Tunable and Controlled Release of Cobalt Ions from Metal-Organic Framework Hydrogel Nanocomposites Enhances Bone Regeneration

3D-Printed In Situ Growth of Bilayer MOF Hydrogels for Accelerated Osteochondral Defect Repair

Repairing osteochondral (OC) defect presents a significant challenge due to the intricate structural requirements and the unpredictable differentiation pathways of bone marrow mesenchymal stem cells (BMSCs). To address this challenge, a novel biomimetic OC hydrogel scaffold is developed that features a structure of soft and hard components. This scaffold incorporates bilayer metal-organic frameworks (MOFs), specifically ZIF-67 in the upper layer and ZIF-8 in the lower layer, achieved through an in situ printing process. This configuration enables the spatial and temporal modulation of BMSC differentiation by controlling the release of Co2⁺ and Zn2⁺. The results demonstrate that the bilayer MOF hydrogels significantly outperform hydrogels that either lack MOFs or contain a single type of MOF in enhancing repair outcomes in rabbit models of knee OC defects. The improved regenerative efficacy is attributed to the distinct chondrogenic and osteogenic differentiation cues provided by the bilayer MOFs, effectively guiding BMSCs toward enhanced tissue regeneration. This customizable biomimetic OC hydrogel scaffold not only opens new avenues for innovative therapeutic strategies but also holds great promise for widespread clinical applications.

A Multifunctional Cobalt-Containing Implant for Treating Biofilm Infections and Promoting Osteointegration in Infected Bone Defects Through Macrophage-Mediated Immunomodulation

Treating bone infections and ensuring bone recovery is one of the major global problems facing modern orthopedics. Prolonged antibiotic use may increase the risk of antimicrobial resistance, and inflammation caused by biofilms can obstruct tissue healing, making bone infection treatment even more challenging. The optimal treatment strategy combines immune response modification to promote osteogenesis with effective bacterial infection removal that does not require long-term antibiotic use. A one-step plasma immersion ion implantation approach is used to create titanium alloy implants incorporating cobalt. According to experimental findings, cobalt-containing titanium implants exhibit improved antibacterial activity by efficiently disrupting biofilm formations and reducing Methicillin-resistant Staphylococcus aureus adherence by over 80%. Additionally, the implants exhibit superior anti-inflammatory and osseointegration properties. RNA sequencing analysis reveals the potential mechanism of Co2+ in regulating the polarization of macrophages toward the anti-inflammatory M2 phenotype, which is crucial for creating an immune environment conducive to bone healing. Concurrently, these implants promote osteogenic differentiation while suppressing osteoclast activity, further supporting bone repair. Overall, without exogenous recombinant proteins or antibiotics, the implants effectively eradicate infections and expedite bone repair, offering a novel therapeutic strategy for complex skeletal diseases with clinical promise.

Rethinking Biomedical Titanium Alloy Design: A Review of Challenges from Biological and Manufacturing Perspectives

Current biomedical titanium alloys have been repurposed from other industries, which has contributed to several biologically driven implant failure mechanisms. This review highlights the added value that may be gained by building an appreciation of implant biological responses at the onset of alloy design. Specifically, the fundamental mechanisms associated with immune response, angiogenesis, osseointegration and the potential threat of infection are discussed, including how elemental selection can modulate these pivotal systems. With a view to expedite inclusion of these interactions in alloy design criteria, methods to analyze these performance characteristics are also summarized. While machine learning techniques are being increasingly used to unearth complex relationships between alloying elements and material properties, much is still unknown about the correlation between composition and some bio-related properties. To bridge this gap, high-throughput methods are also reviewed to validate biological response along with cutting edge manufacturing approaches that may support rapid discovery. Taken together, this review encourages the alloy development community to rethink their approach to enable a new generation of biomedical implants intrinsically designed for a life in the body, including functionality to tackle biological challenges thereby offering improved patient outcomes.

Role of exosomes in dental and craniofacial regeneration - A review

BACKGROUND

The treatment of congenital deformities, traumatic injuries, infectious diseases, and tumors in the craniomaxillofacial (CMF) region is complex due to the intricate nature of the tissues involved. Conventional treatments such as bone grafts and cell transplantation face limitations, including the need for multiple surgeries, complications, and safety concerns.

