Search Results (99)

Bioreactors used for the maturation of cell-seeded tissue-engineered scaffolds should essentially mimic the dynamic in vivo environments experienced by the native tissues they intend to substitute. In addition to perfusion of growth medium to facilitate continuous mass transfer, application of appropriate mechanical stimulation is important to enhance cellular responses in scaffolds for tissues such as tendons, skin, and cardiac muscle that experience dynamic loading. This study focuses on the development of a multi-modal custom bioreactor capable of applying cyclic tensile stimulation and perfusion within physiologically relevant ranges while minimizing shear stress detrimental to cells seeded on scaffolds. To validate the bioreactor design and operation, we assessed the effects of tensile stimulation (0.1 Hz, 2000 cycles/day) and perfusion (media flow rate = 0.15 mL/min) over 21 days on the biofunctional performance of 3D-bioplotted polycaprolactone (PCL) auxetic scaffolds with a representative design (missing-rib pattern) characterized by negative Poisson’s ratio similar to the aforementioned soft tissues. The scaffold had a tensile yield strain of 9.14%, yield strength of 0.25 MPa, elastic modulus of 2.85 MPa, and ultimate tensile strength (UTS) of 1.32 MPa. The application of perfusion and tensile stimulation (0–5% cyclic strain) for 21 days did not adversely affect the yield strength and elastic modulus of the scaffold but affected its UTS (22.5% decrease) compared to the control cultured without perfusion or stimulation. Notably, it resulted in significantly improved fibroblast cellular responses (DNA = 29 µg/g sample and collagen = 371.78 µg/g sample) compared to the control (7.52 µg/g sample and 163.51 µg/g sample, respectively). These results validate the bioreactor system operation and the ability of multi-modal stimulation to control biofunctional responses of auxetic scaffolds, which will serve as the basis for future studies that will optimize auxetic scaffold design and dynamic culture parameters for NPR tissue-specific applications. Full article

This study examines the in-plane compression behavior of sandwich panels produced with additive manufacturing. This study focuses on two types of honeycomb unit cell topologies with larger dimensions: a hexagonal one and a re-entrant one. For each panel geometry, two material configurations were examined: Onyx (a nylon-based composite) and Onyx reinforced with 10% continuous carbon fibers (CCFs) by mass. The objective was to assess the influence of fiber reinforcement on the mechanical performance and deformation response of the panel structures. In-plane compression tests were conducted to determine the stiffness, strength, and failure modes of the specimens. Additionally, the digital image correlation (DIC) technique was used to capture full-field strain distributions and analyze local deformation mechanisms during loading. The results revealed distinct mechanical responses between the two geometries: the re-entrant structure exhibited auxetic behavior and enhanced energy absorption characteristics. Although reinforced honeycomb panels have an average load capacity that is 35% higher, they fail at a displacement that is approximately 55% smaller compared to unreinforced panels. Despite accounting for only 25% of the total number of layers and 10% of the panel’s mass, the reinforcement achieved superior strength. Re-entrant panel testing showed a 25% force increase in favor of the reinforced variant. They fail at a displacement that is 36.5% greater than that of reinforced honeycombs. This demonstrates a more compliant response while also maintaining 4.9% greater strength, indicating the superior behavior of auxetic reinforced sandwich panels. Introducing CCF reinforcement increased the load-bearing capacity and reduced localized strain concentrations without altering the overall deformation pattern. These findings suggest that enhancing materials can increase the strength and flexibility of 3D-printed re-entrant structures, providing valuable insights for lightweight design and optimized material use in structural applications. Full article

Auxetic structures exhibit a negative Poisson’s ratio, enabling enhanced energy absorption and deformation capabilities compared to conventional materials. In this study, a re-entrant auxetic geometry was fabricated using stereolithography (SLA) 3D printing with a high-toughness resin and was tested in tension and compression. Two variants, i.e., a reference and a filleted design, were investigated through finite element analysis and experimental testing. Results showed good agreement between simulations and experiments. The filleted geometry demonstrated smoother deformation, delayed fracture, and higher strain capacity, while the reference absorbed slightly more energy in compression. These findings highlight the role of geometry in tailoring auxetic performance. Full article

