Rotational multimaterial printing of filaments with subvoxel control

Electric field-coupled two-photon polymerization system for on-demand modulation of 3D-printed structural color

Advanced manufacturing has been extensively studied using various resin monomers and customized apparatus. Multimaterial microfabrication tools remain limited due to the size constraints inherent in extrusion-based fabrication methods. In addition, prior research predominantly employs monomers as "inert" resins, with minimal emphasis on altering their properties during fabrication. In this study, we propose a novel approach to field-coupled advanced manufacturing, wherein external stimulative fields are integrated to dynamically modulate the properties of "dynamic" resins during 3D printing. As a demonstration, we utilize an electric field-coupled two-photon polymerization (EF-TPP) technique to fabricate structurally colorful microstructures. To address the challenges of limited fabrication approach and resins in the field of structural color, we present an EF-TPP system that enables the production of 3D structural colorful microstructures. By coupling the electric field with the two-photon polymerization (TPP) process, this method enhances 3D printing capabilities, allowing for the bottom-up fabrication of structural colorful microstructures. Furthermore, it integrates existing electrically tunable heliconical cholesteric liquid crystals, enabling the modulation of structural color during printing while also accelerating the printing speed. This approach facilitates the production of microstructures with multiple structural colors without requiring changes to the resin ink. By eliminating the lithography step, the EF-TPP system promotes green manufacturing practices and introduces an unconventional paradigm for fabricating dynamic, microscale structural colorful devices. Additionally, the electric field-integrated two-photon lithography system provides a foundational strategy for advancing field-coupled manufacturing methodologies.

Hybrid Formative-Additive Manufacturing

Material extrusion additive manufacturing (AM) provides extensive design flexibility and exceptional material versatility, enabling the fabrication of complex, multifunctional objects ranging from embedded electronics to soft robotics and vascularized tissues. The bottom-up creation of these objects typically requires discretization into layers and voxels. However, the voxel size, determined by the nozzle diameter, limits extrusion rate, creating a conflict between resolution and speed. To address these inherent scalability challenges, the study proposes a hybrid formative-additive manufacturing technology that combines the respective strengths of each method-speed and quality with complexity and flexibility. The approach involves 3D-printing complex geometries, multimaterial features, and bounding walls of bulky, lower-resolution volumes, which are rapidly filled via casting or molding. By precisely controlling the materials' rheological properties-while maintaining similar solidified properties and high interfacial strength-several typical AM flaws, such as bulging and internal voids, are eliminated, achieving exponentially faster production speeds for objects with varying feature sizes.

3D bioprinting of collagen-based high-resolution internally perfusable scaffolds for engineering fully biologic tissue systems

Organ-on-a-chip and microfluidic systems have improved the translational relevance of in vitro systems; however, current manufacturing approaches impart limitations on materials selection, non-native mechanical properties, geometric complexity, and cell-driven remodeling into functional tissues. Here, we three-dimensionally (3D) bioprint extracellular matrix (ECM) and cells into collagen-based high-resolution internally perfusable scaffolds (CHIPS) that integrate with a vascular and perfusion organ-on-a-chip reactor (VAPOR) to form a complete tissue engineering platform. We improve the fidelity of freeform reversible embedding of suspended hydrogels (FRESH) bioprinting to produce a range of CHIPS designs fabricated in a one-step process. CHIPS exhibit size-dependent permeability of perfused molecules into the surrounding scaffold to support cell viability and migration. Lastly, we implemented multi-material bioprinting to control 3D spatial patterning, ECM composition, cellularization, and material properties to create a glucose-responsive, insulin-secreting pancreatic-like CHIPS with vascular endothelial cadherin+ vascular-like networks. Together, CHIPS and VAPOR form a platform technology toward engineering full organ-scale function for disease modeling and cell replacement therapy.

Strategic Implementation of Multimaterial Additive Manufacturing: Bridging Research and Real-World Applications

The single-material additive manufacturing revolution has accelerated innovation in the manufacturing field, enabling the combination of multiple materials in one operation using additives of metals, ceramics, and polymers. Although still in its infancy, researchers are adopting this strategy, indicating a shift from research and development to practical applications. By aggregating numerous materials with different properties concurrently, the multimaterial additive manufacturing approach entitles the simplest fabrication of multifunctional systems and devices. A review focuses on the opportunities and challenges presented by the trend toward recent advancements in the multinozzle system. Multinozzle 3D printing has great applications in bioprinting and tissue engineering, electronics integration, and civil/structural engineering. This review highlights the exciting opportunities and challenges that come with it. Additionally, this review showcases the recent advancements in the multinozzle system that have made it a promising solution in this field.

Soft Materials and Devices Enabling Sensorimotor Functions in Soft Robots

Sensorimotor functions, the seamless integration of sensing, decision-making, and actuation, are fundamental for robots to interact with their environments. Inspired by biological systems, the incorporation of soft materials and devices into robotics holds significant promise for enhancing these functions. However, current robotics systems often lack the autonomy and intelligence observed in nature due to limited sensorimotor integration, particularly in flexible sensing and actuation. As the field progresses toward soft, flexible, and stretchable materials, developing such materials and devices becomes increasingly critical for advanced robotics. Despite rapid advancements individually in soft materials and flexible devices, their combined applications to enable sensorimotor capabilities in robots are emerging. This review addresses this emerging field by providing a comprehensive overview of soft materials and devices that enable sensorimotor functions in robots. We delve into the latest development in soft sensing technologies, actuation mechanism, structural designs, and fabrication techniques. Additionally, we explore strategies for sensorimotor control, the integration of artificial intelligence (AI), and practical application across various domains such as healthcare, augmented and virtual reality, and exploration. By drawing parallels with biological systems, this review aims to guide future research and development in soft robots, ultimately enhancing the autonomy and adaptability of robots in unstructured environments.

Chaotic Direct Ink Writing (ChDIW) of Hybrid Hydrogels: Implication for Fabrication of Micro-ordered Multifunctional Cryogels

The modern era demands multifunctional materials to support advanced technologies and tackle complex environmental issues caused by these innovations. Consequently, material hybridization has garnered significant attention as a strategy to design materials with prescribed multifunctional properties. Drawing inspiration from nature, a multi-scale material design approach is proposed to produce 3D-shaped hybrid materials by combining chaotic flows with direct ink writing (ChDIW). This approach enables the formation of predictable multilayered filaments with tunable microscale internal architectures using just a single printhead. By assigning different nanomaterials to each layer, 3D-printed hydrogels and cryogels with diverse functionalities, such as electrical conductivity and magnetism are successfully produced. Furthermore, control over the microscale pore morphology within each cryogel filament is achieved, resulting in a side-by-side dual-pore network sharing a large interfacial area. The ChDIW is compatible with different types of hydrogels as long as the rheological features of the printing materials are well-regulated. To showcase the potential of these multilayered cryogels, their electromagnetic interference shielding performance is evaluated, and they reveal an absorption-dominant mechanism with an excellent absorption coefficient of 0.71. This work opens new avenues in soft matter and cryogel engineering, demonstrating how simplicity can generate complexity.

