Injectable hydrogels: An emerging therapeutic strategy for cartilage regeneration

Recent progress in alginate-based nanocomposites for bone tissue engineering applications

Approximately 5-10 % of fractures are associated with non-union, posing a significant challenge in orthopedic applications. Addressing this issue, innovative approaches beyond traditional grafting techniques like bone tissue engineering (BTE) are required. Biomaterials, combined with cells and bioactive molecules in BTE, are critical in managing non-union. Alginate, a natural polysaccharide, has gained widespread recognition in bone regeneration due to its bioavailability, its ability to form gels through crosslinking with divalent cations, and its cost-effectiveness. However, its inherent mechanical weaknesses necessitate a combinatorial approach with other biomaterials. In recent years, nanoscale biomaterials have gained prominence for bone regeneration due to their structural and compositional resemblance to natural bone, offering a supportive environment that regulates cell proliferation and differentiation for new bone formation. In this review, we briefly outline the synthesis of alginate-based nanocomposites using different fabrication techniques, such as hydrogels, 3D-printed scaffolds, fibers, and surface coatings with polymer, ceramic, carbon, metal, or lipid-based nanoparticles. These alginate-based nanocomposites elicit angiogenic, antibacterial, and immunomodulatory properties, thereby enhancing the osteogenic potential as an insightful measure for treating non-union. Despite the existence of similar literature, this work delivers a recent and focused examination of the latest advancements and insights on the potential of alginate-based nanocomposites for BTE applications. This review also underscores the obstacles that alginate-based nanocomposites must overcome to successfully transition into clinical applications.

A comprehensive review on using injectable chitosan microgels for osteochondral tissue repair

Restoring cartilage to healthy state is challenging due to low cell density and hence low regenerative capacity. The current platforms are not compatible with clinical translation and require dedicated handling of trained personnel. However, by engineering and implanting cell microaggregates in higher concentrations, efficient formation of new cartilage can be achieved, even in the absence of exogenous growth factors. Therefore, one-step surgeries are preferable for novel treatments and we need cell laden microgels allowing the formation of microaggregaets in vivo. Injectability is a key parameter for in situ forming the shape and minimally invasive clinical applications. Hydrogels as bioinks can restore damaged tissues to their primary shape. Chitosan is a polysaccharide derived from chitin with abundant usage in tissue engineering. This review highlights the use of chitosan as an injectable hydrogel for osteochondral defects. Several studies focused on encapsulating mesenchymal stem cells within chitosan hydrogels have been categorized and incorporating microfluidic devices has been identified in the forefront to form microgels. Additionally, the printability is another convenience of chitosan for using in 3D printing for cartilage tissue engineering which is described in this review.

Micelle into gel thermosensitive intra-articular hydrogels for osteoarthritis management

Osteoarthritis (OA) is a chronic and degenerative joint disease with a rising incidence worldwide. Current therapeutic approaches primarily focus on symptom relief through systemic administration, which raises safety concerns related to side effects and long-term use. In this context, the local administration of natural compounds with anti-inflammatory and anti-arthritic properties, such as β-Lapachone constitutes an interesting alternative. In this work, we prepared and characterized injectable thermosensitive hybrid hydrogels loaded with β-Lapachone. A comprehensive characterization of the hydrogel systems was performed, including micellar diameter, mechanical properties at different temperatures, the ability to control drug release and microstructure. The anti-inflammatory activity of the free drug, as well as that of the blank or loaded hydrogels was then evaluated ex vivo, using OA cartilage explants. Additionally, in vivo studies were carried out in a rabbit model of OA to assess their clinical potential. The results suggest that the hydrogel systems possess a composite microstructure integrating micelles, together with a temperature-responsive stiffness and the ability to modulate drug release. In addition, β-Lapachone-loaded hydrogels display an interesting immunomodulatory potential ex vivo, as they were able to efficiently reduce the secretion of several proinflammatory mediators, such as IL-6, MMP9, MMP13 and CXCL8. Furthermore, the drug-loaded hydrogels were found to improve in vivo cartilage and bone histomorphometric markers, such as subchondral bone thickness, as well as early signs of cartilage damage, such as the fibrillation index. Therefore, the developed β-Lapachone-loaded thermosensitive hydrogels constitute a promising alternative for OA management.

