Silencing Gene-Engineered Injectable Hydrogel Microsphere for Regulation of Extracellular Matrix Metabolism Balance

Research progress on intervertebral disc repair strategies and mechanisms based on hydrogel

Intervertebral disc degeneration (IDD) arises from a complex interplay of genetic, environmental, and age-related factors, culminating in a spectrum of low back pain (LBP) disorders that exert significant societal and economic impact. The present therapeutic landscape for IDD poses formidable clinical hurdles, necessitating the exploration of innovative treatment modalities. The hydrogel, as a biomaterial, exhibits superior biocompatibility compared to other biomaterials such as bioceramics and bio-metal materials. It also demonstrates mechanical properties closer to those of natural intervertebral discs (IVDs) and favorable biodegradability conducive to IVD regeneration. Therefore, it has emerged as a promising candidate material in the field of regenerative medicine and tissue engineering for treating IDD. Hydrogels have made significant strides in the field of IDD treatment. Particularly, injectable hydrogels not only provide mechanical support but also enable controlled release of bioactive molecules, playing a crucial role in mitigating inflammation and promoting extracellular matrix (ECM) regeneration. Furthermore, the ability of injectable hydrogels to achieve minimally invasive implantation helps minimize tissue damage. This article initially provides a concise exposition of the structure and function of IVD, the progression of IDD, and delineates extant clinical interventions for IDD. Subsequently, it categorizes hydrogels, encapsulates recent advancements in biomaterials and cellular therapies, and delves into the mechanisms through which hydrogels foster disc regeneration. Ultimately, the article deliberates on the prospects and challenges attendant to hydrogel therapy for IDD.

Manipulation of Oxygen Tension in Damaged Regions via Hypoxia-Induced IPN Hydrogel Microspheres for Intervertebral Disc Regeneration

Disruption of low oxygen tension homeostasis during intervertebral disc degeneration inhibits endogenous stem cell viability and function, posing a challenge for endogenous regeneration. Here, to achieve sustained hypoxia manipulation, constructed hypoxia-inducible interpenetrating polymer network (IPN) hydrogel microspheres (HIMS) are constructed by microfluidics to integrate the hypoxic system with a stabilizing network. The IPN is synthesized through a two-step polymerization process, consisting of rapid photo-crosslinked gelatin methacrylate anhydride (GM) polymer I and slow enzyme-crosslinked vanillin-grafted gelatin (GV) polymer II. The enzymatic reaction between GV and laccase is able to create a hypoxic microenvironment to modulate oxygen tension in situ within the injured region. HIMS can reduce microenvironmental oxygen tension by 1/3 and maintain a hypoxic microenvironment for up to 5 days, thereby activating the PI3K/AKT/HIF-1α signaling pathway in endogenous stem cells to promote differentiation into nucleus pulposus-like cells. Additionally, NSC-Exos are loaded onto HIMS to trigger endogenous progenitor/stem cell recruitment and migration. Both in vitro and in vivo assays demonstrate that NSC-Exos@HIMS facilitates stem cell recruitment, targets differentiation, and stimulates extracellular matrix synthesis. Overall, the microspheres established herein provide a novel strategy for manipulating oxygen tension and enhancing endogenous tissue regeneration in injured regions during intervertebral disc degeneration.

Polysaccharide-based biomaterials for regenerative therapy in intervertebral disc degeneration

Intervertebral disc (IVD) degeneration represents a significant cause of chronic back pain and disability, with a substantial impact on the quality of life. Conventional therapeutic modalities frequently address the symptoms rather than the underlying etiology, underscoring the necessity for regenerative therapies that restore disc function. Polysaccharide-based materials, such as hyaluronic acid, alginate, chitosan, and chondroitin sulfate, have emerged as promising candidates for intervertebral disc degeneration (IVDD) therapy due to their biocompatibility, biodegradability, and ability to mimic the native extracellular matrix (ECM) of the nucleus pulposus (NP). These materials have demonstrated the capacity to support cell viability, facilitate matrix production, and alleviate inflammation in vitro and in vivo, thus supporting tissue regeneration and restoring disc function in comparison to conventional treatment. Furthermore, polysaccharide-based hydrogels have demonstrated the potential to deliver bioactive molecules, including growth factors, cytokines and anti-inflammatory drugs, directly to the degenerated disc environment, thereby enhancing therapeutic outcomes. Therefore, polysaccharide-based materials provide structural support and facilitate the regeneration of native tissue, representing a versatile and effective approach for the treatment of IVDD. Despite their promise, challenges such as limited long-term stability, potential immunogenicity, and the difficulty in scaling up production for clinical use remain. This review delineates the potential of various polysaccharides during the fabrication of hydrogels and scaffolds for disc regeneration, guiding and inspiring future research to focus on optimizing these materials for clinical translation for IVDD repair and regeneration.

