The role of vascular endothelial growth factor in ossification

Growth factor-functionalized titanium implants for enhanced bone regeneration: A review

Titanium and titanium alloys are widely favored materials for orthopedic implants due to their exceptional mechanical properties and biological inertness. The additional benefit of sustained local release of bioactive substances further promotes bone tissue formation, thereby augmenting the osseointegration capacity of titanium implants and attracting increasing attention in bone tissue engineering. Among these bioactive substances, growth factors have shown remarkable osteogenic and angiogenic induction capabilities. Consequently, researchers have developed various physical, chemical, and biological loading techniques to incorporate growth factors into titanium implants, ensuring controlled release kinetics. In contrast to conventional treatment modalities, the localized release of growth factors from functionalized titanium implants not only enhances osseointegration but also reduces the risk of complications. This review provides a comprehensive examination of the types and mechanisms of growth factors, along with a detailed exploration of the methodologies used to load growth factors onto the surface of titanium implants. Moreover, it highlights recent advancements in the application of growth factors to the surface of titanium implants (Scheme 1). Finally, the review discusses current limitations and future prospects for growth factor-functionalized titanium implants. In summary, this paper presents cutting-edge design strategies aimed at enhancing the bone regenerative capacity of growth factor-functionalized titanium implants-a significant advancement in the field of enhanced bone regeneration.

Absence of E2f1 Negates Pro-osteogenic Impacts of p21 Absence

Loss of p21 leads to increased bone formation post-injury; however, the mechanism(s) by which this occurs remains undetermined. E2f1 is downstream of p21 and as a transcription factor can act directly on gene expression; yet it is unknown if E2f1 plays a role in the osteogenic effects observed when p21 is differentially regulated. In this study we aimed to investigate the interplay between p21 and E2f1 and determine if the pro-regenerative osteogenic effects observed with the loss of p21 are E2f1 dependent. To accomplish this, we employed knockout p21 and E2f1 mice and additionally generated a p21/E2f1 double knockout. These mice underwent burr-hole injuries to their proximal tibiae and healing was assessed over 7 days via microCT imaging. We found that p21 and E2f1 play distinct roles in bone regeneration where the loss of p21 increased trabecular bone formation and loss of E2f1 increased cortical bone formation, yet loss of E2f1 led to poorer bone repair overall. Furthermore, when E2f1 was absent, either individually or simultaneously with p21, there was a dramatic decrease of the number of osteoblasts, osteoclasts, and chondrocytes at the site of injury compared to p21-/- and C57BL/6 mice. Together, these results suggest that E2f1 regulates the cell populations required for bone repair and has a distinct role in bone formation/repair compared to p21-/-E2f1-/-. These results highlight the possibility of cell cycle and/or p21/E2f1 being potential druggable targets that could be leveraged in clinical therapies to improve bone healing in pathologies such as osteoporosis.

Bio-integrated scaffold facilitates large bone regeneration dominated by endochondral ossification

Repair of large bone defects caused by severe trauma, non-union fractures, or tumor resection remains challenging because of limited regenerative ability. Typically, these defects heal through mixed routines, including intramembranous ossification (IMO) and endochondral ossification (ECO), with ECO considered more efficient. Current strategies to promote large bone healing via ECO are unstable and require high-dose growth factors or complex cell therapy that cause side effects and raise expense while providing only limited benefit. Herein, we report a bio-integrated scaffold capable of initiating an early hypoxia microenvironment with controllable release of low-dose recombinant bone morphogenetic protein-2 (rhBMP-2), aiming to induce ECO-dominated repair. Specifically, we apply a mesoporous structure to accelerate iron chelation, this promoting early chondrogenesis via deferoxamine (DFO)-induced hypoxia-inducible factor-1α (HIF-1α). Through the delicate segmentation of click-crosslinked PEGylated Poly (glycerol sebacate) (PEGS) layers, we achieve programmed release of low-dose rhBMP-2, which can facilitate cartilage-to-bone transformation while reducing side effect risks. We demonstrate this system can strengthen the ECO healing and convert mixed or mixed or IMO-guided routes to ECO-dominated approach in large-size models with clinical relevance. Collectively, these findings demonstrate a biomaterial-based strategy for driving ECO-dominated healing, paving a promising pave towards its clinical use in addressing large bone defects.

SOXC are critical regulators of adult bone mass

Pivotal in many ways for human health, the control of adult bone mass is governed by complex, incompletely understood crosstalk namely between mesenchymal stem cells, osteoblasts and osteoclasts. The SOX4, SOX11 and SOX12 (SOXC) transcription factors were previously shown to control many developmental processes, including skeletogenesis, and SOX4 was linked to osteoporosis, but how SOXC control adult bone mass remains unknown. Using SOXC loss- and gain-of-function mouse models, we show here that SOXC redundantly promote prepubertal cortical bone mass strengthening whereas only SOX4 mitigates adult trabecular bone mass accrual in early adulthood and subsequent maintenance. SOX4 favors bone resorption over formation by lowering osteoblastogenesis and increasing osteoclastogenesis. Single-cell transcriptomics reveals its prevalent expression in Lepr+ mesenchymal cells and ability to upregulate genes for prominent anti-osteoblastogenic and pro-osteoclastogenic factors, including interferon signaling-related chemokines, contributing to these adult stem cells' secretome. SOXC, with SOX4 predominantly, are thus key regulators of adult bone mass.

Decellularized Bone Matrix/45S5 Bioactive Glass Biocomposite Hydrogel-Based Constructs with Angiogenic and Osteogenic Properties: Ex Ovo and Ex Vivo Evaluations

Decellularized extracellular matrix is often used to create an in vivo-like environment that supports cell growth and proliferation, as it reflects the micro/macrostructure and molecular composition of tissues. On the other hand, bioactive glasses (BG) are surface-reactive glass-ceramics that can convert to hydroxyapatite in vivo and promote new bone formation. This study is designed to evaluate the key properties of a novel angiogenic and osteogenic biocomposite graft made of bovine decellularized bone matrix (DBM) hydrogel and 45S5 BG microparticles (10 and 20 wt%) to combine the existing superior properties of both biomaterial classes. Morphological, physicochemical, mechanical, and thermal characterizations of DBM and DBM/BG composite hydrogels are performed. Their in vitro biocompatibility is confirmed by cytotoxicity and hemocompatibility analyses. Ex vivo chick embryo aortic arch and ex ovo chick chorioallantoic membrane (CAM) assays reveal that the present pro-angiogenic property of DBM hydrogels is enhanced by the incorporation of BG. Histochemical stainings (Alcian blue and Alizarin red) and digital image analysis of ossification on hind limbs of embryos used in the CAM model reveal the osteogenic potential of biomaterials. The findings support the notion that the developed DBM/BG composite hydrogel constructs have the potential to be a suitable graft for bone repair.

The association and underlying mechanism of the digit ratio (2D:4D) in hypospadias

ABSTRACT

The second-to-fourth digit (2D:4D) ratio is thought to be associated with prenatal androgen exposure. However, the relationship between the 2D:4D ratio and hypospadias is poorly understood, and its molecular mechanism is not clear. In this study, by analyzing the hand digit length of 142 boys with hypospadias (23 distal, 68 middle, and 51 proximal) and 196 controls enrolled in Shanghai Children's Hospital (Shanghai, China) from December 2020 to December 2021, we found that the 2D:4D ratio was significantly increased in boys with hypospadias (P < 0.001) and it was positively correlated with the severity of the hypospadias. This was further verified by the comparison of control mice and prenatal low testosterone mice model obtained by knocking out the risk gene (dynein axonemal heavy chain 8 [DNAH8]) associated with hypospadias. Furthermore, the discrepancy was mainly caused by a shift in 4D. Proteomic characterization of a mouse model validated that low testosterone levels during pregnancy can impair the growth and development of 4D. Comprehensive mechanistic explorations revealed that during the androgen-sensitive window, the downregulation of the androgen receptor (AR) caused by low testosterone levels, as well as the suppressed expression of chondrocyte proliferation-related genes such as Wnt family member 5a (Wnt5a), Wnt5b, Smad family member 2 (Smad2), and Smad3; mitochondrial function-related genes in cartilage such as AMP-activated protein kinase (AMPK) and nuclear respiratory factor 1 (Nrf-1); and vascular development-related genes such as myosin light chain (MLC), notch receptor 3 (Notch3), and sphingosine kinase 1 (Sphk1), are responsible for the limitation of 4D growth, which results in a higher 2D:4D ratio in boys with hypospadias via decreased endochondral ossification. This study indicates that the ratio of 2D:4D is a risk marker of hypospadias and provides a potential molecular mechanism.

