Strontium Ion-Functionalized Nano-Hydroxyapatite/Chitosan Composite Microspheres Promote Osteogenesis and Angiogenesis for Bone Regeneration

Chitosan composite with mesenchymal stem cells: Properties, mechanism, and its application in bone regeneration

Bone defects resulting from trauma, illness or congenital abnormalities represent a significant challenge to global health. Conventional treatments such as autographs and allografts have limitations, leading to the exploration of bone tissue engineering (BTE) as an alternative approach. This review aims to provide a comprehensive analysis of bone regeneration mechanisms with a focus on the role of chitosan-based biomaterials and mesenchymal stem cells (MSCs) in BTE. In addition, the physiochemical and biological properties of chitosan, its potential for bone regeneration when combined with other materials and the mechanisms through which MSCs facilitate bone regeneration were investigated. In addition, different methods of scaffold development and the incorporation of MSCs into chitosan-based scaffolds were examined. Chitosan has remarkable biocompatibility, biodegradability and osteoconductivity, making it an attractive choice for BTE. Interactions between transcription factors such as Runx2 and Osterix and signaling pathways such as the BMP and Wnt pathways regulate the differentiation of MSCs and bone regeneration. Various forms of scaffolding, including porous and fibrous injections, have shown promise in BTE. The synergistic combination of chitosan and MSCs in BTE has significant potential for addressing bone defects and promoting bone regeneration, highlighting the promising future of clinical challenges posed by bone defects.

Selective Cellular Uptake and Druggability Efficacy through Functionalized Chitosan-Conjugated Polyamidoamine (PAMAM) Dendrimers

Nanotechnology has ushered in significant advancements in drug design, revolutionizing the prevention, diagnosis, and treatment of various diseases. The strategic utilization of nanotechnology to enhance drug loading, delivery, and release has garnered increasing attention, leveraging the enhanced physical and chemical properties offered by these systems. Polyamidoamine (PAMAM) dendrimers have been pivotal in drug delivery, yet there is room for further enhancement. In this study, we conjugated PAMAM dendrimers with chitosan (CS) to augment cellular internalization in tumor cells. Specifically, doxorubicin (DOX) was initially loaded into PAMAM dendrimers to form DOX-loaded PAMAM (DOX@PAMAM) complexes via intermolecular forces. Subsequently, CS was linked onto the DOX-loaded PAMAM dendrimers to yield CS-conjugated PAMAM loaded with DOX (DOX@CS@PAMAM) through glutaraldehyde crosslinking via the Schiff base reaction. The resultant DOX@CS@PAMAM complexes were comprehensively characterized using Fourier-transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). Notably, while the drug release profile of DOX@CS@PAMAM in acidic environments was inferior to that of DOX@PAMAM, DOX@CS@PAMAM demonstrated effective acid-responsive drug release, with a cumulative release of 70% within 25 h attributed to the imine linkage. Most importantly, DOX@CS@PAMAM exhibited significant selective cellular internalization rates and antitumor efficacy compared to DOX@PAMAM, as validated through cell viability assays, fluorescence imaging, and flow cytometry analysis. In summary, DOX@CS@PAMAM demonstrated superior antitumor effects compared to unconjugated PAMAM dendrimers, thereby broadening the scope of dendrimer-based nanomedicines with enhanced therapeutic efficacy and promising applications in cancer therapy.

Picein alleviates oxidative stress and promotes bone regeneration in osteoporotic bone defect by inhibiting ferroptosis via Nrf2/HO-1/GPX4 pathway

