Cartilage-like protein hydrogels engineered via entanglement

Hierarchical protein nano-crystalline hydrogel with extracellular vesicles for ectopic lymphoid structure formation

Among cancer therapies, immune checkpoint blockade (ICB) has emerged as a prominent approach, substantially enhancing anti-tumor immune responses. However, the efficacy of ICB is often limited in the absence of a pre-existing immune response within the tumor microenvironment. Here, we introduce a novel hierarchical protein hydrogel platform designed to facilitate the formation of artificial tertiary lymphoid structures (aTLS), thereby improving ICB efficacy. Through the integration of self-assembling ferritin protein nanocages, rec1-resilin protein, and CP05 peptide, our hierarchical hydrogels provide a structurally supportive and functionally adaptive scaffold capable of on-demand self-repair in response to mild thermal treatments. The effective encapsulation of extracellular vesicles (EVs) via the CP05 peptide ensures the formation of aTLS with germinal center-like structures within the hierarchical hydrogel. We demonstrate that, combined with ICB therapy, EV-loaded hierarchical hydrogels also induce the TLS within the tumor, markedly promoting immune responses against ICB-resistant tumor. This bioactive hydrogel platform offers a versatile tool for enhancing a broad range of immunotherapies, with potential applications extending beyond TLS to other frameworks that support complex tissue architectures.

Mechanically robust non-swelling cold water fish gelatin hydrogels for 3D bioprinting

Three-dimensional (3D) bioprinting of hydrogels allows embedded cells to be patterned and hosted in an extracellular matrix (ECM)-mimicking environment. This method shows great promise for the engineering of complex tissues on account of the facile spatial control over materials and cells within the printed constructs. Hydrogels, which represent extensively explored and employed biomaterials for 3D bioprinting, are characterized by both their high water content and swelling behavior. Post-printing swelling inevitably alters the geometrical and mechanical properties of printed features, thus causing a deviation from the original design and affecting both cellular function and tissue structure. Despite substantial effort being dedicated to the development of non-swelling hydrogels, their application in 3D encapsulation and bioprinting of living cells is yet to be realized, owing to limitations imposed by their often tedious material syntheses and complex network structures. Herein, we describe a new type of non-swelling hydrogel based fully on cold water fish gelatin (cfGel-Hydrogel) consisting of only a single network formed via thiol-ene "click" chemistry. We show that such cfGel-Hydrogels enable 3D patterning of living cells in a shape-retaining and mechanically robust matrix. These cfGel-Hydrogels show negligible swelling (<2 %) under physiologically relevant conditions (simulated by 37 °C PBS buffer), while also being able to withstand large cyclic deformations (80 % compressive strain) by dissipating around 40 % of the imposed loading energy. Human dermal fibroblast (HDF)-laden cfGel-Hydrogels could be fabricated via extrusion-based 3D printing, allowing for the in vitro culturing of cells in shape-retaining constructs, thus offering new opportunities for hydrogel-based applications in tissue engineering and regenerative medicine.

Unveiling the structure of protein-based hydrogels by overcoming cryo-SEM sample preparation challenges

Protein-based hydrogels have gained significant attention for their potential use in applications such as drug delivery and tissue engineering. Their internal structure is complex, spans across multiple length scales and affects their functionality, yet is not well understood because of folded proteins' sensitivity to physical and chemical perturbations and the high water content of hydrogels. Cryo-scanning electron microscopy (cryo-SEM) has the potential to reveal such hierarchical structure when hydrated hydrogels are prepared with appropriate cryofixation. We show for photochemically cross-linked, folded globular bovine serum albumin (BSA) protein hydrogels that preparation artefacts are reduced by in situ gelation, high pressure freezing (HPF), plasma focused ion beam (pFIB) milling, sublimation, and low dose secondary electron imaging. Cryo-SEM of folded BSA protein hydrogels prepared in this way reveals a heterogeneous network with nanoscale porosity (∼60 nm pores) surrounded by high secondary electron emission regions (∼30 nm diameter) interconnected by narrower, lower emission regions (∼20 nm length). This heterogeneous network structure is consistent with small angle scattering studies of folded protein hydrogels, with fractal-like clusters connected by intercluster regions. We further test the potential of cryo-SEM to detect the impact of protein unfolding on hydrogel network formation and reveal nanoscale differences in cluster sizes consistent with those derived from scattering data. Importantly, cryo-SEM directly images pores for sizing in both systems, with initial results on BSA suggesting protein unfolding induces an increase of ∼10 nm in pore sizes. Our findings on cryo-SEM sample preparation challenges and solutions provide new opportunities to link hydrogel structure to function.

Inorganic Hydrogels can be Flexible and Highly Extensible

Inorganic hydrogels have great potential in many applications as sustainable materials, but lack flexibility due to rigid network structures. Here, a novel strategy is proposed-an inorganic polymer hydrogel, prepared by crosslinking long-chain polyphosphate (LPP) with M2+ ions (Ca2+, Mn2+, Mg2+, Ni2+), which effectively address the rigidity and fragility issues commonly associated with traditional inorganic gels. With the most stable hydration shell among those ions, Ni2+ tends to interact indirectly with LPP through hydrogen bonds rather than coordination bonds. The unique Ni2+-phosphate interaction endows the Ni-LPP hydrogels with ultrahigh elongation at break (≈15 000×). Further experiments reveal that the Ni2+-phosphate motif can be applied to other hydrogels as an extension enhancement factor. The highly extensible, good conductive (1.06 ± 0.08 S m-1), self-healing (within 30 s and without stimulation), arbitrarily shapeable, and nonflammable Ni-LPP inorganic hydrogel indicates a bright future in flexible electronics, environmental remediation, and beyond.

Hierarchical Engineering of Amphiphilic Peptides Nanofibrous Crosslinkers toward Mechanically Robust, Functionally Customable, and Sustainable Supramolecular Hydrogels

Hierarchical architectures spanning multiple length scales are ubiquitous in biological tissues, conferring them with both mechanical robustness and dynamic functionalities via structural reorganization under loads. The design of hierarchical architectures within synthetic hydrogels to concurrently achieve mechanical reinforcement and functional integration remains challenging. Here, a biomimetic hierarchical engineering approach is reported to develop mechanically robust and function-customizable supramolecular hydrogels by utilizing strong yet dynamic fibrous nanoarchitectures of amphiphilic peptides as crosslinkers. This design, on one hand, resolves the strength-toughness trade-off in hydrogel design through energy-dissipative mechanisms involving dynamic detachment and reinsertion of peptides within their assembled nanostructures upon loading. On the other hand, the amphiphilicity and sequence programmability of peptides allow spatially orthogonal integration of multiple dynamic functionalities across distinct structural domains, including lipophilic fluorophore encapsulation, photopatterning capability, and anisotropic contraction. Capitalizing on its ultralow hysteresis and rapid recovery properties, the hydrogel's effectiveness is demonstrated as high-sensitivity strain sensors. Moreover, the fully noncovalent crosslinking strategy permits closed-loop recycling and reprocessing via reversible crosslinker disassembly-reassembly processes. Through systematic extension of this principle across diverse peptide systems, a generalized platform is demonstrated for creating advanced soft materials that synergistically integrate traditionally incompatible attributes of mechanical robustness, customable dynamic functionality, and environmental sustainability.

A skin-mimicking multifunctional hydrogel via hierarchical, reversible noncovalent interactions

Artificial skin is essential for bionic robotics, facilitating human skin-like functions such as sensation, communication, and protection. However, replicating a skin-matched all-in-one material with excellent mechanical properties, self-healing, adhesion, and multimodal sensing remains a challenge. Herein, we developed a multifunctional hydrogel by establishing a consolidated organic/metal bismuth ion architecture (COMBIA). Benefiting from hierarchical reversible noncovalent interactions, the COMBIA hydrogel exhibits an optimal combination of mechanical and functional properties, particularly its integrated mechanical properties, including unprecedented stretchability, fracture toughness, and resilience. Furthermore, these hydrogels demonstrate superior conductivity, optical transparency, freezing tolerance, adhesion capability, and spontaneous mechanical and electrical self-healing. These unified functions render our hydrogel exceptional properties such as shape adaptability, skin-like perception, and energy harvesting capabilities. To demonstrate its potential applications, an artificial skin using our COMBIA hydrogel was configured for stimulus signal recording, which, as a promising soft electronics platform, could be used for next-generation human-machine interfaces.