Robot-Assisted Synthesis of Structure-Controlled Star-Cluster Hydrogels with Targeted Mechanophysical Properties for Biomedical Applications

Advancements in polymer chemistry have enabled the design of macromolecular structures with tailored properties for diverse applications. Reversible addition-fragmentation chain-transfer (RAFT) polymerization is a controlled technique for precise polymer design. Automation tools further enhance polymer synthesis by enabling the rapid, reproducible preparation of polymer libraries. This study utilizes an automated platform and a biologically friendly bio-Fenton RAFT synthesis method to create hydrogels with embedded star polymers derived from complex block copolymers with controlled block lengths and sequences. Automation improves the efficiency compared to manual methods, while the choice of prepolymer and polymerization techniques ensures biocompatibility. Hydrogels formed by cross-linking linear block copolymers exhibit tunable physical, chemical, and mechanical properties. By systematically altering the prepolymer block sequences, promising hydrogel candidates for enhanced cell biocompatibility and proliferation are identified. These synthetic hydrogels mimic cellular microenvironments and offer a robust platform for biomedical applications, paving the way for an efficient hydrogel design and synthesis.

Biomedical applications of functional hydrogels: Innovative developments, relevant clinical trials and advanced products

Functional hydrogels are used for numerous biomedical applications such as tissue engineering, wound dressings, lubricants, contact lenses and advanced drug delivery systems. Most of them are based on synthetic or natural polymers forming a three-dimensional network that contains aqueous media. Among synthetic polymers, poly(meth)acrylates, polyethyleneglycols, poly(vinylalcohols), poly(vinylpyrrolidones), PLGA and poly(urethanes) are of high relevance, whereas natural polymers are mainly polysaccharides such as hyaluronic acid, alginate or chitosan and proteins such as albumin, collagen or elastin. In contrast to most synthetic polymers, natural polymers are biodegradable. Both synthetic and natural polymers are often chemically modified in order to improve or induce favorable properties and functions like high mechanical strength, stiffness, elasticity, high porosity, adhesive properties, in situ gelling properties, high water binding capacity or drug release controlling properties. Within this review we provide an overview about the broad spectrum of biomedical applications of functional hydrogels, summarize innovative approaches, discuss the concept of relevant functional hydrogels that are in clinical trials and highlight advanced products as examples for successful developments.

Unlocking the Potential of Hybrid Nanocomposite Hydrogels: Design, Mechanical Properties and Biomedical Performances

Hybrid nanocomposite hydrogels consist of the homogeneous incorporation of nano‐objects in a hydrogel matrix. The latter, whether made of natural or synthetic materials, possesses a microporous, soft structure that makes it an ideal host for a variety of polymer and lipid‐based nano‐objects as well as metal‐ and silica‐based ones. By carefully choosing the composition and the proportions of the different constituents, hybrid hydrogels can display a wide array of properties, from simple enhancement of mechanical characteristics to specific bioactivity. This review aims to provide an overview of the state of the art in hybrid hydrogels highlighting key aspects that make them a promising choice for a variety of biomedical applications. Strategies for the preparation of hybrid hydrogels are discussed by covering the selection of individual components. The review will also explore the physico‐chemical and rheological characterization of these materials, which is essential for understanding their structure and function, ultimately satisfying specifications for the intended use. Successful examples of biomedical applications will also be presented, and the main challenges to be met will be discussed, with the aim of stimulating the research community to exploit the full potential of these materials.

Therapeutic Controlled Release Strategies for Human Osteoarthritis

Osteoarthritis is a progressive, irreversible debilitating whole joint disease that affects millions of people worldwide. Despite the availability of various options (non-pharmacological and pharmacological treatments and therapy, orthobiologics, and surgical interventions), none of them can definitively cure osteoarthritis in patients. Strategies based on the controlled release of therapeutic compounds via biocompatible materials may provide powerful tools to enhance the spatiotemporal delivery, expression, and activities of the candidate agents as a means to durably manage the pathological progression of osteoarthritis in the affected joints upon convenient intra-articular (injectable) delivery while reducing their clearance, dissemination, or side effects. The goal of this review is to describe the current knowledge and advancements of controlled release to treat osteoarthritis, from basic principles to applications in vivo using therapeutic recombinant molecules and drugs and more innovatively gene sequences, providing a degree of confidence to manage the disease in patients in a close future.