Coaxial Direct Ink Writing of Cholesteric Liquid Crystal Elastomers in 3D Architectures

Cholesteric liquid crystal elastomers (CLCEs) hold great promise for mechanochromic applications in anti-counterfeiting, smart textiles, and soft robotics, thanks to the structural color and elasticity. While CLCEs are printed via direct ink writing (DIW) to fabricate free-standing films, complex 3D structures are not fabricated due to the opposing rheological properties necessary for cholesteric alignment and multilayer stacking. Here, 3D CLCE structures are realized by utilizing coaxial DIW to print a CLC ink within a silicone ink. By tailoring the ink compositions, and thus, the rheological properties, the cholesteric phase rapidly forms without an annealing step, while the silicone shell provides encapsulation and support to the CLCE core, allowing for layer-by-layer printing of self-supported 3D structures. As a demonstration, free-standing bistable thin-shell domes are printed. Color changes due to compressive and tensile stresses can be witnessed from the top and bottom of the inverted domes, respectively. When the domes are arranged in an array and inverted, they can snap back to their base state by uniaxial stretching, thereby functioning as mechanical sensors with memory. The additive manufacturing platform enables the rapid fabrication of 3D mechanochromic sensors thereby expanding the realm of potential applications for CLCEs.

A graphene-based photo-electro-thermal metamaterial for soft fixtures with superior grasping performance

Soft actuators are valued for their adaptability and diverse applications but often face challenges like slow response, high activation energy, and high energy consumption. To address these issues, we developed a graphene-assembled film (GAF) via the redox method, characterized by high thermal conductivity, conductivity, and stiffness. Using GAF as a photothermal and electrothermal driver, we engineered a sandwich-structured metamaterial (SSM) by combining two polymers with vastly different thermal expansion coefficients. The SSM achieved rapid response (<5 s), low actuation energy (≤0.22 W cm⁻2 or ≤3.55 V), and large bending curvature (>0.18 mm⁻1), surpassing conventional designs in response speed (226.2% faster) and curvature (249.1% higher). This metamaterial enables soft fixtures with superior gripping capabilities and low energy consumption, handling up to eight times the object mass of traditional designs. This work highlights advances in multi-stimulus metamaterials, offering significant implications for the development of high-performance soft actuators.

Multi-Physical Lattice Metamaterials Enabled by Additive Manufacturing: Design Principles, Interaction Mechanisms, and Multifunctional Applications

Lattice metamaterials emerge as advanced architected materials with superior physical properties and significant potential for lightweight applications. Recent developments in additive manufacturing (AM) techniques facilitate the manufacturing of lattice metamaterials with intricate microarchitectures and promote their applications in multi-physical scenarios. Previous reviews on lattice metamaterials have largely focused on a specific/single physical field, with limited discussion on their multi-physical properties, interaction mechanisms, and multifunctional applications. Accordingly, this article critically reviews the design principles, structure-mechanism-property relationships, interaction mechanisms, and multifunctional applications of multi-physical lattice metamaterials enabled by AM techniques. First, lattice metamaterials are categorized into homogeneous lattices, inhomogeneous lattices, and other forms, whose design principles and AM processes are critically discussed, including the benefits and drawbacks of different AM techniques for fabricating different types of lattices. Subsequently, the structure-mechanism-property relationships and interaction mechanisms of lattice metamaterials in a range of physical fields, including mechanical, acoustic, electromagnetic/optical, and thermal disciplines, are summarized to reveal critical design principles. Moreover, the multifunctional applications of lattice metamaterials, such as sound absorbers, insulators, and manipulators, sensors, actuators, and soft robots, thermal management, invisible cloaks, and biomedical implants, are enumerated. These design principles and structure-mechanism-property relationships provide effective design guidelines for lattice metamaterials in multifunctional applications.

In Situ Programmable, Active, and Interactive Crystallization by Localized Polymerization

Additive manufacturing has sought active and interactive means of creating predictable structures with diverse materials. Compared to such active manufacturing tools, current crystallization strategies remain in statistical and passive programs of crystals via macroscale thermodynamic controllers, commonly lacking active means to intervene in crystal growth in a spatiotemporal manner. Herein, a strategy toward active and interactive programming and reprogramming of crystals, realized by real-time tangible feedback on growing crystals by delicately controlling the degree of in-situ, localized photopolymerization of polymeric structures via additive manufacturing is presented. Using this strategy, crystals can be seeded, guided, and even reprogrammed in a supersaturated liquid resin. In principle, the localized formation of sparse polymeric networks within supercooled resins can induce density fluctuation to trigger seed nucleation instantaneously, whereas the formation of dense networks can lower molecules' mobilities to inhibit crystal growth. Assisted by these active triggers and deterministic procedural aspects in additive manufacturing, growing crystals can be tangibly interacted through programmed polymeric structures, strengthening deterministic characteristics in crystal growth. It is suggested that crystal growth can be programmable with deterministic hierarchies within the created crystal's morphologies within the background of inherent stochasticity in crystallization, launching an era of convolutional growth of crystals.

3D Printing of Porous Ceramics for Enhanced Thermal Insulation Properties

Porous thermal insulating ceramics play a pivotal role in both industrial processes and daily life by offering effective insulation solutions that reduce energy consumption, enhance building comfort, and contribute to the sustainability of industrial production. This review offers a comprehensive examination of porous thermal insulating ceramics produced by 3D printing, providing an in-depth analysis of various 3D printing techniques and materials used to produce porous ceramics, detailing the fabrication processes, advantages, and limitations of these methods. Recent advances in 3D printed porous thermal insulating ceramics are thoroughly examined, with a particular focus on pore structure design and optimization strategies for high-performance thermal insulation. This review also addresses the challenges and barriers to widespread adoption while highlighting future research directions and emerging trends poised to drive innovation. By showcasing the transformative potential of 3D printing in revolutionizing traditional porous ceramics manufacturing methods and enhancing thermal insulation performance, this review underscores the critical role of 3D printed porous ceramics in advancing thermal insulation technology.

Time Code for multifunctional 3D printhead controls

Direct Ink Writing, an extrusion-based 3D printing technique, has attracted growing interest due to its ability to process a broad range of materials and integrate multifunctional printheads with features such as shape-changing nozzles, in-situ curing, material switching, and material mixing. Despite these advancements, incorporating auxiliary controls into Geometry Code (G-Code), the standard programming language for these printers, remains challenging. G-Code's line-by-line execution requires auxiliary control commands to interrupt the print path motion, causing defects in the printed structure. We propose a generalizable time-based synchronization approach called Time Code (T-Code), which decouples auxiliary control from G-Code, enabling uninterrupted print path enrichment. We demonstrate the method's effectiveness with both high-end and affordable 3D printers by fabricating functional gradients and parallelizing printhead auxiliary devices for mass customization. Our method reduces defects, enhances print speed, and minimizes the mechanical burden on 3D printers, enabling the rapid creation of complex multimaterial structures.

