The role of vasculature in bone development, regeneration and proper systemic functioning

Imaging the development of the human craniofacial arterial system - an experimental study

BACKGROUND

The process of vascular development is essential for shaping complex craniofacial structures. Investigating the interplay between vascular development and orofacial morphogenesis holds critical importance in clinical practice and contributes to advancing our comprehension of (vascular) developmental biology. New insights into specific vascular developmental pathways will have far-reaching implications across various medical disciplines, enhancing clinical understanding, refining surgical techniques, and elucidating the origins of congenital abnormalities. Embryonic development of the craniofacial vasculature remains, however, under-exposed in the current literature. We imaged and created 3-dimensional (D) reconstructed images of the craniofacial arterial system from two early-stage human embryonic samples.

OBJECTIVE

The aim of this study was to investigate the vascular development of the craniofacial region in early-stage human embryos, with a focus on understanding the interplay between vascular development and orofacial morphogenesis.

MATERIALS AND METHODS

Reconstructions (3-D) were generated from high-resolution diffusible iodine-based contrast-enhanced computed tomography (diceCT) images, enabling visualization of the orofacial arterial system in human embryonic samples of Carnegie stages (CS) 14 and 18 from the Dutch Fetal Biobank, corresponding to weeks 7 and 8.5 of gestation.

RESULTS

From two human embryonic samples (ages CS 14 and 18), the vascular development of the orofacial region at two different stages of development was successfully stained with B-Lugol and imaged using a micro-computed tomography (micro-CT) scanner with resolutions of 2.5-μm and 9-μm voxel sizes, respectively. Additionally, educational 3-D reconstructions of the orofacial vascular system were generated using AMIRA 2021.2 software.

CONCLUSION

Micro-CT imaging is an effective strategy for high-resolution visualization of vascular development of the orofacial region in human embryonic samples. The generated interactive 3-D educational models facilitate better understanding of the development of orofacial structures.

Experimental research of different forms of autolyzed antigen-extracted allogeneic bone combined with vascular endothelial growth factor for the repair of bone defects

OBJECTIVE

To investigate the effect of different forms of autolyzed antigen-extracted allogeneic(AAA) bone combined with vascular endothelial growth factor (VEGF) on bone reconstruction.

METHOD

The AAA bone was made into a block and a granule shape, and mixed with VEGF to prepare VEGF bone. Establishment of rat calvarium defect animal model, it is divided into 5 groups. With block bone, granular bone, block VEGF bone, granular VEGF bone was implanted in the bone defect for repair as the experimental group. The defect area was evaluated by histological and CBCT analysis 4 weeks postoperatively.

RESULTS

Postoperative 4 weeks imaging results showed that there was no high-density shadow in the bone defect area of the blank group and the volume of high-density shadow in the bone defect area of the experimental group was different. Histological results showed that no osteoblasts were found in the blank group, and new bone was formed in the experimental group. The effect of bone formation in the granular bone was better than that in the block bone, and the amount of new bone formation in the VEGF bone group was higher than that of the single bone group.

CONCLUSION

Granular bone has a better osteogenesis effect than block bone. The effect of allogeneic bone combined with VEGF in promoting new bone formation in the area of the bone defect is better than that of allogeneic bone alone. These results provide a theoretical and practical basis for its further clinical application.

The association of microvascular disease and endothelial dysfunction with vertebral trabecular bone mineral density : The MESA study

Retinopathy and albuminuria are associated with hip fracture risk. We investigated whether these disorders and endothelial dysfunction (which underlies microvascular diseases) were associated with low trabecular bone density. No significant associations were found, suggesting that microvascular diseases are not related to fracture risk through low trabecular bone density.

PURPOSE

Microvascular diseases of the eye, kidney, and brain are associated with endothelial dysfunction and increased hip fracture risk. To explore the basis for higher hip fracture risk, we comprehensively examined whether markers of microvascular disease and/or endothelial dysfunction are related to trabecular bone mineral density (BMD), a proximate risk factor for osteoporotic fractures.

METHODS

Among 6814 participants in the Multi-Ethnic Study of Atherosclerosis study (MESA), we derived thoracic vertebral trabecular BMD from computed tomography of the chest and measured urine albumin to creatinine ratios (UACR), retinal arteriolar and venular widths, flow mediated dilation (FMD) of the brachial artery after 5 min of ischemia; and levels of five soluble endothelial adhesion markers (ICAM-1, VCAM-1, L-selectin, P-selectin, and E-selectin). Linear regression models were used to examine the association of trabecular BMD with markers of microvascular disease and with markers of endothelial dysfunction.

RESULTS

We observed no significant associations of UACR, retinal arteriolar or venular widths, or FMD with BMD. We also observed no statistically significant association of spine trabecular BMD with levels of endothelial adhesion markers. Men and women had largely similar results.

CONCLUSION

We conclude that there is little evidence to connect thoracic spine trabecular BMD to microvascular disorders or to endothelial dysfunction among multi-ethnic middle-aged and older adults. Other factors beyond trabecular BMD (e.g., bone quality or predisposition to falling) may be responsible for the associations of microvascular disease with osteoporotic fractures.

3D-printed silicate porous bioceramics promoted the polarization of M2-macrophages that enhanced the angiogenesis in bone regeneration

The failure of bone regeneration has been considered as a serious problem that troubling patients for decades, most of which was resulted by the poor angiogenesis and chronic inflammation after surgery. Among multiple materials applied in the repair of bone defect, silicate bioceramics attracted researchers because of its excellent bioactivity. The purpose of this study was to detect the effect of specific bioactive glass ceramic (AP40, based on crystalline phases of apatite and wollastonite) on angiogenesis and the subsequent bone growth through the modulation of macrophages. Two groups were included in this study: control group (macrophages without any stimulation, denominated as Control) and AP40 group (macrophages incubated on AP40). This study investigated the effect of AP40 on macrophages polarization (RAW264.7) and angiogenesis in vitro and in vivo. Additionally, the changes of angiogenic ability regulated by macrophages were explored. AP40 showed excellent angiogenesis potential and the expression of CD31 was promoted through the modulation of macrophages toward M2 subtype. Additionally, the macrophages incubated on AP40 synthesized more PDGF-BB comparing to macrophages without any stimulation, which contributed to the improved angiogenetic ability of human umbilical vein endothelial cells (HUVECs). Results of in vivo studies indicated increased bone ingrowth along the implants, which indicated the potential of bioceramics for bone defect repair clinically.

Exploring versatile applications of a vacuum-assisted bone harvester in orthopedic surgery

BACKGROUND

Orthopedic procedures often require removing bone or pathological tissue, with traditional methods involving instruments like curettes and rongeurs. However, these methods can be time-consuming and lead to increased blood loss. To mitigate these side effects, vacuum-assisted tools have been developed to aid in tissue removal. These devices enable surgeons to suction tissue without discarding it, potentially improving outcomes in conditions such as osteomyelitis or tumor removal while enabling collection of the material for downstream applications. Despite limited research, vacuum-assisted devices show promise beyond bone marrow harvesting. This study assesses infection and clearance rates, estimated blood loss, and total procedure time associated with the use of vacuum-assisted tissue removal, with a goal to understand if these devices can be used for tissue removal across a variety of pathologic conditions.

METHODS

A retrospective cohort study was conducted on patients undergoing orthopedic procedures with the Avitus® Bone Harvester repurposed from its original design from December 1, 2021, to July 1, 2023. Procedures were categorized into oncology, and debridement for infection cases. Infection cases were further categorized into those secondary to trauma and those involving primary infections (osteomyelitis and periprosthetic joint infection). Clinical variables, including demographics, intraoperative details, complications, and follow-up, were reviewed. Statistical analysis included descriptive statistics computed with R Studio.

RESULTS

The study included 44 patients, with debridement for infection cases being the most common (primary infection: 45.5%; infection secondary to trauma: 18.1%), followed by oncology cases (36.4%). In all oncology cases, a definitive diagnosis was established using the device, and no post-operative infections were reported. The infection clearance rate was 85.0% for primary infection cases and 50.0% for cases of infection following trauma. Across the entire cohort, the average blood loss was 314.52 mL (sd: 486.74), and the average total procedure time was 160.93 min (sd: 91.07). The overall reoperation rate was 47.7%, with an unplanned reoperation rate of 11.4%.

CONCLUSION

The vacuum-assisted bone harvester was effectively utilized in a wide range of debridement and curettage procedures across diverse orthopedic surgeries. In oncology cases, the device enabled effective tissue removal with comparable recurrence rates, demonstrating its potential to minimize contamination while preserving tissue for accurate diagnoses. Additionally, a high rate of osteomyelitis eradication was observed in debridement for primary infection cases (85%). Despite the relatively high reoperation rate of 47.7%, it is crucial to interpret this figure within the context of the varied reasons for reoperation. Many of these reoperations were planned as part of a staged approach to treatment or were unrelated to the device's performance. It is crucial to acknowledge that isolating the device's contribution to these results can be difficult. The utilization of the device should be guided by considerations of cost-effectiveness and patient-specific risk factors.