Forty Years of the Use of Cells for Cartilage Regeneration: The Research Side

Background: The treatment of articular cartilage damage has always represented a problem of considerable practical interest for orthopedics. Over the years, many surgical techniques have been proposed to induce the growth of repairing tissue and limit degeneration. In 1994, the turning point occurred: implanted autologous cells paved the way for a new treatment option based more on regeneration than repair. Objectives: This review aims to outline biological and clinical advances, from the use of mature adult chondrocytes to cell-derived products, going through progenitor cells derived from bone marrow or adipose tissue and their concentrates for articular cartilage repair. Moreover, it highlights the relevance of gene therapy as a valuable tool for successfully implementing current regenerative treatments, and overcoming the limitations of the local delivery of growth factors. Conclusions: Finally, this review concludes with an outlook on the importance of understanding the role and mechanisms of action of the different cell compounds with a view to implementing personalized treatments.

Innovative Biotherapies and Nanotechnology in Osteoarthritis: Advancements in Inflammation Control and Cartilage Regeneration

Osteoarthritis (OA) is among the most prevalent degenerative joint disorders worldwide, particularly affecting the aging population and imposing significant disability and economic burdens. The disease is characterized by progressive degradation of articular cartilage and chronic inflammation, with no effective long-term treatments currently available to address the underlying causes of its progression. Conventional therapies primarily manage symptoms such as pain and inflammation but fail to repair damaged tissues. Emerging biotherapies and regenerative medicine approaches offer promising alternatives by addressing cartilage repair and inflammation control at the molecular level. This review explores the recent advancements in biotherapeutic strategies, including mesenchymal stem cell (MSC) therapy, growth factors, and tissue engineering, which hold the potential for promoting cartilage regeneration and modulating the inflammatory microenvironment. Additionally, the integration of nanotechnology has opened new avenues for targeted drug delivery systems and the development of innovative nanomaterials that can further enhance the efficacy of biotherapies by precisely targeting inflammation and cartilage damage. This article concludes by discussing the current clinical applications, the ongoing clinical trials, and the future research directions necessary to confirm the safety and efficacy of these advanced therapies for OA management. With these advancements, biotherapies combined with nanotechnology may revolutionize the future of OA treatment by offering precise and effective solutions for long-term disease management and improved patient outcomes.

An Advanced Mechanically Active Osteoarthritis-on-Chip Model to Test Injectable Therapeutic Formulations: The SYN321 Case Study

Current treatments for osteoarthritis (OA) often fail to address the underlying pathophysiology and may have systemic side effects, particularly associated with long-term use of non-steroidal anti-inflammatory drugs (NSAIDs). Thus, researchers are currently directing their efforts toward innovative polymer-drug combinations, such as mixtures of hyaluronic acid viscoelastic hydrogels and NSAIDs like diclofenac, to ensure sustained release of the NSAID within the joint following intra-articular injection. However, the progress of novel injectable therapies for OA is hindered by the absence of preclinical models that accurately represent the pathology of the disease. The uBeat® MultiCompress platform is here presented as a novel approach for studying anti-OA injectable therapeutics on human mechanically-damaged OA cartilage microtissues, in a physiologically relevant environment. This platform can accommodate injectable therapeutic formulations and is successfully tested with SYN321, a novel diclofenac-sodium hyaluronate conjugate under development as a treatment for knee OA. Results indicate the platform's effectiveness in evaluating therapeutic potential, showing downregulation of inflammatory markers and reduction in matrix degradation in OA cartilage micro-tissues treated with SYN321. The uBeat® MultiCompress platform thus represents a valuable tool for OA research, offering a bridge between traditional in vitro studies and potential clinical applications, with implications for future drug discovery.

Controlled Stimulus-Responsive Delivery Systems for Osteoarthritis Treatment

Osteoarthritis (OA), a common and disabling degenerative joint disease, affects millions of people worldwide and imposes a considerable burden on patients and society due to its high prevalence and economic costs. The pathogenesis of OA is closely related to the progressive degradation of articular cartilage and the accompany inflammation; however, articular cartilage itself cannot heal and modulate the inflammation due to the lack of nerves, blood vessels, and lymph-vessels. Therefore, reliable and effective methods to treat OA remain highly desired. Local administration of drugs or bioactive materials by intra-articular injection of the delivery system represents a promising approach to treat OA, especially considering the prolonged joint retention, cartilage or chondrocytes targeting, and stimuli-responsive release to achieve precision OA therapy. This article summarizes and discusses the advances in the currently used delivery systems (nanoparticle, hydrogel, liposome, and microsphere) and then focuses on their applications in OA treatment from the perspective of endogenous stimulus (redox reactions, pH, enzymes, and temperature) and exogenous stimulus (near-infrared, magnetic, and ultrasound)-responsive release. Finally, the challenges and potential future directions for the development of nano-delivery systems are summarized.

