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Mass-producible near-body temperature-triggered 4D printed shape memory biocomposites and their application in biomimetic intestinal stents
... Lin et al. [166] developed a PEG/PLA-based 4D-printed shape memory biocomposite by melt extrusion and printed it by FDM to produce an intestinal stent with a wave-like network. The biocomposite exhibited stress-strain behavior similar to that of biological tissues, thus effectively reducing the risk of tissue damage. ...
... (F) Feasibility of the 4D-printed shape memory intestinal stent opening simulated obstructed swine intestine. Reproduced with permission from [166]. Copyright 2023 Elsevier. ...
Shape memory polymers (SMPs) and their composites (SMPCs) are smart materials that can be stably deformed and then return to their original shape under external stimulation, thus having a memory of their shape. Three-dimensional (3D) printing is an advanced technology for fabricating products using a digital software tool. Four-dimensional (4D) printing is a new generation of additive manufacturing technology that combines shape memory materials and 3D printing technology. Currently, 4D-printed SMPs and SMPCs are gaining considerable research attention and are finding use in various fields, including biomedical science. This review introduces SMPs, SMPCs, and 4D printing technologies, highlighting several special 4D-printed structures. It summarizes the recent research progress of 4D-printed SMPs and SMPCs in various fields, with particular emphasis on biomedical applications. Additionally, it presents an overview of the challenges and development prospects of 4D-printed SMPs and SMPCs and provides a preliminary discussion and useful reference for the research and application of 4D-printed SMPs and SMPCs.
... It is widely accepted that additive manufacturing, or 3D printing, is the future for the manufacturing industry [5][6][7][8][9][10]. Therefore, it is highly desired that shape memory vitrimers (SMVs) are 3D printable. ...
Vitrimers with self‐healing, recycling, and remolding capabilities are changing the paradigm for thermoset polymer design. In the past several years, vitrimers that exhibit shape memory effects and are curable by ultraviolet (UV) light have made significant progress in the realm of 4D printing. Herein, we report a molecular dynamics (MD) modeling framework to model UV curable shape memory vitrimers. We used our framework and compared our modeling results with one UV curable shape memory vitrimer found in the literature, bisphenol A glycerolate dimethacrylate. The comparison showed reasonable agreement between the modeling and experimental results in terms of thermomechanical and shape memory properties, along with self‐healing efficiency. It was found that during recycling, it was important for the network to percolate through a majority of the system to get reasonably high recovery stress and recycling efficiency. Once this was achieved, a topological descriptor that was found to represent the compactness of the network was identified as having a very high correlation with recovery stress and recycling efficiency for networks that percolated 70% or more of the monomers in a system.
... In contrast, 4D printing enables the creation of systems that can change shape in response to temperature, light, or other environmental stimuli [8,9]. For example, it is possible to create biomedical devices that can change shape in response to body temperature or pH levels [10]. Similarly, aerospace components can be developed that adapt to changing conditions, such as solar cells of a satellite that can change shape in response to sunlight [11]. ...
This research introduces PETG-CB (poly(ethylene terephthalate) glycol modified with carbon black) composites, a new class of shape memory polymers 4D printed using the Fused Deposition Modeling (FDM) method. Nanocomposites with varying concentrations of CB (0.5 %, 1 %, and 3 % by weight) are developed to enhance the functional performance of PETG in 4D printing applications. Comprehensive characterization at the micro- and macro-scale, including dynamic thermal mechanical analysis (DMTA), scanning electron microscopy (SEM), and mechanical testing, is employed to assess the viscoelastic behavior, microstructural integrity, and mechanical strength under thermal stimulation. Experimental results reveal that CB addition significantly alters the glass transition temperature and improves mechanical properties, with the 1 % CB composite demonstrating optimal tensile strength and enhanced shape memory effects. SEM analysis confirms a uniform distribution of CB particles, contributing to the improved mechanical properties and printability of the nanocomposites. The shape memory tests show excellent recovery rates above 97 %, with faster recovery observed in composites with higher CB content. These findings highlight the potential of PETG-CB composites in applications requiring rapid response and high mechanical performance, making them promising materials for future advancements in the 4D printing technology.
... However, beyond their drug encapsulation and release functionalities, material toxicity remains an important issue, particularly upon degradation. To mitigate this, the development of biomaterials for 4D printing [153] and the use of biocompatible initiators [154] with enhanced initiating efficiency can minimize adverse effects. Despite advances in stimulus-responsive polymers for drug delivery systems, achieving precise control over stimuli such as temperature, pH, and ion responsiveness remains a challenge. ...
4D printing, the fabrication of dynamic 3D objects, has emerged as a frontier in additive manufacturing, benefiting from rapid advancements in 3D printing technologies and the development of new stimuli-responsive materials. Among the diverse materials explored for 4D printing, the hydrogel, renowned for its exceptional flexibility, biocompatibility, and tunable mechanical properties, is a class of soft materials well-suited for 4D printing. In addition to selecting and developing appropriate stimuli-responsive materials, it is important to devise suitable printing strategies to enable the fabrication of hydrogel-based structures that can perform complex shape-changing under external stimuli in various applications, such as soft robotics and biomedical areas. In view of this, various printing strategies, including structural design, printing scheme, and stimuli control are systematically summarized. This review aims to provide an up-to-date evolution of 4D-printed hydrogels and insights into the utilization of these printing strategies and printing techniques, such as direct ink writing, stereolithography, and two-photon polymerization, in the 4D printing of hydrogel structures for specific functions and applications.
... As much as 4D printing of polymers has matured in terms of expansion of material candidates, ease of manufacturing, etc., generating hollow tubes of smaller diameters and longer lengths out of thermoplastics with good printing accuracy has always been a challenge. Some studies have modified polymers chemically with supramolecular interactions 5 or via hydrogen bonding 57 , blending, and addition of reinforcing nanomaterials 58 61 , they have all explored the intrinsic shape memory property of polymers and its composites. It will be difficult to achieve complex shape changes, for instance, out-of-plane bending or twisting, in these cases. ...
Current additive manufacturing technologies wherein as-printed simple two-dimensional (2D) structures morph into complex tissue mimetic three-dimensional (3D) shapes are limited to multi-material hydrogel systems, which necessitate multiple fabrication steps and...
... Zamborsky et al. [127] illustrated the applicability of 4D printing in manufacturing blood vessels, tissues, intelligent bandages, and efficient wound healing via 4D printed latticework. With the ability of these 4D implants to be adjusted to the body changes of patients with time and advancements in artificial intelligence (AI) technologies such as robotics, satisfied recovery and repair, a key goal of precise orthopedics could be achieved [128]. Lin et al. [129] demonstrated successful FDM-based 4D printing of biomimetic intestinal stents using shape memory biocomposites. ...