Calcium Phosphates: A Key to Next-Generation In Vitro Bone Modeling

The replication of bone physiology under laboratory conditions is a prime target behind the development of in vitro bone models. The model should be robust enough to elicit an unbiased response when stimulated experimentally, giving reproducible outcomes. In vitro bone tissue generation majorly requires the availability of cellular components, the presence of factors promoting cellular proliferation and differentiation, efficient nutrient supply, and a supporting matrix for the cells to anchor - gaining predefined topology. Calcium phosphates (CaP) are difficult to ignore while considering the above requirements of a bone model. Therefore, the current review focuses on the role of CaP in developing an in vitro bone model addressing the prerequisites of bone tissue generation. Special emphasis is given to the physico-chemical properties of CaP that promote osteogenesis, angiogenesis and provide sufficient mechanical strength for load-bearing applications. Finally, the future course of action is discussed to ensure efficient utilization of CaP in the in vitro bone model development field.

Hydrogel Use in Osteonecrosis of the Femoral Head

Osteonecrosis of the femoral head (ONFH) is a vascular disease of unknown etiology and can be categorized mainly into two types: non-traumatic and traumatic ONFH. Thus, understanding osteogenic-angiogenic coupling is of prime importance in finding a solution for the treatment of ONFH. Hydrogels are biomaterials that are similar to the extracellular matrix (ECM). As they are able to mimic real tissue, they meet one of the most important rules in tissue engineering. In ONFH studies, hydrogels have recently become popular because of their ability to retain water and their adjustable properties, injectability, and mimicry of natural ECM. Because bone regeneration and graft materials are very broad areas of research and ONFH is a complex situation including bone and vascular systems, and there is no settled treatment strategy for ONFH worldwide, in this review paper, we followed a top-down approach by reviewing (1) bone and bone grafting, (2) hydrogels, (3) vascular systems, and (4) ONFH and hydrogel use in ONFH with studies in the literature which show promising results in limited clinical studies. The aim of this review paper is to provide the reader with general information on every aspect of ONFH and to focus on the hydrogel used in ONFH.

Neuronal regulation of bone and tendon injury repair: a focused review

Beyond the sensation of pain, peripheral nerves have been shown to play crucial roles in tissue regeneration and repair. As a highly innervated organ, bone can recover from injury without scar formation, making it an interesting model in which to study the role of nerves in tissue regeneration. As a comparison, tendon is a musculoskeletal tissue that is hypo-innervated, with repair often resulting in scar formation. Here, we reviewed the significance of innervation in 3 stages of injury repair (inflammatory, reparative, and remodeling) in 2 commonly injured musculoskeletal tissues: bone and tendon. Based on this focused review, we conclude that peripheral innervation is essential for phases of proper bone and tendon repair, and that nerves may dynamically regulate the repair process through interactions with the injury microenvironment via a variety of neuropeptides or neurotransmitters. A deeper understanding of neuronal regulation of musculoskeletal repair, and the crosstalk between nerves and the musculoskeletal system, will enable the development of future therapies for tissue healing.

Enhanced vascularization and osseointegration under osteoporotic conditions through functional peptide coating on implant surfaces

Patients with osteoporosis face challenges such as decreased bone density, a sparse trabecular structure, weakened osteogenic ability, and impaired angiogenesis, leading to poor osseointegration and implant failure. Surface modification of implants with biologically active molecules possessing various functions is an effective strategy to improve osseointegration. In this study, we constructed a simple multifunctional coating interface that significantly improves osseointegration. In brief, a multifunctional coating interface was constructed by coupling the Rgd adhesive peptide, Ogp osteogenic peptide, and Ang angiogenic peptide to Lys6 (k6), which self-assembled layer by layer with TA to form the (TA-Rgd@ogp@ang)n composite membrane. This study characterized the surface morphology and biomechanical properties of the coating under both gas and liquid phases and monitored the deposition process and reaction rate of the two peptides with TA using a quartz crystal microbalance. Moreover, (TA-Rgd@ogp@ang)n exhibited a triple synergistic effect on cell migration and adhesion, osteogenic differentiation, and angiogenesis. It also ameliorated the high ROS environment characteristic of osteoporosis pathology, promoted angiogenic bone defect regeneration in osteoporosis, thereby avoiding poor osseointegration. This work provides a new approach for the prevention of implant failure in pathological environments by constructing multifunctional coatings on implants, with tremendous potential applications in the fields of orthopedics and dentistry.

Polyphosphate Nanoparticles: Balancing Energy Requirements in Tissue Regeneration Processes

Nanoparticles of a particular, evolutionarily old inorganic polymer found across the biological kingdoms have attracted increasing interest in recent years not only because of their crucial role in metabolism but also their potential medical applicability: it is inorganic polyphosphate (polyP). This ubiquitous linear polymer is composed of 10-1000 phosphate residues linked by high-energy anhydride bonds. PolyP causes induction of gene activity, provides phosphate for bone mineralization, and serves as an energy supplier through enzymatic cleavage of its acid anhydride bonds and subsequent ATP formation. The biomedical breakthrough of polyP came with the development of a successful fabrication process, in depot form, as Ca- or Mg-polyP nanoparticles, or as the directly effective polymer, as soluble Na-polyP, for regenerative repair and healing processes, especially in tissue areas with insufficient blood supply. Physiologically, the platelets are the main vehicles for polyP nanoparticles in the circulating blood. To be biomedically active, these particles undergo coacervation. This review provides an overview of the properties of polyP and polyP nanoparticles for applications in the regeneration and repair of bone, cartilage, and skin. In addition to studies on animal models, the first successful proof-of-concept studies on humans for the healing of chronic wounds are outlined.

Possible role of annexin A1/FPR2 pathway in COX2/NLRP3 inflammasome regulation in alveolar bone cells of estrogen-deficient female rats with diabetes mellitus

BACKGROUND

Annexin A1 (ANXA1) and the NOD-like receptor family pyrin domain-containing protein 3 (NLRP3) inflammasome play important roles in bone remodeling. However, expression profiles of these factors in bone cells under diabetes mellitus (DM) and estrogen-deficient conditions are poorly understood. This study investigated the immunoexpression of ANXA1 and its formyl peptide receptor 2 (FPR2), as well as NLRP3 inflammasome mediators, during remodeling of the alveolar process in diabetic and estrogen-deficient rats.

METHODS

Twenty adult female Wistar rats were divided into four groups (n = 5): Sham-operated (SHAM) and ovariectomized (OVX) rats received a vehicle solution, and SHAM and OVX rats were intraperitoneally administered 60 mg/kg/body weight (BW) of streptozotocin (STZ) to induce DM (SHAM-Di and OVX-Di groups). After 7 weeks, the rats were euthanized and their maxillae were fixed in phosphate-buffered 4% formaldehyde and embedded in paraffin. Sections were stained with hematoxylin/eosin (H&E) and picrosirius red or subjected to immunohistochemical detection of ANXA1, FPR2, NLRP3, interleukin-1β (IL-1β), and cyclooxygenase-2 (COX2).

RESULTS

Estrogen deficiency and DM were associated with deleterious effects in bone tissue, as evidenced by a lower number of osteocytes and higher number of empty lacunae in the SHAM-Di and OVX-Di groups compared to the nondiabetic groups. Both diabetic groups showed a smaller vascular area and weaker collagen fiber birefringence intensity in alveolar bone tissue. A significantly higher number of ANXA1/FPR2-positive osteoblasts, osteocytes, and osteoclasts was accompanied by a significantly higher number of these cells immunolabeled for COX2, NLRP3, and IL-1β in the diabetic and OVX groups, especially in both estrogen-deficient and diabetic rats.

CONCLUSION

These results indicate a possible role for the ANXA1/FPR2 pathway as a fine-tuning/anti-inflammatory regulator to counterbalance exacerbated COX2/NLRP3/IL-1β activation in bone cells during bone remodeling under estrogen deficiency and DM.

Multilevel neurium-mimetic individualized graft via additive manufacturing for efficient tissue repair

Complicated peripheral nerve injuries or defects, especially at branching sites, remain a prominent clinical challenge after the application of different treatment strategies. Current nerve grafts fail to match the expected shape and size for delicate and precise branched nerve repair on a case-by-case basis, and there is a lack of geometrical and microscale regenerative navigation. In this study, we develop a sugar painting-inspired individualized multilevel epi-/peri-/endoneurium-mimetic device (SpinMed) to customize natural cues, featuring a selectively protective outer sheath and an instructive core, to support rapid vascular reconstruction and consequent efficient neurite extension along the defect area. The biomimetic perineurium dictates host-guest crosslinking in which new vessels secrete multimerin 1 binding to the fibroin filler surface as an anchor, contributing to the biological endoneurium that promotes Schwann cell homing and remyelination. SpinMed implantation into rat sciatic nerve defects yields a satisfactory outcome in terms of structural reconstruction, with sensory and locomotive function restoration. We further customize SpinMed grafts based on anatomy and digital imaging, achieving rapid repair of the nerve trunk and branches superior to that achieved by autografts and decellularized grafts in a specific beagle nerve defect model, with reliable biosafety. Overall, this intelligent art-inspired biomimetic design offers a facile way to customize sophisticated high-performance nerve grafts and holds great potential for application in translational regenerative medicine.

