4D printed hydrogel scaffold with swelling-stiffening properties and programmable deformation for minimally invasive implantation

A bioinspired helical hydrogel scaffold with real-time sensing for enhanced precision in gynecological digital vaginal examination

Precise diagnostic and therapeutic modalities are of utmost significance in driving forward patient care within the sphere of gynecological medicine. Bionics, involving the application of nature-inspired designs in medical apparatus, has emerged as a highly promising approach in this field. Specifically, helical architectures observed in natural organisms like vines display remarkable adaptability and mechanical strength, presenting novel perspectives for the development of ergonomic and effective gynecological examination and surgical instruments. Harnessing these insights, this study presents a helical polydimethylsiloxane (PDMS) scaffold inspired by the deformability of vines. This scaffold not only integrates Janus wettability hydrogel properties to enhance tissue interaction, ensuring increased comfort and adaptability during clinical procedures, but also incorporates sensors for real-time monitoring and feedback, thereby overcoming the limitations of conventional gynecological devices that often lack such capabilities. We meticulously detail the fabrication of this helical finger scaffold, using a sandwich thermoplastic method to produce hydrogel fibers possessing shape memory, thermal responsiveness, and deformation sensing via relative resistance changes. Additionally, the study explores finger motion monitoring through surface electromyography (sEMG) signals, which advances the precision and safety of cervical palpation and related surgeries. Overall, our findings highlight the potential of these responsive and adaptable hydrogels to transform gynecological medical devices, providing a solid theoretical foundation and practical applications for future innovations in gynecological diagnostics and surgical support.

An overview of recent advancements in 4D printing of alginate hydrogels for tissue regeneration

4D printing of alginate hydrogels has emerged as a transformative strategy in tissue engineering, enabling the fabrication of stimuli-responsive scaffolds that recapitulate the temporal and spatial complexities of native tissues. Leveraging alginate's tunable crosslinking, biocompatibility, and easy modification, recent research has demonstrated the successful design of constructs capable of programmable shape morphing in response to physiological stimuli. This review highlights recent advances in polymer design, including methacrylated, oxidized, and ligand-functionalized alginate derivatives, and cutting-edge 4D printing technologies such as extrusion-based and photopolymerization-based printing technologies. Notably, these systems have shown promising outcomes in regenerating cartilage, bone, vascular, and neural tissues. However, key challenges remain, including the standardization of shape-morphing quantification, enhancement of mechanical robustness, improvement of host tissue integration, and the replication of native tissue complexity. This review concludes with a critical evaluation of current limitations and future directions, highlighting the potential of integrating 4D alginate hydrogel systems with emerging technologies such as artificial intelligence, machine learning, organoid models, and bioelectronic interfaces to accelerate innovation and broaden their application in tissue engineering. By synthesizing recent advancements and offering insights into the implementation of 4D alginate hydrogels, this review aims to stimulate continued progress in this rapidly evolving field.

Biocompatible composite hydrogel with on-demand swelling-shrinking properties for 4D bioprinting

Hydrogels with tunable swelling and shrinking properties are of great interest in biomedical applications, particularly in wound healing, tissue regeneration, and drug delivery. Traditional hydrogels often fail to achieve high swelling without mechanical failure. In contrast, high-swelling hydrogels can absorb large amounts of liquid, expanding their volume by 10-1000 times, due to low crosslink density and the presence of hydrophilic groups. Additionally, some high-swelling hydrogels can also shrink in response to external stimuli, making them promising candidates for applications like on-demand drug delivery and biosensing. An emerging application of high-swelling hydrogels is four-dimensional (4D) printing, where controlled swelling induces structural transformations in a 3D printed construct. However, current hydrogel systems show limited swelling capacity, restricting their ability to undergo significant shape changes. To address these limitations, we developed a high-swelling composite hydrogel, termed SwellMA, by combining gelatin methacryloyl (GelMA) and sodium polyacrylate (SPA). SwellMA exhibits a swelling capacity over 500% of its original area and can increase its original water weight by 100-fold, outperforming existing materials in 4D bioprinting. Furthermore, SwellMA constructs can cyclically swell and shrink on-demand upon changing the ionic strength of the aqueous solution. Additionally, SwellMA demonstrates superior cytocompatibility and cell culture properties than SPA, along with enhanced 3D printing fidelity. These findings demonstrate SwellMA's potential for advanced 4D printing and a broad range of biomedical applications requiring precise and dynamic control over hydrogel swelling and shrinking.

