The multifaceted roles of macrophages in bone regeneration: A story of polarization, activation and time

All-in-one design of titanium-based dental implant systems for enhanced soft and hard tissue integration

Enhancing the sealing between titanium abutment and surrounding soft tissue is crucial for preventing peri-implantitis. Meanwhile, exploring non-invasive antibacterial strategies as alternatives for traditional antibiotic therapy is central to improving the effect of peri-implantitis treatment. Furthermore, facilitating effective integration between titanium implant and osteoporotic bone is the cornerstone for ensuring long-term implant stability in patients with osteoporosis. In light of this, this work innovatively constructed multifunctional vertical graphene-based coatings on titanium implants and abutments using plasma-enhanced chemical vapor deposition technology. The results demonstrated that the vertical graphene coatings promoted soft tissue sealing and exhibited inherent antibacterial activities with the bacteriostasis rates of 65.60 % against Staphylococcus aureus (S. aureus) and 43.89 % against Escherichia coli (E. coli) in vitro which could prevent early infections. Moreover, vertical graphene coatings presented photothermal antibacterial effects with the antibacterial rates of 99.99 % and 95.83 % for S. aureus in vitro and in vivo, respectively, and 92.23 % for E. coli in vitro under near-infrared irradiation, which provided a non-invasive and highly effective treatment option for peri-implantitis. Furthermore, teriparatide acetate was loaded on vertical graphene coatings which enhanced osseointegration between titanium implants and osteoporotic bone. By comprehensively considering the critical functional requirements of dental implants and abutments, this work meticulously designed vertical graphene-based coatings on titanium dental implant systems for soft and hard tissue integration. This innovative design demonstrates immense application potential, especially for dental implant restoration in patients with osteoporosis.

The effect of copper content in Ti-Cu alloy with bone regeneration ability on the phenotypic transformation of macrophages

Titanium (Ti) alloys are widely used in bone repair due to their excellent biocompatibility and mechanical properties. However, managing post-implantation inflammatory responses in the defect region and accelerating the healing process remain major challenges in the design of such materials. As a bridge between the innate and adaptive immune systems, macrophages play a pivotal role in bone defect healing through their M2 polarization, which facilitates the secretion of tissue repair-promoting cytokines. Research on the role of copper ions (Cu²⁺) in regulating inflammatory responses at injury sites suggests their potential as active ions for incorporation into alloys as a secondary phase to modulate macrophage polarization. However, the effective concentration and mechanisms in this process remain unclear. Here, we synthesized Ti-xCu (x = 3, 5, 7 wt%) alloys and investigated the effects of copper concentration on macrophage M1/M2 polarization and the underlying mechanisms. In an 8-week rat mandibular bone regeneration experiment, Ti-5Cu demonstrated superior performance compared to pure titanium. At the early stage (2 weeks), Ti-5Cu promoted the dominance of M1 macrophages and upregulated inflammatory cytokines, facilitating the initial inflammatory response. Subsequently, a timely M1-to-M2 phenotype transition was observed, accompanied by elevated expression of the repair-related cytokine IL-10, ultimately leading to improved bone healing. This study provides a theoretical foundation for the development of titanium-copper composite materials with anti-inflammatory and pro-healing properties, paving the way for innovative solutions to promote bone defect repair.

Osteoimmunomodulation unveiled: Enhancing bone regeneration with 3D-printed PLLA/β-TCP/CS scaffolds

Bone tissue engineering shows great potential for repairing large segmental bone defects; however, the immune response to biological scaffolds remains a critical factor influencing bone regeneration. Despite this, there is a paucity of studies investigating the effects of biomaterial components and their degradation products on macrophage polarization and the subsequent process of bone regeneration. This study investigates the role of macrophages in osteogenesis and angiogenesis induced by PLLA(Poly-L-Lactic Acid)/β-TCP(β-Tricalcium Phosphate)/CS(Calcium Sulfate) bone scaffolds in vitro and in vivo. Various PLLA/β-TCP/CS scaffolds were fabricated via 3D printing and characterized for their physicochemical properties. The effect of P/T15/S15 (PLLA/β-TCP/CS scaffold containing 15 % β-TCP and 15 % CS) on macrophage polarization and the secretion of VEGF and BMP-2 was assessed in vitro. Additionally, the conditioned medium derived from macrophages stimulated with P/T15/S15 was evaluated for its effects on the migration and osteogenic differentiation of bone marrow-derived stem cells (BMSCs), as well as the angiogenic potential of human umbilical vein endothelial cells (HUVECs). In vivo, the relationship between macrophage polarization and osteogenesis was examined in a rabbit tibia segmental defect model. The results demonstrated that the 3D-printed P/T15/S15 scaffold exhibited favorable physicochemical properties and compatibility with BMSCs and RAW264.7 macrophages, while not disrupting BMSC apoptosis. P/T15/S15 promoted polarization of M0 macrophages towards the M2 phenotype, resulting in an increased secretion of the anti-inflammatory cytokine IL-10, as well as growth factors such as VEGF and BMP-2. However, it did not suppress TNF-α levels. Additional, the conditioned medium derived from P/T15/S15-stimulated macrophages significantly enhanced the osteogenesis of BMSCs, their migration, and the angiogenesis of HUVECs. In the rabbit model, P/T15/S15 facilitated bone regeneration by promoting macrophage polarization towards the M2 phenotype and reducing inflammation. This study highlights that P/T15/S15 regulates macrophage polarization, enhances osteogenesis and angiogenesis, and positions itself as a promising candidate for bone tissue engineering through osteoimmunomodulation.

A biodegradable magnesium alloy promotes subperiosteal osteogenesis via interleukin-10-dependent macrophage immunomodulation

In situ bone regeneration and vertical bone augmentation have been huge problems in clinical practice, always imposing a significant economic burden and causing patient suffering. Herein, MgZnYNd magnesium alloy rod implantation in mouse femur resulted in substantial subperiosteal new bone formation, with osteoimmunomodulation playing a pivotal role. Abundant macrophages were attracted to the subperiosteal new bone region and proved to be the most important regulation cells for bone regeneration. Periosteum stripping, macrophage depletion, and interleukin-10 (IL-10) blockade effectively diminished the MgZnYNd alloy-induced subperiosteal osteogenesis. Mechanistically, the degradation products of MgZnYNd alloy promoted M2 macrophage polarization and the secretion of anti-inflammatory cytokine IL-10, which enhanced periosteum-derived stem cells (PDSCs) osteogenesis through the JAK1-STAT3 pathway. An anti-IL-10 neutralizing antibody or STAT3 inhibitor significantly inhibited M2 macrophage-mediated osteogenic differentiation of PDSCs. Transcriptomics and proteomics revealed that periostin is the core regulator of PDSCs osteogenic differentiation. Furthermore, a novel clinical translation application of Mg-induced subperiosteal osteogenesis was developed, demonstrating its ability to preserve the height and width of the alveolar crest in rats and rabbits following tooth extraction. Collectively, these findings unveil a previously undefined role for Mg alloy-induced subperiosteal osteogenesis via macrophage-mediated osteoimmunomodulation, suggesting the therapeutic potential of magnesium alloy in bone regeneration and bone augmentation.

Macrophage Depletion Reduces Bone Loss and Alters Inflammatory Responses: A Mouse Peri-Implantitis Model

AIM

To evaluate the impact of macrophage depletion on bone loss and inflammatory responses in a mouse model of peri-implantitis, assessing macrophage depletion potential as a therapeutic strategy.

MATERIALS AND METHODS

Using 6-week-old male C57BL/6 mice, peri-implantitis was induced by placing a silk ligature around osteointegrated dental implants. Mice were divided into three groups: Healthy control (Healthy group); peri-implantitis with liposomal phosphate-buffered saline (PBS group); and peri-implantitis with liposomal clodronate for macrophage depletion (CLOD group). Two weeks after ligature placement, micro-CT, histological and real-time PCR analyses were performed to assess bone density, leukocyte infiltration and cytokine levels.

RESULTS

The CLOD group showed a significantly higher bone-to-implant contact (74%) and bone volume relative to total volume (79%) compared to the PBS group (53% and 54%, respectively) and Healthy group (64% and 66%, respectively). Histological analysis revealed significantly reduced leukocyte and macrophage counts in the CLOD group. Additionally, TNF-α and IL-10 levels were significantly decreased in the CLOD group compared with the PBS group.

CONCLUSION

Macrophage depletion effectively reduces bone loss and inflammation in peri-implantitis. This study highlights targeting macrophages as a promising approach for managing peri-implantitis, although further research is needed to optimize therapeutic strategies.

Macrophage membrane functionalized composite microspheres promote bone regeneration in periodontitis via manipulating inflammation reversing-osteogenesis coupling

Periodontitis is characterized by inflammation and alveolar bone loss, primarily caused by immune cells activated by oral bacteria, leading to an imbalance between osteogenesis and bone resorption. Traditional treatments have limited efficacy, which has led to the exploration of regulating the immune microenvironment and utilizing tissue engineering methods as new research directions. Our study demonstrates that macrophage membranes, activated by LPS and IFN-γ, can effectively neutralize inflammatory factors. By coating the poly-L-lysine (PLL) modified poly (lactic-co-glycolic acid) (PLGA)/β-TCP microspheres with such macrophage membrane vesicles, the MM@PPT microspheres regulate intercellular responses by inhibiting macrophage M1 polarization and osteoclast differentiation, promoting M2 polarization, and enhancing osteogenic differentiation of bone marrow stromal cells (BMSCs) even in an inflammatory environment. By injecting the MM@PPT into sites of periodontitis induced bone resorption, it is found that they can effectively promote bone regeneration by modulating the immune-regeneration microenvironment. This work not only highlights the potential of MM@PPT microspheres in promoting alveolar bone regeneration but also provides insights into how these microspheres modulate cell behavior and interactions. The findings of this study offer novel therapeutic strategies for promoting alveolar bone repair in periodontitis.