Salidroside: A Promising Agent in Bone Metabolism Modulation

Rhodiola rosea, a long-lived herbaceous plant from the Crassulaceae group, contains the active compound salidroside, recognized as an adaptogen with significant therapeutic potential for bone metabolism. Salidroside promotes osteoblast proliferation and differentiation by activating critical signaling pathways, including bone morphogenetic protein-2 and adenosine monophosphate-activated protein kinase, essential for bone formation and growth. It enhances osteogenic activity by increasing alkaline phosphatase activity and mineralization markers, while upregulating key regulatory proteins including runt-related transcription factor 2 and osterix. Additionally, salidroside facilitates angiogenesis via the hypoxia-inducible factor 1-alpha and vascular endothelial growth factor pathway, crucial for coupling bone development with vascular support. Its antioxidant properties offer protection against bone loss by reducing oxidative stress and promoting osteogenic differentiation through the nuclear factor erythroid 2-related factor 2 pathway. Salidroside has the capability to counteract the negative effects of glucocorticoids on bone cells and prevents steroid-induced osteonecrosis. Additionally, it exhibits multifaceted anti-inflammatory actions, notably through the inhibition of tumor necrosis factor-alpha and interleukin-6 expression, while enhancing the expression of interleukin-10. This publication presents a comprehensive review of the literature on the impact of salidroside on various aspects of bone tissue metabolism, emphasizing its potential role in the prevention and treatment of osteoporosis and other diseases affecting bone physiology.

Fabricating vascularized, anatomically accurate bone grafts using 3D bioprinted sectional bone modules, in-situ angiogenesis, BMP-2 controlled release, and bioassembly

Bone grafting is the most common treatment for repairing bone defects. However, current bone grafting methods have several drawbacks. Bone tissue engineering emerges as a promising solution to these problems. An ideal engineered bone graft should exhibit high mechanical strength, osteogenic properties, and pre-vascularization. Both top-down (using bulk scaffold) and bottom-up (using granular modules) approaches face challenges in fulfilling these requirements. In this paper, we propose a novel sectional modular bone approach to construct osteogenic, pre-vascularized bone grafts in anatomical shapes. We 3D-printed a series of rigid, thin, sectional, porous scaffolds from a biodegradable polymer, tailored to the dimensions of a femur bone shaft. These thin sectional modules promote efficient nutrition and waste removal due to a shorter diffusion distance. The modules were pre-vascularized viain-situangiogenesis, achieved through endothelial cell sprouting from the scaffold struts. Angiogenesis was further enhanced through co-culture with bioprinted fibroblast microtissues, which secreted pre-angiogenic growth factors. Sectional modules were assembled around a porous rod incorporated with Bone Morphogenetic Protein-2 (BMP-2), which released over 3 weeks, demonstrating sustained osteogenic activity. The assembled scaffold, in the anatomical shape of a human femur shaft, was pre-vascularized, osteogenic, and possessed high mechanical strength, supporting 12 times the average body weight. The feasibility of implanting the assembled bone graft was demonstrated using a 3D-printed femur bone defect model. Our method provides a novel modular engineering approach for regenerating tissues that require high mechanical strength and vascularization.

Osteostaticytes: A novel osteoclast subset couples bone resorption and bone formation

Background

Osteomyelitis (OM) is an inflammatory condition of bone characterized by cortical bone devascularization and necrosis. Dysregulation of bone remodelling is triggered by OM. Bone remodelling is precisely coordinated by bone resorption and formation via a reversal phase. However, the cellular and molecular mechanisms underlying bone remodelling failure after osteomyelitis remain elusive.

Methods

To elucidate the cellular and molecular mechanism underlying bone healing after osteomyelitis, we employed single-cell RNA sequencing (scRNA-seq) to depict the atlas of human cortical bone in normal, infected and reconstructed states. Dimensionality reduction by t-stochastic neighbourhood embedding (t-SNE) and graph-based clustering were applied to analyse the detailed clusters of osteoclast lineages. After trajectory analysis of osteoclast lineages over pseudotime, real-time PCR and immunofluorescence (IF) staining were applied to identify marker gene expression of various osteoclast lineages in the osteoclast induction model and human bone sections, respectively. The potential function and communication of osteoclasts were analysed via gene set enrichment analysis (GSEA) and CellChat. The chemotactic ability of mesenchymal stem cells (MSCs) and osteoclast lineage cells in various differentiation states was determined by transwell assays and coculture assays. The effects of various osteoclast lineages on the osteogenic differentiation potential of MSCs were also determined by using this coculture system. A normal mouse tibia fracture model and an osteomyelitis-related tibia fracture model were generated via injection of luciferase-labelled Staphylococcus aureus to verify the relationships between a novel osteoclast lineage and MSCs. Then, the infection was detected by a bioluminescence imaging system. Finally, immunofluorescence staining was used to detect the expression of markers of MSCs and novel osteoclast lineages in different remodelling phases in normal and infected bone remodelling models.

Results

In this study, we constructed a cell atlas encompassing normal, infected, and reconstructed cortical bone. Then, we identified a novel subset at the earlier stage of the osteoclast lineage that exhibited increased expression of IDO1, CCL3, and CCL4. These IDO1highCCL3highCCL4high cells, termed osteostaticytes (OSCs), were further regarded as the reservoir of osteoclasts in the reversal phase. Notably, OSCs exhibited the highest chemotactic activity, surpassing other lineage subsets. We also discovered that cells at the earlier stage of the osteoclast lineage play a significant role in recruiting mesenchymal stem cells (MSCs). Finally, the data revealed that OSCs might be positively related to the occurrence of bone MSCs and the contribution of bone remodelling.

Conclusion

Collectively, our findings revealed a novel stage (OSC) within the osteoclast lineage, potentially representing elusive bone reversal cells due to its increased chemotactic ability towards MSCs and potential contribution to bone remodelling. This study provides valuable insights into the intricate mechanisms of the reversal phase during bone remodelling and unveils potential therapeutic strategies for diseases associated with bone uncoupling.

Translational potential of this article

This study identified a new subset, referred to as IDO1(plus symbol) CCL3(plus symbol) CCL4(plus symbol) osteostaticytes which displayed the highest chemotactic activity among all osteoclast lineages and may serve as reversal cells in bone remodelling. These findings offer new insights and insights for understanding bone reversal-related diseases and may serve as novel therapeutic targets for conditions such as osteomyelitis and delayed bone healing.

An injectable and coagulation-independent Tetra-PEG hydrogel bioadhesive for post-extraction hemostasis and alveolar bone regeneration

Effective control of post-extraction hemorrhage and alveolar bone resorption is critical for successful extraction socket treatment, which remains an unmet clinical challenge. Herein, an injectable Tetra-PEG hydrogel that possesses rapid gelation, firm tissue adhesion, high mechanical strength, suitable degradability, and excellent biocompatibility is developed as a sutureless and coagulation-independent bioadhesive for the management of extraction sockets. Our results demonstrate that the rapid and robust adhesive sealing of the extraction socket by the Tetra-PEG hydrogel can provide reliable protection for the underlying wound and stabilize blood clots to facilitate tissue healing. In vivo experiments using an anticoagulated rat tooth extraction model show that the hydrogel significantly outperformed clinically used cotton and gelatin sponge in hemostatic efficacy, wound closure, alveolar ridge preservation, and in situ alveolar bone regeneration. Histomorphological evaluations reveal the mechanisms for accelerated bone repair through suppressed long-term inflammation, elevated collagen deposition, higher osteoblast activity, and enhanced angiogenesis. Together, our study highlights the clinical potential of the developed injectable Tetra-PEG hydrogel for treating anticoagulant-related post-extraction hemorrhage and improving socket healing.

Arterial Perfusion of the Proximal Phalanx Revisited: New Insights Based on Micro-Computed Tomography

PURPOSE

To characterize the periosteal and endosteal arterial perfusion of the proximal phalanx using micro-computed tomography angiography (micro-CTA).

METHODS

Cadaveric upper extremities were injected with a barium sulfate/gelatin suspension. Phalanges were imaged using micro-CTA and analyzed with a focus on osseous arterial anatomy. Periosteal and endosteal perfusion was characterized by number of vessels, length, anatomic course, and caliber.

RESULTS

The base of the proximal phalanx had a significantly greater number (8.0 ± 3.5) of periosteal vessels than those of the shaft (4.1 ± 1.6) and head (1.3 ± 1.1). One-third (34.4%) of the specimens demonstrated a complete absence of periosteal vessels in the head. A nutrient endosteal vessel was noted in 100% of the specimens. Entering at the junction of the middle and distal third of the bone (25.8 ± 3.9 mm from base), the nutrient vessel entered the proximal phalanx of the index finger along its ulnar aspect (8 of 8 specimens), the middle finger along its radial aspect (6 of 8), the ring finger along its ulnar aspect (5 of 8), and the little finger along its radial aspect (7 of 8). The nutrient vessel branched into proximal and distal extensions toward the shaft and head, respectively, with an average endosteal length of 10.7 ± 5.2 mm and average diameter of 0.36 ± 0.11 mm.

CONCLUSIONS

Periosteal contributions to the perfusion of the proximal phalanx appear to diminish distally. The endosteal arterial anatomy remains consistent, with a single nutrient vessel entering the intramedullary canal with reliable laterality on each digit. This is often the only vessel supplying the head of the proximal phalanx, making this area particularly susceptible to vascular compromise.

CLINICAL RELEVANCE

An understanding of the patterns of perfusion of the proximal phalanx provides some insight into clinically observed pathology, as well as guidance for operative management.