The assessment of the dynamic mechanical performance of fiber-reinforced composites has gained importance in specific high-tech applications like aerospace and automobiles. However, three dimensional (3D) auxetic reinforcements offering viable performance have remained unexplored. Hence, this study investigates the energy absorption capabilities and high strain impact behaviors of 3D woven fabric-reinforced composites. Three different types of 3D woven reinforcements i.e., warp interlock (Wp), weft interlock (Wt), and bidirectional interlock (Bi) were developed from jute yarn, and their corresponding composites were fabricated using polycarbonate (PC) and polyvinyl butyral (PVB). Out-of-plane auxeticity was measured for reinforcements while composites were analyzed under dynamic tests. Wp exhibited the highest auxeticity with a value of −1.29, Bi showed the least auxeticity with a value of −0.31, while Wt entailed an intermediate value of −0.46 owing to variable interlacement patterns. The dynamic mechanical analysis (DMA) results revealed that composite samples developed with PC resin showed a higher storage modulus with the least tan delta values less than 0.2, while PVB-based samples exhibited higher loss modulus with tan delta values of 0.6. Split Hopkinson pressure bar (SHPB) results showed that, under 2 and 4 bar pressure tests, PVB-based composites exhibited the highest maximum load while PC-based composites exhibited the least. Warp interlock-based composites with higher auxeticity showed better energy absorption when compared with the bidirectional interlock reinforcement based (with lower auxeticity) composites that exhibited lower peak load and energy dissipation. Full article

This study investigates the mechanical behavior and energy absorption capacity of a novel metamortar composite, developed by embedding re-entrant auxetic cellular structures into a cementitious mortar matrix. Auxetic materials, which exhibit a negative Poisson’s ratio, offer distinct advantages in impact resistance and stress dissipation. Despite their promising properties, their integration into cement-based systems remains limited. In this work, auxetic cells were fabricated using different 3D printing filaments and combined with mortar to form hybrid composites. The specimens were subjected to quasi-static compression tests to evaluate their Young’s modulus, yield strength, and energy absorption capacity. Results indicate that the auxetic inclusions substantially improved the mechanical performance of the mortar, particularly in the case of PLA-based cells, which achieved the highest values across all tested parameters. The enhancements are attributed to the synergistic deformation mechanisms of the auxetic geometry and the surrounding matrix, promoting efficient load distribution and delayed crack propagation. These findings contribute to the advancement of cementitious metamaterials and establish a foundation for scaling toward metaconcrete systems with improved energy dissipation for use in protective, seismic, and infrastructure applications. Full article

This study explores the development of 4D-printed smart structures based on PLA/PETG (75/25) polymer blends reinforced with nanocellulose (0–3 wt%), processed using fused filament fabrication (FFF). Both conventional U-shaped specimens and anti-tri-chiral auxetic architectures were fabricated to evaluate the effects of nanocellulose on mechanical performance and shape memory behavior. Tensile tests demonstrated that nanocellulose reinforcement enhanced both strength and stiffness, with the highest values observed at 2 wt% (tensile strength of 56 MPa and Young’s modulus of 3.3 GPa). In standard U-shaped samples, all compositions showed excellent shape fixity and recovery (100%). For auxetic structures, shape memory behavior and deformation response varied with nanocellulose content. Notably, 2 wt% nanocellulose yielded the highest shape recovery ratio (90.8%) and fixity (99.8%), indicating improved elasticity and structural responsiveness. Meanwhile, 1 wt% nanocellulose resulted in the highest energy absorption and more controlled deformation under compression, suggesting enhanced energy dissipation and stress distribution. A slight decrease in performance at 3 wt% is attributed to nanocellulose agglomeration and reduced polymer chain mobility. These findings highlight nanocellulose as a multifunctional additive that enables fine-tuning of mechanical and functional properties in 4D-printed structures. Depending on the intended application whether focused on energy absorption, mechanical strength, or shape recovery nanocellulose content can be strategically adjusted. This approach opens pathways for designing responsive materials suited for biomedical engineering, adaptive devices, and advanced environmental technologies. Full article