OBJECTIVE

This paper aims to provide a comprehensive analysis of the role of exosomes (EXOs) in CMF and dental tissue regeneration and to explore their potential applications in regenerative dental medicine.

METHODS

An extensive review of advancements in tissue engineering, materials sciences, and nanotechnology was conducted to evaluate the development of delivery systems for EXOs-based therapies. The analysis included how EXOs, as nanovesicles released by cells, can be modified to target specific cells or loaded with functional molecules for drug or gene delivery.

RESULTS

EXOs have emerged as a promising alternative to cell transplant therapy, offering a safer method for cell communication and epigenetic control. EXOs transport important proteins and genetic materials, facilitating intercellular communication and delivering therapeutics effectively. The potential of EXOs in personalized medicine, particularly in diagnosing, customizing treatment, and predicting patient responses, is highlighted.

CONCLUSION

EXO-mediated therapy holds significant potential for advancing tissue regeneration, offering targeted, personalized treatment options with reduced side effects. However, challenges in purification, production, and standardized protocols need to be addressed before its clinical application can be fully realized.

Recombinant human annexin A5 accelerates diabetic wounds healing by regulating skin inflammation

Background

One of the key obstacles to the healing of diabetic wound is the persistence of active inflammation. We previously demonstrated the potential of cell-free fat extract (CEFFE) to promote the healing of diabetic wounds, and annexin A5 (A5) is a crucial anti-inflammatory protein within CEFFE. This study aimed to evaluate the therapeutic potential of A5 in diabetic wounds.

Methods

A5 was loaded into GelMA hydrogels and applied to skin wounds of diabetic mice in vivo. The diabetic wounds with the treatment of GelMA-A5 were observed for 14 days and evaluated by histological analysis. Accessment of inflammation regulation were conducted through anti-CD68 staining, anti-CD86 and anti-CD206 staining, and qRT-PCR of wound tissue. In presence of A5, macrophages stimulated by lipopolysaccharide (LPS) in vitro, and detected through qRT-PCR, flow cytometry, and immunocytofluorescence staining. Besides, epithelial cells were co-cultured with A5 for epithelialization regulation by CCK-8 assay and cell migration assay.

Results

A5 could promote diabetic wound healing and regulate inflammations by promoting the transition of macrophages from M1 to M2 phenotype. In vitro experiments demonstrated that A5 exerted a significant effect on reducing pro-inflammatory factors and inhibiting the polarization of macrophages from M0 toward M1 phenotype. A5 significantly promoted the migration of epithelial cells.

Conclusion

Annexin A5 has a significant impact on the regulation of macrophage inflammation and promotion of epithelialization.

Multifunctional Dual Nano-MOF-Modified Decellularized Small Intestinal Submucosa Membrane Accelerates Healing of Infected Wound

The treatment of complex or chronic skin wounds caused by burns, trauma, surgery, and genetic disorders has been a worldwide challenge. Small intestinal submucosa (SIS) is a biological material that is widely used in wound healing. How to further expand the wound healing application of SIS, especially in repairing infected wounds, remains a hot research topic for many tissue engineering and biomaterial scholars focusing on skin regeneration. This study uses nanometal-organic frameworks (nano-MOFs), which have not been applied to modify the SIS membrane before, to construct multifunctional dual nano-MOFs @ SIS membrane (dnMOF@SISm). Nano-MOFs are functionalized onto the nanofiber of SIS via in situ self-assembly under mild reaction conditions without any toxic reagent or complex instruments. The dnMOF@SISm can release Co2+, Zn2+, and bioactive factors, participating in the whole stage of the repair of infected wounds. In vitro, it can regulate the biological activities of various functional cells such as fibroblasts, endothelial cells, and macrophages and shows good antibacterial ability. In the infected full-thickness skin defect rat model, dnMOF@SISm can release metal ions and ligands, killing pathogenic bacteria colonized on the wound surface at the first stage, and then trigger and accelerate the skin repair process via angiogenesis, immune regulation, and collagen deposition. Above all, an efficient, nontoxic, mild self-assembly strategy realizes the functionalization of dual nano-MOFs on the nanofiber of SIS to expand its clinical application scenarios, especially in infected wounds.