Hypoxia modulates the phenotype of mechanically stressed endothelial cells responding to CoCr-enriched medium

Given the importance of the endothelial cell phenotype in dental peri-implant healing processes, the aim of this study was to better assess the involvement of endothelial cells responding to cobalt-chromium (CoCr)-enriched medium. Biologically, cobalt is widely used molecule to induce chemical experimental hypoxia because it stabilizes hypoxia inducible factors (HIF1α). The aplication of hypoxia models provides better experimental condition to allow its impact on cellular metabolism, by looking for biochemical and molecular issues. Thus, this study looks for understaing whether CoCr-based materials are able to modulate endothelial cells considering the hypoxic effect prmoted by cobalt. Firstly, our data shows there is a siginificant effect on endothelial phenotype by modulating the expression of VEGF and eNOS genes, whith low requirement of genes related with proteasome intracellular complex. Importantly, the data were validated using classical chemical modulators of hypoxia signaling [chrysin (5,7-dihydroxyflavone) and Dimethyloxalylglycine (DMOG)] in functional assays. Altogether, these data validate the hypothesis that hipoxya is important to maintain the phenotype of endothelial cells, and it is properly interesting during the tissue regeneration surrounding implants and so compromising osseointegration process. Finally, it is important to mention that the cobalt released from CoCr devices might contribute with an sufficient microenvironment surrounding implanted devices and it paviments new roads looking for more bioactive surfaces of implantable materials in human health.

A comparative analysis of the cytocompatibility, protein adsorption, osteogenic and angiogenic properties of the 45S5- and S53P4-bioactive glass compositions

Despite their long history of application in orthopedics, the osteogenic and angiogenic properties as well as the cytocompatibility and protein adsorption of the 45S5- (in wt%: 45.0 SiO2, 24.5 Na2O, 24.5 CaO, 6.0 P2O5) and S53P4- (in wt%: 53.0 SiO2, 23.0 Na2O, 20.0 CaO, 4.0 P2O5) bioactive glass (BG) compositions have not yet been directly compared in one and the same experimental setting. In this study, the influence of morphologically equal granules of both BGs on proliferation, viability, osteogenic differentiation and angiogenic response of human bone-marrow-derived mesenchymal stromal cells (BMSCs) was assessed. Furthermore, their impact on vascular tube formation and adsorption of relevant proteins was evaluated. Both BGs showed excellent cytocompatibility and stimulated osteogenic differentiation of BMSCs. The 45S5-BG showed enhanced stimulation of bone morphogenic protein 2 (BMP2) gene expression and protein production compared to S53P4-BG. While gene expression and protein production of vascular endothelial growth factor (VEGF) were stimulated, both BGs had only limited influence on tubular network formation. 45S5-BG adsorbed a higher portion of proteins, namely BMP2 and VEGF, on its surface. In conclusion, both BGs show favorable properties with slight advantages for 45S5-BG. Since protein adsorption on BG surfaces is important for their biological performance, the composition of the proteome formed by osteogenic cells cultured on BGs should be analyzed in order to gain a deeper understanding of the mechanisms that are responsible for BG-mediated stimulation of osteogenic differentiation.

Diagnosis and monitoring denosumab therapy of giant cell tumors of bone: radiologic-pathologic correlation

OBJECTIVE

To determine the value of CT and dynamic contrast-enhanced (DCE-)MRI for monitoring denosumab therapy of giant cell tumors of bone (GCTB) by correlating it to histopathology.

MATERIALS AND METHODS

Patients with GCTB under denosumab treatment and monitored with CT and (DCE-)MRI (2012-2021) were retrospectively included. Imaging and (semi-)quantitative measurements were used to assess response/relapse. Tissue samples were analyzed using computerized segmentation for vascularization and number of neoplastic and giant cells. Pearson's correlation/Spearman's rank coefficient and Kruskal-Wallis tests were used to assess correlations between histopathology and radiology.

RESULTS

Six patients (28 ± 8years; five men) were evaluated. On CT, good responders showed progressive re-ossification (+7.8HU/month) and cortical remodeling (woven bone). MRI showed an SI decrease relative to muscle on T1-weighted (-0.01 A.U./month) and on fat-saturated T2-weighted sequences (-0.03 A.U./month). Time-intensity-curves evolved from a type IV with high first pass, high amplitude, and steep wash-out to a slow type II. An increase in time-to-peak (+100%) and a decrease in Ktrans (-71%) were observed. This is consistent with microscopic examination, showing a decrease of giant cells (-76%), neoplastic cells (-63%), and blood vessels (-28%). There was a strong statistical significant inverse correlation between time-to-peak and microvessel density (ρ = -0.9, p = 0.01). Significantly less neoplastic (p = 0.03) and giant cells (p = 0.04) were found with a time-intensity curve type II, compared to a type IV. Two patients showed relapse after initial good response when stopping denosumab. Inverse imaging and pathological findings were observed.

CONCLUSION

CT and (DCE-)MRI show a good correlation with pathology and allow adequate evaluation of response to denosumab and detection of therapy failure.

Advances with Platelet-Rich Plasma for Bone Healing

Despite significant advances in the understanding and delivery of osteosynthesis, fracture non-union remains a challenging clinical problem in orthopaedic surgery. To bridge the gap, basic science characterization of fracture healing provides a platform to identify and target biological strategies to enhance fracture healing. Of immense interest, Platelet-rich plasma (PRP) is a point of care orthobiologic that has been extensively studied in bone and soft tissue healing given its relative ease of translation from the benchtop to the clinic. The aim of this narrative review is to describe and relate pre-clinical in-vitro and in-vivo findings to clinical observations investigating the efficacy of PRP to enhance bone healing for primary fracture management and non-union treatment. A particular emphasis is placed on the heterogeneity of PRP preparation techniques, composition, activation strategies, and delivery. In the context of existing data, the routine use of PRP to enhance primary fracture healing and non-union management cannot be supported. However, it is acknowledged that extensive heterogeneity of PRP treatments in clinical studies adds obscurity; ultimately, refinement (and consensus) of PRP treatments for specific clinical indications, including repetition studies are warranted.

Serum TNF-α level and probing depth as a combined indicator for peri-implant disease

Peri-implant disease (PID) is a general term for inflammatory diseases of soft and hard tissues that occur around implants, including peri-implant mucositis and peri-implantitis. Cytokines are a class of small molecule proteins, which have various functions such as regulating innate immunity, adaptive immunity, and repairing damaged tissues. In order to explore the characteristics and clinical significance of tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-10, and tumor growth factor (TGF)-β1 expression levels in serum of patients with peri-implant disease, 31 patients with PID and 31 patients without PID were enrolled. The modified plaque index (mPLI), modified sulcus bleeding index (mSBI), and peri-implant probing depth (PD) were recorded. The levels of serum TNF-α, IL-6, IL-10, and TGF-β1 were detected by ELISA. TNF-α, mPLI, mSBI, and PD levels were significantly higher in the PID group. TGF-β1 levels were significantly higher in the control group. There was a significant positive correlation between TNF-α and mPLI, mSBI, and PD. TGF-β1 was negatively associated with TNF-α, mPLI, mSBI, and PD. Multiple logistic regression analysis showed that TNF-α and PD were risk factors for the severity of PID. The receiver operating curve analysis showed that high TNF-α levels (cut-off value of 140 pg/mL) and greater PD values (cut-off value of 4 mm) were good predictors of PID severity with an area under the curve of 0.922. These results indicated that TNF-α and PD can be used as a biological indicator for diagnosing the occurrence and progression of PID.

[Research progress on mechanism of traumatic brain injury promoting fracture healing]

Objective

To summarize the research progress on the mechanism related to traumatic brain injury (TBI) to promote fracture healing, and to provide theoretical basis for clinical treatment of fracture non-union.

