3D Printing of Cantilever-Type Microstructures by Stereolithography of Ferromagnetic Photopolymers

From Unregulated Networks to Designed Microstructures: Introducing Heterogeneity at Different Length Scales in Photopolymers for Additive Manufacturing

Photopolymers have been optimized as protective and decorative coating materials for decades. However, with the rise of additive manufacturing technologies, vat photopolymerization has unlocked the use of photopolymers for three-dimensional objects with new material requirements. Thus, the originally highly cross-linked, amorphous architecture of photopolymers cannot match the expectations for modern materials anymore, revealing the largely unanswered question of how diverse properties can be achieved in photopolymers. Herein, we review how microstructural features in soft matter materials should be designed and implemented to obtain high performance materials. We then translate these findings into chemical design suggestions for enhanced printable photopolymers. Based on this analysis, we have found microstructural heterogenization to be the most powerful tool to tune photopolymer performance. By combining the chemical toolbox for photopolymerization and the analytical toolbox for microstructural characterization, we examine current strategies for physical heterogenization (fillers, inkjet printing) and chemical heterogenization (semicrystalline polymers, block copolymers, interpenetrating networks, photopolymerization induced phase separation) of photopolymers and put them into a material scientific context to develop a roadmap for improving and diversifying photopolymers' performance.

3D Printed Integrated Sensors: From Fabrication to Applications-A Review

The integration of 3D printed sensors into hosting structures has become a growing area of research due to simplified assembly procedures, reduced system complexity, and lower fabrication cost. Embedding 3D printed sensors into structures or bonding the sensors on surfaces are the two techniques for the integration of sensors. This review extensively discusses the fabrication of sensors through different additive manufacturing techniques. Various additive manufacturing techniques dedicated to manufacture sensors as well as their integration techniques during the manufacturing process will be discussed. This review will also discuss the basic sensing mechanisms of integrated sensors and their applications. It has been proven that integrating 3D printed sensors into infrastructures can open new possibilities for research and development in additive manufacturing and sensor materials for smart goods and the Internet of Things.

4-Dimensional printing: exploring current and future capabilities in biomedical and healthcare systems-a Concise review

4-Dimensional Printing (4DP) is the latest concept in the pharmacy and biomedical segment with enormous potential in dosage from personalization and medication designing, which adopts time as the fourth dimension, giving printed structures the flexibility to modify their morphology. It can be defined as the fabrication in morphology with the help of smart/intelligent materials like polymers that permit the final object to alter its properties, shape, or function in response to external stimuli such as heat, light, pH, and moisture. The applications of 4DP in biomedicines and healthcare are explored with a focus on tissue engineering, artificial organs, drug delivery, pharmaceutical and biomedical field, etc. In the medical treatments and pharmaceutical field 4DP is paving the way with unlimited potential applications; however, its mainstream use in healthcare and medical treatments is highly dependent on future developments and thorough research findings. Therefore, previous innovations with smart materials are likely to act as precursors of 4DP in many industries. This review highlights the most recent applications of 4DP technology and smart materials in biomedical and healthcare fields which can show a better perspective of 4DP applications in the future. However, in view of the existing limitations, major challenges of this technology must be addressed along with some suggestions for future research. We believe that the application of proper regulatory constraints with 4DP technology would pave the way for the next technological revolution in the biomedical and healthcare sectors.

Bioprinting the future using light: A review on photocrosslinking reactions, photoreactive groups, and photoinitiators

