Signaling Pathway and Transcriptional Regulation in Osteoblasts during Bone Healing: Direct Involvement of Hydroxyapatite as a Biomaterial

Ultrasound-triggered functional hydrogel promotes multistage bone regeneration

The dysfunction of bone mesenchymal stem cells (BMSCs), caused by the physical and chemical properties of the inflammatory and repair phases of bone regeneration, contributes to the failure of bone regeneration. To meet the spatiotemporal needs of BMSCs in different phases, designing biocompatible materials that respond to external stimuli, improve migration in the inflammatory phase, reduce apoptosis in the proliferative phase, and clear the hurdle in the differentiation phase of BMSCs is an effective strategy for multistage repair of bone defects. In this study, we designed a cascade-response functional composite hydrogel (Gel@Eb/HA) to regulate BMSCs dysfunction in vitro and in vivo. Gel@Eb/HA improved the migration of BMSCs by upregulating the expression of chemokine (C-C motif) ligand 5 (CCL5) during the inflammatory phase. Ultrasound (US) triggered the rapid release of Ebselen (Eb), eliminating the accumulation of reactive oxygen species (ROS) in BMSCs, and reversing apoptosis under oxidative stress. Continued US treatment accelerated the degradation of the materials, thereby providing Ca2+ for the osteogenic differentiation of BMSCs. Altogether, our study highlights the prospects of US-controlled intelligent system, that provides a novel strategy for addressing the complexities of multistage bone repair.

Hydroxyapatite/alginate/gellan gum inks with osteoconduction and osteogenic potential for bioprinting bone tissue analogues

There is a growing demand for engineered bone tissues custom-designed to match the patient-specific defect size and in vitro models for studying bone diseases and/or drug screening. Herein, we propose a bioprinted bone tissue construct using SaOs-2 cells within alginate/gellan gum/hydroxyapatite inks. Different ink formulations were developed with varying hydroxyapatite content and then evaluated for viscoelasticity, printability, biomineralization properties, post-printing viability, proliferation, metabolic activity, and osteogenic phenotype of SaOs-2-encapsulated cells. Results indicate that ink formulations exhibit non-Newtonian shear-thinning behaviour, maintaining shape integrity and structural stability post-printing. Ink mineralization rates increase with the hydroxyapatite content, rendering them suitable for bone defect strategies. Post-printed cells in the developed constructs remain live, spreading, and metabolically active but do not proliferate. Osteogenic gene and protein expression, both early and late, show upregulation at day 7 relative to day 1, followed by downregulation at day 14. Lower hydroxyapatite content inks demonstrate up to fourfold upregulation in genes and proteins at most time points. Additionally, these constructs release calcium and phosphate at levels conducive to mineralization. Overall, the tissue-engineered miniaturized constructs not only meet the criteria for early-stage bone defect/fracture regeneration but also serve as a promising platform for drug screening and evaluating potential therapeutic treatments.

Bioactive Self-Regulated Liquified Microcompartments to Bioengineer Bone-Like Microtissues

Designing a microenvironment that drives autonomous stromal cell differentiation toward osteogenesis while recapitulating the complexity of bone tissue remains challenging. In the current study, bone-like microtissues are created using electrohydrodynamic atomization to form two distinct liquefied microcapsules (mCAPs): i) hydroxypyridinone (HOPO)-modified gelatin (GH mCAPs, 7.5% w/v), and ii) HOPO-modified gelatin and dopamine-modified gelatin (GH+GD mCAPs, 7.5%+1.5% w/v). The ability of HOPO to coordinate with iron ions at physiological pH allows the formation of a semipermeable micro-hydrogel shell. In turn, the dopamine affinity for calcium ions sets a bioactive milieu for bone-like microtissues. After 21 days post encapsulation, GH and GH+GD mCAPs potentiate autonomous osteogenic differentiation of mesenchymal stem cells accompanied by collagen type-I gene upregulation, increased alkaline phosphatase (ALP) expression, and formation of mineralized extracellular matrix. However, the GH+GD mCAPs show higher levels of osteogenic markers starting on day 14, translating into a more advanced and organized mineralized matrix. The GH+GD system also shows upregulation of the receptor activator of nuclear factor kappa-B ligand (RANK-L) gene, enabling the autonomous osteoclastic differentiation of monocytes. These catechol-based mCAPs offer a promising approach to designing multifunctional and autonomous bone-like microtissues to study in vitro bone-related processes at the cell-tissue interface, angiogenesis, and osteoclastogenesis.

