Intensified Stiffness and Photodynamic Provocation in a Collagen-Based Composite Hydrogel Drive Chondrogenesis

Wrecking neutrophil extracellular traps and antagonizing cancer-associated neurotransmitters by interpenetrating network hydrogels prevent postsurgical cancer relapse and metastases

Tumor-promoting niche after incomplete surgery resection (SR) can lead to more aggressive local progression and distant metastasis with augmented angiogenesis-immunosuppressive tumor microenvironment (TME). Herein, elevated neutrophil extracellular traps (NETs) and cancer-associated neurotransmitters (CANTs, e.g., catecholamines) are firstly identified as two of the dominant inducements. Further, an injectable fibrin-alginate hydrogel with high tissue adhesion has been constructed to specifically co-deliver NETs inhibitor (DNase I)-encapsulated PLGA nanoparticles and an unselective β-adrenergic receptor blocker (propranolol). The two components (i.e., fibrin and alginate) can respond to two triggers (thrombin and Ca2+, respectively) in postoperative bleeding to gelate, shaping into an interpenetrating network (IPN) featuring high strength. The continuous release of DNase I and PR can wreck NETs and antagonize catecholamines to decrease microvessel density, blockade myeloid-derived suppressor cells, secrete various proinflammatory cytokines, potentiate natural killer cell function and hamper cytotoxic T cell exhaustion. The reprogrammed TME significantly suppress locally residual and distant tumors, induce strong immune memory effects and thus inhibit lung metastasis. Thus, targetedly degrading NETs and blocking CANTs enabled by this in-situ IPN-based hydrogel drug depot provides a simple and efficient approach against SR-induced cancer recurrence and metastasis.

Structure-optimized and microenvironment-inspired nanocomposite biomaterials in bone tissue engineering

Critical-sized bone defects represent a significant clinical challenge due to their inability to undergo spontaneous regeneration, necessitating graft interventions for effective treatment. The development of tissue-engineered scaffolds and regenerative medicine has made bone tissue engineering a highly viable treatment for bone defects. The physical and biological properties of nanocomposite biomaterials, which have optimized structures and the ability to simulate the regenerative microenvironment of bone, are promising for application in the field of tissue engineering. These biomaterials offer distinct advantages over traditional materials by facilitating cellular adhesion and proliferation, maintaining excellent osteoconductivity and biocompatibility, enabling precise control of degradation rates, and enhancing mechanical properties. Importantly, they can simulate the natural structure of bone tissue, including the specific microenvironment, which is crucial for promoting the repair and regeneration of bone defects. This manuscript provides a comprehensive review of the recent research developments and applications of structure-optimized and microenvironment-inspired nanocomposite biomaterials in bone tissue engineering. This review focuses on the properties and advantages these materials offer for bone repair and tissue regeneration, summarizing the latest progress in the application of nanocomposite biomaterials for bone tissue engineering and highlighting the challenges and future perspectives in the field. Through this analysis, the paper aims to underscore the promising potential of nanocomposite biomaterials in bone tissue engineering, contributing to the informed design and strategic planning of next-generation biomaterials for regenerative medicine.

A Distinctive Insight into Inorganic Sonosensitizers: Design Principles and Application Domains

Sonodynamic therapy (SDT) as a promising non-invasive anti-tumor means features the preferable penetration depth, which nevertheless, usually can't work without sonosensitizers. Sonosensitizers produce reactive oxygen species (ROS) in the presence of ultrasound to directly kill tumor cells, and concurrently activate anti-tumor immunity especially after integration with tumor microenvironment (TME)-engineered nanobiotechnologies and combined therapy. Current sonosensitizers are classified into organic and inorganic ones, and current most reviews only cover organic sonosensitizers and highlighted their anti-tumor applications. However, there have few specific reviews that focus on inorganic sonosensitizers including their design principles, microenvironment regulation, etc. In this review, inorganic sonosensitizers are first classified according to their design rationales rather than composition, and the action rationales and underlying chemistry features are highlighted. Afterward, what and how TME is regulated based on the inorganic sonosensitizers-based SDT nanoplatform with an emphasis on the TME targets-engineered nanobiotechnologies are elucidated. Additionally, the combined therapy and their applications in non-cancer diseases are also outlined. Finally, the setbacks and challenges, and proposed the potential solutions and future directions is pointed out. This review provides a comprehensive and detailed horizon on inorganic sonosensitizers, and will arouse more attentions on SDT.

Collagen short nanofiber-embedded chondroitin sulfate-hyaluronic acid nanocomposite: A cartilage-mimicking in situ-forming hydrogel with fine-tuned properties

In situ-forming hydrogels that possess the ability to be injected in a less invasive manner and mimic the biochemical composition and microarchitecture of the native cartilage extracellular matrix are desired for cartilage tissue engineering. Besides, gelation time and stiffness of the hydrogel are two interdependent factors that affect cells' distribution and fate and hence need to be optimized. This study presented a bioinspired in situ-forming hydrogel composite of hyaluronic acid (HA), chondroitin sulfate (CS), and collagen short nanofiber (CSNF). HA and CS were functionalized with aldehyde and amine groups to form a gel through a Schiff-base reaction. CSNF was fabricated via electrospinning, followed by fragmentation by ultrasonics. Gelation time (11-360 s) and compressive modulus (1.4-16.2 kPa) were obtained by varying the concentrations of CS, HA, CSNFs, and CSNFs length. The biodegradability and biocompatibility of the hydrogels with varying gelation and stiffness were also assessed in vitro and in vivo. At three weeks, the assessment of hydrogels' chondrogenic differentiation also yields varying levels of chondrogenic differentiation. The subcutaneous implantation of the hydrogels in a mouse model indicated no severe inflammation. Results demonstrated that the injectable CS/HA@CSNF hydrogel was a promising hydrogel for tissue engineering and cartilage regeneration.

Ferrous/Ferric Ions Crosslinked Type II Collagen Multifunctional Hydrogel for Advanced Osteoarthritis Treatment

Osteoarthritis (OA) is a highly prevalent and intricate degenerative joint disease affecting an estimated 500 million individuals worldwide. Collagen-based hydrogels have sparked immense interest in cartilage tissue engineering, but substantial challenges persist in developing biocompatible and robust crosslinking strategies, as well as improving their effectiveness against the multifaceted nature of OA. Herein, a novel discovery wherein the simple incorporation of ferrous/ferric ions enables efficient dynamic crosslinking of type II collagen, leading to the development of injectable, self-healing hydrogels with 3D interconnected porous nanostructures, is unveiled. The ferrous/ferric ions crosslinked type II collagen hydrogels demonstrate exceptional physical properties, such as significantly enhanced mechanical strength, minimal swelling ratios, and remarkable resistance to degradation, while also exhibiting extraordinary biocompatibility and bioactivity, effectively promoting cell proliferation, adhesion, and chondrogenic differentiation. Additionally, the hydrogels reveal potent anti-inflammatory effects by upregulating anti-inflammatory cytokines while downregulating pro-inflammatory cytokines. In a rat model of cartilage defects, these hydrogels exhibit impressive efficacy, substantially accelerating cartilage tissue regeneration through enhanced collagen deposition and increased proteoglycan secretion. The innovative discovery of the multifunctional role of ferrous/ferric ions in endowing type II collagen hydrogels with a myriad of beneficial properties presents exciting prospects for developing advanced biomaterials with potential applications in OA.

Endogenous Zinc-Ion-Triggered In Situ Gelation Enables Zn Capture to Reprogram Benign Hyperplastic Prostate Microenvironment and Shrink Prostate

Benign prostatic hyperplasia (BPH) as the leading cause of urination disorder is still a refractory disease, and there have no satisfied drugs or treatment protocols yet. With identifying excessive Zn2+ , inflammation, and oxidative stress as the etiology of aberrant hyperplasia, an injectable sodium alginate (SA) and glycyrrhizic acid (GA)-interconnected hydrogels (SAGA) featuring Zn2+ -triggered in situ gelation are developed to load lonidamine for reprogramming prostate microenvironment and treating BPH. Herein, SAGA hydrogels can crosslink with Zn2+ in BPH via coordination chelation and switch free Zn2+ to bound ones, consequently alleviating Zn2+ -arisen inflammation and glycolysis. Beyond capturing Zn2+ , GA with intrinsic immunoregulatory property can also alleviate local inflammation and scavenge reactive oxygen species (ROS). Intriguingly, Zn2+ chelation-bridged interconnection in SAGA enhances its mechanical property and regulates the degradation rate to enable continuous lonidamine release, favoring hyperplastic acini apoptosis and further inhibiting glycolysis. These multiple actions cooperatively reprogram BPH microenvironment to alleviate characteristic symptoms of BPH and shrink prostate. RNA sequencing reveals that chemotaxis, glycolysis, and tumor necrosis factor (TNF) inflammation-related pathways associated with M1-like phenotype polarization are discerned as the action rationales of such endogenous Zn2+ -triggered in situ hydrogels, providing a candidate avenue to treat BPH.

