Bone/cartilage targeted hydrogel: Strategies and applications

Multifunctional piezoelectric hydrogels under ultrasound stimulation boost chondrogenesis by recruiting autologous stem cells and activating the Ca2+/CaM/CaN signaling pathway

Articular cartilage, owing to the lack of undifferentiated stem cells after injury, faces significant challenges in reconstruction and repair, making it a major clinical challenge. Therefore, there is an urgent need to design a multifunctional hydrogels capable of recruiting autologous stem cells to achieve in situ cartilage regeneration. Here, our study investigated the potential of a piezoelectric hydrogel (Hyd6) for enhancing cartilage regeneration through ultrasound (US) stimulation. Hyd6 has multiple properties including injectability, self-healing capabilities, and piezoelectric characteristics. These properties synergistically promote stem cell chondrogenesis. The fabrication and characterization of Hyd6 revealed its excellent biocompatibility, biodegradability, and electromechanical conversion capabilities. In vitro and in vivo experiments revealed that Hyd6, when combined with US stimulation, significantly promotes the recruitment of autologous stem cells and enhances chondrogenesis by generating electrical signals that promote the influx of Ca2+, activating downstream CaM/CaN signaling pathways and accelerating cartilage formation. An in vivo study in a rabbit model of chondral defects revealed that Hyd6 combined with US treatment significantly improved cartilage regeneration, as evidenced by better integration of the regenerated tissue with the surrounding cartilage, greater collagen type II expression, and improved mechanical properties. The results highlight the potential of Hyd6 as a novel therapeutic approach for treating cartilage injuries, offering a self-powered, noninvasive, and effective strategy for tissue engineering and regenerative medicine.

HAMA-SBMA hydrogel with anti-inflammatory properties delivers cartilage organoids, boosting cartilage regeneration

Cartilage tissue lacks blood supply, which limits its ability to self-repair. Cartilage organoid (CO) technology, which replicates the structure and function of cartilage, holds significant promise. However, it is essential to maintain cellular function and ensure secure fixation at the site of injury. Therefore, we loaded allogeneic bone marrow mesenchymal stem cells (BMSCs) onto decellularized extracellular matrix microparticles of porcine articular cartilage (CEP) to construct CO-CCO, which demonstrated characteristics of articular cartilage. Additionally, betaine sulfonate methacrylate (SBMA) was incorporated into hyaluronic acid methacrylate (HAMA) to synthesize a novel hydrogel, HAMA-SBMA (HS), characterized by its adhesive properties, promotion of chondrogenesis, and inhibition of inflammation. In Vivo studies revealed that the combination of HS and CCO (HS + CCO) exhibited excellent repair efficacy in both rat and sheep models of cartilage defects. Mechanistically, we found that HS + CCO promoted cartilage repair by activating the Frizzled-related protein (Frzb), which inhibited inflammatory factors and enhanced the expression of the adhesion factor integrin ɑ5β1. This strategy, which combines hydrogels and organoids, enhances cartilage repair, offering substantial potential for clinical applications in cartilage regeneration.

Chondrocyte-targeted α-Solanine through HIF-1α regulating glycolysis to reduce the ferroptosis of chondrocyte in osteoarthritis

α-Solanine, a glycoalkaloid (GA) extracted from the stems of the potato plant, exhibits bioactivity and medicinal potential that necessitate further investigation. The impact and underlying mechanisms of α-Solanine on osteoarthritis (OA) remain to be elucidated. To achieve enhanced therapeutic outcomes, we have designed and synthesized a UIO-66-NH2@α-Solanine@PEI charged particle (USP) that amplifies the therapeutic effects of α-Solanine, demonstrating superior efficacy. Our approach involved the synthesis of a novel drug delivery system, the USP, to augment the therapeutic potential of α-Solanine in the treatment of OA. An OA rat model was established, and USP treatment was administered. The therapeutic effects were verified through histochemical staining and micro-CT. In vitro, α-Solanine significantly suppressed the expression of proteins related to glycolysis and notably inhibited ferroptosis. RNA sequencing revealed hypoxia-inducible factor-1α (HIF-1α) as a potential pathway mediating the effects of α-Solanine, and it was found that the co-addition of cycloheximide (CHX) led to a shortened decay time of HIF-1α. In vivo, rats with OA demonstrated significant inhibition of glycolysis and ferroptosis following treatment with USP, along with improvements in OA characteristics. These findings suggest that α-Solanine can inhibit the intense glycolysis associated with OA via the HIF-1α pathway and alleviate ferroptosis in chondrocytes. Treatment with USP demonstrated superior efficacy in the management of OA, providing a new therapeutic strategy for the disease.

Hydrogel Containing Bismuth Molybdate Nanosheets with Piezoelectricity and Nanoenzyme Activity for Promoting Osteoblast Responses

The development of piezoelectric biomaterials with the capability to produce electrical signals and scavenge reactive oxygen species (ROS) is a novel strategy for stimulating osteoblast responses and promoting bone regeneration. Herein, tungsten (W), iridium (Ir), and ruthenium (Ru) codoped bismuth molybdate (4(W/Ru/Ir)-BMO) nanosheets with improved piezoelectricity and enzyme-like (CAT-like and SOD-like) activities were constructed by using the hydrothermal method. A composite hydrogel of oxidized sodium alginate/gelatin (OSA/GEL) and 4(W/Ru/Ir)-BMO (OSA/GEL/4-B) was also prepared. Due to the presence of 4(W/Ru/Ir)-BMO, OSA/GEL/4-B exhibited not only piezoelectricity but also enzyme-like activities. Under ultrasound (US), OSA/GEL/4-B generated electrical signals that significantly promoted the proliferation and osteogenic differentiation of bone marrow stromal cells. Furthermore, the piezoelectric effect of OSA/GEL/4-B improved the CAT-like (production of oxygen) and SOD-like (scavenger of ROS) activities. The improved piezoelectricity of 4(W/Ru/Ir)-BMO was attributed to the codoping of W, Ir, and Ru ions, which resulted in lattice distortion and enhanced crystal asymmetry, which produced electrical signals for regulating the osteogenic microenvironment. Moreover, the improvement of enzyme-like activities was attributed to the enhanced piezoelectric effect by the codoping of W, Ir, and Ru ions, which generated a piezoelectric field triggered by US that accelerated electron transfer for alleviating cellular oxidative stress and provided an antioxidant microenvironment for osteoblast responses. This piezoelectric hydrogel may provide a novel pathway for promoting osteogenic differentiation and bone regeneration.

Extracellular Vesicles for Disease Treatment

Traditional drug therapies suffer from problems such as easy drug degradation, side effects, and treatment resistance. Traditional disease diagnosis also suffers from high error rates and late diagnosis. Extracellular vesicles (EVs) are nanoscale spherical lipid bilayer vesicles secreted by cells that carry various biologically active components and are integral to intercellular communication. EVs can be found in different body fluids and may reflect the state of the parental cells, making them ideal noninvasive biomarkers for disease-specific diagnosis. The multifaceted characteristics of EVs render them optimal candidates for drug delivery vehicles, with evidence suggesting their efficacy in the treatment of various ailments. However, poor stability and easy degradation of natural EVs have affected their applications. To solve the problems of poor stability and easy degradation of natural EVs, they can be engineered and modified to obtain more stable and multifunctional EVs. In this study, we review the shortcomings of traditional drug delivery methods and describe how to modify EVs to form engineered EVs to improve their utilization. An innovative stimulus-responsive drug delivery system for EVs has also been proposed. We also summarize the current applications and research status of EVs in the diagnosis and treatment of different systemic diseases, and look forward to future research directions, providing research ideas for scholars.