MicroSphere 3D Structures Delay Tissue Senescence through Mechanotransduction

The extracellular matrix (ECM) stores signaling molecules and facilitates mechanical and biochemical signaling in cells. However, the influence of biomimetic "rejuvenation" ECM structures on aging- and degeneration-related cellular activities and tissue repair is not well understood. We combined physical extrusion and precise "on-off" alternating cross-linking methods to create anisotropic biomaterial microgels (MicroRod and MicroSphere) and explored how they regulate the cell activities of the nucleus pulposus (NP) and their potential antidegenerative effects on intervertebral discs. NP cells exhibited aligned growth along the surface of the MicroRod, enhanced proliferation, and reduced apoptosis. This suggests an adaptive cellular response involving adhesion and mechanosensing, which causes cytoskeletal extension via environmental cues. NP cells maintain nuclear membrane integrity through the YAP/TAZ pathway, which activates the cGAS-STING pathway to rectify the aging mechanisms. In vivo, MicroRod carries NP cells and reduces inflammatory factor and protease secretion in degenerated intervertebral discs, inhibiting degeneration and promoting NP tissue regeneration. Our findings highlight the role of mechanical stress in maintaining cellular activity and antiaging effects in harsh environments, providing a foundation for further research and development of antidegenerative biomaterials.

The pathogenesis and targeted therapies of intervertebral disc degeneration induced by cartilage endplate inflammation

Intervertebral disc degeneration (IVDD) is the leading cause of low back pain, where degeneration and death of nucleus pulposus cells within the intervertebral disc (IVD) can be obviously revealed. This degeneration can result in an imbalance in the extracellular matrix due to the loss of proteoglycans and water content, which can further lead to catabolic and anabolic dysfunction of the IVD. Recently, the dysfunction of cartilage endplate (CEP) during aging has drawn large attention due to its essential functions in contributing nutrient exchange and maintaining IVD homeostasis. Furthermore, the inflammation and disturbed homeostasis of CEP not only accelerate the degradation of nucleus pulposus extracellular matrix, but also exacerbate IVDD by causing nucleus pulposus cell death through other pathological factors. Here in this review, we summarized the possible pathological factors and the underlying mechanisms of the CEP inflammation-induced IVDD, including exosomes degeneration, CEP calcification, ferroptosis, mechanical changes, and cell senescence. Besides, changes of miRNAs, pain-related neural reflex arc and pathways associated with CEP inflammation-induced IVDD are also reviewed. In addition, new strategies specifically designed for CEP inflammation-induced IVDD are also discussed in the last section. We hope this paper can not only offer some new insights for advancing novel strategies for treating IVDD, but also serve as a valuable reference for researchers in this field.

Current status and future developments of biopolymer microspheres in the field of pharmaceutical preparation

Polymer composite microspheres offer several advantages including highly designable structural properties, adjustable micro-nano particle size distribution, easy surface modification, large specific surface area, and high stability. These features make them valuable in various fields such as medicine, sensing, optics, and display technologies, with significant applications in clinical diagnostics, pathological imaging, and drug delivery in the medical field. Currently, microspheres are primarily used in biomedical research as long-acting controlled-release agents and targeted delivery systems, and are widely applied in bone tissue repair, cancer treatment, and wound healing. Different types of polymer microspheres offer distinct advantages and application prospects. Efforts are ongoing to transition successful experimental research to industrial production by expanding various fabrication technologies. This article provides an overview of materials used in microsphere manufacturing, different fabrication methods, modification techniques to enhance their properties and applications, and discusses the role of microspheres in drug delivery engineering.