Role of integrin β1 and tenascin C mediate TGF-SMAD2/3 signaling in chondrogenic differentiation of BMSCs induced by type I collagen hydrogel

Cartilage defects may lead to severe degenerative joint diseases. Tissue engineering based on type I collagen hydrogel that has chondrogenic potential is ideal for cartilage repair. However, the underlying mechanisms of chondrogenic differentiation driven by type I collagen hydrogel have not been fully clarified. Herein, we explored potential collagen receptors and chondrogenic signaling pathways through bioinformatical analysis to investigate the mechanism of collagen-induced chondrogenesis. Results showed that the super enhancer-related genes induced by collagen hydrogel were significantly enriched in the TGF-β signaling pathway, and integrin-β1 (ITGB1), a receptor of collagen, was highly expressed in bone marrow mesenchymal stem cells (BMSCs). Further analysis showed genes such as COL2A1 and Tenascin C (TNC) that interacted with ITGB1 were significantly enriched in extracellular matrix (ECM) structural constituents in the chondrogenic induction group. Knockdown of ITGB1 led to the downregulation of cartilage-specific genes (SOX9, ACAN, COL2A1), SMAD2 and TNC, as well as the downregulation of phosphorylation of SMAD2/3. Knockdown of TNC also resulted in the decrease of cartilage markers, ITGB1 and the SMAD2/3 phosphorylation but overexpression of TNC showed the opposite trend. Finally, in vitro and in vivo experiments confirmed the involvement of ITGB1 and TNC in collagen-mediated chondrogenic differentiation and cartilage regeneration. In summary, we demonstrated that ITGB1 was a crucial receptor for chondrogenic differentiation of BMSCs induced by collagen hydrogel. It can activate TGF-SMAD2/3 signaling, followed by impacting TNC expression, which in turn promotes the interaction of ITGB1 and TGF-SMAD2/3 signaling to enhance chondrogenesis. These may provide concernful support for cartilage tissue engineering and biomaterials development.

A bibliometric and visualized analysis of nanoparticles in musculoskeletal diseases (from 2013 to 2023)

As the pace of research on nanomedicine for musculoskeletal (MSK) diseases accelerates, there remains a lack of comprehensive analysis regarding the development trajectory, primary authors, and research focal points in this domain. Additionally, there's a need of detailed elucidation of potential research hotspots. The study gathered articles and reviews focusing on the utilization of nanoparticles (NPs) for MSK diseases published between 2013 and 2023, extracted from the Web of Science database. Bibliometric and visualization analyses were conducted using various tools such as VOSviewer, CiteSpace, Pajek, Scimago Graphica, and the R package. China, the USA, and India emerged as the key drivers in this research domain. Among the numerous institutions involved, Shanghai Jiao Tong University, Chinese Academy of Sciences, and Sichuan University exhibited the highest productivity levels. Vallet-Regi Maria emerged as the most prolific author in this field. International Journal of Nanomedicine accounted for the largest number of publications in this area. The top five disorders of utmost significance in this field include osteosarcoma, cartilage diseases, bone fractures, bone neoplasms, and joint diseases. These findings are instrumental in providing researchers with a comprehensive understanding of this domain and offer valuable perspectives for future investigations.

Comparison of the ability of exosomes and ectosomes derived from adipose-derived stromal cells to promote cartilage regeneration in a rat osteochondral defect model

BACKGROUND

Extracellular vesicles (EVs) derived from mesenchymal stromal cells (MSCs) offer promising prospects for stimulating cartilage regeneration. The different formation mechanisms suggest that exosomes and ectosomes possess different biological functions. However, little attention has been paid to the differential effects of EV subsets on cartilage regeneration.

METHODS

Our study compared the effects of the two EVs isolated from adipose-derived MSCs (ASCs) on chondrocytes and bone marrow-derived MSCs (BMSCs) in vitro. Additionally, we loaded the two EVs into type I collagen hydrogels to optimize their application for the treatment of osteochondral defects in vivo.

RESULTS

In vitro experiments demonstrate that ASC-derived exosomes (ASC-Exos) significantly promoted the proliferation and migration of both cells more effectively than ASC-derived ectosomes (ASC-Ectos). Furthermore, ASC-Exos facilitated a stronger differentiation of BMSCs into chondrogenic cells than ASC-Ectos, but both inhibited chondrocyte apoptosis to a similar extent. In the osteochondral defect model of rats, ASC-Exos promoted cartilage regeneration in situ better than ASC-Ectos. At 8 weeks, the hydrogel containing exosomes group (Gel + Exo group) had higher macroscopic and histological scores, a higher value of trabecular bone volume fraction (BV/TV), a lower value of trabecular thickness (Tb.Sp), and a better remodeling of extracellular matrix than the hydrogel containing ectosomes group (Gel + Ecto group). At 4 and 8 weeks, the expression of CD206 and Arginase-1 in the Gel + Exo group was significantly higher than that in the Gel + Ecto group.

CONCLUSION

Our findings indicate that administering ASC-Exos may be a more effective EV strategy for cartilage regeneration than the administration of ASC-Ectos.

Recent progress in biomaterials-driven ferroptosis for cancer therapy

Ferroptosis, first suggested in 2012, is a type of non-apoptotic programmed cell death caused by the buildup of lipid peroxidation and marked by an overabundance of oxidized poly unsaturated fatty acids. During the last decade, researchers have uncovered the formation of ferroptosis and created multiple drugs aimed at it, but due to poor selectivity and pharmacokinetics, clinical application has been hindered. In recent years, biomedical discoveries and developments in nanotechnology have spurred the investigation of ferroptosis nanomaterials, providing new opportunities for the ferroptosis driven tumours treatment. Additionally, hydrogels have been widely studied in ferroptosis because of their unique 3D structure and excellent controllability. By using these biomaterials, it is possible to achieve controlled release and targeted delivery of drugs, thus increasing the potency of the drugs and minimizing adverse effects. Therefore, summarizing the biomedical nanomaterials, including hydrogels, used in ferroptosis for cancer therapy is a must. This article provides an overview of ferroptosis, detailing its properties and underlying mechanisms. It also categorizes and reviews the use of various nanomaterials in ferroptosis, along with relevant explanations and illustrations. In addition, we discuss the opportunities and challenges facing the application of nanomaterials in ferroptosis. Finally, the development prospects of this field are prospected. This review is intended to provide a foundation for the development and application of biomedical nanomaterials in ferroptosis.

Biomimetic Hydrogels as the Inductive Endochondral Ossification Template for Promoting Bone Regeneration

Repairing critical size bone defects (CSBD) is a major clinical challenge and requires effective intervention by biomaterial scaffolds. Inspired by the fact that the cartilaginous template-based endochondral ossification (ECO) process is crucial to bone healing and development, developing biomimetic biomaterials to promote ECO is recognized as a promising approach for repairing CSBD. With the unique highly hydrated 3D polymeric network, hydrogels can be designed to closely emulate the physiochemical properties of cartilage matrix to facilitate ECO. In this review, the various preparation methods of hydrogels possessing the specific physiochemical properties required for promoting ECO are introduced. The materiobiological impacts of the physicochemical properties of hydrogels, such as mechanical properties, topographical structures and chemical compositions on ECO, and the associated molecular mechanisms related to the BMP, Wnt, TGF-β, HIF-1α, FGF, and RhoA signaling pathways are further summarized. This review provides a detailed coverage on the materiobiological insights required for the design and preparation of hydrogel-based biomaterials to facilitate bone regeneration.