The role of lipid metabolism in osteoporosis: Clinical implication and cellular mechanism

In recent years, researchers have become focused on the relationship between lipids and bone metabolism balance. Moreover, many diseases related to lipid metabolism disorders, such as nonalcoholic fatty liver disease, atherosclerosis, obesity, and menopause, are associated with osteoporotic phenotypes. It has been clinically observed in humans that these lipid metabolism disorders promote changes in osteoporosis-related indicators bone mineral density and bone mass. Furthermore, similar osteoporotic phenotype changes were observed in high-fat and high-cholesterol-induced animal models. Abnormal lipid metabolism (such as increased oxidized lipids and elevated plasma cholesterol) affects bone microenvironment homeostasis via cross-organ communication, promoting differentiation of mesenchymal stem cells to adipocytes, and inhibiting commitment towards osteoblasts. Moreover, disturbances in lipid metabolism affect the bone metabolism balance by promoting the secretion of cytokines such as receptor activator of nuclear factor-kappa B ligand by osteoblasts and stimulating the differentiation of osteoclasts. Conclusively, this review addresses the possible link between lipid metabolism disorders and osteoporosis and elucidates the potential modulatory mechanisms and signaling pathways by which lipid metabolism affects bone metabolism balance. We also summarize the possible approaches and prospects of intervening lipid metabolism for osteoporosis treatment.

Magnesium malate-modified calcium phosphate bone cement promotes the repair of vertebral bone defects in minipigs via regulating CGRP

Active artificial bone substitutes are crucial in bone repair and reconstruction. Calcium phosphate bone cement (CPC) is known for its biocompatibility, degradability, and ability to fill various shaped bone defects. However, its low osteoinductive capacity limits bone regeneration applications. Effectively integrating osteoinductive magnesium ions with CPC remains a challenge. Herein, we developed magnesium malate-modified CPC (MCPC). Incorporating 5% magnesium malate significantly enhances the compressive strength of CPC to (6.18 ± 0.49) MPa, reduces setting time and improves disintegration resistance. In vitro, MCPC steadily releases magnesium ions, promoting the proliferation of MC3T3-E1 cells without causing significant apoptosis, proving its biocompatibility. Molecularly, magnesium malate prompts macrophages to release prostaglandin E2 (PGE2) and synergistically stimulates dorsal root ganglion (DRG) neurons to synthesize and release calcitonin gene-related peptide (CGRP). The CGRP released by DRG neurons enhances the expression of the key osteogenic transcription factor Runt-related transcription factor-2 (RUNX2) in MC3T3-E1 cells, promoting osteogenesis. In vivo experiments using minipig vertebral bone defect model showed MCPC significantly increases the bone volume fraction, bone density, new bone formation, and proportion of mature bone in the defect area compared to CPC. Additionally, MCPC group exhibited significantly higher levels of osteogenesis and angiogenesis markers compared to CPC group, with no inflammation or necrosis observed in the hearts, livers, or kidneys, indicating its good biocompatibility. In conclusion, MCPC participates in the repair of bone defects in the complex post-fracture microenvironment through interactions among macrophages, DRG neurons, and osteoblasts. This demonstrates its significant potential for clinical application in bone defect repair.

Copper-based carbon dots modified hydrogel with osteoimmunomodulatory and osteogenesis for bone regeneration

Biomaterials with dual functions of osteoimmunomodulation and bone repair are very promising in the field of orthopedic materials. For this purpose, we prepared copper-based carbon dots (CuCDs) and doped them into oxychondroitin sulfate/poly-acrylamide hydrogel (OPAM) to obtain a hybrid hydrogel (CuCDs/OPAM). We evaluated its osteoimmunomodulatory and bone repair properties in vitro and in vivo. The obtained CuCDs/OPAM exhibited good rBMSCs-cytocompatibility and anti-inflammatory properties in vitro. It also could effectively promote rBMSCs differentiation and the expression of osteogenic differentiation factors from rBMSCs under an inflammatory environment. Moreover, CuCDs/OPAM could induce macrophage phenotype switching (from M1-type macrophages to M2-type macrophages) in vivo, which is beneficial for anti-inflammatory action and presents good osteoimmunomodulation capability to induce a bone immune microenvironment to promote the differentiation of rBMSCs. In conclusion, CuCDs/OPAM hydrogel has dual functions of osteoimmunomodulatory and bone repair and is a promising bone filling and repair material.

The Masquelet induced membrane technique with PRP-FG-nHA/PA66 scaffold can heal a rat large femoral bone defect

BACKGROUND

Masquelet membrane induction technology is one of the treatment strategies for large bone defect (LBD). However, the angiogenesis ability of induced membrane decreases with time and autologous bone grafting is associated with donor site morbidity. This study investigates if the PRP-FG-nHA/PA66 scaffold can be used as a spacer instead of PMMA to improve the angiogenesis ability of induced membrane and reduce the amount of autologous bone graft.

METHODS

Platelet rich plasma (PRP) was prepared and PRP-FG-nHA/PA66 scaffold was synthesized and observed. The sustained release of VEGFA and porosity of the scaffold were analyzed. We established a femur LBD model in male SD rats. 55 rats were randomly divided into four groups depending on the spacer filled in the defect area. "Defect only" group (n = 10), "PMMA" group (n = 15), "PRP-nHA/PA66" group (n = 15) and "PRP-FG-nHA/PA66" group (n = 15 ). At 6 weeks, the spacers were removed and the defects were grafted. The induced membrane and bone were collected and stained. The bone formation was detected by micro-CT and the callus union was scored on a three point system.

RESULTS

The PRP-FG-nHA/PA66 scaffold was porosity and could maintain a high concentration of VEGFA after 30 days of preparation. The induced membrane in PRP-FG-nHA/PA66 group was thinner than PMMA, but the vessel density was higher.The weight of autogenous bone grafted in PRP-FG-nHA/PA66 group was significantly smaller than that of PMMA group. In PRP-FG-nHA/PA66 group, the bone defect was morphologically repaired.

CONCLUSION

The study showed that PRP-FG-nHA/PA66 scaffold can significantly reduce the amount of autologous bone graft, and can achieve similar bone defect repair effect as PMMA. Our findings provide some reference and theoretical support for the treatment of large segmental bone defects in humans.

Effect of M2-macrophage treated lymphatic endothelial cells on angiogenesis that promoted osteointegration

Early vascularization plays an essential role during the whole process in bone regeneration because of the function of secreting cytokines, transporting nutrients and metabolic wastes. As the preliminary basis of bone repair, angiogenesis is regulated by immune cells represented by macrophages to a great extent. However, with the discovery of the endolymphatic circulation system inside bone tissue, the role of vascularization became complicated and confusing. Herein, we developed a macrophage/lymphatic endothelial cells (LECs)/human umbilical vein endothelial cells (HUVECs) co-culture system to evaluate the effect of macrophage treated lymphatic endothelial cells on angiogenesis in vitro and in vivo. In this study, we collected the medium from macrophage (CM) for LECs culture. We found that CM2 could promote the expression of LECs markers and migration ability, which indicated the enhanced lymphogenesis. In addition, the medium from LECs was collected for culturing HUVECs. The CM2-treated LECs showed superior angiogenesis property including the migration capacity and expression of angiogenetic markers, which suggested the superior vascularization. Rat femoral condyle defect model was applied to confirm the hypothesis in vivo. Generally, M2-macrophage treated LECs showed prominent angiogenetic potential coupling with osteogenesis.

Additive manufacturing of degradable metallic scaffolds for material-structure-driven diabetic maxillofacial bone regeneration

The regeneration of maxillofacial bone defects associated with diabetes mellitus remains challenging due to the occlusal loading and hyperglycemia microenvironment. Herein, we propose a material-structure-driven strategy through the additive manufacturing of degradable Zn-Mg-Cu gradient scaffolds. The in situ alloying of Mg and Cu endows Zn alloy with admirable compressive strength for mechanical support and uniform degradation mode for preventing localized rupture. The scaffolds manifest favorable antibacterial, angiogenic, and osteogenic modulation capacity in mimicked hyperglycemic microenvironment, and Mg and Cu promote osteogenic differentiation in the early and late stages, respectively. In addition, the scaffolds expedite diabetic maxillofacial bone ingrowth and regeneration by combining the metabolic regulation effect of divalent metal cations and the hyperboloid and suitable permeability of the gradient structure. RNA sequencing further reveals that RAC1 might be involved in bone formation by regulating the transport and uptake of glucose related to GLUT1 in osteoblasts, contributing to cell function recovery. Inspired by bone healing and structural cues, this study offers an essential understanding of the designation and underlying mechanisms of the material-structure-driven strategy for diabetic maxillofacial bone regeneration.