Reduced Thermal Damage Achieved by High-Conductivity Hydrogel in RF Energy Tissue Welding

Radiofrequency (RF) tissue welding is an innovative tissue anastomosis technique that utilizes bioimpedance to convert electrical energy into thermal energy, enabling the connection and reconstruction of tissues via the denaturation and crosslinking of proteins. However, the high temperatures generated in this process often lead to excessive thermal damage to tissues, thereby adversely impacting cellular activity and impeding tissue repair in practical applications. In this study, we developed a polyacrylamide/alginate (PAAm/Alg) hydrogel with high ionic conductivity (16.8 ± 1.2 S/m) achieved by introducing Ca2+ for the purpose of reducing thermal damage in RF tissue welding. The PAAm/Alg-Ca2+0.5M hydrogel possessed excellent mechanical properties with a stress of 315.6 ± 14.1 kPa and an elongation of 382.7 ± 89.0%. Additionally, the hydrogel exhibited a high water content (83.7 ± 0.3%) and excellent stability of swelling property in water. In addition, the hydrogel extract showed good biocompatibility with no significant adverse effects on cell activity in the cytotoxicity test. At last, we conducted ex vivo experiments to investigate the effectiveness of the hydrogel as a cooling agent during RF tissue welding. The result showed that the maximum temperature was effectively reduced from 137.9 ± 4.7 to 101.8 ± 2.5 °C, while the strength of the anastomotic stoma (12.0 ± 3.2 kPa) was not affected by the intervention of this hydrogel. Histological analysis also revealed that the anastomotic structure of the tissue with hydrogel intervention was more intact than that of the control. Thus, the PAAm/Alg-Ca2+0.5M hydrogel has been demonstrated to function effectively as a cooling agent, offering a new strategy for thermal damage control in RF tissue welding.

Enhanced Bone Targeting of Poly(l-glutamic acid)s through Cationic or Aromatic Substitution

Poly(l-glutamic acid)s (PLGs) are promising bone-targeting ligands due to their high molecular weight and facile preparation. Nevertheless, the bone-targeting efficiency of PLGs is still relatively low, validating the necessity to further enhance targeting through structural optimization. Herein, we report the use of a heteropolypeptide strategy to improve the bone targeting of PLGs through the incorporation of another side-chain functionality for enhanced affinity with bone tissues. Specifically, the introduction of cationic amino or aromatic phenolic side-chain residues resulted in a ∼2.3-fold or ∼1.6-fold increase in the in vivo bone targeting, respectively. Cationic modification not only improved the affinity with bone minerals but also exhibited prolonged retention in the bone tissues for more than 60 days. This work highlights the use of a heteropolypeptide library to screen and optimize the performance of polypeptide materials, offering promising bone-targeting polymeric materials for the design of bone-related nanomedicine.

Effects of hydrogel stiffness and viscoelasticity on organoid culture: a comprehensive review

As an emerging technology, organoids are promising new tools for basic and translational research in disease. Currently, the culture of organoids relies mainly on a type of unknown composition scaffold, namely Matrigel, which may pose problems in studying the effect of mechanical properties on organoids. Hydrogels, a new material with adjustable mechanical properties, can adapt to current studies. In this review, we summarized the synthesis of recent advance in developing definite hydrogel scaffolds for organoid culture and identified the critical parameters for regulating mechanical properties. In addition, classified by different mechanical properties like stiffness and viscoelasticity, we concluded the effect of mechanical properties on the development of organoids and tumor organoids. We hope this review enhances the understanding of the development of organoids by hydrogels and provides more practical approaches to investigating them.

Mechano-Responsive Biomaterials for Bone Organoid Construction

Mechanical force is essential for bone development, bone homeostasis, and bone fracture healing. In the past few decades, various biomaterials have been developed to provide mechanical signals that mimic the natural bone microenvironment, thereby promoting bone regeneration. Bone organoids, emerging as a novel research approach, are 3D micro-bone tissues that possess the ability to self-renew and self-organize, exhibiting biomimetic spatial characteristics. Incorporating mechano-responsive biomaterials in the construction of bone organoids presents a promising avenue for simulating the mechanical bone microenvironment. Therefore, this review commences by elucidating the impact of mechanical force on bone health, encompassing both cellular interactions and alterations in bone structure. Furthermore, the most recent applications of mechano-responsive biomaterials within the realm of bone tissue engineering are highlighted. Three different types of mechano-responsive biomaterials are introduced with a focus on their responsive mechanisms, construction strategies, and efficacy in facilitating bone regeneration. Based on a comprehensive overview, the prospective utilization and future challenges of mechano-responsive biomaterials in the construction of bone organoids are discussed. As bone organoid technology advances, these biomaterials are poised to become powerful tools in bone regeneration.

Construction of pH-responsive hydrogel coatings on titanium surfaces for antibacterial and osteogenic properties

Infection is one of the leading causes of failure in titanium-based implant materials during clinical surgeries, often resulting in delayed or non-union of bone healing. Furthermore, the overuse of antibiotics can lead to bacterial resistance. Therefore, developing a novel titanium-based implant material with both antimicrobial and osteogenic properties is of great significance. In this study, chitosan (CS), polydopamine (PDA), and antimicrobial peptides (AMPs) HHC36 were applied to modify the surface of titanium, resulting in the successful preparation of the composite material Ti-PDA-CS/PDA@HHC36 (abbreviated as T-P-C/P@H). CS promotes osteogenesis and cell adhesion, providing an ideal microenvironment for bone repair. PDA enhances the material's biocompatibility and corrosion resistance, offering cell adhesion sites, while both components exhibit pH-responsive characteristics. The HHC36 effectively prevents infection, protecting the bone repair material from bacterial damage. Overall, the synergistic effects of these components in T-P-C/P@H not only confer excellent antimicrobial and osteogenic properties but also improve biocompatibility, offering a new strategy for applying titanium-based implants in clinical settings.

Gelatin-based biomaterials as a delivery strategy for osteosarcoma treatment

Osteosarcoma is the most common primary malignant bone tumor. Although surgery and chemoradiotherapy have made some progress in the treatment of osteosarcoma. However, the high recurrence and metastasis rate of osteosarcoma and bone defects caused by surgery are still the main problems faced by osteosarcoma. Gelatin has excellent biocompatibility and biodegradability, and has made phased progress in tumor treatment. In the treatment of osteosarcoma, gelatin-based biomaterials can be used in delivery strategies to enhance the anti-tumor activity of osteosarcoma and can improve the appropriate compressive strength to improve the bone defects faced after surgery. At present, gelatin-based hydrogels, gelatin scaffolds, and gelatin-based nanoparticles have been reported in preclinical studies. In this article, we introduce the application of gelatin-based biomaterials in the treatment of osteosarcoma, and summarize and look forward to them.

[Research progress of bioactive scaffolds in repair and regeneration of osteoporotic bone defects]

Objective

To summarize the research progress of bioactive scaffolds in the repair and regeneration of osteoporotic bone defects.

Methods

Recent literature on bioactive scaffolds for the repair of osteoporotic bone defects was reviewed to summarize various types of bioactive scaffolds and their associated repair methods.

Results

The application of bioactive scaffolds provides a new idea for the repair and regeneration of osteoporotic bone defects. For example, calcium phosphate ceramics scaffolds, hydrogel scaffolds, three-dimensional (3D)-printed biological scaffolds, metal scaffolds, as well as polymer material scaffolds and bone organoids, have all demonstrated good bone repair-promoting effects. However, in the pathological bone microenvironment of osteoporosis, the function of single-material scaffolds to promote bone regeneration is insufficient. Therefore, the design of bioactive scaffolds must consider multiple factors, including material biocompatibility, mechanical properties, bioactivity, bone conductivity, and osteogenic induction. Furthermore, physical and chemical surface modifications, along with advanced biotechnological approaches, can help to improve the osteogenic microenvironment and promote the differentiation of bone cells.

Conclusion

With advancements in technology, the synergistic application of 3D bioprinting, bone organoids technologies, and advanced biotechnologies holds promise for providing more efficient bioactive scaffolds for the repair and regeneration of osteoporotic bone defects.

