Ultrafast, tough, and adhesive hydrogel based on hybrid photocrosslinking for articular cartilage repair in water-filled arthroscopy

Immune-modulated adhesive hydrogel for enhancing osteochondral graft adhesion and cartilage repair

Osteochondral autograft transfer system (OATS) can effectively improve cartilage injuries by obtaining bone-cartilage grafts from healthy sites and implanting them into the defective areas. However, in up to 40 % of patients, the lack of a stable adhesive interface between the osteochondral graft and the normal tissue surface reduces the repair efficiency. In this work, we report an injectable and biocompatible poly (N-hydroxyethyl acrylamide-N-hydroxy succinimide)/Gelatin (PHE-Gel) hydrogel, featuring the instant formation of a tough bio-interface, which allows for robust adhesion with osteochondral grafts. Through physicochemical characterization, we found that a system composed of 10%PHE-Gel possesses superior interfacial toughness and excellent biocompatibility. In vitro, mechanistic studies and RNA-seq analysis had shown that 10%PHE-Gel promotes the expression of cartilage anabolic metabolism genes by upregulating the hypoxia-inducible factor alpha (HIF-α) signaling pathway and downregulating the tumor necrosis factor (TNF) signaling pathway. Dimethyloxalylglycine (DMOG) loaded liposome (DMOG-Lip) promotes the transition of M1 macrophages to M2 macrophages, shifting the microenvironment towards a pro-repair direction. Studies on a rabbit OATS model indicated that DMOG-Lip loaded 10%PHE-Gel (10%PHE-Gel@DMOG-Lip) effectively modulated the immune microenvironment, facilitated the repair of the hyaline cartilage, and inhibited further degeneration of cartilage. This composite hydrogel offers a promising solution for enhancing OATS repair in tissue engineering and has the potential to improve outcomes in cartilage restoration procedures.

Injectable and Tissue Adhesive Chitosan/Hyaluronic Acid-Based Hydrogels for Stem Cell Delivery and Cartilage Regeneration

Current therapeutic approaches for knee osteoarthritis (KOA) focus on symptom relief rather than addressing articular cartilage degeneration. Stem cell therapy holds promise for enhancing KOA treatment by promoting tissue regeneration, yet challenges remain in achieving minimally invasive delivery with sustained cell retention and viability. This study introduces an in situ fabricated, biodegradable, injectable, self-healing, tissue-adhesive hydrogel (Ald-HA/Dopa-HBCS). Formed by coinjecting two polymer solutions, it features a uniform, porous 3D structure, ideal for low-trauma administration and supporting human adipose-derived stem cells (hADSCs). We engineered its mechanical properties, gelation time, and degradation rate by adjusting polymer concentrations and ratios, ensuring hADSC viability for at least 14 days postinjection. Catechol groups provide tissue adhesion, enhancing therapeutic potential by retaining hADSCs at defect sites. The hydrogel also preserves chondrogenic gene expression and protein production in hADSCs, indicating broader applications beyond cartilage repair, extending to diverse cell-based therapies.

Integrated biomimetic bioprinting of perichondrium with cartilage for auricle reconstruction

The construction and regeneration of tissue-engineered auricles are pacesetters in tissue engineering and have realized their first international clinical application. However, the unstable regeneration quality and insufficient mechanical strength have become significant obstacles impeding its clinical promotion. The perichondrium is indispensable for the nutritional and vascular supply of the underlying cartilage tissue, as well as for proper anatomical functioning and mechanical performance. This study presents a novel strategy for integrated construction of bioengineered perichondrium with bioprinted cartilage to enhance the regeneration quality and mechanical properties of tissue-engineered auricles. Simulating the anatomical structure of the native auricle designs a sandwich construction model containing bilateral perichondrium and intermediate cartilage, employing a photocrosslinkable acellular cartilage matrix and gelatin bionics matrix microenvironment, applying co-cultured auricular chondrocytes and adipose-derived stem cells creates functional cell populations, designing hatch patterns imitates microscopic arrangement structures, utilizing sacrificial materials forms interlaminar network traffic to enhance the tight connection between layers, and finally, assessing the regenerative quality of the constructs explores their feasibility and stability. The multi-level and multi-scale biomimetic construction strategy overcomes the technical limitation of the integrated construction of perichondrium-wrapped auricles and realizes biomimicry in morphology, structure, and biomechanics. Altogether, this study provides a technical reference for the hierarchical construction of complex tissues and promotes the clinical translation and application of engineered tissues or organs.

PEGNB-Heparin-Liposome composite hydrogels for in situ spraying and ultra-fast adhesion: meeting the challenges of endothelial repair of vascular injury

Carotid atherosclerosis is an essential cause of transient cerebral ischemia, stroke, and other cerebrovascular diseases, and carotid endarterectomy (CEA) is currently the most effective treatment for removing plaque and restoring the vascular lumen. However, the CEA disrupts the integrity and functionality of the endothelium and predisposes it to complications such as restenosis and thrombosis. Hydrogels can closely mimic the natural extracellular matrix, allowing a wide tuning of physical and chemical properties. These properties make hydrogels the most promising candidate materials for the repair of vascular injured intima. In this study, a multifunctional intimal repair hydrogel of poly(ethylene glycol)-norbornene (PEGNB)/ Heparin/ Liposome is proposed with the advantages of ultra-rapid adhesion to the wet tissue of the vascular inner wall, maintenance of adhesion stability under continuous erosion by blood flow. The hydrogel was supplemented with poly(vinyl butyral) (PVB) to reduce its swelling rate, and Rapamycin (RAPA) was encapsulated in this study as the drug into the cationic liposomes. This composite multifunctional (PNHB@Lip(RAPA)) hydrogel has exhibited outstanding anti-coagulation properties, markedly suppressed the proliferation and migration of SMCs, and displayed favourable cytocompatibility and blood compatibility. Concurrently, the capacity of the PNHB@Lip(RAPA) hydrogel to stimulate endovascular regeneration and deter restenosis and thrombus formation was validated through carotid intima damage repair experiments. These findings collectively indicate that the PNHB@Lip(RAPA) hydrogel represents a promising material for intimal injury repair, offering innovative insights into intimal repair methodologies. STATEMENT OF SIGNIFICANCE: Carotid atherosclerosis is a leading cause of transient cerebral ischemia, stroke, and cerebrovascular disorders. Although carotid endarterectomy (CEA) effectively removes plaques, it damages endothelial integrity, increasing the risk of restenosis and thrombosis. To address this, we developed PNHB@Lip(RAPA), a multifunctional intimal repair hydrogel composed of PEGNB, heparin, and rapamycin-encapsulated liposomes. This hydrogel rapidly adheres to wet vascular walls, resists blood flow erosion, and exhibits low swelling. The hydrogel demonstrates superior anticoagulation, inhibits smooth muscle cell proliferation and migration, and shows favourable cytocompatibility. Experimental results confirm its ability to promote endovascular regeneration while preventing restenosis and thrombosis. In summary, PNHB@Lip(RAPA) hydrogel is a promising material for intimal repair, offering innovative solutions to improve CEA postoperative outcomes.

Thiol-functionalized collagen patch channelizes TGFβ1- JNK trafficking and reverses corneal stroma opacity

Pro-regenerative patches are appealing for cornea injuries owing to their robustness, and ease of use in clinical settings. Collagen-based synthetic patches are building blocks for corneal repair, but their cross-linker toxicity, less optical clarity, and deformation instability remain unresolved. In response to these challenges, the study introduces disulfide crosslinked thiolated collagen patches (CSH). Human umbilical cord collagen (UC) comprises abundant lysine; thus, more primary amines are available for thiolation. UC was thiol functionalized, whereby the degree of amine substitution is 38 %, and a 40.4 % increase in disulfide bonds confirms disulfide-mediated crosslinking. CSH exhibits remarkable biomechanics (3.3 MPa), adhesion strength (107.25 kPa), optical clarity (87 %), and proteolytic resistance compared to native collagen. The patches support sustained levofloxacin release for three days. HET-CAM assay and hemocompatibility confirmed non-irritancy. Ex vivo adhesion, drug permeation, and epithelial integrity validated their compatibility in rabbit eyeballs. In vitro studies in human corneal stromal cells evidence that the thiols mimic endogenous peptides, favoring cell adhesion and proliferation. The patches alleviate the fibrotic episodes by reducing TGFβ1 and vimentin, which attenuates the JNK signaling, leading to elevated expression of corneal clarity restoring proteins, TGFβ3 and Keratocan. Thus, disulfide-bonded collagen patches would be an effective therapeutic modality for stromal injury-associated blindness.