Nano-hydroxyapatite structures for bone regenerative medicine: Cell-material interaction

Bone tissue engineering holds great promise for the regeneration of damaged or severe bone defects. However, several challenges hinder its translation into clinical practice. To address these challenges, interdisciplinary efforts and advances in biomaterials, cell biology, and bioengineering are required. In recent years, nano-hydroxyapatite (nHA)-based scaffolds have emerged as a promising approach for the development of bone regenerative agents. The unique similarity of nHA with minerals found in natural bones promotes remineralization and stimulates bone growth, which are crucial factors for efficient bone regeneration. Moreover, nHA exhibits desirable properties, such as strong chemical interactions with bone and facilitation of tissue growth, without inducing inflammation or toxicity. It also promotes osteoblast survival, adhesion, and proliferation, as well as increasing alkaline phosphatase activity, osteogenic differentiation, and bone-specific gene expression. However, it is important to note that the effect of nHA on osteoblast behavior is dose-dependent, with cytotoxic effects observed at higher doses. Additionally, the particle size of nHA plays a crucial role, with smaller particles having a more significant impact. Therefore, in this review, we highlighted the potential of nHA for improving bone regeneration processes and summarized the available data on bone cell response to nHA-based scaffolds. In addition, an attempt is made to portray the current status of bone tissue engineering using nHA/polymer hybrids and some recent scientific research in the field.

Osteogenic Activities of Trifolirhizin as a Bioactive Compound for the Differentiation of Osteogenic Cells

Plant extracts are widely used as traditional medicines. Sophora flavescens Aiton-derived natural compounds exert various beneficial effects, such as anti-inflammatory, anticancer, antioxidant, and antiregenerative activities, through their bioactive compounds, including flavonoids and alkaloids. In the present study, we investigated the biological effects of an S. flavescens-derived flavonoid, trifolirhizin (trifol), on the stimulation of osteogenic processes during osteoblast differentiation. Trifol (>98% purity) was successfully isolated from the root of S. flavescens and characterized. Trifol did not exhibit cellular toxicity in osteogenic cells, but promoted alkaline phosphatase (ALP) staining and activity, with enhanced expression of the osteoblast differentiation markers, including Alp, ColI, and Bsp. Trifol induced nuclear runt-related transcription factor 2 (RUNX2) expression during the differentiation of osteogenic cells, and concomitantly stimulated the major osteogenic signaling proteins, including GSK3β, β-catenin, and Smad1/5/8. Among the mitogen-activated protein kinases (MAPKs), Trifol activated JNK, but not ERK1/2 and p38. Trifol also increased the osteoblast-mediated bone-forming phenotypes, including transmigration, F-actin polymerization, and mineral apposition, during osteoblast differentiation. Overall, trifol exhibits bioactive activities related to osteogenic processes via differentiation, migration, and mineralization. Collectively, these results suggest that trifol may serve as an effective phytomedicine for bone diseases such as osteoporosis.

Bone repair and key signalling pathways for cell-based bone regenerative therapy: A review

Advances in cell-based regenerative therapy create new opportunities for the treatment of bone-related disorders and injuries, by improving the reparative phase of bone healing. Apart from the classical approach of bone grafting, the application of cell-based therapies, particularly stem cells (SCs), has gained a lot of attention in recent years. SCs play an important role in regenerative therapy due to their excellent ability to differentiate into bone-forming cells. Regeneration of new bone is regulated by a wide variety of signalling molecules and intracellular networks, which are responsible for coordinating cellular processes. The activated signalling cascade is significantly involved in cell survival, proliferation, apoptosis, and interaction with the microenvironment and other types of cells within the healing site. Despite the increasing evidence from studies conducted on signalling pathways associated with bone formation, the exact mechanism involved in controlling the differentiation stage of transplanted cells is not well understood. Identifying the key activated pathways involved in bone regeneration may allow for precise manipulation of the relevant signalling molecules within the progenitor cell population to accelerate the healing process. The in-depth knowledge of molecular mechanisms would be advantageous in improving the efficiency of personalised medicine and targeted therapy in regenerative medicine. In this review, we briefly introduce the theory of bone repair mechanism and bone tissue engineering followed by an overview of relevant signalling pathways that have been identified to play an important role in cell-based bone regenerative therapy.