Helical Assemblies of Colloidal Nanocrystals with Long-Range Order and Their Fusion into Continuous Structures

Chirality epitomizes the sophistication of chemistry, representing some of its most remarkable achievements. Yet, the precise synthesis of chiral structures from achiral building blocks remains a profound and enduring challenge in synthetic chemistry and materials science. Here, we demonstrate that achiral colloidal nanocrystals, including Au and Ag nanocrystals, can assemble into long-range-ordered helical assemblies with the assistance of chiral molecules. The synchronized aggregation kinetics between colloidal silver or gold nanocrystals and π-conjugated perylene diimide molecules enables the nanocrystals to precisely follow the helical pathways of the molecular assemblies. This results in the formation of helical nanocrystal assemblies extending over tens of micrometers. These helically organized nanocrystals, exhibiting high positional precision, display linear size-dependent chiroptical properties. Furthermore, more intricate helical assemblies, featuring triple, quadruple, and quintuple nanocrystal strands, can be observed in addition to the commonly encountered double helical assemblies. Finally, these helical assemblies, composed of discrete Ag nanocrystals, can fuse into continuous Ag2S helical structures following a sulfidation reaction, ultimately leading to the formation of diverse metal sulfide helices through cation exchange processes.

Segmented, Side-Emitting Hydrogel Optical Fibers for Multimaterial Extrusion Printing

Side-emitting optical fibers allow light to be deliberately outcoupled along the fiber. Introducing a customized side-emission profile requires modulation of the guiding and emitting properties along the fiber length, which is a particular challenge in continuous processing of soft waveguides. In this work, it is demonstrated that multimaterial extrusion printing can generate hydrogel optical fibers with tailored segments for light-side emission. The fibers are based on diacrylated Pluronic F-127 (PluDA). 1 mm diameter fibers are printed with segments of different optical properties by switching between a PluDA waveguiding ink and a PluDA scattering ink containing nanoparticles. The method allows the fabrication of fibers with segment lengths below 500 microns in a continuous process. The length of the segments is tailored by varying the switching time between inks during printing. Fibers with customized side-emission profiles along their length are presented. The functionality of the printed fibers is demonstrated by exciting fluorescence inside a surrounding 3D hydrogel. The presented technology and material combination allow unprecedented flexibility for designing soft optical fibers with customizable optical properties using simple processes and a medical material. This approach can be of interest to improve illumination inside tissues for photodynamic therapy (PDT).

Bioprinting of a multi-composition array to mimic intra-tumor heterogeneity of glioblastoma for drug evaluation

Microextrusion printing is widely used to precisely manufacture microdevices, microphysiological systems, and biological constructs that feature micropatterns and microstructures consisting of various materials. This method is particularly useful for creating biological models that recapitulate in vivo-like cellular microenvironments. Although there is a recent demand for high-throughput data from a single in vitro system, it remains challenging to fabricate multiple models with a small volume of bioinks in a stable and precise manner due to the spreading and evaporation issues of the extruded hydrogel. As printing time increases, the extruded bioink spreads and evaporates, leading to technical problems that decrease printing resolution and stability, as well as biological problems that affect 3D culture space and cell viability. In this study, we describe a novel microextrusion bioprinting technique to stably fabricate a multi-composition array consisting of massive and nanoliter-scale hydrogel dots by using multi-bioink printing and aerosol-based crosslinking techniques to prevent spreading and evaporation issues. We confirmed that the crosslinking aerosol effectively prevented spreading and evaporation by analyzing the morphological changes of the extruded hydrogel. By adjusting the extruding ratio of the bioinks, we were able to print a multi-composition array. This stable and massive array printing technique allowed us to improve the replicates of biological models and provide various data from a single culture system. The array printing technique was applied to recapitulate the intra-tumor heterogeneity of glioblastoma and assess temozolomide efficacy on the array model.

A Programmable Handheld Extrusion-Based Bioprinting Platform for In Situ Skin Wounds Dressing: Balance Mobility and Customizability

Bioprinting technology plays a crucial role for constructing tissue substitutes. However, the mismatched scaffold shapes and the poor treatment timeliness limit its clinical translational application. In situ printing technology that prints bioregenerants directly inside patient's body can meet the needs of specific tissue repair. This study develops a smartphone controlled handheld bioprinter for in situ skin wounds dressing. The mini bioprinter can be handheld and placed on any printing surface to create strips, complex patterns, and 3D structures, and can be equipped with microchannel needles to expand functionality. The size of the strips as well as the printing path can be programmed and controlled by the smartphone to ensure the precision of the printed product quality. Furthermore, the device not only allows for smooth switching between different bioinks for printing heterogeneous structure, but also allows for fast and uniform coverage of large wound surfaces. When dealing with complex wounds in vitro & vivo, the printer can effectively fill and precisely close wounds, promoting wound healing. The programmable handheld bioprinter can balance mobility and customizability in the management of skin wounds and is expected to realize its potential for emergency medical treatment in condition-constrained scenarios, such as battlefields or disaster areas.

Voxel Interface Control in Multimaterial Extrusion 3D Printing

Interfaces are crucial in natural and engineered systems, dictating essential biological, ecological, and technological properties that augment performance, functionality, and user experience. Yet, achieving precise interfacial control poses significant challenges in both conventional and additive manufacturing, where scalability constraints impede the controlled deposition of quasi-2D layers within 3D objects. This paper introduces Voxel-Interface 3D Printing (VI3DP), which enables comprehensive control over extruded voxel interfaces irrespective of the printhead diameter that conventionally dictates feature size. Various optical, mechanical, and electrical functionalizations, attaining interface thicknesses up to three orders of magnitude smaller than the voxel size are reported. Notable applications include encoding data in soft matter through fluorescent interfaces, creating tight fits and movable mechanisms through non-adhesive interfaces, fabricating bio-inspired composites with tailored failure modes, and developing a single filament capacitive touch sensor. VI3DP opens new avenues for enhanced functionality and efficiency across multiple fields, including biomedical technology, electronics, optics, and nanotechnology.

Wearable and Implantable Soft Robots

Soft robotics presents innovative solutions across different scales. The flexibility and mechanical characteristics of soft robots make them particularly appealing for wearable and implantable applications. The scale and level of invasiveness required for soft robots depend on the extent of human interaction. This review provides a comprehensive overview of wearable and implantable soft robots, including applications in rehabilitation, assistance, organ simulation, surgical tools, and therapy. We discuss challenges such as the complexity of fabrication processes, the integration of responsive materials, and the need for robust control strategies, while focusing on advances in materials, actuation and sensing mechanisms, and fabrication techniques. Finally, we discuss the future outlook, highlighting key challenges and proposing potential solutions.

