Mechanical Metamaterials for Bioengineering: In Vitro, Wearable, and Implantable Applications

Kundumani Janarthanan A.K., Vaidhyanathan B.

Diabetic foot complications pose significant health risks, necessitating innovative approaches in orthotic design. This study explores the potential of additive manufacturing in producing functional footwear components with lattice-based structures for diabetic foot orthoses. Five distinct lattice structures (gyroid, diamond, Schwarz P, Split P, and honeycomb) were designed and fabricated using stereolithography (SLA) with varying strand thicknesses and resin types. Mechanical testing revealed that the Schwarz P lattice exhibited superior compressive strength, particularly when fabricated with flexible resin. Porosity analysis demonstrated significant variations across structures, with the gyroid showing the most pronounced changes with increasing mesh thickness. Real-time pressure distribution mapping, achieved through integrated force-sensitive resistors and Arduino-based data acquisition, enabled the visualization of pressure hotspots across the insole. The correlation between lattice properties and pressure distribution was established, allowing for tailored designs that effectively alleviated high-pressure areas. This study demonstrates the feasibility of creating highly personalized orthotic solutions for diabetic patients using additive manufacturing, offering a promising approach to reducing the plantar pressure in foot and may contribute to improved outcomes in diabetic foot care.

Arrick G., Sticker D., Ghazal A., Lu Y., Duncombe T., Gwynne D., Mouridsen B., Wainer J., Jepsen J.P., Last T.S., Schultz D., Hess K., Medina De Alba E., Min S., Poulsen M., et. al.

Needle-based injections currently enable the administration of a wide range of biomacromolecule therapies across the body, including the gastrointestinal tract1–3, through recent developments in ingestible robotic devices4–7. However, needles generally require training, sharps management and disposal, and pose challenges for autonomous ingestible systems. Here, inspired by the jetting systems of cephalopods, we have developed and evaluated microjet delivery systems that can deliver jets in axial and radial directions into tissue, making them suitable for tubular and globular segments of the gastrointestinal tract. Furthermore, they are implemented in both tethered and ingestible formats, facilitating endoscopic applications or patient self-dosing. Our study identified suitable pressure and nozzle dimensions for different segments of the gastrointestinal tract and applied microjets in a variety of devices that support delivery across the various anatomic segments of the gastrointestinal tract. We characterized the ability of these systems to administer macromolecules, including insulin, a glucagon-like peptide-1 (GLP1) analogue and a small interfering RNA (siRNA) in large animal models, achieving exposure levels similar to those achieved with subcutaneous delivery. This research provides key insights into jetting design parameters for gastrointestinal administration, substantially broadening the possibilities for future endoscopic and ingestible drug delivery devices. Tethered or ingestible delivery systems that deliver liquid microjets in axial and radial directions can be used to deliver macromolecules to different parts of the gastrointestinal tract with good bioavailability.

Kinnicutt L., Gaeta L.T., Rogatinsky J., Lee J., Cameron A., Naik A.J., Hess D.T., Ranzani T.

Bodaghi M., Wang L., Zhang F., Liu Y., Leng J., Xing R., Dickey M.D., Vanaei S., Elahinia M., Hoa S.V., Zhang D., Winands K., Gries T., Zaman S., Soleimanzadeh H., et. al.

Abstract Four-dimensional (4D) printing is an advanced manufacturing technology that has rapidly emerged as a transformative tool with the capacity to reshape various research domains and industries. Distinguished by its integration of time as a dimension, 4D printing allows objects to dynamically respond to external stimuli, setting it apart from conventional 3D printing. This roadmap has been devised, by contributions of 44 active researchers in this field from 32 affiliations world-wide, to navigate the swiftly evolving landscape of 4D printing, consolidating recent advancements and making them accessible to experts across diverse fields, ranging from biomedicine to aerospace, textiles to electronics. The roadmap’s goal is to empower both experts and enthusiasts, facilitating the exploitation of 4D printing’s transformative potential to create intelligent, adaptive objects that are not only feasible but readily attainable. By addressing current and future challenges and proposing advancements in science and technology, it sets the stage for revolutionary progress in numerous industries, positioning 4D printing as a transformative tool for the future.

Lin W., Yan Y., Zhao S., Qin H., Liu Y.