Tissue-Penetrating Ultrasound-Triggered Hydrogel for Promoting Microvascular Network Reconstruction

The microvascular network plays an important role in providing nutrients to the injured tissue and exchanging various metabolites. However, how to achieve efficient penetration of the injured tissue is an important bottleneck restricting the reconstruction of microvascular network. Herein, the hydrogel precursor solution can efficiently penetrate the damaged tissue area, and ultrasound triggers the release of thrombin from liposomes in the solution to hydrolyze fibrinogen, forming a fibrin solid hydrogel network in situ with calcium ions and transglutaminase as catalysts, effectively solving the penetration impedance bottleneck of damaged tissues and ultimately significantly promoting the formation of microvascular networks within tissues. First, the fibrinogen complex solution is effectively permeated into the injured tissue. Second, ultrasound triggered the release of calcium ions and thrombin, activates transglutaminase, and hydrolyzes fibrinogen. Third, fibrin monomers are catalyzed to form fibrin hydrogels in situ in the damaged tissue area. In vitro studies have shown that the fibrinogen complex solution effectively penetrated the artificial bone tissue within 15 s after ultrasonic triggering, and formed a hydrogel after continuous triggering for 30 s. Overall, this innovative strategy effectively solved the problem of penetration resistance of ultrasound-triggered hydrogels in the injured tissues, and finally activates in situ microvascular networks regeneration.

Hydrogel loaded with bone marrow stromal cell-derived exosomes promotes bone regeneration by inhibiting inflammatory responses and angiogenesis

BACKGROUND

Bone healing is a complex process involving early inflammatory immune regulation, angiogenesis, osteogenic differentiation, and biomineralization. Fracture repair poses challenges for orthopedic surgeons, necessitating the search for efficient healing methods.

AIM

To investigate the underlying mechanism by which hydrogel-loaded exosomes derived from bone marrow mesenchymal stem cells (BMSCs) facilitate the process of fracture healing.

METHODS

Hydrogels and loaded BMSC-derived exosome (BMSC-exo) gels were characterized to validate their properties. In vitro evaluations were conducted to assess the impact of hydrogels on various stages of the healing process. Hydrogels could recruit macrophages and inhibit inflammatory responses, enhance of human umbilical vein endothelial cell angiogenesis, and promote the osteogenic differentiation of primary cranial osteoblasts. Furthermore, the effect of hydrogel on fracture healing was confirmed using a mouse fracture model.

RESULTS

The hydrogel effectively attenuated the inflammatory response during the initial repair stage and subsequently facilitated vascular migration, promoted the formation of large vessels, and enabled functional vascularization during bone repair. These effects were further validated in fracture models.

CONCLUSION

We successfully fabricated a hydrogel loaded with BMSC-exo that modulates macrophage polarization and angiogenesis to influence bone regeneration.

The tardigrade-derived mitochondrial abundant heat soluble protein improves adipose-derived stem cell survival against representative stressors

Human adipose-derived stem cell (ASC) grafts have emerged as a powerful tool in regenerative medicine. However, ASC therapeutic potential is hindered by stressors throughout their use. Here we demonstrate the transgenic expression of the tardigrade-derived mitochondrial abundant heat soluble (MAHS) protein for improved ASC resistance to metabolic, mitochondrial, and injection shear stress. In vitro, MAHS-expressing ASCs demonstrate up to 61% increased cell survival following 72 h of incubation in phosphate buffered saline containing 20% media. Following up to 3.5% DMSO exposure for up to 72 h, a 14-49% increase in MAHS-expressing ASC survival was observed. Further, MAHS expression in ASCs is associated with up to 39% improved cell viability following injection through clinically relevant 27-, 32-, and 34-gauge needles. Our results reveal that MAHS expression in ASCs supports survival in response to a variety of common stressors associated with regenerative therapies, thereby motivating further investigation into MAHS as an agent for stem cell stress resistance. However, differentiation capacity in MAHS-expressing ASCs appears to be skewed in favor of osteogenesis over adipogenesis. Specifically, activity of the early bone formation marker alkaline phosphatase is increased by 74% in MAHS-expressing ASCs following 14 days in osteogenic media. Conversely, positive area of the neutral lipid droplet marker BODIPY is decreased by up to 10% in MAHS-transgenic ASCs following 14 days in adipogenic media. Interestingly, media supplementation with up to 40 mM glucose is sufficient to restore adipogenic differentiation within 14 days, prompting further analysis of mechanisms underlying interference between MAHS and differentiation processes.

An Injectable Black Phosphorus Hydrogel for Rapid Tooth Extraction Socket Healing

The excess production of reactive oxygen species (ROS) will delay tooth extraction socket (TES) healing. In this study, we developed an injectable thermosensitive hydrogel (NBP@BP@CS) used to treat TES healing. The hydrogel formulation incorporated black phosphorus (BP) nanoflakes, recognized for their accelerated alveolar bone regeneration and ROS-scavenging properties, and dl-3-n-butylphthalide (NBP), a vasodilator aimed at enhancing angiogenesis. In vivo investigations strongly demonstrated that NBP@BP@CS improved TES healing due to antioxidation and promotion of alveolar bone regeneration by BP nanoflakes. The sustained release of NBP from the hydrogel promoted neovascularization and vascular remodeling. Our results demonstrated that the designed thermosensitive hydrogel provided great opportunity not only for ROS elimination but also for the promotion of osteogenesis and angiogenesis, reflecting the "three birds with one stone" concept, and has tremendous potential for rapid TES healing.

Hydrogel-Based Systems in Neuro-Vascularized Bone Regeneration: A Promising Therapeutic Strategy

Blood vessels and nerve fibers are distributed throughout the skeletal tissue, which enhance the development and function of each other and have an irreplaceable role in bone formation and remodeling. Despite significant progress in bone tissue engineering, the inadequacy of nerve-vascular network reconstruction remains a major limitation. This is partly due to the difficulty of integrating and regulating multiple tissue types with artificial materials. Thus, understanding the anatomy and underlying coupling mechanisms of blood vessels and nerve fibers within bone to further develop neuro-vascularized bone implant biomaterials is an extremely critical aspect in the field of bone regeneration. Hydrogels have good biocompatibility, controllable mechanical characteristics, and osteoconductive and osteoinductive properties, making them important candidates for research related to neuro-vascularized bone regeneration. This review reports the classification and physicochemical properties of hydrogels, with a focus on the application advantages and status of hydrogels for bone regeneration. The authors also highlight the effect of neurovascular coupling on bone repair and regeneration and the necessity of achieving neuro-vascularized bone regeneration. Finally, the recent progress and design strategies of hydrogel-based biomaterials for neuro-vascularized bone regeneration are discussed.

Bone remodelling prediction using mechanical stimulus with bone connectivity theory in porous implants

Strain energy density (SED) is considered to be the primary remodelling stimulus influencing the process of bone growth into porous implants. A bone remodelling algorithm incorporating the concept of bone connectivity, that newly formed bone should only grow from existing bone, was developed to provide a more biologically realistic simulation of bone growth. Results showed that the new algorithm prevented the occurrence of unconnected mature bone within porous implants, an unrealistic phenomenon observed using conventional adaptive elasticity theories. The bone connectivity algorithm had minimal effect (0.67% difference) on the final bone density distribution for standard bending and torsional moment cases. For a porous implant model, both algorithms, with and without bone connectivity implementation, reached the same final stiffness, with a difference of less than 0.01%. The bone connectivity algorithm predicted a slower and more gradual bone remodelling process, requiring at least 50% additional time for full remodelling compared to the conventional adaptive elasticity algorithm, which should be accounted for in the planning of rehabilitation strategies. The developed modelling can be employed to improve porous implant designs to achieve better clinical outcomes.

Vascular study of decellularized porcine long bones: Characterization of a tissue engineering model

INTRODUCTION

Massive bone allografts enable the reconstruction of critical bone defects in numerous conditions (e.g. tumoral, infection or trauma). Unfortunately, their biological integration remains insufficient and the reconstruction may suffer from several postoperative complications. Perfusion-decellularization emerges as a tissue engineering potential solution to enhance osseointegration. Therefore, an intrinsic vascular study of this novel tissue engineering tool becomes essential to understand its efficacy and applicability.

MATERIAL AND METHODS

32 porcine long bones (humeri and femurs) were used to assess the quality of their vascular network prior and after undergoing a perfusion-decellularization protocol. 12 paired bones were used to assess the vascular matrix prior (N = 6) and after our protocol (N = 6) by immunohistochemistry. Collagen IV, Von Willebrand factor and CD31 were targeted then quantified. The medullary macroscopic vascular network was evaluated with 12 bones: 6 were decellularized and the other 6 were, as control, not treated. All 12 underwent a contrast-agent injection through the nutrient artery prior an angio CT-scan acquisition. The images were processed and the length of medullary vessels filled with contrast agent were measured on angiographic cT images obtained in control and decellularized bones by 4 independent observers to evaluate the vascular network preservation. The microscopic cortical vascular network was evaluated on 8 bones: 4 control and 4 decellularized. After injection of gelatinous fluorochrome mixture (calcein green), non-decalcified fluoroscopic microscopy was performed in order to assess the perfusion quality of cortical vascular lacunae.

RESULTS

The continuity of the microscopic vascular network was assessed with Collagen IV immunohistochemistry (p-value = 0.805) while the decellularization quality was observed through CD31 and Von Willebrand factor immunohistochemistry (p-values <0.001). The macroscopic vascular network was severely impaired after perfusion-decellularization; nutrient arteries were still patent but the amount of medullary vascular channels measured was significantly higher in the control group compared to the decellularized group (p-value <0.001). On average, the observers show good agreement on these results, except in the decellularized group where more inter-observer discrepancies were observed. The microscopic vascular network was observed with green fluoroscopic signal in almost every canals and lacunae of the bone cortices, in three different bone locations (proximal metaphysis, diaphysis and distal metaphysis).