3D bioprinted biomimetic MOF-functionalized hydrogel scaffolds for bone regeneration: Synergistic osteogenesis and osteoimmunomodulation

Critical-size bone defects remain a significant clinical challenge. The lack of endogenous stem cells with osteogenic differentiation potential in the defect area, combined with the inflammatory responses induced by scaffold implantation, highlights the need for biomaterials that can deliver stem cells and possess inflammatory regulation properties. In this study, we developed a 3D bioprinted gelatin methacrylate (GelMA) hydrogel scaffold modified with luteolin-loaded ZIF-8 (LUT@ZIF-8) nanoparticles, designed to deliver bone marrow mesenchymal stem cells (BMSCs) to the defect site and release bioactive components that promote osteogenesis and modulate the immune microenvironment. The LUT@ZIF-8/GelMA hydrogel scaffolds demonstrated excellent physical properties and biocompatibility. The sustained release of luteolin and zinc ions from the LUT@ZIF-8 nanoparticles conferred antibacterial, osteoinductive, and inflammatory regulation effects. The immune microenvironment modulated by LUT@ZIF-8/GelMA hydrogel scaffolds facilitated osteogenic differentiation of BMSCs. Furthermore, in vivo experiments confirmed the osteogenic and inflammatory regulation capabilities of the LUT@ZIF-8/GelMA hydrogel scaffolds. In conclusion, the 3D bioprinted LUT@ZIF-8/GelMA hydrogel scaffolds exhibit osteoimmunomodulatory properties, presenting a promising strategy for the treatment of bone defects.

Yoda1-Loaded Microfibrous Scaffolds Accelerate Osteogenesis through Piezo1-F-Actin Pathway-Mediated YAP Nuclear Localization and Functionalization

Yoda1 has been recognized as an effective pharmacological intervention for the treatment of critical bone defects. However, the local delivery strategy of Yoda1 is uncommon, and the underlying mechanism through which Yoda1 enhances osteogenesis has been poorly investigated. Here, we propose utilizing electrohydrodynamic (EHD)-printed microfibrous scaffolds as a drug carrier for loading Yoda1 through a polydopamine (PDA) coating, and the synthetic mechanisms for enhancing bone regeneration are explored. Yoda1 was successfully loaded on the surface of the EHD-printed microfibrous scaffolds with the assistance of PDA. The results of in vitro experiments demonstrated that the Yoda1-loaded microfibrous scaffold group exhibited a more than 2-fold increase in COL-I protein levels compared to the control group. Additionally, the expression levels of osteogenic indicators such as ALP, Runx2, and OCN genes were significantly increased by 2-4-fold compared to those in the control group. We revealed that Yoda1 can effectively activate the Piezo1-F-actin pathway, thereby facilitating YAP nucleation and promoting lysine histone acetylation. Consequently, this mechanism enhanced the functionality of YAP nucleation and upregulated the expression of COL-I. Moreover, when implanted in vivo, the Yoda1-loaded microfibrous scaffold group could promote macrophage M2 polarization, thereby enhancing bone regeneration at defect sites. It is believed that the localized release of Yoda1 via EHD-printed PCL scaffolds might represent a promising strategy for the clinically precise treatment of bone defects.

Osteoimmunomodulation by bone implant materials: harnessing physicochemical properties and chemical composition

Chronic inflammation at bone defect sites can impede regenerative processes, but local immune responses can be adjusted to promote healing. Regulating the osteoimmune microenvironment, particularly through macrophage polarization, has become a key focus in bone regeneration research. While bone implants are crucial for addressing significant bone defects, they are often recognized by the immune system as foreign, triggering inflammation that leads to bone resorption and implant issues like fibrous encapsulation and aseptic loosening. Developing osteoimmunomodulatory implants offers a promising approach to transforming destructive inflammation into healing processes, enhancing implant integration and bone regeneration. This review explores strategies based on tuning the physicochemical attributes and chemical composition of materials in engineering osteoimmunomodulatory and pro-regenerative bone implants.

A bad break: mechanisms and assessment of acute and chronic pain after bone fracture

ABSTRACT

Pain is one of the primary indicators of a bone fracture and serves both a functional and practical role in guiding recovery. However, fracture pain can persist long after the fracture itself has clinically healed. The neural and molecular mechanisms that drive acute pain postfracture, and how these mechanisms are pathologically usurped to trap patients into persistent, debilitating, and often difficult to treat, chronic pain, are not well understood. The aim of this review is to provide insight into the risk factors for pain persistence after fracture, review the physiological and pathophysiological mechanisms of fracture pain, and critically evaluate the literature around fracture pain assessment techniques/models. Taken together, the concepts covered herein will provide a strong foundation to support the development of more effective treatments to better alleviate postfracture pain.

Mechano-immunomodulation of macrophages influences the regenerative environment of fracture healing through the regulation of angiogenesis and osteogenesis

Successful completion of the initial inflammatory phase is critical for the establishment of a regenerative environment conducive to long-term fracture healing. Mechanical signals are among the most potent regulators of bone repair, yet whether local mechanics can modulate inflammation and associated immune response remains poorly understood. In this study, we develop a 3D in vitro model comprising of a purpose-built bioreactor that can replicate distinct loading conditions experienced during ambulation of fixated or unfixed large bone defects, and a haematoma mimetic fibrin hydrogel mirroring the local tissue composition, mechanical properties, and immune environment. Harnessing this system, we demonstrated that macrophages, key regulators of the early immune response, are mechanoresponsive and sensitive to the loading magnitude of local compressive forces. Specifically, moderate loading (5% strain) as experienced within semi-rigid fixation, was capable of driving a hybrid phenotype with a higher regenerative secretome in M0 macrophages, while inhibiting inflammation in pro-inflammatory M1-like macrophages which supported capillary-size vascular formation. Conversely, higher loading (35% strain), representative of mechanically unstable defects, was shown to elicit a poor regenerative immune response detrimental to vascular growth and long-term mineralisation. Collectively, our findings highlight mechanical cues as potent stimuli to modulate early immune responses, thus informing the development of novel materials and mechanotherapies to enhance bone repair. STATEMENT OF SIGNIFICANCE: Mechano-immunology is an emerging field that aims at interrogating how mechanical cues shape immune cell phenotype and function. This study presents for the first time, the design and validation of a purpose-built 3D in vitro platform of a dynamically loaded bone fracture haematoma. Utilising this model, we demonstrate that macrophages are mechanoresponsive and sensitive to compressive loading magnitude, with moderate loading (5% strain) producing a hybrid regenerative macrophage phenotype and secretome, while excessive loading (35% strain) produced a secretome detrimental to angiogenesis and osteogenesis. Moreover, moderate strain can also dampen inflammation in a model of an inflamed compromised fracture. This knowledge may inform the development of novel mechano-immunomodulatory materials and therapeutics that target the early inflammation phase for bone repair.

Near-infrared light driven photodynamic therapy by hyaluronic acid encapsulated ionic polymer integrated with oxygen self-supply and high acetate supplement for chronic wound healing

Hypoxia, persistent inflammation, excessive reactive oxygen species (ROS), bacterial infection, immune regulation disorder, and impaired angiogenesis are critical factors hindering diabetic wound healing. So far, clinical treatment still lacks comprehensive solutions to address these challenges. The main objective of this study is to develop and evaluate a novel multifunctional nanomaterial (Gen-BioCa/i-ZnPPOPs@HA) for enhancing the treatment of bacterial-infected diabetic wounds through a combination of photodynamic therapy, oxygen self-supply, and acetate supplementation. When infection occurs, Hyaluronic Acid (HA) shells are initially decomposed by hyaluronidase (HAase) secreted by the bacteria, releasing Gen, biomass Calcium peroxide (BioCa) and ionic porphyrin-based polyporous organic polymer (i-ZnPPOPs). BioCa decomposes to oxygen and Ca(OH)2, which alleviates the hypoxia in diabetes wounds and neutralize lactic acid released by the damaged blood vessels. Under NIR irradiation, cationic i-ZnPPOPs combined with Gen showed bacteria-targeting capacity, rapid and high-efficient microbicidal activity. The vitro/vivo experiments results revealed that Gen-BioCa/i-ZnPPOPs@HA could promote macrophages toward M2 polarization, accelerating angiogenesis, collagen deposition and tissues remodeling. In addition, further introduction of acetate supplement shorten the inflammatory period and accelerated wound healing process. This study provides a new strategy for the treatment of chronic bacterial infectious diseases, indicating the important potential of multifunctional nanomaterials in chronic wounds treatment.