Three-dimensional (3D) and four-dimensional (4D) printing have emerged as the next-generation fabrication technologies, covering a broad spectrum of areas, including construction, medicine, transportation, and textiles. 3D printing, also known as additive manufacturing (AM), allows the fabrication of complex structures with high precision via a layer-by-layer addition of various materials. On the other hand, 4D printing technology enables printing smart materials that can alter their shape, properties, and functions upon a stimulus, such as solvent, radiation, heat, pH, magnetism, current, pressure, and relative humidity (RH). Myriad of biomedical materials (BMMs) currently serve in many biomedical engineering fields aiding patients’ needs and expanding their life-span. 3D printing of BMMs provides geometries that are impossible via conventional processing techniques, while 4D printing yields dynamic BMMs, which are intended to be in long-term contact with biological systems owing to their time-dependent stimuli responsiveness. This review comprehensively covers the most recent technological advances in 3D and 4D printing towards fabricating BMMs for tissue engineering, drug delivery, surgical and diagnostic tools, and implants and prosthetics. In addition, the challenges and gaps of 3D and 4D printed BMMs, along with their future outlook, are also extensively discussed. The current review also addresses the scarcity in the literature on the composition, properties, and performances of 3D and 4D printed BMMs in medical applications and their pros and cons. Moreover, the content presented would be immensely beneficial for material scientists, chemists, and engineers engaged in AM manufacturing and clinicians in the biomedical field.
... For example, they possess extreme stiffness or flexibility, exceptional energy absorption or dissipation capabilities, or unique wave propagation characteristics. Some metamaterials can have their properties even programmed or tuned (see, e.g., [50,51] where shape memory composites are employed or [29]). Possible applications of mechanical metamaterials are broad and include areas such as vibration damping, impact protection, acoustic insulation, and advanced structural engineering. ...
... In contrast, 4D-printed devices can adapt and adjust themselves according to the body's changing needs [54][55][56]. For instance, a 4D-printed intestinal stent can be designed with near-body temperature-triggered shape-memory biocomposites to respond to changes in the patient's internal environment, allowing them to adjust their shape accordingly to provide optimal support for the affected intestinal region [57]. Additionally, 4D-printed shape-memory vascular stents using βCD-g-Polycaprolactone can automatically adjust their shape in response to changes in blood flow or vessel diameter, providing optimal support for the affected blood vessel and minimising the risk of complications. ...
4D printing has emerged as a transformative technology in the field of biomedical engineering, offering the potential for dynamic, stimuli-responsive structures with applications in tissue engineering, drug delivery, medical devices, and diagnostics. This review paper provides a comprehensive analysis of the advancements, challenges, and future directions of 4D printing in biomedical engineering. We discuss the development of smart materials, including stimuli-responsive polymers, shape-memory materials, and bio-inks, as well as the various fabrication techniques employed, such as direct-write assembly, stereolithography, and multi-material jetting. Despite the promising advances, several challenges persist, including material limitations related to biocompatibility, mechanical properties, and degradation rates; fabrication complexities arising from the integration of multiple materials, resolution and accuracy, and scalability; and regulatory and ethical considerations surrounding safety and efficacy. As we explore the future directions for 4D printing, we emphasise the need for material innovations, fabrication advancements, and emerging applications such as personalised medicine, nanomedicine, and bioelectronic devices. Interdisciplinary research and collaboration between material science, biology, engineering, regulatory agencies, and industry are essential for overcoming challenges and realising the full potential of 4D printing in the biomedical engineering landscape.
There is an increased risk of complications and even surgical failures for various types of medical devices due to difficult to control configurations and performances, incomplete deployments, etc. Shape memory polymers (SMPs)-based 4D printing technology offers the opportunity to create dynamic, personalized, and accurately controllable biomedical devices with complex configurations. SMPs, typical representatives of intelligent materials, are capable of programmable deformation in response to stimuli and dynamic remodeling on demand. 4D printed SMP medical devices not only enable active control of configuration, performance and functionality, but also open the way for minimally invasive treatments and remote controllable deployment. Here, the shape memory mechanism, actuation methods, and printing strategies of active programmable SMPs are reviewed, and cutting-edge advances of 4D printed SMPs in the fields such as bone scaffolds, tracheal stents, cardiovascular stents, cell morphological regulation, and drug delivery are highlighted. In addition, promising and meaningful future research directions for 4D printed SMP biomedical devices are discussed. The development of 4D printed SMP medical devices is inseparable from the in-depth cooperation between doctors and engineers. The application of 4D printed SMP medical devices will facilitate the rapid realization of ‘smart medical care’ and accelerate the process of ‘intelligentization’ of medical devices.
Four-dimensional (4D) printing is regarded as a methodology that links 3D printing to time, which is characterized by the evolution of predetermined structures or functions for the printed object after applying stimulation. This dynamic feature endows 4D printing the potential to be intelligent, attracting wide attention from academia and industry. The transformation of shape and function is both obtained from the programming of the object endowed by the intrinsic characteristics of the material or by the manufacturing technology. Therefore, it is necessary to understand 4D printing from the perspective of both mechanism and manufacturing. Here, the state-of-the-art 4D printing polymer was summarized, beginning with the classifications, and leading to the mechanisms, stimulations, and technologies. The links and differences between 4D printing polymer and shape memory polymer, between 4D printing and 3D printing were highlighted. Finally, the biomedical applications were outlined and the perspectives were discussed.
The rapid evolution of clinical medicine, materials science, and regenerative medicine has rendered traditional implantable scaffolds inadequate for addressing the complex therapeutic demands of various diseases. Currently, implantable scaffolds in clinical practice are mainly made of metal, with the disadvantages of high stiffness, poor toughness, and low deformation. This paper offers a thorough review of shape memory scaffolds (SMSs), emphasizing their distinctive self‐recovery and adaptive functionalities that enhance compatibility with injured tissues, surpassing the capabilities of conventional metallic biomaterials. It delves into the limitations of current clinical scaffolds and the requisite performance metrics for effective implants and outlines the essential materials and fabrication methods for SMSs. Moreover, we enumerate the biomedical applications of SMMs with different response types, including thermology‐responsive, water‐responsive, and light‐responsive. The discussion extends to the burgeoning applications of SMSs in biomedical engineering, including their utility in bone tissue engineering, cardiovascular stenting, tubular structures, and cardiac patches, which underscore their potential in minimally invasive procedures and dynamic tissue interactions. This review concludes with an analysis of current challenges and prospects, providing valuable insights for developing and applying SMSs in the biomedical sector.