Osteoporosis (OP) can result in slower bone regeneration than the normal condition due to abnormal oxidative stress and high levels of reactive oxygen species (ROS), a condition detrimental for bone formation, making the OP-related bone healing a significant clinical challenge. As the osteogenic differentiation ability of bone marrow mesenchymal stem cells (BMSCs) is closely related to bone regeneration; currently, this study assessed the effects of Picein on BMSCs in vitro and bone regeneration in osteoporotic bone defect in vivo. Cell viability was determined by CCK-8 assay. The production of (ROS), malonaldehyde, superoxide dismutase activities, and glutathione was evaluated by using commercially available kits, and a flow cytometry analysis was adopted to detect macrophage polarization. Osteogenic capacity of BMSCs was evaluated by alkaline phosphatase (ALP) activity, ALP staining, and Alizarin red S staining. The expression of osteogenic-related proteins (OPN, Runx-2, OCN) and osteogenic-related genes (ALP, BMP-4, COL-1, and Osterix) were evaluated by Western blotting and real-time PCR (RT-PCR). In addition, proliferation, migration ability, and angiogenic capacity of human umbilical vein endothelial cells (HUVECs) were evaluated by EdU staining, scratch test, transwell assay, and tube formation assay, respectively. Angiogenic-related genes (VEGF, vWF, CD31) were also evaluated by RT-PCR. Results showed that Picein alleviated erastin-induced oxidative stress, enhanced osteogenic differentiation capacity of BMSCs, angiogenesis of HUVECs, and protects cells against ferroptosis through Nrf2/HO-1/GPX4 axis. Moreover, Picein regulate immune microenvironment by promoting the polarization of M2 macrophages in vitro. In addition, Picein also reduce the inflammation levels and promotes bone regeneration in osteoporotic bone defect in OP rat models in vivo. Altogether, these results suggested that Picein can promote bone regeneration and alleviate oxidative stress via Nrf2/HO-1/GPX4 pathway, offering Picein as a novel antioxidant agent for treating osteoporotic bone defect.

Droplet Microfluidics Powered Hydrogel Microparticles for Stem Cell-Mediated Biomedical Applications

Stem cell-related therapeutic technologies have garnered significant attention of the research community for their multi-faceted applications. To promote the therapeutic effects of stem cells, the strategies for cell microencapsulation in hydrogel microparticles have been widely explored, as the hydrogel microparticles have the potential to facilitate oxygen diffusion and nutrient transport alongside their ability to promote crucial cell-cell and cell-matrix interactions. Despite their significant promise, there is an acute shortage of automated, standardized, and reproducible platforms to further stem cell-related research. Microfluidics offers an intriguing platform to produce stem cell-laden hydrogel microparticles (SCHMs) owing to its ability to manipulate the fluids at the micrometer scale as well as precisely control the structure and composition of microparticles. In this review, the typical biomaterials and crosslinking methods for microfluidic encapsulation of stem cells as well as the progress in droplet-based microfluidics for the fabrication of SCHMs are outlined. Moreover, the important biomedical applications of SCHMs are highlighted, including regenerative medicine, tissue engineering, scale-up production of stem cells, and microenvironmental simulation for fundamental cell studies. Overall, microfluidics holds tremendous potential for enabling the production of diverse hydrogel microparticles and is worthy for various stem cell-related biomedical applications.

Remodeling Microenvironment for Implant-Associated Osteomyelitis by Dual Metal Peroxide

Implant-associated osteomyelitis (IAOM) is characterized by bone infection and destruction; current therapy of antibiotic treatment and surgical debridement often results in drug resistance and bone defect. It is challenging to develop an antibiotic-free bactericidal and osteogenic-enhanced strategy for IAOM. Herein, an IAOM-tailored antibacterial and osteoinductive composite of copper (Cu)-strontium (Sr) peroxide nanoparticles (CSp NPs), encapsulated in polyethylene glycol diacrylate (PEGDA) (CSp@PEGDA), is designed. The dual functional CSp NPs display hydrogen peroxide (H2O2) self-supplying and Fenton catalytic Cu2+ ions' release, generating plenty of hydroxyl radical (•OH) in a pH-responsive manner for bacterial killing, while the released Sr2+ promotes the in vitro osteogenicity regarding cell proliferation, alkaline phosphatase activity, extracellular matrix calcification, and osteo-associated genes expression. The integration of Cu2+ and Sr2+ in CSp NPs together with the coated PEGDA hydrogel ensures the stable and sustainable ion release during short- and long-term periods. Benefitted from the injectablity and photo-crosslink ability, CSp@PEGDA is able to thoroughly fill the infectious site and gelate in situ for bacterial elimination and bone regeneration, which is verified through in vivo evaluation using a clinical-simulating IAOM mouse model. These favorable abilities of CSp@PEGDA precisely meet the multiple therapeutic needs and pave a promising way for implant-associated osteomyelitis treatment.