Dominant Role of Distinct Microenvironments on Cartilage Regeneration Fate Using PLGA-Hydrogel Composite Scaffolds

Currently, bioactive composite scaffolds provide an ideal regenerative microenvironment for cartilage tissue engineering. However, the dominant regulatory role of the microenvironment in cartilage regeneration fate remains elusive, such as in situ auricle, ex situ subcutaneous, and osteogenic regions. Therefore, investigating the influence of distinct microenvironments on cartilage regeneration and long-term outcomes is important. In this study, a universal composite scaffold is developed combining 3D-printed poly(lactic-co-glycolic acid) frameworks with cartilage-specific matrix hydrogels and then systematically explored the crucial role of the microenvironment in determining the fate of cartilage regeneration. These results indicate that the in situ auricular microenvironment effectively promotes the maturation of the regenerative cartilage and maintains its chondrogenic phenotype. In contrast, ex situ subcutaneous microenvironment leads to chondrogenic phenotype loss owing to intense immune-inflammatory responses and vascularization conditions. In the osteogenic microenvironments of cranial sites, although autologous chondrocytes show good cartilage regenerative quality within 12 weeks, they are gradually replaced by regenerative bone, ultimately achieving successful cranial defect repair. Interestingly, these findings provide critical theoretical foundations for revealing the long-term outcomes of engineered cartilage and offer practical guidance for optimizing cartilage regeneration strategies in various microenvironments.

Covalently reactive microparticles imbibe blood to form fortified clots for rapid hemostasis and prevention of rebleeding

Owing to the inherently gradual nature of coagulation, the body fails in covalently crosslinking to stabilize clots rapidly, even with the aid of topical hemostats, thus inducing hemostatic failure and potential rebleeding. Although recently developed adhesives confer sealing bleeding sites independently of coagulation, interfacial blood hampers their adhesion and practical applications. Here, we report a covalently reactive hemostat based on blood-imbibing and -crosslinking microparticles. Once contacting blood, the microparticles automatically mix with blood via imbibition and covalently crosslink with blood proteins and the tissue matrix before natural coagulation operates, rapidly forming a fortified clot with enhanced mechanical strength and tissue adhesion. In contrast to commercial hemostats, the microparticles achieve rapid hemostasis (within 30 seconds) and less blood loss (approximately 35 mg and 1 g in the rat and coagulopathic pig models, respectively), while effectively preventing blood-pressure-elevation-induced rebleeding in a rabbit model. This work advances the development and clinical translation of hemostats for rapid hemostasis and rebleeding prevention.

Hyaluronic acid as a versatile building block for the development of biofunctional hydrogels: In vitro models and preclinical innovations

Hyaluronic acid (HyA) is a non-sulphated linear polysaccharide found abundantly in the extracellular matrix, known for its biocompatibility and versatility in tissue engineering. Chemical modifications of HyA, including methacrylate, acrylate, click chemistry, norbornene, or host-guest chemistry, are necessary for the formation of stable hydrogels with tuneable biophysical characteristics. These modifications enable precise control over stiffness, swelling, degradation, and advanced functionalities such as shear-thinning, self-healing, and injectability. Functionalisation further enhances hydrogel bioactivity, enabling controlled cell adhesion, modulation of cell behaviour, hydrogel degradation, and release profiles, as well as inflammation modulation or bacterial growth inhibition. These are achieved by conjugating proteins, peptides, antibodies, or reactive chemical groups. HyA hydrogels find broad applications both in vitro and in vivo. In vitro, HyA-based hydrogels can support the development of models to understand fundamental processes in health and mechanisms behind disease progression, serving as highly tuneable extracellular matrix mimetics. As therapeutic interventions, injectable or implantable HyA-based hydrogels have been developed to repair a range of tissues, including cartilage, bone, muscle, and skin defects. However, issues remain to be addressed before widespread adoption of HyA-based hydrogels as clinical options. Future innovations for HyA hydrogels include its establishment as an enabling technology for the delivery of novel therapeutics, with a particular focus on immunomodulatory molecules, and the development of more dynamic, tissue-mimetic HyA-based hydrogels.

A photo-thermal dual crosslinked chitosan-based hydrogel membrane for guided bone regeneration

Alveolar bone defects caused by inflammation or trauma jeopardize patients' oral functions. Guided bone regeneration (GBR) is widely used in repairing periodontal tissue, with barrier membranes play a crucial role in preserving the bone regeneration space. In this study, an injectable dual-crosslinked hydrogel was developed to improve the existing barrier membranes in flexibility and functionality. The hydrogel matrix, composed of methacrylated carboxymethyl chitosan (CMCS) reinforced with robust silk fibroin (SF), was further functionalized with bioactive glass (BG) particles to promote bone regeneration. The pre-gel solution achieved a fast-curing process under visible light and at body temperature. Further, the composite hydrogels presented good biocompatibility, biodegradability, resilience, alongside in vitro barrier effect against human gingival fibroblasts (HGFs). It significantly enhanced osteogenic differentiation and angiogenesis of bone marrow mesenchymal stem cells (BMSCs), facilitate the tube formation of human umbilical vein endothelial cells (HUVECs), and inhibit Staphylococcus aureus and Porphyromonas gingivalis. In a rat skull defect model, the osteogenic performance of hydrogels was comparable with that of collagen membranes (Bio-Gide®). Overall, this in-situ gel-forming barrier material served as a stable carrier for bioactive ions and a biomineralized scaffold for tissue ingrowth, supporting the enhancement of GBR technique.

Quercetin prevents the loss of chondrogenic capacity in expansion cultured human auricular chondrocytes by alleviating mitochondrial dysfunction

Objective

To explore the characteristics of cellular senescence in human auricular chondrocytes during long-term in vitro culture and to evaluate the effects of anti-senescence treatments on enhancing their chondrogenic function.

Methods

Auricular chondrocytes exhibited senescence-related characteristics after prolonged expansion in culture. To identify senescence inducers, transcriptome sequencing was performed, with findings corroborated by transmission electron microscopy analyses. Quercetin was employed as an intervention to mitigate cellular senescence progression. The alterations in cellular senescence and mitochondrial function were evaluated. Regenerative cartilage tissue was developed through in vitro chondrogenic induction and in vivo implantation with GelMA hydrogel-loaded cells in nude mice. The impact of quercetin was substantiated through histological examinations.

Results

Mitochondrial dysfunction was a key characteristic of auricular chondrocytes after long-term expansion culture. Chondrocytes cultured with quercetin showed a lower proportion of senescent cells and reduced mitochondrial dysfunction. The chondrocytes cultured with continuous application of quercetin formed higher quality regenerative cartilage both in vitro and in vivo compared to the control group.

Conclusion

The results reveal that quercetin attenuates chondrocyte senescence by alleviating mitochondrial dysfunction, thereby preventing the loss of chondrogenic function in chondrocytes subjected to long-term expansion culture.