Methods

The research literature on TBI to promote fracture healing at home and abroad was reviewed, the role of TBI in fracture healing was summarized from three aspects of nerves, body fluids, and immunity, to explore new ideas for the treatment of fracture non-union.

Results

Numerous studies have shown that fracture healing is faster in patients with fracture combined with TBI than in patients with simple fracture. It is found that the expression of various cytokines and hormones in the body fluids of patients with fracture and TBI is significantly higher than that of patients with simple fracture, and the neurofactors released by the nervous system reaches the fracture site through the damaged blood-brain barrier, and the chemotaxis and aggregation of inflammatory cells and inflammatory factors at the fracture end of patients with combined TBI also differs significantly from those of patients with simple fracture. A complex network of humoral, neural, and immunomodulatory networks together promote regeneration of blood vessels at the fracture site, osteoblasts differentiation, and inhibition of osteoclasts activity.

Conclusion

TBI promotes fracture healing through a complex network of neural, humoral, and immunomodulatory, and can treat fracture non-union by intervening in the perifracture microenvironment.

VEGF Secretion Drives Bone Formation in Classical MAP2K1+ Melorheostosis

Patients with classical melorheostosis exhibit exuberant bone overgrowth in the appendicular skeleton, resulting in pain and deformity with no known treatment. Most patients have somatic, mosaic mutations in MAP2K1 (encoding the MEK1 protein) in osteoblasts and overlying skin. As with most rare bone diseases, lack of affected tissue has limited the opportunity to understand how the mutation results in excess bone formation. The aim of this study was to create a cellular model to study melorheostosis. We obtained patient skin cells bearing the MAP2K1 mutation (affected cells), and along with isogenic control normal fibroblasts reprogrammed them using the Sendai virus method into induced pluripotent stem cells (iPSCs). Pluripotency was validated by marker staining and embryoid body formation. iPSCs were then differentiated to mesenchymal stem cells (iMSCs) and validated by flow cytometry. We confirmed retention of the MAP2K1 mutation in iMSCs with polymerase chain reaction (PCR) and confirmed elevated MEK1 activity by immunofluorescence staining. Mutation-bearing iMSCs showed significantly elevated vascular endothelial growth factor (VEGF) secretion, proliferation and collagen I and IV secretion. iMSCs were then differentiated into osteoblasts, which showed increased mineralization at 21 days and increased VEGF secretion at 14 and 21 days of differentiation. Administration of VEGF to unaffected iMSCs during osteogenic differentiation was sufficient to increase mineralization. Blockade of VEGF by bevacizumab reduced mineralization in iMSC-derived affected osteoblasts and in affected primary patient-derived osteoblasts. These data indicate that patient-derived induced pluripotent stem cells recreate the elevated MEK1 activity, increased mineralization, and increased proliferation seen in melorheostosis patients. The increased bone formation is driven, in part, by abundant VEGF secretion. Modifying the activity of VEGF (a known stimulator of osteoblastogenesis) represents a promising treatment pathway to explore. iPSCs may have wide applications to other rare bone diseases. © 2023 American Society for Bone and Mineral Research (ASBMR).

A Molecular Troika of Angiogenesis, Coagulopathy and Endothelial Dysfunction in the Pathology of Avascular Necrosis of Femoral Head: A Comprehensive Review

Avascular necrosis of the femoral head (ANFH) is a painful disorder characterized by the cessation of blood supply to the femoral head, leading to its death and subsequent joint collapse. Influenced by several risk factors, including corticosteroid use, excessive alcohol intake, hypercholesterolemia, smoking and some inflammatory disorders, along with cancer, its clinical consequences are thrombus formation due to underlying inflammation and endothelial dysfunction, which collaborates with coagulopathy and impaired angiogenesis. Nonetheless, angiogenesis resolves the obstructed free flow of the blood by providing alternative routes. Clinical manifestations of early stage of ANFH mimic cysts or lesions in subchondral bone, vasculitis and transient osteoporosis of the hip, rendering it difficult to diagnose, complex to understand and complicated to cure. To date, the treatment methods for ANFH are controversial as no foolproof curative strategy is available, and these depend upon different severity levels of the ANFH. From an in-depth understanding of the pathological determinants of ANFH, it is clear that impaired angiogenesis, coagulopathy and endothelial dysfunction contribute significantly. The present review has set two aims, firstly to examine the role and relevance of this molecular triad (impaired angiogenesis, coagulopathy and endothelial dysfunction) in ANFH pathology and secondly to propose some putative therapeutic strategies, delineating the fact that, for the better management of ANFH, a combined strategy to curtail this molecular triangle must be composed rather than focusing on individual contributions.

DNAzyme Nanoconstruct-Integrated Autonomously-Adaptive Coatings Enhance Titanium-Implant Osteointegration by Cooperative Angiogenesis and Vessel Remodeling

Orthopedic implants have a high failure rate due to insufficient interfacial osseointegration, especially under osteoporotic conditions. Type H vessels are CD31+EMCN+ capillaries with crucial roles in mediating new bone formation, but their abundance in osteoporotic fracture site is highly limited. Herein, we report a nanoengineered composite coating to improve the in situ osseointegration of a Ti implant for osteoporotic fracture repair, which is realized through inhibiting the stimulator of interferon genes (STING) in endothelial cells (ECs) to stimulate type H vessel formation. Autonomously catalytic DNAzyme-ZnO nanoflowers (DNFzns) were prepared through rolling circle amplification (RCA) of STING mRNA-degrading DNAzymes, which were then integrated on the Ti surface and further sequentially complexed with thioketal-bridged polydopamine and naringenin (Ti/DNFzn/PDA-Nar). ECs and mesenchymal stem cells (MSCs) can be recruited to the implant surface by galvanotaxis, accounting for the negative charges of DNFzn/PDA-Nar, subsequently released Nar under reactive oxygen species (ROS) stimulation to upregulate endothelial nitric oxide synthase (eNOS) in recruited ECs, leading to enhanced local angiogenesis. Meanwhile, the coordinately released DNFzns would abolish STING expression in ECs to transform the newly formed vessels into Type H vessels, thus substantially promoting the osseointegration of Ti implants. This study provides application prospects for improving implant osteointegration for osteoporotic fracture treatment.

Biofabrication of functional bone tissue: defining tissue-engineered scaffolds from nature

Damage to bone leads to pain and loss of movement in the musculoskeletal system. Although bone can regenerate, sometimes it is damaged beyond its innate capacity. Research interest is increasingly turning to tissue engineering (TE) processes to provide a clinical solution for bone defects. Despite the increasing biomimicry of tissue-engineered scaffolds, significant gaps remain in creating the complex bone substitutes, which include the biochemical and physical conditions required to recapitulate bone cells' natural growth, differentiation and maturation. Combining advanced biomaterials with new additive manufacturing technologies allows the development of 3D tissue, capable of forming cell aggregates and organoids based on natural and stimulated cues. Here, we provide an overview of the structure and mechanical properties of natural bone, the role of bone cells, the remodelling process, cytokines and signalling pathways, causes of bone defects and typical treatments and new TE strategies. We highlight processes of selecting biomaterials, cells and growth factors. Finally, we discuss innovative tissue-engineered models that have physiological and anatomical relevance for cancer treatments, injectable stimuli gels, and other therapeutic drug delivery systems. We also review current challenges and prospects of bone TE. Overall, this review serves as guide to understand and develop better tissue-engineered bone designs.

Layered Double Hydroxides: A Novel Promising 2D Nanomaterial for Bone Diseases Treatment

Bone diseases including bone defects, bone infections, osteoarthritis, and bone tumors seriously affect life quality of the patient and bring serious economic burdens to social health management, for which the current clinical treatments bear dissatisfactory therapeutic effects. Biomaterial-based strategies have been widely applied in the treatment of orthopedic diseases but are still plagued by deficient bioreactivity. With the development of nanotechnology, layered double hydroxides (LDHs) with adjustable metal ion composition and alterable interlayer structure possessing charming physicochemical characteristics, versatile bioactive properties, and excellent drug loading and delivery capabilities arise widespread attention and have achieved considerable achievements for bone disease treatment in the last decade. However, to the authors' best knowledge, no review has comprehensively summarized the advances of LDHs in treating bone disease so far. Herein, the advantages of LDHs for orthopedic disorders treatment are outlined and the corresponding state-of-the-art achievements are summarized for the first time. The potential of LDHs-based nanocomposites for extended therapeutics for bone diseases is highlighted and perspectives for LDHs-based scaffold design are proposed for facilitated clinical translation.