A novel empirical and rheometric assessment of viscoelastic hydrogel implant cohesiveness

Therapeutic implantable hydrogels are increasingly utilized in medicine due to their versatile viscoelastic properties. Nonetheless, the clinical efficacy and longevity of these products is predicated on their ability to retain structural integrity post-implantation. Gel cohesion, defined as the capacity to resist fragmentation, has lacked empirical standardization, especially in high shear environments, with present methods often conflating this mechanical parameter with gel ductility or qualitative perceptions of tackiness. In this study, we introduce a novel quantitative method of cohesion analysis termed the Modulus of Cohesion (MOC). The MOC is derived from rheometric strain sweep testing by calculating the difference between the elastic and viscous moduli from 0% strain to the crossover point. This novel parameter provides a direct measure of mechanical energy storage and dissipation balance, accounting for linear and nonlinear deformation in shear strain. Eleven commercially available hyaluronic acid gels are evaluated using this method, alongside uniaxial tension and drop weight methods to establish correlations between MOC and existing cohesion metrics. Additionally, haptic sensory analysis and aqueous dispersion methods from previous reports are correlated with rheometric and mechanical tests. Our results demonstrate that MOC provides a reliable, reproducible measure of gel cohesiveness, correlating strongly with other quantitative methods with augmented precision.

Bioinspired nondissipative mechanical energy storage and release in hydrogels via hierarchical sequentially swollen stretched chains

Nature suggests concepts for materials with efficient mechanical energy storage and release, i.e., resilience, involving small energy dissipation upon mechanical loading and unloading, such as in resilin and elastin. These materials facilitate burst-like movements involving high stiffness and low strain and high reversibility. Synthetic hydrogels that allow highly reversible mechanical energy storage have remained a challenge, despite mimicking biological soft tissues. Here we show a synthetic concept using fixed hydrogel polymer compositions based on sequentially swollen and sequentially photopolymerized gelation steps for hierarchical networks. The sequential swellings facilitate the balance of properties between resilience and dissipation upon controlling of the chain extension. At low hierarchical levels, we show resilience with small hysteresis with increased stiffness and resilient energy storage, whereas at high hierarchical levels, a transition is shown to a dissipative and considerably reinforced state. The generality of this approach is shown using several photopolymerizable monomers.

Bioinspired Tough and Antiswelling Hydrogel via in Situ Self-Assembly of Amphiphilic Copolymers within a Hydrophilic Network

Inspired by tropoelastin coacervation, a process in elastic fiber formation driven by hydrophobic interactions, we developed a tough, antiswelling hydrogel, PHEA-(PVA-co-PE), by incorporating amphiphilic poly(vinyl alcohol-co-ethylene) (PVA-co-PE) into a hydrophilic poly(2-hydroxyethyl acrylate) (PHEA) network. The PHEA-(PVA-co-PE) hydrogel was prepared by UV-induced polymerization of a PHEA precursor dimethyl sulfoxide (DMSO) solution containing PVA-co-PE, followed by immersion in water. During solvent exchange, PVA-co-PE self-assembled into micellar structures within the PHEA matrix, mimicking the coacervation of tropoelastin. Compared with PHEA and PVA-co-PE hydrogels, the strength of PHEA-(PVA-co-PE) increased by 83 and 7 times, while the toughness increased by 145 and 97 times. This strategy can be further extended to a variety of amphiphilic copolymers, demonstrating the universality. In vitro and in vivo tests demonstrated that the hydrogel possesses excellent biocompatibility and antiswelling capability. This study provides a simple method for developing a tough, biocompatible, and antiswelling hydrogel.

Preparation, characterization, multidimensional applications and prospects of protein bio-based hydrogels: A review

Protein bio-based hydrogels have emerged as a versatile and functional class of biomaterials due to their unique properties, including biocompatibility, biodegradability, tunable mechanical strength, and environmental responsiveness (pH, enzymes, ions and light). This review comprehensively explores the preparation methods, physicochemical properties, and multidimensional applications of protein-based hydrogels. Various fabrication techniques, such as chemical crosslinking, physical gelation, and enzymatic reactions, are discussed, highlighting their impact on the structure and functionality of hydrogels. The intrinsic properties of protein hydrogels are summarized in detail, including mechanical properties, swelling resistance, frost resistance, adhesion, biocompatibility and degradability. Furthermore, this review delves into their diverse applications, which span tissue engineering, drug delivery, wound healing, food preservation, biosensing, and environmental remediation. Finally, the challenges and future prospects of protein-based hydrogels are addressed, emphasizing the necessity for scalable production, enhanced stability, and multifunctional integration to meet the growing demands of advanced biomedical and industrial applications. This review aims to provide a comprehensive understanding of protein-based hydrogels and to inspire innovative research in this rapidly evolving field.

Co-initiating-system dual-mechanism drives the design of printable entangled polymer multinetworks

Entanglement significantly enhances the mechanical performance and functionality of both natural and synthetic materials. However, developing straightforward, versatile strategies for creating high-performance entangled polymer materials remains a challenge. Here, a co-initiating-system dual-mechanism strategy is designed for fabricating printable entangled polymer multinetworks. This thermal-light dual-initiation process benefits the synthesis of high-molecular-weight polymers and promotes the rapid formation of multinetworks within hydrogels. The resulting long polymer chains enable hydrogels with higher mechanical performance, lower stress relaxation, and activation energy compared to short polymer chain-contained samples. Such a method proves more effective than traditional self-thickening and strengthening techniques for enhancing hydrogel entanglements and is also compatible with additive manufacturing, enabling the design of complex 2D webs with adaptive mechanical performance and capable of detecting and sensing applications. This work provides an effective strategy for designing high-performance entangled polymer materials, which are set to impact numerous fields, from advanced sensing to material science and beyond.

Cartilage-Adaptive Hydrogels via the Synergy Strategy of Protein Templating and Mechanical Training

Cartilage, as a load-bearing tissue with high-water content, exhibits excellent elasticity and high strength. However, it is still a grand challenge to develop cartilage-adaptive biomaterials for replacement or regeneration of damaged cartilage tissue. Herein, protein templating and mechanical training is integrated to fabricate crystal-mediated oriented chitosan nanofibrillar hydrogels (O-CN gels) with similar mechanical properties and water content of cartilage. The O-CN gels with an ≈74 wt% water content exhibit high tensile strength (≈15.4 MPa) and Young's modulus (≈24.1 MPa), as well as excellent biocompatibility, antiswelling properties, and antibacterial capabilities. When implanted in the box defect of rat's tails, the O-CN gels seal the cartilage (annulus fibrosus) defect, maintain the intervertebral disc height and finally prevent the nucleus herniation. This synergy strategy of protein templating and mechanical training opens up a new possibility to design highly mechanical hydrogels, especially for the replacement and regeneration of load-bearing tissues.

Synergistically Toughening Non-Neutral Polyampholyte Hydrogels by Ionic and Coordination Bonds at Low Metal-Ion Contents

Polyampholyte (PA) hydrogels, composed of charged hydrophilic networks with both positive and negative groups, have attracted great attention due to the unique structure and excellent antifouling properties. Yet, the superhydrophilicity usually makes non-neutral PA (n-PA) gels highly swollen and mechanically very weak in aqueous environments, severely limiting their applications. Herein metal-coordination bonds are designed to introduce to synergistically toughen n-PA hydrogels with ionic bonds via a secondary equilibrium strategy. In the design, as-prepared n-PA gels are dialyzed in metal-ion solutions and deionized water in sequence to achieve the tough gels. Through this strategy, the weak n-PA gels can be significantly toughened by the synergy of ionic and metal-coordination bonds. A systematic study indicates that both the molar ratio of oppositely charged monomers and the metal-ion concentration affect the mechanical enhancements clearly. The universality of the proposed strategy is further proved by selecting different gel systems and multivalent metal ions. Notably, low metal-ion concentrations (≤0.1 m) of dialysis solutions can enable synergistic toughening. Theoretical models are also adopted to disclose the toughening mechanism. This work not only expands the understanding on the fabrication of strong and tough PA hydrogels but also provides some insights for PA gels in electrolyte solutions.

