A Three-in-One Strategy: Injectable Biomimetic Porous Hydrogels for Accelerating Bone Regeneration via Shape-Adaptable Scaffolds, Controllable Magnesium Ion Release, and Enhanced Osteogenic Differentiation

Metal Ion-Containing Hydrogels: Synthesis, Properties, and Applications in Bone Tissue Engineering

Hydrogel, as a unique scaffold material, features a three-dimensional network system that provides conducive conditions for the growth of cells and tissues in bone tissue engineering (BTE). In recent years, it has been discovered that metal ion-containing hybridized hydrogels, synthesized with metal particles as the foundation, exhibit excellent physicochemical properties, osteoinductivity, and osteogenic potential. They offer a wide range of research prospects in the field of BTE. This review provides an overview of the current state and recent advancements in research concerning metal ion-containing hydrogels in the field of BTE. Within materials science, it covers topics such as the binding mechanisms of metal ions within hydrogel networks, the types and fabrication methods of various metal ion-containing hydrogels, and the influence of metal ions on the properties of hydrogels. In the context of BTE, the review delves into the osteogenic mechanisms of various metal ions, the applications of metal ion-containing hydrogels in BTE, and relevant experimental studies in vitro and in vivo. Furthermore, future improvements in bone repair can be anticipated through advancements in bone bionics, exploring interactions between metal ions and the development of a wider range of metal ions and hydrogel types.

An injectable magnesium-coordinated phosphate chitosan-based hydrogel loaded with vancomycin for antibacterial and osteogenesis in the treatment of osteomyelitis

Microbial infections of bones, particularly after joint replacement surgery, are a common occurrence in clinical settings and often lead to osteomyelitis (OM). Unfortunately, current treatment approaches for OM are not satisfactory. To address this issue, this study focuses on the development and evaluation of an injectable magnesium oxide (MgO) nanoparticle (NP)-coordinated phosphocreatine-grafted chitosan hydrogel (CMPMg-VCM) loaded with varying amounts of vancomycin (VCM) for the treatment of OM. The results demonstrate that the loading of VCM does not affect the formation of the injectable hydrogel, and the MgO-incorporated hydrogel exhibits anti-swelling properties. The release of VCM from the hydrogel effectively kills S.aureus bacteria, with CMPMg-VCM (50) showing the highest antibacterial activity even after prolonged immersion in PBS solution for 12 days. Importantly, all the hydrogels are non-toxic to MC3T3-E1 cells and promote osteogenic differentiation through the early secretion of alkaline phosphatase and calcium nodule formation. Furthermore, in vivo experiments using a rat OM model reveal that the CMPMg-VCM hydrogel effectively kills and inhibits bacterial growth, while also protecting the infected bone from osteolysis. These beneficial properties are attributed to the burst release of VCM, which disrupts bacterial biofilm, as well as the release of Mg ions and hydroxyl by the degradation of MgO NPs, which inhibits bacterial growth and prevents osteolysis. Overall, the CMPMg-VCM hydrogel exhibits promising potential for the treatment of microbial bone infections.

Preparation of a novel antibacterial magnesium carbonate coating on a titanium surface and its in vitro biocompatibility

Magnesium-based coatings have attracted great attention in surface modification of titanium implants due to their superior angiogenic and osteogenic properties. However, their biological effects as a carbonate-based constituent remain unrevealed. In this study, magnesium carbonate coatings were prepared on titanium surfaces under hydrothermal conditions and subsequently treated with hydrogen peroxide. Also, their antibacterial activity and in vitro cell biocompatibility were evaluated. The obtained coatings consisted of nanoparticles without cracks and exhibited excellent adhesion to the substrate. X-ray diffraction (XRD) results indicated pure magnesium carbonate coatings formed on the Ti surface after hydrothermal treatment. After hydrogen peroxide treatment, the phase composition of the coatings had no obvious change. Compared to the untreated coatings, the hydrogen peroxide-treated coatings showed increased surface roughness and hydrophilicity. Co-culture with Staphylococcus aureus (S. aureus) demonstrated that the obtained coatings had good antibacterial activity. In vitro cell culture results showed that the hydrogen peroxide-treated coatings enhanced the viability, proliferation, and osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). These findings suggest that this MgCO3-based coating exhibits excellent antibacterial performance and osteogenic potential. Based on the above, this study provides a simple method for preparing titanium implants with dual antibacterial and osteogenic capabilities, holding great promise in clinical applications.