Metal-Phenolic Networks-Reinforced Extracellular Matrix Scaffold for Bone Regeneration via Combining Radical-Scavenging and Photo-Responsive Regulation of Microenvironment

The limited regulation strategies of the regeneration microenvironment significantly hinder bone defect repair effectiveness. One potential solution is using biomaterials capable of releasing bioactive ions and biomolecules. However, most existing biomaterials lack real-time control features, failing to meet high regulation requirements. Herein, a new Strontium (Sr) and epigallocatechin-3-gallate (EGCG) based metal-phenolic network with polydopamine (PMPNs) modification is prepared. This material reinforces a biomimetic scaffold made of extracellular matrix (ECM) and hydroxyapatite nanowires (nHAW). The PMPNs@ECM/nHAW scaffold demonstrates exceptional scavenging of free radicals and reactive oxygen species (ROS), promoting HUVECs cell migration and angiogenesis, inducing stem cell osteogenic differentiation, and displaying high biocompatibility. Additionally, the PMPNs exhibit excellent photothermal properties, further enhancing the scaffold's bioactivities. In vivo studies confirm that PMPNs@ECM/nHAW with near-infrared (NIR) stimulation significantly promotes angiogenesis and osteogenesis, effectively regulating the microenvironment and facilitating bone tissue repair. This research not only provides a biomimetic scaffold for bone regeneration but also introduces a novel strategy for designing advanced biomaterials. The combination of real-time photothermal intervention and long-term chemical intervention, achieved through the release of bioactive molecules/ions, represents a promising direction for future biomaterial development.

Injectable, anti-collapse, adhesive, plastic and bioactive bone graft substitute promotes bone regeneration by moderating oxidative stress in osteoporotic bone defect

The treatment of osteoporotic bone defect remains a big clinical challenge because osteoporosis (OP) is associated with oxidative stress and high levels of reactive oxygen species (ROS), a condition detrimental for bone formation. Anti-oxidative nanomaterials such as selenium nanoparticles (SeNPs) have positive effect on osteogenesis owing to their pleiotropic pharmacological activity which can exert anti-oxidative stress functions to prevent bone loss and facilitate bone regeneration in OP. In the current study a strategy of one-pot method by introducing Poly (lactic acid-carbonate) (PDT) and β-Tricalcium Phosphate (β-TCP) with SeNPs, is developed to prepare an injectable, anti-collapse, shape-adaptive and adhesive bone graft substitute material (PDT-TCP-SE). The PDT-TCP-SE bone graft substitute exhibits sufficient adhesion in biological microenvironments and osteoinductive activity, angiogenic effect and anti-inflammatory as well as anti-oxidative effect in vitro and in vivo. Moreover, the PDT-TCP-SE can protect BMSCs from erastin-induced ferroptosis through the Sirt1/Nrf2/GPX4 antioxidant pathway, which, in together, demonstrated the bone graft substitute material as an emerging biomaterial with potential clinical application for the future treatment of osteoporotic bone defect. STATEMENT OF SIGNIFICANCE: Injectable, anti-collapse, adhesive, plastic and bioactive bone graft substitute was successfully synthesized. Incorporation of SeNPs with PDT into β-TCP regenerated new bone in-situ by moderating oxidative stress in osteoporotic bone defects area. The PDT-TCP-SE bone graft substitute reduced high ROS levels in osteoporotic bone defect microenvironment. The bone graft substitute could also moderate oxidative stress and inhibit ferroptosis via Sirt1/Nrf2/GPX4 pathway in vitro. Moreover, the PDT-TCP-SE bone graft substitute could alleviate the inflammatory environment and promote bone regeneration in osteoporotic bone defect in vivo. This biomaterial has the advantages of simple synthesis, biocompatibility, anti-collapse, injectable, and regulation of oxidative stress level, which has potential application value in bone tissue engineering.