Stimulus-assisted in situ bioprinting: advancing direct bench-to-bedside delivery

The fabrication of 3D bioconstructs using bioprinters will advance the field of regenerative medicine owing to its ability to facilitate clinical treatments. Additional stimulations have been applied to the bioconstructs to guide cells laden in the bioconstructs. However, the conventional bench-to-bedside delivery based on separate bioprinting and biostimulating processes may increase the risks of contamination and shape discordance owing to the considerably long process involved. In situ bioprinting is aimed at eliminating these risks, but stimulation strategies implied during in situ printing have not yet been extensively reviewed. Here, we present the concept of stimulus-assisted in situ bioprinting, which integrates the printing and biostimulation processes by directly applying stimuli to the bioink during fabrication.

Recent Advances in 4D-Printed Shape Memory Actuators

4D printing, which combines the design freedom of 3D printing with the responsiveness of smart materials, is revolutionizing the creation of active structures. These structures can change shape in response to external stimuli, paving the way for advancements in robotics, biomedicine, and beyond. However, a comprehensive review article highlighting recent advancements in 4D printed shape memory actuators (SMAAs) is lacking. This review explores the exciting potential of 4D printing for intelligent SMAAs. It examines the concept of shape memory and the materials used, like shape-memory polymers (SMPs), shape-memory alloys (SMAs), and shape-memory polymer composites (SMPCs). It then dives into compatible 3D printing techniques and design principles for achieving programmed shape changes. Different categories of 4D printed SMAAs are explored, showcasing their potential applications in diverse fields. The review concludes by discussing challenges and future directions, emphasizing the massive potential of 4D printing for creating the next generation of actuators, making it a valuable resource for researchers in the field.

Shape Memory Networks With Tunable Self-Stiffening Kinetics Enabled by Polymer Melting-Recrystallization

Shape memory polymers (SMPs) are deformable materials capable of recovering from a programmed temporary shape to a permanent shape under specific stimuli. However, shape recovery of SMPs is often accompanied by the evolution of materials from a stiff to soft state, leading to a significant decrease in strength/modulus and thereby impacting their practical applications. Although some attempts are made to pursue the SMPs with self-stiffening capability after shape recovery, the modulus increase ratio is much limited. Inspired by the recrystallization process of CaCO3 during crab molting, a novel and universal strategy is developed to construct water-free self-stiffening SMPs by using a single thermal stimulus through harnessing the polymer melting-recrystallization. The shape recovery is achieved through the melting of polymer primary crystals, followed by the self-stiffening via polymer recrystallization at the same recovery temperature, in which the modulus increase rate and ratio can be programmed in a wide range. Additionally, conceptual applications of these self-stiffening SMPs as artificial stents with self-enhancing supporting function are successfully demonstrated. This work is believed to provide new insights for developing the advanced shape memory devices.