Background/Objectives: Developing functional tissue constructs via 3D bioprinting relies heavily on scaffold architecture, demanding precise mechanical tunability and high-resolution feature fidelity. Methods: This paper presents a novel approach utilising photocurable resins and resin 3D printing to fabricate auxetic axisymmetric chiral structures (ACSs), which can be used for advanced scaffold engineering. Results: The experimental tests showed that the optimised ACS (optACS) possess superior mechanical properties compared to their non-optimised counterpart. Both analysed structures possess an auxetic behaviour up to 40% longitudinal strain, with a Poisson’s ratio of about −0.1. Conclusions: This auxetic capability is promising for biomedical applications, particularly in developing enhanced stents or tissue scaffolds. Full article

Auxetic structures, characterized by a negative Poisson’s ratio and unique form-fitting deformation, are adopted for designing a bra pad that would facilitate bras with a flexible and adaptive fit. This study compares the pressure distribution between auxetic and traditional molded bra pads, highlighting the advantages of auxetic materials in applying uniform pressure and addressing health concerns. Seven athletic female participants with a bra size of 75B comprise the study sample. Anthropometric data of naked breasts are collected by using three-dimensional (3D) scanning to obtain the underbust and full bust dimensions in the standing and leaning forward positions, while the pressure distribution is measured with the Novel Pliance^® pressure measurement system in three poses: standing, static cycling, and dynamic cycling. The results show that the auxetic designs of bra pads consistently apply a more uniform pressure distribution compared to traditional foam pads, with mean pressures of 2.92 kPa for auxetic pads compared to 4.81 kPa for traditional foam pads during static cycling. Moreover, auxetic pads reduced maximum pressure by 25% compared to molded cups, and spatial variability was halved (SD 0.85 kPa vs. 1.70 kPa). Notably, at the bra neckline, auxetic pads exhibit increased pressure as the body leans forward, demonstrating their ability to adapt to changing breast shapes while maintaining adequate bra-breast contact. In contrast, in the lower breast area, the auxetic pads show a decrease in pressure, which indicates their capacity to accommodate variations in breast girth or volume without exerting excessive force. These findings highlight the superior adaptability and wear comfort provided by an auxetic structure, which shows its potential to address the dynamic support needs of active women. Overall, the auxetic designs of a bra pad in this study represent a significant advancement in sports bra technology and offer a promising alternative to traditional molded cups in activewear design. Full article

Lattice structures have been widely studied in various fields due to their lightweight and high-energy absorption capabilities. In this study, we propose the use of lattice structures in the design of sports protective equipment for contact sports athletes. A total of six specimens were additively manufactured either with a bending-dominated rhombic dodecahedron (RD) structure or stretch-dominated re-entrant (RE) structure. Elastic resin was used to investigate the specimens’ compressive strength and energy absorption, impact reduction, and flexural properties in comparison with those of conventional foam and rigid polyethylene (PU). Despite having a lower relative density, the RE structure exhibits greater stiffness, showing up to 40% greater hardness and averaging 30.5% higher bending rigidity compared with the RD structure. However, it unexpectedly shows less stability and strength under uniaxial loading, which is 3 to 6 times weaker when compared with the non-auxetic RD structure. Although conventional PU has higher loading than 3D-printed lattices, the lattice shows excellent bendability, which is only 1.5 to 3 times stiffer than that of foam. The 3D-printed lattice in this study shows an optimal improvement of 43% in terms of impact absorption compared with foam and a 2.3% improvement compared with PU. Amongst the six different unit cell dimensions and structures studied, the RD lattice with a cell size of 5 mm is the most promising candidate; it has superior elasticity, compressive strength, and impact resistance performance whether it is under low- or high-impact conditions. The findings of this study provide a basis for the development of 3D-printed lattice sports protective chest equipment, which is more comfortable and offers improved protection for contact sports players. Full article