Crosslinking strategies for biomimetic hydrogels in bone tissue engineering

Bone tissue engineering has become a popular area of study for making biomimetic hydrogels to treat bone diseases. In this work, we looked at biocompatible hydrogels that can be injected into bone defects that require the smallest possible surgery. Mineral ions can be attached to polymer chains to make useful hydrogels that help bones heal faster. These ions are very important for the balance of the body. In the chemically-triggered sector, advanced hydrogels cross-linked by different molecular agents have many advantages, such as being selective, able to form gels, and having mechanical properties that can be modified. In addition, different photo-initiators can be used to make photo cross linkable hydrogels react quickly and moderately under certain light bands. Enzyme-triggered hydrogels are another type of hydrogel that can be used to repair bone tissue because they are biocompatible and gel quickly. We also look at some of the important factors mentioned above that could change how well bone tissue engineering works as a therapy. Finally, this review summarizes the problems that still need to be solved to make clinically relevant hydrogels.

Collagen-Based Hydrogels for Cartilage Regeneration

Cartilage regeneration remains difficult due to a lack of blood vessels. Degradation of the extracellular matrix (ECM) causes cartilage defects, and the ECM provides the natural environment and nutrition for cartilage regeneration. Until now, collagen hydrogels are considered to be excellent material for cartilage regeneration due to the similar structure to ECM and good biocompatibility. However, collagen hydrogels also have several drawbacks, such as low mechanical strength, limited ability to induce stem cell differentiation, and rapid degradation. Thus, there is a demanding need to optimize collagen hydrogels for cartilage regeneration. In this review, we will first briefly introduce the structure of articular cartilage and cartilage defect classification and collagen, then provide an overview of the progress made in research on collagen hydrogels with chondrocytes or stem cells, comprehensively expound the research progress and clinical applications of collagen-based hydrogels that integrate inorganic or organic materials, and finally present challenges for further clinical translation.

Mimicking Antioxidases and Hyaluronan Synthase: A Zwitterionic Nanozyme for Photothermal Therapy of Osteoarthritis

Restoring joint homeostasis is crucial for relieving osteoarthritis (OA). Current strategies are limited to unilateral efforts in joint lubrication, inhibition of inflammation, free radicals scavenging, and cartilage regeneration. Herein, by modifying molybdenum disulfide (MoS2 ) with Mg2+ -doped polydopamine and coating with polysulfobetaines, a dual-bionic photothermal nanozyme (MPMP) is constructed to mimic antioxidases/hyaluronan synthase for OA therapy. Photothermally enhanced lubrication lowers the coefficient of friction (0.028) in the early stage of OA treatment. The antioxidases-mimicking properties of MPMP nanozyme contribute to eliminating reactive oxygen and nitrogen species (ROS/RNS) (over 90% of scavenging ratio for H2 O2 /·OH/O· 2 - /DPPH/ABTS+ ) and supplying O2 . With NIR irradiation, the MPMP nanozyme triggers thermogenesis (upregulating HSP70 expression) and Mg2+ release, which promotes the chondrogenesis in inflammatory conditions by deactivating NF-κB/IL-17 signaling pathways and enhancing MAPK signaling pathway. Benefiting from HSP70 and Mg2+ , MPMP-NIR shows HAS-mimicking activity to increase the intracellular (twofold) and extracellular (3.12-fold) HA production. Therefore, MPMP-NIR demonstrates superior spatiotemporally therapeutic effect on OA in mice model, in terms of osteophytes (83.41% of reduction), OARSI scores (88.57% of reduction), and ACAN expression (2.70-fold of increment). Hence, insights into dual-bionic nanozymes can be a promising strategy for OA therapy or other inflammation-related diseases.

A Metal-Organic Framework-Incorporated Hydrogel for Delivery of Immunomodulatory Neobavaisoflavone to Promote Cartilage Regeneration in Osteoarthritis

The treatment of osteoarthritis (OA)-related cartilage defects is a great clinical challenge due to the complex pathogenesis of OA and poor self-repair ability of cartilage tissue. Combining local and long-term anti-inflammatory therapies to promote cartilage repair is an effective method to treat OA. In this study, a zinc-organic framework-incorporated extracellular matrix (ECM)-mimicking hydrogel platform was constructed for the inflammatory microenvironment-responsive delivery of neobavaisoflavone (NBIF) to promote cartilage regeneration in OA. The NBIF was encapsulated in situ in zeolitic imidazolate frameworks (ZIF-8 MOFs). The NBIF@ZIF-8 MOFs were decorated with polydopamine and incorporated into a methacrylate gelatin/hyaluronic acid hybrid network to form the NBIF@ZIF-8/PHG hydrogel. The hydrogel featured excellent cell/tissue affinity, providing a favorable microenvironment for recruiting cells and cytokines to the defect sites. The hydrogel enabled the on-demand NBIF released in response to a weakly acidic microenvironment at the injured joint site to resolve inflammatory responses during the early stages of OA. Consequently, the cooperativity of the loaded NBIF and hydrogel synergistically modulated the immune response and assisted in cartilage defect repair. In summary, the NBIF@ZIF-8/PHG hydrogel delivery platform represents an effective treatment strategy for OA-related cartilage defects and may attract attentions for applications in other inflammatory diseases.

Amyloid Fibril and Clay Nanosheet Dual-Nanoengineered DNA Dynamic Hydrogel for Vascularized Bone Regeneration

Dynamic hydrogels have attracted enormous interest for bone tissue engineering as they demonstrate reversible mechanics to better mimic biophysical cues of natural extracellular matrix (ECM) compared to traditional static hydrogels. However, the facile development of therapeutic dynamic hydrogels that simultaneously recapitulate the filamentous architecture of the ECM of living tissues and induce both osteogenesis and angiogenesis to augment vascularized bone regeneration remains challenging. Herein, we report a dual nanoengineered DNA dynamic hydrogel developed through the supramolecular coassembly of amyloid fibrils and clay nanosheets with DNA strands. The nanoengineered ECM-like fibrillar hydrogel network is facilely formed without a complicated and tedious molecular synthesis. Amyloid fibrils together with clay nanosheets synergistically enhance the mechanical strength and stability of the dynamic hydrogel and, more remarkably, endow the matrix with an array of tunable features, including shear-thinning, injectability, self-healing, self-supporting, and 3D printable properties. The QK peptide is further chemically grafted onto amyloid fibrils, and its sustainable release from the hydrogel matrix stimulates the tube formation and migration with human umbilical vein endothelial cells. Meanwhile, the nanoengineered hydrogel matrix promotes osteogenic differentiation of bone marrow mesenchymal stem cells due to the sustainable release of Si4+ and Mg2+ derived from clay nanosheets. Furthermore, the manipulation of enhanced vascularized bone regeneration by the dynamic hydrogel is revealed in a rat cranial bone defect model. This dual nanoengineered strategy envisions great promise in developing therapeutic dynamic hydrogels for improved and customizable bone regeneration.

Cell unit-inspired natural nano-based biomaterials as versatile building blocks for bone/cartilage regeneration

The regeneration of weight-bearing bone defects and critical-sized cartilage defects remains a significant challenge. A wide range of nano-biomaterials are available for the treatment of bone/cartilage defects. However, their poor compatibility and biodegradability pose challenges to the practical applications of these nano-based biomaterials. Natural biomaterials inspired by the cell units (e.g., nucleic acids and proteins), have gained increasing attention in recent decades due to their versatile functionality, compatibility, biodegradability, and great potential for modification, combination, and hybridization. In the field of bone/cartilage regeneration, natural nano-based biomaterials have presented an unparalleled role in providing optimal cues and microenvironments for cell growth and differentiation. In this review, we systematically summarize the versatile building blocks inspired by the cell unit used as natural nano-based biomaterials in bone/cartilage regeneration, including nucleic acids, proteins, carbohydrates, lipids, and membranes. In addition, the opportunities and challenges of natural nano-based biomaterials for the future use of bone/cartilage regeneration are discussed.