Targeting Osteoblast-Osteoclast Cross-Talk Bone Homeostasis Repair Microcarriers Promotes Intervertebral Fusion in Osteoporotic Rats

Balancing osteoblast-osteoclast (OB-OC) cross-talk is crucial for restoring bone tissue structure and function. Current clinical drugs targeting either osteogenesis or osteoclastogenesis fail to effectively regulate cross-talk, impeding efficient bone repair in osteoporosis patients. Ubiquitin-specific protease 26 (USP26) is shown to coordinate OB-OC cross-talk by independently regulating β-catenin and Iκb-α. However, effective drugs for activating USP26 are still lacking. Here, they constructed bone homeostasis repair microcarriers (BHRC) that encapsulate Usp26 mRNA-loaded lipid nanoparticles (mRNA@LNP) within MMPs-responsive GelMA hydrogel microspheres. These microcarriers target the osteoporotic microenvironment and regulate OB-OC cross-talk, thereby facilitating intervertebral fusion in osteoporotic rats. Results demonstrate that mRNA@LNP exhibits uniform particle size and high transfection efficiency, while GelMA hydrogel microspheres possess excellent biocompatibility and MMP responsiveness, providing favorable cell survival space and controllable release of mRNA@LNP. The released LNP upregulates USP26 protein expression, effectively promoting osteogenesis while suppressing osteoclast formation. In vivo experiments show that injecting BHRC into the defect site of intervertebral discs in osteoporotic rats significantly promotes tail vertebrae fusion by responding to the microenvironment and regulating cell-to-cell cross-talk. Thus, the BHRC holds great potential in regulating osteoporotic homeostasis, particularly in challenging bone defects such as intervertebral fusion in osteoporotic environments.

Injectable Inflammation-Responsive Hydrogels for Microenvironmental Regulation of Intervertebral Disc Degeneration

Chronic local inflammation and excessive cell apoptosis in nucleus pulposus (NP) tissue are the main causes of intervertebral disc degeneration (IDD). Stimuli-responsive hydrogels have great potential in the treatment of IDD by facilitating localized and controlled drug delivery. Herein, an injectable drug-loaded dual stimuli-responsive adhesive hydrogel for microenvironmental regulation of IDD, is developed. The gelatin methacryloyl is functionalized with phenylboronic acid groups to enhance drug loading capacity and enable dual stimuli-responsive behavior, while the incorporation of oxidized hyaluronic acid further improves the adhesive properties. The prepared hydrogel exhibits an enhanced drug loading capacity for diol-containing drugs, pH- and reactive oxygen species (ROS)-responsive behaviors, excellent radical scavenging efficiency, potent antibacterial activity, and favorable biocompatibility. Furthermore, the hydrogel shows a beneficial protective efficacy on NP cells within an in vitro oxidative stress microenvironment. The in vivo results demonstrate the hydrogel's excellent therapeutic effect on treating IDD by maintaining water retention, restoring disc height, and promoting NP regeneration, indicating that this hydrogel holds great potential as a promising therapeutic approach for regulating the microenvironment and alleviating the progression of IDD.

Targeted Protein Fate Modulating Functional Microunits Promotes Intervertebral Fusion

Stable regulation of protein fate is a prerequisite for successful bone tissue repair. As a ubiquitin-specific protease (USP), USP26 can stabilize the protein fate of β-catenin to promote the osteogenic activity of mesenchymal cells (BMSCs) and significantly increased bone regeneration in bone defects in aged mice. However, direct transfection of Usp26 in vivo is inefficient. Therefore, improving the efficient expression of USP26 in target cells is the key to promoting bone tissue repair. Herein, 3D printing combined with microfluidic technology is applied to construct a functional microunit (protein fate regulating functional microunit, denoted as PFFM), which includes GelMA microspheres loaded with BMSCs overexpressing Usp26 and seeded into PCL 3D printing scaffolds. The PFFM provides a microenvironment for BMSCs, significantly promotes adhesion, and ensures cell activity and Usp26 supplementation that stabilizes β-catenin protein significantly facilitates BMSCs to express osteogenic phenotypes. In vivo experiments have shown that PFFM effectively accelerates intervertebral bone fusion. Therefore, PFFM can provide new ideas and alternatives for using USP26 for intervertebral fusion and other hard-to-repair bone defect diseases and is expected to provide clinical translational potential in future treatments.