Geometric mechanics of kiri-origami-based bifurcated mechanical metamaterials

We explore a new design strategy of leveraging kinematic bifurcation in creating origami/kirigami-based three-dimensional (3D) hierarchical, reconfigurable, mechanical metamaterials with tunable mechanical responses. We start from constructing three basic, thick, panel-based structural units composed of 4, 6 and 8 rigidly rotatable cubes in close-looped connections. They are modelled, respectively, as 4R, 6R and 8R (R stands for revolute joint) spatial looped kinematic mechanisms, and are used to create a library of reconfigurable hierarchical building blocks that exhibit kinematic bifurcations. We analytically investigate their reconfiguration kinematics and predict the occurrence and locations of kinematic bifurcations through a trial-correction modelling method. These building blocks are tessellated in 3D to create various 3D bifurcated hierarchical mechanical metamaterials that preserve the kinematic bifurcations in their building blocks to reconfigure into different 3D architectures. By combining the kinematics and considering the elastic torsional energy stored in the folds, we develop the geometric mechanics to predict their tunable anisotropic Poisson's ratios and stiffnesses. We find that kinematic bifurcation can significantly effect mechanical responses, including changing the sign of Poisson's ratios from negative to positive beyond bifurcation, tuning the anisotropy, and overcoming the polarity of structural stiffness and enhancing the number of deformation paths with more reconfigured shapes.This article is part of the theme issue 'Origami/Kirigami-inspired structures: from fundamentals to applications'.

Controlled patterning of crystalline domains by frontal polymerization

Materials with hierarchical architectures that combine soft and hard material domains with coalesced interfaces possess superior properties compared with their homogeneous counterparts1-4. These architectures in synthetic materials have been achieved through deterministic manufacturing strategies such as 3D printing, which require an a priori design and active intervention throughout the process to achieve architectures spanning multiple length scales5-9. Here we harness frontal polymerization spin mode dynamics to autonomously fabricate patterned crystalline domains in poly(cyclooctadiene) with multiscale organization. This rapid, dissipative processing method leads to the formation of amorphous and semi-crystalline domains emerging from the internal interfaces generated between the solid polymer and the propagating cure front. The size, spacing and arrangement of the domains are controlled by the interplay between the reaction kinetics, thermochemistry and boundary conditions. Small perturbations in the fabrication conditions reproducibly lead to remarkable changes in the patterned microstructure and the resulting strength, elastic modulus and toughness of the polymer. This ability to control mechanical properties and performance solely through the initial conditions and the mode of front propagation represents a marked advancement in the design and manufacturing of advanced multiscale materials.

Nozzle Innovations That Improve Capacity and Capabilities of Multimaterial Additive Manufacturing

Multimaterial additive manufacturing incorporates multiple species within a single 3D-printed object to enhance its material properties and functionality. This technology could play a key role in distributed manufacturing. However, conventional layer-by-layer construction methods must operate at low volumetric throughputs to maintain fine feature resolution. One approach to overcome this challenge and increase production capacity is to structure multimaterial components in the printhead prior to deposition. Here we survey four classes of multimaterial nozzle innovations, nozzle arrays, coextruders, static mixers, and advective assemblers, designed for this purpose. Additionally, each design offers unique capabilities that provide benefits associated with accessible architectures, interfacial adhesion, material properties, and even living-cell viability. Accessing these benefits requires trade-offs, which may be mitigated with future investigation. Leveraging decades of research and development of multiphase extrusion equipment can help us engineer the next generation of 3D-printing nozzles and expand the capabilities and practical reach of multimaterial additive manufacturing.

Holographic direct sound printing

Direct sound printing (DSP), an alternative additive manufacturing process driven by sonochemical polymerization, has traditionally been confined to a single acoustic focal region, resulting in a voxel-by-voxel printing approach. To overcome this limitation, we introduce holographic direct sound printing (HDSP), where acoustic holograms, storing cross-sectional images of the desired parts, pattern acoustic waves to induce regional cavitation bubbles and on-demand regional polymerization. HDSP outperforms DSP in terms of printing speed by one order of magnitude and yields layerless printed structures. In our HDSP implementation, the hologram remains stationary while the printing platform moves along a three-dimensional path using a robotic arm. We present sono-chemiluminescence and high-speed imaging experiments to thoroughly investigate HDSP and demonstrate its versatility in applications such as remote ex-vivo in-body printing and complex robot trajectory planning. We showcase multi-object and multi-material printing and provide a comprehensive process characterization, including the effects of hologram design and manufacturing on the HDSP process, polymerization progression tracking, porosity tuning, and robotic trajectory computation. Our HDSP method establishes the integration of acoustic holography in DSP and related applications.

Microphysiological Systems for Cancer Immunotherapy Research and Development

Cancer immunotherapy focuses on the use of patients' adaptive immune systems to combat cancer. In the past decade, FDA has approved many immunotherapy products for cancer patients who suffer from primary tumors, tumor relapse, and metastases. However, these immunotherapies still show resistance in many patients and often lead to inconsistent responses in patients due to variations in tumor genetic mutations and tumor immune microenvironment. Microfluidics-based organ-on-a-chip technologies or microphysiological systems have opened new ways that can provide relatively fast screening for personalized immunotherapy and help researchers and clinicians understand tumor-immune interactions in a patient-specific manner. They also have the potential to overcome the limitations of traditional drug screening and testing, given the models provide a more realistic 3D microenvironment with better controllability, reproducibility, and physiological relevance. This review focuses on the cutting-edge microphysiological organ-on-a-chip devices developed in recent years for studying cancer immunity and testing cancer immunotherapeutic agents, as well as some of the largest challenges of translating this technology to clinical applications in immunotherapy and personalized medicine.

Toward Multiscale, Multimaterial 3D Printing

Biological materials and organisms possess the fundamental ability to self-organize, through which different components are assembled from the molecular level up to hierarchical structures with superior mechanical properties and multifunctionalities. These complex composites inspire material scientists to design new engineered materials by integrating multiple ingredients and structures over a wide range. Additive manufacturing, also known as 3D printing, has advantages with respect to fabricating multiscale and multi-material structures. The need for multifunctional materials is driving 3D printing techniques toward arbitrary 3D architectures with the next level of complexity. In this paper, the aim is to highlight key features of those 3D printing techniques that can produce either multiscale or multimaterial structures, including innovations in printing methods, materials processing approaches, and hardware improvements. Several issues and challenges related to current methods are discussed. Ultimately, the authors also provide their perspective on how to realize the combination of multiscale and multimaterial capabilities in 3D printing processes and future directions based on emerging research.