Advances in the study of metal-organic frameworks and their biomolecule composites for osteoporosis therapeutic applications

With the population aging, osteoporosis (OP) is becoming more and more common, seriously affecting patients' quality of life and their families, and how to prevent and treat osteoporosis has become a hot topic. However, the current conventional method of treating OP is oral anti-osteoporosis medication, which has drawbacks such as first-pass elimination and gastrointestinal adverse effects. At the same time, osteoporosis can lead to microbial infections and the need to promote angiogenesis for bone healing, among other needs that often cannot be met with conventional treatments, and there is a risk of resistance to oral antibiotics for microbial infections. Metal-organic frameworks (MOFs) having a high specific surface area, high porosity, controlled degradation, and variable composition; they can not only be used as a carrier to control drug release, but can also play multiple roles in the treatment of OP and microbial infections by releasing metal ions, etc., so they have inherent advantages for OP, which is a disease that requires long-term treatment. Therefore, this paper reviews the research progress of MOFs and their biomacromolecular composites in therapeutic applications for osteoporosis, categorized by MOF type, and briefly describes the mechanism of osteoporosis, and different synthesis methods of MOFs and MOF-based composites, and finally presents the main existing problems and future perspectives, aiming to make MOFs more helpful for OP treatment.

Application of metal-organic framework materials in regenerative medicine

In the past few decades, scaffolds manufactured from composite or hybrid biomaterials of natural or synthetic origin have made great strides in enhancing wound healing and repairing fractures and pathological bone loss. However, the prevailing use of such scaffolds in tissue engineering is accompanied by numerous constraints, including low mechanical stability, poor biological activity, and impaired cell proliferation and differentiation. The performance of scaffolds in wound and bone tissue engineering may be enhanced by some modifications in the synthesis of nanoscale metal-organic framework (nano-MOF) scaffolds. Nano-MOFs have attracted researchers' attention in recent years due to their distinctive features, which include tenability, biocompatibility, good mechanical stability, and ultrahigh surface area. The biological properties of scaffolds are enhanced and tissue regeneration is facilitated by the introduction of nano-MOFs. Moreover, the physicochemical characteristics, drug loading, and ion release capacities of the scaffolds are improved by the nanoscale structure and topological features of nano-MOFs, which also control stem cell differentiation, proliferation, and attachment. This review provides further comprehensive detail about the most recent uses of nano-MOFs in tissue engineering. The distinct characteristics of nano-MOFs are explored in enhancing tissue repair, wound healing, osteoinduction, and bone conductivity. Significant attributes include high antibacterial activity, substantial drug-loading capacity, and the ability to regulate drug release. Finally, this discussion addresses the obstacles, clinical impediments, and considerations encountered in the application of these nanomaterials to diverse scaffolds, tissue-mimicking structures, dressings, fillers, and implants for bone tissue repair and wound healing.

Mussel-Derived and Bioclickable Peptide Mimic for Enhanced Interfacial Osseointegration via Synergistic Immunomodulation and Vascularized Bone Regeneration

Inadequate osseointegration at the interface is a key factor in orthopedic implant failure. Mechanistically, traditional orthopedic implant interfaces fail to precisely match natural bone regeneration processes in vivo. In this study, a novel biomimetic coating on titanium substrates (DPA-Co/GFO) through a mussel adhesion-mediated ion coordination and molecular clicking strategy is engineered. In vivo and in vitro results confirm that the coating exhibits excellent biocompatibility and effectively promotes angiogenesis and osteogenesis. Crucially, the biomimetic coating targets the integrin α2β1 receptor to promote M2 macrophage polarization and achieves a synergistic effect between immunomodulation and vascularized bone regeneration, thereby maximizing osseointegration at the interface. Mechanical push-out tests reveal that the pull-out strength in the DPA-Co/GFO group is markedly greater than that in the control group (79.04 ± 3.20 N vs 31.47 ± 1.87 N, P < 0.01) and even surpasses that in the sham group (79.04 ± 3.20 N vs 63.09 ± 8.52 N, P < 0.01). In summary, the novel biomimetic coating developed in this study precisely matches the natural process of bone regeneration in vivo, enhancing interface-related osseointegration and showing considerable potential for clinical translation and applications.