Titanium- and Strontium-Infused Calcium Silicates Toward Restorative and Regenerative Purposes

BACKGROUND

Dental materials with dentine regenerative properties are preferred over conventional materials. Calcium silicate cements, such as Biodentine, are bioactive and offer excellent sealing ability, making them ideal for various dental treatments.

OBJECTIVES

This study aimed to fabricate bioactive calcium silicates infused with titanium (Ti) and strontium (Sr) to optimize their neo-angiogenic, antimicrobial, and regenerative properties while maintaining mechanical stability.

METHODOLOGY

Ti- and Sr-infused calcium silicate cements were synthesized, and their mineral phases were characterized using X-ray diffraction. Morphological and elemental analyses were performed using field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDS). Raman spectroscopy was used to confirm the formation of bioactive material. A hemocompatibility assessment was conducted to evaluate blood compatibility.

RESULTS

The presence of Ca2, SiO4, and SrTiO3 mineral phases indicated the successful infusion of Ti and Sr into the calcium silicate cement. FESEM and EDS revealed interconnected small spheres and rods in the silicate network with the relevant elemental compositions. Raman spectra verified that Si-O-Si and Ti-O-Ti vibrations exist, validating the formation of a bioactive material. The hemocompatibility assessment demonstrated optimal blood compatibility.

CONCLUSIONS

This study successfully fabricated an improved calcium silicate-based material with enhanced regenerative properties and excellent biocompatibility. This newly formed substrate holds promise for providing superior restorative solutions and aiding in conservative treatment modalities during dental procedures.

Evaluation of osteogenic properties of a novel injectable bone-repair material containing strontium in vitro and in vivo

Objective: This study aims to develop and evaluate the biocompatibility and osteogenic potential of a novel injectable strontium-doped hydroxyapatite bone-repair material. Methods: The properties of strontium-doped hydroxyapatite/chitosan (Sr-HA/CS), hydroxyapatite/chitosan (HA/CS) and calcium phosphate/chitosan (CAP/CS) were assessed following their preparation via physical cross-linking and a one-step simplified method. Petri dishes containing Escherichia coli and Staphylococcus epidermidis were inoculated with the material for in vitro investigations. The material was also co-cultured with stem cells derived from human exfoliated deciduous teeth (SHEDs), to assess the morphology and proliferation capability of the SHEDs, Calcein-AM staining and the Cell Counting Kit-8 assay were employed. Osteogenic differentiation of SHEDs was determined using alkaline phosphatase (ALP) staining and Alizarin Red staining. For in vivo studies, Sr-HA/CS was implanted into the muscle pouch of mice and in a rat model of ovariectomy-induced femoral defects. Hematoxylin-eosin (HE) staining was performed to determine the extent of bone formation and defect healing. The formation of new bone was determined using Masson's trichrome staining. The osteogenic mechanism of the material was investigated using Tartrate-resistant acid phosphatase (TRAP) staining and immunohistochemical studies. Results: X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) showed that strontium was successfully doped into HA. The Sr-HA/CS material can be uniformly squeezed using a syringe with a 13% swelling rate. Sr-HA/CS had a significant antibacterial effect against both E. coli and S. epidermidis (p < 0.05), with a stronger effect observed against E. coli. The Sr-HA/CS significantly improved cell proliferation and cell viability in vitro studies (p < 0.05). Compared to CAP/CS and CS, Sr-HA/CS generated a substantially greater new bone area during osteoinduction experiments (p < 0.05, p < 0.001). The Sr-HA/CS material demonstrated a significantly higher rate of bone repair in the bone defeat studies compared to the CAP/CS and CS materials (p < 0.01). The OCN-positive area and TRAP-positive cells in Sr-HA/CS were greater than those in control groups (p < 0.05). Conclusion: A novel injectable strontium-doped HA bone-repair material with good antibacterial properties, biocompatibility, and osteoinductivity was successfully prepared.