Cutting-Edge Biomaterials in Intervertebral Disc Degeneration Tissue Engineering

Intervertebral disc degeneration (IVDD) stands as the foremost contributor to low back pain (LBP), imposing a substantial weight on the world economy. Traditional treatment modalities encompass both conservative approaches and surgical interventions; however, the former falls short in halting IVDD progression, while the latter carries inherent risks. Hence, the quest for an efficacious method to reverse IVDD onset is paramount. Biomaterial delivery systems, exemplified by hydrogels, microspheres, and microneedles, renowned for their exceptional biocompatibility, biodegradability, biological efficacy, and mechanical attributes, have found widespread application in bone, cartilage, and various tissue engineering endeavors. Consequently, IVD tissue engineering has emerged as a burgeoning field of interest. This paper succinctly introduces the intervertebral disc (IVD) structure and the pathophysiology of IVDD, meticulously classifies biomaterials for IVD repair, and reviews recent advances in the field. Particularly, the strengths and weaknesses of biomaterials in IVD tissue engineering are emphasized, and potential avenues for future research are suggested.

Nano-Micron Combined Hydrogel Microspheres: Novel Answer for Minimal Invasive Biomedical Applications

Hydrogels, key in biomedical research for their hydrophilicity and versatility, have evolved with hydrogel microspheres (HMs) of micron-scale dimensions, enhancing their role in minimally invasive therapeutic delivery, tissue repair, and regeneration. The recent emergence of nanomaterials has ushered in a revolutionary transformation in the biomedical field, which demonstrates tremendous potential in targeted therapies, biological imaging, and disease diagnostics. Consequently, the integration of advanced nanotechnology promises to trigger a new revolution in the realm of hydrogels. HMs loaded with nanomaterials combine the advantages of both hydrogels and nanomaterials, which enables multifaceted functionalities such as efficient drug delivery, sustained release, targeted therapy, biological lubrication, biochemical detection, medical imaging, biosensing monitoring, and micro-robotics. Here, this review comprehensively expounds upon commonly used nanomaterials and their classifications. Then, it provides comprehensive insights into the raw materials and preparation methods of HMs. Besides, the common strategies employed to achieve nano-micron combinations are summarized, and the latest applications of these advanced nano-micron combined HMs in the biomedical field are elucidated. Finally, valuable insights into the future design and development of nano-micron combined HMs are provided.

siRNA incorporated in slow-release injectable hydrogel continuously silences DDIT4 and regulates nucleus pulposus cell pyroptosis through the ROS/TXNIP/NLRP3 axis to alleviate intervertebral disc degeneration

Aims

In this investigation, we administered oxidative stress to nucleus pulposus cells (NPCs), recognized DNA-damage-inducible transcript 4 (DDIT4) as a component in intervertebral disc degeneration (IVDD), and devised a hydrogel capable of conveying small interfering RNA (siRNA) to IVDD.

Methods

An in vitro model for oxidative stress-induced injury in NPCs was developed to elucidate the mechanisms underlying the upregulation of DDIT4 expression, activation of the reactive oxygen species (ROS)-thioredoxin-interacting protein (TXNIP)-NLRP3 signalling pathway, and nucleus pulposus pyroptosis. Furthermore, the mechanism of action of small interfering DDIT4 (siDDIT4) on NPCs in vitro was validated. A triplex hydrogel named siDDIT4@G5-P-HA was created by adsorbing siDDIT4 onto fifth-generation polyamidoamine (PAMAM) dendrimer using van der Waals interactions, and then coating it with hyaluronic acid (HA). In addition, we established a rat puncture IVDD model to decipher the hydrogel's mechanism in IVDD.

Results

A correlation between DDIT4 expression levels and disc degeneration was shown with human nucleus pulposus and needle-punctured rat disc specimens. We confirmed that DDIT4 was responsible for activating the ROS-TXNIP-NLRP3 axis during oxidative stress-induced pyroptosis in rat nucleus pulposus in vitro. Mitochondria were damaged during oxidative stress, and DDIT4 contributed to mitochondrial damage and ROS production. In addition, siDDIT4@G5-P-HA hydrogels showed good delivery activity of siDDIT4 to NPCs. In vitro studies illustrated the potential of the siDDIT4@G5-P-HA hydrogel for alleviating IVDD in rats.

Conclusion

DDIT4 is a key player in mediating pyroptosis and IVDD in NPCs through the ROS-TXNIP-NLRP3 axis. Additionally, siDDIT4@G5-P-HA hydrogel has been found to relieve IVDD in rats. Our research offers an innovative treatment option for IVDD.