Environmental economics is intensifying the necessity for the advancement of recycling technologies to address the increasing volume of discarded thermoset polymers. The covalent adaptable networks (CANs) provide a new strategy...
Self-expanding biodegradable stents are expected to replace metallic stents in the treatment of peripheral artery disease, which may cause numerous problems to human health. Since the materials used in polymeric-based stents are more suited to human cells, they are considered the next generation of these medical devices. The fabrication of polymeric stents with optimized parametric 3D printing settings can surely improve their mechanical performance including radial strength which is considered as one of the crucial factors for the efficient functioning of the stent. The radial supporting capability of the stent should be taken into consideration by the vessel to restore the patency of blocked peripheral arteries with varying characteristics and functions. In this work, a double arrowhead 3D-printed PLA stent's distinct mechanical properties are developed and described. The fused deposition modeling mechanism of 3D printing was used to manufacture the double arrowhead stent specimens to analyze the radial strength. For the analysis of Stents with different sets of geometric parameters (outer diameter, height of stent, strut diameters, width of strut) were developed. The results demonstrate that for the same set of other dimensional parameters, the lowest diameter stents showed the highest radial strength in the experiments also it is evident that when strut diameter increases along with the angle between the axial direction and support strut (ϕ), and the angle between the axial direction and re-entrant strut (θ), results increase in the support strut cross-sectional (coverage) area resulting in the increased radial strength. Another observation is that the radial recovery ratio and length recovery ratios are 91 to 95% and 92 to 98% respectively which is suitable for polymeric stent application.
Additive manufacturing, widely known as 3D printing, has revolutionized the production of biomaterials. While conventional 3D-printed structures are perceived as static, 4D printing introduces the ability to fabricate materials capable of self-transforming their configuration or function over time in response to external stimuli such as temperature, light, or electric field. This transformative technology has garnered significant attention in the field of biomedical engineering due to its potential to address limitations associated with traditional therapies. Here, we delve into an in-depth review of 4D-printing systems, exploring their diverse biomedical applications and meticulously evaluating their advantages and disadvantages. We emphasize the novelty of this review paper by highlighting the latest advancements and emerging trends in 4D-printing technology, particularly in the context of biomedical applications.
As a steady stream of electronic devices being discarded, a vast amount of electronic substrate waste of petroleum‐based nondegradable polymers is generated, raising endless concerns about resource depletion and environmental pollution. With coupled reagent (CR)‐grafted artificial marble waste (AMW@CR) as functional fillers, polylactic acid (PLA)‐based highly stretchable biodegradable green composite (AMW@CR‐SBGC) is prepared, with elongation at break up to more than 250%. The degradation mechanism of AMW@CR‐SBGC is deeply revealed. AMW@CR not only contributed to the photodegradation of AMW@CR‐SBGC but also significantly promoted the water degradation of AMW@CR‐SBGC. More importantly, AMW@CR‐SBGC showed great potential as sustainable green electronic substrates and AMW@CR‐SBGC‐based electronic skin can simulate the perception of human skin to strain signals. The outstanding programmable degradability, recyclability, and reusability of AMW@CR‐SBGC enabled its application in transient electronics. As the first demonstration of artificial marble waste in electronic substrates, AMW@CR‐SBGC killed three birds with one stone in terms of waste resourcing, e‐waste reduction, and saving nonrenewable petroleum resources, opening up vast new opportunities for green electronics applications in areas such as health monitoring, artificial intelligence, and security.
Stent placement is an effective palliation therapy for malignant colorectal obstruction. However, recurrent obstruction is a common severe complication caused by tumor ingrowth into the stent lumen. Conventional covered stents play a part in preventing the tumor from growing inward but at the expense of significantly increasing the risk of stent migration. Therefore, there is an urgent demand to develop stents with sustained antitumor and antimigration abilities. Herein, we propose a facile method for fabricating multifunctional bioinspired colorectal stents using 3D printing technology. Inspired by high-adhesion biological structures (gecko feet, tree frog toe pads, and octopus suckers) in nature, different types of bioinspired colorectal stents are designed to reduce migration. After functionalization with graphene oxide (GO), bioinspired colorectal stents show excellent and controllable photothermal performance, which is validated by effective ablation of colon cancer cells in vitro and tumors in vivo. Besides, the bioinspired colorectal stents demonstrate the feasibility of transanal placement and opening of the obstructed colon. More importantly, the facile manufacturing process of multifunctional bioinspired colorectal stents is appealing for mass production. Hence, the developed multifunctional bioinspired colorectal stents exhibit a highly promising potential in clinical applications.
4D printing is an emerging fabrication technology that enables 3D printed structures to change configuration over “time” in response to an environmental stimulus. Compared with other soft active materials used for 4D printing, shape‐memory polymers (SMPs) have higher stiffness, and are compatible with various 3D printing technologies. Among them, ultraviolet (UV)‐curable SMPs are compatible with Digital Light Processing (DLP)‐based 3D printing to fabricate SMP‐based structures with complex geometry and high‐resolution. However, UV‐curable SMPs have limitations in terms of mechanical performance, which significantly constrains their application ranges. Here, a mechanically robust and UV‐curable SMP system is reported, which is highly deformable, fatigue resistant, and compatible with DLP‐based 3D printing, to fabricate high‐resolution (up to 2 µm), highly complex 3D structures that exhibit large shape change (up to 1240%) upon heating. More importantly, the developed SMP system exhibits excellent fatigue resistance and can be repeatedly loaded more than 10 000 times. The development of the mechanically robust and UV‐curable SMPs significantly improves the mechanical performance of the SMP‐based 4D printing structures, which allows them to be applied to engineering applications such as aerospace, smart furniture, and soft robots.
Transcatheter closure has been widely accepted as a highly effective way to treat abnormal blood flows and/or embolization of thrombus in the heart. It allows the closure of four types of congenital heart defects (CHDs) and stroke-associated left atrial appendage (LAA). The four types of CHDs include atrial septal defect (ASD), patent foramen ovale (PFO), patent ductus arteriosus (PDA), and ventricular septal defect (VSD). Advancements in the materials and configurations of occlusion devices have spurred the transition from open-heart surgery with high complexity and morbidity, or lifelong medication with a high risk of bleeding, to minimally invasive deployment. A variety of occlusion devices have been developed over the past few decades, particularly novel ones represented by biodegradable and 3D-printed occlusion devices, which are considered as next-generation alternatives to conventional Nitinol-based occlusion devices due to biodegradability, customization, and improved biocompatibility. The aim here is to comprehensively review the next-generation occlusion devices in terms of materials, configurations, manufacturing methods, deployment strategies, and (if available) experimental results or clinical data. The current challenges and the direction of future work are also proposed.