Light-based bioprinting is a type of additive manufacturing technologies that uses light to control the formation of biomaterials, tissues, and organs. It has the potential to revolutionize the adopted approach in tissue engineering and regenerative medicine by allowing the creation of functional tissues and organs with high precision and control. The main chemical components of light-based bioprinting are activated polymers and photoinitiators. The general photocrosslinking mechanisms of biomaterials are described, along with the selection of polymers, functional group modifications, and photoinitiators. For activated polymers, acrylate polymers are ubiquitous but are made of cytotoxic reagents. A milder option that exists is based on norbornyl groups which are biocompatible and can be used in self-polymerization or with thiol reagents for more precision. Polyethylene-glycol and gelatin activated with both methods can have high cell viability rates. Photoinitiators can be divided into types I and II. The best performances for type I photoinitiators are produced under ultraviolet light. Most alternatives for visible-light-driven photoinitiators were of type II, and changing the co-initiator along the main reagent can fine-tune the process. This field is still underexplored and a vast room for improvements still exist, which can open the way for cheaper complexes to be developed. The progress, advantages, and shortcomings of light-based bioprinting are highlighted in this review, with special emphasis on developments and future trends of activated polymers and photoinitiators.

Vat photopolymerization-based 3D printing of polymer nanocomposites: current trends and applications

The synthesis and manufacturing of polymer nanocomposites have garnered interest in recent research and development because of their superiority compared to traditionally employed industrial materials. Specifically, polymer nanocomposites offer higher strength, stronger resistance to corrosion or erosion, adaptable production techniques, and lower costs. The vat photopolymerization (VPP) process is a group of additive manufacturing (AM) techniques that provide the benefit of relatively low cost, maximum flexibility, high accuracy, and complexity of the printed parts. In the past few years, there has been a rapid increase in the understanding of VPP-based processes, such as high-resolution AM methods to print intricate polymer parts. The synergistic integration of nanocomposites and VPP-based 3D printing processes has opened a gateway to the future and is soon expected to surpass traditional manufacturing techniques. This review aims to provide a theoretical background and the engineering capabilities of VPP with a focus on the polymerization of nanocomposite polymer resins. Specifically, the configuration, classification, and factors affecting VPP are summarized in detail. Furthermore, different challenges in the preparation of polymer nanocomposites are discussed together with their pre- and post-processing, where several constraints and limitations that hinder their printability and photo curability are critically discussed. The main focus is the applications of printed polymer nanocomposites and the enhancement in their properties such as mechanical, biomedical, thermal, electrical, and magnetic properties. Recent literature, mainly in the past three years, is critically discussed and the main contributing results in terms of applications are summarized in the form of tables. The goal of this work is to provide researchers with a comprehensive and updated understanding of the underlying difficulties and potential benefits of VPP-based 3D printing of polymer nanocomposites. It will also help readers to systematically reveal the research problems, gaps, challenges, and promising future directions related to polymer nanocomposites and VPP processes.

Multiphoton Lithography of Organic Semiconductor Devices for 3D Printing of Flexible Electronic Circuits, Biosensors, and Bioelectronics

In recent years, 3D printing of electronics have received growing attention due to their potential applications in emerging fields such as nanoelectronics and nanophotonics. Multiphoton lithography (MPL) is considered the state-of-the-art amongst the microfabrication techniques with true 3D fabrication capability owing to its excellent level of spatial and temporal control. Here, a homogenous and transparent photosensitive resin doped with an organic semiconductor material (OS), which is compatible with MPL process, is introduced to fabricate a variety of 3D OS composite microstructures (OSCMs) and microelectronic devices. Inclusion of 0.5 wt% OS in the resin enhances the electrical conductivity of the composite polymer about 10 orders of magnitude and compared to other MPL-based methods, the resultant OSCMs offer high specific electrical conductivity. As a model protein, laminin is incorporated into these OSCMs without a significant loss of activity. The OSCMs are biocompatible and support cell adhesion and growth. Glucose-oxidase-encapsulated OSCMs offer a highly sensitive glucose sensing platform with nearly tenfold higher sensitivity compared to previous glucose biosensors. In addition, this biosensor exhibits excellent specificity and high reproducibility. Overall, these results demonstrate the great potential of these novel MPL-fabricated OSCM devices for a wide range of applications from flexible bioelectronics/biosensors, to nanoelectronics and organ-on-a-chip devices.