Advanced Bioresponsive Drug Delivery Systems for Promoting Diabetic Vascularized Bone Regeneration

The treatment of bone defects in diabetes mellitus (DM) patients remains a major challenge since the diabetic microenvironments significantly impede bone regeneration. Many abnormal factors including hyperglycemia, elevated oxidative stress, increased inflammation, imbalanced osteoimmune, and impaired vascular system in the diabetic microenvironment will result in a high rate of impaired, delayed, or even nonhealing events of bone tissue. Stimuli-responsive biomaterials that can respond to endogenous biochemical signals have emerged as effective therapeutic systems to treat diabetic bone defects via the combination of microenvironmental regulation and enhanced osteogenic capacity. Following the natural bone healing processes, coupling of angiogenesis and osteogenesis by advanced bioresponsive drug delivery systems has proved to be of significant approach for promoting bone repair in DM. In this Review, we have systematically summarized the mechanisms and therapeutic strategies of DM-induced impaired bone healing, outlined the bioresponsive design for drug delivery systems, and highlighted the vascularization strategies for promoting bone regeneration. Accordingly, we then overview the recent advances in developing bioresponsive drug delivery systems to facilitate diabetic vascularized bone regeneration by remodeling the microenvironment and modulating multiple regenerative cues. Furthermore, we discuss the development of adaptable drug delivery systems with unique features for guiding DM-associated bone regeneration in the future.

Advancements in hydrogel design for articular cartilage regeneration: A comprehensive review

This review paper explores the cutting-edge advancements in hydrogel design for articular cartilage regeneration (CR). Articular cartilage (AC) defects are a common occurrence worldwide that can lead to joint breakdown at a later stage of the disease, necessitating immediate intervention to prevent progressive degeneration of cartilage. Decades of research into the biomedical applications of hydrogels have revealed their tremendous potential, particularly in soft tissue engineering, including CR. Hydrogels are highly tunable and can be designed to meet the key criteria needed for a template in CR. This paper aims to identify those criteria, including the hydrogel components, mechanical properties, biodegradability, structural design, and integration capability with the adjacent native tissue and delves into the benefits that CR can obtain through appropriate design. Stratified-structural hydrogels that emulate the native cartilage structure, as well as the impact of environmental stimuli on the regeneration outcome, have also been discussed. By examining recent advances and emerging techniques, this paper offers valuable insights into developing effective hydrogel-based therapies for AC repair.

Polyphenols and Functionalized Hydrogels for Osteoporotic Bone Regeneration

Osteoporosis induces severe oxidative stress and disrupts bone metabolism, complicating the treatment of bone defects. Current therapies often have side effects and require lengthy bone regeneration periods. Hydrogels, known for their flexible mechanical properties and degradability, are promising carriers for drugs and bioactive factors in bone tissue engineering. However, they lack the ability to regulate the local pathological environment of osteoporosis and expedite bone repair. Polyphenols, with antioxidative, anti-inflammatory, and bone metabolism-regulating properties, have emerged as a solution. Combining hydrogels and polyphenols, polyphenol-based hydrogels can regulate local bone metabolism and oxidative stress while providing mechanical support and tissue adhesion, promoting osteoporotic bone regeneration. This review first provides a brief overview of the types of polyphenols and the mechanisms of polyphenols in facilitating adhesion, antioxidant, anti-inflammatory, and bone metabolism modulation in modulating the pathological environment of osteoporosis. Next, this review examines recent advances in hydrogels for the treatment of osteoporotic bone defects, including their use in angiogenesis, oxidative stress modulation, drug delivery, and stem cell therapy. Finally, it highlights the latest research on polyphenol hydrogels in osteoporotic bone defect regeneration. Overall, this review aims to facilitate the clinical application of polyphenol hydrogels for the treatment of osteoporotic bone defects.

Standardization and consensus in the development and application of bone organoids

Organoids, self-organized structures derived from stem cells cultured in a specific three-dimensional (3D) in vitro microenvironment, have emerged as innovative platforms that closely mimic in vivo cellular behavior, tissue architecture, and organ function. Bone organoids, a frontier in organoid research, can replicate the complex structures and functional characteristics of bone tissue. Recent advancements have led to the successful development of bone organoids, including models of callus, woven bone, cartilage, trabecular bone, and bone marrow. These organoids are widely utilized in establishing bone-related disease models, bone injury repair, and drug screening. However, significant discrepancies remain between current bone organoids and human skeletal tissues in terms of morphology and functionality, limiting their ability to accurately model human bone physiology and pathology. To address these challenges and promote standardization in the construction, evaluation, and application of bone organoids, we have convened experts and research teams with substantial expertise in the field. By integrating existing research findings, this consortium aims to establish a consensus to guide future research and application of bone organoids.

Bone-Targeted Fluoropeptide Nanoparticle Inhibits NF-κB Signaling to Treat Osteosarcoma and Tumor-Induced Bone Destruction

Osteosarcoma is a malignant bone cancer usually characterized by symptoms of bone loss due to pathologically enhanced osteoclast activity. Activated osteoclasts enhance bone resorption and promote osteosarcoma cell progression by secreting various cytokines. Intercepting the detrimental interplay between osteoclasts and osteosarcoma cells is considered as an option for osteosarcoma treatment. Here, a bone-targeted fluoropeptide nanoparticle that can inhibit the nuclear factor kappa B (NF-κB) signaling in both osteoclasts and osteosarcoma to address the above issue is developed. The NF-κB essential modulator binding domain (NBD) peptide is conjugated with a fluorous tag to improve its proteolytic stability and intracellular penetration. The NBD peptide is efficiently delivered into cells after fluorination to induce apoptosis of osteocarcoma cells, and inhibits osteoclasts differentiation. The fluorous-tagged NBD peptide is further co-assembled with an oligo (aspartic acid) terminated fluoropeptide to form bone-targeted peptide nanoparticles for osteosarcoma treatment. The targeted nanoparticles efficiently inhibited tumor progression and osteosarcoma-induced bone destruction in vivo. This co-assembled fluoropeptide nanoplatform proposed in this study offers a promising approach for targeted and intracellular delivery of peptide therapeutics in the treatment of various diseases.

Overview of chitin dissolution, hydrogel formation and its biomedical applications

Chitin hydrogel and hydrogel-based products are some of the frequently reported biomaterials for biomedical applications. Yet there is a void in understanding chitin's dissolution mechanism and its most suitable solvent system(s). Chitin is a natural polysaccharide polymer which can be dissolved in solvents such as calcium chloride- methanol, sodium hydroxide/urea (NaOH/urea), lithium chloride diacetamide (LiCl/DMAc), ionic liquids and deep eutectic solvents. Among the alkali/urea dissolution systems such as NaOH/urea, KOH/urea, LiOH/urea for dissolution of chitin we will be focussing on NaOH-based system here for ease of comparison with the other systems. Chitin has been used for decades in the biomedical field; however, new solvent systems are still being explored even to this day to identify the most suitable chemical(s) for dissolving it. Chitin, due to its biocompatibility, allows us to use it for multifaceted purposes. Hence, it is important to consolidate the available studies for better understanding about the most sought-after biomaterial. This overview deeply delves into the mechanism of action of the existing solvent systems and highlights its merits and demerits. It discusses the rheological properties of the chitin gel from different solvent systems and puts forth the current biomedical applications of chitin gel in areas such as tissue engineering, drug delivery, biosensing, hemostasis and wound healing. It also outlines recent advances and highlights the potential gaps which need to be addressed in future studies.