Application of hydrogel microneedles in the oral cavity

Microneedles are a transdermal drug delivery system in which the needle punctures the epithelium to deliver the drug directly to deep tissues, thus avoiding the influence of the first-pass effect of the gastrointestinal tract and minimizing the likelihood of pain induction. Hydrogel microneedles are microneedles prepared from hydrogels that have good biocompatibility, controllable mechanical properties, and controllable drug release and can be modified to achieve environmental control of drug release in vivo. The large epithelial tissue in the oral cavity is an ideal site for drug delivery via microneedles. Hydrogel microneedles can overcome mucosal hindrances to delivering drugs to deep tissues; this prevents humidity and a highly dynamic environment in the oral cavity from influencing the efficacy of the drugs and enables them to obtain better therapeutic effects. This article analyzes the materials and advantages of common hydrogel microneedles and reviews the application of hydrogel microneedles in the oral cavity.

Positioning regulation of organelle network via Chinese microneedle

The organelle network is a key factor in the repair and regeneration of lesion. However, effectively intervening in the organelle network which has complex interaction mechanisms is challenging. In this study, on the basis of electromagnetic laws, we constructed a biomaterial-based physical/chemical restraint device. This device was designed to jointly constrain electrical and biological factors in a conductive screw-threaded microneedle (ST-needle) system, identifying dual positioning regulation of the organelle network. The unique physical properties of this system could accurately locate the lesion and restrict the current path to the lesion cells through electromagnetic laws, and dynamic Van der Waals forces were activated to release functionalized hydrogel microspheres. Subsequently, the mitochondria-endoplasmic reticulum (ER) complex was synergistically targeted by increasing mitochondrial ATP supply to the ER via electrical stimulation and by blocking calcium current from the ER to the mitochondria using microspheres, and then the life activity of the lesion cells was effectively restored.

Progress in regulating inflammatory biomaterials for intervertebral disc regeneration

Intervertebral disc degeneration (IVDD) is rising worldwide and leading to significant health issues and financial strain for patients. Traditional treatments for IVDD can alleviate pain but do not reverse disease progression, and surgical removal of the damaged disc may be required for advanced disease. The inflammatory microenvironment is a key driver in the development of disc degeneration. Suitable anti-inflammatory substances are critical for controlling inflammation in IVDD. Several treatment options, including glucocorticoids, non-steroidal anti-inflammatory drugs, and biotherapy, are being studied for their potential to reduce inflammation. However, anti-inflammatories often have a short half-life when applied directly and are quickly excreted, thus limiting their therapeutic effects. Biomaterial-based platforms are being explored as anti-inflammation therapeutic strategies for IVDD treatment. This review introduces the pathophysiology of IVDD and discusses anti-inflammatory therapeutics and the components of these unique biomaterial platforms as comprehensive treatment systems. We discuss the strengths, shortcomings, and development prospects for various biomaterials platforms used to modulate the inflammatory microenvironment, thus providing guidance for future breakthroughs in IVDD treatment.

The current status and development trend of hydrogel application in spinal surgery

Spinal diseases often result in compromised mobility and diminished quality of life due to the intricate anatomy surrounding the nervous system. Medication and surgical interventions remain the primary treatment methods for spinal conditions. However, currently available medications have limited efficacy in treating spinal surgical diseases and cannot achieve a complete cure. Furthermore, surgical intervention frequently results in inevitable alterations and impairments to the initial anatomical integrity of the spinal structure, accompanied by the consequential loss of certain physiological functionalities. Changes in spine surgery treatment concepts and modalities in the last decade have led to a deepening of minimally invasive treatment, with treatment strategies focusing more on repairing and reconstructing the patient's spine and preserving physiological functions. Therefore, developing novel and more efficient treatment strategies to reduce spinal lesions and iatrogenic injuries is essential. In recent years, significant advancements in biomedical research have led to the discovery that hydrogels possess excellent biocompatibility, biodegradability, and adjustable mechanical properties. The application of hydrogel-based biotechnology in spinal surgery has demonstrated remarkable therapeutic potential. This review presents the therapeutic strategies for spinal diseases based on hydrogel tissue engineering technology.