Auxetic mechanical metamaterials, which expand transversally when axially stretched, are widely used in flexible electronics and aerospace. However, these chiral metamaterials suffer from three severe limitations as a typical auxetic metamaterials: narrow strain range, non‐tunable mechanical behaviors, and fixed properties after fabrication. In this work, 4D printing chiral metamaterials with tunable, programmable, and reconfigurable properties are developed. The deformation mode transforms from bending dominated to stretching dominated under large deformation, leading to the stress–deformation (σ–λ) behavior of the auxetic metamaterials similar to those of the biomaterials (“J”‐shaped), such as tissues or organs. The programmability and reconfigurability of the developed chiral metamaterials allow mechanical behavior to change between different biomaterials with high precision. Furthermore, scaffolds with personalized mechanical properties as well as configurations and metamaterials‐based light‐emitting diode integrated devices demonstrate potential applications in tissue engineering and programmable flexible electronics. Auxetic material expands transversally when axial stretched, and exhibits excellent mechanical properties. This work introduces novel auxetic materials with wavy ligaments through 4D printing. The metamaterials solve the narrow strain range, non‐tunable mechanical behaviors, and fix properties after fabrication of the typical chiral structures. The developed metamaterials demonstrate potential applications in biomaterials, flexible electronics, and tissue engineering.
Advanced mechanical metamaterials with unusual thermal expansion properties represent an area of growing interest, due to their promising potential for use in a broad range of areas. In spite of previous work on metamaterials with large or ultralow coefficient of thermal expansion (CTE), achieving a broad range of CTE values with access to large thermally induced dimensional changes in structures with high filling ratios remains a key challenge. Here, design concepts and fabrication strategies for a kirigami‐inspired class of 2D hierarchical metamaterials that can effectively convert the thermal mismatch between two closely packed constituent materials into giant levels of biaxial/uniaxial thermal expansion/shrinkage are presented. At large filling ratios (>50%), these systems offer not only unprecedented negative and positive biaxial CTE (i.e., −5950 and 10 710 ppm K⁻¹), but also large biaxial thermal expansion properties (e.g., > 21% for 20 K temperature increase). Theoretical modeling of thermal deformations provides a clear understanding of the microstructure–property relationships and serves as a basis for design choices for desired CTE values. An Ashby plot of the CTE versus density serves as a quantitative comparison of the hierarchical metamaterials presented here to previously reported systems, indicating the capability for substantially enlarging the accessible range of CTE.
Over the past decades, interest in shape memory polymers (SMPs) has persisted, and immense efforts have been dedicated to developing SMPs and their multifunctional composites. As a class of stimuli-responsive polymers, SMPs can return to their initial shape from a programmed temporary shape under external stimuli, such as light, heat, magnetism, and electricity. The introduction of functional materials and nanostructures results in shape memory polymer composites (SMPCs) with large recoverable deformation, enhanced mechanical properties, and controllable remote actuation. Because of these unique features, SMPCs have a broad application prospect in many fields covering aerospace engineering, biomedical devices, flexible electronics, soft robotics, shape memory arrays, and 4D printing. Herein, a comprehensive analysis of the shape recovery mechanisms, multifunctionality, applications, and recent advances in SMPs and SMPCs is presented. Specifically, the combination of functional, reversible, multiple, and controllable shape recovery processes is discussed. Further, established products from such materials are highlighted. Finally, potential directions for the future advancement of SMPs are proposed.
Endothelialization is of great significance for vascular remodeling, as well as for the success of implanted vascular grafts/stents in cardiovascular disease treatment. However, desirable endothelialization on synthetic biomaterials remains greatly challenging owing to extreme difficulty in offering dynamic guidance on endothelial cell (EC) functions resembling the native extracellular matrix-mediated effects. Here, we demonstrate a bilayer platform with near-infrared-triggered transformable topographies, which can alter the geometries and functions of human ECs by tunable topographical cues in a remote-controlled manner, yet cause no damage to the cell viability. The migration and the adhesion/spreading of human ECs are respectively promoted by the temporary anisotropic and permanent isotropic topographies of the platform in turn, which appropriately meet the requirements of stage-specific EC manipulation for endothelialization. In addition to the potential of promoting the development of a new generation of vascular grafts/stents enabling rapid endothelialization, this stage-specific cell-manipulation platform also holds promise in various biomedical fields, since the needs for stepwise control over different cell functions are common in wound healing and various tissue-regeneration processes.
Origami has received significant interest from the science and engineering community as a design method and used to construct expandable mechanical metamaterials by folding and unfolding along the crease line. Here, we adopted a 4D printing method with shape memory polymer to create a smart origami metamaterial with tunable stress-strain curves, controllable compression twist deformation, shape programming and self-expansion, and develop its deformation theory model. The effects of unit structure parameters and temperature field on the mechanical properties and functional deformation of the metamaterial are analyzed using experiments, theory model and finite element method. The origami structure can realize the shape programming, self-expansion and mechanically tunable by control temperature, and switch between monostability and bistability by adjusting the parameters. The structure parameters, temperature field, and series combination method are used to adjust and control the stress-strain curves and compression twist deformation behavior of the metamaterials. This multifunctional metamaterial may find a wide range of applications, such as, mechanical storage, tunable shock absorption interface and soft robots.
Many biological tissues offer J-shaped stress–strain responses, since their microstructures exhibit a three-dimensional (3D) network construction of curvy filamentary structures that lead to a bending-to-stretching transition of the deformation mode under an external tension. The development of artificial 3D soft materials and device systems that can reproduce the nonlinear, anisotropic mechanical properties of biological tissues remains challenging. Here we report a class of soft 3D network materials that can offer defect-insensitive, nonlinear mechanical responses closely matched with those of biological tissues. This material system exploits a lattice configuration with different 3D topologies, where 3D helical microstructures that connect the lattice nodes serve as building blocks of the network. By tailoring geometries of helical microstructures or lattice topologies, a wide range of desired anisotropic J-shaped stress–strain curves can be achieved. Demonstrative applications of the developed conducting 3D network materials with bio-mimetic mechanical properties suggest potential uses in flexible bio-integrated devices.