Unraveling the role of calcium in the osteogenic behavior of mesoporous bioactive glass nanoparticles

The use of bioactive materials has emerged as a promising strategy to circumvent bone-related diseases. Because of their chemical composition, calcium-containing bioactive glasses, including mesoporous bioactive glass nanoparticles (nMBG), have long demonstrated their bone regeneration features. In this work, SiO₂-CaO nMBG were synthesized varying Si/Ca ratio from 10 % to 40 % to explore the role of Ca in the osteogenic properties of such materials. We have performed an in-depth physicochemical and biological evaluation of samples by TEM, FTIR, adsorption nitrogen and solid state NMR, revealing that increasing calcium weakens the silica network and consequently, the osteogenic properties. In addition, we have evaluated the protein corona in human serum, obtaining varying protein patterns depending on the Si/Ca ratio and the incubation time. The cellular studies have shown that only certain amounts of calcium up-regulate the osteogenic differentiation, although exceeding such concentrations does not provide improved effects. Finally, All Ca-containing samples promoted calcium phosphate mineralization in biological fluids, while those with higher Si/Ca ratios enhanced significantly hMSC and hOB mineralization. Calcium also modulated hMSC gene expression, with samples containing up to 20 % calcium up-regulating OC and RUNX2. Furthermore, nMBG exhibited immunomodulatory properties, inducing a shift toward the M2 reparative phenotype. Overall, this comprehensive study highlights the crucial role of calcium in osteogenic responses, demonstrating that calcium quantity alone does not surpass the importance of structural and compositional quality in nanosized MBG. STATEMENT OF SIGNIFICANCE: Bone-related diseases are becoming a major socioeconomic issue owing to the increased aging of our society. Therefore, bioactive materials based on silicon, calcium and phosphorus have been used for years due to the osteogenic properties of these elements. In the last few years, the preparation of these materials as nanoparticles has increased their range of applications. In this sense, the novelty of our work relies on the in-depth physicochemical and biological evaluation of those mesoporous bioactive glass nanoparticles based on silicon and calcium, which remained unexplored so far. Couple with the establishment of the range of atomic percentage of calcium with respect to silicon that up-regulate the osteogenic differentiation, although exceeding such concentrations does not provide improved effects.

CD163 + M2-like monocytes increase in pregnant women with first-attempted frozen embryo transfer

Macrophages play a vital role in endometrial receptivity and embryo implantation. However, it remains unclear if macrophages in peripheral blood is associated with pregnancy outcomes of frozen embryo transfer during implantation window. 50 patients preparing for the first time of frozen embryo transfer (FET) and 17 patients with recurrent implantation failure (RIF) from December 2022 to March 2023 were included in our present study. The percentages of peripheral macrophages and other immune cells (B-cell, T-cell, NK cell) were evaluated by flow cytometry. The concentrations of cytokines were verified with an IMMULITE 1000 Immunoassay System. FET patients were categorized into pregnant and nonpregnant groups according to clinical outcomes, respectively. The proportion of peripheral CD68+CD163+ M2 macrophages was increased in pregnant women than in nonpregnant women among the first time of FET patients. CD4+ T helper cells were positively correlated with M2-like macrophages in these women. The pregnancy rate of women with higher peripheral CD163 + M2-like monocytes increased compared with women with lower peripheral CD163 + M2-like monocytes in an independent cohort according to the cutoff value of CD163 + M2-like monocytes in ROC curve. Our findings revealed that peripheral CD163+ M2 macrophages in implantation window were associated with pregnancy outcomes. This indicated that the importance of peripheral M2 macrophages at the implantation site for pregnancy success.

Engineered Probiotics with Low Oxygen Targeting Porphyromonas gingivalis and Gingival Fibroblasts for the Treatment of Periodontitis

The overuse of antibiotics has increased the prevalence of drug-resistant bacteria in periodontitis. "Sentinel" gingival fibroblasts, stimulated by pathogenic bacteria, continue to release signaling factors that affect stem cell repair and recruit immune cells, resulting in persistent inflammation in periodontal tissues, eventually leading to the loosening and loss of teeth. Periodontal pathogenic bacteria cause surface hypoxia, and gingival fibroblasts in the inflammatory microenvironment express HIF-1α, promoting hypoxic areas in periodontal pockets. No drug delivery system is available for the hypoxic region of periodontal pockets. We synthesized BI NPs via berberine (BBR) and indocyanine green (ICG) and formed BIP NPs by wrapping BI NPs with polydopamine (PDA), and the BIP NPs were delivered to the hypoxic region of the periodontal pocket by hitchhiking with the anaerobic probiotic Bifidobacterium bifidum (Bif). The BIP NPs released berberin (BBR) under near-infrared (NIR) irradiation, which inhibited the sulfur metabolism of Porphyromonas gingivalis via mild photothermal action and BBR-targeted serine acetyltransferase, resulting in a decrease in resistance to oxidative stress, thus exerting a nonantibiotic bacteriostatic effect. This mild photothermal effect facilitated the uptake of BIP NPs bygingival fibroblasts. Moreover, BBR targeted nuclear factor-erythroid 2-related factor 2 (NRF2) to reduce ferroptosis, and the gingival fibroblast supernatant modulated macrophage polarization through the NF-κB pathway. In the periodontitis rat model, Bif@BIP+NIR treatment carried the drug to deep periodontal pockets, decreasing local gingival ferroptosis and alleviating periodontitis symptoms. To summarize, engineered probiotics target low-oxygen periodontal pockets for drug delivery, P. gingivalis for nonantibiotic bacterial inhibition, and gingival fibroblasts to mitigate ferroptosis, thus alleviating periodontitis to reduce periodontitis.

Efferocytosis in inflammatory bone disorders

Efferocytosis, the clearance of apoptotic cells (ACs) by phagocytes, is crucial for bone homeostasis and immune balance. This tightly regulated process depends on molecular markers such as phosphatidylserine on ACs and MERTK on phagocytes. In the bone microenvironment, multiple cell types participate in efferocytosis, including osteal macrophages, mesenchymal stem cells, osteoblasts, and osteoclasts, directly influencing bone remodeling and immune responses. Impaired efferocytosis disrupts bone turnover, exacerbates inflammation, and contributes to inflammatory bone diseases. Despite its recognized importance, the precise mechanisms regulating efferocytosis in osteoimmunology remain underexplored, including specific signaling pathways, cell-specific interactions, and therapeutic applications. Recent advances highlight the therapeutic potential of targeting efferocytosis using modalities and biomaterial-based strategies. This review systematically examines the role of efferocytosis in osteoimmunology, discusses key challenges in its therapeutic translation, and explores emerging strategies to optimize efferocytosis-based interventions for inflammatory bone disorders.

COX-2 inhibition as a therapeutic strategy for bone loss in Staphylococcus aureus osteomyelitis

Bone loss in Staphylococcus aureus (S. aureus) osteomyelitis poses a serious challenge to orthopedic treatment, but the underlying mechanism of systemic osteoporosis caused by chronic infection is not completely clear. In this study, γ-irradiation-killed S. aureus (IKSA) was applied to simulate the inflammation and explore the mechanism of systemic bone loss caused by it. In this study, we found that the systemic application of IKSA caused bone loss in mice through increasing osteoclasts and decreasing osteoblasts. An immune response profile with up-regulated COX-2 is identified based on our transcriptional data from IKSA mice bone marrow cells. COX-2 expression is widely up-regulated in bone marrow immune cells, such as myeloid-derived suppressor cells (MDSCs), neutrophils and macrophages in the IKSA-treated mice. Mechanistically, COX-2 stimulated the increasing proportion of MDSCs and neutrophils and the inflammatory response of the bone marrow immune cells, that may regulate bone metabolism. Importantly, COX-2 inhibitor, celecoxib could rescue the bone loss induced by IKSA, which may reason from decrease of inflammatory gene expression in MDSCs, neutrophils and macrophages. Excitingly, COX-2 expression is also increased in bone marrow from mice and patients with S. aureus osteomyelitis. These findings suggested a therapeutic potential for inhibiting COX-2 in combating bone loss in S. aureus osteomyelitis.

Silicon Enhances Functional Mitochondrial Transfer to Improve Neurovascularization in Diabetic Bone Regeneration

Diabetes mellitus is a metabolic disorder associated with an increased risk of fractures and delayed fracture healing, leading to a higher prevalence of bone defects. Recent advancements in strategies aim at regulating immune responses and enhancing neurovascularization have not met expectations. This study demonstrates that a silicon-based strategy significantly enhances vascularization and innervation, thereby optimizing the repair of diabetic bone defects. Silicon improves mitochondrial function and modulates mitochondrial fission dynamics in macrophages via the Drp1-Mff signaling pathway. Subsequently, functional mitochondria are transferred from macrophages to endothelial and neuronal cells through microvesicles, providing a protective mechanism for blood vessels and peripheral nerves during early wound healing. On this basis, an optimized strategy combining a silicified collagen scaffold with a Drp1-Fis1 interaction inhibitor is used to further regulate mitochondrial fission in macrophages and enhance the trafficking of functional mitochondria into stressed receptor cells. In diabetic mice with critical-sized calvarial defects, the silicon-based treatment significantly promotes vessel formation, nerve growth, and mineralized tissue development. These findings provide therapeutic insights into the role of silicon in promoting diabetic bone regeneration and highlight the importance of intercellular communication in diabetic conditions.