Orthoses are external devices designed to provide structural and functional support for disorders affecting the musculoskeletal or nervous systems. While these devices have a long history, recent technological advancements offer significant opportunities to enhance their therapeutic performance. This review examines three key innovations shaping the future of orthotic devices: additive manufacturing, auxetic metamaterials, and smart sensors. Additive manufacturing (AM), commonly known as 3D printing, is gaining prominence for its ability to create patient-specific solutions, improve design flexibility, and reduce production time. Despite these advantages, traditional fabrication methods remain dominant due to cost and regulatory challenges. Auxetic metamaterials, characterized by a negative Poisson’s ratio, allow an orthosis to dynamically conform to the patient’s anatomy and movements while maintaining stability and comfort. Thanks to synclastic deformation, auxetic structures reduce the formation of wrinkles during motion, improving body fit, and potentially enhancing comfort as well as adherence to orthosis usage recommendations. However, their integration into orthoses is still in the early stages, requiring further research and clinical validation. Finally, smart sensors have been extensively studied for the real-time monitoring of joint movement and rehabilitation progress, enabling personalized therapy and improved clinical outcomes. In conclusion, these emerging technologies—additive manufacturing, auxetic metamaterials, and smart sensors—hold great promise for next-generation orthotic devices, but widespread adoption will depend on addressing technical, economic, and practical limitations. Full article

Auxetic structures, also known as metamaterials, exhibit a negative Poisson’s ratio under applied load and have found use across a variety of applications. This behavior may arise from material properties or from the structural design itself. Depending on the intended application, such structures can be subjected to either static or dynamic loading conditions. New geometries that potentially enhance energy absorption or damping in both static and dynamic conditions were investigated in this work, using the well-known Reentrant design reported in earlier research articles as a benchmark. As an alternative to the cellular limb angles employed in the well-known Reentrant model, the effect of radial limb radius was analyzed in the novel cell designs called Arched-Reentrant. Four alternative designs have been proposed, and all analyses were conducted in ANSYS-2025-R1. The specimens were manufactured by using the 3D printing method with thermoplastic polyurethane (TPU) material having a shore hardness of 95A. In the evaluation of the outcomes resulting from different designs, the specimens were analyzed under static, impulsive, and harmonic loading conditions. The energy absorption capacities of the samples were examined in relation to their design modifications. Within the scope of the study, it was observed that Arched-Reentrant structures are capable of absorbing higher amounts of energy under static loading and exhibit greater stiffness under dynamic loads compared to conventional Reentrant structures. The impulse analysis’s findings demonstrate that the suggested Arched-Reentrant-V3 model performs better, with over 50% less displacement and comparable reaction forces. In addition, the harmonic analysis findings show that the Arched-Reentrant-V3 model has lower ground reaction forces and displacement values. As a result, the suggested model can be regarded as an efficient damping component when dynamic loading occurs. Full article

This study explores the free vibration behavior of carbon fiber-reinforced sandwich open circular cylindrical shells featuring 3D reentrant auxetic cores (3D RSOCCSs). For theoretical predictions, a model integrating the Rayleigh–Ritz method (RRM) and Reddy’s third-order shear deformation theory (TOSDT) is adopted, whereas the finite element analysis approach is used for simulation predictions. All-composite 3D RSOCCSs specimens are produced via hot-press molding and interlocking assembly, and the modal characteristics of 3D RSOCCSs are obtained through hammer excitation modal tests. The predicted modal properties are in good agreement with the experimental results. In addition, the influences of fiber ply angles and geometric parameters on the natural frequency in the free vibration are thoroughly analyzed, which can offer insights for the vibration analysis of lightweight auxetic metamaterial cylindrical shells and promote their practical use in engineering scenarios focused on vibration mitigation. Full article