Advances in Field-Assisted 3D Printing of Bio-Inspired Composites: From Bioprototyping to Manufacturing

Biocomposite systems evolve to superior structural strategies in adapting to their living environments, using limited materials to form functionality superior to their inherent properties. The synergy of physical-field and Three-dimensional （3D） printing technologies creates unprecedented opportunities that overcome the limitations of traditional manufacturing methods and enable the precise replication of bio-enhanced structures. Here, an overview of typical structural designs in biocomposite systems, their functions and properties, are provided and the recent advances in bio-inspired composites using mechanical, electrical, magnetic, and ultrasound-field-assisted 3D printing techniques are highlighted. Finally, in order to realize the preparation of bionic functional devices and equipment with more superior functions, here an outlook on the development of field-assisted 3D printing technology from three aspects are provided: Materials, technology, and post-processing.

Stereolithography 3D printing technology in pharmaceuticals: a review

Three-dimensional printing (3DP) technology is an innovative tool used in manufacturing medical devices, producing alloys, replacing biological tissues, producing customized dosage forms and so on. Stereolithography (SLA), a 3D printing technique, is very rapid and highly accurate and produces finished products of uniform quality. 3D formulations have been optimized with a perfect tool of artificial intelligence learning techniques. Complex designs/shapes can be fabricated through SLA using the photopolymerization principle. Different 3DP technologies are introduced and the most promising of these, SLA, and its commercial applications, are focused on. The high speed and effectiveness of SLA are highlighted. The working principle of SLA, the materials used and applications of the technique in a wide range of different sectors are highlighted in this review. An innovative idea of 3D printing customized pharmaceutical dosage forms is also presented. SLA compromises several advantages over other methods, such as cost effectiveness, controlled integrity of materials and greater speed. The development of SLA has allowed the development of printed pharmaceutical devices. Considering the present trends, it is expected that SLA will be used along with conventional methods of manufacturing of 3D model. This 3D printing technology may be utilized as a novel tool for delivering drugs on demand. This review will be useful for researchers working on 3D printing technologies.

Establishing a point-of-care additive manufacturing workflow for clinical use

Additive manufacturing, or 3-Dimensional (3-D) Printing, is built with technology that utilizes layering techniques to build 3-D structures. Today, its use in medicine includes tissue and organ engineering, creation of prosthetics, the manufacturing of anatomical models for preoperative planning, education with high-fidelity simulations, and the production of surgical guides. Traditionally, these 3-D prints have been manufactured by commercial vendors. However, there are various limitations in the adaptability of these vendors to program-specific needs. Therefore, the implementation of a point-of-care in-house 3-D modeling and printing workflow that allows for customization of 3-D model production is desired. In this manuscript, we detail the process of additive manufacturing within the scope of medicine, focusing on the individual components to create a centralized in-house point-of-care manufacturing workflow. Finally, we highlight a myriad of clinical examples to demonstrate the impact that additive manufacturing brings to the field of medicine.

The Recent Progress of MEMS/NEMS Resonators

MEMS/NEMS resonators are widely studied in biological detection, physical sensing, and quantum coupling. This paper reviews the latest research progress of MEMS/NEMS resonators with different structures. The resonance performance, new test method, and manufacturing process of single or double-clamped resonators, and their applications in mass sensing, micromechanical thermal analysis, quantum detection, and oscillators are introduced in detail. The material properties, resonance mode, and application in different fields such as gyroscope of the hemispherical structure, microdisk structure, drum resonator are reviewed. Furthermore, the working principles and sensing methods of the surface acoustic wave and bulk acoustic wave resonators and their new applications such as humidity sensing and fast spin control are discussed. The structure and resonance performance of tuning forks are summarized. This article aims to classify resonators according to different structures and summarize the working principles, resonance performance, and applications.