Lignin nanoparticle/MXene-based conductive hydrogel with mechanical robustness and strain-sensitivity property via rapid self-gelation process towards flexible sensor

Conductive hydrogels have been showcased with substantial potential for soft wearable devices. However, the tedious preparation process and poor trade-off among overall properties, i.e., mechanical and sensing performance, severely limits flexibility of electronics' applications. Herein, we have developed a rapid self-gelation system for achieving high-performance conductive hydrogel within several minutes at ambient condition. The rapid gelation mechanism is attributed to the hydroxyl radical species generated with the help of lignin nanoparticle-Mn+1 (Ag+, Ca2+, Mg2+, Al3+ and Fe3+) based on reversible redox reaction and MXene activization effect. By adjusting the material components, the cross-linked polymer network can be highly strengthened by multiple physical interactions and nano-reinforcement, strongly supporting the mechanical performance. Comparatively, Fe3+-based conductive hydrogel displays integrated merits of mechanical robustness, high stretchability and good electrical conductivity. Meanwhile, due to excellent mechanical and electrical performance, such hydrogel-based sensor possesses good sensing performance, i.e., high sensitivity (maximum GF: 1.08), cyclic reliability and wide work window (0-860 %), displaying promising application in strain-induced detection. Our sensors also produce stable and reliable signal output for signature/vocal recognition. Apparently, the strategy developed herein sets up an innovative concept for highly-efficient green fabricating advanced hydrogel materials for emerging wearable electronics.

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.

Multifunctional Adhesive Hydrogels: From Design to Biomedical Applications

Adhesive hydrogels characterized by structural properties similar to the extracellular matrix, excellent biocompatibility, controlled degradation, and tunable mechanical properties have demonstrated significant potential in biomedical applications, including tissue engineering, biosensors, and drug delivery systems. These hydrogels exhibit remarkable adhesion to target substrates and can be rationally engineered to meet specific requirements. In recent decades, adhesive hydrogels have experienced significant advancements driven by the introduction of numerous multifunctional design strategies. This review initially summarizes the chemical bond-based design strategies for tissue adhesion, encompassing static covalent bonds, dynamic covalent bonds, and non-covalent interactions. Subsequently, the multiple functionalities imparted by these diverse design strategies, including highly stretchable and tough performances, responsiveness to microenvironments, anti-freezing/heating properties, conductivity, antibacterial activity, and hemostatic properties are discussed. In addition, recent advances in the biomedical applications of adhesive hydrogels, focusing on tissue repair, drug delivery, medical devices, and wearable sensors are reviewed. Finally, the current challenges are highlighted and future trends in this rapidly evolving field are discussed.

Photoinitiator-free light-mediated crosslinking of dynamic polymer and pristine protein networks

Light-based patterning of synthetic and biological hydrogels enables precise spatial and temporal control over the formation of chemical bonds. However, photoinitiators are typically used to generate free radicals, which are detrimental to human cells. Here, we report a photoinitiator- and radical-free method based on ortho-nitrobenzyl alcohol (oNBA) photolysis, which gives rise to highly reactive nitroso and benzaldehyde groups. Synthetic hydrogel and pristine protein networks can rapidly form in the presence of these photo-generated reactive species. Thiol -oNBA bonds yield dynamic hydrogel networks (DHNs) via N-semimercaptal linkages that exhibit thixotropy, stress relaxation, and on-demand reversible gel-to-liquid transitions, while amine-oNBA bonds can be exploited to crosslink pristine proteins, such as gelatin and fibrinogen, by targeting their primary amines. Since this approach does not require incorporation of photoreactive moieties along the backbone, the resulting crosslinked proteins are well suited for bioadhesives. Our photoinitiator-free platform provides a versatile approach for rapidly creating synthetic and biological hydrogels for applications ranging from tissue engineering to biomedical devices.

Measurement of Covalent Bond Formation in Light-Curing Hydrogels Predicts Physical Stability under Flow

Photo-crosslinking hydrogels are promising for tissue engineering and regenerative medicine, but challenges in reaction monitoring often leave their optimization subject to trial and error. The stability of crosslinked gels under fluid flow, as in the case of a microfluidic device, is particularly challenging to predict, both because of obstacles inherent to solid-state macromolecular analysis that prevent accurate chemical monitoring and because stability is dependent on size of the patterned features. To solve both problems, we obtained 1H NMR spectra of cured hydrogels which were enzymatically degraded. This allowed us to take advantage of the high-resolution that solution NMR provides. This unique approach enabled the measurement of degree of cross-linking (DoC) and prediction of material stability under physiological fluid flow. We showed that NMR spectra of enzyme-digested gels successfully reported on DoC as a function of light exposure and wavelength within two classes of photo-cross-linkable hydrogels: methacryloyl-modified gelatin and a composite of thiol-modified gelatin and norbornene-terminated polyethylene glycol. This approach revealed that a threshold DoC was required for patterned features in each material to become stable and that smaller features required a higher DoC for stability. Finally, we demonstrated that DoC was predictive of the stability of architecturally complex features when photopatterning, underscoring the value of monitoring DoC when using light-reactive gels. We anticipate that the ability to quantify chemical cross-links will accelerate the design of advanced hydrogel materials for structurally demanding applications such as photopatterning and bioprinting.

Design Strategy, On-Demand Control, and Biomedical Engineering Applications of Wet Adhesion

The adhesion of tissues to external devices is fundamental to numerous critical applications in biomedical engineering, including tissue and organ repair, bioelectronic interfaces, adhesive robotics, wearable electronics, biomedical sensing and actuation, as well as medical monitoring, treatment, and healthcare. A key challenge in this context is that tissues are typically situated in aqueous and dynamic environments, which poses a bottleneck to further advancements in these fields. Wet adhesion technology (WAT) presents an effective solution to this issue. In this review, we summarize the three major design strategies and control methods of wet adhesion, comprehensively and systematically introducing the latest applications and advancements of WAT in the field of biomedical engineering. First, single adhesion mechanism under the frameworks of the three design strategies is systematically introduced. Second, control methods for adhesion are comprehensively summarized, including spatiotemporal control, detachment control, and reversible adhesion control. Third, a systematic summary and discussion of the latest applications of WAT in biomedical engineering research and education were presented, with a particular focus on innovative applications such as tissue-electronic interface devices, ingestible devices, end-effector components, in vivo medical microrobots, and medical instruments and equipment. Finally, opportunities and challenges encountered in the design and development of wet adhesives with advanced adhesive performance and application prospects are discussed.

Novel injectable adhesive hydrogel loaded with exosomes for holistic repair of hemophilic articular cartilage defect

Hemophilic articular cartilage damage presents a significant challenge for surgeons, characterized by recurrent intraarticular bleeding, a severe inflammatory microenvironment, and limited self-repair capability of cartilage tissue. Currently, there is a lack of tissue engineering-based integrated therapies that address both early hemostasis, anti-inflammation, and long-lasting chondrogenesis for hemophilic articular cartilage defects. Herein, we developed an adhesive hydrogel using oxidized chondroitin sulfate and gelatin, loaded with exosomes derived from bone marrow stem cells (BMSCs) (Hydrogel-Exos). This hydrogel demonstrated favorable injectability, self-healing, biocompatibility, biodegradability, swelling, frictional and mechanical properties, providing a comprehensive approach to treating hemophilic articular cartilage defects. The adhesive hydrogel, featuring dynamic Schiff base bonds and hydrogen bonds, exhibited excellent wet tissue adhesiveness and hemostatic properties. In a pig model, the hydrogel could be smoothly injected into the knee joint cartilage defect site and gelled in situ under fluid-irrigated arthroscopic conditions. Our in vitro and in vivo experiments confirmed that the sustained release of exosomes yielded anti-inflammatory effects by modulating macrophage M2 polarization through the NF-κB pathway. This immunoregulatory effect, coupled with the extracellular matrix components provided by the adhesive hydrogel, enhanced chondrogenesis, promoted the cartilage repair and joint function restoration after hemophilic articular cartilage defects. In conclusion, our results highlight the significant application potential of Hydrogel-Exos for early hemostasis, immunoregulation, and long-term chondrogenesis in hemophilic patients with cartilage injuries. This innovative approach is well-suited for application during arthroscopic procedures, offering a promising solution for addressing the complex challenges associated with hemophilic articular cartilage damage.