Synthesis, Characterization and Osteogenic Properties of Chitin-Polydioxanone Composite Gel

In this study, we have developed a Chitin(Ch)-Poly(dioxanone)(PDO) gel system, which can be potentially used for tissue engineering. Hydrogel has been widely used in biomedical applications for its tuneable properties and biocompatibility. Chitin (Ch) is a natural biopolymer used for its ability to mimic the natural extracellular matrix due to its N-acetyl glucosamine structural units. Poly (dioxanone) (PDO) is a FDA-approved synthetic biopolymer known for its mechanical properties, good biocompatibility, and poor inflammatory response. Based on this, we have developed Ch-PDO composite gel using simple regeneration chemistry and characterized it using FT-IR and SEM. The developed composite gel showed improved gel strength, good swelling ability, and controlled degradation behaviour. It also showed good inject ability with shear thinning properties and hemocompatibility. Further, the biocompatibility and cell adhesion studies of the prepared gels were studied using dental follicle stem cells (DFSCs). The prepared Ch-PDO gel was biocompatible and showed DFSCs cell attachment. Osteogenic mineralization, RUNX2 and OPN expression of the prepared Ch and Ch-PDO gel was studied and Ch-PDO gel showed an enhanced mineralization and RUNX2 and OPN expression showed enhanced osteogenic activity in Ch-PDO. Therefore, the developed chitin-PDO gel could be potentially used for bone tissue engineering.

Nanoengineered Endocytic Biomaterials for Stem Cell Therapy

Stem cells, ideal for the tissue repair and regeneration, possess extraordinary capabilities of multidirectional differentiation and self‐renewal. However, the limited spontaneous differentiation potential makes it challenging to harness them for tissue repair without external intervention. Although conventional approaches using biomolecules, small organic molecules, and ions have shown specific and effective functions, they face challenges such as in vivo diffusion and degradation, poor internalization, and side effects on adjacent cells. Nanoengineered biomaterials offer a solution by solidifying and nanosizing these soluble regulating molecules and ions, facilitating their uptake by stem cells. Once inside lysosomes, these nanoparticles release their contents in a controlled “molecule or ion storm,” efficiently altering the intracellular biological and chemical microenvironment to tune the differentiation of stem cells. This newly emerged approach for regulating stem cell fate has attracted much attention in recent years. This method has shown promising results and is poised to enhance clinical stem cell therapy. This review provides an overview of the design principles for nanoengineered biomaterials, discusses the categories and characteristics of nanoparticles, summarizes the application of nanoparticles in tissue repair and regeneration, and discusses the direction of nanoparticle‐enhanced stem cell therapy and prospects for its clinical application in regenerative medicine.

Engineering gene-activated bioprinted scaffolds for enhancing articular cartilage repair

Untreated articular cartilage injuries often result in severe chronic pain and dyskinesia. Current repair strategies have limitations in effectively promoting articular cartilage repair, underscoring the need for innovative therapeutic approaches. A gene-activated matrix (GAM) is a promising and comprehensive therapeutic strategy that integrates tissue-engineered scaffold-guided gene therapy to promote long-term articular cartilage repair by enhancing gene retention, reducing gene loss, and regulating gene release. However, for effective articular cartilage repair, the GAM scaffold must mimic the complex gradient structure of natural articular cartilage. Three-dimensional (3D) bioprinting technology has emerged as a compelling solution, offering the ability to precisely create complex microstructures that mimic the natural articular cartilage. In this review, we summarize the recent research progress on GAM and 3D bioprinted scaffolds in articular cartilage tissue engineering (CTE), while also exploring future challenges and development directions. This review aims to provide new ideas and concepts for the development of gene-activated bioprinted scaffolds with specific properties tailored to meet the stringent requirements of articular cartilage repair.

Advances in the Development of Gradient Scaffolds Made of Nano-Micromaterials for Musculoskeletal Tissue Regeneration

The intricate hierarchical structure of musculoskeletal tissues, including bone and interface tissues, necessitates the use of complex scaffold designs and material structures to serve as tissue-engineered substitutes. This has led to growing interest in the development of gradient bone scaffolds with hierarchical structures mimicking the extracellular matrix of native tissues to achieve improved therapeutic outcomes. Building on the anatomical characteristics of bone and interfacial tissues, this review provides a summary of current strategies used to design and fabricate biomimetic gradient scaffolds for repairing musculoskeletal tissues, specifically focusing on methods used to construct compositional and structural gradients within the scaffolds. The latest applications of gradient scaffolds for the regeneration of bone, osteochondral, and tendon-to-bone interfaces are presented. Furthermore, the current progress of testing gradient scaffolds in physiologically relevant animal models of skeletal repair is discussed, as well as the challenges and prospects of moving these scaffolds into clinical application for treating musculoskeletal injuries.

Organoids and organoid extracellular vesicles-based disease treatment strategies

Organoids are "mini-organs" that self-organize and differentiate from stem cells under in vitro 3D culture conditions, mimicking the spatial structure and function of tissues in vivo. Extracellular vesicles (EVs) are nanoscale phospholipid bilayer vesicles secreted by living cells, rich in bioactive molecules, with excellent biocompatibility and low immunogenicity. Compared to EVs, organoid-derived EVs (OEVs) exhibit higher yield and enhanced biological functions. Organoids possess stem cell characteristics, and OEVs are capable of delivering active substances, making both highly promising for medical applications. In this review, we provide an overview of the fundamental biological principles of organoids and OEVs, and discuss their current applications in disease treatment. We then focus on the differences between OEVs and traditional EVs. Subsequently, we present methods for the engineering modification of OEVs. Finally, we critically summarize the advantages and challenges of organoids and OEVs. In conclusion, we believe that a deeper understanding of organoids and OEVs will provide innovative solutions to complex diseases.

Hydrogel Strategies for Female Reproduction Dysfunction

Infertility is an important issue for human reproductive health, with over half of all cases of infertility associated with female factors. Dysfunction of the complex female reproductive system may cause infertility. In clinical practice, female infertility is often treated with oral medications and/or surgical procedures, and ultimately with assisted reproductive technologies. Owing to their excellent biocompatibility, low immunogenicity, and adjustable mechanical properties, hydrogels are emerging as valuable tools in the reconstruction of organ function, supplemented by tissue engineering techniques to increase their structure and functionality. Hydrogel-based female reproductive reconstruction strategies targeting the pathological mechanisms of female infertility may provide alternatives for the treatment of ovarian, endometrium/uterine, and fallopian tube dysfunction. In this review, we provide a general introduction to the basic physiology and pathology of the female reproductive system, the limitations of current infertility treatments, and the lack of translation from animal models to human reproductive physiology. We further provide an overview of the current and future potential applications of hydrogels in the treatment of female reproductive system dysfunction, highlighting the great prospects of hydrogel-based strategies in the field of translational medicine, along with the significant challenges to be overcome.

Polysaccharide-based hydrogels for cartilage regeneration

Cartilage defect is one of the common tissue defect clinical diseases and may finally lead to osteoarthritis (OA) which threat patients' physical and psychological health. Polysaccharide is the main component of extracellular matrix (ECM) in cartilage tissue. In the past decades, polysaccharide-based hydrogels have shown great potential for cartilage regeneration considering unique qualities such as biocompatibility, enhanced cell proliferation, drug delivery, low toxicity, and many others. Structures such as chain length and chain branching make polysaccharides have different physical and chemical properties. In this review, cartilage diseases and current treatment options of polysaccharide-based hydrogels for cartilage defection repair were illustrated. We focus on how components and structures of recently developed materials affect the performance. The challenges and perspectives for polysaccharide-based hydrogels in cartilage repair and regeneration were also discussed in depth.