Four-dimensional (4D) printing, integrates transformation information into three-dimensional (3D)-printed structures, which means that 3D-printed structures are able to change their shapes, properties, or functionalities over time. Here, two types of shape memory personalized vascular stents with negative Poisson’s ratio structure are developed via 4D printing. The genetic algorithm is used to optimize the structure. Axial compression tests, radial compression tests and three-point bending tests are carried out to study the mechanical properties of the stents. In addition, fluid-structure interaction and stress distribution during the shape recovery process are investigated based on finite element method. The shape memory behaviors of the stents are excellent and in vitro feasibility tests demonstrate that the stents can expand the simulated narrow blood vessel rapidly. Therefore, 4D printed shape memory stents with negative Poisson’s ratio structure are highly promising for the treatment of vascular stenosis.
Soft biomaterials have wide applications in many areas. However, one material can only cover a specific range of mechanical performance such as the elastic modulus and stretchability. In order to improve the mechanical performance of soft biomaterials, lattice structures are embedded to reinforce the biomaterials. In this paper, rectangular and triangular lattice structures formed by modified horseshoe microstructures are used because their mechanical properties are tunable and can be tailored precisely to match the desire properties by adjusting four geometrical parameters, the length L, radius R, width w and arc angle 0. A theoretical design framework for the modified horseshoe lattice structures is developed to predict the dependence of the mechanical behaviors on geometrical parameters. Both experiments and finite element simulations on lattice structures are conducted to validate the theoretical models. Results show that a wide range of design space for the elastic modulus (a few kPa to hundreds of MPa), stretchability (strain up to 180%) and Poisson ratio (ranging from -0.5 to 1.2) can be achieved. Experiments on lattice-hydrogel composites are also conducted to verify the reinforcement effect of lattice structures on the hydrogel. This work provides a theoretical method to predict the mechanical behaviors of the lattice structures and aid the rational design of the reinforced biomaterials, which has applications in tissue engineering, drug delivery and intraocular lenses.
Most natural materials expand uniformly in all directions upon heating. Artificial, engineered systems offer opportunities to tune thermal expansion properties in interesting ways. Previous reports exploit diverse design principles and fabrication techniques to achieve a negative or ultralow coefficient of thermal expansion, but very few demonstrate tunability over different behaviors. This work presents a collection of 2D material structures that exploit bimaterial serpentine lattices with micrometer feature sizes as the basis of a mechanical metamaterials system capable of supporting positive/negative, isotropic/anisotropic, and homogeneous/heterogeneous thermal expansion properties, with additional features in unusual shearing, bending, and gradient modes of thermal expansion. Control over the thermal expansion tensor achieved in this way provides a continuum-mechanics platform for advanced strain-field engineering, including examples of 2D metamaterials that transform into 3D surfaces upon heating. Integrated electrical and optical sources of thermal actuation provide capabilities for reversible shape reconfiguration with response times of less than 1 s, as the basis of dynamically responsive metamaterials.
Implantation of occlusion devices is an effective approach for the treatment of congenital heart diseases in the clinic. However, most commercial clinical occlusion devices are currently made of nondegradable metals, which may lead to complications such as perforation, allergies, and erosion. In this work, 4D‐printed novel, biodegradable, remotely controllable, and personalized shape memory occlusion devices are demonstrated and atrial septal defect occluders are exemplified. By incorporating Fe3O4 magnetic particles into the shape memory poly(lactic acid) matrix, the deployment of the occluders can be controlled remotely after implantation. The excellent cytocompatibility and histocompatibility are conducive to cell adhesion and ingrowth of granulation tissues into the occluders, thus facilitating rapid endothelialization. In addition, personalized shape memory occluders ensure an ideal fit and provide sufficient support for defects. Therefore, 4D‐printed shape memory occluders can be used as a potential substitute for metal occlusion devices. 4D printed novel, biodegradable, remotely controllable, and personalized shape memory occluders are proposed. The occluders can avoid serious complications that are caused by using metal occluders and can avoid potential dangers of nondegradable metal occluders remaining in the body forever. In addition, their good biocompatibility facilitates endothelialization, and excellent shape recovery performance ensures a rapid and perfect sealing of defects.
Most of the current concepts for a visual prosthesis are based on neuronal electric stimulation. However, existing visual prostheses confront several challenges in electrodes that limit the effectiveness of stimulation. First, there is an inherent conflict between the needs of minimally invasive implantation for minimizing traumas and the requirements of implanted electrodes with large areas for obtaining wide field and high‐resolution vision. Second, the mechanical and geometrical mismatches between implanted electrodes and retina tissues also affect the effectiveness of stimulation. To address these challenges, flexible microelectrode arrays (fMEAs) with expanded areas, high‐density electrodes, and unique self‐unfolding capabilities are here reported, which will be feasible for minimally invasive implantation and accommodate large strain and geometrical curvature for potentially improving both the visual field and visual acuity. To obtain the flexible nature and programmable self‐unfolding property, the fMEAs are formulated based on a shape memory polymer with appropriate physicochemical properties. At the physiological temperature (37 °C), programmable shape deformation from a tubular shape to a unfolded film shape is enabled by the fMEAs with a large area (10 × 10 mm²) and high‐density electrodes (126 channels), implying their superior potential for minimally invasive implantation, excellent shape adaption to retinal tissues, and high‐efficiency stimulation.
Advances in areas such as data analytics, genomics, and imaging have revealed individual patient complexities and exposed the inherent limitations of generic therapies for patient treatment. These observations have also fueled the development of precision medicine approaches, where therapies are tailored for the individual rather than the broad patient population. 3D printing is a field that intersects with precision medicine through the design of precision implants with patient-directed shapes, structures, and materials or for the development of patient-specific in vitro models that can be used for screening precision therapeutics. Toward their success, advances in 3D printing and biofabrication technologies are needed with enhanced resolution, complexity, reproducibility, and speed and that encompass a broad range of cells and materials. The overall goal of this progress report is to highlight recent advances in 3D printing technologies that are helping to enable advances important in precision medicine.
Heart valves are characterized to be highly flexible yet tough, and exhibit complex deformation characteristics such as nonlinearity, anisotropy, and viscoelasticity, which are, at best, only partially recapitulated in scaffolds for heart valve tissue engineering (HVTE). These biomechanical features are dictated by the structural properties and microarchitecture of the major tissue constituents, in particular collagen fibers. In this study, the unique capabilities of melt electrowriting (MEW) are exploited to create functional scaffolds with highly controlled fibrous microarchitectures mimicking the wavy nature of the collagen fibers and their load‐dependent recruitment. Scaffolds with precisely‐defined serpentine architectures reproduce the J‐shaped strain stiffening, anisotropic and viscoelastic behavior of native heart valve leaflets, as demonstrated by quasistatic and dynamic mechanical characterization. They also support the growth of human vascular smooth muscle cells seeded both directly or encapsulated in fibrin, and promote the deposition of valvular extracellular matrix components. Finally, proof‐of‐principle MEW trileaflet valves display excellent acute hydrodynamic performance under aortic physiological conditions in a custom‐made flow loop. The convergence of MEW and a biomimetic design approach enables a new paradigm for the manufacturing of scaffolds with highly controlled microarchitectures, biocompatibility, and stringent nonlinear and anisotropic mechanical properties required for HVTE.