Magnetic Soft Catheter Robot System for Minimally Invasive Treatments of Articular Cartilage Defects

Articular cartilage defects are among the most common orthopedic diseases, which seriously affect patients' health and daily activities, without prompt treatment. The repair biocarrier-based treatment has shown great promise. Total joint injection and open surgery are two main methods to deliver functional repair biocarriers into the knee joint. However, the exhibited drawbacks of these methods hinder their utility. The repair effect of total joint injection is unstable due to the low targeting rate of the repair biocarriers, whereas open surgery causes serious trauma to patients, thereby prolonging the postoperative healing time. In this study, we develop a magnetic soft catheter robot (MSCR) system to perform precise in situ repair of articular cartilage defects with minimal incision. The MSCR processes a size of millimeters, allowing it to enter the joint cavity through a tiny skin incision to reduce postoperative trauma. Meanwhile, a hybrid control strategy combining neural network and visual servo is applied to sequentially complete the coarse and fine positioning of the MSCR on the cartilage defect sites. After reaching the target, the photosensitive hydrogel is injected and anchored into the defect sites through the MSCR, ultimately completing the in situ cartilage repair. The in vitro and ex vivo experiments were conducted on a 3D printed human femur model and an isolated porcine femur, respectively, to demonstrate the potential of our system for the articular cartilage repair.

Photocrosslinkable Biomaterials for 3D Bioprinting: Mechanisms, Recent Advances, and Future Prospects

Constructing scaffolds with the desired structures and functions is one of the main goals of tissue engineering. Three-dimensional (3D) bioprinting is a promising technology that enables the personalized fabrication of devices with regulated biological and mechanical characteristics similar to natural tissues/organs. To date, 3D bioprinting has been widely explored for biomedical applications like tissue engineering, drug delivery, drug screening, and in vitro disease model construction. Among different bioinks, photocrosslinkable bioinks have emerged as a powerful choice for the advanced fabrication of 3D devices, with fast crosslinking speed, high resolution, and great print fidelity. The photocrosslinkable biomaterials used for light-based 3D printing play a pivotal role in the fabrication of functional constructs. Herein, this review outlines the general 3D bioprinting approaches related to photocrosslinkable biomaterials, including extrusion-based printing, inkjet printing, stereolithography printing, and laser-assisted printing. Further, the mechanisms, advantages, and limitations of photopolymerization and photoinitiators are discussed. Next, recent advances in natural and synthetic photocrosslinkable biomaterials used for 3D bioprinting are highlighted. Finally, the challenges and future perspectives of photocrosslinkable bioinks and bioprinting approaches are envisaged.

Hydrogel-Enhanced Autologous Chondrocyte Implantation for Cartilage Regeneration-An Update on Preclinical Studies

Autologous chondrocyte implantation (ACI) and matrix-induced ACI (MACI) have demonstrated improved clinical outcomes and reduced revision rates for treating osteochondral and chondral defects. However, their ability to achieve lasting, fully functional repair remains limited. To overcome these challenges, scaffold-enhanced ACI, particularly utilizing hydrogel-based biomaterials, has emerged as an innovative strategy. These biomaterials are intended to mimic the biological composition, structural organization, and biomechanical properties of native articular cartilage. This review aims to provide comprehensive and up-to-date information on advancements in hydrogel-enhanced ACI from the past decade. We begin with a brief introduction to cartilage biology, mechanisms of cartilage injury, and the evolution of surgical techniques, particularly looking at ACI. Subsequently, we review the diversity of hydrogel scaffolds currently undergoing development and evaluation in preclinical studies for articular cartilage regeneration, emphasizing chondrocyte-laden hydrogels applicable to ACI. Finally, we address the key challenges impeding effective clinical translation, with particular attention to issues surrounding fixation and integration, aiming to inform and guide the future progression of tissue engineering strategies.

Robust tetra-armed poly (ethylene glycol)-based hydrogel as tissue bioadhesive for the efficient repair of meniscus tears

Repair and preservation of the injured meniscus has become paramount in clinical practice. However, the complexities of various clinic stitching techniques for meniscus repair pose challenges for grassroots doctors. Hence, there is a compelling interest in innovative therapeutic strategies such as bioadhesives. An ideal bioadhesive must cure quickly in aqueous and blood environments, bind strongly, endure arthroscopic washing pressures, and degrade appropriately for tissue regeneration. Here, we present a tetra-poly (ethylene glycol) (PEG)-based hydrogel bioadhesive, boasting high biocompatibility, ultrafast gelation, facile injectable operation, and favorable mechanical strength. In view of the synergistic effects of chemical anchor and physical chain entanglement to tightly bind the meniscus, a seamless interface was formed between the surrounding meniscal tissues and hydrogels, enabling the longitudinal tear of the meniscus fused in situ to withstand large tensile force with the adhesive strength of 541.5 ± 31.4 kPa and arthroscopic washout resistance of 29.4 kPa. Superior to existing commercial adhesives, ours allows sutureless application and arthroscopic assistance, without requiring specialized clinical skills. This research is expected to significantly impact our understanding of meniscal healing and ultimately promote a simpler process for achieving functional and structural recovery in torn menisci.

Self-adhesive poly-l-lysine/tannic acid hybrid hydrogel for synergistic antibacterial activity against biofilms

Biomedical implants are crucial for enhancing various human physiological functions. However, they are susceptible to microbial contamination after implantation, posing a risk of implant failure. To address this issue, hydrogel-based coatings are used, but achieving both effective antibacterial properties and stable adhesion remains challenging. This study introduces a hybrid hydrogel network made from Tannic Acid (TA) and Poly-l-Lysine (PLL), cross-linked through ionic and hydrogen bonds, which imparts adhesive and anti-infective properties. The physicochemical analysis revealed that the hydrogels exhibited significant porosity, favorable mechanical characteristics, and demonstrated in vitro enzymatic biodegradation. Moreover, the hydrogels demonstrated adhesion to various substrates, including Ti alloy with an adhesive strength of 42.5 kPa, and retained their integrity even after immersion in water for a minimum of 10 days. The modified Ti surfaces significantly reduced protein adsorption (∼70 %), indicating antifouling properties. The hydrogels prevented bacterial adhesion on titanium surfaces through a "contact-kill" mode of action and inhibited biofilm formation by around 94.5 % for Staphylococcus aureus and 90.8 % for Pseudomonas aeruginosa. The modified Ti retained biofilm inhibitory effects for at least six days without significant performance decline. In vitro cytotoxicity assay confirmed the biocompatibility of the hydrogels with NIH3T3 cells. Overall, these results highlight the competence of hybrid hydrogels as effective coatings for Ti implants, offering strong adhesion and biofilm prevention to mitigate implant-related infections.

Application of adhesives in the treatment of cartilage repair

From degeneration causing intervertebral disc issues to trauma‐induced meniscus tears, diverse factors can injure the different types of cartilage. This review highlights adhesives as a promising and rapidly implemented repair strategy. Compared to traditional techniques such as sutures and wires, adhesives offer several advantages. Importantly, they seamlessly connect with the injured tissue, deliver bioactive substances directly to the repair site, and potentially alleviate secondary problems like inflammation or degeneration. This review delves into the cutting‐edge advancements in adhesive technology, specifically focusing on their effectiveness in cartilage injury treatment and their underlying mechanisms. We begin by exploring the material characteristics of adhesives used in cartilage tissue, focusing on essential aspects like adhesion, biocompatibility, and degradability. Subsequently, we investigate the various types of adhesives currently employed in this context. Our discussion then moves to the unique role adhesives play in addressing different cartilage injuries. Finally, we acknowledge the challenges currently faced by this promising technology.

Introductory Review of Soft Implantable Bioelectronics Using Conductive and Functional Hydrogels and Hydrogel Nanocomposites

Interfaces between implantable bioelectrodes and tissues provide critical insights into the biological and pathological conditions of targeted organs, aiding diagnosis and treatment. While conventional bioelectronics, made from rigid materials like metals and silicon, have been essential for recording signals and delivering electric stimulation, they face limitations due to the mechanical mismatch between rigid devices and soft tissues. Recently, focus has shifted toward soft conductive materials, such as conductive hydrogels and hydrogel nanocomposites, known for their tissue-like softness, biocompatibility, and potential for functionalization. This review introduces these materials and provides an overview of recent advances in soft hydrogel nanocomposites for implantable electronics. It covers material strategies for conductive hydrogels, including both intrinsically conductive hydrogels and hydrogel nanocomposites, and explores key functionalization techniques like biodegradation, bioadhesiveness, injectability, and self-healing. Practical applications of these materials in implantable electronics are also highlighted, showcasing their effectiveness in real-world scenarios. Finally, we discuss emerging technologies and future needs for chronically implantable bioelectronics, offering insights into the evolving landscape of this field.