NIR-programmable 3D-printed shape-memory scaffold with dual-thermal responsiveness for precision bone regeneration and bone tumor management

Clinically, intraoperative treatment of bone tumors presents several challenges, including the effective inactivation of tumors and filling of irregular bone defects after tumor removal. In this study, intelligent thermosensitive composite materials with shape-memory properties were constructed using polylactic acid (PLA) and polycaprolactone (PCL), which have excellent biocompatibility and degradability. Additionally, beta-tricalcium phosphate (β-TCP), with its osteogenic properties, and magnesium (Mg) powder, with its photothermal and bone-promoting abilities, were incorporated to improve the osteogenic potential of the composite and enable the material to respond intelligently to near-infrared (NIR) light. Utilizing 3D printing technology, the composite material was prepared into an NIR-responsive shape-memory bone-filling implant that deforms when the scaffold temperature increases to 48 ℃ under NIR laser irradiation. Moreover, at a lower temperature of 42 ℃, mild photothermal therapy promotes macrophage polarization toward the M2 phenotype. This process regulates the secretion of interleukin (IL)-4, IL-10, tumor necrosis factor-α, IL-6, and bone morphogenetic protein (BMP)-2, reducing local inflammation, enhancing the release of pro-healing factors, and improving osteogenesis. Overall, this innovative scaffold is a promising and efficient treatment for filling irregular bone defects after bone tumor surgery.

4D Printing: A Comprehensive Review of Technologies, Materials, Stimuli, Design, and Emerging Applications

4D printing is a groundbreaking technology that seamlessly integrates additive manufacturing with smart materials, enabling the creation of multiscale objects capable of changing shapes and/or functions in a controlled and programmed manner in response to applied energy inputs. Printing technologies, mathematical modeling, responsive materials, stimuli, and structural design constitute the blueprint of 4D printing, all of which have seen rapid advancement in the past decade. These advancements have opened up numerous possibilities for dynamic and adaptive structures, finding potential use in healthcare, textiles, construction, aerospace, robotics, photonics, and electronics. However, current 4D printing primarily focuses on proof-of-concept demonstrations. Further development is necessary to expand the range of accessible materials and address fabrication complexities for widespread adoption. In this paper, we aim to deliver a comprehensive review of the state-of-the-art in 4D printing, probing into shape programming, exploring key aspects of resulting constructs including printing technologies, materials, structural design, morphing mechanisms, and stimuli-responsiveness, and elaborating on prominent applications across various fields. Finally, we discuss perspectives on limitations, challenges, and future developments in the realm of 4D printing. While the potential of this technology is undoubtedly vast, continued research and innovation are essential to unlocking its full capabilities and maximizing its real-world impact.

Diverse reactivity of maleimides in polymer science and beyond

Maleimides are remarkably versatile functional groups, capable of participating in homo- and copolymerizations, Diels-Alder and (photo)cycloadditions, Michael additions, and other reactions. Their reactivity has afforded materials ranging from polyimides with high upper service temperatures to hydrogels for regenerative medicine applications. Moreover, maleimides have proven to be an enabling chemistry for pharmaceutical development and bioconjugation via straightforward modification of cysteine residues. To exert spatiotemporal control over reactions with maleimides, multiple approaches have been developed to photocage nucleophiles, dienes, and dipoles. Additionally, further substitution of the maleimide alkene (e.g., mono- and di-halo-, thio-, amino-, and methyl-maleimides, among other substituents) confers tunable reactivity and dynamicity, as well as responsive mechanical and optical properties. In this mini-review, we highlight the diverse functionality of maleimides, underscoring their notable impact in polymer science. This moiety and related heterocycles will play an important role in future innovations in chemistry, biomedical, and materials research.

Cellular mechanical memory: a potential tool for mesenchymal stem cell-based therapy

Recent studies have shown that mechanical properties such as extracellular matrix stiffness, fluid flow, weight loading, compression, and stretching can affect cellular functions. Some examples of cell responses to mechanical properties could be the migration of cancer cells from rigid to soft surfaces or the differentiation of fibroblasts into myofibroblasts. Cellular responses to mechanical changes can modify the insertion of proteins in the extracellular matrix (ECM), causing an increase in tissue stiffness with functional consequences. In general, mechanical and physical factors can affect any kind of cell phenotype in culture conditions and in vivo tissues. Cells sense mechanical stimuli by applying force and restructuring their shape and functions in response to the resistance of the stimuli. Furthermore, mechanical triggers can develop a "memory" for altering cellular plasticity and adaptation. This phenomenon is called cellular mechanical memory (CMM), a singular feature of mesenchymal stem cells (MSCs). Controlled targeting of CMM may resolve the scarcity of viable cells needed for cell based therapy (CBT) and implement studies concerning cancer research, fibrosis, and senescence. This review focusses on cells from the mesodermal lineage, such as MSCs, fibroblasts and chondrocytes, and the role of CMM as a potential target for CBT.