Pollen-like mesoporous silica nanoparticles facilitate macrophage-mediated anti-inflammatory response via physical contact cues in the osteoimmune microenvironment

Nanomaterial-mediated macrophage immune response plays a crucial role in bone regeneration microenvironment. Mesoporous silica nanoparticles are widely used as nano-drug carriers, imaging agents, and bioactivity regulators for potential tissue regeneration. It is known that surface topography features of nanomaterials play an important regulatory role in the immune response. In this study, it was found that the pollen-like surface morphology of mesoporous silica nanoparticles (PMSNs) inhibited the expression of pro-inflammatory markers at gene and protein levels in macrophages (RAW 264.7 cells) compared to the smooth surface morphology of mesoporous silica nanoparticles (MSNs). Scanning electron microscopy images showed distinct macrophage membrane surface binding patterns of MSNs and PMSNs. MSNs were more evenly dispersed across the macrophage cell membrane, while PMSNs were aggregated on the membrane and prevented the M1 polarization of macrophages. PMSNs-induced macrophage anti-inflammatory responses were associated with up-regulation of the cell surface receptor CD28 and inhibition of ERK phosphorylation. TEM images showed that macrophages phagocytosed both MSNs and PMSNs while inhibiting nanoparticle phagocytosis did not affect the expression of anti-inflammatory genes and proteins. Moreover, PMSNs-induced conditioned medium from macrophages promoted osteogenic differentiation of mouse bone marrow-derived stromal cells (mBMSCs), evidenced by increased mineralization and osteogenic marker BMP2 expression via Alizarin Red S and LSCM assays compared to MSNs-induced conditioned medium. Moreover, a lipopolysaccharide (LPS)-induced osteolysis model in mouse cranial bone further demonstrated that PMSNs prevent bone resorption by mitigating LPS-induced inflammation. Our results revealed that PMSNs-mediated macrophage immunomodulation promotes bone regeneration via surface topology-related physical contact cues. STATEMENT OF SIGNIFICANCE: Nanomaterials have been widely used in bone regeneration. The immune response of macrophages induced by nanomaterials, plays a crucial role in bone regeneration. However, most nanomaterial immunomodulatory research focus on macrophage internalization or phagocytosis. The early contact between the cell membrane and nanomaterials is often easily overlooked. To clarify how early contact between nanomaterial-cell membrane regulates macrophage immune response. We developed MSN particles with special pollen-like surface morphology and studied the impact of nanoparticle morphology on the early contact between materials and macrophage cell membranes, as well as the subsequent impact on macrophage immune response and bone regeneration and related regulatory mechanisms. The results can provide new guidance for the design and development of osteoimmunomodulatory nanomaterials.

Inhibition of M2 macrophage-mediated mesenchymal stem cell migration: Boldine attenuates elbow heterotopic ossification

BACKGROUND

Heterotopic ossification (HO) is characterized by abnormal bone formation in soft tissues, often following trauma or surgery. Transforming growth factor-beta (TGF-β) signaling and M2 macrophage polarization play critical roles in the recruitment and differentiation of mesenchymal stromal/progenitor cells (MSPCs), promoting HO.

METHODS

An elbow joint trauma-induced HO mouse model was established, where model mice were treated with dichloromethylene-bisphosphonate (Cl2MBP) liposomes or PBS liposomes to deplete macrophages. In addition, boldine was administered to evaluate its therapeutic effect on HO formation. Bone marrow mesenchymal stem cells (BMSCs) were also extracted for in vitro experiments. Quantitative real-time PCR (qRT-PCR) and Western blot were conducted to assess gene and protein expression. In vivo methods included Micro-Computed Tomography (Micro-CT) to assess bone formation, histological staining to evaluate tissue changes, immunohistochemistry (IHC) and immunofluorescence to analyze macrophage, CD73+ and CD105+ cells infiltration. In vitro, BMSCs were identified by flow cytometry and treated with interleukin-10 (IL-10) and/or boldine, and assays such as cell viability (Cell Counting Kit 8 (CCK8)), migration (Transwell), immunofluorescence, ALP staining, and Alizarin Red S staining, were conducted to assess osteogenic differentiation.

RESULTS

Boldine treatment significantly reduced HO formation, decreased collagen deposition, and inhibited M2 macrophage infiltration (P < 0.05). In vitro, boldine reduced IL-10-induced cell activity, migration, and osteogenic differentiation of BMSCs and inhibited TGF-β and pSmad2/3/Smad2/3 protein (P < 0.05).

CONCLUSION

Boldine attenuates HO by inhibiting M2 macrophage-mediated MSPC migration and might involve the TGF-β signaling, suggesting its potential as a therapeutic approach for managing HO.

Re-Evaluating Platelet-Rich Plasma Dosing Strategies in Sports Medicine: The Role of the "10 Billion Platelet Dose" in Optimizing Therapeutic Outcomes-A Narrative Review

Platelet-rich plasma (PRP) therapy is increasingly recognized as a promising treatment for musculoskeletal disorders, including osteoarthritis (OA), tendinopathy, and muscle injuries. This narrative review synthesizes the current literature to evaluate the efficacy of PRP, with a focus on platelet dosing strategies, leukocyte composition, and preparation protocols. Evidence suggests that optimal therapeutic outcomes are achieved when platelet doses exceed 3.5 billion per injection, with cumulative doses of 10-12 billion across multiple treatments. In intra-articular applications, leukocyte-poor PRP (LP-PRP), characterized by reduced neutrophil content, demonstrates superior efficacy compared to leukocyte-rich PRP (LR-PRP). However, its effectiveness in tendon and muscle regeneration remains a subject of debate. Preliminary data suggest that the inclusion of peripheral blood mononuclear cells (PBMNCs) may enhance PRP efficacy, though robust clinical trials are required to confirm these findings. Furthermore, red blood cell contamination and pre-activation have been identified as detrimental to PRP effectiveness, highlighting the need for standardized preparation protocols. This review emphasizes the importance of tailoring PRP formulations to patient-specific factors and musculoskeletal conditions. Future research should focus on refining PRP preparation techniques, identifying optimal leukocyte compositions, and establishing standardized guidelines to enhance clinical outcomes.

Exploring the mechanical and biological interplay in the periodontal ligament

The periodontal ligament (PDL) plays a crucial role in transmitting and dispersing occlusal force, acting as mechanoreceptor for muscle activity during chewing, as well as mediating orthodontic tooth movement. It transforms mechanical stimuli into biological signals, influencing alveolar bone remodeling. Recent research has delved deeper into the biological and mechanical aspects of PDL, emphasizing the importance of understanding its structure and mechanical properties comprehensively. This review focuses on the latest findings concerning both macro- and micro- structural aspects of the PDL, highlighting its mechanical characteristics and factors that influence them. Moreover, it explores the mechanotransduction mechanisms of PDL cells under mechanical forces. Structure-mechanics-mechanotransduction interplay in PDL has been integrated ultimately. By providing an up-to-date overview of our understanding on PDL at various scales, this study lays the foundation for further exploration into PDL-related biomechanics and mechanobiology.

CircAars-Engineered ADSCs Facilitate Maxillofacial Bone Defects Repair Via Synergistic Capability of Osteogenic Differentiation, Macrophage Polarization and Angiogenesis

Adipose-derived stem cells (ADSCs) hold significant promise in bone tissue engineering due to their self-renewal capacity and easy accessibility. However, their limited osteogenic potential remains a critical challenge for clinical application in bone repair. Emerging evidence suggests that circular RNAs (circRNAs) play a key role in regulating stem cell fate and osteogenesis. Despite this, the specific mechanisms by which circRNAs influence ADSCs in the context of bone tissue engineering are largely unexplored. This study introduces a novel strategy utilizing circAars, a specific circRNA, to modify ADSCs, which are then incorporated into gelatin methacryloyl (GelMA) hydrogels for the repair of critical-sized maxillofacial bone defects. The findings reveal that circAars predominantly localizes in the cytoplasm of ADSCs, where it acts as a competitive sponge for miR-128-3p, enhancing the osteogenic differentiation and migration capabilities of ADSCs. Furthermore, circAars-engineered ADSCs facilitate macrophage polarization from the M1 to M2 phenotype and enhance endothelial cell (EC) angiogenic potential through a paracrine mechanism. Additionally, GelMA scaffolds loaded with circAars-engineered ADSCs accelerate the repair of critical-sized maxillofacial bone defects by synergistically promoting osteogenesis, macrophage M2 polarization, and angiogenesis. This approach offers a promising therapeutic strategy for the treatment of critical-sized maxillofacial defects.

Macrophage ATF6 accelerates corticotomy-assisted orthodontic tooth movement through promoting Tnfα transcription

Corticotomy is a clinical procedure to accelerate orthodontic tooth movement characterized by the regional acceleratory phenomenon (RAP). Despite its therapeutic effects, the surgical risk and unclear mechanism hamper the clinical application. Numerous evidences support macrophages as the key immune cells during bone remodeling. Our study discovered that the monocyte-derived macrophages primarily exhibited a pro-inflammatory phenotype that dominated bone remodeling in corticotomy by CX3CR1CreERT2; R26GFP lineage tracing system. Fluorescence staining, flow cytometry analysis, and western blot determined the significantly enhanced expression of binding immunoglobulin protein (BiP) and emphasized the activation of sensor activating transcription factor 6 (ATF6) in macrophages. Then, we verified that macrophage specific ATF6 deletion (ATF6f/f; CX3CR1CreERT2 mice) decreased the proportion of pro-inflammatory macrophages and therefore blocked the acceleration effect of corticotomy. In contrast, macrophage ATF6 overexpression exaggerated the acceleration of orthodontic tooth movement. In vitro experiments also proved that higher proportion of pro-inflammatory macrophages was positively correlated with higher expression of ATF6. At the mechanism level, RNA-seq and CUT&Tag analysis demonstrated that ATF6 modulated the macrophage-orchestrated inflammation through interacting with Tnfα promotor and augmenting its transcription. Additionally, molecular docking simulation and dual-luciferase reporter system indicated the possible binding sites outside of the traditional endoplasmic reticulum-stress response element (ERSE). Taken together, ATF6 may aggravate orthodontic bone remodeling by promoting Tnfα transcription in macrophages, suggesting that ATF6 may represent a promising therapeutic target for non-invasive accelerated orthodontics.