Biomaterial scaffolds in maxillofacial bone tissue engineering: A review of recent advances

Maxillofacial bone defects caused by congenital malformations, trauma, tumors, and inflammation can severely affect functions and aesthetics of maxillofacial region. Despite certain successful clinical applications of biomaterial scaffolds, ideal bone regeneration remains a challenge in maxillofacial region due to its irregular shape, complex structure, and unique biological functions. Scaffolds that address multiple needs of maxillofacial bone regeneration are under development to optimize bone regeneration capacity, costs, operational convenience. etc. In this review, we first highlight the special considerations of bone regeneration in maxillofacial region and provide an overview of the biomaterial scaffolds for maxillofacial bone regeneration under clinical examination and their efficacy, which provide basis and directions for future scaffold design. Latest advances of these scaffolds are then discussed, as well as future perspectives and challenges. Deepening our understanding of these scaffolds will help foster better innovations to improve the outcome of maxillofacial bone tissue engineering.

Preparation, properties and in vitro osteogensis of self-reinforcing injectable hydrogel

As an attractive biomaterial for bone reconstruction, injectable biomaterials have many prominent characteristics such as good biocompatibility and bone-filling ability. However, there are weak as load-bearing scaffolds. In this study, polyvinyl alcohol (PVA) and bioactive glass (BAG) were interpenetrated into sodium alginate (SA) network to obtain self-enhanced injectable hydrogel. The optimum ratio of PVA/SA/BAG hydrogel was determined based on injectability, gelation time and chemical characterization. Results showed that the selected ratio had the shortest gelation time of 3.5min, and the hydrogel had a rough surface and good coagulation property. The hydrogel was capable of carrying 1kg of weight by mineralization for 14 d The compressive strength, compressive modulus, and fracture energy of the hydrogel reached 0.12MPa, 0.376MPa and 17.750kJ m-2, respectively. Meanwhile, the hydrogel had high moisture content and dissolution rate, and it was sensitive to temperature and ionic strength. Hydroxyapatite was generated on the hydrogel surface, and the hydrogel pores increased, and the pore size enlarged. The biocompatibility of PVA/SA/BAG hydrogel was analyzed using hemolysis and cytotoxicity assays. Results revealed its good biocompatibility with low hemolysis rate and no cytotoxicity to MC3T3-E1 cells. The hydrogel was also found to promote the differentiation of MC3T3-E1 cells with significantly increased in ALP activity and expression of relevant differentiation factors. In vitro mineralization assay showed an increase in calcium nodules and calcification area, indicating the ability of hydrogel to promote mineralization MC3T3-E1 cells. These findings indicated that PVA/SA/BAG hydrogel had potential uses in the field of irregular bone-defect repair due to its injectability, cytocompatibility, and tailorable functionality.

Exogeneous metal ions as therapeutic agents in cardiovascular disease and their delivery strategies

Metal ions participate in many metabolic processes in the human body, and their homeostasis is crucial for life. In cardiovascular diseases (CVDs), the equilibriums of metal ions are frequently interrupted, which are related to a variety of disturbances of physiological processes leading to abnormal cardiac functions. Exogenous supplement of metal ions has the potential to work as therapeutic strategies for the treatment of CVDs. Compared with other therapeutic drugs, metal ions possess broad availability, good stability and safety and diverse drug delivery strategies. The delivery strategies of metal ions are important to exert their therapeutic effects and reduce the potential toxic side effects for cardiovascular applications, which are also receiving increasing attention. Controllable local delivery strategies for metal ions based on various biomaterials are constantly being designed. In this review, we comprehensively summarized the positive roles of metal ions in the treatment of CVDs from three aspects: protecting cells from oxidative stress, inducing angiogenesis, and adjusting the functions of ion channels. In addition, we introduced the transferability of metal ions in vascular reconstruction and cardiac tissue repair, as well as the currently available engineered strategies for the precise delivery of metal ions, such as integrated with nanoparticles, hydrogels and scaffolds.