Extracorporeal shock wave treatment for post‑surgical fracture nonunion: Insight into its mechanism, efficacy, safety and prognostic factors (Review)

Post-surgical fracture nonunion (PSFN) represents the failure to achieve cortical continuity at radiological examination after an orthopedic operation, which causes a considerable disease burden in patients with fractures. As one of the traditional treatment modalities, surgical therapy is associated with a high fracture union rate; however, post-surgical complications are not negligible. Therefore, less invasive therapies are needed to improve the prognosis of patients with PSFN. Extracorporeal shock wave treatment (ESWT) is a noninvasive method that presents a similar efficacy profile and favorable safety profile compared with surgical treatment. However, the application and detailed mechanism of ESWT in patients with PSFN remain unclear. The present review focuses on the mechanism, efficacy, safety and prognostic factors of ESWT in patients with PSFN, aiming to provide a theoretical basis for its application and improve the prognosis of these patients.

Skeletal-Vascular Interactions in Bone Development, Homeostasis, and Pathological Destruction

Bone is a highly vascularized organ that not only plays multiple roles in supporting the body and organs but also endows the microstructure, enabling distinct cell lineages to reciprocally interact. Recent studies have uncovered relevant roles of the bone vasculature in bone patterning, morphogenesis, homeostasis, and pathological bone destruction, including osteoporosis and tumor metastasis. This review provides an overview of current topics in the interactive molecular events between endothelial cells and bone cells during bone ontogeny and discusses the future direction of this research area to find novel ways to treat bone diseases.

Anatomy, molecular structures, and hyaluronic acid - Gelatin injectable hydrogels as a therapeutic alternative for hyaline cartilage recovery: A review

Cartilage damage caused by trauma or osteoarthritis is a common joint disease that can increase the social and economic burden in society. Due to its avascular characteristics, the poor migration ability of chondrocytes, and a low number of progenitor cells, the self-healing ability of cartilage defects has been significantly limited. Hydrogels have been developed into one of the most suitable biomaterials for the regeneration of cartilage because of its characteristics such as high-water absorption, biodegradation, porosity, and biocompatibility similar to natural extracellular matrix. Therefore, the present review article presents a conceptual framework that summarizes the anatomical, molecular structure and biochemical properties of hyaline cartilage located in long bones: articular cartilage and growth plate. Moreover, the importance of preparation and application of hyaluronic acid - gelatin hydrogels for cartilage tissue engineering are included. Hydrogels possess benefits of stimulating the production of Agc1, Col2α1-IIa, and SOX9, molecules important for the synthesis and composition of the extracellular matrix of cartilage. Accordingly, they are believed to be promising biomaterials of therapeutic alternatives to treat cartilage damage.

The roles of bone remodeling in normal hematopoiesis and age-related hematological malignancies

Prior research establishing that bone interacts in coordination with the bone marrow microenvironment (BMME) to regulate hematopoietic homeostasis was largely based on analyses of individual bone-associated cell populations. Recent advances in intravital imaging has suggested that the expansion of hematopoietic stem cells (HSCs) and acute myeloid leukemia cells is restricted to bone marrow microdomains during a distinct stage of bone remodeling. These findings indicate that dynamic bone remodeling likely imposes additional heterogeneity within the BMME to yield differential clonal responses. A holistic understanding of the role of bone remodeling in regulating the stem cell niche and how these interactions are altered in age-related hematological malignancies will be critical to the development of novel interventions. To advance this understanding, herein, we provide a synopsis of the cellular and molecular constituents that participate in bone turnover and their known connections to the hematopoietic compartment. Specifically, we elaborate on the coupling between bone remodeling and the BMME in homeostasis and age-related hematological malignancies and after treatment with bone-targeting approaches. We then discuss unresolved questions and ambiguities that remain in the field.

Molecular Biomarkers in Perthes Disease: A Review

BACKGROUND

Perthes disease is a juvenile form of osteonecrosis of the femoral head that affects children under the age of 15. One hundred years after its discovery, some light has been shed on its etiology and the biological factors relevant to its etiology and disease severity.

METHODS

The aim of this study was to summarize the literature findings on the biological factors relevant to the pathogenesis of Perthes disease, their diagnostic and clinical significance, and their therapeutic potential. A special focus on candidate genes as susceptibility factors and factors relevant to clinical severity was made, where studies reporting clinical or preclinical results were considered as the inclusion criteria. PubMed databases were searched by two independent researchers. Sixty-eight articles were included in this review. Results on the factors relevant to vascular involvement and inflammatory molecules indicated as factors that contribute to impaired bone remodeling have been summarized. Moreover, several candidate genes relevant to an active phase of the disease have been suggested as possible biological therapeutic targets.

CONCLUSIONS

Delineation of molecular biomarkers that underlie the pathophysiological process of Perthes disease can allow for the provision of earlier and more accurate diagnoses of the disease and more precise follow-ups and treatment in the early phases of the disease.

Targeting STING: From antiviral immunity to treat osteoporosis

The cGAS-STING signaling pathway can trigger innate immune responses by detecting dsDNA from outside or within the host. In addition, the cGAS-STING signaling pathway has emerged as a critical mediator of the inflammatory response and a new target for inflammatory diseases. STING activation leads to dimerization and translocation to the endoplasmic reticulum Golgi intermediate compartment or Golgi apparatus catalyzed by TBK1, triggers the production of IRF3 and NF-κB and translocates to the nucleus to induce a subsequent interferon response and pro-inflammatory factor production. Osteoporosis is a degenerative bone metabolic disease accompanied by chronic sterile inflammation. Activating the STING/IFN-β signaling pathway can reduce bone resorption by inhibiting osteoclast differentiation. Conversely, activation of STING/NF-κB leads to the formation of osteoporosis by increasing bone resorption and decreasing bone formation. In addition, activation of STING inhibits the generation of type H vessels with the capacity to osteogenesis, thereby inhibiting bone formation. Here, we outline the mechanism of action of STING and its downstream in osteoporosis and discuss the role of targeting STING in the treatment of osteoporosis, thus providing new ideas for the treatment of osteoporosis.

Tissue engineering in growth plate cartilage regeneration: Mechanisms to therapeutic strategies

The repair of growth plate injuries is a highly complex process that involves precise spatiotemporal regulation of multiple cell types. While significant progress has been made in understanding the pathological mechanisms underlying growth plate injuries, effectively regulating this process to regenerate the injured growth plate cartilage remains a challenge. Tissue engineering technology has emerged as a promising therapeutic approach for achieving tissue regeneration through the use of functional biological materials, seed cells and biological factors, and it is now widely applied to the regeneration of bone and cartilage. However, due to the unique structure and function of growth plate cartilage, distinct strategies are required for effective regeneration. Thus, this review provides an overview of current research on the application of tissue engineering to promote growth plate regeneration. It aims to elucidates the underlying mechanisms by which tissue engineering promotes growth plate regeneration and to provide novel insights and therapeutic strategies for future research on the regeneration of growth plate.

Comparison ofin-situversusex-situdelivery of polyethylenimine-BMP-2 polyplexes for rat calvarial defect repair via intraoperative bioprinting

Gene therapeutic applications combined with bio- and nano-materials have been used to address current shortcomings in bone tissue engineering due to their feasibility, safety and potential capability for clinical translation. Delivery of non-viral vectors can be altered using gene-activated matrices to improve their efficacy to repair bone defects.Ex-situandin-situdelivery strategies are the most used methods for bone therapy, which have never been directly compared for their potency to repair critical-sized bone defects. In this regard, we first time explore the delivery of polyethylenimine (PEI) complexed plasmid DNA encoding bone morphogenetic protein-2 (PEI-pBMP-2) using the two delivery strategies,ex-situandin-situdelivery. To realize these gene delivery strategies, we employed intraoperative bioprinting (IOB), enabling us to 3D bioprint bone tissue constructs directly into defect sites in a surgical setting. Here, we demonstrated IOB of an osteogenic bioink loaded with PEI-pBMP-2 for thein-situdelivery approach, and PEI-pBMP-2 transfected rat bone marrow mesenchymal stem cells laden bioink for theex-situdelivery approach as alternative delivery strategies. We found thatin-situdelivery of PEI-pBMP-2 significantly improved bone tissue formation compared toex-situdelivery. Despite debates amongst individual advantages and disadvantages ofex-situandin-situdelivery strategies, our results ruled in favor of thein-situdelivery strategy, which could be desirable to use for future clinical applications.

