig.\u0026nbsp;5, the manufacturing process does not currently allow for reliable scaling beyond three layers. This limitation could be addressed by the application of Freeform Reversible Embedding of Suspended Hydrogels (FRESH) technology, an embedded printing method that extrudes ink into a bath of yield stress support, holding the bioink in place until curing [\u003cspan class=\"CitationRef\"\u003e14\u003c/span\u003e]. Therefore, FRESH technology could be applied to meniscus fabrication using this type of ink. Alternatively, if yield stress-bearing baths are not used, the system could be optimized for printing thin structures such as ligaments. By adjusting parameters such as needle gauge and layer height, structures of around 1\u0026ndash;2 mm could be achieved. This could enable the fabrication of medical devices or models of thin ligaments, such as the meniscotibial ligament [\u003cspan class=\"CitationRef\"\u003e15\u003c/span\u003e]. Notably, this ligament is frequently torn together with the anterior cruciate ligament (ACL), highlighting its potential as an implantable structure to improve ACL reconstruction procedures.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThis study explored the feasibility of 3D printing PVA hydrogels for the fabrication of meniscus implants using a modified DIW approach. The proposed ink formulation demonstrated promising printability, with dimensional accuracy influenced the F\u003csub\u003eR\u003c/sub\u003e. However, scalability in the Z-axis remains a limitation, as deviations in layer height and inconsistencies in deposition beyond three layers were observed. Mechanical characterization of the printed PVA structures showed that post-process treatments, in particular autoclaving, significantly improved E, σ\u003csub\u003eF\u003c/sub\u003e and overall mechanical stability. Tuning the properties of PVA allows the fabrication of structures with mechanical characteristics comparable to those of the native meniscus, reinforcing its potential as a biomaterial for meniscal replacement. Furthermore, the molding method validated the ability of PVA hydrogels to form meniscus-like structures with shock-absorbing properties. Future work should focus on overcoming Z-axis scalability limitations using advanced techniques such as FRESH printing. This method could provide structural support during fabrication, enabling the production of fully three-dimensional meniscus implants. Furthermore, optimization of printing parameters for the fabrication of thinner ligament-like structures could open up new possibilities for soft tissue engineering, including applications in ligament and cartilage repair. In conclusion, this research highlights the potential of DIW-printed PVA hydrogels as a customizable and mechanically tunable solution for meniscus implants. With further technological advances, 3D printing could become a viable alternative for patient-specific meniscal prostheses, improving surgical outcomes and reducing postoperative complications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003e\u003cem\u003eFunding\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the Generalitat de Catalunya through the Ayudas SGR-Cat 2021 program.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eConflicts of interest/Competing interests\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflicts of interest regarding the publication of this work. The authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eAuthors' contributions\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Enric Casanova-Batlle, Pau Escutia, and Aniol Bosch. The first draft of the manuscript was written by Enric Casanova-Batlle and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003eEnric Casanova-Batlle: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Writing - Original Draft, and Visualization.\u003c/p\u003e\n\u003cp\u003ePau Escutia: Methodology, Investigation, Writing - Review \u0026amp; Editing.\u003c/p\u003e\n\u003cp\u003eAniol Bosch: Methodology, Investigation, Writing - Review \u0026amp; Editing.\u003c/p\u003e\n\u003cp\u003eAntonio Guerra: Conceptualization, Writing - Review \u0026amp; Editing, Supervision, and Project administration.\u003c/p\u003e\n\u003cp\u003eJoaquim Ciurana: Conceptualization, Resources, Writing - Review \u0026amp; Editing, Supervision, Project administration, and Funding acquisition.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eKobayashi M, Toguchida J, Oka M (2003) Development of an artificial meniscus using polyvinyl alcohol-hydrogel for early return to, and continuance of, athletic life in sportspersons with severe meniscus injury. 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Rev Bras Ortop (Sao Paulo) 58(2):206\u0026ndash;210. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1055/S-0042-1749199\u003c/span\u003e\u003cspan address=\"10.1055/S-0042-1749199\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"the-international-journal-of-advanced-manufacturing-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jamt","sideBox":"Learn more about [The International Journal of Advanced Manufacturing Technology](https://www.springer.com/journal/170)","snPcode":"170","submissionUrl":"https://submission.nature.com/new-submission/170/3","title":"The International Journal of Advanced Manufacturing Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Polyvinyl alcohol, Direct Ink Write, Meniscus","lastPublishedDoi":"10.21203/rs.3.rs-6609618/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6609618/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eMeniscectomy is a common surgical procedure to treat meniscal injuries, but it often leads to long-term complications such as osteoarthritis. Polyvinyl alcohol (PVA) hydrogel implants offer a promising alternative due to their viscoelastic properties, which closely mimic the natural meniscus. However, conventional manufacturing methods rely on manual shaping, which limits precision and customization. This study explores the feasibility of 3D printing PVA hydrogels by direct ink writing (DIW) for patient-specific meniscus implants. A syringe-based extrusion system was developed and printing parameters were optimized using a factorial design experiment, evaluating the effects of speed and flow rate on dimensional accuracy and layer scaling. In addition, tensile tests and post-treatments, including autoclaving, demonstrated that the printed PVA structures could achieve mechanical properties comparable to those of native meniscus. In addition, a molding method validated the formation of meniscus-shaped structures with shock absorption capabilities. Future research should focus on refining printing methods that provide structural support during fabrication to achieve reliable 3D architectures. This work demonstrates the potential of 3D printed PVA hydrogels for meniscal replacement, offering a possible approach for the manufacture of customized implants.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e","manuscriptTitle":"3D Printing of Polyvinyl Alcohol for Meniscus Implant Fabrication","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-20 09:55:27","doi":"10.21203/rs.3.rs-6609618/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Minor Revisions Needed","date":"2025-06-08T11:00:53+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2025-05-28T13:29:03+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-05-15T10:24:21+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-05-14T13:06:52+00:00","index":"","fulltext":""},{"type":"submitted","content":"The International Journal of Advanced Manufacturing Technology","date":"2025-05-12T12:36:30+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"the-international-journal-of-advanced-manufacturing-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jamt","sideBox":"Learn more about [The International Journal of Advanced Manufacturing Technology](https://www.springer.com/journal/170)","snPcode":"170","submissionUrl":"https://submission.nature.com/new-submission/170/3","title":"The International Journal of Advanced Manufacturing Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"4396dd7b-d1b3-4d0f-8a2a-a7b7849c1d92","owner":[],"postedDate":"May 20th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-07-14T16:00:06+00:00","versionOfRecord":{"articleIdentity":"rs-6609618","link":"https://doi.org/10.1007/s00170-025-16014-8","journal":{"identity":"the-international-journal-of-advanced-manufacturing-technology","isVorOnly":false,"title":"The International Journal of Advanced Manufacturing Technology"},"publishedOn":"2025-07-10 15:57:11","publishedOnDateReadable":"July 10th, 2025"},"versionCreatedAt":"2025-05-20 09:55:27","video":"","vorDoi":"10.1007/s00170-025-16014-8","vorDoiUrl":"https://doi.org/10.1007/s00170-025-16014-8","workflowStages":[]},"version":"v1","identity":"rs-6609618","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6609618","identity":"rs-6609618","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}