A photothermal responsive system accelerating nitric oxide release to enhance bone repair by promoting osteogenesis and angiogenesis

Managing bone defects remains a formidable clinical hurdle, primarily attributed to the inadequate orchestration of vascular reconstruction and osteogenic differentiation in both spatial and temporal dimensions. This challenge persists due to the constrained availability of autogenous grafts and the limited regenerative capacity of allogeneic or synthetic bone substitutes, thus necessitating continual exploration and innovation in the realm of functional and bioactive bone graft materials. While synthetic scaffolds have emerged as promising carriers for bone grafts, their efficacy is curtailed by deficiencies in vascularization and osteoinductive potential. Nitric oxide (NO) plays a key role in revascularization and bone tissue regeneration, yet studies related to the use of NO for the treatment of bone defects remain scarce. Herein, we present a pioneering approach leveraging a photothermal-responsive system to augment NO release. This system comprises macromolecular mPEG-P nanoparticles encapsulating indocyanine green (ICG) (NO-NPs@ICG) and a mPEG-PA-PP injectable thermosensitive hydrogel carrier. By harnessing the synergistic photothermal effects of near-infrared radiation and ICG, the system achieves sustained NO release, thereby activating the soluble guanylate cyclase (SGC)-cyclic guanosine monophosphate (cGMP) signaling pathway both in vitro and in vivo. This orchestrated cascade culminates in the facilitation of angiogenesis and osteogenesis, thus expediting the reparative processes in bone defects. In a nutshell, the NO release-responsive system elucidated in this study presents a pioneering avenue for refining the bone tissue microenvironment and fostering enhanced bone regeneration.

Collagen Type II-Based Injectable Materials for In situ Repair and Regeneration of Articular Cartilage Defect

Repairing and regenerating articular cartilage defects (ACDs) have long been challenging for physicians and scientists. The rise of injectable materials provides a novel strategy for minimally invasive surgery to repair ACDs. In this study, we successfully developed injectable materials based on collagen type II, achieving hyaline cartilage repair and regeneration of ACDs. Analysis was conducted on the regenerated cartilage after materials injection. The histology staining demonstrated complete healing of the ACDs with the attainment of a hyaline cartilage phenotype. The biochemical and biomechanical properties are similar to the adjacent native cartilage without noticeable adverse effects on the subchondral bone. Further transcriptome analysis found that compared with the Native cartilage adjacent to the defect area, the Regenerated cartilage in the defect area repaired with type II collagen-based injection materials showed changes in cartilage-related pathways, as well as down-regulation of T cell receptor signaling pathways and interleukin-17 signaling pathways, which changed the immune microenvironment of the ACD area. Overall, these findings offer a promising injectable approach to treating ACDs, providing a potential solution to the challenges associated with achieving hyaline cartilage in situ repair and regeneration while minimizing damage to the surrounding cartilage.

Hydrogel-exosome system in tissue engineering: A promising therapeutic strategy

Characterized by their pivotal roles in cell-to-cell communication, cell proliferation, and immune regulation during tissue repair, exosomes have emerged as a promising avenue for "cell-free therapy" in clinical applications. Hydrogels, possessing commendable biocompatibility, degradability, adjustability, and physical properties akin to biological tissues, have also found extensive utility in tissue engineering and regenerative repair. The synergistic combination of exosomes and hydrogels holds the potential not only to enhance the efficiency of exosomes but also to collaboratively advance the tissue repair process. This review has summarized the advancements made over the past decade in the research of hydrogel-exosome systems for regenerating various tissues including skin, bone, cartilage, nerves and tendons, with a focus on the methods for encapsulating and releasing exosomes within the hydrogels. It has also critically examined the gaps and limitations in current research, whilst proposed future directions and potential applications of this innovative approach.

High-precision bioactive scaffold with dECM and extracellular vesicles targeting 4E-BP inhibition for cartilage injury repair

The restoration of cartilage injuries remains a formidable challenge in orthopedics, chiefly attributed to the absence of vascularization and innervation in cartilage. Decellularized extracellular matrix (dECM) derived from cartilage, following antigenic removal through decellularization processes, has exhibited remarkable biocompatibility and bioactivity, rendering it a viable candidate for cartilage repair. Additionally, extracellular vesicles (EVs) generated from cartilage have demonstrated a synergistic effect when combined with dECM, potentially mitigating the inhibitory impact on protein synthesis by phosphorylating 4ebp, thereby promoting the synthesis of cartilage-related proteins such as collagen. In pursuit of this objective, we have innovated a novel bioink and repair scaffold characterized by exceptional biocompatibility, bioactivity, and biodegradability, establishing a tissue-specific microenvironment conducive to chondrogenesis. Within rat osteochondral defects, the biologically active scaffold successfully prompted the formation of transparent cartilage, featuring adequate mechanical strength, favorable elasticity, and dECM deposition indicative of cartilage. In summary, this study has effectively engineered a hydrogel bioink tailored for cartilage repair and devised a bioactive cartilage repair scaffold proficient in instigating cell differentiation and fostering cartilage repair.

Nanoclay Reinforced Integrated Scaffold for Dual-Lineage Regeneration of Cartilage and Subchondral Bone

Tissue engineering is theoretically considered a promising approach for repairing osteochondral defects. Nevertheless, the insufficient osseous support and integration of the cartilage layer and the subchondral bone frequently lead to the failure of osteochondral repair. Drawing from this, it was proposed that incorporating glycine-modified attapulgite (GATP) into poly(1,8-octanediol-co-citrate) (POC) scaffolds via the one-step chemical cross-linking is proposed to enhance cartilage and subchondral bone defect repair simultaneously. The effects of the GATP incorporation ratio on the physicochemical properties, chondrocyte and MC3T3-E1 behavior, and osteochondral defect repair of the POC scaffold were also evaluated. In vitro studies indicated that the POC/10% GATP scaffold improved cell proliferation and adhesion, maintained cell phenotype, and upregulated chondrogenesis and osteogenesis gene expression. Animal studies suggested that the POC/10% GATP scaffold has significant repair effects on both cartilage and subchondral bone defects. Therefore, the GATP-incorporated scaffold system with dual-lineage bioactivity showed potential application in osteochondral regeneration.

Multifunctional hydrogel-based engineered extracellular vesicles delivery for complicated wound healing

The utilization of extracellular vesicles (EVs) in wound healing has been well-documented. However, the direct administration of free EVs via subcutaneous injection at wound sites may result in the rapid dissipation of bioactive components and diminished therapeutic efficacy. Functionalized hydrogels provide effective protection, as well as ensure the sustained release and bioactivity of EVs during the wound healing process, making them an ideal candidate material for delivering EVs. In this review, we introduce the mechanisms by which EVs accelerate wound healing, and then elaborate on the construction strategies for engineered EVs. Subsequently, we discuss the synthesis strategies and application of hydrogels as delivery systems for the sustained release of EVs to enhance complicated wound healing. Furthermore, in the face of complicated wounds, functionalized hydrogels with specific wound microenvironment regulation capabilities, such as antimicrobial, anti-inflammatory, and immune regulation, used for loading engineered EVs, provide potential approaches to addressing these healing challenges. Ultimately, we deliberate on potential future trajectories and outlooks, offering a fresh viewpoint on the advancement of artificial intelligence (AI)-energized materials and 3D bio-printed multifunctional hydrogel-based engineered EVs delivery dressings for biomedical applications.

Engineering Large-Scale Self-Mineralizing Bone Organoids with Bone Matrix-Inspired Hydroxyapatite Hybrid Bioinks

Addressing large bone defects remains a significant challenge owing to the inherent limitations in self-healing capabilities, resulting in prolonged recovery and suboptimal regeneration. Although current clinical solutions are available, they have notable shortcomings, necessitating more efficacious approaches to bone regeneration. Organoids derived from stem cells show great potential in this field; however, the development of bone organoids has been hindered by specific demands, including the need for robust mechanical support provided by scaffolds and hybrid extracellular matrices (ECM). In this context, bioprinting technologies have emerged as powerful means of replicating the complex architecture of bone tissue. The research focused on the fabrication of a highly intricate bone ECM analog using a novel bioink composed of gelatin methacrylate/alginate methacrylate/hydroxyapatite (GelMA/AlgMA/HAP). Bioprinted scaffolds facilitate the long-term cultivation and progressive maturation of extensive bioprinted bone organoids, foster multicellular differentiation, and offer valuable insights into the initial stages of bone formation. The intrinsic self-mineralizing quality of the bioink closely emulates the properties of natural bone, empowering organoids with enhanced bone repair for both in vitro and in vivo applications. This trailblazing investigation propels the field of bone tissue engineering and holds significant promise for its translation into practical applications.