Three-dimensional (3D) printing offers the potential for rapid customization of medical devices. The advent of 3D-printable biomaterials has created the potential for device control in the fourth dimension: 3D-printed objects that exhibit a designed shape change under tissue growth and resorption conditions over time. Tracheobronchomalacia (TBM) is a condition of excessive collapse of the airways during respiration that can lead to life-threatening cardiopulmonary arrests. We demonstrate the successful application of 3D printing technology to produce a personalized medical device for treatment of TBM, designed to accommodate airway growth while preventing external compression over a predetermined time period before bioresorption. We implanted patient-specific 3D-printed external airway splints in three infants with severe TBM. At the time of publication, these infants no longer exhibited life-threatening airway disease and had demonstrated resolution of both pulmonary and extrapulmonary complications of their TBM. Long-term data show continued growth of the primary airways. This process has broad application for medical manufacturing of patient-specific 3D-printed devices that adjust to tissue growth through designed mechanical and degradation behaviors over time.
Copyright © 2015, American Association for the Advancement of Science.
Biodegradable stents are an attractive alternative to self-expanding metal stents in the treatment of intestinal strictures. Biodegradable stent can be made of biodegradable polymers and biodegradable metals (magnesium alloys). An overview on current biodegradable intestinal stents is presented. The future trends and perspectives in the development of biodegradable intestinal stents are proposed. For the biodegradable polymer intestinal stents, the clinical trials have shown promising results, although improved design of stents and reduced migration rate are expected. For the biodegradable magnesium intestinal stents, results of preliminary studies indicate magnesium alloys to have good biocompatibility. With many of the key fundamental and practical issues resolved and better methods for adjusting corrosion resistance and progressing biocompatibilities of magnesium alloys, it is possible to use biodegradable intestinal stents made of magnesium alloys in hospital in the not too distant future.
The existing mechanical metamaterials are often designed with periodic inter-connected structs with simple cylindrical or uniform hierarchical geometries, which relies on their parent materials to either have a good mechanical performance with low recoverability, or significantly sacrifices their mechanical performances to be highly recoverable. Biological fibrous structures are often evolved with a composition of different fibrous morphologies to possess a desired balance of mechanical performances and recovery. In this study, we developed digital design algorithms to generate the next-generation metamaterials with composite bio-inspired twisting fibrotic structs that are rubber-like recoverable without significant scarification of their mechanical performances. A machine learning predictive model is trained based on experimental data to reveal the resulted specific energy absorption (SEA) and SEA recoveries for such metamaterials with complicated fiber-composition mechanisms. To further understand the fundamental structural recovery mechanisms of the natural fibers, we derived the elastoplastic theories of the twisting fibrotic structs, and revealed that such structs possesses a rubber-like fracture strain with significantly improved specific energy absorption. Our studies combined the structural recovery mechanisms of the composite natural fibrous structures and mechanical metamaterials, liberates the design potential of materials with engineerable optimal balances of their mechanical performances and recoverability.
Rapid development in 3D printing technology has stimulated enthusiasm in the functional design of metamaterials with unique properties, in which multiple properties should be simultaneously optimized. However, this is challenging because different properties, such as mechanical and mass-transport properties, are often coupled strongly and cannot be adjusted independently. Herein, we propose an anisotropy-inspired and simulation-guided microlattice metamaterial design strategy that realizes independent tailoring of the elastic response and fluid transport performances. Diamond microlattice metamaterials are used for demonstration, constructed by using different facets ([001], [110] and [111]) and rotation degrees (15°/step), inspired from the atoms’ arrangements. Through computational analyses, it is proven that the coupled relationship of mechanical and transport properties are abated and have directional dependence on crystal planes and orientation directions. Three microlattice metamaterials and a gradient microlattice metamaterial were fabricated by 3D printing for experimental verification. The assigned layer-by-layer deformation process and specific mass-transport characteristic of the gradient microlattice metamaterial were easily endowed. This study offers an approach to decouple synergy and enable separate tailoring for multi-physical metamaterials in a much larger performance regulation space, which can effectively guide simultaneous improvements toward practical applications.
Quasicrystals can enhance wave transmission and boost nonlinear phenomena due to rotational symmetry forbidden in conventional periodic crystals. As a projection of higher-dimensional quasicrystal lattice, quasiperiodic structures represent a novel platform that exhibits robust microwave-absorbing capacity in thin thickness and digs out the influence of structural configurations on electromagnetic wave absorption from local and global aspects. Due to the synergy effect of composites and structure, quasiperiodic metamaterials with Penrose tiling achieve 12.2 GHz in effective absorption bandwidth (reflection loss < −10 dB), from 5.78 GHz to 18.00 GHz with 2 mm thickness. It has obvious advantages in absorbing electromagnetic wave compared with corresponding periodic absorbers according to the characteristic of local anisotropy and higher order translational symmetry in Brillouin zone. By enhancing multiple scattering and nonlinear coupling effects, Penrose tiling provides new insights to design absorbers with outstanding electromagnetic performance and higher flexibility and tunability.
4D printing adds time as the fourth dimension to 3D printing, which has been actively explored in the biomedical field to develop patient-specific implants due to the ease of manufacturing complex architectures and the capability of dynamic transformations. However, the 4D printing filament used for fused deposition modeling (FDM) is quite limited. Here, 4D printing shape memory polybutylene succinate/polylactic acid (PBS/PLA) composite filament is prepared. The mechanical properties, surface morphology, and shape memory performances of the printed specimens are investigated. Besides, graphene oxide functionalized PBS/PLA shows attractive photothermal properties under near-infrared (NIR) irradiation, and a dynamic, remote, and accurate controlled 4D transformation of a porous scaffold is exhibited. As the first demonstration of 4D printing filament of PBS/PLA for FDM, this work shows its promising application prospects in tissue engineering, photothermal therapy, etc. Additionally, NIR-triggered 4D transformation solves the problem that the conventional thermal-trigger transformation process is difficult to control.