Hydrogel-Based Continuum Soft Robots

This paper comprehensively reviews the latest advances in hydrogel-based continuum soft robots. Hydrogels exhibit exceptional flexibility and adaptability compared to traditional robots reliant on rigid structures, making them ideal as biomimetic robotic skins and platforms for constructing highly accurate, real-time responsive sensory interfaces. The article systematically summarizes recent research developments across several key dimensions, including application domains, fabrication methods, actuator technologies, and sensing mechanisms. From an application perspective, developments span healthcare, manufacturing, and agriculture. Regarding fabrication techniques, the paper extensively explores crosslinking methods, additive manufacturing, microfluidics, and other related processes. Additionally, the article categorizes and thoroughly discusses various hydrogel-based actuators responsive to solute/solvent variations, pH, chemical reactions, temperature, light, magnetic fields, electric fields, hydraulic/electro-osmotic stimuli, and humidity. It also details the strategies for designing and implementing diverse sensors, including strain, pressure, humidity, conductive, magnetic, thermal, gas, optical, and multimodal sensors. Finally, the paper offers an in-depth discussion of the prospective applications of hydrogel-based continuum soft robots, particularly emphasizing their potential in medical and industrial fields. Concluding remarks include a forward-looking outlook highlighting future challenges and promising research directions.

3D printed scaffolds with multistage osteogenic activity for bone defect repair

The bone defect repair is a complex process including immune regulation, stem cell osteogenic differentiation and extracellular matrix mineralization. Current bone tissue engineering approaches often fail to adapt throughout the above osteogenic process, resulting in suboptimal repair outcomes. To address this problem, a 3D-printed scaffold with multistage osteogenic activity based on shape-memory elastomer and electroactive material is developed. The scaffold exhibits excellent shape memory performance and can trigger shape recovery by physiological temperature. The physiological temperature-triggered shape-memory behavior makes the scaffold promising for minimally invasive implantation. After electric field polarization, the scaffold's surface carries the negative charge, which can activate the PI3K/Akt signaling pathway to promote the polarization of macrophages to M2 phenotype and activate the FAK/ERK signaling pathway to promote osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), indicating that the scaffold can effectively participate in immune microenvironment regulation and stem cell osteogenic differentiation. Additionally, the negative charge on the scaffold's surface can attract calcium and phosphate ions, forming a mineralized matrix and promoting late-stage extracellular matrix mineralization by continuously supplying mineralizing ions such as calcium and phosphate. Overall, this study introduces a 3D-printed scaffold with multistage osteogenic activity, offering a promising strategy for bone defect repair.

Fast Reverse Design of 4D-Printed Voxelized Composite Structures Using Deep Learning and Evolutionary Algorithm

Designing voxelized composite structures via 4D printing involves creating voxel units with distinct material properties that transform in response to stimuli; however, optimally distributing these properties to achieve specific target shapes remains a significant challenge. This study introduces an optimization method combining deep learning (DL) and an evolutionary algorithm, focusing on a solvent-responsive hydrogel as the target material. A sequence-enhanced parallel convolutional neural network is developed and generated a dataset through finite element simulations. This DL model enables high-precision prediction of hydrogel deformation. Furthermore, a progressive evolutionary algorithm (PEA) is proposed by integrating the DL model to construct a DL-PEA framework. This framework supports rapid reverse engineering of the desired shape, and the average design time for specified target shapes is reduced to ≈3.04 s. The present findings illustrate how 4D printing of optimized hydrogel designs can effectively transform in response to environmental stimuli. This work provides a new perspective on the application of hydrogels in 4D printing and presents an efficient tool for optimizing 4D-printed voxelized composite structures.