3D Printed Room Temperature Phosphorescence Materials Enabled by Edible Natural Konjac Glucomannan

Shaping room temperature phosphorescence (RTP) materials into 3D bodies is important for stereoscopic optoelectronic displays but remains challenging due to their poor processability and mechanical properties. Here, konjac glucomannan (KGM) is employed to anchor arylboronic acids with various π conjugations via a facile B─O covalent reaction to afford printable inks, using which full-color high-fidelity 3D RTP objects with high mechanical strength can be obtained via direct ink writing-based 3D printing and freeze-drying. The doubly rigid structure supplied by the synergy of hydrogen bonding and B─O covalent bonding can protect the triplet excitons; thus, the prepared 3D RTP object shows a striking lifetime of 2.14 s. The printed counterparts are successfully used for 3D anti-counterfeiting and can be recycled and reprinted nondestructively by dissolving in water. This success expands the scope of printable 3D luminescent materials, providing an eco-friendly platform for the additive manufacturing of sophisticated 3D RTP architectures.

4D Printing of Shape-Morphing Liquid Crystal Elastomers

In nature, biological systems can sense environmental changes and alter their performance parameters in real time to adapt to environmental changes. Inspired by these, scientists have developed a range of novel shape-morphing materials. Shape-morphing materials are a kind of "intelligent" materials that exhibit responses to external stimuli in a predetermined way and then display a preset function. Liquid crystal elastomer (LCE) is a typical representative example of shape-morphing materials. The emergence of 4D printing technology can effectively simplify the preparation process of shape-morphing LCEs, by changing the printing material compositions and printing conditions, enabling precise control and macroscopic design of the shape-morphing modes. At the same time, the layer-by-layer stacking method can also endow the shape-morphing LCEs with complex, hierarchical orientation structures, which gives researchers a great degree of design freedom. 4D printing has greatly expanded the application scope of shape-morphing LCEs as soft intelligent materials. This review systematically reports the recent progress of 3D/4D printing of shape-morphing LCEs, discusses various 4D printing technologies, synthesis methods and actuation modes of 3D/4D printed LCEs, and summarizes the opportunities and challenges of 3D/4D printing technologies in preparing shape-morphing LCEs.

Light-Based 3D Multi-Material Printing of Micro-Structured Bio-Shaped, Conducting and Dry Adhesive Electrodes for Bioelectronics

In this work, a new method of multi-material printing in one-go using a commercially available 3D printer is presented. The approach is simple and versatile, allowing the manufacturing of multi-material layered or multi-material printing in the same layer. To the best of the knowledge, it is the first time that 3D printed Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) micro-patterns combining different materials are reported, overcoming mechanical stability issues. Moreover, the conducting ink is engineered to obtain stable in-time materials while retaining sub-100 µm resolution. Micro-structured bio-shaped protuberances are designed and 3D printed as electrodes for electrophysiology. Moreover, these microstructures are combined with polymerizable deep eutectic solvents (polyDES) as functional additives, gaining adhesion and ionic conductivity. As a result of the novel electrodes, low skin impedance values showed suitable performance for electromyography recording on the forearm. Finally, this concluded that the use of polyDES conferred stability over time, allowing the usability of the electrode 90 days after fabrication without losing its performance. All in all, this demonstrated a very easy-to-make procedure that allows printing PEDOT:PSS on soft, hard, and/or flexible functional substrates, opening up a new paradigm in the manufacturing of conducting multi-functional materials for the field of bioelectronics and wearables.

Additive Manufacturing Provides Infinite Possibilities for Self-Sensing Technology

Integrating sensors and other functional parts in one device can enable a new generation of integrated intelligent devices that can perform self-sensing and monitoring autonomously. Applications include buildings that detect and repair damage, robots that monitor conditions and perform real-time correction and reconstruction, aircraft capable of real-time perception of the internal and external environment, and medical devices and prosthetics with a realistic sense of touch. Although integrating sensors and other functional parts into self-sensing intelligent devices has become increasingly common, additive manufacturing has only been marginally explored. This review focuses on additive manufacturing integrated design, printing equipment, and printable materials and stuctures. The importance of the material, structure, and function of integrated manufacturing are highlighted. The study summarizes current challenges to be addressed and provides suggestions for future development directions.

Photoreaction Drives Efficient, Precise, and Sustainable Additive Manufacturing

Additive manufacturing, normally referred to as three-dimensional (3D) printing, has been maturing rapidly in recent years and widely utilized in various industrial fields, because it can create predesigned functional products with sophisticated structures that are basically difficult to achieve using traditional methods. Among all 3D printing technologies, vat photopolymerization has attracted much attention because of its outstanding advantages such as fast printing speed, high precision, and ease of formulating. In recent years, many breakthroughs in photopolymerization based 3D printing have been achieved by photoreaction design regarding photopolymerizable monomers, photoinitiating systems, inhibition functions, light sourcs, etc., but challenges remain. This Perspective attempts to highlight these great advances regarding the promotion of printing efficiency, accuracy, and sustainability. At the end, several challenges, such as longer-wavelength printing, printing of functional materials, and multimaterial printing, are discussed, which must be carefully addressed to meet the increasing requirements of future high-performance additive manufacturing.

Multiscale 3D printing via active nozzle size and shape control

Three-dimensional (3D) printers extruding filaments through a fixed nozzle encounter a conflict between high resolution, requiring small diameters, and high speed, requiring large diameters. This limitation is especially pronounced in multiscale architectures featuring both bulk and intricate elements. Here, we introduce adaptive nozzle 3D printing (AN3DP), a technique enabling dynamic alteration of nozzle diameter and cross-sectional shape during printing. The AN3DP nozzle consists of eight independently controllable, tendon-driven pins arrayed around a flexible, pressure-resistant membrane. The design incorporates a tapered angle optimized for extruding shear-thinning inks and a pointed tip suitable for constrained-space printing, such as conformal and embedded printing. AN3DP's efficacy is demonstrated through the fabrication of components with continuous gradients, eliminating the need for discretization, and achieving enhanced density and contour precision compared to traditional 3D printing methods. This platform substantially expands the scope of extrusion-based 3D printers, thus facilitating diverse applications, including bioprinting cell-laden and hierarchical implants with bone-like microarchitecture.

Programmed multimaterial assembly by synergized 3D printing and freeform laser induction

In nature, structural and functional materials often form programmed three-dimensional (3D) assembly to perform daily functions, inspiring researchers to engineer multifunctional 3D structures. Despite much progress, a general method to fabricate and assemble a broad range of materials into functional 3D objects remains limited. Herein, to bridge the gap, we demonstrate a freeform multimaterial assembly process (FMAP) by integrating 3D printing (fused filament fabrication (FFF), direct ink writing (DIW)) with freeform laser induction (FLI). 3D printing performs the 3D structural material assembly, while FLI fabricates the functional materials in predesigned 3D space by synergistic, programmed control. This paper showcases the versatility of FMAP in spatially fabricating various types of functional materials (metals, semiconductors) within 3D structures for applications in crossbar circuits for LED display, a strain sensor for multifunctional springs and haptic manipulators, a UV sensor, a 3D electromagnet as a magnetic encoder, capacitive sensors for human machine interface, and an integrated microfluidic reactor with a built-in Joule heater for nanomaterial synthesis. This success underscores the potential of FMAP to redefine 3D printing and FLI for programmed multimaterial assembly.