Soft network materials represent a class of emerging cellular materials that have well-organized micro-architectures inspired by network microstructures found in many soft biological tissues. Apart from a good combination of low density, high stretchability and high air permeability, the high degree of design flexibility of soft network materials allows precise customization of mechanical properties by rationally tailoring their microstructural architecture and optimizing selections of constituent materials. These intriguing properties have enabled a range of promising applications in cutting-edge technologies, such as bio-integrated electronics and regenerative medicine. This review summarizes the latest progress in the design and fabrication of soft network materials, as well as their representative applications in biomedical devices, tissue engineering and other areas. It focuses on fundamental principles, design concepts and fabrication techniques of soft network materials that consist of either periodically or randomly distributed microstructures. Rational designs of these soft network materials result in customized mechanical properties that mimic or even exceed those of soft biological tissues. Finally, perspectives on the remaining challenges and open opportunities are provided.
Mechanical metamaterials with tunable thermal expansion are of increasing interest due to their capability for matching the thermal expansion of surrounding components to maintain high-level thermal-mechanical stability upon a temperature change and show their promising applications in the fields of flexible electronics, aerospace, MEMS, and precision instruments. Though numerous of studies on metamaterials with zero thermal expansion of coefficient (CTE) has been developed to access these demands, the experimentally demonstrated designs with a remarkable zero CTE value (e.g. <0.5ppm/K) still remain a challenge. In this paper, a design concept of metamaterial capable of offering a tailorable CTE, especially the excellent thermal-mechanical stability, is systematically studied, whose underlying mechanism is the conversion of thermal-induced deflection of bilayer beams (in Al and Ti) into unusual, effective thermal expansion or shrinkage of metamaterials. Notably, the experimentally demonstrated CTE of this metamaterial is 0.42ppm/K, which is the unprecedented zero CTE result as compared to the previously reported studies. The theoretical model for CTE and elastic modulus of this design, which is verified by FEA and experiments, provides a clear understanding of relationships between configuration parameters and effective thermal and mechanical performances. Combined theoretical predictions, FEA, and experimental studies demonstrate the capability of this metamaterial to serve as a design platform for devices or components that require excellent thermal-mechanical stability.
The significant mismatch of mechanical properties between the implanted medical device and biological tissue is prone to cause wear and even perforation. In addition, the limited biocompatibility and nondegradability of commercial Nitinol-based occlusion devices can easily lead to other serious complications, such as allergy and corrosion. The present study aims to develop a 4D printed patient-specific absorbable left atrial appendage occluder (LAAO) that can match the deformation of left atrial appendage (LAA) tissue to reduce complications. The desirable bioinspired network is explored by iterative optimization to mimic the stress-strain curve of LAA tissue and LAAOs are designed based on the optimal network. In vitro degradation tests are carried out to evaluate the effects of degradation on mechanical properties. In addition, 48 weeks of long-term subcutaneous implantation of the occluder shows favorable biocompatibility, and the 20-cycle compression test demonstrates outstanding durability of LAAO. Besides, a rapid, complete, and remote-controlled 4D transformation process of LAAO is achieved under the trigger of the magnetic field. The deployment of the LAAO in an isolated swine heart initially exhibits its feasibility for transcatheter LAA occlusion. To the best of our knowledge, this is the first demonstration of the 4D printed LAA occlusion device. It is worth noting that the bioinspired design concept is not only applicable to occlusion devices, but also to many other implantable medical devices, which is conducive to reducing complications, and a broad range of appealing application prospects can be foreseen.
Emerging wearable and implantable biodevices have been significantly revolutionizing the diagnosis and treatment of disease. However, the geometrical mismatch between tissues and biodevices remains a great challenge for achieving optimal performances and functionalities for biodevices. Shape-adaptable biodevices enabling active compliance with human body tissues offer promising opportunities for addressing the challenge through programming their geometries on demand. This article reviews the design principles and control strategies for shape-adaptable biodevices with programmable shapes and actively compliant capabilities, which have offered innovative diagnostic/therapeutic tools and facilitated a variety of wearable and implantable applications. The state-of-the-art progress in applications of shape-adaptable biodevices in the fields of smart textiles, wound care, healthcare monitoring, drug and cell delivery, tissue repair and regeneration, nerve stimulation and recording, and biopsy and surgery, is highlighted. Despite the remarkable advances already made, shape-adaptable biodevices still confront many challenges on the road toward the clinic, such as enhanced intelligence for actively sensing and operating in response to physiological environments. Next-generation paradigms will shed light on future directions for extending the breadth and performance of shape-adaptable biodevices for wearable and implantable applications.
Negative stiffness (NS) mechanical metamaterials have excellent application prospect in a broad range of fields such as energy trapping, repeated energy absorption and so on. Although various kinds of NS mechanical metamaterials have been proposed, one configuration cannot simultaneously achieve multi-stability and mono-stability. This paper presented a novel multifunctional NS mechanical metamaterial structure, which possessed tailored functions of multi-stable and compressive mono-stable state without geometrical parameters adjustment. The novel multifunctional NS mechanical metamaterial structure with a conical shape consisted of both soft and hard material part and was fabricated by additive manufacturing technology. NS behaviors were achieved by the instability of the soft counterpart. Mechanical performance of this novel multifunctional NS mechanical metamaterial structure under axial compression was experimentally and numerically investigated. Influences of geometrical parameters tailoring stable state were systematically investigated and the ratio of offset distance, tilt angle, slenderness were found the key factors. Effective methods to make sure the tri-layer metamaterial structure achieving multi-stable after unloading from completely compacted state were proposed.
Four-dimensional (4D) printing is an emerging and highly innovative additive manufacturing process by which to fabricate pre-designed, self-assembly structures with the ability to transform over time. However, one of the critical challenges of 4D printing is the lack of advanced 4D printing systems that not only meet all the essential requirements of shape change but also possess smart, dynamic capabilities to spatiotemporally and instantly control the shape-transformation process. Here, we present a facile 4D printing platform which incorporates nanomaterials into the conventional stimuli-responsive polymer, allowing the 4D printed object to achieve a dynamic and remote controlled, on-time and position shape transformation. A proof-of-concept 4D printed brain model was created using near-infrared light (NIR) responsive nanocomposite to evaluate the capacity for controllable 4D transformation, and the feasibility of photothermal stimulation for modulating neural stem cell behaviors. This novel 4D printing strategy can not only be used to create dynamic 3D patterned biological structures that can spatiotemporally control their shapes or behaviors of transformation under a human benign stimulus (NIR), but can also provide a potential method for building complex self-morphing objects for widespread applications.