Mechanical Regulation of Polymer Gels

The mechanical properties of polymer gels devote to emerging devices and machines in fields such as biomedical engineering, flexible bioelectronics, biomimetic actuators, and energy harvesters. Coupling network architectures and interactions has been explored to regulate supportive mechanical characteristics of polymer gels; however, systematic reviews correlating mechanics to interaction forces at the molecular and structural levels remain absent in the field. This review highlights the molecular engineering and structural engineering of polymer gel mechanics and a comprehensive mechanistic understanding of mechanical regulation. Molecular engineering alters molecular architecture and manipulates functional groups/moieties at the molecular level, introducing various interactions and permanent or reversible dynamic bonds as the dissipative energy. Molecular engineering usually uses monomers, cross-linkers, chains, and other additives. Structural engineering utilizes casting methods, solvent phase regulation, mechanochemistry, macromolecule chemical reactions, and biomanufacturing technology to construct and tailor the topological network structures, or heterogeneous modulus compositions. We envision that the perfect combination of molecular and structural engineering may provide a fresh view to extend exciting new perspectives of this burgeoning field. This review also summarizes recent representative applications of polymer gels with excellent mechanical properties. Conclusions and perspectives are also provided from five aspects of concise summary, mechanical mechanism, biofabrication methods, upgraded applications, and synergistic methodology.

Injectable and in situ foaming shape-adaptive porous Bio-based polyurethane scaffold used for cartilage regeneration

Irregular articular cartilage injury is a common type of joint trauma, often resulting from intense impacts and other factors that lead to irregularly shaped wounds, the limited regenerative capacity of cartilage and the mismatched shape of the scaffods have contributed to unsatisfactory therapeutic outcomes. While injectable materials are a traditional solution to adapt to irregular cartilage defects, they have limitations, and injectable materials often lack the porous microstructures favorable for the rapid proliferation of cartilage cells. In this study, an injectable porous polyurethane scaffold named PU-BDO-Gelatin-Foam (PUBGF) was prepared. After injection into cartilage defects, PUBGF forms in situ at the site of the defect and exhibits a dynamic microstructure during the initial two weeks. This dynamic microstructure endows the scaffold with the ability to retain substances within its interior, thereby enhancing its capacity to promote chondrogenesis. Furthermore, the chondral repair efficacy of PUBGF was validated by directly injecting it into rat articular cartilage injury sites. The injectable PUBGF scaffold demonstrates a superior potential for promoting the repair of cartilage defects when compared to traditional porous polyurethane scaffolds. The substance retention ability of this injectable porous scaffold makes it a promising option for clinical applications.

Collagen-based hydrogels induce stem cell chondrogenesis and hyaline cartilage regeneration: an in vivo study

Injectable, self-crosslinking collagen-based hydrogels are beneficial for chondrocytes to secrete matrix, positioning them as promising candidates for cartilage tissue engineering. However, previous studies lacked insight into the ability of cell-free collagen-based hydrogels to regenerate hyaline cartilage defect. Therefore, this study aimed to evaluate the potential of collagen-based hydrogels (Col and ColHA) to induce chondrogenic differentiation of stem cells and in situ hyaline cartilage regeneration. Both Col and ColHA hydrogels self-crosslinked in situ and exhibited similar physical properties. In vitro experiments showed they supported the survival, adhesion, spreading, and proliferation of bone marrow stem cells (BMSCs). Moreover, both hydrogels induced ectopic differentiation of BMSCs into chondrocytes when implanted subcutaneously into the back of nude mice. ColHA hydrogel notably enhanced type II collagen secretion. The results of repairing cartilage defects in situ revealed both hydrogels facilitated hyaline cartilage regeneration and maintained cartilage phenotype without exogenous BMSCs. Hydrogels encapsulating BMSCs expedited cartilage repair, and ColHA/BMSC constructs showed better mechanical properties, suggesting their potential for cartilage repair applications. This study implies that collagen-based hydrogels are good candidates for hyaline cartilage regeneration.

Mussel-Inspired Injectable Adhesive Hydrogels for Biomedical Applications

The impressive adhesive capacity of marine mussels has inspired various fascinating designs in biomedical fields. Mussel-inspired injectable adhesive hydrogels, as a type of promising mussel-inspired material, have attracted much attention due to their minimally invasive property and desirable functions provided by mussel-inspired components. In recent decades, various mussel-inspired injectable adhesive hydrogels have been designed and widely applied in numerous biomedical fields. The rational incorporation of mussel-inspired catechol groups endows the injectable hydrogels with the potential to exhibit many properties, including tissue adhesiveness and self-healing, antimicrobial, and antioxidant capabilities, broadening the applications of injectable hydrogels in biomedical fields. In this review, we first give a brief introduction to the adhesion mechanism of mussels and the characteristics of injectable hydrogels. Further, the typical design strategies of mussel-inspired injectable adhesive hydrogels are summarized. The methodologies for integrating catechol groups into polymers and the crosslinking methods of mussel-inspired hydrogels are discussed in this section. In addition, we systematically overview recent mussel-inspired injectable adhesive hydrogels for biomedical applications, with a focus on how the unique properties of these hydrogels benefit their applications in these fields. The challenges and perspectives of mussel-inspired injectable hydrogels are discussed in the last section. This review may provide new inspiration for the design of novel bioinspired injectable hydrogels and facilitate their application in various biomedical fields.

Polysaccharide-protein based scaffolds for cartilage repair and regeneration

Cartilage repair and regeneration have become a global issue that millions of patients from all over the world need surgical intervention to repair the articular cartilage annually due to the limited self-healing capability of the cartilage tissues. Cartilage tissue engineering has gained significant attention in cartilage repair and regeneration by integration of the chondrocytes (or stem cells) and the artificial scaffolds. Recently, polysaccharide-protein based scaffolds have demonstrated unique and promising mechanical and biological properties as the artificial extracellular matrix of natural cartilage. In this review, we summarize the modification methods for polysaccharides and proteins. The preparation strategies for the polysaccharide-protein based hydrogel scaffolds are presented. We discuss the mechanical, physical and biological properties of the polysaccharide-protein based scaffolds. Potential clinical translation and challenges on the artificial scaffolds are also discussed.

Measurement of covalent bond formation in light-curing hydrogels predicts physical stability under flow

Photocrosslinking hydrogels are promising for tissue engineering and regenerative medicine, but challenges in reaction monitoring often leave their optimization subject to trial and error. The stability of crosslinked gels under fluid flow, as in the case of a microfluidic device, is particularly challenging to predict, both because of obstacles inherent to solid-state macromolecular analysis that prevent accurate chemical monitoring, and because stability is dependent on size of the patterned features. To solve both problems, we obtained 1H NMR spectra of cured hydrogels which were enzymatically degraded. This allowed us to take advantage of the high-resolution that solution NMR provides. This unique approach enabled the measurement of degree of crosslinking (DoC) and prediction of material stability under physiological fluid flow. We showed that NMR spectra of enzyme-digested gels successfully reported on DoC as a function of light exposure and wavelength within two classes of photocrosslinkable hydrogels: methacryloyl-modified gelatin and a composite of thiol-modified gelatin and norbornene-terminated polyethylene glycol. This approach revealed that a threshold DoC was required for patterned features in each material to become stable, and that smaller features required a higher DoC for stability. Finally, we demonstrated that DoC was predictive of the stability of architecturally complex features when photopatterning, underscoring the value of monitoring DoC when using light-reactive gels. We anticipate that the ability to quantify chemical crosslinks will accelerate the design of advanced hydrogel materials for structurally demanding applications such as photopatterning and bioprinting.