Visible light-induced 3D bioprinted injectable scaffold for minimally invasive tissue regeneration

Pre-formed hydrogel scaffolds have emerged as favorable vehicles for tissue regeneration, promoting minimally invasive treatment of native tissue. However, due to the high degree of swelling and inherently poor mechanical properties, development of complex structural hydrogel scaffolds at different dimensional scales has been a continuous challenge. Herein, we take a novel approach at the intersections of engineering design and bio-ink chemistry to develop injectable pre-formed structural hydrogel scaffolds fabricated via visible light (VL) induced digital light processing (DLP). In this study, we first determined the minimum concentration of poly(ethylene glycol) diacrylate (PEGDA) to be added to the gelatin methacrylate (GelMA) bio-ink in order to achieve scalable and high printing-fidelity with desired cell adhesion, viability, spreading, and osteogenic differentiation characteristics. Despite the advantages of hybrid GelMA-PEGDA bio-ink in improving scalability and printing-fidelity, compressibility, shape-recovery, and injectability of the 3D bioprinted scaffolds were compromised. To restore these needed characteristics for minimally invasive tissue regeneration applications, we performed topological optimization to design highly compressible and injectable pre-formed (i.e., 3D bioprinted) microarchitectural scaffolds. The designed injectable pre-formed microarchitectural scaffolds showed a great capacity to retain the viability of the encapsulated cells (>72 % after 10 cycles of injection). Lastly, ex ovo chicken chorioallantoic membrane (CAM) studies revealed that the optimized injectable pre-formed hybrid hydrogel scaffold is biocompatible and supports angiogenic growth.

Engineering a triple-functional magnetic gel driving mutually-synergistic mild hyperthermia-starvation therapy for osteosarcoma treatment and augmented bone regeneration

Malignant bone tumors result in high rates of disability and death and are difficult to treat in terms of killing tumors and repairing bone defects. Compared with other hyperthermia strategies, magnetic hyperthermia has become an effective therapy for treating malignant bone tumors due to its lack of depth limitations. However, tumor cells express heat shock protein (HSP) to resist hyperthermia, which reduces its curative effect. Competitive ATP consumption can reduce HSP production; fortunately, the basic principle of starvation therapy by glucose oxidase (GOx) is consuming glucose to control ATP production, thereby restricting HSP generation. We developed a triple-functional magnetic gel (Fe₃O₄/GOx/MgCO₃@PLGA) as a magnetic bone repair hydrogels (MBRs) with liquid‒solid phase transition capability to drive magneto-thermal effects to simultaneously trigger GOx release and inhibit ATP production, reducing HSP expression and thereby achieving synergistic therapy for osteosarcoma treatment. Moreover, magnetic hyperthermia improves the effect of starvation therapy on the hypoxic microenvironment and achieves a reciprocal strengthening therapeutic effect. We further demonstrated that in situ MBRs injection effectively suppressed tumor growth in 143B osteosarcoma tumor-bearing mice and an in-situ bone tumor model in the rabbit tibial plateau. More importantly, our study also showed that liquid MBRs could effectively match bone defects and accelerate their reconstruction via magnesium ion release and enhanced osteogenic differentiation to augment the regeneration of bone defects caused by bone tumors, which generates fresh insight into malignant bone tumor treatment and the acceleration of bone defect repair.

Incorporation of Magnesium and Zinc Metallic Particles in PLGA Bi-layered Membranes with Sequential Ion Release for Guided Bone Regeneration

Guided bone regeneration (GBR) membranes are commonly used for periodontal tissue regeneration. Due to the complications of existing GBR membranes, the design of bioactive membranes is still relevant. GBR membranes with an asymmetric structure can accommodate the functional requirements of different interfacial tissues. Here, poly(lactic acid-glycolic acid) (PLGA) was selected as the matrix for preparing a bi-layered membrane with both dense and porous structure. The dense layer for blocking soft tissues was incorporated with zinc (Zn) particles, while the porous layer for promoting bone regeneration was co-incorporated with magnesium (Mg) and Zn particles. Mg/Zn-embedded PLGA membranes exhibited 166% higher mechanical strength in comparison with pure PLGA membranes and showed suitable degradation properties with a sequential ion release behavior of Mg²⁺ first and continuously Zn²⁺. More importantly, the release of Zn²⁺ from bi-layered PLGA endowed GBR membranes with excellent antibacterial activity (antibacterial rate > 69.3%) as well as good cytocompatibility with MC3T3-E1 (mouse calvaria pre-osteoblastic cells) and HGF-1 (human gingival fibroblast cells). Thus, the asymmetric bi-layered PLGA membranes embedded with Mg and Zn particles provide a simple and effective strategy to not only reinforce the PLGA membrane but also endow membranes with osteogenic and antibacterial activity due to the continuous ion release profile, which serves as a promising candidate for use in GBR therapy.