In‐stent restenosis caused by tumor ingrowth is a major problem for patients undergoing stent placement because conventional stents often lack sustainable antitumor capabilities. The aim of this work is to develop a silk fibroin (SF)‐based nanofibrous membrane that is loaded with combined‐therapy drugs by using electrospinning technologies, which is further coated on a polydioxanone (PDO) stent and used for the treatment of colorectal cancer (CRC). In order to improve treatment effectiveness, a combination of therapeutic drugs, i.e., curcumin (CUR) and 5‐fluorouracil (5‐FU), is dissolved into SF solution and then eletrospun onto the surface of the PDO stent. The morphology, secondary structure, and in vitro drug release profiles of the membranes are characterized. The antitumor efficacy is assessed in vitro and in vivo using a human CRC cell line and normal cells, and tumor‐bearing nude mice. In vitro and in vivo studies on the nanofibrous memembrane‐coating demonstrate improved antitumor effects for the CUR/5‐FU dual drug system which can be attributed to cell cycle arrest in the S phase in association with induced apoptosis in tumor cells by blocking signal transducer and activator of transcription3 (Stat3) and nuclear factor kappa beta (NF‐kB) signaling pathways, suggesting potential in the treatment of CRC in the future. Intestinal obstruction and stenosis are the main symptoms of patients with colorectal cancer. This paper describes a drug‐loaded fibrous silk fibroin (SF) membrane produced by adding curcumin and 5‐fluorouracil into the SF spinning solution for sustained drug release. The membranes as the coating of stent placement have potential in the management of cancer progress and drug‐resistance of tumor cells.
Objectives:
The goal of this study was to report the early and late complications experienced in atrial septal defect (ASD) transcatheter closure.
Background:
Atrial septal defect transcatheter occlusion techniques have become an alternative to surgical procedures. A number of different devices are available for transcatheter ASD closure. The type and rate of complications are different for different devices.
Methods:
Between December 1996 and January 2001, 417 patients (mean age: 26.6 +/- 19 years) underwent transcatheter occlusion of secundum type ASD. Complications were categorized into major and minor. Two different devices were used: the CardioSEAL/STARFlex in 159 patients and the Amplatzer septal occluder in 258 patients.
Results:
Thirty-four patients experienced 36 complications during the hospitalization (8.6%, 95% confidence interval: 6.1% to 11.1%). Ten patients underwent elective surgical repair because of device malposition (three patients) or device embolization (seven patients). Twenty-four patients experienced 25 minor complications: unsatisfactory device position or embolization. Devices were retrieved using a gooseneck snare and/or a basket; 11 patients experienced arrhythmic problems. Other complications were: pericardial effusion, thrombus formation on the left atrial disc, right iliac vein dissection, groin hematoma, hemorrhage in the retropharynx and sizing balloon rupture. Two patients had late complications: peripheral embolization in the left leg one year after implantation of an Amplatzer device and sudden death 1.5 year later.
Conclusions:
Our series of patients with ASD by transcatheter occlusion shows that the procedure is safe and effective in the vast majority of cases. To further reduce the complications rate, the criteria of device selection according to ASD morphology and some technical tips during implantation are discussed.
Transcatheter closure of secundum atrial septal defect (ASD) using clamshell or buttoned devices is accompanied by a high incidence of residual shunt. Recently, a new self-centering device, the Amplatzer septal occluder (ASO), has been evaluated in an animal model with very good results. Therefore, our purpose is to report on our initial clinical experience with this device. Thirty patients underwent an attempt at catheter closure of their ASDs at a median age of 6.1 yr (range, 2.9–62.4 yr) and median weight of 22 kg (range, 13–69 kg) using the ASO. The median ASD diameter measured by transesophageal echocardiography (TEE) was 12.5 mm (range, 5–21 mm), and the median ASD balloon stretched diameter was 14 mm (range, 7–19 mm). All patients had right atrial and ventricular volume overload with a mean ± SD Qp/Qs of 2.3 ± 0.6. A 7F catheter was used for delivery of the device in all patients. The device was placed correctly in all patients. There was immediate and complete closure (C) in 17/30 patients, 10 patients had trivial residual shunt (TS), and 3 had moderate residual shunt (MS). The median fluoroscopy time was 15 min (range, 8–35 min), and the median total procedure time was 92.5 min (range, 40–135 min). There was no episode of device embolization or any other complication. Follow-up was performed using transthoracic echocardiography (TTE) 1 day, 1 mo, 3 mo, and yearly thereafter. At 1 day, there was C of the ASD in 24/30 patients, 3 had TS, 1 had small shunt (SS), and 2 had MS. At a median follow-up interval of 6 mo, there have been no episodes of endocarditis, thromboembolism, or wire fracture. We conclude that the use of the new ASO is safe and effective in complete closure of secundum ASDs up to a diameter of 21 mm in the majority of patients. Further clinical trials are underway. Cathet. Cardiovasc. Diagn. 42:388–393, 1997. © 1997 Wiley-Liss, Inc.
The objectives of this study were to identify possible risk factors that may lead to erosion of the Amplatzer septal occluder (ASO) and recommend ways to minimize future risk. There have been rare occurrences of adverse events with development of pericardial effusion after ASO placement. Identification of high-risk cases, early recognition, and prompt intervention may minimize the future risks of adverse events. In all patients who developed hemodynamic compromise after ASO placement, echocardiograms (pre-, intra-, and postprocedure), atrial septal defect (ASD) size (nonstretched, stretched), size of the device used, cineangiograms, and operative records were reviewed by a panel selected by AGA Medical Corporation. The findings were compared to the premarket approval data obtained from FDA-approved clinical trials that were conducted in the United States, before the device was approved. A total of 28 cases (14 in United States) of adverse events were reported to AGA Medical. All erosions occurred at the dome of the atria, near the aortic root. Deficient aortic rim was seen in 89% and the defect described as high ASD, suggesting deficient superior rim. The device to unstretched ASD ratio was significantly larger in the adverse event group when compared to the FDA trial group. The incidence of device erosion in the United States was 0.1%. The risk of device erosion with ASO is low and complications can be decreased by identifying high-risk patients and following them closely. Patients with deficient aortic rim and/or superior rim may be at higher risk for device erosion. Oversized ASO may increase the risk of erosion. The defect should not be overstretched during balloon sizing. Patients with small pericardial effusion at 24 hr should have closer follow-up.
Percutaneous occlusion techniques of secundum type atrial septal defects have recently become the treatment of choice, delivering excellent results and being associated with a low rate of early and late complications. The investigators report an unusually delayed presentation of acute right heart failure due to Amplatzer septal device embolisation into the main pulmonary artery, 2 years after implantation.