Carbene-mediated gelatin and hyaluronic acid hydrogel paints with ultra adhesive ability for arthroscopic cartilage repair

In articular cartilage defect, particularly in arthroscopy, regenerative hydrogels are urgently needed. It should be able to firmly adhere to the cartilage tissue and maintain sufficient mechanical strength to withstand approximately 10 kPa of arthroscopic hydraulic flushing. In this study, we report a carbene-mediated ultra adhesive hybrid hydrogel paints for arthroscopic cartilage repair, which combined the photo initiation of double crosslinking system with the addition of diatomite, as a further reinforcing agent and biological inorganic substances. The double network consisting of ultraviolet initiated polymerization of hyaluronic acid methacrylate (HAMA) and carbene insertion chemistry of diazirine-grafted gelatin (GelDA) formed an ultra-strong adhesive hydrogel paint (H2G5DE). Diatomite helped the H2G5DE hydrogel paint firmly adhere to the cartilage defect, withstanding nearly 100 kPa of hydraulic pressure, almost 10 times that in clinical arthroscopy. Furthermore, the H2G5DE hydrogel supported cell growth, proliferation, and migration, thus successfully repairing cartilage defects. Overall, this study demonstrates a proof-of-concept of ultra-adhesive polysaccharide hydrogel paints, which can firmly adhere to the articular cartilage defects, can resist continuous hydraulic pressure, can promote effective cartilage regeneration, and is very suitable for minimally invasive arthroscopy.

In Situ Rapid-Formation Sprayable Hydrogels for Challenging Tissue Injury Management

Rapid-acting, convenient, and broadly applicable medical materials are in high demand for the treatment of extensive and intricate tissue injuries in extremely medical scarcity environment, such as battlefields, wilderness, and traffic accidents. Conventional biomaterials fail to meet all the high criteria simultaneously for emergency management. Here, a multifunctional hydrogel system capable of rapid gelation and in situ spraying, addressing clinical challenges related to hemostasis, barrier establishment, support, and subsequent therapeutic treatment of irregular, complex, and urgent injured tissues, is designed. This hydrogel can be fast formed in less than 0.5 s under ultraviolet initiation. The precursor maintains an impressively low viscosity of 0.018 Pa s, while the hydrogel demonstrates a storage modulus of 0.65 MPa, achieving the delicate balance between sprayable fluidity and the mechanical strength requirements in practice, allowing flexible customization of the hydrogel system for differentiated handling and treatment of various tissues. Notably, the interactions between the component of this hydrogel and the cell surface protein confer upon its inherently bioactive functionalities such as osteogenesis, anti-inflammation, and angiogenesis. This research endeavors to provide new insights and designs into emergency management and complex tissue injuries treatment.

Anisotropic Liesegang pattern for the nonlinear elastic biomineral-hydrogel complex

The Liesegang pattern is a beautiful natural anisotropic patterning phenomenon observed in rocks and sandstones. This study reveals that the Liesegang pattern can induce nonlinear elasticity. Here, a Liesegang-patterned complex with biomineral-hydrogel repetitive layers is prepared. This Liesegang-patterned complex is obtained only when the biomineralization is performed under the supersaturated conditions. The Liesegang-patterned complex features a nonlinear elastic response, whereas a complex with a single biomineral shell shows a linear behavior, thus demonstrating that the Liesegang pattern is essential in achieving nonlinear elasticity. The stiff biomineral layers have buffered the concentrated energy on behalf of soft hydrogels, thereby exposing the hydrogel components to reduced stress and, in turn, enabling them to perform the elasticity continuously. Moreover, the nonlinear elastic Liesegang-patterned complex exhibits excellent stress relaxation to the external loading, which is the biomechanical characteristic of cartilage. This stress relaxation allows the bundle of fiber-type Liesegang-patterned complex to endure greater deformation.

X-ray-activated polymerization expanding the frontiers of deep-tissue hydrogel formation

Photo-crosslinking polymerization stands as a fundamental pillar in the domains of chemistry, biology, and medicine. Yet, prevailing strategies heavily rely on ultraviolet/visible (UV/Vis) light to elicit in situ crosslinking. The inherent perils associated with UV radiation, namely the potential for DNA damage, coupled with the limited depth of tissue penetration exhibited by UV/Vis light, severely restrict the scope of photo-crosslinking within living organisms. Although near-infrared light has been explored as an external excitation source, enabling partial mitigation of these constraints, its penetration depth remains insufficient, particularly within bone tissues. In this study, we introduce an approach employing X-ray activation for deep-tissue hydrogel formation, surpassing all previous boundaries. Our approach harnesses a low-dose X-ray-activated persistent luminescent phosphor, triggering on demand in situ photo-crosslinking reactions and enabling the formation of hydrogels in male rats. A breakthrough of our method lies in its capability to penetrate deep even within thick bovine bone, demonstrating unmatched potential for bone penetration. By extending the reach of hydrogel formation within such formidable depths, our study represents an advancement in the field. This application of X-ray-activated polymerization enables precise and safe deep-tissue photo-crosslinking hydrogel formation, with profound implications for a multitude of disciplines.

Intelligent and Bioactive Osseointegration of the Implanted Piezoelectric Bone Cement with the Host Bone Is Realized by Biomechanical Energy

Poly methyl methacrylate (PMMA) bone cement is widely used in orthopedic surgeries, including total hip/knee arthroplasty and vertebral compression fracture treatment. However, loosening due to bone resorption is a common mid-to-late complication. Therefore, developing bioactive bone cement that promotes bone growth and integration is key to reducing aseptic loosening. In this study, we developed a piezoelectric bone cement comprising PMMA and BaTiO3 with excellent electrobioactivity and further analyzed its ability to promote bone integration. Experiments demonstrate that the PMMA and 15 wt % BaTiO3 cement generated an open-circuit voltage of 37.109 V under biomimetic mechanical stress, which effectively promoted bone regeneration and interfacial bone integration. In vitro experiments showed that the protein expression levels of ALP and RUNX-2 in the 0.65 Hz and 20 min group increased by 1.74 times and 2.31 times. In vivo experiments confirmed the osteogenic ability of PMMA and 15 wt % BaTiO3, with the increment of bone growth in the non-movement and movement groups being 4.67 and 4.64 times, respectively, at the second month after surgery. Additionally, Fluo-4 AM fluorescence staining and protein blotting experiments verified that PMMA and 15 wt % BaTiO3 electrical stimulation promoted osteogenic differentiation of BMSCs by activating calcium-sensitive receptors and increasing calcium ion inflow by 1.41 times when the stimulation reached 30 min. Therefore, piezoelectric bioactive PMMA and 15 wt % BaTiO3 cement has excellent application value in orthopedic surgery systems where stress transmission is prevalent.

Advances in Polysaccharides for Cartilage Tissue Engineering Repair: A Review

Cartilage repair has been a significant challenge in orthopedics that has not yet been fully resolved. Due to the absence of blood vessels and the almost cell-free nature of mature cartilage tissue, the limited ability to repair cartilage has resulted in significant socioeconomic pressures. Polysaccharide materials have recently been widely used for cartilage tissue repair due to their excellent cell loading, biocompatibility, and chemical modifiability. They also provide a suitable microenvironment for cartilage repair and regeneration. In this Review, we summarize the techniques used clinically for cartilage repair, focusing on polysaccharides, polysaccharides for cartilage repair, and the differences between these and other materials. In addition, we summarize the techniques of tissue engineering strategies for cartilage repair and provide an outlook on developing next-generation cartilage repair and regeneration materials from polysaccharides. This Review will provide theoretical guidance for developing polysaccharide-based cartilage repair and regeneration materials with clinical applications for cartilage tissue repair and regeneration.