Acemannan coated, cobalt-doped biphasic calcium phosphate nanoparticles for immunomodulation regulated bone regeneration

Biomaterials are used as scaffolds in bone regeneration to facilitate the restoration of bone tissues. The local immune microenvironment affects bone repair but the role of immune response in biomaterial-facilitated osteogenesis has been largely overlooked and it presents a major knowledge gap in the field. Nanomaterials that can modulate M1 to M2 macrophage polarization and, thus, promote bone repair are known. This study investigates a novel approach to accelerate bone healing by using acemannan coated, cobalt-doped biphasic calcium phosphate nanoparticles to promote osteogenesis and modulate macrophage polarization to provide a prohealing microenvironment for bone regeneration. Different concentrations of cobalt were doped in biphasic calcium phosphate nanoparticles, which were further coated with acemannan polymer and characterized. The nanoparticles showed >90% cell viability and enhanced cell proliferation along with osteogenic differentiation as demonstrated by the enhanced alkaline phosphatase activity and osteogenic calcium deposition. The morphology of MC3T3-E1 cells remained unchanged even after treatment with nanoparticles. Acemannan coated nanoparticles were also able to decrease the expression of M1 markers, iNOS, and CD68 and enhance the expression of M2 markers, CD206, CD163, and Arg-1 as indicated by RT-qPCR, flow cytometry, and ICC studies. The findings show that acemannan coated nanoparticles can create a supportive immune milieu by inducing and promoting the release of osteogenic markers, and by causing a reduction in inflammatory markers, thus helping in efficient bone regeneration. As per our knowledge, this is the first study showing the combined effect of acemannan and cobalt for bone regeneration using immunomodulation. The work presents a novel approach for enhancing osteogenesis and macrophage polarization, thus, offering a potent strategy for effective bone regeneration.

Metal-Organic Framework-Based Nanomaterials for Regulation of the Osteogenic Microenvironment

As the global population ages, bone diseases have become increasingly prevalent in clinical settings. These conditions often involve detrimental factors such as infection, inflammation, and oxidative stress that disrupt bone homeostasis. Addressing these disorders requires exogenous strategies to regulate the osteogenic microenvironment (OME). The exogenous regulation of OME can be divided into four processes: induction, modulation, protection, and support, each serving a specific purpose. To this end, metal-organic frameworks (MOFs) are an emerging focus in nanomedicine, which show tremendous potential due to their superior delivery capability. MOFs play numerous roles in OME regulation such as metal ion donors, drug carriers, nanozymes, and photosensitizers, which have been extensively explored in recent studies. This review presents a comprehensive introduction to the exogenous regulation of OME by MOF-based nanomaterials. By discussing various functional MOF composites, this work aims to inspire and guide the creation of sophisticated and efficient nanomaterials for bone disease management.

Research progress of vascularization strategies of tissue-engineered bone

The bone defect caused by fracture, bone tumor, infection, and other causes is not only a problematic point in clinical treatment but also one of the hot issues in current research. The development of bone tissue engineering provides a new way to repair bone defects. Many animal experimental and rising clinical application studies have shown their excellent application prospects. The construction of rapid vascularization of tissue-engineered bone is the main bottleneck and critical factor in repairing bone defects. The rapid establishment of vascular networks early after biomaterial implantation can provide sufficient nutrients and transport metabolites. If the slow formation of the local vascular network results in a lack of blood supply, the osteogenesis process will be delayed or even unable to form new bone. The researchers modified the scaffold material by changing the physical and chemical properties of the scaffold material, loading the growth factor sustained release system, and combining it with trace elements so that it can promote early angiogenesis in the process of induced bone regeneration, which is beneficial to the whole process of bone regeneration. This article reviews the local vascular microenvironment in the process of bone defect repair and the current methods of improving scaffold materials and promoting vascularization.