Differentiation of osteoblasts: the links between essential transcription factors

Osteoblasts, cells derived from mesenchymal stem cells (MSCs) in the bone marrow, are cells responsible for bone formation and remodeling. The differentiation of osteoblasts from MSCs is triggered by the expression of specific genes, which are subsequently controlled by pro-osteogenic pathways. Mature osteoblasts then differentiate into osteocytes and are embedded in the bone matrix. Dysregulation of osteoblast function can cause inadequate bone formation, which leads to the development of bone disease. Various key molecules are involved in the regulation of osteoblastogenesis, which are transcription factors. Previous studies have heavily examined the role of factors that control gene expression during osteoblastogenesis, both in vitro and in vivo. However, the systematic relationship of these transcription factors remains unknown. The involvement of ncRNAs in this mechanism, particularly miRNAs, lncRNAs, and circRNAs, has been shown to influence transcriptional factor activity in the regulation of osteoblast differentiation. Here, we discuss nine essential transcription factors involved in osteoblast differentiation, including Runx2, Osx, Dlx5, β-catenin, ATF4, Ihh, Satb2, and Shn3. In addition, we summarize the role of ncRNAs and their relationship to these essential transcription factors in order to improve our understanding of the transcriptional regulation of osteoblast differentiation. Adequate exploration and understanding of the molecular mechanisms of osteoblastogenesis can be a critical strategy in the development of therapies for bone-related diseases.Communicated by Ramaswamy H. Sarma.

DP2, a Carbohydrate Derivative, Enhances In Vitro Osteoblast Mineralisation

Bone fracture healing is a complex biological process involving four phases coordinated over time: hematoma formation, granulation tissue formation, bony callus formation, and bone remodelling. Bone fractures represent a significant health problem, particularly among the elderly population and patients with comorbidities. Therapeutic strategies proposed to treat such fractures include the use of autografts, allografts, and tissue engineering strategies. It has been shown that bone morphogenetic protein 2 (BMP-2) has a therapeutic potential to enhance fracture healing. Despite the clinical efficacy of BMP-2 in osteoinduction and bone repair, adverse side effects and complications have been reported. Therefore, in this in vitro study, we propose the use of a disaccharide compound (DP2) to improve the mineralisation process. We first evaluated the effect of DP2 on primary human osteoblasts (HOb), and then investigated the mechanisms involved. Our findings showed that (i) DP2 improved osteoblast differentiation by inducing alkaline phosphatase activity, osteopontin, and osteocalcin expression; (ii) DP2 induced earlier in vitro mineralisation in HOb cells compared to BMP-2 mainly by earlier activation of Runx2; and (iii) DP2 is internalized in HOb cells and activates the protein kinase C signalling pathway. Consequently, DP2 is a potential therapeutical candidate molecule for bone fracture repair.

Hydrothermal extraction and physicochemical characterization of biogenic hydroxyapatite nanoparticles from buffalo waste bones for in vivo xenograft in experimental rats

Hydroxyapatite (HA) can be used in odontology and orthopedic grafts to restore damaged bone due to its stable chemical characteristics, composition, and crystal structural affinity for human bone. A three-step hydrothermal method was used for the extraction of biogenic calcined HA from the buffalo waste bones at 700 °C (HA-700) and 1000 °C (HA-1000). Extracts were analyzed by thermogravimetric analysis, differential scanning calorimetry, X-ray fluorescence, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and in vivo examination of HA xenografts for femoral lesions in experimental rats. Crystallinity, purity, and morphology patterns showed that the HA main phase purity was 84.68% for HA-700 and 88.99% for HA-1000. Spherical HA nanoparticles were present for calcined HA-700 samples in the range 57-423 nm. Rats with critical bone lesions of 3 mm in diameter in the left femur treated with calcined HA-700 nanoparticles healed significantly (p < 0.001) faster than rats treated with HA-1000 or negative controls. These findings showed that spherical biogenic HA-700 NPs with a bud-like structure have the potential to stimulate both osteoconduction and bone remodeling, leading to greater bone formation potential in vivo. Thus, the calcined biogenic HA generated from buffalo waste bones may be a practical tool for biomedical applications.