Ginsenoside Rg1 interferes with the progression of diabetic osteoporosis by promoting type H angiogenesis modulating vasculogenic and osteogenic coupling

Ginsenoside Rg1 (Rg1) has been demonstrated to have antidiabetic and antiosteoporotic activities. The aim of this study was to investigate the protective effect of Rg1 against diabetic osteoporosis and the underlying mechanism. In vitro, we found that Rg1 increased the number of osteoprogenitors and alleviated high glucose (HG) induced apoptosis of osteoprogenitors by MTT assays and flow cytometry. qRT‒PCR and western blot analysis suggested that Rg1 can also promote the secretion of vascular endothelial growth factor (VEGF) by osteoprogenitors and promote the coupling of osteogenesis and angiogenesis. Rg1 can also promote the proliferation of human umbilical vein endothelial cells (HUVECs) cultured in high glucose, enhance the angiogenic ability of endothelial cells, and activate the Notch pathway to promote endothelial cells to secrete the osteogenesis-related factor Noggin to regulate osteogenesis, providing further feedback coupling of angiogenesis and osteogenesis. Therefore, we speculated that Rg1 may have similar effects on type H vessels. We used the Goto-Kakizaki (GK) rat model to perform immunofluorescence staining analysis on two markers of type H vessels, Endomucin (Emcn) and CD31, and the osteoblast-specific transcription factor Osterix, and found that Rg1 stimulates type H angiogenesis and bone formation. In vivo experiments also demonstrated that Rg1 promotes VEGF secretion, activates the Noggin/Notch pathway, increases the level of coupling between type H vessels and osteogenesis, and improves the bone structure of GK rats. All of these data reveal that Rg1 is a promising candidate drug for treating diabetic osteoporosis as a potentially bioactive molecule that promotes angiogenesis and osteointegration coupling.

Hypoxia-Inducible Factors Signaling in Osteogenesis and Skeletal Repair

Sufficient oxygen is required to maintain normal cellular and physiological function, such as a creature’s development, breeding, and homeostasis. Lately, some researchers have reported that both pathological hypoxia and environmental hypoxia might affect bone health. Adaptation to hypoxia is a pivotal cellular event in normal cell development and differentiation and in pathological settings such as ischemia. As central mediators of homeostasis, hypoxia-inducible transcription factors (HIFs) can allow cells to survive in a low-oxygen environment and are essential for the regulation of osteogenesis and skeletal repair. From this perspective, we summarized the role of HIF-1 and HIF-2 in signaling pathways implicated in bone development and skeletal repair and outlined the molecular mechanism of regulation of downstream growth factors and protein molecules such as VEGF, EPO, and so on. All of these present an opportunity for developing therapies for bone regeneration.

Structural and Metabolic Changes in Bone

Simple Summary

Bone is an extremely metabolically active tissue that is regenerated and repaired over its lifetime by bone remodeling. Most bone diseases are caused by abnormal restructure processes that undermine bone structure and mechanical strength and trigger clinical symptoms, such as pain, deformity, fracture, and abnormalities of calcium and phosphate homoeostasis. The article examines the main aspects of bone development, anatomy, structure, and the mechanisms of cell and molecular regulation of bone remodeling.

Abstract

As an essential component of the skeleton, bone tissue provides solid support for the body and protects vital organs. Bone tissue is a reservoir of calcium, phosphate, and other ions that can be released or stored in a controlled manner to provide constant concentration in body fluids. Normally, bone development or osteogenesis occurs through two ossification processes (intra-articular and intra-chondral), but the first produces woven bone, which is quickly replaced by stronger lamellar bone. Contrary to commonly held misconceptions, bone is a relatively dynamic organ that undergoes significant turnover compared to other organs in the body. Bone metabolism is a dynamic process that involves simultaneous bone formation and resorption, controlled by numerous factors. Bone metabolism comprises the key actions. Skeletal mass, structure, and quality are accrued and maintained throughout life, and the anabolic and catabolic actions are mostly balanced due to the tight regulation of the activity of osteoblasts and osteoclasts. This activity is also provided by circulating hormones and cytokines. Bone tissue remodeling processes are regulated by various biologically active substances secreted by bone tissue cells, namely RANK, RANKL, MMP-1, MMP-9, or type 1 collagen. Bone-derived factors (BDF) influence bone function and metabolism, and pathophysiological conditions lead to bone dysfunction. This work aims to analyze and evaluate the current literature on various local and systemic factors or immune system interactions that can affect bone metabolism and its impairments.

Effects of Triiodothyronine on Human Osteoblast-Like Cells: Novel Insights From a Global Transcriptome Analysis

Background: Thyroid hormones play a significant role in bone development and maintenance, with triiodothyronine (T3) particularly being an important modulator of osteoblast differentiation, proliferation, and maintenance. However, details of the biological processes (BPs) and molecular pathways affected by T3 in osteoblasts remain unclear.

Methods: To address this issue, primary cultures of human adipose-derived mesenchymal stem cells were subjected to our previously established osteoinduction protocol, and the resultant osteoblast-like cells were treated with 1 nm or 10 nm T3 for 72 h. RNA sequencing (RNA-Seq) was performed using the Illumina platform, and differentially expressed genes (DEGs) were identified from the raw data using Kallisto and DESeq2. Enrichment analysis of DEGs was performed against the Gene Ontology Consortium database for BP terms using the R package clusterProfiler and protein network analysis by STRING.

Results: Approximately 16,300 genes were analyzed by RNA-Seq, with 343 DEGs regulated in the 1 nm T3 group and 467 upregulated in the 10 nm T3 group. Several independent BP terms related to bone metabolism were significantly enriched, with a number of genes shared among them (FGFR2, WNT5A, WNT3, ROR2, VEGFA, FBLN1, S1PR1, PRKCZ, TGFB3, and OSR1 for 1nM T3; and FZD1, SMAD6, NOG, NEO1, and ENG for 10 nm T3). An osteoblast-related search in the literature regarding this set of genes suggests that both T3 doses are unfavorable for osteoblast development, mainly hindering BMP and canonical and non-canonical WNT signaling.

Conclusions: Therefore, this study provides new directions toward the elucidation of the mechanisms of T3 action on osteoblast metabolism, with potential future implications for the treatment of endocrine-related bone pathologies.

In situ microenvironment remodeling using a dual-responsive system: photodegradable hydrogels and gene activation by visible light

A 3D microenvironment with dynamic cell-biomaterial interactions was developed using a dual-responsive system for in situ microenvironment remodeling and control of cellular function. A visible-light-responsive polymer was utilized to prepare a hydrogel with photodegradation properties, enabling in situ microenvironment remodeling. Additionally, a vascular endothelial growth factor (VEGF) gene activation unit that was responsive to the same wavelength of light was incorporated to support the potential application of the system in regenerative medicine. Following light exposure, the mechanical properties of the photodegradable hydrogel gradually deteriorated, and product analysis confirmed the degradation of the hydrogel, and thereby, 3D microenvironment remodeling. In situ microenvironment remodeling influenced stem cell proliferation and enlargement within the hydrogel. Furthermore, stem cells engineered to express light-activated VEGF and incorporated into the dual-responsive system were applied to wound healing and an ischemic hindlimb model, proving their potential application in regenerative medicine.