Enhanced Immune Modulation and Bone Tissue Regeneration through an Intelligent Magnetic Scaffold Targeting Macrophage Mitochondria

During the bone tissue repair process, the highly dynamic interactions between the host and materials hinder precise, stable, and sustained immune modulation. Regulating the immune response based on potential mechanisms of macrophage phenotypic changes may represent an effective strategy for promoting bone healing. This study successfully constructs a co-dispersed pFe₃O₄-MXene nanosystem by loading positively charged magnetite (pFe₃O₄) nanoparticles onto MXene nanosheets using electrostatic self-assembly. Subsequently, this work fabricates a biomimetic porous bone scaffold (PFM) via selective laser sintering, which exhibit superior magnetic properties, mechanical performance, hydrophilicity, and biocompatibility. Further investigations demonstrate that the PFM scaffold could precisely and remotely modulate macrophage polarization toward the M2 phenotype under a static magnetic field, significantly enhancing osteogenesis and angiogenesis. Proteomic analysis reveal that the scaffold upregulates Arg2 expression, enhancing mitochondrial function and accelerating oxidative phosphorylation, thereby inducing the M2 transition. In vivo experiments validated the scaffold's immune regulatory capacity in subcutaneous and cranial defect repairs in rats, effectively promoting new bone formation. Overall, this strategy of immune modulation targeting macrophage metabolism and mitochondrial function offers novel insights for material design in tissue engineering and regenerative medicine.

Hybrid Outer Membrane Vesicles with Genetically Engineering for Treatment of Implant-Associated Infections and Relapse Prevention Through Host Immunomodulation

Implant-associated infections (IAIs) are refractory to elimination, and the local immunosuppressive microenvironment (IME) exacerbates therapeutic difficulties, ultimately causing persistence and relapse. Therefore, exploring immunostrengthening treatments holds great promise for reversing IME and thoroughly eradicating chronic or repetitive infections. Bacterial outer membrane vesicles (OMVs) have emerged as potential immunostimulatory candidates; however, they lack active targeting capabilities and cause non-specific inflammatory side effects. In this study, bone marrow-derived mesenchymal stem cells (BMSCs) are genetically engineered to overexpress CXCR4 and isolated cell membranes (mBMSCCXCR4) for hybridization with OMVs derived from Escherichia coli (E. coli) to produce nanovesicles (mBMSCCXCR4@OMV). The resulting mBMSCCXCR4@OMV nanovesicles demonstrate excellent bone marrow targeting capability and are effectively taken up by bone marrow-derived macrophages, triggering the efficient transition to pro-inflammatory M1 status through TLR/NF-κB pathway. This alteration promotes innate bactericidal capacity and antigen presentation. Subsequent activation of T and B cells and inhibition of myeloid-derived suppressor cells (MDSCs) facilitated in vivo adaptive immunity in mouse models. Additionally, mBMSCCXCR4@OMV boosted memory B cell and bacteria-specific antibody responses. Together, these data highlight the potential of mBMSCCXCR4@OMV to eradicate complicated IAIs and provide whole-stage protection against postsurgical relapse, thus marking a significant immunotherapeutic advancement in the post-antibiotic era.

Sustained slow-release TGF-β3 in a three-dimensional-printed titanium microporous scaffold composite system promotes ligament-to-bone healing

The treatment of tendon/ligament-to-bone injury is a long-standing research challenge in orthopedics and bone tissue engineering. Orderly healing of the fibrocartilage layer and mineralized bone layer is crucial for treating tendon-bone interface injuries. We designed a three-dimensional printed porous titanium scaffold composite system with thermosensitive collagen hydrogel loaded with transforming growth factor β3 (TGF-β3), formulated for the sustained slow release of TGF-β3 at a constant rate. In vitro, the composite system exhibited good biocompatibility and was beneficial for the adhesion and proliferation of bone marrow mesenchymal stem cells (BMSCs), which showed high growth activity. Moreover, the composite system promoted the differentiation of BMSCs via osteogenesis and chondrogenesis. In vivo, the composite system provided active substances at the injured site, promoting the repair of the fibrocartilage layer and of the mineralized bone layer at the interface between the ligament and bone. Micro-CT results demonstrated that the complex promotes the osseointegration of titanium scaffolds in bone defects. Hard tissue sections showed that the new bone, ligament, and the titanium alloy scaffold system formed a closely integrated whole; the composite system provided suitable attachment points for ligament growth. Additionally, the biomechanical strength of the tendon interface improved to some extent. Our results indicate that the composite system has potential as a bioactive implant interface for repairing ligament and bone injuries.

It is not waste if it is therapy: cellular, secretory and functional properties of reamer-irrigator-aspirator (RIA)-derived autologous bone grafts

BACKGROUND

Large bone defects resulting from trauma, disease, or resection often exceed the intrinsic capacity of bones to heal. The current gold standard addressing these defects is autologous bone grafting (ABG). Procedures such as reamer-irrigator-aspirator (RIA) and conventional bone grafting from the iliac crest are widely recognized as highly effective interventions for critical-size bone defects. The early phase of fracture healing is particularly crucial, as it can determine whether a complete bony union occurs, or if delayed healing or non-unions develop. The initial composition of the bone marrow (BM)-rich ABG transplant, with its unique cellular (e.g., leukocytes, monocytes, and granulocytes) and acellular (e.g., growth factors and extracellular proteins) components, plays a key role in this process. However, despite many successful case reports, the role of ABG cells, growth factors, and their precise contributions to bone healing remain largely elusive.

MATERIALS AND METHODS

We characterized the native cellularity of both solid and liquid RIA-derived ABG by analyzing primary, minimally manipulated populations of monocytes, macrophages, and T cells, as well as hematopoietic, endothelial, and mesenchymal progenitor cells by flow cytometry. Growth factor and cytokine contents were assessed through antibody arrays. Possible functional and immunomodulatory properties of RIA liquid were evaluated in functional in vitro assays.

RESULTS

Growth factor and protein arrays revealed a plethora of soluble factors that can be linked to specific immunomodulatory and angiogenic properties, which were evaluated for their potency using functional in vitro assays. We could demonstrate a strong M2-macrophage phenotype inducing the effect of RIA liquid on macrophages. Additionally, we observed an increase in anti-inflammatory T cell subsets generated from peripheral blood mononuclear cells and BM mononuclear cells upon stimulation with RIA liquid . Finally, in vitro endothelial tube formation assays revealed highly significant angiogenic properties of RIA liquid, even at further dilutions.

CONCLUSION

The cytokine and protein content of RIA liquid exhibits potent immunomodulatory and angiogenic properties. These findings suggest significant therapeutic potential for RIA liquid in modulating immune responses and promoting angiogenesis. Anti-inflammatory and angiogenic properties demonstrated in this study might also help to further define and understand its particular mode of action while also providing explanations to the excellent bone-healing properties of ABG in general.

LEVEL OF EVIDENCE

Case-series (Level 4).

3D printed shape-memory piezoelectric scaffolds with in-situ self-power properties for bone defect repair

Electrical stimulation has been shown to regulate early immunity and late-stage osteogenesis in bone repair. However, achieving in-situ electrical stimulation in the form of self-power in vivo during the initial postoperative stages when the patients have limited mobility remains challenging. In this study, we developed a 3D-printed in-situ self-powered composite scaffold composed of shape memory polyurethane elastomers (SMPU) and polyvinylidene fluoride (PVDF) piezoelectric nanofibers. The composite scaffold demonstrates excellent shape memory performance, allowing for minimally invasive implantation. During the shape memory process, the composite scaffold can provide mechanical force stimulation to PVDF nanofibers to generate charge. Therefore, self-power was achieved through the integration of the shape memory process and piezoelectric effects, and it can be used for in-situ electrical stimulation during the initial postoperative period. Additionally, the composite scaffold can output voltage under continuous mechanical force stimulation, indicating that the patients can apply sustained mechanical force stimulation to the composite scaffold to output voltage through rehabilitation exercises when the patients regain mobility. Both cell experiments and animal studies confirmed that this composite scaffold can effectively regulate the immune microenvironment and enhance osteogenesis. This study successfully achieves in-situ electrical stimulation in the form of self-power by integrating the shape memory process and piezoelectric effects, which is expected to be an effective repair strategy for bone tissue engineering.

Gas-powered extracellular vesicles promote bone regeneration

The signaling gas hydrogen sulfide (H2S) has recently been implicated in the regulation of bone remodeling and the maintenance of periodontal health. Exploring the underlying mechanisms for this regulation holds promise for the development of new treatment strategies to block bone resorption and stimulate bone regeneration. A recent study by Zhou et al. (Bioactive Materials, 2024) showed that treatment with H2S stimulated changes in the extracellular vesicles (EVs) released by M2 macrophages, enhancing their capacity to promote the osteogenic differentiation of mesenchymal stem cells in vitro. The H2S-stimulated EVs, given together with mesenchymal stem cells (MSCs), also promoted bone regeneration in vivo in a mouse calvarial critical-size defect model. This activity was linked to augmented expression of moesin, a membrane-cytoskeletal linkage protein, which was found at increased levels in EVs from cells stimulated by H2S. The study identifies a new strategy for generating EVs that are pro-osteogenic. It also uncovers a surprising role for moesin in stimulating osteogenesis in MSCs.