Functional Hydrogels and Their Applications in Craniomaxillofacial Bone Regeneration

Craniomaxillofacial bone defects are characterized by an irregular shape, bacterial and inflammatory environment, aesthetic requirements, and the need for the functional recovery of oral-maxillofacial areas. Conventional clinical treatments are currently unable to achieve high-quality craniomaxillofacial bone regeneration. Hydrogels are a class of multifunctional platforms made of polymers cross-linked with high water content, good biocompatibility, and adjustable physicochemical properties for the intelligent delivery of goods. These characteristics make hydrogel systems a bright prospect for clinical applications in craniomaxillofacial bone. In this review, we briefly demonstrate the properties of hydrogel systems that can come into effect in the field of bone regeneration. In addition, we summarize the hydrogel systems that have been developed for craniomaxillofacial bone regeneration in recent years. Finally, we also discuss the prospects in the field of craniomaxillofacial bone tissue engineering; these discussions can serve as an inspiration for future hydrogel design.

Injectable versatile liquid-solid transformation implants alliance checkpoint blockade for magnetothermal dynamic-immunotherapy

The ongoing circulating energy loss, low reactive oxygen species (ROS) accumulation and poor immunogenicity of tumors make it difficult to induce sufficient immunogenic cell death (ICD) in the tumor immunosuppressive microenvironment (TIME), resulting in unsatisfactory immunotherapy efficacy. Furthermore, for highly malignant tumors, simply enhancing ICD is insufficient for exhaustively eliminating the tumor and inhibiting metastasis. Herein, we propose a unique magnetothermal-dynamic immunotherapy strategy based on liquid-solid transformation porous versatile implants (Fe₃O₄/AIPH@PLGA) that takes advantage of less energy loss and avoids ongoing circulating losses by minimally invasive injection into tumors. In addition, the magnetothermal effect regresses and eliminates tumors that are not limited by penetration to simultaneously trigger 2,2′-azobis[2-(2-imidazolin-2-yl) propane] dihydrochloride (AIPH) decomposition and generate a large amount of oxygen-irrelevant free radicals and heat shock protein (HSP) accumulation by heating, evoking both intracellular oxidative stress and endoplasmic reticulum (ER) stress to induce large-scale ICD and enhance tumor immunogenicity. More importantly, in orthotopic bilateral breast tumor models, a significant therapeutic effect was obtained after combining amplified ICD with CTLA4 checkpoint blockade. The 21-day primary and distant tumor inhibition rates reached 90%, and the underlying mechanism of the effective synergetic strategy of inducing the T-cell-related response, the immune memory effect and TIME reprogramming in vivo was verified by immune cell analyses. This remarkable therapeutic effect provides a new direction for antitumor immunotherapy based on magnetothermally controlled oxygen-independent free radical release.

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Injectable versatile liquid-solid phase transformation Fe₃O₄/AIPH@PLGA gel implants are constructed for the first time.

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The implants triggered magnetothermal dynamic therapy and successfully addressed two key barriers limiting the efficacy of immunogenic cell death (ICD): low reactive oxygen species (ROS) accumulation and poor immunogenicity.

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The implants promoting DC maturation, recognition and presentation of antigens. Combined with CTLA4 blockade, the function of Treg cells was inhibited to transform the “cold” TIME into “hot”.