Evaluation of Silk Fibroin/Gellan Gum Hydrogels with Controlled Molecular Weight through Silk Fibroin Hydrolysis for Tissue Engineering Application

Hydrogel is a versatile material that can be manipulated to achieve the desired physicochemical properties, such as stiffness, pore size, and viscoelasticity. Traditionally, these properties have been controlled through parameters such as concentration and pH adjustments. In this study, we focused on exploring the potential of hydrolyzed silk fibroin (HSF) as a molecular weight-modulating agent to control the physicochemical properties of double-composite hydrogels. We developed a synergistic dual-crosslinked hydrogel by combining ionically crosslinked silk fibroin with gellan gum (GG). The hydrolysis of silk fibroin not only enhanced its hydrophilicity but also enabled adjustments in its mechanical properties, including the pore size, initial modulus elasticity, and relaxation time. Moreover, biocompatibility assessments based on cell viability tests confirmed the potential of these hydrogels as biocompatible materials. By highlighting the significance of developing an HSF/GG dual-crosslinked hydrogel, this study contributes to the advancement of novel double-composite hydrogels with remarkable biocompatibility. Overall, our findings demonstrate the capability of controlling the mechanical properties of hydrogels through molecular weight modulation via hydrolysis and highlight the development of a biocompatible HSF/GG dual-crosslinked hydrogel with potential biomedical applications.

Feather keratin-montmorillonite nanocomposite hydrogel promotes bone regeneration by stimulating the osteogenic differentiation of endogenous stem cells

Bone defects caused by bone trauma, infection, surgery, or other systemic diseases remain a severe challenge for the medical field. To address this clinical problem, different hydrogels were exploited to promote bone tissue regrowth and regeneration. Keratins are natural fibrous proteins found in wool, hair, horns, nails, and feather. Due to their unique characteristics of outstanding biocompatibility, great biodegradability, and hydrophilic, keratins have been widely applicated in different fields. In our study, the feather keratin-montmorillonite nanocomposite hydrogels that consist of keratin hydrogels serving as the scaffold support to accommodate endogenous stem cells and montmorillonite is synthesized. The introduction of montmorillonite greatly improves the osteogenic effect of the keratin hydrogels via bone morphogenetic protein 2 (BMP-2)/phosphorylated small mothers against decapentaplegic homolog 1/5/8 (p-SMAD 1/5/8)/runt-related transcription factor 2 (RUNX2) expression. Moreover, the incorporation of montmorillonite into hydrogels can improve the mechanical properties and bioactivity of the hydrogels. The morphology of feather keratin-montmorillonite nanocomposite hydrogels was shown by scanning electron microscopy (SEM) to have an interconnected porous structure. The incorporation of montmorillonite into the keratin hydrogels was confirmed by the energy dispersive spectrum (EDS). We prove that the feather keratin-montmorillonite nanocomposite hydrogels enhance the osteogenic differentiation of BMSCs. Furthermore, micro-CT and histological analysis of rat cranial bone defect demonstrated that feather keratin-montmorillonite nanocomposite hydrogels dramatically stimulated bone regeneration in vivo. Collectively, feather keratin-montmorillonite nanocomposite hydrogels can regulate BMP/SMAD signaling pathway to stimulate osteogenic differentiation of endogenous stem cells and promote bone defect healing, indicating their promising candidate in bone tissue engineering.

Ultrasound-Targeted Microbubble Destruction-Mediated Cell-Mimetic Nanodrugs for Treating Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease that mainly affects joints, and it can lead to disability and damage to vital organs if not diagnosed and treated in time. However, all current therapeutic agents for RA have limitations such as high dose, severe side effects, long-term use, and unsatisfactory therapeutic effects. The long-term use and dose escalation of methotrexate (MTX) may cause mild and severe side effects. To overcome the limitations, it is critical to target drug delivery to the inflamed joints. In this work, we constructed a folic acid-targeted and cell-mimetic nanodrug, MTX-loaded mesoporous silica composite nanoplatform (MMPRF), which can regulate drug release under ultrasound (US) and microbubble (MB) mediation. The targeted delivery and drug therapy were investigated through in vitro RAW264.7 cell experiments and in vivo collagen-induced arthritis animal experiments. The result showed that the targeting ability to the joints of MMPRF was strong and was more significant after US and MB mediation, which can potently reduce joint swelling, bone erosion, and inflammation in joints. This work indicated that the US- and MB-mediated MMPRF not only would be a promising method for synergistic targeted treatment of RA but also may show high potential for serving as a nanomedicine for many other biomedical fields.

Multileveled Hierarchical Hydrogel with Continuous Biophysical and Biochemical Gradients for Enhanced Repair of Full-Thickness Osteochondral Defect

The repair of hierarchical osteochondral defect requires sophisticated gradient reestablishment; however, few strategies for continuous gradient casting consider the relevance to clinical practice regarding cell adaptability, multiple gradient elements, and precise gradient mirroring native tissue. Here, a hydrogel with continuous gradients in nano-hydroxyapatite (HA) content, mechanical, and magnetism is developed using synthesized superparamagnetic HA nanorods (MagHA) that easily respond to a brief magnetic field. To precisely reconstruct osteochondral tissue, the optimized gradient mode is calculated according to magnetic resonance imaging (MRI) of healthy rabbit knees. Then, MagHA are patterned to form continuous biophysical and biochemical gradients, consequently generating incremental HA, mechanical, and electromagnetic cues under an external magnetic stimulus. To make such depth-dependent biocues work, an adaptable hydrogel is developed to facilitate cell infiltration. Furthermore, this approach is applied in rabbit full-thickness osteochondral defects equipped with a local magnetic field. Surprisingly, this multileveled gradient composite hydrogel repairs osteochondral unit in a perfect heterogeneous feature, which mimics the gradual cartilage-to-subchondral transition. Collectively, this is the first study that combines an adaptable hydrogel with magneto-driven MagHA gradients to achieve promising outcomes in osteochondral regeneration.

Nanodrugs with intrinsic radioprotective exertion: Turning the double-edged sword into a single-edged knife

Ionizing radiation (IR) poses a growing threat to human health, and thus ideal radioprotectors with high efficacy and low toxicity still receive widespread attention in radiation medicine. Despite significant progress made in conventional radioprotectants, high toxicity, and low bioavailability still discourage their application. Fortunately, the rapidly evolving nanomaterial technology furnishes reliable tools to address these bottlenecks, opening up the cutting-edge nano-radioprotective medicine, among which the intrinsic nano-radioprotectants characterized by high efficacy, low toxicity, and prolonged blood retention duration, represent the most extensively studied class in this area. Herein, we made the systematic review on this topic, and discussed more specific types of radioprotective nanomaterials and more general clusters of the extensive nano-radioprotectants. In this review, we mainly focused on the development, design innovations, applications, challenges, and prospects of the intrinsic antiradiation nanomedicines, and presented a comprehensive overview, in-depth analysis as well as an updated understanding of the latest advances in this topic. We hope that this review will promote the interdisciplinarity across radiation medicine and nanotechnology and stimulate further valuable studies in this promising field.

Extracellular Matrix Viscosity Reprogramming by In Situ Au Bioreactor-Boosted Microwavegenetics Disables Tumor Escape in CAR-T Immunotherapy

Incomplete microwave ablation (iMWA) caused by uncontrollable heat diffusion enhances the immunosuppressive tumor microenvironment (ITM), consequently disabling the prevalent immune checkpoint blockade-combined immunotherapy against tumor recurrence. Herein, we successfully constructed an intratumorally synthesized Au bioreactor to disperse heat in thermally sensitive hydrogel-filled tumors and improve the energy utilization efficiency, which magnified the effective ablation zone (EAZ), counteracted iMWA, and simultaneously established and enhanced multiple biological process-regulated microwavegenetics. More significantly, we identified the extracellular matrix (ECM) viscosity as a general immune escape "target". After remodeling ECM, including ECM ingredients and cell adhesion molecules, this physical target was blocked by viscosity reprogramming, furnishing an effective tool to regulate the viscosity target. Thereby, such in situ Au bioreactor-enlarged EAZ and enhanced microwavegenetics reversed the immune-desert tumor microenvironment, mitigated ITM, secreted immune cell-attracting chemokines, recruited and polarized various immune cells, and activated or reactivated them like dendritic cells, natural killing cells, M1-type macrophages, and effector CD8+ or CAR-T cells. Contributed by these multiple actions, the in situ oncolytic Au bioreactors evoked CAR-T immunotherapy to acquire a considerably increased inhibition effect against tumor progression and recurrence after iMWA, thus providing a general method to enhance iMWA and CAR-T immunotherapy.