From Stents to Smart Implants Employing Biomimetic Materials: The Impact of 4D Printing on Modern Healthcare

The sector of 4D printing represents a new frontier in additive manufacturing that allows for a material's capability to adapt and respond to various stimuli, such as thermal transitions, humidity, and pH levels. The adaptability of such a material has great potential in healthcare applications, especially in designing personalized and responsive medical devices. This article looks into the revolutionary potential of healthcare applications of 4D printing, referencing applications in self-repairable implants, smart stents, personalized drug delivery systems, and response-based prosthetic devices. The advances in 3D printing have created a platform for such innovations to take place, while the material properties unique to 4D printing allow new methods of tackling existing health issues. However, the large-scale application of 4D printing in medicine is currently hampered by material limitations, regulation challenges, and financial challenges. In spite of these challenges, ongoing advances in technologies, combined with artificial intelligence and machine learning, provide the potential to surpass such challenges, hence improving the precision, efficacy, and personalization of medical devices. This work outlines existing applications, looks at potential areas of application in the future, and analyzes potential applications of 4D printing contributing to healthcare, recognizing challenges that need to be overcome in order to unlock its full potential.

Progress of AI assisted synthesis of polysaccharides-based hydrogel and their applications in biomedical field

Polymeric hydrogels, characterized by their highly hydrophilic three-dimensional network structures, boast exceptional physical and chemical properties alongside high biocompatibility and biodegradability. These attributes make them indispensable in various biomedical applications such as drug delivery, tissue engineering, wound dressings and sensor technologies. With the integration of artificial intelligence (AI), hydrogels are undergoing significant transformations in design, leveraging human-machine interaction, machine learning, neural networks, and 3D/4D printing technology. This article provides a concise yet comprehensive overview of polysaccharide-based hydrogels, exploring their intrinsic properties, functionalities, preparation techniques, and classifications, alongside their progress in biomedical research. Special emphasis is placed on AI-enhanced hydrogels, underscoring their transformative potential in redefining hydrogel performance and functionality. By integrating AI technologies, these intelligent hydrogels open unprecedented opportunities in precision medicine, adaptive biomaterials, and smart healthcare systems, highlighting promising directions for future research.

Cotton cellulose nanofiber/chitosan scaffolds for skin tissue engineering and wound healing applications

Chitosan (CS) is a promising polymeric biomaterial for use in scaffolds forin vitroskin models and wound dressings, owing to its non-antigenic and antimicrobial properties. However, CS often exhibits insufficient physicochemical properties, mechanical strength, and bioactivity, limiting its efficacy in demanding applications. To address these challenges, cotton cellulose nanofibers (CNFs) represent a promising nanomaterial for enhancing CS-based scaffolds in tissue engineering. CNF offers superior stiffness, and mechanical properties that enhance cellular adhesion and proliferation, both crucial for effective tissue regeneration and healing. This study aimed to develop and characterize a scaffold combining cotton CNF and CS, focusing on its cytocompatibility with human fibroblasts and keratinocytes. The cotton CNF/CS scaffold was fabricated using the casting technique, and its physicochemical properties and cellular compatibility were assessedin vitro. The results demonstrated that incorporating cotton CNF significantly enhanced the stability of the CS matrix. The CS scaffold with 1000 μg ml-1of cotton CNF exhibited increased roughness and reduced rupture strain compared to the pure CS scaffold. The cotton CNF/CS scaffold effectively promoted the adhesion, viability, proliferation, migration, and collagen synthesis of skin cells. Notably, increased cell viability was observed in human fibroblasts cultured on scaffolds with higher concentrations of cotton CNF (100 and 1000 μg ml-1). Based on the findings, the cotton CNF/CS scaffold demonstrates enhanced physicochemical properties and bioactivity, making it a promising candidate for the development ofin vitrohuman skin models and wound healing dressings.