CONCLUSION

Despite the aggressiveness of the decellularization protocol on medullary vessels, total porcine long bones decellularized by perfusion retain an acellular cortical microvascular network. By injection through the intact nutrient arteries, this latter vascular network can still be used as a total bone infusion access for bone tissue engineering in order to enhance massive bone allografts prior implantation.

Reconstruction of Segmental Bone Defect in Canine Tibia Model Utilizing Bi-Phasic Scaffold: Pilot Study

The reunion and restoration of large segmental bone defects pose significant clinical challenges. Conventional strategies primarily involve the combination of bone scaffolds with seeded cells and/or growth factors to regulate osteogenesis and angiogenesis. However, these therapies face inherent issues related to immunogenicity, tumorigenesis, bioactivity, and off-the-shelf transplantation. The biogenic micro-environment created by implanted bone grafts plays a crucial role in initiating the bone regeneration cascade. To address this, a highly porous bi-phasic ceramic synthetic bone graft, composed of hydroxyapatite (HA) and alumina (Al), was developed. This graft was employed to repair critical segmental defects, involving the creation of a 2 cm segmental defect in a canine tibia. The assessment of bone regeneration within the synthetic bone graft post-healing was conducted using scintigraphy, micro-CT, histology, and dynamic histomorphometry. The technique yielded pore sizes in the range of 230-430 μm as primary pores, 40-70 μm as secondary inner microchannels, and 200-400 nm as tertiary submicron surface holes. These three components are designed to mimic trabecular bone networks and to provide body fluid adsorption, diffusion, a nutritional supply, communication around the cells, and cell anchorage. The overall porosity was measured at 82.61 ± 1.28%. Both micro-CT imaging and histological analysis provided substantial evidence of robust bone formation and the successful reunion of the critical defect. Furthermore, an histology revealed the presence of vascularization within the newly formed bone area, clearly demonstrating trabecular and cortical bone formation at the 8-week mark post-implantation.

ALPL regulates pro-angiogenic capacity of mesenchymal stem cells through ATP-P2X7 axis controlled exosomes secretion

BACKGROUND

Early-onset bone dysplasia is a common manifestation of hypophosphatasia (HPP), an autosomal inherited disease caused by ALPL mutation. ALPL ablation induces prototypical premature bone ageing characteristics, resulting in impaired osteogenic differentiation capacity of human bone marrow mesenchymal stem cells (hBMMSCs). As angiogenesis is tightly coupled with osteogenesis, it also plays a necessary role in sustaining bone homeostasis. We have previously observed a decrease in expression of angiogenesis marker gene CD31 in the metaphysis of long bone in Alpl+/- mice. However, the role of ALPL in regulation of angiogenesis in bone has remained largely unknown.

METHODS

Exosomes derived from Normal and HPP hBMMSCs were isolated and identified by ultracentrifugation, transmission electron microscopy, and nanoparticle size measurement. The effects of ALPL on the angiogenic capacity of hBMMSCs from HPP patients were assessed by immunofluorescence, tube formation, wound healing and migration assay. exo-ELISA and Western Blot were used to evaluate the exosomes secretion of hBMMSCs from HPP, and the protein expression of VEGF, PDGFBB, Angiostatin and Endostatin in exosomes respectively.

RESULTS

We verified that ALPL ablation resulted in impaired pro-angiogenic capacity of hBMMSCs, accounting for reduced migration and tube formation of human umbilical vein endothelial cells, as the quantities and proteins composition of exosomes varied with ALPL expression. Mechanistically, loss of function of ALPL enhanced ATP release. Additional ATP, in turn, led to markedly elevated level of ATP receptor P2X7, which consequently promoted exosomes secretion, resulting in a decreased capacity to promote angiogenesis. Conversely, inhibition of P2X7 increased the angiogenic induction capacity by preventing excessive release of anti-angiogenic exosomes in ALPL deficient-hBMMSCs.

CONCLUSION

The ALPL-ATP axis regulates the pro-angiogenic ability of hBMMSCs by controlling exosomes secretion through the P2X7 receptor. Thus, P2X7 may be proved as an effective therapeutic target for accelerating neovascularization in ALPL-deficient bone defects.

Senescent-like macrophages mediate angiogenesis for endplate sclerosis via IL-10 secretion in male mice

Endplate sclerosis is a notable aspect of spine degeneration or aging, but the mechanisms remain unclear. Here, we report that senescent macrophages accumulate in the sclerotic endplates of lumbar spine instability (LSI) or aging male mouse model. Specifically, knockout of cdkn2a (p16) in macrophages abrogates LSI or aging-induced angiogenesis and sclerosis in the endplates. Furthermore, both in vivo and in vitro studies indicate that IL-10 is the primary elevated cytokine of senescence-related secretory phenotype (SASP). Mechanistically, IL-10 increases pSTAT3 in endothelial cells, leading to pSTAT3 directly binding to the promoters of Vegfa, Mmp2, and Pdgfb to encourage their production, resulting in angiogenesis. This study provides information on understanding the link between immune senescence and endplate sclerosis, which might be useful for therapeutic approaches.

Improved Biocompatibility and Angiogenesis of the Bone Titanium Scaffold through ERK1/2 Signaling Mediated by an Attached Strontium Element

The promotion of early osseointegration is crucial for the success of biomedical titanium implants. Physical and chemical modifications to the material surface can significantly compensate for the lack of biocompatibility and early osseointegration of the implant. In this study, we implanted strontium onto titanium plates and analyzed the effect of strontium-doped materials on angiogenesis and biocompatibility in the human bone structure. Our findings demonstrated that strontium-loaded titanium sheet materials effectively promote human umbilical vein endothelial cell (HUVEC) biocompatibility and vascular differentiation ability, as evidenced by proliferation-apoptosis assays, RT-qPCR for vascular neogenesis markers, ELISA for vascular endothelial growth factor (VEGF) levels, and nitric oxide (NO) analysis. Mechanism studies based on RNAseq and Western blotting analysis revealed that strontium can promote titanium material biocompatibility with HUVEC cells and vascular neovascularization ability by activating the extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway. Meanwhile, blocking the ERK1/2 signaling pathway could reverse the promotional effect of vascular formation. Overall, we have successfully fabricated a multifunctional biocompatible bone implant with better histocompatibility and angiogenesis compared to uncoated implants.

The bone-protective benefits of kaempferol combined with metformin by regulation of osteogenesis-angiogenesis coupling in OVX rats

This study was to investigate the potential mechanisms of treatment with metformin (Met) combined with kaempferol (Kae) against postmenopausal osteoporosis. Experiments were conducted in both ovariectomy (OVX)-induced osteoporosis rats and in vitro using RAW264.7 cells, MC3T3-E1 cells, and HUVECs. Results demonstrated the therapeutic effect of Met combined with Kae on osteoporosis. In vivo, Kae alone and in combination with Met treatments enhanced tibial trabecular microstructure, bone mineral density (BMD), and mechanical properties in OVX rats without causing hepatotoxicity and nephrotoxicity. It also reduced bone resorption markers (CTX-1 and TRAP) and increased the bone formation marker (PINP) level in the serum of OVX rats. The expression of bone resorption marker TRAP was reduced, while bone formation markers Runx2 and ALP were enhanced in the bone tissue of OVX rats. Furthermore, Met combined with Kae also promoted the expression of angiogenesis-related markers CD31 and VEGF in OVX rats. In vitro, MC3T3-E1s cells treated with Met combined with Kae showed higher expression of ALP, Runx2, and VEGF. Interestingly, the treatment did not directly promote HUVECs migration and angiogenesis, but enhanced osteoblast-mediated angiogenesis by upregulating VEGF levels. Additionally, Met combined with Kae treatment promoted VEGF secretion in MC3T3-E1, and activated the Notch intracelluar pathway by upregulating HES1 and HEY1 in HUVECs. Meantime, their stimulation on CD31 expression were inhibited by DAPT, a Notch signaling inhibitor. Overall, this study demonstrates the positive effects of Met combined with Kae on osteoporotic rats by promoting osteogenesis-angiogenesis coupling, suggesting their potential application in postmenopausal osteoporosis.

Zhuang-Gu-Fang intervenes vasculogenic and osteogenic coupling in GK rats through Notch1/Noggin/VEGF pathway

Background

Zhuang-Gu-Fang (ZGF) has been proved to treat osteoporosis in ovariectomized rats by increasing osteogenic related factors Leptin, Ghrelin and Peptide YY(PYY). However, the mechanism of ZGF in the treatment of diabetic osteoporosis (DOP) remains unclear. The aim of this study was to explore the therapeutic effect of ZGF on DOP and its potential molecular mechanism.

Methods

Using GK rats as models, the pharmacodynamic effects of ZGF on bone loss were evaluated by hematoxylin-eosin (H&E) staining and micro-computed.tomography (micro-CT). The expression levels of CD31 and endomucin (Emcn) were detected by immunofluorescence to assess the role of ZGF in angiogenic osteogenic coupling. Finally, real-time quantitative PCR (RT-PCR) and Western Blot (WB)were used to detect the expression levels of osteogenic and angiogenesis-related genes and proteins Notch1, Noggin and vascular endothelial growth factor (VEGF).