Photo-crosslinked bioactive BG/BMSCs@GelMA hydrogels for bone-defect repairs

The clinical treatments of bone defects remain a challenge. Hydrogels containing bone marrow mesenchymal stem cells (BMSCs) are extensively used to bone regeneration because of excellent biocompatibility and hydrophilicity. However, the insufficient osteo-induction capacity of the BMSC-loaded hydrogels limits their clinical applications. In this study, bio-active glass (BG) and BMSCs were combined with gelatin methacryloyl (GelMA) to fabricate composite hydrogels via photo-crosslinking, and the regulation of bone regeneration was investigated. In vitro experiments showed that the BG/BMSCs@GelMA hydrogel had excellent cytocompatibility and promoted osteogenic differentiation in BMSCs. Furthermore, the BG/BMSCs@GelMA hydrogel was injected into critical-sized calvarial defects, and the results further confirmed its excellent angiogenetic and bone regeneration capacity. In addition, BG/BMSCs@GelMA promoted the polarization of macrophages towards the M2 phenotype. In summary, this novel composite hydrogel demonstrated remarkable potential for application in bone regeneration due to its immunomodulatory, excellent angiogenetic as well as osteo-induction capacity.

Recent advancement in vascularized tissue-engineered bone based on materials design and modification

Bone is one of the most vascular network-rich tissues in the body and the vascular system is essential for the development, homeostasis, and regeneration of bone. When segmental irreversible damage occurs to the bone, restoring its vascular system by means other than autogenous bone grafts with vascular pedicles is a therapeutic challenge. By pre-generating the vascular network of the scaffold in vivo or in vitro, the pre-vascularization technique enables an abundant blood supply in the scaffold after implantation. However, pre-vascularization techniques are time-consuming, and in vivo pre-vascularization techniques can be damaging to the body. Critical bone deficiencies may be filled quickly with immediate implantation of a supporting bone tissue engineered scaffold. However, bone tissue engineered scaffolds generally lack vascularization, which requires modification of the scaffold to aid in enhancing internal vascularization. In this review, we summarize the relationship between the vascular system and osteogenesis and use it as a basis to further discuss surgical and cytotechnology-based pre-vascularization strategies and to describe the preparation of vascularized bone tissue engineered scaffolds that can be implanted immediately. We anticipate that this study will serve as inspiration for future vascularized bone tissue engineered scaffold construction and will aid in the achievement of clinical vascularized bone.

Interfacing metal organic frameworks with polymers or carbon-based materials: from simple to hierarchical porous and nanostructured composites

In the past few years, metal organic frameworks (MOFs) have been assembled with (bio)polymers and a series of carbon-based materials (graphene, graphene oxide, carbon nanotubes, carbon quantum dots, etc.) leading to a wide range of composites differing in their chemical composition, pore structure and functionality. The objective was mainly to overcome the limitations of MOFs in terms of mechanical properties, chemical stability and processability while imparting novel functionality (electron conductivity, (photo)catalytic activity, etc.) and hierarchical porosity. These composites were considered for numerous applications including gas/liquid adsorption and separation, (photo)catalysis, biomedicine, energy storage, conversion and so on. The performance of such composites depends strongly on their microstructural and physico-chemical properties which are mainly driven by the chemical strategies used to design and process such composites. In this perspective article, we propose to cover this topic and provide a useful survey of recent progress in the synthesis and design of MOFs-carbon material composites. This article will describe the development of composites with increasing complexity in terms of porous architecture, spatial structuration and organisation, and functionality.

Metal-organic gels: recent advances in their classification, characterization, and application in the pharmaceutical field

Metal-organic gels (MOGs) are a type of functional soft substance with a three-dimensional (3D) network structure and solid-like rheological behavior, which are constructed by metal ions and bridging ligands formed under the driving force of coordination interactions or other non-covalent interactions. As the homologous substances of metal-organic frameworks (MOFs) and gels, they exhibit the potential advantages of high porosity, flexible structure, and adjustable mechanical properties, causing them to attract extensive research interest in the pharmaceutical field. For instance, MOGs are often used as excellent vehicles for intelligent drug delivery and programmable drug release to improve the clinical curative effect with reduced side effects. Also, MOGs are often applied as advanced biomedical materials for the repair and treatment of pathological tissue and sensitive detection of drugs or other molecules. However, despite the vigorous research on MOGs in recent years, there is no systematic summary of their applications in the pharmaceutical field to date. The present review systematically summarize the recent research progress on MOGs in the pharmaceutical field, including drug delivery systems, drug detection, pharmaceutical materials, and disease therapies. In addition, the formation principles and classification of MOGs are complemented and refined, and the techniques for the characterization of the structures/properties of MOGs are overviewed in this review.