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

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

Mechanical forces couple bone matrix mineralization with inhibition of angiogenesis to limit adolescent bone growth

Bone growth requires a specialised, highly angiogenic blood vessel subtype, so-called type H vessels, which pave the way for osteoblasts surrounding these vessels. At the end of adolescence, type H vessels differentiate into quiescent type L endothelium lacking the capacity to promote bone growth. Until now, the signals that switch off type H vessel identity and thus limit adolescent bone growth have remained ill defined. Here we show that mechanical forces, associated with increased body weight at the end of adolescence, trigger the mechanoreceptor PIEZO1 and thereby mediate enhanced production of the kinase FAM20C in osteoblasts. FAM20C, the major kinase of the secreted phosphoproteome, phosphorylates dentin matrix protein 1, previously identified as a key factor in bone mineralization. Thereupon, dentin matrix protein 1 is secreted from osteoblasts in a burst-like manner. Extracellular dentin matrix protein 1 inhibits vascular endothelial growth factor signalling by preventing phosphorylation of vascular endothelial growth factor receptor 2. Hence, secreted dentin matrix protein 1 transforms type H vessels into type L to limit bone growth activity and enhance bone mineralization. The discovered mechanism may suggest new options for the treatment of diseases characterised by aberrant activity of bone and vessels such as osteoarthritis, osteoporosis and osteosarcoma.

Neuron-to-vessel signaling is a required feature of aberrant stem cell commitment after soft tissue trauma

The functional interdependence of nerves and blood vessels is a well-established concept during tissue morphogenesis, yet the role of neurovascular coupling in proper and aberrant tissue repair is an emerging field of interest. Here, we sought to define the regulatory relationship of peripheral nerves on vasculature in a severe extremity trauma model in mice, which results in aberrant cell fate and heterotopic ossification (HO). First, a high spatial degree of neurovascular congruency was observed to exist within extremity injury associated heterotopic ossification. Vascular and perivascular cells demonstrate characteristic responses to injury, as assessed by single cell RNA sequencing. This vascular response to injury was blunted in neurectomized mice, including a decrease in endothelial proliferation and type H vessel formation, and a downregulation of key transcriptional networks associated with angiogenesis. Independent mechanisms to chemically or genetically inhibit axonal ingrowth led to similar deficits in HO site angiogenesis, a reduction in type H vessels, and heterotopic bone formation. Finally, a combination of single cell transcriptomic approaches within the dorsal root ganglia identified key neural-derived angiogenic paracrine factors that may mediate neuron-to-vascular signaling in HO. These data provide further understanding of nerve-to-vessel crosstalk in traumatized soft tissues, which may reflect a key determinant of mesenchymal progenitor cell fate after injury.

Characterization of Dental Pulp Stem Cells Response to Bone Substitutes Biomaterials in Dentistry

Bone substitute biomaterials (BSBs) represent a promising alternative to bone autografts, due to their biocompatibility, osteoconduction, slow resorption rates, and the ability to define and maintain volume for bone gain in dentistry. Many biomaterials are tailored to provide structural and biological support for bone regeneration, and allow the migration of bone-forming cells into the bone defect. Neural crest-derived stem cells isolated from human dental pulp (hDPSCs) represent a suitable stem cell source to study the biological effects of BSBs on osteoprogenitor cells involved in the physiological bone regenerative processes. This study aimed to evaluate how three different BSBs affect the stem cell properties, osteogenic differentiation, and inflammatory properties of hDPSCs. Our data highlight that BSBs do not alter cell proliferation and stemness markers expression, nor induce any inflammatory responses. Bone metabolism data show that hDPSCs exposed to the three BSBs distinctively secrete the factors supporting osteoblast activity and osteoclast activity. Our data indicate that (i) hDPSCs are a suitable stem cell source to study the effects of BSBs, and that (ii) the formulation of BSBs may condition the biological properties of stem cells, suggesting their versatile suitability to different dentistry applications.

Impact of heterotopic ossification following lumbar total disk replacement: a systematic review

Background context

Lumbar total disc replacement (TDR) is an alternative to lumbar fusion in the treatment of lower back pain and reduces the risk of adjacent segment degeneration. Heterotopic ossification (HO) has been identified as a common complication following lumbar TDR.

Purpose

This systematic review aims to determine the prevalence, risk factors and clinical and radiological impact of HO following lumbar TDR.

Study Design

Systematic Review.

Methods

MEDLINE, Scopus, PubMed and Cochrane Central were searched for articles that referred to lumbar TDR and HO. The hits were assessed against inclusion and exclusion criteria. Data from each included study was extracted and analysed with respect to the study aims.

Results

Twenty-six studies were included in this review and the pooled prevalence of HO was estimated to be between 13.2% (participants) and 15.3% (vertebral levels). TDR clinical outcomes were not found to be reduced by HO and there was insufficient data to identify a given impact upon radiological outcomes. Age and follow up time were identified as potential risk factors for HO.

Conclusions

This review was hampered by inconsistencies in the reporting of HO across the studies. We therefore recommend that a set of guidelines should be produced to aid future researchers and reduce the risk of bias.

Search for Key Genes and Functional Pathways of Ulcerative Colitis to Colon Cancer Based on Bioinformatics

Ulcerative colitis (UC) is a persistent and diffuse inflammatory disease of the intestine. It is widely prevalent in developed countries. Approximately 30% of patients with UC suffer from widespread and aggressive colitis and are at increased risk of colon cancer. In this study, the genetic features and potential molecular mechanisms shared between UC and colorectal cancer were investigated. The datasets from GEO and TCGA were analyzed to obtain differentially expressed genes, of which there were 116 overlapping genes. A module containing 15 genes was obtained using String and Cytoscape to analyze the module and identify hub genes. Weighted gene co-expression network analysis (WGCNA) was used to identify co-expression modules associated with UC and colon cancer, with 52 overlapping genes. Functional clustering of the two gene cohorts was performed using the Metascape online tool, with three significant functions or pathways associated with both gene cohorts. A total of 19 key genes were included, and CCT2 was identified after expression and survival analyses. CCT2 is highly expressed in colon cancer and lowly expressed in UC, and its low expression is associated with a poor prognostic ratio. This study reveals, for the first time, that CCT2 may be a promoter of UC transformation into colon cancer and identifies new gene candidates that could be used as biomarkers or potential therapeutic targets.

Clinically relevant preclinical animal models for testing novel cranio-maxillofacial bone 3D-printed biomaterials

Bone tissue engineering is a rapidly developing field with potential for the regeneration of craniomaxillofacial (CMF) bones, with 3D printing being a suitable fabrication tool for patient‐specific implants. The CMF region includes a variety of different bones with distinct functions. The clinical implementation of tissue engineering concepts is currently poor, likely due to multiple reasons including the complexity of the CMF anatomy and biology, and the limited relevance of the currently used preclinical models. The ‘recapitulation of a human disease’ is a core requisite of preclinical animal models, but this aspect is often neglected, with a vast majority of studies failing to identify the specific clinical indication they are targeting and/or the rationale for choosing one animal model over another. Currently, there are no suitable guidelines that propose the most appropriate animal model to address a specific CMF pathology and no standards are established to test the efficacy of biomaterials or tissue engineered constructs in the CMF field. This review reports the current clinical scenario of CMF reconstruction, then discusses the numerous limitations of currently used preclinical animal models employed for validating 3D‐printed tissue engineered constructs and the need to reduce animal work that does not address a specific clinical question. We will highlight critical research aspects to consider, to pave a clinically driven path for the development of new tissue engineered materials for CMF reconstruction.

Controlled growth factor delivery system with osteogenic-angiogenic coupling effect for bone regeneration

Objective

Bone regeneration involves a coordinated cascade of events that are regulated by several cytokines and growth factors, among which bone morphogenic protein-2 (BMP-2), vascular endothelial growth factor (VEGF) and fibroblast growth factor-2 (FGF-2) play important roles. In this study, we investigated the effects of dual release of the three growth factors on bone regeneration in femur defects.

Methods

A composite consisting of Gelatin microparticles loaded with VEGF/FGF-2 and poly(lactic-co-glycolic acid)-poly(ethylene glycol)-carboxyl (PLGA-PEG-COOH) microparticles loaded with BMP-2 encapsulated in a nano hydroxyapatite-poly actic-co-glycolic acid (nHA-PLGA) scaffold was prepared for the dual release of the growth factors.