Mitochondria-loading erythrocytes transfer mitochondria to ameliorate inflammatory bone loss

Inflammatory diseases frequently result in bone loss, a condition for which effective therapeutic interventions are lacking. Mitochondrial transfer and transplantation hold promise in tissue repair and disease treatments. However, the application of mitochondrial transfer in alleviating disorders has been limited due to its uncontrollable nature. Moreover, the key challenge in this field is maintaining the quality of isolated mitochondria (Mito), as dysfunctional Mito can exacerbate disease progression. Therefore, we employ Mito-loading erythrocytes (named MiLE) to achieve maintenance of mitochondrial quality. In addition, MiLE can be cryopreserved, allowing for long-term preservation of mitochondrial quality and facilitating the future application of mitochondrial transfer. In the inflammatory microenvironment, MiLE supplies Mito as well as O2 to macrophages. By undergoing metabolic reprogramming, MiLE suppresses lipopolysaccharide-induced osteoclast differentiation and promotes macrophage polarization from M1 to M2 phenotype, ultimately ameliorating inflammatory bone destruction. In summary, this work tackles the challenges of uncontrollable mitochondrial transfer and mitochondrial quality maintenance, and offers an opportunity for future exploration of organelle transplantation. STATEMENT OF SIGNIFICANCE: The application of mitochondrial transfer for the alleviation of pathologies has been hindered by the intrinsic limitations in terms of control and selectivity. Furthermore, maintaining mitochondrial integrity and functionality following isolation poses a significant challenge. In a pioneering approach, we develop a method for encapsulating mitochondria within erythrocytes, termed mitochondria-loading erythrocytes (MiLE), which ensures extended mitochondrial functionality and controlled transfer. Within an inflammatory microenvironment, MiLE supplies both mitochondria and O2 to macrophages. By undergoing metabolic reprogramming, MiLE alleviates lipopolysaccharide-induced osteoclast differentiation and promotes macrophage polarization from M1 to M2 phenotype, ultimately ameliorating inflammatory bone destruction.

Boosting mRNA-Engineered Monocytes via Prodrug-Like Microspheres for Bone Microenvironment Multi-Phase Remodeling

Monocytes, as progenitors of macrophages and osteoclasts, play critical roles in various stages of bone repair, necessitating phase-specific regulatory mechanisms. Here, icariin (ICA) prodrug-like microspheres (ICA@GM) are developed, as lipid nanoparticle (LNP) transfection boosters, to construct mRNA-engineered monocytes for remodeling the bone microenvironment across multiple stages, including the acute inflammatory and repair phases. Initially, ICA@GM is prepared from ICA-conjugated gelatin methacryloyl via a microfluidics system. Then, monocyte-targeting IL-4 mRNA-LNPs are then prepared and integrated into injectable microspheres (mRNA-ICA@GM) via electrostatic and hydrogen bond interactions. After bone-defect injection, LNPs are controlled released from mRNA-ICA@GM within 3 days, rapidly transfecting monocytes for monocyte IL-4 mRNA-engineering, which effectively suppressed acute inflammatory responses via polarization programming and paracrine signaling. Afterwards, ICA is sustainably released as well via cleavable boronate esters across multiple stages, cooperatively boosting the mRNA-engineered monocytes to inhibit coenocytic fusion and osteoclastic function. Both in vitro and in vivo data indicated that mRNA-ICA@GM can not only reverse the inflammatory environment but also suppress monocyte-derived osteoclast formation to accelerate bone repair. In summary, mRNA-engineered monocytes and ICA prodrug-like microspheres are combined to achieve long-lasting multi-stage bone microenvironment regulation, offering a promising repair strategy.

T cell related osteoimmunology in fracture healing: Potential targets for augmenting bone regeneration

Last decade has witnessed increasing evidence which highlights the roles of immune cells in bone regeneration. Numerous immune cell types, including macrophages, T cells, and neutrophils are involved in fracture healing by orchestrating a series of events that modulate bone formation and remodeling. In this review, the role of T cell immunity in fracture healing has been summarized, and the modulatory effects of T cell immunity in inflammation, bone formation and remodeling have been highlighted. The review also summarizes the specific roles of different T cell subsets, including CD4+ T cells, CD8+ T cells, regulatory T cells, T helper 17 cells, and γδ T cells in modulating fracture healing. The current therapeutics targeting T cell immunity to enhance fracture healing have also been reviewed, aiming to provide insights from a translational standpoint. Overall, this work discusses recent advances and challenges in the interdisciplinary research field of T cell related osteoimmunology and its implications in fracture healing.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

Delayed unions or non-unions of bone fractures remain a challenge in clinical practice. Developing a deep understanding of the roles of immune cells, including T cells, in fracture healing will facilitate the advancement of novel therapeutics of fracture nonunion. This review summarizes the current understanding of different T cell subsets involved in various phases of fracture healing, providing insights for targeting T cells as an alternative strategy to enhance bone regeneration.

Synthetic nanointerfacial bioengineering of Ti implants: on-demand regulation of implant-bone interactions for enhancing osseointegration

Titanium and its alloys are the most commonly used biometals for developing orthopedic implants to treat various forms of bone fractures and defects, but their clinical performance is still challenged by the unfavorable mechanical and biological interactions at the implant-tissue interface, which substantially impede bone healing at the defects and reduce the quality of regenerated bones. Moreover, the impaired osteogenesis capacity of patients under certain pathological conditions such as diabetes and osteoporosis may further impair the osseointegration of Ti-based implants and increase the risk of treatment failure. To address these issues, various modification strategies have been developed to regulate the implant-bone interactions for improving bone growth and remodeling in situ. In this review, we provide a comprehensive analysis on the state-of-the-art synthetic nanointerfacial bioengineering strategies for designing Ti-based biofunctional orthopedic implants, with special emphasis on the contributions to (1) promotion of new bone formation and binding at the implant-bone interface, (2) bacterial elimination for preventing peri-implant infection and (3) overcoming osseointegration resistance induced by degenerative bone diseases. Furthermore, a perspective is included to discuss the challenges and potential opportunities for the interfacial engineering of Ti implants in a translational perspective. Overall, it is envisioned that the insights in this review may guide future research in the area of biometallic orthopedic implants for improving bone repair with enhanced efficacy and safety.

Liraglutide promotes osteogenic differentiation of mesenchymal stem cells by inhibiting M1 macrophage polarization and CXCL9 release in vitro

As a GLP-1 receptor agonist widely used in treating type 2 diabetes, liraglutide shows potential applications in bone tissue engineering. This study investigated liraglutide's direct effects on rat bone marrow mesenchymal stem cells (BMSCs) osteogenic differentiation and its regulatory mechanism through macrophage polarization. Results showed that liraglutide significantly enhanced BMSC migration and osteogenic differentiation. Additionally, liraglutide markedly inhibited M1 macrophage polarization induced by LPS and IFN-γ, reducing inflammatory factors CXCL9 and TNF-α secretion, possibly by partially reversing M1 macrophage regulatory signals (AMPK and NF-κB pathways). Compared to M1 macrophage-conditioned medium (M1-CM), conditioned medium from liraglutide-treated macrophages showed stronger promotion of BMSC osteogenic differentiation, though this effect was reversed by CXCL9 addition. The study demonstrates that liraglutide enhances BMSC osteogenic capacity both directly and by inhibiting M1 macrophage polarization and CXCL9 secretion, offering a new therapeutic option for severe bone defects with inflammatory responses.

Manipulation of Surface Potential Distribution Enhances Osteogenesis by Promoting Pro-Angiogenic Macrophage Polarization via Activation of the PI3K-Akt Signaling Pathway

Regulation of the immune response is key to promoting bone regeneration by electroactive biomaterials. However, how electrical signals at the micro- and nanoscale regulate the immune response and subsequent angiogenesis during bone regeneration remains to be elucidated. Here, the distinctly different surface potential distributions on charged poly(vinylidene fluoridetrifluoroethylene) (P(VDF-TrFE)) matrix surfaces are established by altering the dimensions of ferroelectric nanofillers from 0D BaTiO3 nanoparticles (homogeneous surface potential distribution, HOPD) to 1D BaTiO3 nanofibers (heterogeneous surface potential distribution, HEPD). Compared to HOPD, HEPD is significantly better at inducing the M2 polarization of macrophages and promoting neovascularization, which results in accelerated bone regeneration in vivo. The transcriptomic analysis reveals that macrophages modulated by HEPD display high expression levels of pro-angiogenic genes, which is corroborated by tube-formation assays, RT-qPCR, and western blot analyses in vitro. Mechanistic explorations elucidate activation of the PI3K-Akt signaling pathway, which in turn induces the polarization of macrophages toward a pro-angiogenic phenotype. This study elucidates the cascade of biological processes by which heterogeneous electrical signals at the micro- and nanoscale modulate macrophage functions to promote vascularization and bone regeneration. Hence, this study provides new insights into how the micro- and nanoscale distribution characteristics of electrical signals facilitate bone regeneration.