Antibacterial and antibiofilm activities of ZIF-67

Currently, antibiotic-resistant bacteria represent a serious threat to public health worldwide. Biofilm formation potentiates both virulence and antibiotic resistance of bacteria. Therefore, the discovery of new antibacterial and antibiofilm compounds is an issue of paramount importance to combat and prevent hard-to-treat bacterial infections. Zeolitic-imidazolate-frameworks (ZIFs) are metallo-organic compounds known to have various interesting chemical and biological applications, including antibacterial properties. In this study, we synthesized ZIF-67 nanoparticles, formed by imidazolate anions and cobalt cations, and found that they inhibit the growth of Acinetobacter baumannii, Pseudomonas aeruginosa, and Staphylococcus aureus. Sub-inhibitory concentrations of ZIF-67 were also able to significantly reduce the biomass of pre-established biofilms of these pathogenic bacteria. On the other hand, the ZIF-67 nanoparticles had null or low cytotoxicity in mammalian cells at those concentrations showing antibacterial or antibiofilm activities. Thus, our results reveal the potential of ZIF-67 nanoparticles to be used against pathogenic bacteria.

Applications of Degradable Hydrogels in Novel Approaches to Disease Treatment and New Modes of Drug Delivery

Hydrogels are particularly suitable materials for loading drug delivery agents; their high water content provides a biocompatible environment for most biomolecules, and their cross-linked nature protects the loaded agents from damage. During delivery, the delivered substance usually needs to be released gradually over time, which can be achieved by degradable cross-linked chains. In recent years, biodegradable hydrogels have become a promising technology in new methods of disease treatment and drug delivery methods due to their many advantageous properties. This review briefly discusses the degradation mechanisms of different types of biodegradable hydrogel systems and introduces the specific applications of degradable hydrogels in several new methods of disease treatment and drug delivery methods.

Novel pH-Responsive CaO2@ZIF-67-HA-ADH Coating That Efficiently Enhances the Antimicrobial, Osteogenic, and Angiogenic Properties of Titanium Implants

Titanium-based implants often lead to premature implant failure due to the lack of antimicrobial, osteogenic, and angiogenic properties. To this end, a new strategy was developed to fabricate CaO2@ZIF-67-HA-ADH coating on titanium surfaces by combining calcium peroxide (CaO2) nanoparticles, zeolite imidazolate framework-67 (ZIF-67), and the chemical coupling hyaluronic acid-adipic acid dihydrazide (HA-ADH). We characterized CaO2@ZIF-67-HA-ADH with scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-atomic emission spectrometry (ICP-AES). The results demonstrated that CaO2@ZIF-67-HA-ADH was pH-sensitive and decomposed rapidly under acidic conditions, and it released inclusions slowly under neutral conditions. Antibacterial experiments showed that the CaO2@ZIF-67-HA-ADH coating had excellent antibacterial properties and effectively killed methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa (PAO-1). Cell experiments revealed that the CaO2@ZIF-67-HA-ADH coating promoted pro-osteoblast adhesion, proliferation, and differentiation and also promoted the migration and angiogenesis of human umbilical vein endothelial cells (HUVECs), exhibiting excellent osteogenic and angiogenic properties. In in vivo animal implantation experiments, the CaO2@ZIF-67-HA-ADH coating exhibited strong antimicrobial activity early after implantation and excellent osseointegration later after implantation. In conclusion, the pH-responsive CaO2@ZIF-67-HA-ADH coating conferred excellent antibacterial, osteogenic, and angiogenic properties to titanium implants, which effectively enhanced osseointegration of the implants and prevented bacterial infection; the coating shows promise for use in the treatment of bone defects.