Emerging Nano-/Biotechnology Drives Oncolytic Virus-Activated and Combined Cancer Immunotherapy

Oncolytic viruses (OVs) as one promising antitumor methods have made important contributions to tumor immunotherapy, which arouse increasing attention. They provide the dual mechanisms including direct killing effect toward tumor cells and immune activation for elevating antitumor responses, which have been proved in many preclinical studies. Especially, natural or genetically modified viruses as clinical immune preparations have emerged as a new promising approach objective to oncology treatment. The approval of talimogene laherparepvec (T-VEC) by the U.S. Food and Drug Administration (FDA) for the therapy of advanced melanoma could be considered as a milestone achievement in the clinical translation of OV. In this review, we first discussed the antitumor mechanisms of OVs with an emphasis on targeting, replication, and propagation. We further outlined the state of the art of current OVs in tumor and underlined the activated biological effects especially including immunity. More significantly, the enhanced immune responses based on OVs were systematically discussed from different perspectives such as combination with immunotherapy, genetic engineering of OVs, integration with nanobiotechnology or nanoparticles, and antiviral response counteraction, where their principles were shed light on. The development of OVs in the clinics was also highlighted to analyze the actuality and concerns of different OV applications in clinical trials. At last, the future perspectives and challenges of OVs as an already widely accepted treatment means were discussed. This review will provide a systematic review and deep insight into OV development and also offer new opportunities and guidance pathways to drive the further clinical translation.

Phosphoserine-loaded chitosan membranes promote bone regeneration by activating endogenous stem cells

Bone defects that result from trauma, infection, surgery, or congenital malformation can severely affect the quality of life. To address this clinical problem, a phosphoserine-loaded chitosan membrane that consists of chitosan membranes serving as the scaffold support to accommodate endogenous stem cells and phosphoserine is synthesized. The introduction of phosphoserine greatly improves the osteogenic effect of the chitosan membranes via mutual crosslinking using a crosslinker (EDC, 1-ethyl-3-(3-dimethyl aminopropyl)-carbodiimide). The morphology of PS-CS membranes was shown by scanning electron microscopy (SEM) to have an interconnected porous structure. The incorporation of phosphoserine into chitosan membranes was confirmed by energy dispersive spectrum (EDS), Fourier Transforms Infrared (FTIR), and X-ray diffraction (XRD) spectrum. The CCK8 assay and Live/Dead staining, Hemolysis analysis, and cell adhesion assay demonstrated that PS-CS membranes had good biocompatibility. The osteogenesis-related gene expression of BMSCs was higher in PS-CS membranes than in CS membranes, which was verified by alkaline phosphatase (ALP) activity, immunofluorescence staining, and real-time quantitative PCR (RT-qPCR). Furthermore, micro-CT and histological analysis of rat cranial bone defect demonstrated that PS-CS membranes dramatically stimulated bone regeneration in vivo. Moreover, H&E staining of the main organs (heart, liver, spleen, lung, or kidney) showed no obvious histological abnormalities, revealing that PS-CS membranes were no additional systemic toxicity in vivo. Collectively, PS-CS membranes may be a promising candidate for bone tissue engineering.

NIR-II live imaging study on the degradation pattern of collagen in the mouse model

The degradation of collagen in different body parts is a critical point for designing collagen-based biomedical products. Here, three kinds of collagens labeled by second near-infrared (NIR-II) quantum dots (QDs), including collagen with low crosslinking degree (LC), middle crosslinking degree (MC) and high crosslinking degree (HC), were injected into the subcutaneous tissue, muscle and joints of the mouse model, respectively, in order to investigate the in vivo degradation pattern of collagen by NIR-II live imaging. The results of NIR-II imaging indicated that all tested collagens could be fully degraded after 35 days in the subcutaneous tissue, muscle and joints of the mouse model. However, the average degradation rate of subcutaneous tissue (k = 0.13) and muscle (k = 0.23) was slower than that of the joints (shoulder: k = 0.42, knee: k = 0.55). Specifically, the degradation rate of HC (k = 0.13) was slower than LC (k = 0.30) in muscle, while HC showed the fastest degradation rate in the shoulder and knee joints. In summary, NIR-II imaging could precisely identify the in vivo degradation rate of collagen. Moreover, the degradation rate of collagen was more closely related to the implanted body parts rather than the crosslinking degree of collagen, which was slower in the subcutaneous tissue and muscle compared to the joints in the mouse model.

Novel Temperature-Sensitive Hydrogel Promotes Wound Healing Through YAP and MEK-Mediated Mechanosensitivity

Wound healing is a significant problem in clinical management. Various functional dressings are studied to promote wound healing through biochemical factors. They are generally expensive, complex to fabricate, and may adversely affect the wound. Mechanical forces are the critical regulators of tissue repair. Although contraction is shown to promote wound healing, the underlying mechanisms are not fully understood. In this study, a novel adhesive temperature-sensitive mechanically active hydrogel with a simple and inexpensive preparation process is developed. The dressing is able to adhere to the wound surface and actively contract the wound in response to body temperature. This mechanical contraction enhances the proliferative activity of basal cells, reduces the inflammatory response of the wound, and promotes wound healing. Furthermore, RNA-seq clarifies how the gene regulatory network is regulated by contraction. Finally, using pharmacological inhibitors, YAP and MEK are identified as the key signaling molecules for contraction-mediated tissue healing in vivo.

Advanced application of collagen-based biomaterials in tissue repair and restoration

In tissue engineering, bioactive materials play an important role, providing structural support, cell regulation and establishing a suitable microenvironment to promote tissue regeneration. As the main component of extracellular matrix, collagen is an important natural bioactive material and it has been widely used in scientific research and clinical applications. Collagen is available from a wide range of animal origin, it can be produced by synthesis or through recombinant protein production systems. The use of pure collagen has inherent disadvantages in terms of physico-chemical properties. For this reason, a processed collagen in different ways can better match the specific requirements as biomaterial for tissue repair. Here, collagen may be used in bone/cartilage regeneration, skin regeneration, cardiovascular repair and other fields, by following different processing methods, including cross-linked collagen, complex, structured collagen, mineralized collagen, carrier and other forms, promoting the development of tissue engineering. This review summarizes a wide range of applications of collagen-based biomaterials and their recent progress in several tissue regeneration fields. Furthermore, the application prospect of bioactive materials based on collagen was outlooked, aiming at inspiring more new progress and advancements in tissue engineering research.

Graphical Abstract

Suramin enhances chondrogenic properties by regulating the p67phox/PI3K/AKT/SOX9 signalling pathway

Aims

Autologous chondrocyte implantation (ACI) is a promising treatment for articular cartilage degeneration and injury; however, it requires a large number of human hyaline chondrocytes, which often undergo dedifferentiation during in vitro expansion. This study aimed to investigate the effect of suramin on chondrocyte differentiation and its underlying mechanism.

Methods

Porcine chondrocytes were treated with vehicle or various doses of suramin. The expression of collagen, type II, alpha 1 (COL2A1), aggrecan (ACAN); COL1A1; COL10A1; SRY-box transcription factor 9 (SOX9); nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX); interleukin (IL)-1β; tumour necrosis factor alpha (TNFα); IL-8; and matrix metallopeptidase 13 (MMP-13) in chondrocytes at both messenger RNA (mRNA) and protein levels was determined by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and western blot. In addition, the supplementation of suramin to redifferentiation medium for the culture of expanded chondrocytes in 3D pellets was evaluated. Glycosaminoglycan (GAG) and collagen production were evaluated by biochemical analyses and immunofluorescence, as well as by immunohistochemistry. The expression of reactive oxygen species (ROS) and NOX activity were assessed by luciferase reporter gene assay, immunofluorescence analysis, and flow cytometry. Mutagenesis analysis, Alcian blue staining, reverse transcriptase polymerase chain reaction (RT-PCR), and western blot assay were used to determine whether p67^phox was involved in suramin-enhanced chondrocyte phenotype maintenance.

Results

Suramin enhanced the COL2A1 and ACAN expression and lowered COL1A1 synthesis. Also, in 3D pellet culture GAG and COL2A1 production was significantly higher in pellets consisting of chondrocytes expanded with suramin compared to controls. Surprisingly, suramin also increased ROS generation, which is largely caused by enhanced NOX (p67^phox) activity and membrane translocation. Overexpression of p67^phox but not p67^phoxAD (deleting amino acid (a.a) 199 to 212) mutant, which does not support ROS production in chondrocytes, significantly enhanced chondrocyte phenotype maintenance, SOX9 expression, and AKT (S473) phosphorylation. Knockdown of p67^phox with its specific short hairpin (sh) RNA (shRNA) abolished the suramin-induced effects. Moreover, when these cells were treated with the phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) inhibitor LY294002 or shRNA of AKT1, p67^phox-induced COL2A1 and ACAN expression was significantly inhibited.