Therapeutic factors and biomaterial-based delivery tools for degenerative intervertebral disc repair

Intervertebral disc degeneration (IDD) is the main cause of low back pain (LBP), which significantly impacts global wellbeing and contributes to global productivity declines. Conventional treatment approaches, encompassing conservative and surgical interventions, merely serve to postpone the advancement of IDD without offering a fundamental reversal. Consequently, there is an urgent demand for an effective approach to prevent the progression of IDD. Recent investigations focusing on the treatment of IDD utilizing diverse bioactive substances integrated within various biomaterials have exhibited promising outcomes. Various bioactive substances, encompassing conventional small molecule drugs, small molecule nucleic acids, and cell therapies, exhibit distinct capacities for repairing IDD. Additionally, various biological material delivery systems, such as nano micelles, microspheres, and hydrogels, possess diverse biological and release characteristics. Consequently, these diverse materials and drugs hold promise for advancing the treatment of IDD. This article aims to provide a concise overview of the IDD process and investigate the research advancements in biomaterials and bioactive substances for IDD treatment, delving into their mechanisms.

Mitochondrial-Oriented Injectable Hydrogel Microspheres Maintain Homeostasis of Chondrocyte Metabolism to Promote Subcellular Therapy in Osteoarthritis

Subcellular mitochondria serve as sensors for energy metabolism and redox balance, and the dynamic regulation of functional and dysfunctional mitochondria plays a crucial role in determining cells' fate. Selective removal of dysfunctional mitochondria at the subcellular level can provide chondrocytes with energy to prevent degeneration, thereby treating osteoarthritis. Herein, to achieve an ideal subcellular therapy, cartilage affinity peptide (WYRGRL)-decorated liposomes loaded with mitophagy activator (urolithin A) were integrated into hyaluronic acid methacrylate hydrogel microspheres through microfluidic technology, named HM@WY-Lip/UA, that could efficiently target chondrocytes and selectively remove subcellular dysfunctional mitochondria. As a result, this system demonstrated an advantage in mitochondria function restoration, reactive oxygen species scavenging, cell survival rescue, and chondrocyte homeostasis maintenance through increasing mitophagy. In a rat post-traumatic osteoarthritis model, the intra-articular injection of HM@WY-Lip/UA ameliorated cartilage matrix degradation, osteophyte formation, and subchondral bone sclerosis at 8 weeks. Overall, this study indicated that HM@WY-Lip/UA provided a protective effect on cartilage degeneration in an efficacious and clinically relevant manner, and a mitochondrial-oriented strategy has great potential in the subcellular therapy of osteoarthritis.

Hydrogel and Nanomedicine-Based Multimodal Therapeutic Strategies for Spinal Cord Injury

Spinal cord injury (SCI) is a severe neurodegenerative disease caused by mechanical and biological factors, manifesting as a loss of motor and sensory functions. Inhibition of injury expansion and even reversal of injury in the acute damage stage of SCI are important strategies for treating this disease. Hydrogels and nanoparticle (NP)-based drugs are the most effective, widely studied, and clinically valuable therapeutic strategies in the field of repair and regeneration. Hydrogels are 3D flow structures that fill the pathological gaps in SCI and provide a microenvironment similar to that of the spinal cord extracellular matrix for nerve cell regeneration. NP-based drugs can easily penetrate the blood-spinal cord barrier, target SCI lesions, and are noninvasive. Hydrogels and NPs as drug carriers can be loaded with various drugs and biological therapeutic factors for slow release in SCI lesions. They help drugs function more efficiently by exerting anti-inflammatory, antioxidant, and nerve regeneration effects to promote the recovery of neurological function. In this review, the use of hydrogels and NPs as drug carriers and the role of both in the repair of SCI are discussed to provide a multimodal strategic reference for nerve repair and regeneration after SCI.

Mechanical Signal-Tailored Hydrogel Microspheres Recruit and Train Stem Cells for Precise Differentiation

The aberrant mechanical microenvironment in degenerated tissues induces misdirection of cell fate, making it challenging to achieve efficient endogenous regeneration. Herein, a hydrogel microsphere-based synthetic niche with integrated cell recruitment and targeted cell differentiation properties via mechanotransduction is constructed . Through the incorporation of microfluidics and photo-polymerization strategies, fibronectin (Fn) modified methacrylated gelatin (GelMA) microspheres are prepared with the independently tunable elastic modulus (1-10Kpa) and ligand density (2 and 10 µg mL-1 ), allowing a wide range of cytoskeleton modulation to trigger the corresponding mechanobiological signaling. The combination of the soft matrix (2Kpa) and low ligand density (2 µg mL-1 ) can support the nucleus pulposus (NP)-like differentiation of intervertebral disc (IVD) progenitor/stem cells by translocating Yes-associated protein (YAP), without the addition of inducible biochemical factors. Meanwhile, platelet-derived growth factor-BB (PDGF-BB) is loaded onto Fn-GelMA microspheres (PDGF@Fn-GelMA) via the heparin-binding domain of Fn to initiate endogenous cell recruitment. In in vivo experiments, hydrogel microsphere-niche maintained the IVD structure and stimulated matrix synthesis. Overall, this synthetic niche with cell recruiting and mechanical training capabilities offered a promising strategy for endogenous tissue regeneration.