Absorbable calcium and phosphorus bioactive membranes promote bone marrow mesenchymal stem cells osteogenic differentiation for bone regeneration

Large segmental bone defects are commonly operated with autologous bone grafting, which has limited bone sources and poses additional surgical risks. In this study, we fabricated poly(lactide-co-glycolic acid) (PLGA)/β-tricalcium phosphate (β-TCP) composite membranes by electrostatic spinning and further promoted osteogenesis by regulating the release of β-TCP in the hope of replacing autologous bone grafts in the clinical practice. The addition of β-TCP improved the mechanical strength of PLGA by 2.55 times. Moreover, β-TCP could accelerate the degradation of PLGA and neutralize the negative effects of acidification of the microenvironment caused by PLGA degradation. In vitro experiments revealed that PLGA/TCP10 membranes are biocompatible and the released β-TCP can modulate the activity of osteoblasts by enhancing the calcium ions concentration in the damaged area and regulating the pH of the local microenvironment. Simultaneously, an increase in β-TCP can moderate the lactate content of the local microenvironment, synergistically enhancing osteogenesis by promoting the tube-forming effect of human umbilical vein endothelial cells. Therefore, it is potential to utilize PLGA/TCP bioactive membranes to modulate the microenvironment at the site of bone defects to promote bone regeneration.

Biomimetic fabrication of sr-silk fibroin co-assembly hydroxyapatite based microspheres with angiogenic and osteogenic properties for bone tissue engineering

Bone defects caused by trauma, tumor resection, or developmental abnormalities are important issues in clinical practice. The vigorous development of tissue engineering technology provides new ideas and directions for regenerating bone defects. Hydroxyapatite (HAp), a bioactive ceramic, is extensively used in bone tissue engineering because of its excellent osteoinductive performance. However, its application is challenged by its single function and conventional environment-unfriendly synthesis methods. In this study, we successfully "green" synthesized sr-silk fibroin co-assembly hydroxyapatite nanoparticles (Sr-SF-HA) using silk fibroin (SF) as a biomineralized template, thus enabling it to have angiogenic activity and achieving the combination of organic and inorganic substances. Then, the rough composite microspheres loaded with Sr-SF-HA (CS/Sr-SF-HA) through electrostatic spraying technology and freeze-drying method were prepared. The CCK-8 test and live/dead cell staining showed excellent biocompatibility of CS/Sr-SF-HA. Alkaline phosphatase (ALP) staining, alizarin red staining (ARS), immunofluorescence, western blotting, and qRT-PCR test showed that CS/Sr-SF-HA activated the expression of related genes and proteins, thus inducing the osteogenic differentiation of rBMSCs. Moreover, tube formation experiments, scratch experiments, immunofluorescence, and qRT-PCR detection indicated that CS/Sr-SF-HA have good angiogenic activity. Furthermore, in vivo studies showed that the CS/Sr-SF-HA possesses excellent biocompatibility, vascular activity, as well as ectopic osteogenic ability in the subcutaneous pocket of rats. This study indicates that the construction of CS/Sr-SF-HA with angiogenic and osteogenic properties has great potential for bone tissue engineering.

Ion incorporation into bone grafting materials

The use of biomaterials in regenerative medicine has expanded to treat various disorders caused by trauma or disease in orthopedics and dentistry. However, the treatment of large and complex bone defects presents a challenge, leading to a pressing need for optimized biomaterials for bone repair. Recent advances in chemical sciences have enabled the incorporation of therapeutic ions into bone grafts to enhance their performance. These ions, such as strontium (for bone regeneration/osteoporosis), copper (for angiogenesis), boron (for bone growth), iron (for chemotaxis), cobalt (for B12 synthesis), lithium (for osteogenesis/cementogenesis), silver (for antibacterial resistance), and magnesium (for bone and cartilage regeneration), among others (e.g., zinc, sodium, and silica), have been studied extensively. This review aims to provide a comprehensive overview of current knowledge and recent developments in ion incorporation into biomaterials for bone and periodontal tissue repair. It also discusses recently developed biomaterials from a basic design and clinical application perspective. Additionally, the review highlights the importance of precise ion introduction into biomaterials to address existing limitations and challenges in combination therapies. Future prospects and opportunities for the development and optimization of biomaterials for bone tissue engineering are emphasized.