Reconstructed three-dimensional structure of gas-foamed polycaprolactone/cellulose nanofibrous scaffold for biomedical applications

One of the unavoidable issues with the bio-scaffolding process is the collapse of the visually appealing external three-dimensional (3D) sponge-like structure and the internal porous and multilayered morphology of a gas-foamed nanofibrous scaffold. Herein, a gas-foamed polycaprolactone/cellulose (g-PCL/CL) nanofibers scaffold is first prepared by electrospinning PCL/cellulose acetate, followed by deacetylation and then Sodium borohydride-assisted gas-foaming technique. The deformed 3D architecture of g-PCL/CL nanofiber is finally reconstructed by mixing it with chitosan (CS) solution and molding. This straightforward method leverages the mechanical strength of PCL, the hydrophilic properties of CL, and the curing characteristics of chitosan. The physical characterization validated the successful reformation of the 3D architecture of the CS + PCL/CL scaffold demonstrating the unique porous interior structure assembled with nanofiber-reinforced pore walls. This molding process with chitosan solution enables the formation of mechanically enhanced 3D scaffolds with improved structural integrity, as evidenced by the increased compressive strength of the CS + PCL/CL scaffold (~95 kPa). In vitro studies further demonstrate improved cell adhesion, differentiation, and proliferation for the CS + PCL/CL scaffold. These findings suggest that the structurally reconstructed CS + PCL/CL composite scaffold possesses suitable characteristics to act as a potential bioscaffold, paving the way for promising strategies to retain the structural integrity of collapse scaffolds.

Exploring the Adaptability of 4D Printed Shape Memory Polymer Featuring Dynamic Covalent Bonds

4D printing (4DP) of high-performance shape memory polymers (SMPs), particularly using digital light processing (DLP), has garnered intense global attention due to its capability for rapid and high-precision fabrication of complex configurations, meeting diverse application requirements. However, the development of high-performance dynamic shape memory polymers (DSMPs) for DLP printing remains a significant challenge due to the inherent incompatibilities between the photopolymerization process and the curing/polymerization of high-strength polymers. Here, a mechanically robust DSMP compatible is developed with DLP printing, which incorporates dynamic covalent bonds of imine linking polyimide rigid segments, exhibiting remarkable mechanical performance (tensile strength ≈41.7 MPa, modulus ≈1.63 GPa) and thermal stability (Tg ∼ 113 °C, Td ∼ 208 °C). More importantly, benefiting from the solid-state plasticity conferred by dynamic covalent bonds, 4D printed structures demonstrate rapid network adaptiveness, enabling effortless realization of reconfiguration, self-healing, and recycling. Meanwhile, the extensive π-π conjugated structures bestow DSMP with an intrinsic photothermal effect, allowing controllable morphing of the 4D configuration through dual-mode triggering. This work not only greatly enriches the application scope of high-performance personalized configurations but also provides a reliable approach to addressing environmental pollution and energy crises.

Stretchable and Shape-Transformable Organohydrogel with Gallium Mesh Frame

Shape-memory materials are widely utilized in biomedical devices and tissue engineering, particularly for their ability to undergo predefined shape changes in response to external stimuli. In this study, a shape-transformable organohydrogel was developed by incorporating a gallium mesh into a polyacrylamide/alginate/glycerol matrix. The gallium mesh, which transitions between solid and liquid states at moderate temperatures (~29.8 °C), enhanced the hydrogel's mechanical properties and enabled shape-memory functionality. The composite organohydrogel exhibited a high elastic modulus of ~900 kPa in the solid gallium state and ~30 kPa in the liquid gallium state, enabling reversible deformation and structural stability. Glycerol improved the hydrogel's moisture retention, maintaining stretchability and repeated heating and cooling cycles. After multiple cycles of the shape-changing process, the organohydrogel retained its mechanical integrity, achieving shape-fixation and recovery ratios of ~96% and 95%, respectively. This combination of shape-memory functionality, stretchability, and mechanical stability makes this organohydrogel highly suitable for applications in flexible electronics, soft robotics, and biomedical devices, where adaptability and shape retention are essential.