Reversible Deactivation Radical Polymerization: From Polymer Network Synthesis to 3D Printing

3D printing has changed the fabrication of advanced materials as it can provide customized and on-demand 3D networks. However, 3D printing of polymer materials with the capacity to be transformed after printing remains a great challenge for engineers, material, and polymer scientists. Radical polymerization has been conventionally used in photopolymerization-based 3D printing, as in the broader context of crosslinked polymer networks. Although this reaction pathway has shown great promise, it offers limited control over chain growth, chain architecture, and thus the final properties of the polymer networks. More fundamentally, radical polymerization produces dead polymer chains incapable of postpolymerization transformations. Alternatively, the application of reversible deactivation radical polymerization (RDRP) to polymer networks allows the tuning of network homogeneity and more importantly, enables the production of advanced materials containing dormant reactivatable species that can be used for subsequent processes in a postsynthetic stage. Consequently, the opportunities that (photoactivated) RDRP-based networks offer have been leveraged through the novel concepts of structurally tailored and engineered macromolecular gels, living additive manufacturing and photoexpandable/transformable-polymer networks. Herein, the advantages of RDRP-based networks over irreversibly formed conventional networks are discussed.

Steroid Eluting Esophageal-Targeted Drug Delivery Devices for Treatment of Eosinophilic Esophagitis

Eosinophilic esophagitis (EoE) is a chronic atopic disease that has become increasingly prevalent over the past 20 years. A first-line pharmacologic option is topical/swallowed corticosteroids, but these are adapted from asthma preparations such as fluticasone from an inhaler and yield suboptimal response rates. There are no FDA-approved medications for the treatment of EoE, and esophageal-specific drug formulations are lacking. We report the development of two novel esophageal-specific drug delivery platforms. The first is a fluticasone-eluting string that could be swallowed similar to the string test "entero-test" and used for overnight treatment, allowing for a rapid release along the entire length of esophagus. In vitro drug release studies showed a target release of 1 mg/day of fluticasone. In vivo pharmacokinetic studies were carried out after deploying the string in a porcine model, and our results showed a high local level of fluticasone in esophageal tissue persisting over 1 and 3 days, and a minimal systemic absorption in plasma. The second device is a fluticasone-eluting 3D printed ring for local and sustained release of fluticasone in the esophagus. We designed and fabricated biocompatible fluticasone-loaded rings using a top-down, Digital Light Processing (DLP) Gizmo 3D printer. We explored various strategies of drug loading into 3D printed rings, involving incorporation of drug during the print process (pre-loading) or after printing (post-loading). In vitro drug release studies of fluticasone-loaded rings (pre and post-loaded) showed that fluticasone elutes at a constant rate over a period of one month. Ex vivo pharmacokinetic studies in the porcine model also showed high tissue levels of fluticasone and both rings and strings were successfully deployed into the porcine esophagus in vivo. Given these preliminary proof-of-concept data, these devices now merit study in animal models of disease and ultimately subsequent translation to testing in humans.

3D printed microneedles for transdermal drug delivery: A brief review of two decades

Microneedle (MN) technology shows excellent potential in controlled drug delivery, which has got rising attention from investigators and clinics. MNs can pierce through the stratum corneum layer of the skin into the epidermis, evading interaction with nerve fibers. MN patches have been fabricated using various types of materials and application processes. Recently, three-dimensional (3D) printing gives the prototyping and manufacturing methods the flexibility to produce the MN patches in a one-step manner with high levels of shape complexity and duplicability. This review aims to go through the last successes in 3D printed MN-based patches. In this regard, after the evaluation of various types of MNs and fabrication techniques, we will study different 3D printing approaches applied for MN patch fabrication. We further highlight the state of the art of the long-acting MNs and related progress with a specific look at what should come within the scope of upcoming researches.