Results

On the 14th day, decreased release rate of BMP-2 compared with FGF-2 and VEGF was observed. However, after 14 days, compared to FGF-2 and VEGF, BMP-2 showed an increased release rate. Controlled dual release of BMP-2 and VEGF, FGF-2 resulted in a significant osteogenic differentiation of bone mesenchymal stem cells (BMSCs). Moreover, effects of the composite scaffold on functional connection of osteoblast-vascular cells during bone development were evaluated. The synergistic effects of dual delivery of growth factors were shown to promote the expression of VEGF in BMSCs. Increased secretion of VEGF from BMSCs promoted the proliferation and angiogenic differentiation of human umbilical vein endothelial cells (HUVECs) in the co-culture system. At 12 weeks after implantation, blood vessel and bone formation were analyzed by micro-CT and histology. The composite scaffold significantly promoted the formation of blood vessels and new bone in femur defects.

Conclusions

These findings demonstrate that dual delivery of angiogenic factors and osteogenic factors from Gelatin and PLGA-PEG-COOH microparticles-based composite scaffolds exerted an osteogenic-angiogenic coupling effect on bone regeneration. This approach will inform on the development of appropriate designs of high-performance bioscaffolds for bone tissue engineering.

Articulation inspired by nature: A review of biomimetic and biologically active 3D printed scaffolds for cartilage tissue engineering

In the human body, articular cartilage facilitates the frictionless movement of synovial joints. However, due to its avascular and aneural nature, it has a limited ability to self-repair when damaged due to injury or wear and tear over time. Current surgical treatment options for cartilage defects often lead to the formation of fibrous, non-durable tissue and thus a new solution is required. Nature is the best innovator and so recent advances in the field of tissue engineering have aimed to recreate the microenvironment of native articular cartilage using biomaterial scaffolds. However, the inability to mirror the complexity of native tissue has hindered the clinical translation of many products thus far. Fortunately, the advent of 3D printing has provided a potential solution. 3D printed scaffolds, fabricated using biomimetic biomaterials, can be designed to mimic the complex zonal architecture and composition of articular cartilage. The bioinks used to fabricate these scaffolds can also be further functionalised with cells and/or bioactive factors or gene therapeutics to mirror the cellular composition of the native tissue. Thus, this review investigates how the architecture and composition of native articular cartilage is inspiring the design of biomimetic bioinks for 3D printing of scaffolds for cartilage repair. Subsequently, we discuss how these 3D printed scaffolds can be further functionalised with cells and bioactive factors, as well as looking at future prospects in this field.

The tissue engineering triad of biomaterials, cells and therapeutics as it applies to the formulation of biomimetic bioinks for cartilage repair. These bioinks can be functionalised with cells or cellular therapeutics to promote cartilage repair.

Ellagic acid and hydroxyapatite promote angiogenesis marker in bone defect

The combination of hydroxyapatite and the herbal extract ellagic acid is expected to accelerate the bone healing process (osteogenesis) due to the extract's anti-inflammatory and antioxidant properties. The osteogenesis process is closely associated with angiogenesis markers, such as fibroblast growth factor 2 (FGF-2), vascular endothelial growth factor (VEGF) and alkali phosphatase (ALP). The objective of this study is to analyse the combination of ellagic acid and hydroxyapatite to promote FGF-2, VEGF and ALP expression as angiogenesis markers in a bone defect model. The research sample comprised 30 male Wistar rats with a defect introduced on the left femur; these were divided into three groups for treatment with ellagic acid and hydroxyapatite, hydroxyapatite and polyethylene glycol (PEG) (control). On days 7 and 14 days after treatment, the Wistar rats were euthanised, and the femoral bone tissue was removed for the immunohistochemical analysis of FGF-2, VEGF and ALP expression. FGF-2 and ALP expression increased in the group treated with ellagic acid and hydroxyapatite on days 7 and 14 post treatment (p < 0.05), and there was an increase in VEGF expression on day 7 post treatment (p < 0.05). The combination of ellagic acid and hydroxyapatite promoted FGF-2, VEGF and ALP expression as angiogenesis markers in the bone defect model.

Tissue Engineering in Stomatology: A Review of Potential Approaches for Oral Disease Treatments

Tissue engineering is an emerging discipline that combines engineering and life sciences. It can construct functional biological structures in vivo or in vitro to replace native tissues or organs and minimize serious shortages of donor organs during tissue and organ reconstruction or transplantation. Organ transplantation has achieved success by using the tissue-engineered heart, liver, kidney, and other artificial organs, and the emergence of tissue-engineered bone also provides a new approach for the healing of human bone defects. In recent years, tissue engineering technology has gradually become an important technical method for dentistry research, and its application in stomatology-related research has also obtained impressive achievements. The purpose of this review is to summarize the research advances of tissue engineering and its application in stomatology. These aspects include tooth, periodontal, dental implant, cleft palate, oral and maxillofacial skin or mucosa, and oral and maxillofacial bone tissue engineering. In addition, this article also summarizes the commonly used cells, scaffolds, and growth factors in stomatology and discusses the limitations of tissue engineering in stomatology from the perspective of cells, scaffolds, and clinical applications.

Taurine is an effective therapy against thiram induced tibial dyschondroplasia via HIF-1α/VEGFA and β-catenin/ GSK-3β pathways in broilers

Thiram causes tibial dyschondroplasia in broilers, leading to a significant economic loss in the poultry industry. Our study explored the effects of taurine in thiram induced tibial dyschondroplasia (TD) through in vivo and in vitro approches. In in vivo study, thiram resulted in lameness disorder, low production parameters ALP, ACP, and a high level of NOS. While, the taurine exhibited promising effect by reducing lameness, increasing ALP, ACP levels, and significantly lowering NOS level with the restoration of the growth plate. In in vitro study, thiram caused distortion and disintegration of chondrocytes. The CCK-8 technique revealed the lower cell activity in TD as compared with the treatment group. Even, the treatment and taurine groups had higher cell activity than control group. Also, the chondrocyte morphology progressively reverted to normal after taurine treatment. It might effectively decreased the symptoms of TD in broilers and their production performance. Further research found that the taurine effectively improved chondrocytes' cell viability and recovered lameness disorder by regulation of HIF-1α, VEGFA, and Wnt/β-catenin signaling pathways. In summary, these results indicate that taurine has a protective effect on thiram-induced broilers and it can enhance the growth activity by directly affecting the development of chondrocytes and blood vessels.

An Avascular Niche Created by Axitinib-Loaded PCL/Collagen Nanofibrous Membrane Stabilized Subcutaneous Chondrogenesis of Mesenchymal Stromal Cells

Engineered cartilage derived from mesenchymal stromal cells (MSCs) always fails to maintain the cartilaginous phenotype in the subcutaneous environment due to the ossification tendency. Vascular invasion is a prerequisite for endochondral ossification during the development of long bone. As an oral antitumor medicine, Inlyta (axitinib) possesses pronounced antiangiogenic activity, owing to the inactivation of the vascular endothelial growth factor (VEGF) signaling pathway. In this study, axitinib-loaded poly(ε-caprolactone) (PCL)/collagen nanofibrous membranes are fabricated by electrospinning for the first time. Rabbit-derived MSCs-engineered cartilage is encapsulated in the axitinib-loaded nanofibrous membrane and subcutaneously implanted into nude mice. The sustained and localized release of axitinib successfully inhibits vascular invasion, stabilizes cartilaginous phenotype, and helps cartilage maturation. RNA sequence further reveals that axitinib creates an avascular, hypoxic, and low immune response niche. Timp1 is remarkably upregulated in this niche, which probably plays a functional role in inhibiting the activity of matrix metalloproteinases and stabilizing the engineered cartilage. This study provides a novel strategy for stable subcutaneous chondrogenesis of mesenchymal stromal cells, which is also suitable for other medical applications, such as arthritis treatment, local treatment of tumors, and regeneration of other avascular tissues (cornea and tendon).