AbstractDigitization has brought a new era to the world, liberating information from physical media. The material structure–property relation is high‐dimensional and nonlinear, and the digitization of structure–property relations may bring unprecedented functional programmability and diversity. Here, a new concept of digital mechanical metamaterial (DMM) is presented, where property design is realized by programming the digital states of the DMM to decouple the design of the structure and property. Transforming the binary stable states of a curved beam to the digital bit, one unit cell of DMM manifests three distinct deformation responses under compression, i.e., compression–twist coupling (CTC), compression–shear coupling (CSC), and pure compression (PC). These deformation modes show notable differences in motion and stiffness, which, by digitally programming a series of DMM, can yield a spectrum of functionalities, including information encryption, stress–strain relation customization, energy absorption in cushioning, effective vibration isolation, and tunable force transmission. This study pioneers a versatile material design paradigm that provides much greater freedom for the property design of intelligent mechanical metamaterials.

Ghofrani S., Mehrizi A.A., Nasrollahi V., Dimov S.

Conventional stents have some limitations, such as dogboning and foreshortening, that can lead to issues like in-stent restenosis and thrombosis. Negative Poisson's ratio stents, called auxetic stents, are known as a solution to overcome these challenges due to their unique deformation mechanism. Auxetic stents are scale-independent, and their behavior depends solely on their geometry. In this study, a novel auxetic unit cell inspired by aestivation mechanism of the Hibiscus flower is designed, developed, and implemented in plane, and a tube to achieve a novel NPR cardiovascular stent. The stent structure is fabricated using two methods, including a novel 7-axis laser cut method capable of producing stents the same size as human blood vessels from an SS 316L tube, and fused deposition modelling 3D printing at a scale 20 times larger than the metallic sample using PLA filaments. Novel laser cut effectively overcame some challenges in laser cutting stents, including HAZ and thermal shocks. SEM images are taken from the laser cut sample, and the manufacturing method's accuracy and surface quality are investigated. Fabricated metallic and polymeric stent samples proposed negative Poisson's ratio equal to 0.89 with an average of 4.38 and 14.8 % errors, respectively, compared with finite element analysis. Finally, the structure's stress, strain energy distribution pattern, and unit cell distribution have been examined. Furthermore, the stent thickness parameter, drug release patch application, and stent implementation process are also investigated using FEM method. Proposed geometry in stent application showed solutions to conventional positive Poisson's ratio stent challenges.

Singh M., Roubertie F., Ozturk C., Borchiellini P., Rames A., Bonnemain J., Gollob S.D., Wang S.X., Naulin J., El Hamrani D., Dugot-Senant N., Gosselin I., Grenet C., L’Heureux N., Roche E.T., et. al.

Tetralogy of Fallot is a congenital heart disease affecting newborns and involves stenosis of the right ventricular outflow tract (RVOT). Surgical correction often widens the RVOT with a transannular enlargement patch, but this causes issues including pulmonary valve insufficiency and progressive right ventricle failure. A monocusp valve can prevent pulmonary regurgitation; however, valve failure resulting from factors including leaflet design, morphology, and immune response can occur, ultimately resulting in pulmonary insufficiency. A multimodal platform to quantitatively evaluate the effect of shape, size, and material on clinical outcomes could optimize monocusp design. This study introduces a benchtop soft biorobotic heart model, a computational fluid model of the RVOT, and a monocusp valve made from an entirely biological cell-assembled extracellular matrix (CAM) to tackle the multifaceted issue of monocusp failure. The hydrodynamic and mechanical performance of RVOT repair strategies was assessed in biorobotic and computational platforms. The monocusp valve design was validated in vivo in ovine models through echocardiography, cardiac magnetic resonance, and catheterization. These models supported assessment of surgical feasibility, handling, suturability, and hemodynamic and mechanical monocusp capabilities. The CAM-based monocusp offered a competent pulmonary valve with regurgitation of 4.6 ± 0.9% and a transvalvular pressure gradient of 4.3 ± 1.4 millimeters of mercury after 7 days of implantation in sheep. The biorobotic heart model, in silico analysis, and in vivo RVOT modeling allowed iteration in monocusp design not now feasible in a clinical environment and will support future surgical testing of biomaterials for complex congenital heart malformations.

Glazko K., Portnova-Fahreeva A., Mankoff-Dey A., Psarra A., Mankoff J.

Sun M., Hu X., Tian L., Yang X., Min L.