Functional hydrogels for the repair and regeneration of tissue defects

Tissue defects can be accompanied by functional impairments that affect the health and quality of life of patients. Hydrogels are three-dimensional (3D) hydrophilic polymer networks that can be used as bionic functional tissues to fill or repair damaged tissue as a promising therapeutic strategy in the field of tissue engineering and regenerative medicine. This paper summarises and discusses four outstanding advantages of hydrogels and their applications and advances in the repair and regeneration of tissue defects. First, hydrogels have physicochemical properties similar to the extracellular matrix of natural tissues, providing a good microenvironment for cell proliferation, migration and differentiation. Second, hydrogels have excellent shape adaptation and tissue adhesion properties, allowing them to be applied to a wide range of irregularly shaped tissue defects and to adhere well to the defect for sustained and efficient repair function. Third, the hydrogel is an intelligent delivery system capable of releasing therapeutic agents on demand. Hydrogels are capable of delivering therapeutic reagents and releasing therapeutic substances with temporal and spatial precision depending on the site and state of the defect. Fourth, hydrogels are self-healing and can maintain their integrity when damaged. We then describe the application and research progress of functional hydrogels in the repair and regeneration of defects in bone, cartilage, skin, muscle and nerve tissues. Finally, we discuss the challenges faced by hydrogels in the field of tissue regeneration and provide an outlook on their future trends.

Blocking Cholesterol Metabolism with Tumor-Penetrable Nanovesicles to Improve Photodynamic Cancer Immunotherapy

Photodynamic therapy (PDT)-mediated cancer immunotherapy is attenuated due to the dysfunction of T cells in immunosuppressive tumor microenvironment (TME). Cholesterol metabolism plays a vital role in T cell signaling and effector. While the metabolic fitness of tumor infiltrating CD8⁺ T cells is impaired by nutrition restriction in TME and accumulated metabolites by tumor cells. Here a matrix metalloproteinase-2-sensitive tumor-penetrable nanovesicle is designed to regulate cholesterol metabolism pathway for enhancing photodynamic cancer immunotherapy. The nanovesicles accumulate in tumor and release internalizing RGD to promote deep penetration. Released avasimibe from the nanovesicles simultaneously blocks cholesterol metabolism in CD8⁺ T and tumor cells, thus reinvigorating the functions of T cells and suppressing the migration of tumor cells. Immune responses induced by PDT-triggered immunogenic cell death are further improved with cholesterol metabolism blockage. Compared with PDT alone, the designed nanovesicles display enhanced tumor growth inhibition in B16-F10 mouse tumor model. The approach provides an alternative strategy to improve photodynamic cancer immunotherapy by cholesterol metabolism intervention.

Exosome inspired photo-triggered gelation hydrogel composite on modulating immune pathogenesis for treating rheumatoid arthritis

Although exosome therapy has been recognized as a promising strategy in the treatment of rheumatoid arthritis (RA), sustained modulation on RA specific pathogenesis and desirable protective effects for attenuating joint destruction still remain challenges. Here, silk fibroin hydrogel encapsulated with olfactory ecto-mesenchymal stem cell-derived exosomes (Exos@SFMA) was photo-crosslinked in situ to yield long-lasting therapeutic effect on modulating the immune microenvironment in RA. This in situ hydrogel system exhibited flexible mechanical properties and excellent biocompatibility for protecting tissue surfaces in joint. Moreover, the promising PD-L1 expression was identified on the exosomes, which potently suppressed Tfh cell polarization via inhibiting the PI3K/AKT pathway. Importantly, Exos@SFMA effectively relieved synovial inflammation and joint destruction by significantly reducing T follicular helper (Tfh) cell response and further suppressing the differentiation of germinal center (GC) B cells into plasma cells. Taken together, this exosome enhanced silk fibroin hydrogel provides an effective strategy for the treatment of RA and other autoimmune diseases.