Mesenchymal stem cells plus bone repair materials as a therapeutic strategy for abnormal bone metabolism: Evidence of clinical efficacy and mechanisms of action implied

The regeneration process of human bones is very complicated, the management and treatment of bone damage caused by diseases are the main problems faced by clinicians worldwide. It is known that cell-based stem cell therapy together with biomaterials is a fast-developing method of tissue regeneration. This review focuses on the different types and main characteristics of scaffolds and stem cells suitable for bone regeneration, and aims to provide a state-of-the-art description of the current treatment of common bone metabolism related diseases such as osteoarthritis, osteoporosis and osteosarcoma and the strategies based on stem cell biological scaffolds used in bone tissue engineering. This method may provide a new treatment option for the treatment of common bone metabolism-related diseases that cannot be cured by ordinary and routine applications. Three databases (PubMed, CNKI and Web of Science) search terms used to write this review are: "arthritis", "osteoporosis", "osteosarcoma", "bone tissue engineering", "mesenchymal stem cells", "materials", "bioactive scaffolds" and their combinations, and the most relevant studies are selected. As a conclusion, it needs to be emphasized that despite the encouraging results, further development is needed due to the need for more in-depth research, standardization of stem cell manufacturing processes, large-scale development of clinical methods for bone tissue engineering, and market regulatory approval. Although the research and application of tissue regeneration technology and stem cells are still in their infancy, the application prospect is broad and it is expected to solve the current clinical problems.

Microsphere embedded hydrogel construct - binary delivery of alendronate and BMP-2 for superior bone regeneration

Biomimetic delivery of osteoinductive growth factors via an osteoconductive matrix is an interesting approach for stimulating bone regeneration. In this context, the bone extracellular matrix (ECM) has been explored as an optimal delivery system, since it releases growth factors in a spatiotemporal manner from the matrix. However, a bone ECM hydrogel alone is weak, unstable, and prone to microbial contamination and also has been reported to have significantly reduced bone morphogenic protein-2 (BMP-2) post decellularization. In the present work, a microsphere embedded osteoinductive decellularized bone ECM/oleoyl chitosan based hydrogel construct (BOC) was developed as a matrix allowing dual delivery of an anti-resorptive drug (alendronate, ALN, via the microspheres) and BMP-2 (via the hydrogel) for a focal tibial defect in a rabbit model. The synthesized gelatin microspheres (GMs) were spherical in shape with diameter ∼32 μm as assessed by SEM analysis. The BOC construct showed sustained release of ALN and BMP-2 under the studied conditions. Interestingly, amniotic membrane-derived stem cells (HAMSCs) cultivated on the hydrogel construct demonstrated excellent biocompatibility, cell viability, and active proliferation potential. Additionally, cell differentiation on the constructs showed an elevated expression of osteogenic genes in an RT-PCR study along with enhanced mineralized matrix deposition as demonstrated by alkaline phosphatase (ALP) assay and alizarin red assay. The hydrogel construct was witnessed to have improved neo-vascularization potential in a chick chorioalantoic membrane (CAM) assay. Also, histological and computed tomographic findings evidenced enhanced bone regeneration in the group treated with the BOC/ALN/BMP hydrogel construct in a rabbit tibial defect model. To conclude, the developed multifunctional hydrogel construct acts as an osteoinductive and osteoconductive platform facilitating controlled delivery of ALN and BMP-2, essential for stimulating bone tissue regeneration.

Anti-VEGF antibody delivered locally reduces bony bar formation following physeal injury in rats

Physeal injuries can result in the formation of a "bony bar" which can lead to bone growth arrest and deformities in children. Vascular endothelial growth factor (VEGF) has been shown to play a role in bony bar formation, making it a potential target to inhibit bony repair tissue after physeal injury. The goal of this study was to investigate whether the local delivery of anti-VEGF antibody (α-VEGF; 7.5 μg) from alginate:chitosan hydrogels to the tibial physeal injury site in rats prevents bony bar formation. We tested the effects of quick or delayed delivery of α-VEGF using both 90:10 and 50:50 ratio alginate:chitosan hydrogels, respectively. Male and female 6-week-old Sprague-Dawley rats received a tibial physeal injury and the injured site injected with alginate-chitosan hydrogels: (1) 90:10 (Quick Release); (2) 90:10 + α-VEGF (Quick Release + α-VEGF); (3) 50:50 (Slow Release); (4) 50:50 +  α-VEGF (Slow Release +  α-VEGF); or (5) Untreated. At 2, 4, and 24 weeks postinjury, animals were euthanized and tibiae assessed for bony bar and vessel formation, repair tissue type, and limb lengthening. Our results indicate that Quick Release + α-VEGF reduced bony bar and vessel formation, while also increasing cartilage repair tissue. Further, the quick release of α-VEGF neither affected limb lengthening nor caused deleterious side-effects in the adjacent, uninjured physis. This α-VEGF treatment, which inhibits bony bar formation without interfering with normal bone elongation, could have positive implications for children suffering from physeal injuries.

Spatio-temporal immunolocalization of VEGF-A, Runx2, and osterix during the early steps of intramembranous ossification of the alveolar process in rat embryos

Vascular endothelial growth factor A (VEGF-A) is expressed by several cell types and is a crucial factor for angiogenic-osteogenic coupling. However, the immunolocalization of VEGF-A during the early stages of the alveolar process formation remains underexplored. Thus, we analyzed the spatio-temporal immunolocalization of VEGF-A and its relationship with Runt-related transcription factor 2 (Runx2) and osterix (Osx) during the early steps of intramembranous ossification of the alveolar process in rat embryos. Embryo heads (E) of 16, 18 and 20-day-old rats were processed for paraffin embedding. Histomorphometry and immunohistochemistry to detect VEGF-A, Runx2, and Osx (osteoblast differentiation markers) were performed. The volume density of bone tissue including bone cells and blood vessels increased significantly in E18 and E20. Cells showing high VEGF-A immunoreactivity were initially observed within a perivascular niche in the ectomesenchyme; afterwards, these cells were diffusely located near bone formation sites. Runx2-and Osx-immunopositive cells were observed in corresponded regions of cells showing strong VEGF-A immunoreactivity. Although these immunostained cells were observed in all specimens, this immunolocalization pattern was more evident in E16 specimens and gradually decreased in E18 and E20 specimens. Double immunofluorescence labelling showed intracellular co-localization of Osx and VEGF-A in cells surrounding the developing alveolar process, indicating a crucial role of VEGF-A in osteoblast differentiation. Our results showed VEGF-A immunoexpression in osteoblasts and its precursors during the maxillary alveolar process formation of rat embryos. Moreover, the VEGF-A-positive cells located within a perivascular niche at the early stages of the alveolar process development suggest a crosstalk between endothelium and ectomesenchymal cells, reinforcing the angiogenic-osteogenic coupling in this process.

Induced Pluripotent Stem Cell-Derived Endothelial Networks Accelerate Vascularization But Not Bone Regeneration

Vascularization is critical for engineering mineralized tissues. It has been previously shown that biomaterials containing preformed endothelial networks anastomose to host vasculature following implantation. However, the networks alone may not increase regeneration. In addition, a clinically applicable source of cells for vascularization is needed. In this study, vascular networks were generated from endothelial cells (ECs) derived from human induced pluripotent stem cells (iPSCs). Network formation by iPSC-ECs within fibrin gels was investigated in a mesenchymal stem cells (MSCs) coculture spheroid model. Statistical design of experiments technique was evaluated for its predicting capability during the optimization of experimental parameters. The prevascularized units were combined with hydroxyapatite nanoparticles to develop a vascularized composite hydrogel that was implanted in a rodent critical-sized cranial defect model. Immunohistological staining for human-specific CD31 at week 1 indicated the presence and maintenance of the implanted vessels. At 8 weeks, the prevascularized systems resulted in higher vessel density over MSC-only scaffolds. The implanted vessels appeared to establish flow with host vasculature. While there was a slight increase in bone volume in the prevascularized bone construct compared to MSC-only bone constructs, there was not a profound increase in bone regeneration. These results show that scaffolds with network structures can be generated from ECs derived from iPSC and that the networks survive and inosculate with the host postimplantation in a bone model. Impact statement Vascularization is critical for engineering bone. Prevascularized scaffolds have been shown to improve postimplantation vascularization. Herein, vascularized networks were generated from induced pluripotent cells derived from endothelial cells. These vascularized units were combined with a fibrin/hydroxyapatite scaffold to develop a prevascularized construct for bone regeneration. Implantation of these scaffolds in a small animal cranial defect model resulted in network inosculation and increased vascularization, but exhibited only a limited effect on bone formation. This study provides insight into the challenges of generating vascularized bone.