Conclusion

Suramin could redifferentiate dedifferentiated chondrocytes dependent on p67^phox activation, which is mediated by the PI3K/AKT/SOX9 signalling pathway.

Cite this article: Bone Joint Res 2022;11(10):723–738.

Rational Nanomedicine Design Enhances Clinically Physical Treatment-Inspired or Combined Immunotherapy

Independent of tumor type and non-invasive or minimally-invasive feature, current physical treatments including ultrasound therapy, microwave ablation (MWA), and radiofrequency ablation (RFA) are widely used as the local treatment methods in clinics for directly killing tumors and activating systematic immune responses. However, the activated immune responses are inadequate and incompetent for tumor recession, and the incomplete thermal ablation even aggravates the immunosuppressive tumor microenvironment (ITM), resulting in the intractable tumor recurrence and metastasis. Intriguingly, nanomedicine provides a powerful platform as they can elevate energy utilization efficiency and augment oncolytic effects for mitigating ITM and potentiating the systematic immune responses. Especially after combining with clinical immunotherapy, the anti-tumor killing effect by activating or enhancing the human anti-tumor immune system is reached, enabling the effective prevention against tumor recurrence and metastasis. This review systematically introduces the cutting-edge progress and direction of nanobiotechnologies and their corresponding nanomaterials. Moreover, the enhanced physical treatment efficiency against tumor progression, relapse, and metastasis via activating or potentiating the autologous immunity or combining with exogenous immunotherapeutic agents is exemplified, and their rationales are analyzed. This review offers general guidance or directions to enhance clinical physical treatment from the perspectives of immunity activation or magnification.

Multifaceted Catalytic ROS-Scavenging via Electronic Modulated Metal Oxides for Regulating Stem Cell Fate

Developing reactive oxygen species (ROS)-scavenging nanostructures to protect and regulate stem cells has emerged as an intriguing strategy for promoting tissue regeneration, especially in trauma microenvironments or refractory wounds. Here, an electronic modulated metal oxide is developed via Mn atom substitutions in Co₃ O₄ nanocrystalline (Mn-Co₃ O₄ ) for highly efficient and multifaceted catalytic ROS-scavenging to reverse the fates of mesenchymal stem cells (MSCs) in oxidative-stress microenvironments. Benefiting from the atomic Mn-substitution and charge transfer from Mn to Co, the Co site in Mn-Co₃ O₄ displays an increased ratio of Co²⁺ /Co³⁺ and improved redox properties, thus enhancing its intrinsic and broad-spectrum catalytic ROS-scavenging activities, which surpasses most of the currently reported metal oxides. Consequently, the Mn-Co₃ O₄ can efficiently protect the MSCs from ROS attack and rescue their functions, including adhesion, spreading, proliferation, and osteogenic differentiation. This work not only establishes an efficient material for catalytic ROS-scavenging in stem-cell-based therapeutics but also provides a new avenue to design biocatalytic metal oxides via modulation of electronic structure.

Lipid nanoparticle-encapsulated VEGFa siRNA facilitates cartilage formation by suppressing angiogenesis

Cartilage is an important tissue that is widely found in joints, ears, nose and other organs. The limited capacity to regenerate makes cartilage reconstruction an urgent clinical demand. Due to the avascular nature of cartilage, we hypothesized that inhibition of vascularization contributes to cartilage formation. Here, we used VEGFa siRNA to inhibit the infiltration of the local vascular system. Optimized lipid nanoparticles were prepared by microfluidics for the delivery of siRNA. Then, we constructed a tissue engineering scaffold. Both seed cells and VEGFa siRNA-LNPs were loaded in a GELMA hydrogel. Subcutaneous implantation experiments in nude mice indicate that this is a promising strategy for cartilage reconstruction. The regenerated cartilage was superior, with significant upregulation of SOX9, COL-II and ACAN. This is attributed to an environment deficient in oxygen and nutrients, which facilitates cartilage formation by upregulating HIF-1α and FOXO transcription factors. In conclusion, a GelMA/Cells+VEGFa siRNA-LNPs scaffold was constructed to achieve superior cartilage regeneration.

Adhesive Gelatin-Catechol Complex Reinforced Poly(Acrylic Acid) Hydrogel with Enhanced Toughness and Cell Affinity for Cartilage Regeneration

The repair of cartilage damage caused by trauma, wear, or degenerative deformation remains a major challenge in modern medicine. Therefore, it is essential to develop a mechanically compatible and bioactive scaffold for cartilage tissue regeneration. In this study, a mussel-inspired, tough, adhesive polydopamine/gelatin-poly(acrylic acid) (PDA/Gel-PAA) composite hydrogel was developed for cartilage regeneration. The hydrogel achieved a high compressive strength of up to 0.67 MPa and a toughness of 420 J/m2 because of the unique chemical-physical cross-linking structure by introducing the PDA/Gel complex into the PAA network. PAA chains with rich carboxyl groups mimic the negatively charged glycosaminoglycans (GAGs) in the natural cartilage extracellular matrix (ECM), leading to strong water retention in the hydrogel. The incorporation of the PDA/Gel complex with catechol groups on PDA and arginine-glycine-aspartic acid (RGD) sequences on gelatin chains provided abundant adhesive motifs to improve the cell affinity and tissue adhesiveness of PAA, thereby facilitating the adhesion and proliferation of bone marrow stromal cells (BMSCs). In addition, transforming growth factor-β3 (TGFβ3) was stably immobilized and released from the PDA/Gel-PAA hydrogel. Thus, adhesive hydrogels can provide a suitable microenvironment to promote cell migration in the defect area and induce chronogenesis for cartilage regeneration.

Emerging nanobiotechnology-encoded relaxation tuning establishes new MRI modes to localize, monitor and predict diseases

Magnetic resonance imaging (MRI) is one of the most important techniques in the diagnosis of many diseases including cancers, where contrast agents (CAs) are usually necessary to improve its precision and sensitivity. Previous MRI CAs are confined to the signal-to-noise ratio (SNR) elevation of lesions for precisely localizing lesions. As nanobiotechnology advances, some new MRI CAs or nanobiotechnology-enabled MRI modes have been established to vary the longitudinal or transverse relaxation of CAs, which are harnessed to detect lesion targets, monitor disease evolution, predict or evaluate curative effect, etc. These distinct cases provide unexpected insights into the correlation of the design principles of these nanobiotechnologies and corresponding MRI CAs with their potential applications. In this review, first, we briefly present the principles, classifications and applications of conventional MRI CAs, and then elucidate the recent advances in relaxation tuning via the development of various nanobiotechnologies with emphasis on the design strategies of nanobiotechnology and the corresponding MRI CAs to target the tumor microenvironment (TME) and biological targets or activities in tumors or other diseases. In addition, we exemplified the advantages of these strategies in disease theranostics and explored their potential application fields. Finally, we analyzed the present limitations, potential solutions and future development direction of MRI after its combination with nanobiotechnology.

Cross-Linking Agents for Electrospinning-Based Bone Tissue Engineering

Electrospun nanofibers are promising bone tissue scaffolds that support bone healing due to the body’s structural similarity to the extracellular matrix (ECM). However, the insufficient mechanical properties often limit their potential in bone tissue regeneration. Cross-linking agents that chemically interconnect as-spun electrospun nanofibers are a simple but effective strategy for improving electrospun nanofibers’ mechanical, biological, and degradation properties. To improve the mechanical characteristic of the nanofibrous bone scaffolds, two of the most common types of cross-linking agents are used to chemically crosslink electrospun nanofibers: synthetic and natural. Glutaraldehyde (GTA) is a typical synthetic agent for electrospun nanofibers, while genipin (GP) is a natural cross-linking agent isolated from gardenia fruit extracts. GP has gradually gained attention since GP has superior biocompatibility to synthetic ones. In recent studies, much more progress has been made in utilizing crosslinking strategies, including citric acid (CA), a natural cross-linking agent. This review summarizes both cross-linking agents commonly used to improve electrospun-based scaffolds in bone tissue engineering, explains recent progress, and attempts to expand the potential of this straightforward method for electrospinning-based bone tissue engineering.