Genetically engineered chondrocytes overexpressing elastin improve cell retention and chondrogenesis in a three-dimensional GelMA culture system

Elastic cartilage possesses many elastic fibers and has a high degree of elasticity. However, insufficient elastic fiber production remains unsolved in elastic cartilage tissue engineering. Exogenous elastin is difficult to degrade and violates cell proliferation and migration during cartilage regeneration. Moreover, exogenous elastic fibers are difficult to assemble with endogenous extracellular matrix components. We produced genetically engineered chondrocytes overexpressing elastin to boost endogenous elastic fiber production. After identifying that genetic manipulation hardly impacted the cell viability and chondrogenesis of chondrocytes, we co-cultured genetically engineered chondrocytes with untreated chondrocytes in a three-dimensional gelatin methacryloyl (GelMA) system. In vitro study showed that the co-culture system produced more elastic fibers and increased cell retention, resulting in strengthened mechanics than the control system with untreated chondrocytes. Moreover, in vivo implantation revealed that the co-culture GelMA system greatly resisted host tissue invasion by promoting elastic fiber production and cartilage tissue regeneration compared with the control system. In summary, our study indicated that genetically engineered chondrocytes overexpressing elastin are efficient and safe for promoting elastic fiber production and cartilage regeneration in elastic cartilage tissue engineering.

Application of single and cooperative different delivery systems for the treatment of intervertebral disc degeneration

Intervertebral disc (IVD) degeneration (IDD) is the most universal pathogenesis of low back pain (LBP), a prevalent and costly medical problem across the world. Persistent low back pain can seriously affect a patient's quality of life and even lead to disability. Furthermore, the corresponding medical expenses create a serious economic burden to both individuals and society. Intervertebral disc degeneration is commonly thought to be related to age, injury, obesity, genetic susceptibility, and other risk factors. Nonetheless, its specific pathological process has not been completely elucidated; the current mainstream view considers that this condition arises from the interaction of multiple mechanisms. With the development of medical concepts and technology, clinicians and scientists tend to intervene in the early or middle stages of intervertebral disc degeneration to avoid further aggravation. However, with the aid of modern delivery systems, it is now possible to intervene in the process of intervertebral disc at the cellular and molecular levels. This review aims to provide an overview of the main mechanisms associated with intervertebral disc degeneration and the delivery systems that can help us to improve the efficacy of intervertebral disc degeneration treatment.

Responsive Hydrogels Based on Triggered Click Reactions for Liver Cancer

Globally, liver cancer, which is one of the major cancers worldwide, has attracted the growing attention of technological researchers for its high mortality and limited treatment options. Hydrogels are soft 3D network materials containing a large number of hydrophilic monomers. By adding moieties such as nitrobenzyl groups to the network structure of a cross-linked nanocomposite hydrogel, the click reaction improves drug-release efficiency in vivo, which improves the survival rate and prolongs the survival time of liver cancer patients. The application of a nanocomposite hydrogel drug delivery system can not only enrich the drug concentration at the tumor site for a long time but also effectively prevents the distant metastasis of residual tumor cells. At present, a large number of researches have been working toward the construction of responsive nanocomposite hydrogel drug delivery systems, but there are few comprehensive articles to systematically summarize these discoveries. Here, this systematic review summarizes the synthesis methods and related applications of nanocomposite responsive hydrogels with actions to external or internal physiological stimuli. With different physical or chemical stimuli, the structural unit rearrangement and the controlled release of drugs can be used for responsive drug delivery in different states.

New Hope for Treating Intervertebral Disc Degeneration: Microsphere-Based Delivery System

Intervertebral disc (IVD) degeneration (IVDD) has been considered the dominant factor in low back pain (LBP), and its etiological mechanisms are complex and not yet fully elucidated. To date, the treatment of IVDD has mainly focused on relieving clinical symptoms and cannot fundamentally solve the problem. Recently, a novel microsphere-based therapeutic strategy has held promise for IVD regeneration and has yielded encouraging results with in vitro experiments and animal models. With excellent injectability, biocompatibility, and biodegradability, this microsphere carrier allows for targeted delivery and controlled release of drugs, gene regulatory sequences, and other bioactive substances and supports cell implantation and directed differentiation, aiming to improve the disease state of IVD at the source. This review discusses the possible mechanisms of IVDD and the limitations of current therapies, focusing on the application of microsphere delivery systems in IVDD, including targeted delivery of active substances and drugs, cellular therapy, and gene therapy, and attempts to provide a new understanding for the treatment of IVDD.