3D printed hybrid scaffolds for bone regeneration using calcium methoxyethoxide as a calcium source

Introduction: Hybrids consist of inorganic and organic co-networks that are indistinguishable above the nanoscale, which can lead to unprecedented combinations of properties, such as high toughness and controlled degradation. Methods: We present 3D printed bioactive hybrid scaffolds for bone regeneration, produced by incorporating calcium into our "Bouncy Bioglass", using calcium methoxyethoxide (CME) as the calcium precursor. SiO2-CaOCME/PTHF/PCL-diCOOH hybrid "inks" for additive manufacturing (Direct Ink Writing) were optimised for synergy of mechanical properties and open interconnected pore channels. Results and Discussion: Adding calcium improved printability. Changing calcium content (5, 10, 20, 30, and 40 mol.%) of the SiO2-CaOCME/PTHF/PCL-diCOOH hybrids affected printability and mechanical properties of the lattice-like scaffolds. Hybrids containing 30 mol.% calcium in the inorganic network (70S30CCME-CL) printed with 500 µm channels and 100 µm strut size achieved the highest strength (0.90 ± 0.23 MPa) and modulus of toughness (0.22 ± 0.04 MPa). These values were higher than Ca-free SiO2/PTHF/PCL-diCOOH hybrids (0.36 ± 0.14 MPa strength and 0.06 ± 0.01 MPa toughness modulus). Over a period of 90 days of immersion in simulated body fluid (SBF), the 70S30CCME-CL hybrids also kept a stable strain to failure (~30 %) and formed hydroxycarbonate apatite within three days. The extracts released by the 70S30CCME-CL hybrids in growth medium did not cause cytotoxic effects on human bone marrow stromal cells over 24 h of culture.

Molecular events in the jaw vascular unit: A traditional review of the mechanisms involved in inflammatory jaw bone diseases

Inflammatory jaw bone diseases are common in stomatology, including periodontitis, peri-implantitis, medication-related osteonecrosis of the jaw, radiation osteomyelitis of the jaw, age-related osteoporosis, and other specific infections. These diseases may lead to tooth loss and maxillofacial deformities, severely affecting patients' quality of life. Over the years, the reconstruction of jaw bone deficiency caused by inflammatory diseases has emerged as a medical and socioeconomic challenge. Therefore, exploring the pathogenesis of inflammatory diseases associated with jaw bones is crucial for improving prognosis and developing new targeted therapies. Accumulating evidence indicates that the integrated bone formation and dysfunction arise from complex interactions among a network of multiple cell types, including osteoblast-associated cells, immune cells, blood vessels, and lymphatic vessels. However, the role of these different cells in the inflammatory process and the 'rules' with which they interact are still not fully understood. Although many investigations have focused on specific pathological processes and molecular events in inflammatory jaw diseases, few articles offer a perspective of integration. Here, we review the changes and mechanisms of various cell types in inflammatory jaw diseases, with the hope of providing insights to drive future research in this field.

Bovine hydroxyapatite-based scaffold accelerated the inflammatory phase and bone growth in rats with bone defect

Hydroxyapatite (HA) is a biomaterial widely used to treat bone defect, such as due to traffic accident. The HA scaffold is obtained from synthetic HA or natural sources, such as bovine hydroxyapatite (BHA). This study aims to compare the characteristics and in vivo performance of BHA-based and HA-based scaffolds. For this purpose, the scaffold was formulated with gelatin (GEL) and characterised by SEM-EDX, FTIR and mini autograph. The defect model was carried out on the femur area of Wistar rats classified into three animal groups: defect, HA-GEL and BHA-GEL. Postoperatively (7, 14 and 28 days), the bone was radiologically evaluated, and stained with haematoxylin-eosin, anti-CD80 and anti-CD163. The BHA-GEL scaffold showed a regular surface and spherical particle shape, whereas the HA-GEL scaffold exhibited irregular surface. The BHA-GEL scaffold had higher pore size and compressive strength and lower calcium-to-phosphorus ratio than the HA-GEL scaffold. In vivo study showed that the expression of CD80 in the three experimental groups was not significantly different. However, the expression of CD163 differed significantly between the groups. The BHA-GEL group showed robust expression of CD163 on day 7, which rapidly decreased over time. It also showed increased osteoclasts, osteoblasts and osteocytes cell count that contributed to the integrity of the defect area. In conclusion, the BHA-based scaffold exhibited the desired physical and chemical characteristics that benefit in vivo performance versus the HA-based scaffold. Thus, the BHA-based scaffold may be used as a bone graft.

The administration of bovine hydroxyapatite-alendronate implant accelerates bone defect healing in an osteoporotic rat

BACKGROUND

Bone fracture is the main consequence of osteoporosis, which may become a neglected disease.

OBJECTIVE

This study aims to fabricate bovine hydroxyapatite-gelatine (BHA-GEL) based bone-implant with alendronate (ALE) in vivo.