A versatile platform based on matrix metalloproteinase-sensitive peptides for novel diagnostic and therapeutic strategies in arthritis

Matrix metalloproteinases (MMPs), coupled with other proteinases and glycanases, can degrade proteoglycans, collagens, and other extracellular matrix (ECM) components in inflammatory and non-inflammatory arthritis, making them important pathogenic molecules and ideal disease indicators and pharmaceutical intervention triggers. For MMP responsiveness, MMP-sensitive peptides (MSPs) are among the most easily synthesized and cost-effective substrates, with free terminal amine and/or carboxyl groups extensively employed in multiple designs. We hereby provide a comprehensive review over the mechanisms and advances in MSP applications for the management of arthritis. These applications include early and precise diagnosis of MMP activity via fluorescence probe technologies; acting as nanodrug carriers to enable on-demand drug release triggered by pathological microenvironments; and facilitating cartilage engineering through MMP-mediated degradation, which promotes cell migration, matrix synthesis, and tissue integration. Specifically, the ultra-sensitive MSP diagnostic probes could significantly advance the early diagnosis and detection of osteoarthritis (OA), while MSP-based drug carriers for rheumatoid arthritis (RA) can intelligently release anti-inflammatory drugs effectively during flare-ups, or even before symptoms manifest. The continuous progress in MSP development may acceleratedly lead to novel management regimens for arthropathy in the future.

Stable-Dynamic Hydrogels Mimicking the Pericellular Matrix for Articular Cartilage Repair

Cartilage regeneration requires a specialized biomechanical environment. Macroscopically, cartilage repair requires a protracted, stable mechanical environment, whereas microscopically, it involves dynamic interactions between cells and the extracellular matrix. Therefore, this study aims to design a hydrogel that meets the complex biomechanical requirements for cartilage repair. Dynamic hybrid hydrogels with temporal stability at the macroscale and dynamic properties at the microscale are successfully synthesized. The dynamic hybrid hydrogel simulates the stress relaxation and viscoelasticity of the pericellular matrix, facilitating effective interactions between the extracellular matrix and cells. The in vitro and in vivo experiments demonstrated that the hybrid hydrogel significantly promoted cartilage repair. The dynamic hybrid hydrogel alleviates abnormal actin polymerization, reduces intracellular stress, and increases the volume of individual cells. By modulating the cytoskeleton, the hybrid hydrogel inhibits Notch signal transduction in both the receptor and ligand cells, resulting in an improved cartilage phenotype. This study introduces an effective hybrid hydrogel scaffold that modulates the chondrocyte cytoskeleton and Notch signaling pathways by establishing an appropriate biomechanical environment, thus offering a promising material for cartilage repair.

Implanted Magnetoelectric Bionic Cartilage Hydrogel

Enhancing defective cartilage repair by creating a bionic cartilage hydrogel supplemented with in situ electromagnetic stimulation, replicating endogenous electromagnetic effects, remains challenging. To achieve this, a unique three-phase solvent system is designed to prepare a magnetoelectric bionic cartilage hydrogel incorporating piezoelectric poly(3-hydroxybutyric acid-3-hydroxyvaleric acid) (PHBV) and magnetostrictive triiron tetraoxide nanoparticles (Fe3O4 NPs) into sodium alginate (SA) hydrogel to form a dual-network, semi-crosslinked chain entanglement structure. The synthesized hydrogel features similar composition, structure, and mechanical properties to natural cartilage. In addition, after the implantation of cartilage, the motion-driven magnetoelectric-coupled cyclic transformation model is triggered by gentle joint forces, initiating a piezoelectric response that leads to magnetoelectric-coupled cyclic transformation. The freely excitable and cyclically enhanced electromagnetic stimulation it can provide, by simulating and amplifying endogenous electromagnetic effects, obtains induced defective cartilage repair efficacy superior to piezoelectric or magnetic stimulation alone.

A Facile Strategy to Construct Stretchable and Thermoreversible Double Network Hydrogels with Low Hysteresis and High Toughness Based on Entanglement and Hydrogen Bond Networks

High toughness and low hysteresis are of great significance for stretchable hydrogels to strengthen their reliability and practicability for cycle-loaded applications. Whereas, it is still challenging to simultaneously gain mutually repulsive properties due to the existence of dissipation structure. Here, stretchable and recoverable double network (DN) hydrogels comprising highly entangled network structure and temperature-induced dense hydrogen bond (HB)-associated network structure are synthesized, in which slidable entanglements and dense HBs act as the effective crosslinking in first and second networks, respectively. Moveable entanglements and stable HB structures endow hydrogels with high stretchability (999%), high tensile strength (0.82 MPa) and high fracture toughness (4.51 MJ·m-3) through stress transmission along long chains and HB clusters energy dissipation. Moreover, the imposed energy on hydrogels can saved in oriented polymer chains by disentanglement as an entropy loss, thus ensuring the low hysteresis (6.2% at 100% tensile strain) of hydrogels. In addition, deformed hydrogel can be well remodeled and recovered (stress recovery of 95.5%) by temperature-triggered sol-gel transition of HB network. By means of entanglement and hydrogen bond strategies, stretchable DN hydrogels not only equilibrate the conflict of low hysteresis and high toughness, but also provides a new perspective to design high-property hydrogels for cycle-loaded applications.

Tuning Network Topology through Polymerization-Induced Entanglements for Tough and Low-Hysteresis Double Network Hydrogels

In conventional double network (CDN) hydrogels, dense chemical cross-linking in the first network frequently induces structural imperfections, resulting in significant energy dissipation and substantial hysteresis under stress. To improve structural uniformity, spatial heterogeneities can be minimized by introducing mobile cross-linking, which facilitates the creation of a more homogeneous network. Herein, we employed a polymerization-induced entanglements (PIEs) strategy to tune the first network from a traditional net-like to a fabric-inspired topology, simultaneously promoting greater chain entanglement with the second network. This innovative approach enables PIEs DN hydrogels with exceptional performance, including significantly reduced hysteresis (0.15), high tensile strength (1.25 MPa), and excellent toughness (5800 J/m2), overcoming the long-standing trade-off between toughness and hysteresis observed in CDN hydrogels and offering insights and avenues for expanding DN hydrogel applications.

Advancements in the Field of Protein-Based Hydrogels: Main Types, Characteristics, and Their Applications

Regenerative medicine is a challenging field in current research and development, whilst translating the findings of novel tissue regenerative agents into clinical application. Protein-based hydrogels are derived from various sources, with animal-derived products being primarily utilized to deliver cells and promote cell genesis and proliferation, thereby aiding in numerous indications, including bone tissue regeneration, cartilage regeneration, spinal cord injury, and wound healing. As biocompatible and biodegradable systems, they are tolerated by the human body, allowing them to exert their beneficial effects in many indications. In this review article, multiple types of animal-derived proteins (e.g., collagen, gelatin, serum albumin, fibrin) were described, and a selection of the recent literature was collected to support the claims behind these innovative systems. During the literature review, special indications were found when applying these hydrogels, including the therapeutic option to treat post-myocardial infarct sites, glaucoma, and others. Maintaining their structure and mechanical integrity is still challenging. It is usually solved by adding (semi)synthetic polymers or small molecules to strengthen or loosen the mechanical stress in the hydrogel's structure. All in all, this review points out the potential application of value-added delivery systems in regenerative medicine.