Urine-Microenvironment-Initiated Composite Hydrogel Patch Reconfiguration Propels Scarless Memory Repair and Reinvigoration of the Urethra

The harsh urine microenvironment (UME), as an inherent hurdle, endangers and renders urethral repair unreachable. Innovatively, the unfavorable UME is utilized as the design source to construct a UME-responsive 3D-printed hydrogel patch for realizing scarless memory repair, wherein laser-excited reactive oxygen species (ROS) production and mechanical strength elevation using chemically crosslinked silicon quantum dots are accessible. Intriguingly, the proposed composite scaffolds can respond to Ca²⁺ in urine, cause structure reconfiguration, and repress swelling to further enhance scaffold stiffness. Systematic experiments validate that ROS birth and unexpected stiffness elevation in such UME-responsive scaffolds can realize scarless memory repair of the urethra in vivo. Comprehensive mechanism explorations uncover that the activations of cell proliferation and collagen-related genes (e.g., MMP-1 and COL3A1) and the dampening of fibrosis-related (e.g., TGF-β/Smad) and mechanosensitive genes (e.g., YAP/TAZ) are responsible for the scarless memory repair of such UME-responsive scaffolds via enhancing collagen deposition, recalling mechanical memory, decreasing fibrosis and inflammation, and accelerating angiogenesis. The design rationales (e.g., UME-initiated structure reconfiguration and antiswelling) can serve as an instructive and general approach for urethra repair.

Recent strategies of collagen-based biomaterials for cartilage repair: from structure cognition to function endowment

Collagen, characteristic in biomimetic composition and hierarchical structure, boasts a huge potential in repairing cartilage defect due to its extraordinary bioactivities and regulated physicochemical properties, such as low immunogenicity, biocompatibility and controllable degradation, which promotes the cell adhesion, migration and proliferation. Therefore, collagen-based biomaterial has been explored as porous scaffolds or functional coatings in cell-free scaffold and tissue engineering strategy for cartilage repairing. Among those forming technologies, freeze-dry is frequently used with special modifications while 3D-printing and electrospinning serve as the structure-controller in a more precise way. Besides, appropriate cross-linking treatment and incorporation with bioactive substance generally help the collagen-based biomaterials to meet the physicochemical requirement in the defect site and strengthen the repairing performance. Furthermore, comprehensive evaluations on the repair effects of biomaterials are sorted out in terms of in vitro, in vivo and clinical assessments, focusing on the morphology observation, characteristic production and critical gene expression. Finally, the challenge of biomaterial-based therapy for cartilage defect repairing was summarized, which is, the adaption to the highly complex structure and functional difference of cartilage.

Graphical abstract

Biomimetic radiosensitizers unlock radiogenetics for local interstitial radiotherapy to activate systematic immune responses and resist tumor metastasis

Background

Similar to other local therapeutic methods, local interstitial radiotherapy (IRT) also suffers from insufficient systematic immune activation, resulting in tumor metastasis.

Results

Mn-based IRT radiosensitizers consisting of ¹³¹I, MnO₂ and bovine serum albumin (BSA) (¹³¹I-MnO₂-BSA) were engineered. Such Mn-based IRT radiosensitizers successfully unlocked radiogenetics to magnify systematic immune responses of local IRT via remodeling hypoxic and immunosuppressive microenvironments and resist tumor metastasis. The MnO₂ in ¹³¹I-MnO₂-BSA caused decomposition of H₂O₂ enriched in tumors to generate O₂ for alleviating hypoxic microenvironment and removing tumor resistances to IRT. Concurrently, hypoxia mitigation by such radiosensitizers-unlocked radiogenetics can effectively remodel immunosuppressive microenvironment associated with regulatory T (Treg) cells and tumor-associated macrophages (TAMs) infiltration inhibition to induce immunogenic cell death (ICD), which, along with hypoxia mitigation, activates systematic immune responses. More intriguingly, ¹³¹I-MnO₂-BSA-enabled radiogenetics can upregulate PD-L1 expression, which allows anti-PD-L1-combined therapy to exert a robust antitumor effect on primary tumors and elicit memory effects to suppress metastatic tumors in both tumor models (4T1 and CT26).

Conclusions

IRT radiosensitizer-unlocked radiogenetics and the corresponding design principle provide a general pathway to address the insufficient systematic immune responses of local IRT.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01324-w.

Cross-linking methods of type I collagen-based scaffolds for cartilage tissue engineering

Cartilage defects are one of the hardest injures to cure, given the limited regenerative ability of cartilage tissues. Moreover, cartilage defects affect an increasing number of people worldwide. Therefore, scientists have attempted to develop effective strategies to repair cartilage defects in recent years. Recent advances in tissue engineering have led to the strategies for inducing cartilage regeneration. Among the emerging strategies, scaffolds are commonly used in cartilage tissue engineering (CTE) as they provide favorable environment for the growth and proliferation of chondrocytes. An ideal scaffolding material should be highly biocompatible. Type I collagen is one such material, which is widely used in CTE. However, type I collagen has poor mechanical properties and stability, which limit its use. Cross-linking is a simple method known to improve degradability, biological and mechanical properties of biomaterials by enhancing chemical and physical interactions between polymers. Cross-linking can be induced through chemical, physical or biological processes. In this review, we present cross-linking methods that can enhance the mechanical strength of type I collagen for CTE and highlight future directions in this field.

Soft substrates direct stem cell differentiation into the chondrogenic lineage without the use of growth factors

Mesenchymal stem cells (MSCs) hold great promise for the treatment of cartilage related injuries. However, selectively promoting stem cell differentiation in vivo is still challenging. Chondrogenic differentiation of MSCs usually requires the use of growth factors that lead to the overexpression of hypertrophic markers. In this study, for the first time the effect of stiffness on MSC differentiation has been tested without the use of growth factors. Three-dimensional collagen and alginate scaffolds were developed and characterised. Stiffness significantly affected gene expression and ECM deposition. While, all hydrogels supported chondrogenic differentiation and allowed deposition of collagen type II and aggrecan, the 5.75 kPa hydrogel showed limited production of collagen type I compared to the other two formulations. These findings demonstrated for the first time that stiffness can guide MSCs differentiation without the use of growth factors within a tissue engineering scaffold suitable for the treatment of cartilage defects.

Anti-Inflammatory and Prochondrogenic In Situ-Formed Injectable Hydrogel Crosslinked by Strontium-Doped Bioglass for Cartilage Regeneration

Directed differentiation of bone marrow mesenchymal stem cells (BMSCs) toward chondrogenesis plays a predominant role in cartilage repair. However, the uncontrolled inflammatory response to implants is found to impair the stability of scaffolds and the cartilage regeneration outcome. Herein, we fabricated an injectable hydrogel crosslinked by strontium-doped bioglass (SrBG) to modulate both human BMSC (hBMSC) differentiation and the inflammatory response. The results revealed that the introduction of Sr ions could simultaneously enhance the proliferation of hBMSCs, upregulate cartilage-specific gene expression, and improve the secretion of glycosaminoglycan. Moreover, after cultured with SA/SrBG extracts in vitro, a majority of macrophages were polarized toward the M2 phenotype and subsequently facilitated the chondrogenic differentiation of hBMSCs. Furthermore, after the composite hydrogel was injected into a cartilage defect model, neonatal cartilage-like tissues with a smooth surface and tight integration with original tissues could be found. This study suggests that the synergistic strategy based on an enhanced differentiation ability and a regulated inflammatory response is promising and may lead the way to new anti-inflammatory biomaterials.

Current hydrogel advances in physicochemical and biological response-driven biomedical application diversity

Hydrogel is a type of versatile platform with various biomedical applications after rational structure and functional design that leverages on material engineering to modulate its physicochemical properties (e.g., stiffness, pore size, viscoelasticity, microarchitecture, degradability, ligand presentation, stimulus-responsive properties, etc.) and influence cell signaling cascades and fate. In the past few decades, a plethora of pioneering studies have been implemented to explore the cell-hydrogel matrix interactions and figure out the underlying mechanisms, paving the way to the lab-to-clinic translation of hydrogel-based therapies. In this review, we first introduced the physicochemical properties of hydrogels and their fabrication approaches concisely. Subsequently, the comprehensive description and deep discussion were elucidated, wherein the influences of different hydrogels properties on cell behaviors and cellular signaling events were highlighted. These behaviors or events included integrin clustering, focal adhesion (FA) complex accumulation and activation, cytoskeleton rearrangement, protein cyto-nuclei shuttling and activation (e.g., Yes-associated protein (YAP), catenin, etc.), cellular compartment reorganization, gene expression, and further cell biology modulation (e.g., spreading, migration, proliferation, lineage commitment, etc.). Based on them, current in vitro and in vivo hydrogel applications that mainly covered diseases models, various cell delivery protocols for tissue regeneration and disease therapy, smart drug carrier, bioimaging, biosensor, and conductive wearable/implantable biodevices, etc. were further summarized and discussed. More significantly, the clinical translation potential and trials of hydrogels were presented, accompanied with which the remaining challenges and future perspectives in this field were emphasized. Collectively, the comprehensive and deep insights in this review will shed light on the design principles of new biomedical hydrogels to understand and modulate cellular processes, which are available for providing significant indications for future hydrogel design and serving for a broad range of biomedical applications.