Understanding three-dimensional (3D) auxetic structural responses to impact loading remains challenging due to large deformations involving failure evolution and the interaction between geometric and material instabilities. In this study, the Generalized Interpolation Material Point Method (GIMP) is used to investigate representative auxetic structures, with the focus on the negative Poisson’s ratio effect on the responses to impact loading. Using a cubic lattice model for 3D re-entrant structures, simulations with different impact speeds are performed to evaluate corresponding energy absorption characteristics and deformation behaviors. Three constitutive models for lattice materials (linear elasticity, elastoplasticity, and damage) are employed to analyze the corresponding variations in auxetic structural performance. The computational results indicate that distinct deformation mechanisms are mainly associated with microstructural geometry, while the constitutive modeling effect is not significant. The findings demonstrate the importance of the process–structure–property relationship in the impact performance of protective structures. Verification against theoretical predictions of the Poisson’s ratio–strain relationship confirms the potential of GIMP in effectively engineering auxetic structures for general applications. Full article

Hernia is a physiological condition that significantly impacts patients’ quality of life. Surgical treatment for hernias often involves the use of specialized meshes to support the abdominal wall. While this method is highly effective, it frequently leads to complications such as pain, infections, inflammation, adhesions, and even the need for revision surgeries. According to the Food and Drug Administration (FDA), hernia recurrence rates can reach up to 11%, surgical site infections occur in up to 21% of cases, and chronic pain incidence ranges from 0.3% to 68%. These statistics highlight the urgent need to improve mesh technologies to minimize such complications. The design and material composition of meshes are critical in reducing postoperative complications. Moreover, integrating drug-eluting properties into the meshes could address issues like infections and inflammation by enabling localized delivery of antibiotics and anti-inflammatory agents. Mesh design is equally important, with innovative structures like auxetic designs offering enhanced mechanical properties, flexibility, and tissue integration. These advanced designs can distribute stress more evenly, reduce fatigue, and improve performance in areas subjected to high pressures, such as during intense coughing, sneezing, or heavy lifting. Technological advancements, such as 3D printing, enable the precise fabrication of meshes with tailored designs and properties, providing new opportunities for innovation. By addressing these challenges, the development of next-generation mesh implants has the potential to reduce complications, improve patient outcomes, and significantly enhance quality of life for individuals undergoing hernia repair. Full article

This study aimed to examine the effect of the orientation angle of center facing arms on the elongation and strength of 3D-printed textiles with two different re-entrant cellular auxetic structures. An experimental research design, consisting of 6 (auxetic-structure textiles) × 3 (repetition), was employed. Star-shaped re-entrant auxetic structures (star re-entrant) with orientation angles of 25°, 30°, and 35° and floral-based star-shaped re-entrant auxetic structures (floral re-entrant) with orientation angles of 55°, 60°, and 65° were developed using the fused deposition modeling 3D-printing method through identifying commonly used auxetic structures in the 3D-printed textiles’ development. A statistically significant relationship was found between load and elongation of both star re-entrant and floral re-entrant. The findings indicated that 3D-printed textiles with both star re-entrant and floral re-entrant structures exhibited an enhanced elongation with the increase in orientation angle, making the textile products more flexible and potentially providing better wear comfort. However, the strength of both star re-entrant and floral re-entrant textiles was not significantly affected by the orientation angle of center facing arms. The findings demonstrated the potential to enhance the elongation of 3D-printed auxetic-structure textiles without compromising their strength for ensuing comfort by adjusting the orientation angle of center facing arms. Full article