Harnessing the potential of hydrogels for advanced therapeutic applications: current achievements and future directions

The applications of hydrogels have expanded significantly due to their versatile, highly tunable properties and breakthroughs in biomaterial technologies. In this review, we cover the major achievements and the potential of hydrogels in therapeutic applications, focusing primarily on two areas: emerging cell-based therapies and promising non-cell therapeutic modalities. Within the context of cell therapy, we discuss the capacity of hydrogels to overcome the existing translational challenges faced by mainstream cell therapy paradigms, provide a detailed discussion on the advantages and principal design considerations of hydrogels for boosting the efficacy of cell therapy, as well as list specific examples of their applications in different disease scenarios. We then explore the potential of hydrogels in drug delivery, physical intervention therapies, and other non-cell therapeutic areas (e.g., bioadhesives, artificial tissues, and biosensors), emphasizing their utility beyond mere delivery vehicles. Additionally, we complement our discussion on the latest progress and challenges in the clinical application of hydrogels and outline future research directions, particularly in terms of integration with advanced biomanufacturing technologies. This review aims to present a comprehensive view and critical insights into the design and selection of hydrogels for both cell therapy and non-cell therapies, tailored to meet the therapeutic requirements of diverse diseases and situations.

Pyroptosis-related crosstalk in osteoarthritis: Macrophages, fibroblast-like synoviocytes and chondrocytes

The pathogenesis of osteoarthritis (OA) involves a multifaceted interplay of inflammatory processes. The initiation of pyroptosis involves the secretion of pro-inflammatory cytokines and has been identified as a critical factor in regulating the development of OA. Upon initiation of pyroptosis, a multitude of inflammatory mediators are released and can be disseminated throughout the synovial fluid within the joint cavity, thereby facilitating intercellular communication across the entire joint. The main cellular components of joints include chondrocytes (CC), fibroblast-like synoviocytes (FLS) and macrophages (MC). Investigating their interplay can enhance our understanding of OA pathogenesis. Therefore, we comprehensively examine the mechanisms underlying pyroptosis and specifically investigate the intercellular interactions associated with pyroptosis among these three cell types, thereby elucidating their collective contribution to the progression of OA. We propose the concept of ' CC-FLS-MC pyroptosis-related crosstalk', describe the various pathways of pyroptotic interactions among these three cell types, and focus on recent advances in intervening pyroptosis in these three cell types for treating OA. We hope this will provide a possible direction for diversification of treatment for OA. The Translational potential of this article. The present study introduces the concept of 'MC-FLS-CC pyroptosis-related crosstalk' and provides an overview of the mechanisms underlying pyroptosis, as well as the pathways through which it affects MC, FLS, and CC. In addition, the role of regulation of these three types of cellular pyroptosis in OA has also been concerned. This review offers novel insights into the interplay between these cell types, with the aim of providing a promising avenue for diversified management of OA.

An injectable magnesium-loaded hydrogel releases hydrogen to promote osteoporotic bone repair via ROS scavenging and immunomodulation

Background: The repair of osteoporotic bone defects remains challenging due to excessive reactive oxygen species (ROS), persistent inflammation, and an imbalance between osteogenesis and osteoclastogenesis. Methods: Here, an injectable H2-releasing hydrogel (magnesium@polyethylene glycol-poly(lactic-co-glycolic acid), Mg@PEG-PLGA) was developed to remodel the challenging bone environment and accelerate the repair of osteoporotic bone defects. Results: This Mg@PEG-PLGA gel shows excellent injectability, shape adaptability, and phase-transition ability, can fill irregular bone defect areas via minimally invasive injection, and can transform into a porous scaffold in situ to provide mechanical support. With the appropriate release of H2 and magnesium ions, the 2Mg@PEG-PLGA gel (loaded with 2 mg of Mg) displayed significant immunomodulatory effects through reducing intracellular ROS, guiding macrophage polarization toward the M2 phenotype, and inhibiting the IκB/NF-κB signaling pathway. Moreover, in vitro experiments showed that the 2Mg@PEG-PLGA gel inhibited osteoclastogenesis while promoting osteogenesis. Most notably, in animal experiments, the 2Mg@PEG-PLGA gel significantly promoted the repair of osteoporotic bone defects in vivo by scavenging ROS and inhibiting inflammation and osteoclastogenesis. Conclusions: Overall, our study provides critical insight into the design and development of H2-releasing magnesium-based hydrogels as potential implants for repairing osteoporotic bone defects.

Hydrogel-Based Systems in Neuro-Vascularized Bone Regeneration: A Promising Therapeutic Strategy

Blood vessels and nerve fibers are distributed throughout the skeletal tissue, which enhance the development and function of each other and have an irreplaceable role in bone formation and remodeling. Despite significant progress in bone tissue engineering, the inadequacy of nerve-vascular network reconstruction remains a major limitation. This is partly due to the difficulty of integrating and regulating multiple tissue types with artificial materials. Thus, understanding the anatomy and underlying coupling mechanisms of blood vessels and nerve fibers within bone to further develop neuro-vascularized bone implant biomaterials is an extremely critical aspect in the field of bone regeneration. Hydrogels have good biocompatibility, controllable mechanical characteristics, and osteoconductive and osteoinductive properties, making them important candidates for research related to neuro-vascularized bone regeneration. This review reports the classification and physicochemical properties of hydrogels, with a focus on the application advantages and status of hydrogels for bone regeneration. The authors also highlight the effect of neurovascular coupling on bone repair and regeneration and the necessity of achieving neuro-vascularized bone regeneration. Finally, the recent progress and design strategies of hydrogel-based biomaterials for neuro-vascularized bone regeneration are discussed.

N6-Methyladenosine in Cell-Fate Determination of BMSCs: From Mechanism to Applications

The methylation of adenosine base at the nitrogen-6 position is referred to as "N6-methyladenosine (m6A)" and is one of the most prevalent epigenetic modifications in eukaryotic mRNA and noncoding RNA (ncRNA). Various m6A complex components known as "writers," "erasers," and "readers" are involved in the function of m6A. Numerous studies have demonstrated that m6A plays a crucial role in facilitating communication between different cell types, hence influencing the progression of diverse physiological and pathological phenomena. In recent years, a multitude of functions and molecular pathways linked to m6A have been identified in the osteogenic, adipogenic, and chondrogenic differentiation of bone mesenchymal stem cells (BMSCs). Nevertheless, a comprehensive summary of these findings has yet to be provided. In this review, we primarily examined the m6A alteration of transcripts associated with transcription factors (TFs), as well as other crucial genes and pathways that are involved in the differentiation of BMSCs. Meanwhile, the mutual interactive network between m6A modification, miRNAs, and lncRNAs was intensively elucidated. In the last section, given the beneficial effect of m6A modification in osteogenesis and chondrogenesis of BMSCs, we expounded upon the potential utility of m6A-related therapeutic interventions in the identification and management of human musculoskeletal disorders manifesting bone and cartilage destruction, such as osteoporosis, osteomyelitis, osteoarthritis, and bone defect.