Edge advances in nanodrug therapies for osteoarthritis treatment

As global population and lifestyles change, osteoarthritis (OA) is becoming a major healthcare challenge world. OA, a chronic condition characterized by inflammatory and degeneration, often present with joint pain and can lead to irreversible disability. While there is currently no cure for OA, it is commonly managed using nonsteroidal anti-inflammatory drugs (NSAIDs), glucocorticoids, and glucosamine. Although these treatments can alleviate symptoms, it is difficult to effectively deliver and sustain therapeutic agents within joints. The emergence of nanotechnology, particularly in form of smart nanomedicine, has introduced innovative therapeutic approaches for OA treatment. Nanotherapeutic strategies offer promising advantages, including more precise targeting of affected areas, prolonged therapeutic effects, enhanced bioavailability, and reduced systemic toxicity compared to traditional treatments. While nanoparticles show potential as a viable delivery system for OA therapies based on encouraging lab-based and clinical trials results, there remails a considerable gap between current research and clinical application. This review highlights recent advances in nanotherapy for OA and explore future pathways to refine and optimize OA treatments strategies.

Delivery Strategies of Growth Factors in Cartilage Tissue Engineering

Cartilage plays an important role in supporting soft tissues, reducing joint friction, and distributing pressure. However, its self-repair capacity is limited due to the lack of blood vessels, nerves, and lymphatic systems. Tissue engineering offers a potential solution to promote cartilage regeneration by combining scaffolds, seed cells, and growth factors. Among these, growth factors play a critical role in regulating cell proliferation, differentiation, and extracellular matrix remodeling. However, their instability, susceptibility to degradation and potential side effects limit their effectiveness. This article reviews the main growth factors used in cartilage tissue engineering and their delivery strategies, including affinity-based delivery, carrier-assisted delivery, stimuli-responsive delivery, spatial structure-based delivery, and cell system-based delivery. Each method shows unique advantages in enhancing the delivery efficiency and specificity of growth factors but also faces challenges such as cost, biocompatibility, and safety. Future research needs to further optimize these strategies to achieve more efficient, safe, and economical delivery of growth factors, thereby advancing the clinical application of cartilage tissue engineering.

Poison Turned Panacea: Arsenic Trioxide Loaded Hydrogel for Inhibiting Scar Formation in Wound Healing

Without intervention, the natural wound healing process can often result in scarring, which can have detrimental effects on both the physical and mental well-being of patients. Therefore, it is crucial to develop biomaterials that can promote healing without scarring. Regulating the Yes-associated protein-1/PDZ-binding motif (YAP/TAZ) signaling pathway is possible to reduce excessive fibrosis of fibroblasts and proliferation of vascular endothelial cells, ultimately impacting scar formation. Arsenic trioxide (ATO), an ancient drug with medicinal and toxic properties, has shown promise in regulating this pathway. An ATO-loaded hydrogel dressing (ATO@CS/SA) was created to facilitate scarless wound healing, utilizing chitosan (CS) and sodium alginate (SA) to prevent direct contact of ATO with the wound tissue and minimize potential side effects. In vitro studies demonstrated that low concentrations of ATO did not impact cell viability and even promoted proliferation and migration. Co-culturing the hydrogel with fibroblasts and vascular endothelial cells led to decreased expression levels of YAP and TAZ. Animal studies over a 90-day period revealed significant inhibition of scar formation with this system. Histological experiments further confirmed that the decreased expression of YAP and TAZ was responsible for this outcome. In conclusion, when administered at the appropriate dose, ATO can be repurposed from a traditional poison to a therapeutic agent, effectively suppressing excessive cell fibrosis and blood vessel proliferation and offering a novel approach to scar-free treatment.