Advances in the application and research of biomaterials in promoting bone repair and regeneration through immune modulation

With the ongoing development of osteoimmunology, increasing evidence indicates that the local immune microenvironment plays a critical role in various stages of bone formation. Consequently, modulating the immune inflammatory response triggered by biomaterials to foster a more favorable immune microenvironment for bone regeneration has emerged as a novel strategy in bone tissue engineering. This review first examines the roles of various immune cells in bone tissue injury and repair. Then, the contributions of different biomaterials, including metals, bioceramics, and polymers, in promoting osteogenesis through immune regulation, as well as their future development directions, are discussed. Finally, various design strategies, such as modifying the physicochemical properties of biomaterials and integrating bioactive substances, to optimize material design and create an immune environment conducive to bone formation, are explored. In summary, this review comprehensively covers strategies and approaches for promoting bone tissue regeneration through immune modulation. It offers a thorough understanding of current research trends in biomaterial-based immune regulation, serving as a theoretical reference for the further development and clinical application of biomaterials in bone tissue engineering.

Mesenchymal stem cell-derived extracellular vesicles in periodontal bone repair

Periodontitis is a chronic inflammatory disease that destroys tooth-supporting structures and poses significant public health challenges due to its high prevalence and links to systemic health conditions. Traditional treatments are effective in reducing the inflammatory response and improving the clinical symptoms of periodontitis. However, these methods are challenging to achieve an ideal treatment effect in alveolar bone repair. Mesenchymal stem cells (MSCs) represent a potential alternative for the treatment of periodontal bone defects due to their self-renewal and differentiation capabilities. Recent research indicates that MSCs exert their effects primarily through paracrine mechanisms. Mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) serve as pivotal mediators in intercellular communication, transferring microRNAs (miRNAs), messenger RNAs (mRNAs), proteins, and cytokines to recipient cells, thereby emulating the therapeutic effects of MSCs. In periodontitis, MSC-EVs play a pivotal role in immunomodulation and bone remodeling, thereby facilitating periodontal bone repair. As a cell-free therapy, MSC-EVs demonstrate considerable clinical potential due to their specialized membrane structure, minimal immunogenicity, low toxicity, high biocompatibility, and nanoscale size. This review indicates that MSC-EVs represent a promising approach for periodontitis treatment, with the potential to overcome the limitations of traditional therapies and offer a more effective solution for bone repair in periodontal disease. In this review, we introduce MSC-EVs, emphasizing their mechanisms and clinical applications in periodontal bone repair. It synthesizes recent advances, existing challenges, and future prospects to present up-to-date information and novel techniques for periodontal regeneration and to guide the improvement of MSC-EV therapy in clinical practice.

Dual release scaffolds as a promising strategy for enhancing bone regeneration: an updated review

Advancements in tissue regeneration, particularly bone regeneration is key area of research due to potential of novel therapeutic approaches. Efforts to reduce reliance on autologous and allogeneic bone grafts have led to the development of biomaterials that promote synchronized and controlled bone healing. However, the use of growth factors is limited by their short half-life, slow tissue penetration, large molecular size and potential toxicity. These factors suggest that traditional delivery methods may be inadequate hence, to address these challenges, new strategies are being explored. These novel approaches include the use of bioactive substances within advanced delivery systems that enable precise spatiotemporal control. Dual-release composite scaffolds offer a promising solution by reducing the need for multiple surgical interventions and simplifying the treatment process. These scaffolds allow for sustained and controlled drug release, enhancing bone repair while minimizing the drawbacks of conventional methods. This review explores various dual-drug release systems, discussing their modes of action, types of drugs used and release mechanisms to improve bone regeneration.

Macrophage-derived extracellular vesicles as new players in chronic non-communicable diseases

Macrophages are innate immune cells present in all tissues and play an important role in almost all aspects of the biology of living organisms. Extracellular vesicles (EVs) are released by cells and transport their contents (micro RNAs, mRNA, proteins, and long noncoding RNAs) to nearby or distant cells for cell-to-cell communication. Numerous studies have shown that macrophage-derived extracellular vesicles (M-EVs) and their contents play an important role in a variety of diseases and show great potential as biomarkers, therapeutics, and drug delivery vehicles for diseases. This article reviews the biological functions and mechanisms of M-EVs and their contents in chronic non-communicable diseases such as cardiovascular diseases, metabolic diseases, cancer, inflammatory diseases and bone-related diseases. In addition, the potential application of M-EVs as drug delivery systems for various diseases have been summarized.

Dentin tubules as a long-term sustained release carrier to accelerate bone repair by loading FTY720

The controlled release of drugs remains a huge challenge in the field of tissue engineering. Current research focuses on the construction of drug carriers by using various advanced technologies. However, the pore-like structure that exists within our human body is ignored. Herein, a dental particle loaded with FTY720 by using dentin tubules (Dent-FTY720) was successfully prepared, which could achieve long-term sustained release of drugs. Meanwhile, Dent-FTY720 significantly promoted bone defect repair because of the similarity in composition to bone including hydroxyapatite and collagen. Furthermore, the loaded drugs exhibited both anti-immune and anti-inflammatory properties. This research introduces a novel concept in drug loading, highlighting the potential of dentin tubules as a drug delivery system.

An Overview on Bioactive Glasses for Bone Regeneration and Repair: Preparation, Reinforcement, and Applications

Synthetic bone transplantation has emerged in recent years as a highly promising strategy to address the major clinical challenge of bone tissue defects. In this field, bioactive glasses (BGs) have been widely recognized as a viable alternative to traditional bone substitutes due to their unique advantages, including favorable biocompatibility, pronounced bioactivity, excellent biodegradability, and superior osseointegration properties. This article begins with a comprehensive overview of the development and success of BGs in bone tissue engineering, and then focuses on their composite reinforcement systems with biodegradable metals, calcium-phosphorus (Ca-P)-based bioceramics, and biodegradable medical polymers, respectively. Moreover, the article outlines some frequently used manufacturing methods for three-dimensional BG-based bone bioscaffolds and highlights the remarkable achievements of these scaffolds in the field of bone defect repair in recent years. Lastly, based on the many potential challenges encountered in the preparation and application of BGs, a brief outlook on their future directions is presented. This review may help to provide new ideas for researchers to develop ideal BG-based bone substitutes for bone reconstruction and functional recovery.

Immunomodulatory and osteogenic effects of chitosan-based injectable hydrogel with geniposide-loaded mesoporous bioactive glass

The immune response dominated by macrophages plays a pivotal role in the regeneration of bone tissue. In this work, an injectable temperature-responsive hydrogel composed of geniposide-loaded mesoporous bioactive glass, chitosan and β-glycerophosphate (G-M Gel) was prepared, showing robustly networks, uniform pore structure, excellent biocompatibility, immunomodulatory effect and osteogenic potential. In an inflammatory microenvironment elicited by lipopolysaccharide (LPS), the proportion of M1 and M2 macrophages measured by flow cytometry were 33.17 % and 2.07 %, respectively. After G-M Gel treatment, the proportion of M1 macrophages decreased to 14.4 %, while the proportion of M2 macrophages increased significantly to 16.2 %. LPS treated macrophage conditioned medium inhibited the expression of osteogenic related factors (OCN, OPN, Runx2), alkaline phosphatase (ALP) and alizarin red S (ARS) in MC3T3-E1 cells. In contrast, LPS + G-M Gel treated macrophage conditioned medium significantly increased the expression of osteogenic related factors, ALP and ARS. These results demonstrated that G-M Gel can augment bone formation by promoting the polarization of M2 macrophages, showing great potential clinical application of G-M Gel in bone regeneration field.

Current status of nano-embedded growth factors and stem cells delivery to bone for targeted repair and regeneration

Bone-related diseases like osteoarthritis and osteoporosis impact millions globally, affecting quality of life. Osteoporosis considerably enhances the probability of bone fractures of the wrist, hip, and spine. Enhancement and acceleration of functional bone development can be achieved through the sustained delivery of growth factors (GFs) and cells in biomaterial carriers. The delivery of bioactive compounds in a targeted, spatiotemporal way that most closely resembles the natural defect repair process can be achieved by designing the carrier system with established release kinetics. Furthermore, the carrier can serve as a substrate that mimics the extracellular matrix, facilitating osteoprogenitor cell infiltration and growth for integrative tissue healing. In this report, we explore the significance of GFs within the realm of bone and cartilage tissue engineering, encompassing their encapsulation and delivery methodologies, the kinetics of release, and their amalgamation with biomaterials and stem cells (SCs) to facilitate the mending of bone fractures. Moreover, the significance of GFs in evaluating the microenvironment of bone tissue through reciprocal signaling with cells and biomaterial scaffolds is emphasized which will serve as the foundation for prospective advances in bone and cartilage tissue engineering as well as therapeutic equipment. Nanoparticles are being used in regenerative medicine to promote bone regeneration and repair by delivering osteoinductive growth factors like BMP-2, VEGF, TGF-β. These nanocarriers allow controlled release, minimizing adverse effects and ensuring growth factors are concentrated at the injury site. They are also mixed with mesenchymal stem cells (MSCs) to improve their engraftment, differentiation, and survival. This approach is a key step in developing multi-model systems that more efficiently facilitate bone regeneration. Researchers are exploring smart nanoparticles with immunomodulatory qualities to improve bonre regeneration and reduce inflammation in injury site. Despite promising preclinical results, challenges include cost management, regulatory approval, and long term safety. However, incorporating stem cell transport and growth factors in nanoparticles could revolutionize bone regeneration and offer more personalized therapies for complex bone disorders and accidents.