Poisson's ratio in auxetic materials shifts from typically positive to negative, causing lateral expansion during axial tension. This scale‐independent characteristic, originating from tailored architectures, exhibits specific physical properties, including energy adsorption, shear resistance, and fracture resistance. These metamaterials demonstrate exotic mechanical properties with potential applications in several engineering fields, but biomedical applications seem to be one of the most relevant, with an increasing number of articles published in recent years, which present opportunities ranging from cellular repair to organ reconstruction with outstanding mechanical performance, mechanical conduction, and biological activity compared with traditional biomedical metamaterials. Therefore, focusing on understanding the potential of these structures and promoting theoretical and experimental investigations into the benefits of their unique mechanical properties is necessary for achieving high‐performance biomedical applications. Considering the demand for advanced biomaterial implants in surgical technology and the profound advancement of additive manufacturing technology that are particularly relevant to fabricating complex and customizable auxetic mechanical metamaterials, this review focuses on the fundamental geometric configuration and unique physical properties of negative Poisson's ratio materials, then categorizes and summarizes auxetic material applications across some surgical departments, revealing efficacy in joint surgery, spinal surgery, trauma surgery, and sports medicine contexts. Additionally, it emphasizes the substantial potential of auxetic materials as innovative biomedical solutions in orthopedics and demonstrates the significant potential for comprehensive surgical application in the future.

Zhou Y., Pan Y., Sun B., Gao Q.

Auxetic metamaterials have shown great significance in the field of cardiovascular stents, but improving their applicability remains an issue. Here, we develop a type of improved auxetic metamaterial called the Re-entrant-Arrow-Snake (RAS) structure by adding arrow-shaped and snake-shaped structures to the Re-entrant (RE) structure. We first systematically study its in-plane elastic properties and compression behaviors. It is observed that the RAS structure exhibits improved vertical stiffness, horizontal flexibility, and clear auxetic effect in the vertical direction. The influence of the additional structures on the deformation pattern and the stability is also discussed by the in-plane compression analysis. Furthermore, we propose a new self-expanding (SE) vascular stent named RAS-SE based on the RAS structure. Numerical analysis demonstrates that the RAS-SE stent possesses enhanced dual-plateau radial force, negative foreshortening behavior, and improved bending flexibility, indicating better deployment performance and support in clinical applications. Biomechanical studies also show that axial deformation caused by the auxetic effect of the RAS-SE stent only slightly increases stress damage to plaque without affecting stress damage of the intima. This study further expands the application of metamaterials in SE vascular stents, and the proposed RAS structure shows high applicability on the SE stent, thus warranting further attention.

Goswami D., Kazim M., Nguyen C.T.

Abstract Purpose of Review 3D printing (3DP) technology has emerged as a valuable tool for surgeons and cardiovascular interventionalists in developing and tailoring patient-specific treatment strategies, especially in complex and rare cases. This short review covers advances, primarily in the last three years, in the use of 3DP in the diagnosis and management of heart failure and related cardiovascular conditions. Recent Findings Latest studies include utilization of 3DP in ventricular assist device placement, congenital heart disease identification and treatment, pre-operative planning and management in hypertrophic cardiomyopathy, clinician as well as patient education, and benchtop mock circulatory loops. Summary Studies reported benefits for patients including significantly reduced operation time, potential for lower radiation exposure, shorter mechanical ventilation times, lower intraoperative blood loss, and less total hospitalization time, as a result of the use of 3DP. As 3DP technology continues to evolve, clinicians, basic science researchers, engineers, and regulatory authorities must collaborate closely to optimize the utilization of 3D printing technology in the diagnosis and management of heart failure.

Zhang J., Lu S., Yang Y., Liu Y., Guo Y., Wang H.

IntroductionDesigning footwear for comfort is vital for preventing foot injuries and promoting foot health. This study explores the impact of auxetic structured shoe soles on plantar biomechanics and comfort, motivated by the integration of 3D printing in footwear production and the superior mechanical properties of auxetic designs. The shoe sole designs proposed in this study are based on a three-dimensional re-entrant auxetic lattice structure, orthogonally composed of re-entrant hexagonal honeycombs with internal angles less than 90 degrees. Materials fabricated using this lattice structure exhibit the characteristic of a negative Poisson's ratio, displaying lateral expansion under tension and densification under compression.MethodsThe study conducted a comparative experiment among three different lattice structured (auxetic 60°, auxetic 75° and non-auxetic 90°) thermoplastic polyurethane (TPU) shoe soles and conventional polyurethane (PU) shoe sole through pedobarographic measurements and comfort rating under walking and running conditions. The study obtained peak plantar pressures (PPPs) and contact area across seven plantar regions of each shoe sole and analyzed the correlation between these biomechanical parameters and subjective comfort.ResultsCompared to non-auxetic shoe soles, auxetic structured shoe soles reduced PPPs across various foot regions and increased contact area. The Auxetic 60°, which had the highest comfort ratings, significantly lowered peak pressures and increased contact area compared to PU shoe sole. Correlation analysis showed that peak pressures in specific foot regions (hallux, second metatarsal head, and hindfoot when walking; second metatarsal head, third to fifth metatarsal head, midfoot, and hindfoot when running) were related to comfort. Furthermore, the contact area in all foot regions was significantly associated with comfort, regardless of the motion states.ConclusionThe pressure-relief performance and conformability of the auxetic lattice structure in the shoe sole contribute to enhancing footwear comfort. The insights provided guide designers in developing footwear focused on foot health and comfort using auxetic structures.