Childhood Cartilage ECM Enhances the Chondrogenesis of Endogenous Cells and Subchondral Bone Repair of the Unidirectional Collagen-dECM Scaffolds in Combination with Microfracture

Despite the formation of mechanically inferior fibrocartilage, microfracture (MF) still remains the gold standard to repair the articular cartilage defects in clinical settings. To date, although many tissue-engineering scaffolds have been developed to enhance the MF outcome, the clinical outcomes remain inconsistent. Decellularized extracellular matrix (dECM) is among the most promising scaffold for cartilage repair due to its inheritance of the natural cartilage components. However, the impact of dECM from different developmental stages on cellular chondrogenesis and therapeutic effect remains elusive, as the development of native cartilage involves the distinct temporal dependency of the ECM components and various growth factors. Herein, we hypothesized that the immature cartilage dECM at various developmental stages was inherently different, and would consequently impact the chondrogenic potential BMSCs. In this study, we fabricated three different unidirectional collagen-dECM scaffolds sourced from neonatal, childhood, and adolescent rabbit cartilage tissues, and identified the age-dependent biological variations, including DNA, cartilage-specific proteins, and growth factors; along with the mechanical and degradation differences. Consequently, the different local cellular microenvironments provided by these scaffolds led to the distinctive cell morphology, circularity, proliferation, chondrogenic genes expression, and chondrogenesis of BMSCs in vitro, and the different gross morphology, cartilage-specific protein production, and subchondral bone repair when in combination with microfracture in vivo. Together, this work highlights the immature cartilage dECM at different developmental stages that would result in the diversified effects to BMSCs, and childhood cartilage would be considered the optimal dECM source for the further development of dECM-based tissue engineering scaffolds in articular cartilage repair.

Collagen-based biocomposites inspired by bone hierarchical structures for advanced bone regeneration: ongoing research and perspectives

Bone is a hard-connective tissue composed of matrix, cells and bioactive factors with a hierarchical structure, where the matrix is mainly composed of type I collagen and hydroxyapatite. Collagen fibers assembled by collagen are the template for mineralization and make an important contribution to bone formation and the bone remodeling process. Therefore, collagen has been widely clinically used for bone/cartilage defect regeneration. However, pure collagen implants, such as collagen scaffolds or sponges, have limitations in the bone/cartilage regeneration process due to their poor mechanical properties and osteoinductivity. Different forms of collagen-based composites prepared by incorporating natural/artificial polymers or bioactive inorganic substances are characterized by their interconnected porous structure and promoting cell adhesion, while they improve the mechanical strength, structural stability and osteogenic activities of the collagen matrix. In this review, various forms of collagen-based biocomposites, such as scaffolds, sponges, microspheres/nanoparticles, films and microfibers/nanofibers prepared by natural/synthetic polymers, bioactive ceramics and carbon-based materials compounded with collagen are reviewed. In addition, the application of collagen-based biocomposites as cytokine, cell or drug (genes, proteins, peptides and chemosynthetic) delivery platforms for proangiogenesis and bone/cartilage tissue regeneration is also discussed. Finally, the potential application, research and development direction of collagen-based biocomposites in future bone/cartilage tissue regeneration are discussed.

Controlled domain gels with a biomimetic gradient environment for osteochondral tissue regeneration

In order to repair an osteochondral defect, it is critical to advance a bi-lineage constructive scaffold with gradient transition. In this study, we developed a simple and straightforward approach for fabricating a multi-domain gel scaffold through the assembly/disassembly of low-molecular-weight gels (LMWGs) inside a stable PEGDA network by photopolymerization. The versatility of this technology enabled to vary biological, topological, and mechanical properties through material selection and to generate a chondrogenic-osteogenic gradient transition. The multi-domain gel exhibited an increasing stiffness gradient along the longitudinal direction from the cartilage layer at approximately 20 kPa to the bone layer at approximately 300 kPa as well as spatial variation at the gradient interface. Moreover, the transitional layer with a condensed structure and intermediate stiffness prevented delamination of the contrasting layers and maintained microenvironmental differences in the upper and lower layers. The in vitro results indicated that each domain had an individual capacity to spatially control the differentiation of MSCs toward osteoblastic lineage and chondrocytic lineage. This was mainly because the mechanical and topographical cues from the respective domains played an important role in modulating the Rho-ROCK signaling pathway, whereas the blockage of ROCK signals significantly impaired domain-modulated osteogenesis and enhanced chondrogenesis. Additionally, the quantity and quality of osteochondral repair were evaluated at 4 and 8 weeks through histological analysis and micro-computed tomography (micro-CT). The results indicated that the multi-domain gels distinctly improved the regeneration of subchondral bone and cartilage tissues. Overall, the outcomes of this study can motivate future bioinspired gradient and heterogeneity strategies for osteochondral tissue regeneration. STATEMENT OF SIGNIFICANCE: The regeneration of osteochondral defects remains a major challenge due to the complexity of osteochondral structure and the limited self-repair capacity of cartilage. The gradient design to mimic the transition between the calcified cartilage and the subchondral bone plate as well as the zones of cartilage is an effective strategy. In this study, controlled multi-domain gels were fabricated through the assembly/disassembly of low-molecular-weight gels inside a stable PEGDA network by photopolymerization. The prepared multi-domain gels showed a chondrogenic-osteogenic gradient transition, which decreased the possibility of delamination and stimulated osteochondral tissue regeneration in vivo. Overall, our study promotes new strategies of bioinspired gradients and heterogeneities for more challenging applications.

Three-dimensional bioprinting of polysaccharide-based self-healing hydrogels with dual cross-linking

Three-dimensional (3D) bioprinting technique is useful to fabricate constructs with functional and biological structures for various biomedical applications. Oxidized hyaluronate (OHA) and glycol chitosan (GC) can form autonomous self-healing hydrogels when adipic acid dihydrazide (ADH) is used. We demonstrate that hyaluronate-alginate hybrid (HAH) polymers can be used for secondary physical cross-linking of OHA/GC/ADH hydrogel with calcium ions after 3D printing. The molecular weight of hyaluronate can be varied while keeping the molecular weight of alginate in HAH. The mechanical stiffness and stability of gels after 3D printing are strongly dependent on the molecular weight of HAH at the same cross-linking density. In vitro chondrogenic differentiation of ATDC5 cells encapsulated in 3D-printed constructs is dependent on the molecular weight of HAH in gels. This dual cross-linking system consisting of naturally occurring biocompatible polysaccharides may have potential in the 3D bioprinting of custom-made scaffolds for tissue engineering applications.

Bioengineered Protein-based Adhesives for Biomedical Applications

Protein-based adhesives with their robust adhesion performance and excellent biocompatibility have been extensively explored over years. In particular, the unique adhesion behaviours of mussel and sandcastle worm inspired the development of synthetic adhesives. However, the chemical synthesized adhesives often demonstrate weak underwater adhesion performance and poor biocompatibility/biodegradability, limiting their further biomedical applications. In sharp contrast, genetically engineering endows the protein-based adhesives the ability to maintain underwater adhesion property as well as biocompatibility/biodegradability. Herein, we outline recent advances in the design and development of protein-based adhesives by genetic engineering. We summarize the fabrication and adhesion performance of elastin-like polypeptide-based adhesives, followed by mussel foot protein (mfp) based adhesives and other sources protein-based adhesives, such as, spider silk spidroin and suckerin. In addition, the biomedical applications of these bioengineered protein-based adhesives are presented. Finally, we give a brief summary and perspective on the future development of bioengineered protein-based adhesives.