Results

Administration of ZGF demonstrated a significant mitigation of bone loss attributable to elevated glucose levels. H&E staining and micro-CT showed that ZGF notably improved the integrity of the trabecular and cortical bone microarchitecture. Moreover, ZGF was found to augment the density of type H vessels within the bone tissue, alongside elevating the expression levels of Osterix, a transcription factor pivotal for bone formation. Furthermore, our findings suggest that ZGF facilitates the activation of the Notch1/Noggin/VEGF pathway, indicating a potential mechanism through which ZGF exerts its osteoprotective effects.

Conclusion

Our results suggest that ZGF potentially facilitates the formation of type H vessels through the Notch1/Noggin/VEGF pathway. This action not only enhances angiogenic-osteogenic coupling but also contributes to the improvement of bone structure and density. Consequently, ZGF emerges as a promising therapeutic agent for the prevention and management of DOP, offering a novel approach by leveraging angiogenesis-dependent osteogenesis.

Sensory neuron transient receptor potential vanilloid-1 channel regulates angiogenesis through CGRP in vivo

Angiogenesis plays a key role in bone regeneration. The role of neurons of peripheral nerves involved in angiogenesis of bone defects needs to be explored. The transient receptor potential vanilloid 1 (TRPV1), a nociceptor of noxious stimuli, is expressed on sensory neurons. Apart from nociception, little is known about the role of sensory innervation in angiogenesis. Calcitonin gene-related peptide (CGRP), a neuropeptide secreted by sensory nerve terminals, has been associated with vascular regeneration. We characterized the reinnervation of vessels in bone repair and assessed the impact of TRPV1-CGRP signaling on early vascularization. We investigated the pro-angiogenic effect of neuronal TRPV1 in the mouse model of femur defect. Micro-CT analysis with Microfil® reagent perfusion demonstrated neuronal TRPV1 activation enhanced angiogenesis by increasing vessel volume, number, and thickness. Meanwhile, TRPV1 activation upregulated the mRNA and protein expression of vascular endothelial growth factor A (VEGF-A), cell adhesion molecule-1 (CD31), and CGRP. Immunostaining revealed the co-localization of TRPV1 and CGRP in dorsal root ganglia (DRG) sensory neurons. By affecting neuronal TRPV1 channels, the release of neuronal and local CGRP was controlled. We demonstrated that TRPV1 influenced on blood vessel development by promoting CGRP release from sensory nerve terminals. Our results showed that neuronal TRPV1 played a crucial role in regulating angiogenesis during bone repair and provided important clinical implications for the development of novel therapeutic approaches for angiogenesis.

Bone ingrowth into a porous structure is achieved by preceding fibrogenesis and vascularization

Porous structures are frequently used in surgical implants to strengthen the interlocking power produced by bone ingrowth. Therefore, we aimed to elucidate the mechanism underlying bone ingrowth into a porous structure accompanied by vascularization. A nonbioactive polyetheretherketone implant with a 3D-printed porous structure was prepared and implanted in a bone hole created in the tibias of rabbits. We observed bone ingrowth in the same individual specimens immediately and at 2, 4, 8, and 12 weeks post-implantation using in-vivo computed tomography (CT). Furthermore, a detailed evaluation with blood vessels of each specimen at 2, 4, and 12 weeks was performed with ex-vivo CT and histological specimen. Additional histological evaluation was performed using thin sections of an implant made with thermoplastic polyurethane having the same structure. As a result, the bone invasion began after four weeks, when the construction of fibrous tissue and the spread of new blood vessels within the voids matured. As the bone matured in the load-bearing area, new blood vessels outside the bone matrix regressed. This longitudinal evaluation study suggests that preceding fibrogenesis and vascularization may be key in developing bone ingrowth. STATEMENT OF SIGNIFICANCE: A porous structure is an essential structure for dental and orthopedic implants because it provides strong fixation through bone invasion. Although it was known that vascularization was involved in this, the details were not known. This in vivo study revealed that in order for bone ingrowth to begin, a preparatory period of approximately 4 weeks was required to establish blood flow inside and outside the implant. Furthermore, it was confirmed that by spreading the fibrous structure in advance, it has an advantageous effect on the migration of cells involved in the formation of bones and blood vessels. We pointed out that it is necessary to consider fibrogenesis and vascularization when creating future implants.

Dual siRNA-Loaded Cell Membrane Functionalized Matrix Facilitates Bone Regeneration with Angiogenesis and Neurogenesis

Vascularization and innervation play irreplaceable roles in bone regeneration and bone defect repair. However, the reconstruction of blood vessels and neural networks is often neglected in material design. This study aims to design a genetically functionalized matrix (GFM) and enable it to regulate angiogenesis and neurogenesis to accelerate the process of bone defect repair. The dual small interfering RNA (siRNA)-polyvinylimide (PEI) (siRP) complexes that locally knocked down soluble vascular endothelial growth factor receptor 1 (sFlt-1) and p75 neurotrophic factor receptor (p75NTR ) are prepared. The hybrid cell membrane (MM) loaded siRP is synthesized as siRNA@MMs to coat on polylactone (PCL) electrospun fibers for mimicking the natural bone matrix. The results indicates that siRNA@MMs could regulate the expression of vascular-related and neuro-related cytokines secreted by mesenchymal stem cells (MSCs). GFMs promote the expression of osteogenic differentiation through paracrine function in vitro. GFMs attenuates inflammation and promotes osseointegration by regulating the coupling of vascularization and innervation in vivo. This study uses the natural hybrid cell membrane to carry genetic material and assist in the vascularization and innervation function of two siRNA. The results present the significance of neuro-vascularized organoid bone and may provide a promising choice for the design of bone tissue engineering scaffold.

DLP fabrication of HA scaffold with customized porous structures to regulate immune microenvironment and macrophage polarization for enhancing bone regeneration

The immune microenvironment plays a pivotal role in osteoanagenesis. Biomaterials can modulate osteogenic efficacy by inducing specific local immune reactions. As 3D-printing technology advances, digital light projection printing has emerged as a promising method for creating large scale, high-precision biomaterial scaffolds. By adjusting the solid content and the sintering conditions during printing, the pore size of biomaterials can be meticulously controlled. Yet, the systematic influence of pore size on the immune microenvironment remains uncharted. We fabricated 3D-printed hydroxyapatite bioceramic scaffolds with three distinct pore sizes: 400 μm, 600 μm, and 800 μm. Our study revealed that scaffolds with a pore size of 600 μm promote macrophage M2 polarization, which is achieved by upregulating interferon-beta and HIF-1α production. When these materials were implanted subcutaneously in rats and within rabbit skulls, we observed that the 600 μm scaffolds notably improved the long-term inflammatory response, fostered vascular proliferation, and augmented new bone growth. This research paves the way for innovative therapeutic strategies for treating large segmental bone defects in clinical settings.

Cobalt-doped layered hydroxide coating on titanium implants promotes vascularization and osteogenesis for accelerated fracture healing

Angiogenesis at the fracture site plays crucial roles in the endogenous osteogenesis process and is a prerequisite for the efficient repair of implant fixed bone defects. To improve the peri-implant vascularization of titanium implant for accelerating defect healing, we developed a Co-doped Mg-Al layered hydroxide coating on the surface of titanium using hydrothermal reaction and then modified the surface with gallic acid (Ti-LDH/GA). Gallic acid coating enabled the sustained release of Co2+ and Mg2+ to the defect site over a month. Ti-LDH/GA treatment profoundly stimulated the angiogenic potential of endothelial cells by upregulating the vascularization regulators such as vascular endothelial growth factor VEGF) and hypoxia-inducible factor-1α (HIF-1α), leading to enhanced osteogenic capability of mesenchymal stem cells (MSCs). These pro-bone healing benefits were attributed to the synergistic effects of Co ions and Mg ions in promoting angiogenesis and new bone formation. These insights collectively suggested the potent pro-osteogenic effect of Ti-LDH/GA through leveraging peri-implant vascularization, offering a new approach for developing biofunctional titanium implants.

Diabetes and the Microvasculature of the Bone and Marrow

PURPOSE OF REVIEW

The purpose of this review is to highlight the evidence of microvascular dysfunction in bone and marrow and its relation to poor skeletal outcomes in diabetes mellitus.

RECENT FINDINGS

Diabetes mellitus is characterized by chronic hyperglycemia, which may lead to microangiopathy and macroangiopathy. Micro- and macroangiopathy have been diagnosed in Type 1 and Type 2 diabetes, coinciding with osteopenia, osteoporosis, enhanced fracture risk and delayed fracture healing. Microangiopathy has been reported in the skeleton, correlating with reduced blood flow and perfusion, vasomotor dysfunction, microvascular rarefaction, reduced angiogenic capabilities, and augmented vascular permeability. Microangiopathy within the skeleton may be detrimental to bone and manifest as, among other clinical abnormalities, reduced mass, enhanced fracture risk, and delayed fracture healing. More investigations are required to elucidate the various mechanisms by which diabetic microvascular dysfunction impacts the skeleton.