Yang X., Chen Y., Chen T., Li J., Wang Y.

AbstractAssistive interfaces enable collaborative interactions between humans and robots. In contrast to traditional rigid devices, conformable fabrics with tunable mechanical properties have emerged as compelling alternatives. However, existing assistive fabrics actuated by fluidic or thermal stimuli struggle to adapt to complex body contours and are hindered by challenges such as large volumes after actuation and slow response rates. To overcome these limitations, we draw inspiration from biological protective organisms combining hard and soft phases, and propose active assistive fabrics consisting of architectured rigid tiles interconnected with flexible actuated fibers. Through programmable tessellation of target body shapes into architectured tiles and controlling their interactions by the actuated fibers, our active fabrics can rapidly (within seconds) transition between soft compliant configurations and rigid states conformable to the body (> 350 times stiffness change, loading capacity to weight ratio > 50) while minimizing the device volume after actuation. We demonstrate the versatility of our active fabrics as exosuits for tremor suppression and lifting assistance. We also present its potential as body armors for impact mitigation. Electrothermal actuators are integrated for smart actuation with convenient folding capabilities. Our work offers a practical framework for designing customizable active fabrics with shape adaptivity and controllable stiffness, these active fabrics have wide applications in wearable exosuits, haptic devices, and medical rehabilitation systems.This article is protected by copyright. All rights reserved

Chansoria P., Chaudhari A., Etter E.L., Bonacquisti E.E., Heavey M.K., Le J., Maruthamuthu M.K., Kussatz C.C., Blackwell J., Jasiewicz N.E., Sellers R.S., Maile R., Wallet S.M., Egan T.M., Nguyen J.

AbstractBioadhesive materials and patches are promising alternatives to surgical sutures and staples. However, many existing bioadhesives do not meet the functional requirements of current surgical procedures and interventions. Here, we present a translational patch material that exhibits instant adhesion to tissues (2.5-fold stronger than Tisseel, an FDA-approved fibrin glue), ultra-stretchability (stretching to >300% its original length without losing elasticity), compatibility with rapid photo-projection (<2 min fabrication time/patch), and ability to deliver therapeutics. Using our established procedures for the in silico design and optimization of anisotropic-auxetic patches, we created next-generation patches for instant attachment to tissues while conforming to a broad range of organ mechanics ex vivo and in vivo. Patches coated with extracellular vesicles derived from mesenchymal stem cells demonstrate robust wound healing capability in vivo without inducing a foreign body response and without the need for patch removal that can cause pain and bleeding. We further demonstrate a single material-based, void-filling auxetic patch designed for the treatment of lung puncture wounds.

Dong Z., Ren X., Jia B., Zhang X., Wan X., Wu Y., Huang H.

Developing patches that effectively merge intrinsic deformation characteristics of cardiac with superior tunable mechanical properties remains a crucial biomedical pursuit. Currently used traditional block-shaped or mesh patches, typically incorporating a positive Poisson's ratio, often fall short of matching the deformation characteristics of cardiac tissue satisfactorily, thus often diminishing their repairing capability. By introducing auxeticity into the cardiac patches, this study is trying to present a beneficial approach to address these shortcomings of the traditional patches. The patches, featuring the auxetic effect, offer unparalleled conformity to the cardiac complex mechanical challenges. Initially, scaffolds demonstrating the auxetic effect were designed by merging chiral rotation and concave angle units, followed by integrating scaffolds with a composite hydrogel through thermally triggering, ensuring excellent biocompatibility closely mirroring heart tissue. Tensile tests revealed that auxetic patches possessed superior elasticity and strain capacity exceeding cardiac tissue's physiological activity. Notably, Model III showed an equivalent modulus ratio and Poisson's ratio closely toward cardiac tissue, underscoring its outstanding mechanical potential as cardiac patches. Cyclic tensile loading tests demonstrated that Model III withstood continuous heartbeats, showcasing outstanding cyclic loading and recovery capabilities. Numerical simulations further elucidated the deformation and failure mechanisms of these patches, leading to an exploration of influence on mechanical properties with alternative design parameters, which enabled the customization of mechanical strength and Poisson's ratio. Therefore, this research presents substantial potential for designing cardiac auxetic patches that can emulate the deformation properties of cardiac tissue and possess adjustable mechanical parameters.

Islam M.J., Harun-Ur-Rashid M., Rahman S., Jahan I., Asthana N., Mohsin M.E., Mousa S.