An Injectable Kartogenin-Incorporated Hydrogel Supports Mesenchymal Stem Cells for Cartilage Tissue Engineering

BACKGROUND

Cartilage defects and injuries often lead to osteoarthritis, posing significant challenges for cartilage repair. Traditional treatments have limited efficacy, necessitating innovative therapeutic strategies. This study aimed to develop an injectable hydrogel-based tissue engineering construct to enhance cartilage regeneration by combining mesenchymal stem cells (MSCs) and the small molecule drug kartogenin (KGN).

METHODS

An injectable hydrogel was synthesized by crosslinking carboxymethyl chitosan (CMC) with aldehyde-modified cellulose nanocrystals (DACNCs). KGN was incorporated into the hydrogel during crosslinking to achieve sustained drug release. Three hydrogels with varying CMC/DACNC molar ratios (MR = 0.11, 0.22, and 0.33) were developed and characterized for their structural, mechanical, and biocompatible properties. The hydrogel with the optimal ratio (MR = 0.33) was further evaluated for its ability to support MSC viability and differentiation in vitro. Additionally, signaling pathways (TGF-β, FOXO, and PI3K-AKT) were investigated to elucidate the underlying mechanisms. In vivo efficacy was assessed using a rabbit femoral trochlear cartilage defect model.

RESULTS

The hydrogel with a higher CMC/DACNC molar ratio (MR = 0.33) exhibited increased compressive modulus, a reduced swelling rate, and superior biocompatibility, effectively promoting MSC differentiation in vitro. Signaling pathway analysis revealed activation of the TGF-β, FOXO, and PI3K-AKT pathways, suggesting enhanced chondrogenic potential. In vivo experiments demonstrated that the KGN-MSC-encapsulated hydrogel significantly improved cartilage repair.

CONCLUSIONS

The injectable CMC/DACNC hydrogel, combined with KGN and MSCs, synergistically enhanced cartilage regeneration both in vitro and in vivo. This study highlights the potential of this hydrogel as a promising scaffold for cartilage tissue engineering, offering a novel therapeutic approach for cartilage defects and injuries.

Highly Entangled Hydrogels by Photoiniferter-Mediated Polymerization

We report the synthesis of ultra-high molecular weight (UHMW) poly(N,N-dimethylacrylamide) (PDMAm) hydrogels with extremely low crosslinking densities by trithiocarbonate photoiniferter-mediated reversible deactivation radical polymerization (RDRP). Fixing the photoiniferter to crosslinker ratio and gradually increasing the targeted degree of polymerization (DPtarget) allowed for simultaneous control over the crosslinking density and the average molecular weight (Mn) of the primary chains, both below and above the critical molecular weight of entanglement (Mc). Interestingly, a plateau in storage moduli (G') was observed for UHMW PDMAm hydrogels with a sufficiently high DPtarget (>5,000), indicating a transition to the entanglement-dominated regime, with no contribution from crosslinks to the overall modulus, thus indicating the formation of highly entangled hydrogels. These hydrogels exhibit enhanced properties such as high toughness and resistance to swelling despite their vanishingly small crosslinking densities. Furthermore, even when equipped with cleavable crosslinkers, the UHMW PDMAm hydrogels resist degradation due to dense entanglements which act as transient crosslinks preventing the gels from swelling, while sparse covalent crosslinks help to maintain their structural integrity and avoid chain disentanglement. This approach allows simple synthesis of elastic and tough hydrogels with a well-defined structure and tuneable contributions from both crosslinks and entanglements.

Hydrogels with prestressed tensegrity structures

Tensegrity structures are isolated rigid compression components held in place by a continuous network of tensile components, and are central to natural systems such as the extracellular matrix and the cell cytoskeleton. These structures enable the nonreciprocal mechanical properties essential for dynamic biological functions. Here, we introduce a synthetic approach to engineer hydrogels with tensegrity architectures, drawing inspiration from the mechanochemical principles underlying biological systems. By employing in-situ enzyme-induced amino acid crystal growth within preformed polymeric networks, we achieve a hierarchical integration of micro crystal sticks randomly interlocked in the prestressed polymer matrice. This design mirrors natural tensegrity structures, balancing mechanical forces to maintain high stiffness (tensile moduli up to 30 MPa), fracture toughness (2600 J m⁻²), and water content (exceeding 80%). The resultant hydrogels exhibit bimodulus behavior due to their tensegrity structure, featuring a tensile-to-compressive modulus ratio of 13. This biomimetic approach provides a strategy for creating robust, adaptive materials for applications in tissue engineering and beyond.

Hydrogels with programmed spatiotemporal mechanical cues for stem cell-assisted bone regeneration

Hydrogels are extensively utilized in stem cell-based tissue regeneration, providing a supportive environment that facilitates cell survival, differentiation, and integration with surrounding tissues. However, designing hydrogels for regenerating hard tissues like bone presents significant challenges. Here, we introduce macroporous hydrogels with spatiotemporally programmed mechanical properties for stem cell-driven bone regeneration. Using liquid-liquid phase separation and interfacial supramolecular self-assembly of protein fibres, the macroporous structure of hydrogels provide ample space to prevent contact inhibition during proliferation. The rigid protein fibre-coated pore shell provides sustained mechanical cues for guiding osteodifferentiation and protecting against mechanical loads. Temporally, the hydrogel exhibits tunable degradation rates that can synchronize with new tissue deposition to some extent. By integrating localized mechanical heterogeneity, macroporous structures, surface chemistry, and regenerative degradability, we demonstrate the efficacy of these stem cell-encapsulated hydrogels in rabbit and porcine models. This marks a substantial advancement in tailoring the mechanical properties of hydrogels for stem cell-assisted tissue regeneration.

A review on recent progress in polysaccharide/protein hydrogels in winter sports: Classification, synthesis routes, and application

In today's world, emerging materials play prominent roles in competitive sport applications. Among them, hydrogels gained increasing attention in winter sports applications owing to their unique advantages, such as flexibility, conductivity, and adhesion. However, traditional hydrogels prepared by synthetic routes from petroleum materials lose performance at freezing temperatures below zero degrees, limiting their direct use in winter sports. The emergence of natural polymer materials has brought new opportunities for winter sports. Polysaccharide or protein (polysaccharides/proteins) hydrogels obtained from biomass resources are renewable and abundant, especially when taking into consideration the depletion of resources and environmental pollution in contemporary society. The development and utilization of polysaccharide/protein hydrogels may contribute to solving the resource shortage problem. In this paper, the latest research dealing with natural polymer hydrogels for winter sports applications is reviewed. In the first section, recent research trends of hydrogel classification and crosslinking methods are summarized. The performance advantages and specific applications of polysaccharide/protein hydrogels in winter sports are then discussed, with the application scope covering index monitoring, event violation detection, protective equipment, rehabilitation, and venues. Finally, the practical challenges faced by polysaccharide/protein hydrogels in winter sports are prospected along with the innovation and optimization design routes, such as the introduction of natural crosslinking agents and bionic structures. These insights aim to provide a reference for the development of advanced materials for winter sports applications.

Matrix Viscoelasticity Orchestrates Osteogenesis via Mechanotransduction Mediated Metabolic Switch in Macrophages

Understanding the interplay between extracellular matrix (ECM) mechanics and macrophage cellular processes is crucial for bone regeneration. While ECM stiffness has been extensively studied, the role of ECM viscoelasticity (e.g., stress relaxation) in the bone marrow niche and its effects on macrophage function remain unclear. Here, this study reveals how matrix viscoelasticity orchestrates osteogenesis by modulating macrophage metabolism through vasodilator-stimulated phosphoprotein (VASP) / hypoxia-inducible factor 1 alpha (HIF1α) signaling. In the rapid maxillary expansion (RME) model, significant stress relaxation occurs in regenerated bone marrow during the initial 17 days, coinciding with increased transforming growth factor-beta 1 (TGF-β1+) F4/80+ macrophages. Fast stress relaxation enhances macrophage recruitment of mesenchymal stem cells (MSCs) by upregulating TGF-β1. Using a hydrogel-macrophage system mimicking bone marrow viscoelasticity, cranial defect regeneration is significantly improved. Moreover, fast stress relaxation shifts macrophage metabolism from glycolysis to oxidative phosphorylation (OXPHOS) via VASP/HIF1α signaling, facilitating a reparative phenotype. These findings elucidate the relationship between ECM viscoelasticity and macrophage metabolism, suggesting new therapeutic avenues for bone regeneration through mechanomedicine.