Cutting-Edge Hydrogel Technologies in Tissue Engineering and Biosensing: An Updated Review

Hydrogels, known for their unique ability to retain large amounts of water, have emerged as pivotal materials in both tissue engineering and biosensing applications. This review provides an updated and comprehensive examination of cutting-edge hydrogel technologies and their multifaceted roles in these fields. Initially, the chemical composition and intrinsic properties of both natural and synthetic hydrogels are discussed, highlighting their biocompatibility and biodegradability. The manuscript then probes into innovative scaffold designs and fabrication techniques such as 3D printing, electrospinning, and self-assembly methods, emphasizing their applications in regenerating bone, cartilage, skin, and neural tissues. In the realm of biosensing, hydrogels' responsive nature is explored through their integration into optical, electrochemical, and piezoelectric sensors. These sensors are instrumental in medical diagnostics for glucose monitoring, pathogen detection, and biomarker identification, as well as in environmental and industrial applications like pollution and food quality monitoring. Furthermore, the review explores cross-disciplinary innovations, including the use of hydrogels in wearable devices, and hybrid systems, and their potential in personalized medicine. By addressing current challenges and future directions, this review aims to underscore the transformative impact of hydrogel technologies in advancing healthcare and industrial practices, thereby providing a vital resource for researchers and practitioners in the field.

Cartilage Repair: Promise of Adhesive Orthopedic Hydrogels

Cartilage repair remains a major challenge in human orthopedic medicine, necessitating the application of innovative strategies to overcome existing technical and clinical limitations. Adhesive hydrogels have emerged as promising candidates for cartilage repair promotion and tissue engineering, offering key advantages such as enhanced tissue integration and therapeutic potential. This comprehensive review navigates the landscape of adhesive hydrogels in cartilage repair, discussing identified challenges, shortcomings of current treatment options, and unique advantages of adhesive hydrogel products and scaffolds. While emphasizing the critical need for in situ lateral integration with surrounding tissues, we dissect current limitations and outline future perspectives for hydrogel scaffolds in cartilage repair. Moreover, we examine the clinical translation pathway and regulatory considerations specific to adhesive hydrogels. Overall, this review synthesizes the existing insights and knowledge gaps and highlights directions for future research regarding adhesive hydrogel-based devices in advancing cartilage tissue engineering.

Kinetics and Retention of Polystyrenesulfonate for Proteoglycan Replacement in Cartilage

Tissue hydration provides articular cartilage with dynamic viscoelastic properties. Early stage osteoarthritis (OA) is marked by loss of proteoglycans and glycosaminoglycans (GAG), lowering fixed charge density, and impairing tissue osmotic function. The most common GAG replacement, chondroitin sulfate (CS), has failed to show effectiveness. Here, we investigated a synthetic polyelectrolyte, poly(styrenesulfonate) (PSS), both as a model compound to investigate polyelectrolyte transport in cartilage, and as a potential candidate to restore bulk fixed charge density in cartilage with GAG loss. Through bovine explants and histology, we determined zonal-based effective diffusion coefficients for three different molecular weights of PSS. Compared to CS, PSS was retained longer in GAG-depleted cartilage in static and compression-based desorption experiments. We explained enhanced solute performance of PSS by its more compact morphology and higher charge density by small-angle X-ray scattering. This study may improve design of GAG mimetic molecules for repairing osmotic function in OA cartilage.

Functionalized hydrogels as smart gene delivery systems to treat musculoskeletal disorders