3D printing with a 3D printed digital material filament for programming functional gradients

Additive manufacturing, or 3D printing attracts growing attention as a promising method for creating functionally graded materials. Fused deposition modeling (FDM) is widely available, but due to its simple process, creating spatial gradation of diverse properties using FDM is challenging. Here, we present a 3D printed digital material filament that is structured towards 3D printing of functional gradients, utilizing only a readily available FDM printer and filaments. The DM filament consists of multiple base materials combined with specific concentrations and distributions, which are FDM printed. When the DM filament is supplied to the same printer, its constituent materials are homogeneously blended during extrusion, resulting in the desired properties in the final structure. This enables spatial programming of material properties in extreme variations, including mechanical strength, electrical conductivity, and color, which are otherwise impossible to achieve with traditional FDMs. Our approach can be readily adopted to any standard FDM printer, enabling low-cost production of functional gradients.

Stopping Microfluidic Flow

A cross-comparison of three stop-flow configurations-such as low-pressure (LSF), high-pressure open-circuit (OC-HSF), and high-pressure short-circuit (SC-HSF) stop-flow-is presented to rapidly bring a high velocity flow O(m s-1) within a microchannel to a standstill O(µm s-1). The performance of three stop-flow configurations is assessed by measuring residual flow velocities within microchannels having three orders of magnitude different flow resistances. The LSF configuration outperforms the OC-HSF and SC-HSF configurations within a high flow resistance microchannel and results in a residual velocity of <10 µm s-1. The OC-HSF configuration results in a residual velocity of <150 µm s-1 within a low flow resistance microchannel. The SC-HSF configuration results in a residual velocity of <200 µm s-1 across the three orders-of-magnitude different flow resistance microchannels, and <100 µm s-1 for the low flow resistance channel. It is hypothesized that residual velocity results from compliance in fluidic circuits, which is further investigated by varying the elasticity of microchannel walls and connecting tubing. A numerical model is developed to estimate the expanded volumes of the compliant microchannel and connecting tubings under a pressure gradient and to calculate the distance traveled by the sample fluid. A comparison of the numerically and experimentally obtained traveling distances confirms the hypothesis that the residual velocities are an outcome of the compliance in the fluidic circuit.

Direct laser writing-enabled 3D printing strategies for microfluidic applications

Over the past decade, additive manufacturing-or "three-dimensional (3D) printing"-has attracted increasing attention in the Lab on a Chip community as a pathway to achieve sophisticated system architectures that are difficult or infeasible to fabricate via conventional means. One particularly promising 3D manufacturing technology is "direct laser writing (DLW)", which leverages two-photon (or multi-photon) polymerization (2PP) phenomena to enable high geometric versatility, print speeds, and precision at length scales down to the 100 nm range. Although researchers have demonstrated the potential of using DLW for microfluidic applications ranging from organ on a chip and drug delivery to micro/nanoparticle processing and soft microrobotics, such scenarios present unique challenges for DLW. Specifically, microfluidic systems typically require macro-to-micro fluidic interfaces (e.g., inlet and outlet ports) to facilitate fluidic loading, control, and retrieval operations; however, DLW-based 3D printing relies on a micron-to-submicron-sized 2PP volume element (i.e., "voxel") that is poorly suited for manufacturing these larger-scale fluidic interfaces. In this Tutorial Review, we highlight and discuss the four most prominent strategies that researchers have developed to circumvent this trade-off and realize macro-to-micro interfaces for DLW-enabled microfluidic components and systems. In addition, we consider the possibility that-with the advent of next-generation commercial DLW printers equipped with new dynamic voxel tuning, print field, and laser power capabilities-the overall utility of DLW strategies for Lab on a Chip fields may soon expand dramatically.

Gradient matters via filament diameter-adjustable 3D printing

Gradient matters with hierarchical structures endow the natural world with excellent integrity and diversity. Currently, direct ink writing 3D printing is attracting tremendous interest, and has been used to explore the fabrication of 1D and 2D hierarchical structures by adjusting the diameter, spacing, and angle between filaments. However, it is difficult to generate complex 3D gradient matters owing to the inherent limitations of existing methods in terms of available gradient dimension, gradient resolution, and shape fidelity. Here, we report a filament diameter-adjustable 3D printing strategy that enables conventional extrusion 3D printers to produce 1D, 2D, and 3D gradient matters with tunable heterogeneous structures by continuously varying the volume of deposited ink on the printing trajectory. In detail, we develop diameter-programmable filaments by customizing the printing velocity and height. To achieve high shape fidelity, we specially add supporting layers at needed locations. Finally, we showcase multi-disciplinary applications of our strategy in creating horizontal, radial, and axial gradient structures, letter-embedded structures, metastructures, tissue-mimicking scaffolds, flexible electronics, and time-driven devices. By showing the potential of this strategy, we anticipate that it could be easily extended to a variety of filament-based additive manufacturing technologies and facilitate the development of functionally graded structures.

Quantitative Biofabrication Platform for Collagen-Based Peripheral Nerve Grafts with Structural and Chemical Guidance

Owing to its crucial role in the human body, collagen has immense potential as a material for the biofabrication of tissues and organs. However, highly refined fabrication using collagen remains difficult, primarily because of its notably soft properties. A quantitative biofabrication platform to construct collagen-based peripheral nerve grafts, incorporating bionic structural and chemical guidance cues, is introduced. A viscoelastic model for collagen, which facilitates simulating material relaxation and fabricating collagen-based neural grafts, achieving a maximum channel density similar to that of the native nerve structure of longitudinal microchannel arrays, is established. For axonal regeneration over considerable distances, a gradient printing control model and quantitative method are developed to realize the high-precision gradient distribution of nerve growth factor required to obtain nerve grafts through one-step bioprinting. Experiments verify that the bioprinted graft effectively guides linear axonal growth in vitro and in vivo. This study should advance biofabrication methods for a variety of human tissue-engineering applications requiring tailored cues.