Magnetic Field-Assisted Stereolithography for Productions of Multimaterial Hierarchical Surface Structures

Natural organisms provide inspirations for various functional structures and surfaces with significant applications in multidisciplinary fields. These biological systems are generally composed of multiscale surface structures with high geometric complexity and a variety of materials, making it challenging to replicate their characteristics in engineering. This study presents a novel multiscale multimaterial 3D printing method, magnetic field-assisted stereolithography (M-SL), for fabricating hierarchical particle-polymer structures with surface features ranging from a few nanometers to millimeters or even centimeters. Taking inspiration from nature, this study describes the design and fabrication of a bioinspired multiscale hierarchical surface structure, which is characterized of microscale cones, nanoscale pores, and surface wrinkles at a few nanometers. To understand the fundamental physics underlying the hierarchical surface structure fabrication in the proposed M-SL process, the complexities among the M-SL process parameters, material parameters, and printed geometries are discussed. The accuracy of the developed printing method is investigated by comparing the printed geometries and digital designs. Effects of the printed hierarchical surface structure on hydrophobicity and cell viability were characterized and discussed. It was found that the highly hierarchical surface structure changed the polymer composite surface from hydrophilic (contact angle: ∼38°) to hydrophobic (∼146°). In addition, the hierarchical surface structure also created a better environment for cell attachment and growth, with 900% more living cells at 72 h after cell seeding, compared with cells on the nonstructured smooth surface. Local and selective cell seeding can also be enabled by the surface structure design. Experimental results validated the effectiveness of the M-SL 3D printing method on fabricating multimaterial functional objects with hierarchically structured surfaces for a wide spectrum of applications.

Cellulose, hemicellulose, lignin, and their derivatives as multi-components of bio-based feedstocks for 3D printing

Three-dimensional (3D) printing, known as revolutionary and disruptive innovation in manufacturing technology, supports great opportunities to rapidly construct a wide range of tailored object geometries. Cellulose, hemicellulose, and lignin as the three most common natural polymers and main components of plant resources, possess great economical potential for bio-based products due to their attractive advantages. The integration of 3D printing technology involved with cellulose, hemicellulose and lignin as the major bio-based feedstock for high-performance 3D printed products has received great concern in the R&D areas. In this review, the aim is to shed light on a cutting-edge review on the most recent progress based on cellulose, hemicellulose and lignin, as well as their derivatives as multi-components of bio-feedstock for 3D printing, in which the applications, roles and functions of the plant-derived biomass for 3D printing are also highlighted. The challenges and perspectives for future work are provided, to underscore critical issues and opportunities.

Progressive 3D Printing Technology and Its Application in Medical Materials

Three-dimensional (3D) printing enables patient-specific anatomical level productions with high adjustability and resolution in microstructures. With cost-effective manufacturing for high productivity, 3D printing has become a leading healthcare and pharmaceutical manufacturing technology, which is suitable for variety of applications including tissue engineering models, anatomical models, pharmacological design and validation model, medical apparatus and instruments. Today, 3D printing is offering clinical available medical products and platforms suitable for emerging research fields, including tissue and organ printing. In this review, our goal is to discuss progressive 3D printing technology and its application in medical materials. The additive overview also provides manufacturing techniques and printable materials.

Superstretchable and Processable Silicone Elastomers by Digital Light Processing 3D Printing

A series of photosensitive resins suitable for the production of silicone elastomers through digital light processing 3D printing are reported. Based on thiol-ene click reaction between a branched mercaptan-functionalized polysiloxane and different-molecular-weight vinyl-terminated poly(dimethylsiloxane), silicone elastomers with tunable hardness and mechanical properties are obtained. Printed elastomeric objects show high printing resolution and excellent mechanical properties. The break elongation of the silicone elastomers can get up to 1400%, which is much higher than the reported UV-cured elastomers and is even higher than the most stretchable thermocuring silicone elastomers. The superstretchable silicone elastomers are then applied to fabricate stretchable electronics with carbon nanotubes-doped hydrogel. The printable and processable silicone elastomers have great potential applications in various fields, including soft robotics, flexible actuators, and medical implants.