Engineered Shape-Morphing Transitions in Hydrogels Through Suspension Bath Printing of Temperature-Responsive Granular Hydrogel Inks

4D printing of hydrogels is an emerging technology used to fabricate shape-morphing soft materials that are responsive to external stimuli for use in soft robotics and biomedical applications. Soft materials are technically challenging to process with current 4D printing methods, which limits the design and actuation potential of printed structures. Here, a simple multi-material 4D printing technique is developed that combines dynamic temperature-responsive granular hydrogel inks based on hyaluronic acid, whose actuation is modulated via poly(N-isopropylacrylamide) crosslinker design, with granular suspension bath printing that provides structural support during and after the printing process. Granular hydrogels are easily extruded upon jamming due to their shear-thinning properties and their porous structure enables rapid actuation kinetics (i.e., seconds). Granular suspension baths support responsive ink deposition into complex patterns due to shear-yielding to fabricate multi-material objects that can be post-crosslinked to obtain anisotropic shape transformations. Dynamic actuation is explored by varying printing patterns and bath shapes, achieving complex shape transformations such as 'S'-shaped and hemisphere structures. Furthermore, stepwise actuation is programmed into multi-material structures by using microgels with varied transition temperatures. Overall, this approach offers a simple method to fabricate programmable soft actuators with rapid kinetics and precise control over shape morphing.

Ultra-Tough, yet Rigid and Healable Supramolecular Polymers with Variable Stiffness for Multimodal Actuators

Variable stiffness materials have shown considerable application in soft robotics. However, previously reported materials often struggle to reconcile high stiffness, stretchability, toughness, and self-healing ability, because of the inherently conflicting requisite of these properties in molecular design. Herein, we propose a novel strategy that involves incorporating acid-base ionic pairs capable of from strong crosslinking sites into a dense and robust hydrogen-bonding network to construct rigid self-healing polymers with tunable stiffness and excellent toughness. To demonstrate these distinct features, the polymer was employed to serve as the strain-regulation layers within a fiber-reinforced pneumatic actuator (FPA). The exceptional synergy between the configuration versatility of FPA and the dynamic molecular behavior of the supramolecular polymers equips the actuator with simultaneous improvement in motion dexterity, multimodality, loading capacity, robustness, and durability. Additionally, the concept of integrating high dexterity at both macro- and micro-scale is prospective to inspire the design of intelligent yet robust devices across various domains.

Integrative Modeling and Experimental Insights into 3D and 4D Printing Technologies

This review focuses on advancements in polymer science as it relates to three-dimensional (3D) and four-dimensional (4D) printing technologies, with a specific emphasis on applications in the biomedical field. While acknowledging the breadth of 3D and 4D printing applications, this paper concentrates on the use of polymers in creating biomedical devices and the challenges associated with their implementation. It explores integrative modeling and experimental insights driving innovations in these fields, focusing on sustainable manufacturing with biodegradable polymers, a comparative analysis of 3D and 4D printing techniques, and applications in biomedical devices. Additionally, the review examines the materials used in both 3D and 4D printing, offering a detailed comparison of their properties and applications. By highlighting the transformative potential of these technologies in various industrial and medical applications, the paper underscores the importance of continued research and development. The scope of this review also includes an overview of future research directions to address current challenges, enhance material capabilities, and explore practical applications.