METHODS

Wistar rats were used for an osteoporotic animal model induced by ovariectomy. There were three groups: negative control, BHA-GEL implant, and BHA-GEL-ALE implant. Each group performed a defect by drilling the femur (diameter of 2.2 mm and depth of 2 mm). Observations on the closure of bone defects were performed by X-ray radiography at the second and sixth week after surgery. The mechanism of bone healing was observed by using hematoxylin-eosin (HE) staining and immunohistochemical technique with anti-vascular endothelial growth factor (VEGF) and anti-alkaline phosphatase (ALP) antibodies.

RESULTS

The radiograph examination showed the implanted group had accelerated bone growth. In addition, the osteoblast, osteoclast and osteocyte had accelerated migration to the defect area. Moreover, the immunoreactive score (IRS) of VEGF at the sixth week in the BHA-GEL-ALE group was lower than the other groups. Meanwhile, the IRS of ALP in BHA-GEL-ALE was higher compared to other groups.

CONCLUSION

The BHA-GEL-ALE implant accelerates the healing of bone defect in the osteoporotic rat by increasing the ALP expression and the total number of cells.

Trifloroside Induces Bioactive Effects on Differentiation, Adhesion, Migration, and Mineralization in Pre-Osteoblast MC3T3E-1 Cells

Gentianae Scabrae Radix is used in traditional medicine and is known to possess bioactive compounds, including secoiridoid glycosides, flavonoids, lignans, and triterpenes. Trifloroside (TriFs) is a secoiridoid glycoside known for its antioxidant activity; however, its other effects have not been studied. In the present study, we investigated the biological effects of TriFs isolated from the roots of Gentianae Scabrae Radix using pre-osteoblast MC3T3E-1 cells. No cellular toxicity was observed with 1 μM TriFs, whereas 5-100 μM TriFs showed a gradual increase in cell viability. Alkaline phosphatase staining and microscopic observations revealed that 1-10 μM TriFs stimulated osteogenic activity during early osteoblast differentiation. Trifloroside also increased mineral apposition during osteoblast maturation. Biochemical analyses revealed that TriFs promoted nuclear RUNX2 expression and localization by stimulating the major osteogenic BMP2-Smad1/5/8-RUNX2 pathway. Trifloroside also increased p-GSK3β, β-catenin, p-JNK, and p-p38, but not Wnt3a, p-AKT, and p-ERK. Moreover, TriFs increased the MMP13 levels and promoted cell migration and adhesion. In contrast, TriFs-induced osteoblast differentiation and maturation had negligible effects on autophagy and necrosis. Our findings suggest that TriFs induces osteogenic effects through differentiation, adhesion, migration, and mineral apposition. Therefore, TriFs is suggested as a potential drug target in osteoblast-mediated bone diseases.

Functional engineering strategies of 3D printed implants for hard tissue replacement

Three-dimensional printing technology with the rapid development of printing materials are widely recognized as a promising way to fabricate bioartificial bone tissues. In consideration of the disadvantages of bone substitutes, including poor mechanical properties, lack of vascularization and insufficient osteointegration, functional modification strategies can provide multiple functions and desired characteristics of printing materials, enhance their physicochemical and biological properties in bone tissue engineering. Thus, this review focuses on the advances of functional engineering strategies for 3D printed biomaterials in hard tissue replacement. It is structured as introducing 3D printing technologies, properties of printing materials (metals, ceramics and polymers) and typical functional engineering strategies utilized in the application of bone, cartilage and joint regeneration.

Osteogenic differentiation and proliferation potentials of human bone marrow and umbilical cord-derived mesenchymal stem cells on the 3D-printed hydroxyapatite scaffolds