Challenges and Opportunities in Preserving Key Structural Features of 3D-Printed Metal/Covalent Organic Framework

Metal-organic framework (MOF) and covalent organic framework (COF) are a huge group of advanced porous materials exhibiting attractive and tunable microstructural features, such as large surface area, tunable pore size, and functional surfaces, which have significant values in various application areas. The emerging 3D printing technology further provides MOF and COFs (M/COFs) with higher designability of their macrostructure and demonstrates large achievements in their performance by shaping them into advanced 3D monoliths. However, the currently available 3D printing M/COFs strategy faces a major challenge of severe destruction of M/COFs' microstructural features, both during and after 3D printing. It is envisioned that preserving the microstructure of M/COFs in the 3D-printed monolith will bring a great improvement to the related applications. In this overview, the 3D-printed M/COFs are categorized into M/COF-mixed monoliths and M/COF-covered monoliths. Their differences in the properties, applications, and current research states are discussed. The up-to-date advancements in paste/scaffold composition and printing/covering methods to preserve the superior M/COF microstructure during 3D printing are further discussed for the two types of 3D-printed M/COF. Throughout the analysis of the current states of 3D-printed M/COFs, the expected future research direction to achieve a highly preserved microstructure in the 3D monolith is proposed.

4D printing for biomedical applications

While three-dimensional (3D) printing excels at fabricating static constructs, it fails to emulate the dynamic behavior of native tissues or the temporal programmability desired for medical devices. Four-dimensional (4D) printing is an advanced additive manufacturing technology capable of fabricating constructs that can undergo pre-programmed changes in shape, property, or functionality when exposed to specific stimuli. In this Perspective, we summarize the advances in materials chemistry, 3D printing strategies, and post-printing methodologies that collectively facilitate the realization of temporal dynamics within 4D-printed soft materials (hydrogels, shape-memory polymers, liquid crystalline elastomers), ceramics, and metals. We also discuss and present insights about the diverse biomedical applications of 4D printing, including tissue engineering and regenerative medicine, drug delivery, in vitro models, and medical devices. Finally, we discuss the current challenges and emphasize the importance of an application-driven design approach to enable the clinical translation and widespread adoption of 4D printing.

Advanced Nanomaterials in Medical 3D Printing

3D printing is now recognized as a significant tool for medical research and clinical practice, leading to the emergence of medical 3D printing technology. It is essential to improve the properties of 3D-printed products to meet the demand for medical use. The core of generating qualified 3D printing products is to develop advanced materials and processes. Taking advantage of nanomaterials with tunable and distinct physical, chemical, and biological properties, integrating nanotechnology into 3D printing creates new opportunities for advancing medical 3D printing field. Recently, some attempts are made to improve medical 3D printing through nanotechnology, providing new insights into developing advanced medical 3D printing technology. With high-resolution 3D printing technology, nano-structures can be directly fabricated for medical applications. Incorporating nanomaterials into the 3D printing material system can improve the properties of the 3D-printed medical products. At the same time, nanomaterials can be used to expand novel medical 3D printing technologies. This review introduced the strategies and progresses of improving medical 3D printing through nanotechnology and discussed challenges in clinical translation.

Grayscale Color 3D/4D Printing via Orthogonal Photochemistry

Coloration is essential for enhancing visual aesthetics and facilitating information communication, but it is difficult to apply to highly complex surfaces. Efficient manufacturing of 3D printed colored products is particularly challenging, given the arbitrary nature of the surfaces. We accomplish this goal with 3D/4D color printing using a photoprintable resin containing a free radical initiator, photocurable monomers, a photoacid generator, and an acid-sensitive dye. The free radical initiator is activated with a long wavelength light (405 nm) for 3D/4D photoprinting. Independently, the photoacid generator is triggered with a shorter wavelength light (365 nm) to activate acid-sensitive dye for coloration. This allows decoupling 3D/4D printing with coloration to yield geometrically complex 3D objects with designable surface color patterns as a highly efficient yet simple way to produce colored 3D objects.

Deciphering the ultra-high plasticity in metal monochalcogenides

The quest for electronic devices that offer flexibility, wearability, durability and high performance has spotlighted two-dimensional (2D) van der Waals materials as potential next-generation semiconductors. Especially noteworthy is indium selenide, which has demonstrated surprising ultra-high plasticity. To deepen our understanding of this unusual plasticity in 2D van der Waals materials and to explore inorganic plastic semiconductors, we have conducted in-depth experimental and theoretical investigations on metal monochalcogenides (MX) and transition metal dichalcogenides (MX2). We have discovered a general plastic deformation mode in MX, which is facilitated by the synergetic effect of phase transitions, interlayer gliding and micro-cracks. This is in contrast to crystals with strong atomic bonding, such as metals and ceramics, where plasticity is primarily driven by dislocations, twinning or grain boundaries. The enhancement of gliding barriers prevents macroscopic fractures through a pinning effect after changes in stacking order. The discovery of ultra-high plasticity and the phase transition mechanism in 2D MX materials holds significant potential for the design and development of high-performance inorganic plastic semiconductors.

Organic chiral nano- and microfilaments: types, formation, and template applications

Organic chiral nanofilaments are part of an important class of nanoscale chiral materials that has recently been receiving significant attention largely due to their potential use in applications such as optics, photonics, metameterials, and potentially a range of medical as well as sensing applications. This review will focus on key examples of the formation of such nano- and micro-filaments based on carbon nanofibers, polymers, synthetic oligo- and polypeptides, self-assembled organic molecules, and one prominent class of liquid crystals. The most critical aspects discussed here are the underlying driving forces for chiral filament formation, potentially answering why specific sizes and shapes are formed, what molecular design strategies are working equally well or rather differently among these materials classes, and what uses and applications are driving research in this fascinating field of materials science.

Superstretchable Liquid-Metal Electrodes for Dielectric Elastomer Transducers and Flexible Circuits

Dielectric elastomer transducers (DETs), with a dielectric elastomer (DE) film sandwiched between two compliant electrodes, are highly sought after in the fields of soft robotics, energy harvesting, and human-machine interaction. To achieve a high-performance DET, it is essential to develop electrodes with high conductivity, strain-insensitive resistance, and adaptability. Herein, we design an electrode (Supra-LMNs) based on multiple dynamic bond cross-linked supramolecular networks (Ns) and liquid metal (LM), which realizes high conductivity (up to 16,000 S cm-1), negligible resistance changes at high strain (1.3-fold increase at 1000% strain), instantaneous self-healability at ambient temperature, and rapid recycling. The conductive pathway can be activated through simple friction by transmitting stress through the silver nanowires (AgNWs) and cross-linking sites of LM particles. This method is especially attractive for printing circuits on flexible substrates, especially DE films. Utilized as dielectric elastomer generator (DEG) electrodes, it reduces the charge loss by 3 orders of magnitude and achieves high generating energy density and energy conversion efficiency on a low-resistance load. Additionally, serving as sensor (DES) and actuator (DEA) electrodes, it enables a highly sensitive sensing capability and complex interaction.