Polydopamine-Functionalized Strontium Alginate/Hydroxyapatite Composite Microhydrogel Loaded with Vascular Endothelial Growth Factor Promotes Bone Formation and Angiogenesis

Critical-size bone defects are a common and intractable clinical problem that typically requires filling in with surgical implants to facilitate bone regeneration. Considering the limitations of autologous bone and allogeneic bone in clinical applications, such as secondary damage or immunogenicity, injectable microhydrogels with osteogenic and angiogenic effects have received considerable attention. Herein, polydopamine (PDA)-functionalized strontium alginate/nanohydroxyapatite (Sr-Alg/nHA) composite microhydrogels loaded with vascular endothelial growth factor (VEGF) were prepared using microfluidic technology. This composite microhydrogel released strontium ions stably for at least 42 days to promote bone formation. The PDA coating can release VEGF in a controlled manner, effectively promote angiogenesis around bone defects, and provide nutritional support for new bone formation. In in vitro experiments, the composite microhydrogels had good biocompatibility. The PDA coating greatly improves cell adhesion on the composite microhydrogel and provides good controlled release of VEGF. Therefore, this composite microhydrogel effectively promotes osteogenic differentiation and vascularization. In in vivo experiments, composite microhydrogels were injected into critical-size bone defects in the skull of rats, and they were shown by microcomputed tomography and tissue sections to be effective in promoting bone regeneration. These findings demonstrated that this novel microhydrogel effectively promotes bone formation and angiogenesis at the site of bone defects.

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.

The microspheres/hydrogels scaffolds based on the proteins, nucleic acids, or polysaccharides composite as carriers for tissue repair: A review

There are many studies on specific macromolecules and their contributions to tissue repair. Macromolecules have supporting and protective effects in organisms and can help regrow, reshape, and promote self-repair and regeneration of damaged tissues. Macromolecules, such as proteins, nucleic acids, and polysaccharides, can be constructed into hydrogels for the preparation of slow-release drug agents, carriers for cell culture, and platforms for gene delivery. Hydrogels and microspheres are fabricated by chemical crosslinking or mixed co-deposition often used as scaffolds, drug carriers, or cell culture matrix, provide proper mechanical support and nutrient delivery, a well-conditioned environment that to promote the regeneration and repair of damaged tissues. This review provides a comprehensive overview of recent developments in the construction of macromolecules into hydrogels and microspheres based on the proteins, nucleic acids, polysaccharides and other polymer and their application in tissue repair. We then discuss the latest research trends regarding the advantages and disadvantages of these composites in repair tissue. Further, we examine the applications of microspheres/hydrogels in different tissue repairs, such as skin tissue, cartilage, tumor tissue, synovial, nerve tissue, and cardiac repair. The review closes by highlighting the challenges and prospects of microspheres/hydrogels composites.

Neuro-bone tissue engineering: emerging mechanisms, potential strategies, and current challenges

The skeleton is a highly innervated organ in which nerve fibers interact with various skeletal cells. Peripheral nerve endings release neurogenic factors and sense skeletal signals, which mediate bone metabolism and skeletal pain. In recent years, bone tissue engineering has increasingly focused on the effects of the nervous system on bone regeneration. Simultaneous regeneration of bone and nerves through the use of materials or by the enhancement of endogenous neurogenic repair signals has been proven to promote functional bone regeneration. Additionally, emerging information on the mechanisms of skeletal interoception and the central nervous system regulation of bone homeostasis provide an opportunity for advancing biomaterials. However, comprehensive reviews of this topic are lacking. Therefore, this review provides an overview of the relationship between nerves and bone regeneration, focusing on tissue engineering applications. We discuss novel regulatory mechanisms and explore innovative approaches based on nerve-bone interactions for bone regeneration. Finally, the challenges and future prospects of this field are briefly discussed.