Advances and Future Perspectives in 4D Bioprinting

Three-dimensionally printed constructs are static and do not recapitulate the dynamic nature of tissues. Four-dimensional (4D) bioprinting has emerged to include conformational changes in printed structures in a predetermined fashion using stimuli-responsive biomaterials and/or cells. The ability to make such dynamic constructs would enable an individual to fabricate tissue structures that can undergo morphological changes. Furthermore, other fields (bioactuation, biorobotics, and biosensing) will benefit from developments in 4D bioprinting. Here, the authors discuss stimuli-responsive biomaterials as potential bioinks for 4D bioprinting. Natural cell forces can also be incorporated into 4D bioprinted structures. The authors introduce mathematical modeling to predict the transition and final state of 4D printed constructs. Different potential applications of 4D bioprinting are also described. Finally, the authors highlight future perspectives for this emerging technology in biomedicine.

Hydroprinted Electronics: Ultrathin Stretchable Ag-In-Ga E-Skin for Bioelectronics and Human-Machine Interaction

We introduce a soft ultrathin and stretchable electronic skin with surface-mounted components that can be transferred and wrapped around any three-dimensional (3D) surface or self-adhere to the human skin. The ∼5 μm thick circuit is fabricated by printing the pattern over a temporary tattoo paper using a desktop laser printer, which is then coated with a silver ink and eutectic gallium-indium (EGaIn) liquid metal alloy. The resulting "Ag-In-Ga" traces are highly conductive and maintain low electrical resistivity as the circuit is stretched to conform to nondevelopable 3D surfaces. We also address integration of surface-mounted microelectronic chips by introducing a novel z-axis conductive interface composed of magnetically aligned EGaIn-coated Ag-Ni microparticles embedded in polyvinyl alcohol (PVA). This " zPVA conductive glue" allows for robust electrical contacts with microchips that have pins with dimensions as small as 300 μm. If printed on the temporary tattoo transfer paper, the populated circuit can be attached to a 3D surface using hydrographic transfer. Both printing and interfacing processes can be performed at the room temperature. We demonstrate examples of applications, including an electronic tattoo over the human epidermis for electromyography signal acquisition, an interactive circuit with touch buttons, and light-emitting diodes transferred over the 3D printed shell of a robotic prosthetic hand, and a proximity measurement skin transferred over a 3D surface.

Functional Polymers and Nanocomposites for 3D Printing of Smart Structures and Devices

Three-dimensional printing (3DP) has attracted a considerable amount of attention during the past years, being globally recognized as one of the most promising and revolutionary manufacturing technologies. Although the field is rapidly evolving with significant technological advancements, materials research remains a spotlight of interest, essential for the future developments of 3DP. Smart polymers and nanocomposites, which respond to external stimuli by changing their properties and structure, represent an important group of materials that hold a great promise for the fabrication of sensors, actuators, robots, electronics, and medical devices. The interest in exploring functional materials and their 3DP is constantly growing in an attempt to meet the ever-increasing manufacturing demand of complex functional platforms in an efficient manner. In this review, we aim to outline the recent advances in the science and engineering of functional polymers and nanocomposites for 3DP technologies. The report covers temperature-responsive polymers, polymers and nanocomposites with electromagnetic, piezoresistive and piezoelectric behaviors, self-healing polymers, light- and pH-responsive materials, and mechanochromic polymers. The main objective is to link the performance and functionalities to the fundamental properties, chemistry, and physics of the materials, and to the process-driven characteristics, in an attempt to provide a multidisciplinary image and a deeper understanding of the topic. The challenges and opportunities for future research are also discussed.

3D printing of photopolymers

Recent progress in the photoinitiators and monomers/oligomers of photopolymers for 3D printing is presented in the review.