3D Printing of Naturally Derived Adhesive Hemostatic Sponge

Hydrogel hemostatic sponges have been recognized for its effectiveness in wound treatment due to its excellent biocompatibility, degradability, as well as multi-facet functionalities. Current research focuses on optimizing the composition and structure of the sponge to enhance its therapeutic effectiveness. Here, we propose an adhesive hydrogel made from purely natural substances extracted from okra and Panax notoginseng. We utilize 3-dimensional (3D) printing technology to fabricate the hemostatic hydrogel scaffold, incorporating gelatin into the hydrogel and refining the mixing ratio. The interaction between gelatin and okra polyphenols contributes to successful injectability as well as stability of the printed scaffold. The okra in the scaffold exhibits favorable adhesion and hemostatic effects, and the total saponins of Panax notoginseng facilitate angiogenesis. Through in vitro experiments, we have substantiated the scaffold's excellent stability, adhesion, biocompatibility, and angiogenesis-promoting ability. Furthermore, in vivo experiments have demonstrated its dual functionality in rapid hemostasis and wound repair. These features suggest that the 3D-printed, natural substance-derived hydrogel scaffolds have valuable potential in wound healing and related applications.

Hydrogel for light delivery in biomedical applications

Traditional optical waveguides or mediums are often silica-based materials, but their applications in biomedicine and healthcare are limited due to the poor biocompatibility and unsuitable mechanical properties. In term of the applications in human body, a biocompatible hydrogel system with excellent optical transparency and mechanical flexibility could be beneficial. In this review, we explore the different designs of hydrogel-based optical waveguides derived from natural and synthetic sources. We highlighted key developments such as light emitting contact lenses, implantable optical fibres, biosensing systems, luminating and fluorescent materials. Finally, we expand further on the challenges and perspectives for hydrogel waveguides to achieve clinical applications.

Ligand Dissociation of Metal-Complex Photocatalysts toward pH-Photomanipulation in Dynamic Covalent Hydrogels for Printing Reprocessable and Recyclable Devices

Dynamic covalent hydrogels are gaining attention for their potential in smart materials, soft devices, electronics, and more thanks to their impressive mechanical properties, biomimetic structures, and dynamic behavior. However, a significant challenge lies in designing precise and efficient dynamic photochemistry for their preparation, allowing for complex structures and control over the dynamic process. Herein, we propose a general and straightforward orthogonal dynamic covalent photochemistry strategy for preparing high-performance printable dynamic covalent hydrogels, thereby broadening their advanced applications. This photochemical strategy uses a bifunctional photocatalyst to initiate radical polymerization and release ligands through a rapid light-mediated dissociation mechanism. This process leads to a controlled increase in system pH from mildly acidic to alkaline conditions within one hundred seconds, which in turn triggers the pH-sensitive model reactions of boronic acid/diol complexation and Knoevenagel condensation. The orthogonal photochemistry enables the formation of interpenetrated and conjoined networks, significantly enhancing the mechanical properties of the hydrogels. The reversible bonds formed during the process, i.e., boronic ester and unsaturated ketone bonds, confer excellent self-healing, reprocessable, and recyclable properties on the hydrogels through photochemical pH variations. Furthermore, this rapid, controlled fabrication process and dynamic behavior are highly compatible with printing techniques, enabling the design of adaptive and recyclable sensors with different structures. These advancements are promising for various material science, medicine, and engineering applications.

Shape Memory Hydrogels for Biomedical Applications

The ability of shape memory polymers to change shape upon external stimulation makes them exceedingly useful in various areas, from biomedical engineering to soft robotics. Especially, shape memory hydrogels (SMHs) are well-suited for biomedical applications due to their inherent biocompatibility, excellent shape morphing performance, tunable physiochemical properties, and responsiveness to a wide range of stimuli (e.g., thermal, chemical, electrical, light). This review provides an overview of the unique features of smart SMHs from their fundamental working mechanisms to types of SMHs classified on the basis of applied stimuli and highlights notable clinical applications. Moreover, the potential of SMHs for surgical, biomedical, and tissue engineering applications is discussed. Finally, this review summarizes the current challenges in synthesizing and fabricating reconfigurable hydrogel-based interfaces and outlines future directions for their potential in personalized medicine and clinical applications.