Despite critical advances in regenerative medicine, the generation of definitive, reliable treatments for musculoskeletal diseases remains challenging. Gene therapy based on the delivery of therapeutic genetic sequences has strong value to offer effective, durable options to decisively manage such disorders. Furthermore, scaffold-mediated gene therapy provides powerful alternatives to overcome hurdles associated with classical gene therapy, allowing for the spatiotemporal delivery of candidate genes to sites of injury. Among the many scaffolds for musculoskeletal research, hydrogels raised increasing attention in addition to other potent systems (solid, hybrid scaffolds) due to their versatility and competence as drug and cell carriers in tissue engineering and wound dressing. Attractive functionalities of hydrogels for musculoskeletal therapy include their injectability, stimuli-responsiveness, self-healing, and nanocomposition that may further allow to upgrade of them as "intelligently" efficient and mechanically strong platforms, rather than as just inert vehicles. Such functionalized hydrogels may also be tuned to successfully transfer therapeutic genes in a minimally invasive manner in order to protect their cargos and allow for their long-term effects. In light of such features, this review focuses on functionalized hydrogels and demonstrates their competence for the treatment of musculoskeletal disorders using gene therapy procedures, from gene therapy principles to hydrogel functionalization methods and applications of hydrogel-mediated gene therapy for musculoskeletal disorders, while remaining challenges are being discussed in the perspective of translation in patients. STATEMENT OF SIGNIFICANCE: Despite advances in regenerative medicine, the generation of definitive, reliable treatments for musculoskeletal diseases remains challenging. Gene therapy has strong value in offering effective, durable options to decisively manage such disorders. Scaffold-mediated gene therapy provides powerful alternatives to overcome hurdles associated with classical gene therapy. Among many scaffolds for musculoskeletal research, hydrogels raised increasing attention. Functionalities including injectability, stimuli-responsiveness, and self-healing, tune them as "intelligently" efficient and mechanically strong platforms, rather than as just inert vehicles. This review introduces functionalized hydrogels for musculoskeletal disorder treatment using gene therapy procedures, from gene therapy principles to functionalized hydrogels and applications of hydrogel-mediated gene therapy for musculoskeletal disorders, while remaining challenges are discussed from the perspective of translation in patients.

Advances on carbon nanomaterials and their applications in medical diagnosis and drug delivery

Carbon nanomaterials are indispensable due to their unique properties of high electrical conductivity, mechanical strength and thermal stability, which makes them important nanomaterials in biomedical applications and waste management. Limitations of conventional nanomaterials, such as limited surface area, difficulty in fine tuning electrical or thermal properties and poor dispersibility, calls for the development of advanced nanomaterials to overcome such limitations. Commonly, carbon nanomaterials were synthesized by chemical vapor deposition (CVD), laser ablation or arc discharge methods. The advancement in these techniques yielded monodispersed carbon nanotubes (CNTs) and allows p-type and n-type doping to enhance its electrical and catalytic activities. The functionalized CNTs showed exceptional mechanical, electrical and thermal conductivity (3500-5000 W/mK) properties. On the other hand, carbon quantum dots (CQDs) exhibit strong photoluminescence properties with high quantum yield. Carbon nanohorns are another fascinating type of nanomaterial that exhibit a unique structure with high surface area and excellent adsorption properties. These carbon nanomaterials could improve waste management by adsorbing pollutants from water and soil, enabling precise environmental monitoring, while enhancing wastewater treatment and drug delivery systems. Herein, we have discussed the potentials of all these carbon nanomaterials in the context of innovative waste management solutions, fostering cleaner environments and healthier ecosystems for diverse biomedical applications such as biosensing, drug delivery, and environmental monitoring.

Exploring Platelet-Rich Plasma Therapy for Knee Osteoarthritis: An In-Depth Analysis

The use of platelet-rich plasma (PRP) in all medical fields is currently gaining popularity (1). PRP is a biological product that can be defined as a segment of the plasma fraction of autologous blood with a platelet concentration level above the baseline (2). The fact that it has uses in tissue regeneration and wound healing has caught the eye of orthopedic surgeons as well, as intra-articular treatments have continued to evolve. Its benefits in the treatment of different osteoarticular pathologies are of great interest in the evolving orthopedic community, targeting mostly knee osteoarthritis, meniscus and ligament injuries (3). The purpose of this review is to update the reader on the current uses of platelet-rich plasma (PRP) in the treatment of knee osteoarthritis pathology and to provide clinical feedback on its uses in the fields of orthopedic and sports medicine practice (4). We proceeded in studying 180 titles and abstracts eligible for inclusion. Compared to alternative treatments, PRP injections greatly improve the function of the knee joint.

Carboxymethyl cellulose/quaternized chitosan hydrogel loaded with polydopamine nanoparticles promotes spinal cord injury recovery by anti-ferroptosis and M1/M2 polarization modulation