Injectable Bioadhesive Photocrosslinkable Hydrogels with Sustained Release of Kartogenin to Promote Chondrogenic Differentiation and Partial-Thickness Cartilage Defects Repair

Partial-thickness cartilage defect (PTCD) is a common and formidable clinical challenge without effective therapeutic approaches. The inherent anti-adhesive characteristics of the extracellular matrix within cartilage pose a significant impediment to the integration of cells or biomaterials with the native cartilage during cartilage repair. Here, an injectable photocrosslinked bioadhesive hydrogel, consisting of gelatin methacryloyl (GM), acryloyl-6-aminocaproic acid-g-N-hydroxysuccinimide (AN), and poly(lactic-co-glycolic acid) microspheres loaded with kartogenin (KGN) (abbreviated as GM/AN/KGN hydrogel), is designed to enhance interfacial integration and repair of PTCD. After injected in situ at the irregular defect, a stable and robust hydrogel network is rapidly formed by ultraviolet irradiation, and it can be quickly and tightly adhered to native cartilage through amide bonds. The hydrogel exhibits good adhesion strength up to 27.25 ± 1.22 kPa by lap shear strength experiments. The GM/AN/KGN hydrogel demonstrates good adhesion, low swelling, resistance to fatigue, biocompatibility, and chondrogenesis properties in vitro. A rat model with PTCD exhibits restoration of a smoother surface, stable seamless integration, and abundant aggrecan and type II collagen production. The injectable stable adhesive hydrogel with long-term chondrogenic differentiation capacity shows great potential to facilitate repair of PTCD.

Injectable silk fibroin peptide nanofiber hydrogel composite scaffolds for cartilage regeneration

Transforming growth factor-β1 (TGF-β1) is essential for cartilage regeneration, but its susceptibility to enzymatic denaturation and high cost limit its application. Herein, we report Ac-LIANAKGFEFEFKFK-NH2 (LKP), a self-assembled peptide nanofiber hydrogel that can mimic the function of TGF-β1. The LKP hydrogel is simple to synthesize, and in vitro experiments confirmed its good biocompatibility and cartilage-promoting ability. However, LKP hydrogels suffer from poor mechanical properties and are prone to fragmentation; therefore, we prepared a series of injectable hydrogel composite scaffolds (SF-GMA/LKP) by combining LKP with glycidyl methacrylate (GMA)-modified silk fibroin (SF). SF-GMA/LKP composite scaffolds instantaneously induced in-situ filling of cartilage defects and, at the same time, relied on the interaction between LKP and SF-GMA interaction to prolong the duration of action of LKP. The SF-GMA/LKP10 and SF-GMA/LKP20 composite scaffolds had the best effect on neocartilage and subchondral bone reconstruction. This composite hydrogel scaffold can be used for high-quality cartilage repair.

Silk fibroin hydrogel adhesive enables sealed-tight reconstruction of meniscus tears

Despite orientationally variant tears of the meniscus, suture repair is the current clinical gold treatment. However, inaccessible tears in company with re-tears susceptibility remain unresolved. To extend meniscal repair tools from the perspective of adhesion and regeneration, we design a dual functional biologic-released bioadhesive (S-PIL10) comprised of methacrylated silk fibroin crosslinked with phenylboronic acid-ionic liquid loading with growth factor TGF-β1, which integrates chemo-mechanical restoration with inner meniscal regeneration. Supramolecular interactions of β-sheets and hydrogen bonds richened by phenylboronic acid-ionic liquid (PIL) result in enhanced wet adhesion, swelling resistance, and anti-fatigue capabilities, compared to neat silk fibroin gel. Besides, elimination of reactive oxygen species (ROS) by S-PIL10 further fortifies localized meniscus tear repair by affecting inflammatory microenvironment with dynamic borate ester bonds, and S-PIL10 continuously releases TGF-β1 for cell recruitment and bridging of defect edge. In vivo rabbit models functionally evidence the seamless and dense reconstruction of torn meniscus, verifying that the concept of meniscus adhesive is feasible and providing a promising revolutionary strategy for preclinical research to repair meniscus tears.

A Visible Light Cross-Linked Underwater Hydrogel Adhesive with Biodegradation and Hemostatic Ability

Hydrogel adhesives with integrated functionalities are still required to match their ever-expanding practical applications in the field of tissue repair and regeneration. A simple and effective safety strategy is reported, involving an in situ injectable polymer precursor and visible light-induced cross-linking. This strategy enables the preparation of a hydrogel adhesive in a physiological environment, offering wet adhesion to tissue surfaces, molecular flexibility, biodegradability, biocompatibility, efficient hemostatic performance, and the ability to facilitate liver injury repair. The proposed one-step preparation process of this polymer precursor involves the mixing of gelatin methacryloyl (GelMA), poly(thioctic acid) [P(TA)], poly(acrylic acid)/amorphous calcium phosphate (PAAc/ACP, PA) and FDA-approved photoinitiator solution, and a subsequent visible light irradiation after in situ injection into target tissues that resulted in a chemically-physically cross-linked hybrid hydrogel adhesive. Such a combined strategy shows promise for medical scenarios, such as uncontrollable post-traumatic bleeding.

Network of cyano-p-aramid nanofibres creates ultrastiff and water-rich hydrospongels

The structure-property paradox of biological tissues, in which water-rich porous structures efficiently transfer mass while remaining highly mechanically stiff, remains unsolved. Although hydrogel/sponge hybridization is the key to understanding this phenomenon, material incompatibility makes this a challenging task. Here we describe hydrogel/sponge hybrids (hydrospongels) that behave as both ultrastiff water-rich gels and reversibly squeezable sponges. The self-organizing network of cyano-p-aramid nanofibres holds approximately 5,000 times more water than its solid content. Hydrospongels, even at a water concentration exceeding 90 wt%, are hard as cartilage with an elastic modulus of 50-80 MPa, and are 10-1,000 times stiffer than typical hydrogels. They endure a compressive strain above 85% through poroelastic relaxation and hydrothermal pressure at 120 °C. This performance is produced by amphiphilic surfaces, high rigidity and an interfibrillar, interaction-driven percolating network of nanofibres. These features can inspire the development of future biofunctional materials.

A guanosine/konjac glucomannan supramolecular hydrogel with antioxidant, antibacterial and immunoregulatory properties for cutaneous wound treatment

Developing naturally-derived wound dressing materials with intrinsic therapeutic effects is desirable for the clinical applications. Recently, guanosine-based supramolecular G-quadruplex (G4) hydrogel exhibited great potential in preparing biological materials due to its simple fabrication method and responsive gel networks. However, the weak mechanical properties and the consequent burst release of bioactive molecules restrict its clinical applications. Herein, we found that konjac glucomannan (KGM) with immunoregulatory effect did not affect the self-assembly of G-quadruplexes and thus effectively enhancing the mechanical properties of G4 hydrogel. Aloin, as a model drug, was in situ loaded into gel networks, finally obtaining the G4/Aloin-KGM hydrogel. This hydrogel exhibited porous morphology, swelling ability and hemostatic capability. Boronate bonds in G4 networks and aloin collectively endowed the hydrogel with excellent antioxidant performance. Meanwhile, aloin also provided outstanding in vitro and in vivo bactericidal ability. The wounds treated with this biocompatible hydrogel demonstrated faster regeneration of epithelial and dermal tissues, and the whole wound healing stages were accelerated by promoting collagen deposition, facilitating macrophage polarization towards M2 phenotype, down-regulating the expression level of IL-6, and up-regulating the expression level of IL-10, CD31 and α-SMA.

Tough double network hydrogels with rapid self-reinforcement and low hysteresis based on highly entangled networks

Most tough hydrogels are reinforced by introducing energy dissipation mechanisms, but simultaneously realizing a high toughness and low hysteresis is challenging because the energy dissipation structure cannot recover rapidly. In this work, high mechanical performance highly entangled double network hydrogels without energy dissipation structure are fabricated, in which physical entanglements act as the primary effective crosslinking in the first network. This sliding entanglement structure allows the hydrogel network to form a highly uniform oriented structure during stretching, resulting in a high tensile strength of ~3 MPa, a fracture energy of 8340 J m-2 and a strain-stiffening capability of 47.5 in 90% water content. Moreover, almost 100% reversibility is obtained in this hydrogel via energy storage based on entropy loss. The highly entangled double network structure not only overcomes the typical trade-off between the high toughness and low hysteresis of hydrogels, but more importantly, it provides an insight into the application of entanglement structures in high-performance hydrogels.