Mesenchymal stem cells (MSCs) are a promising candidate for bone repair. However, the maintenance of MSCs injected into the bone injury site remains inefficient. A potential approach is to develop a bone-liked platform that incorporates MSCs into a biocompatible 3D scaffold to facilitate bone grafting into the desired location. Bone tissue engineering is a multistep process that requires optimizing several variables, including the source of cells, osteogenic stimulation factors, and scaffold properties. This study aims to evaluate the proliferation and osteogenic differentiation potentials of MSCs cultured on 2 types of 3D-printed hydroxyapatite, including a 3D-printed HA and biomimetic calcium phosphate-coated 3D-printed HA. MSCs from bone marrow (BM-MSCs) and umbilical cord (UC-MSCs) were cultured on the 3D-printed HA and coated 3D-printed HA. Scanning electron microscopy and immunofluorescence staining were used to examine the characteristics and the attachment of MSCs to the scaffolds. Additionally, the cell proliferation was monitored, and the ability of cells to differentiate into osteoblast was assessed using alkaline phosphatase (ALP) activity and osteogenic gene expression. The BM-MSCs and UC-MSCs attached to a plastic culture plate with a spindle-shaped morphology exhibited an immunophenotype consistent with the characteristics of MSCs. Both MSC types could attach and survive on the 3D-printed HA and coated 3D-printed HA scaffolds. The MSCs cultured on these scaffolds displayed sufficient osteoblastic differentiation capacity, as evidenced by increased ALP activity and the expression of osteogenic genes and proteins compared to the control. Interestingly, MSCs grown on coated 3D-printed HA exhibited a higher ALP activity and osteogenic gene expression than those cultured on the 3D-printed HA. The finding indicated that BM-MSCs and UC-MSCs cultured on the 3D-printed HA and coated 3D-printed HA scaffolds could proliferate and differentiate into osteoblasts. Thus, the HA scaffolds could provide a suitable and favorable environment for the 3D culture of MSCs in bone tissue engineering. Additionally, biomimetic coating with octacalcium phosphate may improve the biocompatibility of the bone regeneration scaffold.

Acceleration of Bone Fracture Healing through the Use of Bovine Hydroxyapatite or Calcium Lactate Oral and Implant Bovine Hydroxyapatite-Gelatin on Bone Defect Animal Model

Bone grafts a commonly used therapeutic technique for the reconstruction and facilitation of bone regeneration due to fractures. BHA-GEL (bovine hydroxyapatite-gelatin) pellet implants have been shown to be able accelerate the process of bone repair by looking at the percentage of new bone, and the contact between the composite and bone. Based on these results, a study was conducted by placing BHA-GEL (9:1) pellet implants in rabbit femoral bone defects, accompanied by 500 mg oral supplement of BHA or calcium lactate to determine the effectiveness of addition supplements. The research model used was a burr hole defect model with a diameter of 4.2 mm in the cortical part of the rabbit femur. On the 7th, 14th and 28th days after treatment, a total of 48 New Zealand rabbits were divided into four groups, namely defect (control), implant, implant + oral BHA, and implant + oral calcium lactate. Animal tests were terminated and evaluated based on X-ray radiology results, Hematoxylin-Eosin staining, vascular endothelial growth Factor (VEGF), osteocalcin, and enzyme-linked immunosorbent assay (ELISA) for bone alkaline phosphatase (BALP) and calcium levels. From this research can be concluded that Oral BHA supplementation with BHA-GEL pellet implants showed faster healing of bone defects compared to oral calcium lactate with BHA-GEL pellet implants.

New PCL/PEC Blends: In Vitro Cell Response of Preosteoblasts and Human Mesenchymal Stem Cells

In this study, new blends of PCL/PEC have been prepared in an easy manner by casting with the objective of obtaining new biomaterials to apply to tissue engineering and bone regeneration. The PCL/PEC blends obtained, together with neat polymer blends, were characterized by infrared spectroscopy (FTIR), atomic force microscopy (AFM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). This full characterization is the key to disentangle the miscibility, which means good compatibility, of the polymer blends used in this work. The addition of increasing amounts of PEC, has shown in the new biomaterials obtained, a remarkable improvement in relation with the mechanical properties (manageable materials) and above all, in terms of an increase in their hydrophilic character with respect to the PCL neat polymer. The improvement of all these properties is reflected in their biological properties. With these thoughts in mind, the blends obtained were tested through the assessment of several biological parameters such as cell viability, proliferation, and differentiation of both the MC3T3-E1 osteoblastic cell line and hMSCs to evaluate their cell response to different polymer membranes aimed at bone tissue regeneration. “In vitro” biocompatibility methods have been chosen rather than in vivo studies due to their lower cost, faster procedure time, and minimum ethical concerns, and because it was the first time that the biological effects of these blends were studied. The results show that the PCL/PEC blends obtained, with tunable properties in terms of hydrophilic character and hydrolytic degradation, may be regarded as good candidates to perform “in vivo” tests and check their real-life applicability for bone regeneration. The polymer acronym (the weight percentage in the sub index) is PCLx/PECy as noted in table one with the summary of compositions.