Spinal cord injury (SCI) represents a catastrophic neurological condition resulting in long-term loss of motor, autonomic, and sensory functions. Recently, ferroptosis, an iron-regulated form of cell death distinct from apoptosis, has emerged as a potential therapeutic target for SCI. In this study, we developed an injectable hydrogel composed of carboxymethyl cellulose (CMC), and quaternized chitosan (QCS), loaded with modified polydopamine nanoparticles (PDA NPs), referred to as CQP hydrogel. This hydrogel effectively scavenged reactive oxygen species (ROS), prevented the accumulation of Fe2+ and lipid peroxidation associated with ferroptosis, and restored mitochondrial functions in primary neuronal cells. When administered to animal models (rats) with SCI, the CQP hydrogels improved motor function by regulating iron homeostasis, inhibiting ferroptosis, and mitigating oxidative stress injury. Both in vitro and in vivo studies corroborated the capacity of CQP hydrogels to promote the shift from M1 to M2 polarization of microglia/macrophages. These findings suggest that CQP hydrogels, functioning as a localized iron-chelating system, have potential as biomaterials to enhance recovery from SCI by targeting ferroptosis and modulating anti-inflammatory macrophages activity.

Propelling Minimally Invasive Tissue Regeneration With Next-Era Injectable Pre-Formed Scaffolds

The growing aging population, with its associated chronic diseases, underscores the urgency for effective tissue regeneration strategies. Biomaterials play a pivotal role in the realm of tissue reconstruction and regeneration, with a distinct shift toward minimally invasive (MI) treatments. This transition, fueled by engineered biomaterials, steers away from invasive surgical procedures to embrace approaches offering reduced trauma, accelerated recovery, and cost-effectiveness. In the realm of MI tissue repair and cargo delivery, various techniques are explored. While in situ polymerization is prominent, it is not without its challenges. This narrative review explores diverse biomaterials, fabrication methods, and biofunctionalization for injectable pre-formed scaffolds, focusing on their unique advantages. The injectable pre-formed scaffolds, exhibiting compressibility, controlled injection, and maintained mechanical integrity, emerge as promising alternative solutions to in situ polymerization challenges. The conclusion of this review emphasizes the importance of interdisciplinary design facilitated by synergizing fields of materials science, advanced 3D biomanufacturing, mechanobiological studies, and innovative approaches for effective MI tissue regeneration.

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.

Tissue engineering and future directions in regenerative medicine for knee cartilage repair: a comprehensive review

This review evaluates the current landscape and future directions of regenerative medicine for knee cartilage repair, with a particular focus on tissue engineering strategies. In this context, scaffold-based approaches have emerged as promising solutions for cartilage regeneration. Synthetic scaffolds, while offering superior mechanical properties, often lack the biological cues necessary for effective tissue integration. Natural scaffolds, though biocompatible and biodegradable, frequently suffer from inadequate mechanical strength. Hybrid scaffolds, combining elements of both synthetic and natural materials, present a balanced approach, enhancing both mechanical support and biological functionality. Advances in decellularized extracellular matrix scaffolds have shown potential in promoting cell infiltration and integration with native tissues. Additionally, bioprinting technologies have enabled the creation of complex, bioactive scaffolds that closely mimic the zonal organization of native cartilage, providing an optimal environment for cell growth and differentiation. The review also explores the potential of gene therapy and gene editing techniques, including CRISPR-Cas9, to enhance cartilage repair by targeting specific genetic pathways involved in tissue regeneration. The integration of these advanced therapies with tissue engineering approaches holds promise for developing personalized and durable treatments for knee cartilage injuries and osteoarthritis. In conclusion, this review underscores the importance of continued multidisciplinary collaboration to advance these innovative therapies from bench to bedside and improve outcomes for patients with knee cartilage damage.

A review of recent advances of cellulose-based intelligent-responsive hydrogels as vehicles for controllable drug delivery system

To realize the maximum therapeutic activity of medicine and protect the body from the adverse effects of active ingredients, drug delivery systems (DDS) featured with targeted transportation sites and controllable release have captured extensive attention over the past decades. Hydrogels with unique three-dimensional (3D) porous structures present tunable capacity, controllable degradation, various stimuli sensitivity, therapeutic agents encapsulation, and loaded drugs protection properties, which endow hydrogels with bred-in-the-bone advantages as vehicles for drug delivery. In recent years, with the impressive consciousness of the "back-to-nature" concept, biomass materials are becoming the 'rising star' as the hydrogels building blocks for controlled drug release carriers due to their biodegradability, biocompatibility, and non-toxicity properties. In particular, cellulose and its derivatives are promising candidates for fabricating hydrogels as their rich sources and high availability, and various smart cellulose-based hydrogels as targeted carriers under exogenous such as light, electric field, and magnetic field or endogenous such as pH, temperature, ionic strength, and redox gradients. In this review, we summarized the main synthetic strategies of smart cellulose-based hydrogels including physical and chemical cross-linking, and illustrated the detailed intelligent-responsive mechanism of hydrogels in DDS under external stimulus. Additionally, the ongoing development and challenges of cellulose-based hydrogels in the biomedical field are also presented.