Metal Ion-Doped Hydroxyapatite-Based Materials for Bone Defect Restoration

Hydroxyapatite (HA)-based materials are widely used in the bone defect restoration field due to their stable physical properties, good biocompatibility, and bone induction potential. To further improve their performance with extra functions such as antibacterial activity, various kinds of metal ion-doped HA-based materials have been proposed and synthesized. This paper offered a comprehensive review of metal ion-doped HA-based materials for bone defect restoration based on the introduction of the physicochemical characteristics of HA followed by the synthesis methods, properties, and applications of different kinds of metal ion (Ag+, Zn2+, Mg2+, Sr2+, Sm3+, and Ce3+)-doped HA-based materials. In addition, the underlying challenges for bone defect restoration using these materials and potential solutions were discussed.

Punicalagin attenuates TNF-α-induced oxidative damage and promotes osteogenic differentiation of bone mesenchymal stem cells by activating the Nrf2/HO-1 pathway

Oxidative stress is one of the most important factors in changing bone homeostasis. Redox homeostasis plays a key role in the osteogenic differentiation of bone mesenchymal stem cells (BMSCs) and the angiogenesis ability of human umbilical vein endothelial cells (HUVECs) for bone regeneration. Currently, this study assessed the effects of punicalagin (PUN) on BMSCs and HUVECs. Cell viability was determined by CCK-8 assay. A flow cytometry analysis was adopted to detect macrophage polarization. The production of reactive oxygen stress (ROS), glutathione (GSH), malonaldehyde (MDA) and superoxide dismutase (SOD) activities were evaluated by using commercially-available kits. Osteogenic capacity of BMSCs was evaluated by ALP activity, ALP staining and ARS staining. The expression of osteogenic-related proteins (OCN, Runx-2, OPN) and Nrf/HO-1 levles were evaluated by Western blotting. Osteogenic-related genes (Osterix, COL-1, BMP-4, ALP) were evaluated by RT-PCR. Migration ability and invasion ability of HUVECs were evaluated by wound healing assay and Transwell assay. Angiogenic ability was detected by tube formation assay and the expression of angiogenic-related genes (VEGF, vWF, CD31) were evaluated by RT-PCR. Results showed that PUN alleviated oxidative stress by TNF-α, enhanced osteogenic differentiation in BMSCs and angiogenesis in HUVECs. Moreover, PUN regulate immune microenvironment by promoting the polarization of M2 macrophages and reduce the oxidative stress related products by activating Nrf2/HO-1 pathway. Altogether, these results suggested that PUN can promote osteogenic capacity of BMSCs, angiogenesis of HUVECs, alleviate oxidative stress via Nrf2/HO-1 pathway, offering PUN as a novel antioxidant agent for treating bone loss diseases.

Osteogenic Potential of Nano-Hydroxyapatite and Strontium-Substituted Nano-Hydroxyapatite

Nanohydroxyapatite (nanoHA) is the major mineral component of bone. It is highly biocompatible, osteoconductive, and forms strong bonds with native bone, making it an excellent material for bone regeneration. However, enhanced mechanical properties and biological activity for nanoHA can be achieved through enrichment with strontium ions. Here, nanoHA and nanoHA with a substitution degree of 50 and 100% of calcium with strontium ions (Sr-nanoHA_50 and Sr-nanoHA_100, respectively) were produced via wet chemical precipitation using calcium, strontium, and phosphorous salts as starting materials. The materials were evaluated for their cytotoxicity and osteogenic potential in direct contact with MC3T3-E1 pre-osteoblastic cells. All three nanoHA-based materials were cytocompatible, featured needle-shaped nanocrystals, and had enhanced osteogenic activity in vitro. The Sr-nanoHA_100 indicated a significant increase in the alkaline phosphatase activity at day 14 compared to the control. All three compositions revealed significantly higher calcium and collagen production up to 21 days in culture compared to the control. Gene expression analysis exhibited, for all three nanoHA compositions, a significant upregulation of osteonectin and osteocalcin on day 14 and of osteopontin on day 7 compared to the control. The highest osteocalcin levels were found for both Sr-substituted compounds on day 14. These results demonstrate the great osteoinductive potential of the produced compounds, which can be exploited to treat bone disease.