The translational potential of this article

Stem cell transport and growth factors encapsulated in nanoparticles are becoming revolutionary methods for bone regeneration and repair. By encouraging stem cells to develop into osteoblasts, osteoinductive GFs like BMP-2, VEGF, and TGF-β can be delivered under control due to nanomaterials like nanoparticles, nanofibers, and nanotubes. By ensuring sustained release, these nanocarriers lessen adverse effects and enhance therapeutic results. In order to prove their survival and development, MCSs, which are essential for bone regeneration, are mixed with nanoparticles, frequently using scaffolds that resemble the ECM of bone. Furthermore, by adjusting to the injured environment and lowering inflammation, immunomodulatory nanostructures and stimuli-responsive nanomaterials can further maximize. While there are still shotcomings to overcome, including managing expenses, negotiating regulatory processes, and guaranteeing long-term safety, this method promises to outperform traditional bone grafting by providing quicker, more individualized, and more efficient treatments. Nano-embedded growth factors and stem cell technologies have the potential to revolutionize orthopedic therapy and significantly enhance patient outcomes with further research.

Phase-transformed lactoferrin/strontium-doped nanocoatings enhance antibacterial, anti-inflammatory and vascularised osteogenesis of titanium

Failure of orthopedic implants due to localized bacterial infections, inflammation and insufficient blood supply is always problematic. In this study, strontium-doped titanium dioxide nanotubes (STN) were firstly prepared on titanium surface, and then lactoferrin (LF) was loaded into strontium-doped nanotubes (STN) by the phase transition method, eventually the LF/TCEP-STN composite coating was successfully prepared. With the innate antimicrobial properties of LF, LF/TCEP-STN was effected against E. coli and S. aureus. Cellular assays showed that RAW264.7 (immune), HUVEC (angiogenic) and MC3T3-E1 (osteogenic) exhibited good adhesion and proliferative activity on the surface of LF/TCEP-STN. At the molecular level, LF/TCEP-STN modulated RAW264.7 polarization toward M2-type while promoting MC3T3-E1 differentiation toward osteogenesis. Meanwhile LF/TCEP-STN coating effectively promoted angiogenesis. The results of the bone defect model with or without infection demonstrated that the LF/TCEP-STN material had good anti-inflammatory, antibacterial, and vascularization-promoting osteogenesis. In addition, LF/TCEP-STN offered excellent blood compatibility and biosafety. As a multifunctional coating on implant surfaces, the study's results highlighted the viability of LF/TCEP-STN and offered fresh concepts for the clinical design of next-generation artificial bone implants with antibacterial, anti-inflammatory, and osteogenic properties.

Comprehensive Overview of Interface Strategies in Implant Osseointegration

With the improvement of implant design and the expansion of application scenarios, orthopedic implants have become a common surgical option for treating fractures and end‐stage osteoarthritis. Their common goal is rapidly forming and long‐term stable osseointegration. However, this fixation effect is limited by implant surface characteristics and peri‐implant bone tissue activity. Therefore, this review summarizes the strategies of interface engineering (osteogenic peptides, growth factors, and metal ions) and treatment methods (porous nanotubes, hydrogel embedding, and other load‐release systems) through research on its biological mechanism, paving the way to achieve the adaptation of both and coordination between different strategies. With the transition of the osseointegration stage, interface engineering strategies have demonstrated varying therapeutic effects. Especially, the activity of osteoblasts runs almost through the entire process of osseointegration, and their physiological activities play a dominant role in bone formation. Furthermore, diseases impacting bone metabolism exacerbate the difficulty of achieving osseointegration. This review aims to assist future research on osseointegration engineering strategies to improve implant‐bone fixation, promote fracture healing, and enhance post‐implantation recovery.

Functionalized 3D-printed GelMA/Laponite hydrogel scaffold promotes BMSCs recruitment through osteoimmunomodulatory enhance osteogenic via AMPK/mTOR signaling pathway

The migration and differentiation of bone marrow mesenchymal stem cells (BMSCs) play crucial roles in bone repair processes. However, conventional scaffolds often lack of effectively inducing and recruiting BMSCs. In our study, we present a novel approach by introducing a 3D-bioprinted scaffold composed of hydrogels, with the addition of laponite to the GelMA solution, aimed at enhancing scaffold performance. Both in vivo and in vitro experiments have confirmed the outstanding biocompatibility of the scaffold. Furthermore, for the first time, Apt19s has been chemically modified onto the surface of the hydrogel scaffold, resulting in a remarkable enhancement in the migration and adhesion of BMSCs. Moreover, the scaffold has demonstrated robust osteogenic differentiation capability in both in vivo and in vitro environments. Additionally, the hydrogel scaffold has shown the ability to induce the polarization of macrophages from M1 to M2, thereby facilitating the osteogenic differentiation of BMSCs via the bone immune pathway. Through RNA-seq analysis, it has been revealed that macrophages regulate the osteogenic differentiation of BMSCs through the AMPK/mTOR signaling pathway. In summary, the functionalized GelMA/Laponite scaffold offers a cost-effective approach for tailored in situ bone regeneration.

The Role of Macrophage Death in Periodontitis: A Review

Periodontitis, an infectious inflammatory disease influenced by various factors, disrupts the delicate balance between the host microbiota and immunity. The resulting excessive immune response exacerbates the progressive destruction of the supporting periodontal tissue. Macrophages are essential elements of the host innate immune system. They are pivotal components in the periodontal immune microenvironment and actively participate in both physiological and pathological processes of periodontal tissue. When confronted with periodontitis-related irritant factors, macrophages may differentiate to pro- or anti-inflammatory subtypes that affect tissue homeostasis. Additionally, macrophages may die in response to bacterial infections, potentially affecting the severity of periodontitis. This article reviews the typical mechanisms underlying macrophage death and its effects on periodontitis. We describe five forms of macrophage death in periodontitis: apoptosis, pyroptosis, necroptosis, ferroptosis, and ETosis. Our review of macrophage death in the pathophysiology of periodontitis enhances comprehension of the pathogenesis of periodontitis that will be useful for clinical practice. Although our review elucidates the complex mechanisms by which macrophage death and inflammatory pathways perpetuate periodontitis, unresolved issues remain, necessitating further research.

Microbial- and host immune cell-derived extracellular vesicles in the pathogenesis and therapy of periodontitis: A narrative review

Periodontitis is a chronic inflammatory disease caused by dysbiotic biofilms and destructive host immune responses. Extracellular vesicles (EVs) are circulating nanoparticles released by microbes and host cells involved in cell-to-cell communication, found in body biofluids, such as saliva and gingival crevicular fluid (GCF). EVs are mainly involved in cell-to-cell communication, and may hold promise for diagnostic and therapeutic purposes. Periodontal research has examined the potential involvement of bacterial- and host-cell-derived EVs in disease pathogenesis, diagnosis, and therapy, but data remains scarce on immune cell- or microbial-derived EVs. In this narrative review, we first provide an overview of the role of microbial and host-derived EVs on disease pathogenesis. Recent studies reveal that Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans-derived outer membrane vesicles (OMVs) can activate inflammatory cytokine release in host cells, while M1 macrophage EVs may contribute to bone loss. Additionally, we summarised current in vitro and pre-clinical research on the utilisation of immune cell and microbial-derived EVs as potential therapeutic tools in the context of periodontal treatment. Studies indicate that EVs from M2 macrophages and dendritic cells promote bone regeneration in animal models. While bacterial EVs remain underexplored for periodontal therapy, preliminary research suggests that P. gingivalis OMVs hold promise as vaccine candidates. Finally, we acknowledge the current limitations present in the field of translating immune cell derived EVs and microbial derived EVs in periodontology. It is concluded that microbial and host immune cell-derived EVs have a role in periodontitis pathogenesis and hence may be useful for studying disease pathophysiology, and as diagnostic and treatment monitoring biomarkers.

Drug delivery for age-related bone diseases: From therapeutic targets to common and emerging therapeutic strategies

With the accumulation of knowledge on aging, people have gradually realized that among the many factors that cause individual aging, the accumulation of aging cells is an essential cause of organ degeneration and, ultimately, age-related diseases. Most cells present in the bone microenvironment gradually age over time, leading to an imbalance of osteogenesis, osteoclastogenesis, adipogenesis, and chondrogenesis. This imbalance contributes to age-related bone loss and the development of age-related bone diseases, such as osteoporosis. Bone aging can prolong the lifespan and delay the development of age-related diseases. Nanoparticles have controllable and stable physical and chemical properties and can precisely target different tissues and organs. By preparing multiple easily modified and biocompatible nanoparticles as different drug delivery carriers, specifically targeting various diseased tissues for controlled-release and sustained-release administration, the delivery efficiency of drugs can be significantly improved, and the toxicity and side effects of drugs can be substantially reduced, thereby improving the therapeutic effect of age-related bone diseases. In addition, other novel anti-aging strategies (such as stem cell exosomes) also have significant scientific and practical significance in anti-aging research on age-related bone diseases. This article reviews the research progress of various nano-drug-loaded particles and emerging anti-aging methods for treating age-related bone diseases, offering new insights and directions for precise targeted clinical therapies.