Instant trachea reconstruction using 3D-bioprinted C-shape biomimetic trachea based on tissue-specific matrix hydrogels

Currently, 3D-bioprinting technique has emerged as a promising strategy to offer native-like tracheal substitutes for segmental trachea reconstruction. However, there has been very limited breakthrough in tracheal repair using 3D-bioprinted biomimetic trachea owing to the lack of ideal bioinks, the requirement for precise structural biomimicking, and the complexity of multi-step surgical procedures by mean of intramuscular pre-implantation. Herein, we propose a one-step surgical technique, namely direct end-to-end anastomosis using C-shape 3D-bioprinted biomimetic trachea, for segmental trachea defect repair. First, two types of tissue-specific matrix hydrogels were exploited to provide mechanical and biological microenvironment conducive to the specific growth ways of cartilage and fibrous tissue respectively. In contrast to our previous O-shape tracheal design, the tubular structure of alternating C-shape cartilage rings and connecting vascularized-fibrous-tissue rings was meticulously designed for rapid 3D-bioprinting of tracheal constructs with optimal printing paths and models. Furthermore, in vivo trachea regeneration in nude mice showed satisfactory mechanical adaptability and efficient physiological regeneration. Finally, in situ segmental trachea reconstruction by direct end-to-end anastomosis in rabbits was successfully achieved using 3D-bioprinted C-shape biomimetic trachea. This study demonstrates the potential of advanced 3D-bioprinting for instant and efficient repair of segmental trachea defects.

Photo-Controllable Smart Hydrogels for Biomedical Application: A Review

Nowadays, smart hydrogels are being widely studied by researchers because of their advantages such as simple preparation, stable performance, response to external stimuli, and easy control of response behavior. Photo-controllable smart hydrogels (PCHs) are a class of responsive hydrogels whose physical and chemical properties can be changed when stimulated by light at specific wavelengths. Since the light source is safe, clean, simple to operate, and easy to control, PCHs have broad application prospects in the biomedical field. Therefore, this review timely summarizes the latest progress in the PCHs field, with an emphasis on the design principles of typical PCHs and their multiple biomedical applications in tissue regeneration, tumor therapy, antibacterial therapy, diseases diagnosis and monitoring, etc. Meanwhile, the challenges and perspectives of widespread practical implementation of PCHs are presented in biomedical applications. This study hopes that PCHs will flourish in the biomedical field and this review will provide useful information for interested researchers.

Photo-Cross-Linkable, Injectable, and Highly Adhesive GelMA-Glycol Chitosan Hydrogels for Cartilage Repair

Hydrogels provide a promising platform for cartilage repair and regeneration. Although hydrogels have shown some efficacy, they still have shortcomings including poor mechanical properties and suboptimal integration with surrounding cartilage. Herein, hydrogels that are injectable, cytocompatible, mechanically robust, and highly adhesive to cartilage are developed. This approach uses GelMA-glycol chitosan (GelMA-GC) that is crosslinkable with visible light and photoinitiators (lithium acylphosphinate and tris (2,2'-bipyridyl) dichlororuthenium (II) hexahydrate ([RuII(bpy)3 ]2+ and sodium persulfate (Ru/SPS)). Ru/SPS-cross-linked hydrogels have higher compressive and tensile modulus, and most prominently higher adhesive strength with cartilage, which also depends on inclusion of GC. Tensile and push-out tests of the Ru/SPS-cross-linked GelMA-GC hydrogels demonstrate adhesive strength of ≈100 and 46 kPa, respectively. Hydrogel precursor solutions behave in a Newtonian manner and are injectable. After injection in focal bovine cartilage defects and in situ cross-linking, this hydrogel system remains intact and integrated with cartilage following joint manipulation ex vivo. Cells remain viable (>85%) in the hydrogel system and further show tissue regeneration potential after three weeks of in vitro culture. These preliminary results provide further motivation for future research on bioadhesive hydrogels for cartilage repair and regeneration.

Ultra-durable cell-free bioactive hydrogel with fast shape memory and on-demand drug release for cartilage regeneration

Osteoarthritis is a worldwide prevalent disease that imposes a significant socioeconomic burden on individuals and healthcare systems. Achieving cartilage regeneration in patients with osteoarthritis remains challenging clinically. In this work, we construct a multiple hydrogen-bond crosslinked hydrogel loaded with tannic acid and Kartogenin by polyaddition reaction as a cell-free scaffold for in vivo cartilage regeneration, which features ultra-durable mechanical properties and stage-dependent drug release behavior. We demonstrate that the hydrogel can withstand 28000 loading-unloading mechanical cycles and exhibits fast shape memory at body temperature (30 s) with the potential for minimally invasive surgery. We find that the hydrogel can also alleviate the inflammatory reaction and regulate oxidative stress in situ to establish a microenvironment conducive to healing. We show that the sequential release of tannic acid and Kartogenin can promote the migration of bone marrow mesenchymal stem cells into the hydrogel scaffold, followed by the induction of chondrocyte differentiation, thus leading to full-thickness cartilage regeneration in vivo. This work may provide a promising solution to address the problem of cartilage regeneration.

Four-dimensional hydrogel dressing adaptable to the urethral microenvironment for scarless urethral reconstruction

The harsh urethral microenvironment (UME) after trauma severely hinders the current hydrogel-based urethral repair. In fact, four-dimensional (4D) consideration to mimic time-dependent physiological processes is essential for scarless urethral reconstruction, which requires balancing extracellular matrix (ECM) deposition and remodeling at different healing stages. In this study, we develop a UME-adaptable 4D hydrogel dressing to sequentially provide an early-vascularized microenvironment and later-antifibrogenic microenvironment for scarless urethral reconstruction. With the combination of dynamic boronic ester crosslinking and covalent photopolymerization, the resultant gelatin methacryloyl phenylboronic acid/cis-diol-crosslinked (GMPD) hydrogels exhibit mussel-mimetic viscoelasticity, satisfactory adhesion, and acid-reinforced stability, which can adapt to harsh UME. In addition, a temporally on-demand regulatory (TOR) technical platform is introduced into GMPD hydrogels to create a time-dependent 4D microenvironment. As a result, physiological urethral recovery is successfully mimicked by means of an early-vascularized microenvironment to promote wound healing by activating the vascular endothelial growth factor (VEGF) signaling pathway, as well as a later-antifibrogenic microenvironment to prevent hypertrophic scar formation by timing transforming growth factor-β (TGFβ) signaling pathway inhibition. Both in vitro molecular mechanisms of the physiological healing process and in vivo scarless urethral reconstruction in a rabbit model are effectively verified, providing a promising alternative for urethral injury treatment.

Microgel-Modified Bilayered Hydrogels Dramatically Boosting Load-Bearing and Lubrication

Hydrogel-based articular cartilage replacement materials are promising candidates for their potential to provide both high load-bearing capacity and low friction performance, similar to natural cartilage. Nevertheless, the design of these materials presents a significant challenge in reconciling the conflicting demands of the load-bearing capacity and lubrication. Despite extensive research in this area, there is still room for improvement in the creation of hydrogel-based materials that effectively meet these demands. Herein, a facile strategy is provided to realize simultaneously high load-bearing and low friction properties on the proposed hydrogel by modifying the surface of mechanically strong annealled PVA-PAAc hydrogel with a high hydration potential PAAm-co-PAMPS microgel. Consequently, a bilayer hydrogel with a porous surface and a compact substrate has been obtained. Compressive experiments confirmed that the bilayer hydrogel exhibited excellent mechanical strength with a compressive strength of 32.23 MPa at 90% strain. A high load-bearing (applied load up to 30 N), extremely low friction coefficiency (0.01-0.05) and excellent wear resistance (COF low to 0.03 after a 4 h test at 10 N using a steel ball as the contact pair) are successfully achieved. These findings provide new perspectives for the design of articular cartilage materials.