High temperature oxidation treated 3D printed anatomical WE43 alloy scaffolds for repairing periarticular bone defects: In vitro and in vivo studies

Reconstruction of subarticular bone defects is an intractable challenge in orthopedics. The simultaneous repair of cancellous defects, fractures, and cartilage damage is an ideal surgical outcome. 3D printed porous anatomical WE43 (magnesium with 4 wt% yttrium and 3 wt% rare earths) scaffolds have many advantages for repairing such bone defects, including good biocompatibility, appropriate mechanical strength, customizable shape and structure, and biodegradability. In a previous investigation, we successfully enhanced the corrosion resistance of WE43 samples via high temperature oxidation (HTO). In the present study, we explored the feasibility and effectiveness of HTO-treated 3D printed porous anatomical WE43 scaffolds for repairing the cancellous bone defects accompanied by split fractures via in vitro and in vivo experiments. After HTO treatment, a dense oxidation layer mainly composed of Y2O3 and Nd2O3 formed on the surface of scaffolds. In addition, the majority of the grains were equiaxed, with an average grain size of 7.4 μm. Cell and rabbit experiments confirmed the non-cytotoxicity and biocompatibility of the HTO-treated WE43 scaffolds. After the implantation of scaffolds inside bone defects, their porous structures could be maintained for more than 12 weeks without penetration and for more than 6 weeks with penetration. During the postoperative follow-up period for up to 48 weeks, radiographic examinations and histological analysis revealed that abundant bone gradually regenerated along with scaffold degradation, and stable osseointegration formed between new bone and scaffold residues. MRI images further demonstrated no evidence of any obvious damage to the cartilage, ligaments, or menisci, confirming the absence of traumatic osteoarthritis. Moreover, finite element analysis and biomechanical tests further verified that the scaffolds was conducive to a uniform mechanical distribution. In conclusion, applying the HTO-treated 3D printed porous anatomical WE43 scaffolds exhibited favorable repairing effects for subarticular cancellous bone defects, possessing great potential for clinical application.

Augmented physical, mechanical, and cellular responsiveness of gelatin-aldehyde modified xanthan hydrogel through incorporation of silicon nanoparticles for bone tissue engineering

Bioactive scaffolds fabricated from a combination of organic and inorganic biomaterials are a promising approach for addressing defects in bone tissue engineering. In the present study, a self-crosslinked nanocomposite hydrogel, composed of gelatin/aldehyde-modified xanthan (Gel-AXG) is successfully developed by varying concentrations of porous silicon nanoparticles (PSiNPs). The effect of PSiNPs incorporation on physical, mechanical, and biological performance of the nanocomposite hydrogel is evaluated. Morphological analysis reveals formation of highly porous 3D microstructures with interconnected pores in all nanocomposite hydrogels. Increased content of PSiNPs results in a lower swelling ratio, reduced porosity and pore size, which in turn impeded media penetration and slowed down the degradation process. In addition, remarkable enhancements in dynamic mechanical properties are observed in Gel-AXG-8%Si (compressive strength: 0.6223 MPa at 90 % strain and compressive modulus: 0.054 MPa), along with improved biomineralization ability via hydroxyapatite formation after immersion in simulated body fluid (SBF). This optimized nanocomposite hydrogel provides a sustained release of Si ions at safe dose levels. Furthermore, in-vitro cytocompatibility studies using MG-63 cells exhibited remarkable performance in terms of cell attachment, proliferation, and ALP activity for Gel-AXG-8%Si. These findings suggest that the prepared nanocomposite hydrogel holds promising potential as a scaffold for bone tissue engineering.

Small Joint Organoids 3D Bioprinting: Construction Strategy and Application

Osteoarthritis (OA) is a chronic disease that causes pain and disability in adults, affecting ≈300 million people worldwide. It is caused by damage to cartilage, including cellular inflammation and destruction of the extracellular matrix (ECM), leading to limited self-repairing ability due to the lack of blood vessels and nerves in the cartilage tissue. Organoid technology has emerged as a promising approach for cartilage repair, but constructing joint organoids with their complex structures and special mechanisms is still challenging. To overcome these boundaries, 3D bioprinting technology allows for the precise design of physiologically relevant joint organoids, including shape, structure, mechanical properties, cellular arrangement, and biological cues to mimic natural joint tissue. In this review, the authors will introduce the biological structure of joint tissues, summarize key procedures in 3D bioprinting for cartilage repair, and propose strategies for constructing joint organoids using 3D bioprinting. The authors also discuss the challenges of using joint organoids' approaches and perspectives on their future applications, opening opportunities to model joint tissues and response to joint disease treatment.

Hydrogel Breakthroughs in Biomedicine: Recent Advances and Implications

OBJECTIVE

The objective of this review is to present a succinct summary of the latest advancements in the utilization of hydrogels for diverse biomedical applications, with a particular focus on their revolutionary impact in augmenting the delivery of drugs, tissue engineering, along with diagnostic methodologies.

METHODS

Using a meticulous examination of current literary works, this review systematically scrutinizes the nascent patterns in applying hydrogels for biomedical progress, condensing crucial discoveries to offer a comprehensive outlook on their ever-changing importance.

RESULTS

The analysis presents compelling evidence regarding the growing importance of hydrogels in biomedicine. It highlights their potential to significantly enhance drug delivery accuracy, redefine tissue engineering strategies, and advance diagnostic techniques. This substantiates their position as a fundamental element in the progress of modern medicine.

CONCLUSION

In summary, the constantly evolving advancement of hydrogel applications in biomedicine calls for ongoing investigation and resources, given their diverse contributions that can revolutionize therapeutic approaches and diagnostic methods, thereby paving the way for improved patient well-being.

Biofabrication methods for reconstructing extracellular matrix mimetics

In the human body, almost all cells interact with extracellular matrices (ECMs), which have tissue and organ-specific compositions and architectures. These ECMs not only function as cellular scaffolds, providing structural support, but also play a crucial role in dynamically regulating various cellular functions. This comprehensive review delves into the examination of biofabrication strategies used to develop bioactive materials that accurately mimic one or more biophysical and biochemical properties of ECMs. We discuss the potential integration of these ECM-mimics into a range of physiological and pathological in vitro models, enhancing our understanding of cellular behavior and tissue organization. Lastly, we propose future research directions for ECM-mimics in the context of tissue engineering and organ-on-a-chip applications, offering potential advancements in therapeutic approaches and improved patient outcomes.

From cells to organs: progress and potential in cartilaginous organoids research

While cartilage tissue engineering has significantly improved the speed and quality of cartilage regeneration, the underlying metabolic mechanisms are complex, making research in this area lengthy and challenging. In the past decade, organoids have evolved rapidly as valuable research tools. Methods to create these advanced human cell models range from simple tissue culture techniques to complex bioengineering approaches. Cartilaginous organoids in part mimic the microphysiology of human cartilage and fill a gap in high-fidelity cartilage disease models to a certain extent. They hold great promise to elucidate the pathogenic mechanism of a diversity of cartilage diseases and prove crucial in the development of new drugs. This review will focus on the research progress of cartilaginous organoids and propose strategies for cartilaginous organoid construction, study directions, and future perspectives.

Biomaterial-Based Gene Delivery: Advanced Tools for Enhanced Cartilage Regeneration

Gene therapy has emerged as a promising and innovative approach in cartilage regeneration. Integrating biomaterials into gene therapy offers a unique opportunity to enhance gene delivery efficiency, optimize gene expression dynamics, modulate immune responses, and promote tissue regeneration. Despite the rapid progress in biomaterial-based gene delivery, there remains a deficiency of comprehensive discussions on recent advances and their specific application in cartilage regeneration. Therefore, this review aims to provide a thorough overview of various categories of biomaterials employed in gene delivery, including both viral and non-viral vectors, with discussing their distinct advantages and limitations. Furthermore, the diverse strategies employed in gene therapy are discussed and summarized, such as the utilization of growth factors, anti-inflammatory cytokines, and chondrogenic genes. Additionally, we highlights the significant challenges that hinder biomaterial-based gene delivery in cartilage regeneration, including immune response modulation, gene delivery efficiency, and the sustainability of long-term gene expression. By elucidating the functional properties of biomaterials-based gene therapy and their pivotal roles in cartilage regeneration, this review aims to enhance further advances in the design of sophisticated gene delivery systems for improved cartilage regeneration outcomes.