Engineered protein-based materials for tissue repair: A review

The human body may suffer multiple injuries and losses due to various external factors, such as tumors, diseases, traffic accidents, and war conflicts. Under such circumstances, engineered protein-based materials, as an innovative adjunctive material, can not only effectively promote the natural repair process of tissues, but also greatly circumvent the negative effects and complications that may be associated with conventional surgery. In this review, we first trace the definition and development of engineered protein-based materials and explain in detail their mechanism of action in promoting tissue repair. Subsequently, the advantages and disadvantages of various engineered protein-based materials in tissue repair are analyzed by comparison. In addition, the present review reveals in depth how material properties can be optimized by scientific means to meet different tissue repair needs. In addition, we present in detail specific application cases of engineered protein-based materials in the field of tissue repair. Finally, we summarize current challenges in engineered protein-based materials and provide an outlook for the future. This review not only provides theoretical support for the further exploration and development of engineered protein-based materials in the field of tissue repair, but also provides valuable references and inspiration for research in related fields.

Aggregation-induced emission-based phototheranostics to combat bacterial infection at wound sites: A review

The healing of chronic wounds infected by bacteria has attracted increasing global concerns. In the past decades, antibiotics have certainly brought hope to cure bacteria-infected chronic wounds. However, the misuse of antibiotics leads to the emergence of numerous multidrug-resistant bacteria, which aggravate the health threat to clinical patients. To address these increasing challenges, scientists are committed to creating novel non-antibiotic strategies to kill bacteria and promote bacteria-infected chronic wound healing. Fortunately, with the quick development of nanotechnology, the representatives of phototherapy, such as photothermal therapy (PTT) and photodynamic therapy (PDT), exhibit promising possibilities in promoting bacteria-infected wound healing. Well-known, photothermal agents and photosensitizers largely determine the effects of PTT and PDT. A common problem for these molecules is the aggregation-induced quenching effect, which highly limits their further applicability in biomedical and clinical fields. Fortunately, the occurrence of aggregation-induced emission luminogens (AIEgens) efficiently overcomes the photobleaching and exhibit advantages, such as strongly aggregated emission, superior photostability, aggregation-enhanced reactive oxygen species (ROS), and heat generation, which makes great sense to the development of PTT and PDT. This article reviews various studies conducted on novel AIEgen-based materials that can mediate potent PDT, PTT, and a combination of PDT and PTT to promote bacteria-infected chronic wound healing.

Chitin nanocrystal-reinforced chitin/collagen composite hydrogels for annulus fibrosus repair after discectomy

Discectomy is a widely utilized approach for alleviating disc herniation; however, effective repair of postoperative annulus fibrosus (AF) defects remains a significant challenge. This study introduces a hydrogel patch with enhanced mechanical properties for AF repair fabricated using chitin (Ch), collagen (Col), and chitin nanocrystals (ChNCs) through a freeze-thaw cycling technique. The Ch and Col components constitute the matrix of the hydrogel patch, while uniformly dispersed ChNCs act as a nanofiller, markedly improving the mechanical performance (compression strain: 95 %; compression modulus: 0.27 MPa) of the resulting Ch/Col@ChNCs hydrogel patch. The patch demonstrates advantageous properties, including high porosity, superior water absorption, thermal stability, and biodegradability in simulated body fluid. In vitro assessments reveal excellent biocompatibility with AF cells and enhanced collagen deposition. Furthermore, in vivo studies confirm that the patch effectively repairs postoperative disc defects, exhibiting strong integration with surrounding tissues and facilitating the orderly regeneration of fibrous tissue. This innovative hydrogel patch, combining exceptional properties with a straightforward fabrication process, presents a viable strategy for advancing clinical biomaterials for postoperative AF repair.

Biomimetic bone cartilage scaffolds based on trilayer methacrylated hydroxyapatite/GelMA composites for full-thickness osteochondral regeneration

Since cartilage injury is often accompanied by subchondral bone damage, conventional single-phase materials cannot accurately simulate the osteochondral structure or repair osteochondral injury. In this work, a gradient gelatin-methacryloyl (GelMA) hydrogel scaffold was constructed by a layer-by-layer stacking method to realize full-thickness regeneration of cartilage, calcified cartilage and subchondral bone. Of note, to surmount the inadequate mechanical property of GelMA hydrogel, nanohydroxyapatite (nHA) was incorporated and further functionalized with hydroxyethyl methacrylate (nHA-hydroxyethyl methacrylate, nHAMA) to enhance the interfacial adhesion with the hydrogel, resulting in better mechanical strength akin to human bone. Specifically, the biomimetic nHAMA/GelMA (B-nHAMA) scaffold involved a pure GelMA top layer for cartilage, a 30/70% (w/w) nHAMA/GelMA intermediate layer for calcified cartilage, and a 70/30% (w/w) nHAMA/GelMA bottom layer for subchondral bone. This B-nHAMA scaffold exhibited optimal porosity (continuous-gradient pore size), mechanical performance (Young's modulus, 181.48 ± 29.94 kPa), biodegradability (degradation rate in 25 day, 66.04 ± 7.19%) and swelling properties (swelling ratio in 25 h, 424.8 ± 9.9%) that cater to osteochondral tissue environment. It also showed excellent biocompatibility, cell adaptability, chondrogenic and osteogenic properties, leading to effective osteochondral regeneration. Collectively, the developed B-nHAMA scaffold with similar osteochondral microenvironment of trilayered structure could facilitate simultaneous osteochondral regeneration, providing a promising strategy to improve the full-thickness cartilage injury regeneration. STATEMENT OF SIGNIFICANCE: This research presents a significant advancement in osteochondral repair with the development of a biomimetic B-nHAMA scaffold. The scaffold's design overcomes the inadequate stiffness of gelatin-methacryloyl (GelMA) by incorporating hydroxyethyl methacrylate-functionalized nanohydroxyapatite (nHAMA), enhancing interfacial adhesion and achieving mechanical strength equivalent to human bone. Through a layer-by-layer stacking approach, the B-nHAMA scaffold features a gradient composition that replicates the anisotropic nature of osteochondral tissue, with distinct layers tailored for cartilage, calcified cartilage and subchondral bone. Its biomimetic structure, closely resembling native cartilage in physicochemical and osteogenic properties, positions the B-nHAMA scaffold as a potent therapeutic candidate for the full-thickness repair of osteochondral defects, offering a clinically viable solution.

Intelligent Nanomaterials Design for Osteoarthritis Managements

Osteoarthritis (OA) is the most prevalent degenerative joint disorder, characterized by progressive joint degradation, pain, and diminished mobility, all of which collectively impair patients' quality of life and escalate healthcare expenditures. Current treatment options are often inadequate due to limited efficacy, adverse side effects, and temporary symptom relief, underscoring the urgent need for more effective therapeutic strategies. Recent advancements in nanomaterials and nanomedicines offer promising solutions by improving drug bioavailability, reducing side effects and providing targeted therapeutic benefits. This review critically examines the pathogenesis of OA, highlights the limitations of existing treatments, and explores the latest innovations in intelligent nanomaterials design for OA therapy, with an emphasis on their engineered properties, therapeutic mechanisms, and translational potential in clinical application. By compiling recent findings, this work aims to inspire further exploration and innovation in nanomedicine, ultimately advancing the development of more effective and personalized OA therapies.