Poly(methyl methacrylate) in Orthopedics: Strategies, Challenges, and Prospects in Bone Tissue Engineering

Poly(methyl methacrylate) (PMMA) is widely used in orthopedic applications, including bone cement in total joint replacement surgery, bone fillers, and bone substitutes due to its affordability, biocompatibility, and processability. However, the bone regeneration efficiency of PMMA is limited because of its lack of bioactivity, poor osseointegration, and non-degradability. The use of bone cement also has disadvantages such as methyl methacrylate (MMA) release and high exothermic temperature during the polymerization of PMMA, which can cause thermal necrosis. To address these problems, various strategies have been adopted, such as surface modification techniques and the incorporation of various bioactive agents and biopolymers into PMMA. In this review, the physicochemical properties and synthesis methods of PMMA are discussed, with a special focus on the utilization of various PMMA composites in bone tissue engineering. Additionally, the challenges involved in incorporating PMMA into regenerative medicine are discussed with suitable research findings with the intention of providing insightful advice to support its successful clinical applications.

Pericytes as the Orchestrators of Vasculature and Adipogenesis

Pericytes (PCs) are located surrounding the walls of small blood vessels, particularly capillaries and microvessels. In addition to their functions in maintaining vascular integrity, participating in angiogenesis, and regulating blood flow, PCs also serve as a reservoir for multi-potent stem/progenitor cells in white, brown, beige, and bone marrow adipose tissues. Due to the complex nature of this cell population, the identification and characterization of PCs has been challenging. A comprehensive understanding of the heterogeneity of PCs may enhance their potential as therapeutic targets for metabolic syndromes or bone-related diseases. This mini-review summarizes multiple PC markers commonly employed in lineage-tracing studies, with an emphasis on their contribution to adipogenesis and functions in different adipose depots under diverse metabolic conditions.

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.

Bioceramic scaffolds with two-step internal/external modification of copper-containing polydopamine enhance antibacterial and alveolar bone regeneration capability

Magnesium-doped calcium silicate (CS) bioceramic scaffolds have unique advantages in mandibular defect repair; however, they lack antibacterial properties to cope with the complex oral microbiome. Herein, for the first time, the CS scaffold was functionally modified with a novel copper-containing polydopamine (PDA(Cu2+‍)) rapid deposition method, to construct internally modified (*P), externally modified (@PDA), and dually modified (*P@PDA) scaffolds. The morphology, degradation behavior, and mechanical properties of the obtained scaffolds were evaluated in vitro. The results showed that the CS*P@PDA had a unique micro-/nano-structural surface and appreciable mechanical resistance. During the prolonged immersion stage, the release of copper ions from the CS*P@PDA scaffolds was rapid in the early stage and exhibited long-term sustained release. The in vitro evaluation revealed that the release behavior of copper ions ascribed an excellent antibacterial effect to the CS*P@PDA, while the scaffolds retained good cytocompatibility with improved osteogenesis and angiogenesis effects. Finally, the PDA(Cu2+)-modified scaffolds showed effective early bone regeneration in a critical-size rabbit mandibular defect model. Overall, it was indicated that considerable antibacterial property along with the enhancement of alveolar bone regeneration can be imparted to the scaffold by the two-step PDA(Cu2+) modification, and the convenience and wide applicability of this technique make it a promising strategy to avoid bacterial infections on implants.

In vivo depiction of cortical bone vascularization with ultra-high resolution-CT and deep learning algorithm reconstruction using osteoid osteoma as a model

PURPOSE

The purpose of this study was to evaluate the ability to depict in vivo bone vascularization using ultra-high-resolution (UHR) computed tomography (CT) with deep learning reconstruction (DLR) and hybrid iterative reconstruction algorithm, compared to simulated conventional CT, using osteoid osteoma as a model.

MATERIALS AND METHODS

Patients with histopathologically proven cortical osteoid osteoma who underwent UHR-CT between October 2019 and October 2022 were retrospectively included. Images were acquired with a 1024 × 1024 matrix and reconstructed with DLR and hybrid iterative reconstruction algorithm. To simulate conventional CT, images with a 512 × 512 matrix were also reconstructed. Two radiologists (R1, R2) independently evaluated the number of blood vessels entering the nidus and crossing the bone cortex, as well as vessel identification and image quality with a 5-point scale. Standard deviation (SD) of attenuation in the adjacent muscle and that of air were used as image noise and recorded.

RESULTS

Thirteen patients with 13 osteoid osteomas were included. There were 11 men and two women with a mean age of 21.8 ± 9.1 (SD) years. For both readers, UHR-CT with DLR depicted more nidus vessels (11.5 ± 4.3 [SD] (R1) and 11.9 ± 4.6 [SD] (R2)) and cortical vessels (4 ± 3.8 [SD] and 4.3 ± 4.1 [SD], respectively) than UHR-CT with hybrid iterative reconstruction (10.5 ± 4.3 [SD] and 10.4 ± 4.6 [SD], and 4.1 ± 3.8 [SD] and 4.3 ± 3.8 [SD], respectively) and simulated conventional CT (5.3 ± 2.2 [SD] and 6.4 ± 2.5 [SD], 2 ± 1.2 [SD] and 2.4 ± 1.6 [SD], respectively) (P < 0.05). UHR-CT with DLR provided less image noise than simulated conventional CT and UHR-CT with hybrid iterative reconstruction (P < 0.05). UHR-CT with DLR received the greatest score and simulated conventional CT the lowest score for vessel identification and image quality.

CONCLUSION

UHR-CT with DLR shows less noise than UHR-CT with hybrid iterative reconstruction and significantly improves cortical bone vascularization depiction compared to simulated conventional CT.

Coxa Magna following treatment of developmental dysplasia of the hip: investigation for associated potential factors

Coxa Magna (CM) is defined as a condition in which the horizontal (transverse) diameter of the femoral head is larger on the affected side than on the intact side. CM can occur as a manifestation of avascular necrosis (AVN) following treatment for the developmental dysplasia of the hip (DDH). Alternatively, it can also be secondary to other hip disorders, such as Perthes' disease. This study aimed to determine the prevalence and indicators of CM and AVN of the femoral head that can be detected during follow-up in patients with unilateral DDH treated with closed reduction (CR) or open reduction (OR) surgery. The files of 143 patients treated for unilateral DDH between January 1997 and December 2017 were reviewed retrospectively. A total of 104 patients, including Group 1 ( n = 49) patients who underwent CR under general anesthesia and Group 2 ( n = 55) patients who underwent OR were included in the study. CM; It was considered as the case where the femoral head was 15% or more larger than the intact side. A total of 104 patients were followed up for 77.27 ± 13.96 months, with a mean age of 15.43 ± 7.76 months. When Group 1 and Group 2 were compared, there was no statistical difference in terms of sex, side, adductor tenotomy, and AVN ( P > 0.05). CM developed in 22.4% ( n = 11) of the patients in Group 1 and in 49.1% ( n = 27) in Group 2, and the difference was statistically significant ( P = 0.008). When the effect of independent variables on the development of CM is evaluated with the multivariate logistic regression model, the risk of developing CM is 3474 times higher in those who underwent iliopsoas tenotomy compared with those who did not. The primary outcome of this study is that CM is more frequent in patients treated with OR for DDH. CM may be a nonpathological condition that occurs in connection with iliopsoas tenotomy or surgical treatment. Prospective studies with a larger number of cases, designed to minimize confounding factors, are required.

Internal surface modification of additively manufactured macroporous TiAl6V4 biomimetic implants via a calciothermic reaction-based process and osteogenic in vivo responses

Three-dimensional macroporous titanium-aluminum-vanadium (TiAl6V4) implants produced by additive manufacturing (AM) can be grit blasted (GB) to yield microtextured exterior surfaces, with additional micro/nano-scale surface features provided by subsequent acid etching (AE). However, the line-of-sight nature of GB causes the topography of exterior GB + AE-modified surfaces to differ from internal GB-inaccessible surfaces. Previous in vitro studies using dense TiAl6V4 substrates indicated that a nonline-of-sight, calciothermic-reaction (CaR)-based process provided homogeneous osteogenic nanotextures on GB + AE surfaces, suggesting it could be used to achieve a homogeneous nanotopography on external and internal surfaces of macroporous AM constructs. Macroporous TiAl6V4 (3D) constructs were produced by direct laser melting and modified by GB + AE, with the CaR process then applied to 50% of constructs (3DCaR). The CaR process yielded nanoporous/nanorough internal surfaces throughout the macroporous constructs. Skeletally mature, male Sprague-Dawley rats were implanted with these constructs using a cranial on-lay model. Prior to implantation, a Cu++-free click hydrogel was applied to half of the constructs (3D + H, 3DCaR + H) to act as a challenge to osseointegration. Osseointegration was compared between the four implant groups (3D, 3DCaR, 3D + H, 3DCaR + H) at 4w. 3D + H implants exhibited lower bone volume (BV) and percent bone ingrowth (%BI) than the 3D implants. In contrast, osseointegrated 3DCaR + H implants had similar BV and %BI as the 3DCaR implants. Implant pull-off forces correlated with these results. In vitro analyses indicated that human bone marrow stromal cells (MSCs) exhibited enhanced production of osteoblast differentiation markers and factors associated with osteogenesis when grown on CaR-modified 3D substrates relative to control (TCPS) substrates. This work confirms that the CaR process provides osteogenic nanotextures on internal surfaces of macroporous 3D implants, and suggests that CaR-modified surfaces can promote osseointegration in cases where osteogenesis is impaired.

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.