Minimally invasive delivery of human umbilical cord-derived mesenchymal stem cells by an injectable hydrogel via Diels-Alder click reaction for the treatment of intrauterine adhesions

Intrauterine adhesions (IUA) are the most common cause of uterine infertility, and conventional treatments have not consistently achieved satisfactory pregnancy rates. Stem cell therapy shows promising potential for the clinical treatment of IUA. Although various advanced biomaterials have been designed for delivering stem cells to the uterine cavity, there remain significant challenges, particularly in devising therapeutic strategies for clinical application that minimize surgical incisions and conform to the intricate structure of uterine cavity. Herein, an injectable hydrogel loaded with human umbilical cord-derived mesenchymal stem cells (UCMSCs) was synthesized via the Diels-Alder click reaction for endometrial regeneration and fertility restoration, exhibiting suitable mechanical properties, good biocompatibility, and desirable degradation properties. Notably, this hydrogel permitted minimally invasive administration and integrated seamlessly with surrounding tissue. Our study revealed that the UCMSCs-laden injectable hydrogel enhanced cell proliferation, migration, angiogenesis, and exhibited anti-fibrotic effects in vitro. The implantation of this hydrogel significantly facilitated endometrium regeneration and restored fertility in a rat endometrial damage model. Mechanistically, in vivo results indicated that the UCMSCs-laden injectable hydrogel effectively promoted macrophage recruitment and facilitated M2 phenotype polarization. Collectively, this hydrogel demonstrated efficacy in regenerating damaged endometrium, leading to the restoration of fertility. Consequently, it holds promise as a potential therapeutic strategy for endometrial damage and fertility decline arising from intrauterine adhesions. STATEMENT OF SIGNIFICANCE: Severe endometrial traumas frequently lead to intrauterine adhesions and subsequent infertility. Stem cell therapy shows promising potential for the clinical treatment of IUA; however, challenges remain, including low delivery efficiency and compromised stem cell activity during the delivery process. In this study, we fabricated an injectable hydrogel loaded with UCMSCs via the Diels-Alder click reaction, which exhibited unique bioorthogonality. The in situ-gelling hydrogels could be introduced through a minimally invasive procedure and adapt to the intricate anatomy of the uterus. The UCMSCs-laden injectable hydrogel promoted endometrial regeneration and fertility restoration in a rat endometrial damage model, efficaciously augmenting macrophage recruitment and promoting their polarization to the M2 phenotype. The administration of UCMSCs-laden injectable hydrogel presents a promising therapeutic strategy for patients with severe intrauterine adhesion.

Delivery of dental pulp stem cells by an injectable ROS-responsive hydrogel promotes temporomandibular joint cartilage repair via enhancing anti-apoptosis and regulating microenvironment

Temporomandibular joint (TMJ) cartilage repair poses a considerable clinical challenge, and tissue engineering has emerged as a promising solution. In this study, we developed an injectable reactive oxygen species (ROS)-responsive multifunctional hydrogel (RDGel) to encapsulate dental pulp stem cells (DPSCs/RDGel in short) for the targeted repair of condylar cartilage defect. The DPSCs/RDGel composite exhibited a synergistic effect in the elimination of TMJ OA (osteoarthritis) inflammation via the interaction between the hydrogel component and the DPSCs. We first demonstrated the applicability and biocompatibility of RDGel. RDGel encapsulation could enhance the anti-apoptotic ability of DPSCs by inhibiting P38/P53 mitochondrial apoptotic signal in vitro. We also proved that the utilization of DPSCs/RDGel composite effectively enhanced the expression of TMJOA cartilage matrix and promoted subchondral bone structure in vivo. Subsequently, we observed the synergistic improvement of DPSCs/RDGel composite on the oxidative stress microenvironment of TMJOA and its regulation and promotion of M2 polarization, thereby confirmed that M2 macrophages further promoted the condylar cartilage repair of DPSCs. This is the first time application of DPSCs/RDGel composite for the targeted repair of TMJOA condylar cartilage defects, presenting a novel and promising avenue for cell-based therapy.