Type H blood vessels in coupling angiogenesis-osteogenesis and its application in bone tissue engineering

One specific capillary subtype, termed type H vessel, has been found with unique functional characteristics in coupling angiogenesis with osteogenesis. Researchers have fabricated a variety of tissue engineering scaffolds to enhance bone healing and regeneration through the accumulation of type H vessels. However, only a limited number of reviews discussed the tissue engineering strategies for type H vessel regulation. The object of this review is to summary the current utilizes of bone tissue engineering to regulate type H vessels through various signal pathways including Notch, PDGF-BB, Slit3, HIF-1α, and VEGF signaling. Moreover, we give an insightful overview of recent research progress about the morphological, spatial and age-dependent characteristics of type H blood vessels. Their unique role in tying angiogenesis and osteogenesis together via blood flow, cellular microenvironment, immune system and nervous system are also summarized. This review article would provide an insight into the combination of tissue engineering scaffolds with type H vessels and identify future perspectives for vasculized tissue engineering research.

Metal-Organic Framework Functionalized Bioceramic Scaffolds with Antioxidative Activity for Enhanced Osteochondral Regeneration

Osteoarthritis (OA) is a degenerative disease that often causes cartilage lesions and even osteochondral damage. Osteochondral defects induced by OA are accompanied by an inflammatory arthrosis microenvironment with overproduced reactive oxygen species (ROS), resulting in the exacerbation of defects and difficulty regenerating osteochondral tissues. Therefore, it is urgently needed to develop osteochondral scaffolds that can not only promote the integrated regeneration of cartilage and subchondral bone, but also possess ROS-scavenging ability to protect tissues from oxidative stress. Herein, zinc-cobalt bimetallic organic framework (Zn/Co-MOF) functionalized bioceramic scaffolds are designed for repairing osteochondral defects under OA environment. By functionalizing Zn/Co-MOF on the 3D-printed beta-tricalcium phosphate (β-TCP) scaffolds, the Zn/Co-MOF functionalized β-TCP (MOF-TCP) scaffolds with broad-spectrum ROS-scavenging ability are successfully developed. Benefiting from its catalytic active sites and degradation products, Zn/Co-MOF endows the scaffolds with excellent antioxidative and anti-inflammatory properties to protect cells from ROS invasion, as well as dual-bioactivities of simultaneously inducing osteogenic and chondrogenic differentiation in vitro. Furthermore, in vivo results confirm that MOF-TCP scaffolds accelerate the integrated regeneration of cartilage and subchondral bone in severe osteochondral defects. This study offers a promising strategy for treating defects induced by OA as well as other inflammatory diseases.

Applications of Stimuli-Responsive Hydrogels in Bone and Cartilage Regeneration

Bone and cartilage regeneration is an area of tremendous interest and need in health care. Tissue engineering is a potential strategy for repairing and regenerating bone and cartilage defects. Hydrogels are among the most attractive biomaterials in bone and cartilage tissue engineering, mainly due to their moderate biocompatibility, hydrophilicity, and 3D network structure. Stimuli-responsive hydrogels have been a hot topic in recent decades. They can respond to external or internal stimulation and are used in the controlled delivery of drugs and tissue engineering. This review summarizes current progress in the use of stimuli-responsive hydrogels in bone and cartilage regeneration. The challenges, disadvantages, and future applications of stimuli-responsive hydrogels are briefly described.

Hydrogel scaffolds in bone regeneration: Their promising roles in angiogenesis

Bone tissue engineering (BTE) has become a hopeful potential treatment strategy for large bone defects, including bone tumors, trauma, and extensive fractures, where the self-healing property of bone cannot repair the defect. Bone tissue engineering is composed of three main elements: progenitor/stem cells, scaffold, and growth factors/biochemical cues. Among the various biomaterial scaffolds, hydrogels are broadly used in bone tissue engineering owing to their biocompatibility, controllable mechanical characteristics, osteoconductive, and osteoinductive properties. During bone tissue engineering, angiogenesis plays a central role in the failure or success of bone reconstruction via discarding wastes and providing oxygen, minerals, nutrients, and growth factors to the injured microenvironment. This review presents an overview of bone tissue engineering and its requirements, hydrogel structure and characterization, the applications of hydrogels in bone regeneration, and the promising roles of hydrogels in bone angiogenesis during bone tissue engineering.