Controlled magnesium ion delivery system for in situ bone tissue engineering

Magnesium cation (Mg²⁺) has been an emerging therapeutic agent for inducing vascularized bone regeneration. However, the therapeutic effects of current magnesium (Mg) -containing biomaterials are controversial due to the concentration- and stage-dependent behavior of Mg²⁺. Here, we first provide an overview of biochemical mechanism of Mg²⁺ in various concentrations and suggest that 2-10 mM Mg²⁺in vitro may be optimized. This review systematically summarizes and discusses several types of controlled Mg²⁺ delivery systems based on polymer-Mg composite scaffolds and Mg-containing hydrogels, as well as their design philosophy and several parameters that regulate Mg²⁺ release. Given that the continuous supply of Mg²⁺ may prevent biomineral deposition in the later stage of bone regeneration and maturation, we highlight the controlled delivery of Mg²⁺ based dual- or multi-ions system, especially for the hierarchical therapeutic ion release system, which shows enhanced biomineralization. Finally, the remaining challenges and perspectives of Mg-containing biomaterials for future in situ bone tissue engineering are discussed as well.

PgC3Mg metal-organic cages functionalized hydrogels with enhanced bioactive and ROS scavenging capabilities for accelerated bone regeneration

The repair of large bone defects is an urgent problem in the clinic. Note that the disruption of redox homeostasis around bone defect sites might hinder the new bone reconstruction. The rational design of hydrogels for bone regeneration still faces the challenges of insufficient antioxidant capability and weak osteogenesis performance. Here, motivated by the versatile therapeutic functions of metal-organic cages, magnesium-seamed C-propylpyrogallol[4]arene (PgC₃Mg) functionalized biodegradable and porous gelatin methacrylate (GelMA) hydrogels are constructed. The novel metal-organic cages endow hydrogels with highly bioactive characteristics and strong reactive oxygen species (ROS)-scavenging ability owing to the simultaneous release of bioactive Mg²⁺ ions and antioxidant phenolic hydroxyl-rich moieties. The in vitro results reveal that the PgC₃Mg modified biocompatible hydrogels show higher expression of osteo-related genes and significantly eliminate the intracellular ROS levels of bone marrow-derived mesenchymal stem cells (BMSCs) against oxidative damage. Meanwhile, the bioactive and ROS scavenging hydrogels can accelerate bone regeneration in large cranial defects. Overall, this study may provide new insights into the designing of regenerative bone grafts with simultaneously enhanced osteogenic and antioxidant capabilities.

Effects of Zinc, Magnesium, and Iron Ions on Bone Tissue Engineering

Large-sized bone defects are a great challenge in clinics and considerably impair the quality of patients' daily life. Tissue engineering strategies using cells, scaffolds, and bioactive molecules to regulate the microenvironment in bone regeneration is a promising approach. Zinc, magnesium, and iron ions are natural elements in bone tissue and participate in many physiological processes of bone metabolism and therefore have great potential for bone tissue engineering and regeneration. In this review, we performed a systematic analysis on the effects of zinc, magnesium, and iron ions in bone tissue engineering. We focus on the role of these ions in properties of scaffolds (mechanical strength, degradation, osteogenesis, antibacterial properties, etc.). We hope that our summary of the current research achievements and our notifications of potential strategies to improve the effects of zinc, magnesium, and iron ions in scaffolds for bone repair and regeneration will find new inspiration and breakthroughs to inspire future research.

Exosome-Laden Hydrogels: A Novel Cell-free Strategy for In-situ Bone Tissue Regeneration

In-situ bone tissue regeneration, which harnesses cell external microenvironment and their regenerative potential to induce cell functions and bone reconstruction through some special properties of biomaterials, has been deeply developed. In which, hydrogel was widely applied due to its 3D network structure with high water absorption and mimicking native extracellular matrix (ECM). Additionally, exosomes can participate in a variety of physiological processes such as cell differentiation, angiogenesis and tissue repair. Therefore, a novel cell-free tissue engineering (TE) using exosome-laden hydrogels has been explored and developed for bone regeneration in recent years. However, related reviews in this field are limited. Therefore, we elaborated on the shortcomings of traditional bone tissue engineering, the challenges of exosome delivery and emphasized the advantages of exosome-laden hydrogels for in-situ bone tissue regeneration. The encapsulation strategies of hydrogel and exosomes are listed, and the research progress and prospects of bioactive hydrogel composite system for continuous delivery of exosomes for in-situ bone repair are also discussed in this review.

A review of recent advances in metal ion hydrogels: mechanism, properties and their biological applications

The mechanisms, common properties and biological applications of different types of metal ion hydrogels are summarized.