Effects of Triterpene Soyasapogenol B from Arachis hypogaea (Peanut) on Differentiation, Mineralization, Autophagy, and Necroptosis in Pre-Osteoblasts

Triterpenes are a diverse group of natural compounds found in plants. Soyasapogenol B (SoyB) from Arachis hypogaea (peanut) has various pharmacological properties. This study aimed to elucidate the pharmacological properties and mechanisms of SoyB in bone-forming cells. In the present study, 1–20 μM of SoyB showed no cell proliferation effects, whereas 30–100 μM of SoyB increased cell proliferation in MC3T3-E1 cells. Next, osteoblast differentiation was analyzed, and it was found that SoyB enhanced ALP staining and activity and bone mineralization. SoyB also induced RUNX2 expression in the nucleus with the increased phosphorylation of Smad1/5/8 and JNK2 during osteoblast differentiation. In addition, SoyB-mediated osteoblast differentiation was not associated with autophagy and necroptosis. Furthermore, SoyB increased the rate of cell migration and adhesion with the upregulation of MMP13 levels during osteoblast differentiation. The findings of this study provide new evidence that SoyB possesses biological effects in bone-forming cells and suggest a potentially beneficial role for peanut-based foods.

Immunomodulation Effect of Biomaterials on Bone Formation

Traditional bone replacement materials have been developed with the goal of directing the osteogenesis of osteoblastic cell lines toward differentiation and therefore achieving biomaterial-mediated osteogenesis, but the osteogenic effect has been disappointing. With advances in bone biology, it has been revealed that the local immune microenvironment has an important role in regulating the bone formation process. According to the bone immunology hypothesis, the immune system and the skeletal system are inextricably linked, with many cytokines and regulatory factors in common, and immune cells play an essential role in bone-related physiopathological processes. This review combines advances in bone immunology with biomaterial immunomodulatory properties to provide an overview of biomaterials-mediated immune responses to regulate bone regeneration, as well as methods to assess the bone immunomodulatory properties of bone biomaterials and how these strategies can be used for future bone tissue engineering applications.

Synergistic effects of nanoattapulgite and hydroxyapatite on vascularization and bone formation in a rabbit tibia bone defect model

Hydroxyapatite (HA) is a promising scaffold material for the treatment of bone defects. However, the lack of angiogenic properties and undesirable mechanical properties (such as fragility) limits the application of HA. Nanoattapulgite (ATP) is a nature-derived clay mineral and has been proven to be a promising bioactive material for bone regeneration due to its ability to induce osteogenesis. In this study, polyvinyl alcohol/collagen/ATP/HA (PVA/COL/ATP/HA) scaffolds were printed. Mouse bone marrow mesenchymal stem/stromal cells (BMSCs) and human umbilical vein endothelial cells (HUVECs) were used in vitro to assess the biocompatibility and the osteogenesis and vascularization induction potentials of the scaffolds. Subsequently, in vivo micro-CT and histological staining were carried out to evaluate new bone formation in a rabbit tibial defect model. The in vitro results showed that the incorporation of ATP increased the printing fidelity and mechanical properties, with values of compressive strengths up to 200% over raw PC-H scaffolds. Simultaneously, the expression levels of osteogenic-related genes and vascularization-related genes were significantly increased after the incorporation of ATP. The in vivo results showed that the PVA/COL/ATP/HA scaffolds exhibited synergistic effects on promoting vascularization and bone formation. The combination of ATP and HA provides a promising strategy for vascularized bone tissue engineering.

Overexpression of Neurogenin 1 Negatively Regulates Osteoclast and Osteoblast Differentiation

Neurogenin 1 (Ngn1) belongs to the basic helix–loop–helix (bHLH) transcription factor family and plays important roles in specifying neuronal differentiation. The present study aimed to determine whether forced Ngn1 expression contributes to bone homeostasis. Ngn1 inhibited the p300/CREB-binding protein-associated factor (PCAF)-induced acetylation of nuclear factor of activated T cells 1 (NFATc1) and runt-related transcription factor 2 (Runx2) through binding to PCAF, which led to the inhibition of osteoclast and osteoblast differentiation, respectively. In addition, Ngn1 overexpression inhibited the TNF-α- and IL-17A-mediated enhancement of osteoclast differentiation and IL-17A-induced osteoblast differentiation. These findings indicate that Ngn1 can serve as a novel therapeutic agent for treating ankylosing spondylitis with abnormally increased bone formation and resorption.