Application of bioactive metal ions in the treatment of bone defects

The treatment of bone defects is an important problem in clinical practice. The rapid development of bone tissue engineering (BTE) may provide a new method for bone defect treatment. Metal ions have been widely studied in BTE and demonstrated a significant effect in promoting bone tissue growth. Different metal ions can be used to treat bone defects according to specific conditions, including promoting osteogenic activity, inhibiting osteoclast activity, promoting vascular growth, and exerting certain antibacterial effects. Multiple studies have confirmed that metal ions-modified composite scaffolds can effectively promote bone defect healing. By studying current extensive research on metal ions in the treatment of bone defects, this paper reviews the mechanism of metal ions in promoting bone tissue growth, analyzes the loading mode of metal ions, and lists some specific applications of metal ions in different types of bone defects. Finally, this paper summarizes the advantages and disadvantages of metal ions and analyzes the future research trend of metal ions in BTE. This article can provide some new strategies and methods for future research and applications of metal ions in the treatment of bone defects.

In vivo prevascularization strategy enhances neovascularization of β-tricalcium phosphate scaffolds in bone regeneration

Background

Neovascularization is critical for bone regeneration. Numerous studies have explored prevascularization preimplant strategies, ranging from calcium phosphate cement (CPC) scaffolds to co-culturing CPCs with stem cells. The aim of the present study was to evaluate an alternative in vivo prevascularization approach, using preimplant-prepared macroporous beta-tricalcium phosphate (β-TCP) scaffolds and subsequent transplantation in bone defect model.

Methods

The morphology of β-TCPs was characterized by scanning electron microscopy. After 3 weeks of prevascularization within a muscle pouch at the lateral size of rat tibia, we transplanted prevascularized macroporous β-TCPs in segmental tibia defects, using blank β-TCPs as a control. Extent of neovascularization was determined by angiography and immunohistochemical (IHC) evaluations. Tibia samples were collected at different time points for biomechanical, radiological, and histological analyses. RT-PCR and western blotting were used to evaluate angio- and osteo-specific markers.

Results

With macroporous β-TCPs, we documented more vascular and supporting tissue invasion in the macroporous β-TCPs with prior in vivo prevascularization. Radiography, biomechanical, IHC, and histological analyses revealed considerably more vascularity and bone consolidation in β-TCP scaffolds that had undergone the prevascularization step compared to the blank β-TCP scaffolds. Moreover, the prevascularization treatment remarkably upregulated mRNA and protein expression of BMP2 and vascular endothelial growth factor (VEGF) during bone regeneration.

Conclusion

This novel in vivo prevascularization strategy successfully accelerated vascular formation to bone regeneration. Our findings indicate that prevascularized tissue-engineered bone grafts have promising potential in clinical applications.

The translational potential of this article

This study indicates a novel in vivo prevascularization strategy for growing vasculature on β-TCP scaffolds to be used for repair of large segmental bone defects, might serve as a promising tissue-engineered bone grafts in the future.

In Situ Forming Hydrogel as a Tracer and Degradable Lacrimal Plug for Dry Eye Treatment

Lacrimal plug is an effective and widely therapeutic strategy to treat dry eye. However, almost all commercialized plugs are fixed in a certain design and associated with many complications, such as spontaneous plug extrusion, epiphora, and granuloma and cannot be traced in the long-term. Herein, a simple in situ forming hydrogel is developed as a tracer and degradable lacrimal plug to achieve the best match with the irregular lacrimal passages. In this strategy, methacrylate-modified silk fibroin (SFMA) is served as a network, and a self-assembled indocyanine green fluorescence tracer nanoparticle (FTN) is embedded as an indicator to develop the hydrogel plug using visible photo-crosslinking. This SFMA/FTN hydrogel plug has excellent biocompatibility and biodegradability, which can be noninvasively monitored by near-infrared light. In vivo tests based on dry eye rabbits show that the SFMA/FTN hydrogel plug can completely block the lacrimal passages and greatly improve the various clinical indicators of dry eye. These results demonstrate that the SFMA/FTN hydrogel is suitable as an injectable and degradable lacrimal plug with a long-term tracking function. The work offers a new approach to the development of absorbable plugs for the treatment of dry eye.