Biotinylated Photopolymers for 3D-Printed Unibody Lab-on-a-Chip Optical Platforms

The present work reports the first demonstration of straightforward fabrication of monolithic unibody lab-on-a-chip (ULOCs) integrating bioactive micrometric 3D scaffolds by means of multimaterial stereolithography (SL). To this end, a novel biotin-conjugated photopolymer is successfully synthesized and optimally formulated to achieve high-performance SL-printing resolution, as demonstrated by the SL-fabrication of biotinylated structures smaller than 100 µm. By optimizing a multimaterial single-run SL-based 3D-printing process, such biotinylated microstructures are incorporated within perfusion microchambers whose excellent optical transparency enables real-time optical microscopy analyses. Standard biotin-binding assays confirm the existence of biotin-heads on the surfaces of the embedded 3D microstructures and allow to demonstrate that the biofunctionality of biotin is not altered during the SL-printing, thus making it exploitable for further conjugation with other biomolecules. As a step forward, an in-line optical detection system is designed, prototyped via SL-printing and serially connected to the perfusion microchambers through customized world-to-chip connectors. Such detection system is successfully employed to optically analyze the solution flowing out of the microchambers, thus enabling indirect quantification of the concentration of target interacting biomolecules. The successful application of this novel biofunctional photopolymer as SL-material enables to greatly extend the versatility of SL to directly fabricate ULOCs with intrinsic biofunctionality.

Polymeric 3D Printed Functional Microcantilevers for Biosensing Applications

In this study, we show for the first time the production of mass-sensitive polymeric biosensors by 3D printing technology with intrinsic functionalities. We also demonstrate the feasibility of mass-sensitive biosensors in the form of microcantilever in a one-step printing process, using acrylic acid as functional comonomer for introducing a controlled amount of functional groups that can covalently immobilize the biomolecules onto the polymer. The effectiveness of the application of 3D printed microcantilevers as biosensors is then demonstrated with their implementation in a standard immunoassay protocol. This study shows how 3D microfabrication techniques, material characterization, and biosensor development could be combined to obtain an engineered polymeric microcantilever with intrinsic functionalities. The possibility of tuning the composition of the starting photocurable resin with the addition of functional agents, and consequently controlling the functionalities of the 3D printed devices, paves the way to a new class of mass-sensing microelectromechanical system devices with intrinsic properties.

The Boom in 3D-Printed Sensor Technology

Future sensing applications will include high-performance features, such as toxin detection, real-time monitoring of physiological events, advanced diagnostics, and connected feedback. However, such multi-functional sensors require advancements in sensitivity, specificity, and throughput with the simultaneous delivery of multiple detection in a short time. Recent advances in 3D printing and electronics have brought us closer to sensors with multiplex advantages, and additive manufacturing approaches offer a new scope for sensor fabrication. To this end, we review the recent advances in 3D-printed cutting-edge sensors. These achievements demonstrate the successful application of 3D-printing technology in sensor fabrication, and the selected studies deeply explore the potential for creating sensors with higher performance. Further development of multi-process 3D printing is expected to expand future sensor utility and availability.

Three-Dimensional Printing of Shape Memory Composites with Epoxy-Acrylate Hybrid Photopolymer

Four-dimensional printing, a new process to fabricate active materials through three-dimensional (3D) printing developed by MIT's Self-Assembly Lab in 2014, has attracted more and more research and development interests recently. In this paper, a type of epoxy-acrylate hybrid photopolymer was synthesized and applied to fabricate shape memory polymers through a stereolithography 3D printing technique. The glass-to-rubbery modulus ratio of the printed sample determined by dynamic mechanical analysis is as high as 600, indicating that it may possess good shape memory properties. Fold-deploy and shape memory cycle tests were applied to evaluate its shape memory performance. The shape fixity ratio and the shape recovery ratio in ten cycles of fold-deploy tests are about 99 and 100%, respectively. The shape recovery process takes less than 20 s, indicating its rapid shape recovery rate. The shape fixity ratio and shape recovery ratio during 18 consecutive shape memory cycles are 97.44 ± 0.08 and 100.02 ± 0.05%, respectively, showing that the printed sample has high shape fixity ratio, shape recovery ratio, and excellent cycling stability. A tensile test at 62 °C demonstrates that the printed samples combine a relatively large break strain of 38% with a large recovery stress of 4.7 MPa. Besides, mechanical and thermal stability tests prove that the printed sample has good thermal stability and mechanical properties, including high strength and good toughness.