Injectable hydrogel with selenium nanoparticles delivery for sustained glutathione peroxidase activation and enhanced osteoarthritis therapeutics

Reactive oxygen burst in articular chondrocytes is a major contributor to osteoarthritis progression. Although selenium is indispensable role in the antioxidant process, the narrow therapeutic window, delicate toxicity margins, and lack of an efficient delivery system have hindered its translation to clinical applications. Herein, transcriptomic and biochemical analyses revealed that osteoarthritis was associated with selenium metabolic abnormality. A novel injectable hydrogel to deliver selenium nanoparticles (SeNPs) was proposed to intervene selenoprotein expression for osteoarthritis treatment. The hydrogels based on oxidized hyaluronic acid (OHA) cross-linked with hyaluronic acid-adipic acid dihydrazide (HA-ADH) was formulated to load SeNPs through a Schiff base reaction. The hydrogels were further incorporated with SeNPs, which exhibited minimal toxicity, mechanical properties, self-healing capability, and sustained drug release. Encapsulated with SeNPs, the hydrogels facilitated cartilage repair through synergetic effects of scavenging reactive oxygen species (ROS) and depressing apoptosis. Mechanistically, the hydrogel restored redox homeostasis by targeting glutathione peroxidase-1 (GPX1). Therapeutic outcomes of the SeNPs-laden hydrogel were demonstrated in an osteoarthritis rat model created by destabilization of the medial meniscus, including cartilage protection, subchondral bone sclerosis improvement, inflammation attenuation, and pain relief were demonstrated. These results highlight therapeutic potential of OHA/HA-ADH@SeNPs hydrogels, providing fundamental insights into remedying selenium imbalance for osteoarthritis biomaterial development.

Endothelial Stat3 activation promotes osteoarthritis development

The mechanism of the balance between subchondral angiogenesis and articular damage within osteoarthritis (OA) progression remains a mystery. However, the lack of specific drugs leads to limited clinical treatment options for OA, frequently failing to prevent eventual joint destruction in patients. Increasing evidence suggests that subchondral bone angiogenesis precedes cartilage injury, while proliferating endothelial cells (ECs) induce abnormal bone formation. Signal transducer and activator of transcription 3 (Stat3) is triggered by multiple cytokines in the OA microenvironment. Here, we observed elevated Stat3 activation in subchondral bone H-type vessels. Endothelial Stat3 activation will lead to stronger cell proliferation, migration and angiogenesis by simulating ECs in OA. In contrast, either Stat3 activation inhibition or knockdown of Stat3 expression could relieve such alterations. More interestingly, blocking Stat3 in ECs alleviated angiogenesis-mediated osteogenic differentiation and chondrocyte lesions. Stat3 inhibitor reversed surgically induced subchondral bone H-type vessel hyperplasia in vivo, significantly downregulating vessel volume and vessel number. Due to the reduced angiogenesis, subchondral bone deterioration and cartilage loss were alleviated. Overall, our data suggest that endothelial Stat3 activation is an essential trigger for OA development. Therefore, targeted Stat3 blockade is a novel promising therapeutic regimen for OA.

Biomimetic Antibacterial Gelatin Hydrogels with Multifunctional Properties for Biomedical Applications

A facile novel approach of introducing dopamine and [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide via dopamine-triggered in situ synthesis into gelatin hydrogels in the presence of ZnSO4 is presented in this study. Remarkably, the resulting hydrogels showed 99.99 and 100% antibacterial efficiency against Gram-positive and Gram-negative bacteria, respectively, making them the highest performing surfaces in their class. Furthermore, the hydrogels showed adhesive properties, self-healing ability, antifreeze properties, electrical conductivity, fatigue resistance, and mechanical stability from -100 to 80 °C. The added multifunctional performance overcomes several disadvantages of gelatin-based hydrogels such as poor mechanical properties and limited thermostability. Overall, the newly developed hydrogels show significant potential for numerous biomedical applications, such as wearable monitoring sensors and antibacterial coatings.

Annexin A5 derived from matrix vesicles protects against osteoporotic bone loss via mineralization

Matrix vesicles (MVs) have shown strong effects in diseases such as vascular ectopic calcification and pathological calcified osteoarthritis and in wound repair of the skeletal system due to their membranous vesicle characteristics and abundant calcium and phosphorus content. However, the role of MVs in the progression of osteoporosis is poorly understood. Here, we report that annexin A5, an important component of the matrix vesicle membrane, plays a vital role in bone matrix homeostasis in the deterioration of osteoporosis. We first identified annexin A5 from adherent MVs but not dissociative MVs of osteoblasts and found that it could be sharply decreased in the bone matrix during the occurrence of osteoporosis based on ovariectomized mice. We then confirmed its potential in mediating the mineralization of the precursor osteoblast lineage via its initial binding with collagen type I to achieve MV adhesion and the subsequent activation of cellular autophagy. Finally, we proved its protective role in resisting bone loss by applying it to osteoporotic mice. Taken together, these data revealed the importance of annexin A5, originating from adherent MVs of osteoblasts, in bone matrix remodeling of osteoporosis and provided a new strategy for the treatment and intervention of bone loss.

Metal ions: the unfading stars of bone regeneration-from bone metabolism regulation to biomaterial applications

In recent years, bone regeneration has emerged as a remarkable field that offers promising guidance for treating bone-related diseases, such as bone defects, bone infections, and osteosarcoma. Among various bone regeneration approaches, the metal ion-based strategy has surfaced as a prospective candidate approach owing to the extensive regulatory role of metal ions in bone metabolism and the diversity of corresponding delivery strategies. Various metal ions can promote bone regeneration through three primary strategies: balancing the effects of osteoblasts and osteoclasts, regulating the immune microenvironment, and promoting bone angiogenesis. In the meantime, the complex molecular mechanisms behind these strategies are being consistently explored. Moreover, the accelerated development of biomaterials broadens the prospect of metal ions applied to bone regeneration. This review highlights the potential of metal ions for bone regeneration and their underlying mechanisms. We propose that future investigations focus on refining the clinical utilization of metal ions using both mechanistic inquiry and materials engineering to bolster the clinical effectiveness of metal ion-based approaches for bone regeneration.

Alleviation of Photoreceptor Degeneration Based on Fullerenols in rd1 Mice by Reversing Mitochondrial Dysfunction via Modulation of Mitochondrial DNA Transcription and Leakage

Poor therapeutic outcomes of antioxidants in ophthalmologic clinical applications, including glutathione during photoreceptor degeneration in retinitis pigmentosa (RP), are caused by limited anti-oxidative capacity. In this study, fullerenols are synthesized and proven to be highly efficient in vitro radical scavengers. Fullerenol-based intravitreal injections significantly improve the flash electroretinogram and light/dark transition tests performed for 28 days on rd1 mice, reduce the thinning of retinal outer nuclear layers, and preserve the Rhodopsin, Gnat-1, and Arrestin expressions of photoreceptors. RNA-sequencing, RT-qPCR, and Western blotting validate that mitochondrial DNA (mt-DNA)-encoded genes of the electron transport chain (ETC), such as mt-Nd4l, mt-Co1, mt-Cytb, and mt-Atp6, are drastically downregulated in the retinas of rd1 mice, whereas nuclear DNA (n-DNA)-encoded genes, such as Ndufa1 and Atp5g3, are abnormally upregulated. Fullerenols thoroughly reverse the abnormal mt-DNA and n-DNA expression patterns of the ETC and restore mitochondrial function in degenerating photoreceptors. Additionally, fullerenols simultaneously repress Flap endonuclease 1 (FEN1)-mediated mt-DNA cleavage and mt-DNA leakage via voltage-dependent anion channel (VDAC) pores by downregulating the transcription of Fen1 and Vdac1, thereby inactivating the downstream pro-inflammatory cGAS-STING pathway. These findings demonstrate that fullerenols can effectively alleviate photoreceptor degeneration in rd1 mice and serve as a viable treatment for RP.