Chain entanglement enhanced strong and tough wool keratin/albumin fibers for bioabsorbable and immunocompatible surgical sutures

High-performance fibers derived from non-silk proteins have garnered significant interest in biomedical applications because of their high accessibility and biocompatibility. Nonetheless, considerable challenges persist in addressing their structural defects to fabricate fibers with an optimal balance of strength and toughness. Herein, an entanglement-reinforced strategy is proposed to reconstruct high-performance non-silk protein fibers. Regenerated keratin and bovine serum albumin (BSA) are unfolded by denaturant and complementarily composited, leveraging their intrinsic cysteine re-oxidation to generate a robust mechanical cross-linking network without the requirement of an external crosslinker. The resulting drawn keratin/BSA composite fiber (DKBF) exhibits balanced mechanical performances with a breaking strength of approximately 250 MPa and a toughness of around 70 MJ m-3, outperforming that of reported regenerated keratin fibers and comparable to many natural or artificial silk fibers. Additionally, DKBFs demonstrate redox-responsive mechanical behavior and hydration-induced reversible shape memory. The DKBFs show good suturing capability for wound repair in female animal models due to their excellent bioabsorbability and immunocompatibility. This work offers valuable insights into addressing the current challenges in manufacturing mechanically robust and tough non-silk protein fibers, bringing hope for the development of more sustainable and versatile materials.

Ultrastrong eutectogels engineered via integrated mechanical training in molecular and structural engineering

Ultrastrong gels possess generally ultrahigh modulus and strength yet exhibit limited stretchability owing to hardening and embrittlement accompanied by reinforcement. This dilemma is overcome here by using hyperhysteresis-mediated mechanical training that hyperhysteresis allows structural retardation to prevent the structural recovery of network after training, resulting in simply single pre-stretching training. This training strategy introduces deep eutectic solvent into polyvinyl alcohol hydrogels to achieve hyperhysteresis via hydrogen bonding nanocrystals on molecular engineering, performs single pre-stretching training to produce hierarchical nanofibrils on structural engineering, and fabricates chemically cross-linked second network to enable stretchability. The resultant eutectogels display exceptional mechanical performances with enormous fracture strength (85.2 MPa), Young's modulus (98 MPa) and work of rupture (130.6 MJ m-3), which compare favorably to those of previous gels. The presented strategy is generalizable to other solvents and polymer for engineering ultrastrong organogels, and further inspires advanced fabrication technologies for force-induced self-reinforcement materials.

Genetically Programmed Single-Component Protein Hydrogel for Spinal Cord Injury Repair

Protein self-assembly allows for the formation of diverse supramolecular materials from relatively simple building blocks. In this study, a single-component self-assembling hydrogel is developed using the recombinant protein CsgA, and its successful application for spinal cord injury repair is demonstrated. Gelation is achieved by the physical entanglement of CsgA nanofibrils, resulting in a self-supporting hydrogel at low concentrations (≥5 mg mL-1). By leveraging the programmability of the CsgA gene sequence, the bioactive hydrogel is enhanced by fusing functional peptide GHK. GHK is recognized for its anti-inflammatory, antioxidant, and neurotrophic factor-stimulating properties, making it a valuable addition to the hydrogel for spinal cord injury repair applications. In vitro experiments demonstrate that the CsgA-GHK hydrogel can modulate microglial M2 polarization, promote neuronal differentiation of neural stem cells, and inhibit astrocyte differentiation. Additionally, the hydrogel shows efficacy in alleviating inflammation and promotes neuronal regeneration at the injury site, leading to significant functional recovery in a rat model with compression injury spinal cord cavity. These findings lay the groundwork for developing a modular design platform for recombinant CsgA protein hydrogels in tissue repair applications.

High-performance supercapacitors based on coarse nanofiber bundle and ordered network hydrogels

Most of the developed flexible hydrogel supercapacitors struggle to maintain their electrochemical stability and structural integrity under tensile strain. Therefore, developing a flexible supercapacitor with excellent mechanical properties and stable electrochemical performance under different strains remains a challenge. Based on the previous cartilage-like structure, we designed a new coarse nanofiber bundle and ordered network. A coarse nanofiber bundle and ordered network skeleton was constructed by directional freezing and filled with polyvinyl alcohol (PVA) to serve as a soft matrix to prepare PVA-SNF-CNTs-PPy-3 hydrogel electrode, which has high tensile strength (6.22 MPa) and fatigue threshold (8759.8 J/m2). In addition, the loading of carbon nanotubes and polypyrrole onto the SNF-ordered network enabled the conductive material to form an ordered conductive energy storage network along the skeleton, providing an area-specific capacitance of up to 23.96 F/cm2. The coarse nanofiber bundle and ordered network provided supercapacitors with the least capacitance consumption under 150 % deformation, and the capacitance retention was >98.2 %. After repeated stretching (3000 times), the capacitance remained >91.45 %. This study provides new ideas for the development of flexible supercapacitors with high capacitance and high mechanical reliability.

Proteins for Hyperelastic Materials

Meticulous engineering and the yielded hyperelastic performance of structural proteins represent a new frontier in developing next-generation functional biomaterials. These materials exhibit outstanding and programmable mechanical properties, including elasticity, resilience, toughness, and active biological characteristics, such as degradability and tissue repairability, compared with their chemically synthetic counterparts. However, there are several critical issues regarding the preparation approaches of hyperelastic protein-based materials: limited natural sequence modules, non-hierarchical assembly, and imbalance between compressive and tensile elasticity, leading to unmet demands. Therefore, it is pivotal to develop an alternative strategy for biofabricating hyperelastic materials. Herein, the molecular design, engineering, and property regulation of hyperelastic structural proteins are overviewed. First, methodologies for deeper exploration of mechanical modules, including machine learning-aided de novo design, random mutations of natural sequences, and multiblock fusion techniques, are actively introduced. These methodologies facilitate the generation of elastomeric protein modules and demonstrate enhanced structural and functional versatility. Subsequently, assembly tactics of hyperelastic proteins (i.e., physical modulation, genetic adaptations, and chemical modifications) are reviewed, yielding hierarchically ordered structures. Finally, advances in biophysical techniques for more nuanced characterization of protein ensembles are discussed, unveiling the tuning mechanisms of protein elasticity across scales. Future developments in structural hyperelastic protein-based biomaterials are also envisioned.

Capturing the impact of protein unfolding on the dynamic assembly of protein networks

The rapid assembly of molecular or nanoscale building blocks into extended arrays is crucial to the construction of functional networks in vivo and in vitro and depends on various factors. One factor seldom considered is the dynamic changes of the building block shape. Folded protein building blocks offer a unique system to investigate dynamic shape changes due to their intrinsic ability to change from a compact and specific folded structure to an extended unfolded structure in response to a perturbation such as force. Here, we use photochemically crosslinked folded protein hydrogels constructed from force labile protein building blocks as a model dynamic shape-changing network system and characterise them by combining time-resolved rheology and small-angle X-ray scattering (SAXS). This approach probes both the load-bearing network structures, using rheology, and network architectures, using SAXS, thereby providing a crosslength scale understanding of the network formation. We propose a triple assembly model for the structural evolution of networks constructed from force labile protein building block consisting of: primary formation where monomeric folded proteins create the preliminary protein network scaffold; a subsequent secondary formation phase, where larger oligomers of protein diffuse to join the preliminary network scaffold; and finally in situ unfolding and relaxation which leads to the mature network structure of connected larger and denser fractal-like clusters. The time-resolved SAXS data provides evidence that protein unfolding occurs on the edges of the fractal-like clusters, resulting in a population of unfolded proteins in the space between clusters. Identifying the key stages of assembly in protein networks constructed from force labile proteins provides a greater understanding of the importance of protein unfolding in hierarchical biomechanics in vivo and creates future opportunities to develop bespoke biomaterials for novel biomedical applications.