3D Printing of Flow-Inspired Anisotropic Patterns with Liquid Crystalline Polymers

Anisotropic materials formed by living organisms possess remarkable mechanical properties due to their intricate microstructure and directional freedom. In contrast, human-made materials face challenges in achieving similar levels of directionality due to material and manufacturability constraints. To overcome these limitations, an approach using 3D printing of self-assembling thermotropic liquid crystal polymers (LCPs) is presented. Their high stiffness and strength is granted by nematic domains aligning during the extrusion process. Here, a remarkably wide range of Young's modulus from 3 to 40 GPa is obtained by utilizing directionality of the nematic flow the printing process.   By determining a relationship between stiffness, nozzle diameter, and line width, a design space where shaping and mechanical performance can be combined is identified. The ability to print LCPs with on-the-fly width changes to accommodate arbitrary spatially varying directions is demonstrated. This unlocks the possibility to manufacture exquisite patterns inspired by fluid dynamics with steep curvature variations. Utilizing the synergy between this path-planning method and LCPs, functional objects with stiffness and curvature gradients can be 3D-printed, offering potential applications in lightweight sustainable structures embedding crack-mitigation strategies. This method also opens avenues for studying and replicating intricate patterns observed in nature, such as wood or turbulent flow using 3D printing.

Self-enhancing sono-inks enable deep-penetration acoustic volumetric printing

Volumetric printing, an emerging additive manufacturing technique, builds objects with enhanced printing speed and surface quality by forgoing the stepwise ink-renewal step. Existing volumetric printing techniques almost exclusively rely on light energy to trigger photopolymerization in transparent inks, limiting material choices and build sizes. We report a self-enhancing sonicated ink (or sono-ink) design and corresponding focused-ultrasound writing technique for deep-penetration acoustic volumetric printing (DAVP). We used experiments and acoustic modeling to study the frequency and scanning rate-dependent acoustic printing behaviors. DAVP achieves the key features of low acoustic streaming, rapid sonothermal polymerization, and large printing depth, enabling the printing of volumetric hydrogels and nanocomposites with various shapes regardless of their optical properties. DAVP also allows printing at centimeter depths through biological tissues, paving the way toward minimally invasive medicine.

Pressure-Activatable Liquid Metal Composites Flexible Sensor with Antifouling and Drag Reduction Functional Surface

Flexible sensors produced through three-dimensional (3D) printing have exhibited promising results in the context of underwater sensing detection (for applications in navigational vehicles and human activities). However, underwater vehicles and activities such as swimming and diving are highly susceptible to drag, which can cause negative impacts such as reduced speed and increased energy consumption. Additionally, microbial adhesion can shorten the service life of these vehicles. However, natural organisms are able to circumvent such problems, with shark skin offering excellent barrier properties and ruffled papillae providing effective protection against fouling. Here, we show that a sandwich system consisting of a spraying layer, conductive elastomer composite, and encapsulation layer can be printed for multifunctional integrated underwater sensors. The modulated viscoelastic properties of liquid metal form the foundation for printing features, while its pressure-activated properties offer the potential for switchable sensors. An integrated drag reduction and antifouling layer were created by combining the shark skin surface shield scale structure with the lotus leaf surface papillae structure. A 3D-printed flexible sensor was designed using our approach to monitor attitude changes and strain in underwater environments, showcasing its capabilities. Our printed sensors can reduce biological attachment density by more than 50% and reduce underwater drag by 8.6-10.3%.

Multifunctional nacre-like materials

Nacre, the iridescent inner layer of seashells, displays an exceptional combination of strength and toughness due to its 'brick-wall' architecture. Significant research has been devoted to replicating nacre's architecture and its associated deformation and failure mechanisms. Using the resulting materials in applications necessitates adding functionalities such as self-healing, force sensing, bioactivity, heat conductivity and resistance, transparency, and electromagnetic interference shielding. Herein, progress in the fabrication, mechanics, and multi-functionality of nacre-like materials, particularly over the past three years is systematically and critically reviewed. The fabrication techniques reviewed include 3D printing, freeze-casting, mixing/coating-assembling, and laser engraving. The mechanical properties of the resulting materials are discussed in comparison with their constituents and previously developed nacre mimics. Subsequently, the progress in incorporating multifunctionalities and the resulting physical, chemical, and biological properties are evaluated. We finally provide suggestions based on 3D/4D printing, advanced modelling techniques, and machine elements to make reprogrammable nacre-like components with complex shapes and small building blocks, tackling some of the main challenges in the science and translation of these materials.

Development and Prospective Applications of 3D Membranes as a Sensor for Monitoring and Inducing Tissue Regeneration

For decades, tissue regeneration has been a challenging issue in scientific modeling and human practices. Although many conventional therapies are already used to treat burns, muscle injuries, bone defects, and hair follicle injuries, there remains an urgent need for better healing effects in skin, bone, and other unique tissues. Recent advances in three-dimensional (3D) printing and real-time monitoring technologies have enabled the creation of tissue-like membranes and the provision of an appropriate microenvironment. Using tissue engineering methods incorporating 3D printing technologies and biomaterials for the extracellular matrix (ECM) containing scaffolds can be used to construct a precisely distributed artificial membrane. Moreover, advances in smart sensors have facilitated the development of tissue regeneration. Various smart sensors may monitor the recovery of the wound process in different aspects, and some may spontaneously give feedback to the wound sites by releasing biological factors. The combination of the detection of smart sensors and individualized membrane design in the healing process shows enormous potential for wound dressings. Here, we provide an overview of the advantages of 3D printing and conventional therapies in tissue engineering. We also shed light on different types of 3D printing technology, biomaterials, and sensors to describe effective methods for use in skin and other tissue regeneration, highlighting their strengths and limitations. Finally, we highlight the value of 3D bioengineered membranes in various fields, including the modeling of disease, organ-on-a-chip, and drug development.

Design and Analysis of a Rotational Mixer to produce 3D Bioprinting Gyroid-Helical-Patterned Scaffolds for Tissue Engineering Applications

Tissue engineering scaffolds require complex networks for nutrient diffusion and cell attachment. They must have specific surface area and curvature, and often need a multimaterial composition, demanding advanced micro-fabrication methods. 3D extrusion bioprinting offers versatility to manufacture different scaffold, and strategies for multimaterial printing have been introduced. We propose a method to fabricate scaffolds based on gyroid-helical-patterned microfibers, providing a platform to study the effect of the gyroid minimum curvature on cellular processes, since the geometry wont be layer-by-layer approximated. The pattern is obtained by mixing inks using a gyroid-helix shaped rotational mixer, modifying the extruder of a conventional 3D printer. The mixer was simulated using computational fluid dynamics tools, varying the volumetric flow to obtain different gyroid-thickness. Due to its surface area minimization, it shows lower energy requirements than state-of-art fluid mixers, with a pressure drop of 1.7%, a power number of 39, and a rotation-induced shear stress of ∼400 Pa, enabling the use of cell-embedded bioinks.