Network design for soft materials: addressing elasticity and fracture resistance challenges

Soft materials, such as elastomers and gels, feature crosslinked polymer chains that provide stretchable and elastic mechanical properties. These properties are derived from entropic elasticity, which limits energy dissipation and makes the material susceptible to fracture. To address this issue, network designs that dissipate energy through the plastic zone have been introduced to enhance toughness; however, this approach compromises elasticity, preventing the material from fully recovering its original shape after deformation. In this review, we describe the trade-off between fracture resistance and elasticity, exploring network designs that overcome this limitation to achieve both high toughness and low hysteresis. The development of soft materials that are both elastic and fracture-resistant holds significant promise for applications in stretchable electronics, soft robotics, and biomedical devices. By analyzing successful network designs, we identify strategies to further improve these materials and discuss potential enhancements based on existing limitations.

A Flexible-Integrated Multimodal Hydrogel-Based Sensing Patch

Sleep monitoring is an important part of health management because sleep quality is crucial for restoration of human health. However, current commercial products of polysomnography are cumbersome with connecting wires and state-of-the-art flexible sensors are still interferential for being attached to the body. Herein, we develop a flexible-integrated multimodal sensing patch based on hydrogel and its application in unconstraint sleep monitoring. The patch comprises a bottom hydrogel-based dual-mode pressure-temperature sensing layer and a top electrospun nanofiber-based non-contact detection layer as one integrated device. The hydrogel as core substrate exhibits strong toughness and water retention, and the multimodal sensing of temperature, pressure, and non-contact proximity is realized based on different sensing mechanisms with no crosstalk interference. The multimodal sensing function is verified in a simulated real-world scenario by a robotic hand grasping objects to validate its practicability. Multiple multimodal sensing patches integrated on different locations of a pillow are assembled for intelligent sleep monitoring. Versatile human-pillow interaction information as well as their evolution over time are acquired and analyzed by a one-dimensional convolutional neural network. Track of head movement and recognition of bad patterns that may lead to poor sleep are achieved, which provides a promising approach for sleep monitoring.

In situ forming and self-crosslinkable protein hydrogels for localized cancer therapy and topical wound healing

Proteins, inherently biocompatible and biodegradable, face a challenge in forming stable hydrogels without external chemical crosslinkers. Here, we construct a ring-shaped trimeric SpyTag-fused Proliferating Cell Nuclear Antigen Protein (ST-PCNA) as a core protein building block, and a dumbbell-shaped tandem dimeric SpyCatcher (SC-SC) as a bridging component. Self-crosslinked PCNA/SC-SC Protein (2SP) hydrogels are successfully formed by simply mixing the solutions of ST-PCNA and SC-SC, without chemical crosslinkers. During their formation by mixing, various cargo molecules, including anti-cancer drugs, photosensitizers, and functional proteins, are efficiently incorporated, producing cargo@2SP hydrogels. Most of the entrapped cargo molecules gradually release as the hydrogels erode. Anti-cancer drug- or photosensitizer-incorporated 2SP hydrogels are successfully formed through localized injection beneath the 4 T1 tumor in mice. The localized gradual release of drugs in physiological microenvironment substantially suppresses tumor growth, and highly localized photosensitizers retained in the 2SP hydrogels raises the local temperature above 45 °C upon laser irradiation, resulting in a significant suppression of tumor growth. Additionally, the topical administration of growth factor proteins-incorporated 2SP hydrogels to the incision wound area effectively regenerates the skin, with rapid reconstruction of extracellular matrix. The injectable and self-crosslinkable 2SP hydrogels developed here offer promise as novel biocompatible scaffolds for local therapy.

Molecular self-assembly strategy tuning a dry crosslinking protein patch for biocompatible and biodegradable haemostatic sealing

Uncontrolled haemorrhage is a leading cause of trauma-related fatalities, highlighting the critical need for rapid and effective haemostasis. Current haemostatic materials encounter limitations such as slow clotting and weak mechanical strength, while most of bioadhesives compromise their adhesion performance to wet tissues for biocompatibility and degradability. In this study, a molecular self-assembly strategy is proposed, developing a biocompatible and biodegradable protein-based patch with excellent adhesion performance. This strategy utilizes fibrinogen modified with hydrophobic groups to induce self-assembly into a hydrogel, which is converted into a dry patch. The protein patch enhances adhesion performance on the wet tissue through a dry cross-linking method and robust intra/inter-molecular interactions. This patch demonstrates excellent haemostatic efficacy in  both porcine oozing wound and porcine severe acute haemorrhage. It maintains biological functionality, and ensures sustained wound sealing while gradually degrading in vivo, making it a promising candidate for clinical tissue sealing applications.

Metabolic Reprogramming of Neural Stem Cells by Chiral Nanofiber for Spinal Cord Injury

Exogenous neural stem cells (NSCs) have great potential to reconstitute damage spinal neural circuitry. However, regulating the metabolic reprogramming of NSCs for reliable nerve regeneration has been challenging. This report discusses the biomimetic dextral hydrogel (DH) with right-handed nanofibers that specifically reprograms the lipid metabolism of NSCs, promoting their neural differentiation and rapid regeneration of damaged axons. The underlying mechanism is the intrinsic stereoselectivity between DH and fatty acid-binding protein 5 (FABP5), which facilitates the transportation of fatty acids bound to FABP5 into the mitochondria and endoplasmic reticulum, subsequently augmenting fatty acid oxidation (FAO) levels and enriching sphingosine biosynthesis. In the rat SCI model, DH significantly improved the Basso-Beattie-Bresnahan (BBB) locomotor scores (over 3-fold) and the hindlimbs' compound muscle action potential (over 4-fold) compared with the untreated group, conveying a significant return of functional recovery. This finding of nanoscale chirality-dependent NSCs metabolic reprogramming provides insights into understanding stem cell physiology and presents opportunities for regenerative medicine.

Biomaterial-assisted organoid technology for disease modeling and drug screening

Developing disease models and screening for effective drugs are key areas of modern medical research. Traditional methodologies frequently fall short in precisely replicating the intricate architecture of bodily tissues and organs. Nevertheless, recent advancements in biomaterial-assisted organoid technology have ushered in a paradigm shift in biomedical research. This innovative approach enables the cultivation of three-dimensional cellular structures in vitro that closely emulate the structural and functional attributes of organs, offering physiologically superior models compared to conventional techniques. The evolution of biomaterials plays a pivotal role in supporting the culture and development of organ tissues, thereby facilitating more accurate disease state modeling and the rigorous evaluation of drug efficacy and safety profiles. In this review, we will explore the roles that various biomaterials play in organoid development, examine the fundamental principles and advantages of utilizing these technologies in constructing disease models, and highlight recent advances and practical applications in drug screening using disease-specific organoid models. Additionally, the challenges and future directions of organoid technology are discussed. Through continued research and innovation, we aim to make remarkable strides in disease treatment and drug development, ultimately enhancing patient quality of life.

Current Concepts and Clinical Applications in Cartilage Tissue Engineering

Cartilage injuries are extremely common in the general population, and conventional interventions have failed to produce optimal results. Tissue engineering (TE) technology has been developed to produce neocartilage for use in a variety of cartilage-related conditions. However, progress in the field of cartilage TE has historically been difficult due to the high functional demand and avascular nature of the tissue. Recent advancements in cell sourcing, biostimulation, and scaffold technology have revolutionized the field and made the clinical application of this technology a reality. Cartilage engineering technology will continue to expand its horizons to fully integrate three-dimensional printing, gene editing, and optimal cell sourcing in the future. This review focuses on the recent advancements in the field of cartilage TE and the landscape of clinical treatments for a variety of cartilage-related conditions.

Tailorable biosensors for real-time monitoring of stress distribution in soft biomaterials and living tissues

Visualizing mechanical stress distribution in soft and live biomaterials is essential for understanding biological processes and improving material design. However, it remains challenging due to their complexity, dynamic nature, and sensitivity requirements, necessitating innovative techniques. Since polysaccharides are common in various biomaterials, a biosensor integrating a Förster resonance energy transfer (FRET)-based tension sensor module and carbohydrate-binding modules (FTSM-CBM) has been designed for real-time monitoring of the stress distribution of these biomaterials. By simple dripping or soaking, FTSM-CBM enables fast, reproducible and semiquantitative detection of both 2D and 3D stress distributions in polysaccharide-based hydrogels. Additionally, it provides valuable information such as microstructure hints and fracture site warnings. FTSM-CBM can also monitor the locomotion of maggots, which is not feasible with most existing techniques. Furthermore, by changing the CBM, FTSM-CBM can be expanded for various polysaccharide-based biomaterials. This study provides a powerful tool that may promote related research in life and materials science.

Water-regulated viscosity-plasticity phase transitions in a peptide self-assembled muscle-like hydrogel

The self-assembly of small molecules through non-covalent interactions is an emerging and promising strategy for building dynamic, stable, and large-scale structures. One remaining challenge is making the non-covalent interactions occur in the ideal positions to generate strength comparable to that of covalent bonds. This work shows that small molecule YAWF can self-assemble into a liquid-crystal hydrogel (LCH), the mechanical properties of which could be controlled by water. LCH can be used to construct stable solid threads with a length of over 1 meter by applying an external force on 2 µL of gel solution followed by water-regulated crystallization. These solid threads can support 250 times their weight. Cryogenic electron microscopy (Cryo-EM) analysis unravels the three-dimensional structure of the liquid-crystal fiber (elongated helix with C2 symmetry) at an atomic resolution. The multiscale mechanics of this material depend on the specificity of the molecular structure, and the water-controlled hierarchical and sophisticated self-assembly.

Dynamic Peptide Nanoframework-Guided Protein Coassembly: Advancing Adhesion Performance with Hierarchical Structures

Hierarchical structures are essential in natural adhesion systems. Replicating these in synthetic adhesives is challenging due to intricate molecular mechanisms and multiscale processes. Here, we report three phosphorylated peptides featuring a hydrophobic self-assembly motif linked to a hydrophilic phosphorylated sequence (pSGSS), forming peptide fibril nanoframeworks. These nanoframeworks effectively coassemble with elastin-derived positively charged proteins (PCP), resulting in complex coacervate-based adhesives with hierarchical structures. Our method enables the controlled regulation of both cohesion and adhesion properties in the adhesives. Notably, the complex adhesives formed by the dityrosine-containing peptide and PCP demonstrate an exceptional interfacial adhesion strength of up to 30 MPa, outperforming most known supramolecular adhesives and rivaling cross-linked chemical adhesives. Additionally, these adhesives show promising biocompatibility and bioactivity, making them suitable for applications such as visceral hemostasis and tissue repair. Our findings highlight the utility of bioinspired hierarchical assembly combined with bioengineering techniques in advancing biomedical adhesives.

Competition between cross-linking and force-induced local conformational changes determines the structure and mechanics of labile protein networks

Folded protein hydrogels are emerging as promising new materials for medicine and healthcare applications. Folded globular proteins can be modelled as colloids which exhibit site specific cross-linking for controlled network formation. However, folded proteins have inherent mechanical stability and unfolded in response to an applied force. It is not yet understood how colloidal network theory maps onto folded protein hydrogels and whether it models the impact of protein unfolding on network properties. To address this, we study a hybrid system which contains folded proteins (patchy colloids) and unfolded proteins (biopolymers). We use a model protein, bovine serum albumin (BSA), to explore network architecture and mechanics in folded protein hydrogels. We alter both the photo-chemical cross-linking reaction rate and the mechanical properties of the protein building block, via illumination intensity and redox removal of robust intra-protein covalent bonds, respectively. This dual approach, in conjunction with rheological and structural techniques, allows us to show that while reaction rate can 'fine-tune' the mechanical and structural properties of protein hydrogels, it is the force-lability of the protein which has the greatest impact on network architecture and rigidity. To understand these results, we consider a colloidal model which successfully describes the behaviour of the folded protein hydrogels but cannot account for the behaviour observed in force-labile hydrogels containing unfolded protein. Alternative models are needed which combine the properties of colloids (folded proteins) and biopolymers (unfolded proteins) in cross-linked networks. This work provides important insights into the accessible design space of folded protein hydrogels without the need for complex and costly protein engineering, aiding the development of protein-based biomaterials.

Photodegradable polyacrylamide tanglemers enable spatiotemporal control over chain lengthening in high-strength and low-hysteresis hydrogels

Covalent hydrogel networks suffer from a stiffness-toughness conflict, where increased crosslinking density enhances the modulus of the material but also leads to embrittlement and diminished extensibility. Recently, strategies have been developed to form highly entangled hydrogels, colloquially referred to as tanglemers, by optimizing polymerization conditions to maximize the density and length of polymer chains and minimize the crosslinker concentration. It is challenging to assess entanglements in crosslinked networks beyond approximating their theoretical contribution to mechanical properties; thus, in this work, we synthesize and characterize polyacrylamide tanglemers using a photolabile crosslinker, which allows for direct assessment of covalent trapping of entanglements under tension. Further, this chemistry allows tuning of the modulus in situ by crosslink photocleavage (from tensile modulus (ET) = 100 kPa to <25 kPa). Beyond cleavage of crosslinks, we demonstrate that even non-degradable tanglemer formulations can be photo-softened and completely degraded through Fe3+-mediated oxidation of the polyacrylamide backbone. While both photodegradation methods are useful for spatial patterning and result in softer gels with reduced fracture strength, only crosslink photocleavage improves gel extensibility via light-induced chain lengthening (εF = 700% to >1500%). Crosslink photocleavage in tanglemers also affords significant control over localized swelling and diffusivity. In sum, we introduce a simple and user-directed approach for probing entanglements and asserting spatiotemporal control over stress-strain responses and small molecule diffusivity in polyacrylamide tanglemers, suggesting a multitude of potential soft matter applications including controlled release and tunable bioadhesive interfaces.

Engineered 3D DNA Crystals: A Molecular Design Perspective

Recent advances in biomolecular self-assembly have transformed material science, enabling the creation of novel materials with unparalleled precision and functionality. Among these innovations, 3D DNA crystals have emerged as a distinctive class of macroscopic materials, engineered through the bottom-up approach by DNA self-assembly. These structures uniquely combine precise molecular ordering with high programmability, establishing their importance in advanced material design. This review delves into the molecular design of engineered 3D DNA crystals, classifying current crystal structures based on "crystal bond orientations" and examining key aspects of in-silico molecular design, self-assembly, and crystal modifications. The functionalization of 3D DNA crystals for applications in crystallization scaffolding, biocatalysis, biosensing, electrical and optical devices, as well as in the emerging fields of DNA computing and data storage are explored. Finally, the ongoing challenges are addressed and future directions to advance the field of engineered 3D DNA crystals are proposed.

Hierarchically aligned heterogeneous core-sheath hydrogels

Natural materials with highly oriented heterogeneous structures are often lightweight but strong, stiff but tough and durable. Such an integration of diverse incompatible mechanical properties is highly desired for man-made materials, especially weak hydrogels which are lack of high-precision structural design. Herein, we demonstrate the fabrication of hierarchically aligned heterogeneous hydrogels consisting of a compactly crosslinked sheath and an aligned porous core with alignments of nanofibrils at multi-scales by a sequential self-assembly assisted salting out method. The produced hydrogel offers ultrahigh mechanical properties among the reported hydrogels, elastomers and natural materials, including a toughness of 1031 MJ · m-3, strength of 55.3 MPa, strain of 3300%, stiffness of 6.8 MPa, fracture energy of 552.7 kJ · m-2 and fatigue threshold of 40.9 kJ · m-2. Furthermore, such a tough and strong hydrogel facilely achieves stable regeneration and rapid adhesion owing to the highly crystallized and aligned network structure. The regenerated specimen presents the reinforced strength, toughness and fatigue resistance over 10 regeneration cycles. This work provides a simple method to produce hydrogels with bioinspired heterostructures and combinational properties for real applications.