The Osteoinductivity of Calcium Phosphate-Based Biomaterials: A Tight Interaction With Bone Healing

Calcium phosphate (CaP)-based bioceramics are the most widely used synthetic biomaterials for reconstructing damaged bone. Accompanied by bone healing process, implanted materials are gradually degraded while bone ultimately returns to its original geometry and function. In this progress report, we reviewed the complex and tight relationship between the bone healing response and CaP-based biomaterials, with the emphasis on the in vivo degradation mechanisms of such material and their osteoinductive properties mediated by immune responses, osteoclastogenesis and osteoblasts. A deep understanding of the interaction between biological healing process and biomaterials will optimize the design of CaP-based biomaterials, and further translate into effective strategies for biomaterials customization.

Bioprinted hASC ‐laden collagen/ HA constructs with meringue‐like macro/micropores

Extrusion‐based bioprinting is one of the most effective methods for fabricating cell‐laden mesh structures. However, insufficient cellular activities within the printed cylindrical cell‐matrix blocks, inducing low cell‐to‐cell interactions due to the disturbance of the matrix hydrogel, remain to be addressed. Hence, various sacrificial materials or void‐forming methods have been used; however, most of them cannot solve the problem completely or require complicated fabricating procedures. Herein, we suggest a bioprinted cell‐laden collagen/hydroxyapatite (HA) construct comprising meringue‐like porous cell‐laden structures to enhance osteogenic activity. A porous bioink is generated using a culinary process, i.e., the whipping method, and the whipping conditions, such as the material concentration, time, and speed, are selected appropriately. The constructs fabricated using the meringue‐like bioink with MG63 cells and human adipose stem cells exhibit outstanding metabolic and osteogenic activities owing to the synergistic effects of the efficient cell‐to‐cell interactions and HA stimulation released from the porous structure. The in vitro cellular responses indicate that the meringue‐like collagen bioink for achieving an extremely porous cell‐laden construct can be a highly promising cell‐laden material for various tissue regeneration applications.

Fabrication and Characterization of Submicron-Scale Bovine Hydroxyapatite: A Top-Down Approach for a Natural Biomaterial

Submicron hydroxyapatite has been reported to have beneficial effects in bone tissue engineering. This study aimed to fabricate submicron-scale bovine hydroxyapatite (BHA) using the high-energy dry ball milling method. Bovine cortical bone was pretreated and calcined to produce BHA powder scaled in microns. BHA was used to fabricate submicron BHA with milling treatment for 3, 6, and 9 h and was characterized by using dynamic light scattering, scanning electron microscope connected with energy dispersive X-Ray spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffractometry to obtain its particle size, calcium-to-phosphorus (Ca/P) ratio, functional chemical group, and XRD peaks and crystallinity. Results showed that the particle size of BHA had a wide distribution range, with peaks from ~5 to ~10 µm. Milling treatment for 3, 6, and 9 h successfully gradually reduced the particle size of BHA to a submicron scale. The milled BHA's hydrodynamic size was significantly smaller compared to unmilled BHA. Milling treatment reduced the crystallinity of BHA. However, the treatment did not affect other characteristics; unmilled and milled BHA was shaped hexagonally, had carbonate and phosphate substitution groups, and the Ca/P ratio ranged from 1.48 to 1.68. In conclusion, the fabrication of submicron-scale BHA was successfully conducted using a high-energy dry ball milling method. The milling treatment did not affect the natural characteristics of BHA. Thus, the submicron-scale BHA may be potentially useful as a biomaterial for bone grafts.

Melatonin enhances osteogenic differentiation of dental pulp mesenchymal stem cells by regulating MAPK pathways and promotes the efficiency of bone regeneration in calvarial bone defects

Background

Mesenchymal stem cell (MSC)-based tissue engineering plays a major role in regenerative medicine. However, the efficiency of MSC transplantation and survival of engrafted stem cells remain challenging. Melatonin can regulate MSC biology. However, its function in the osteogenic differentiation of dental pulp-derived MSCs (DPSCs) remains unclear. We investigated the effects and mechanisms of melatonin on the osteogenic differentiation and bone regeneration capacities of DPSCs.

Methods

The biological effects and signaling mechanisms of melatonin with different concentrations on DPSCs were evaluated using a proliferation assay, the quantitative alkaline phosphatase (ALP) activity, Alizarin red staining, a real-time polymerase chain reaction, and a western blot in vitro cell culture model. The in vivo bone regeneration capacities were assessed among empty control, MBCP, MBCP + DPSCs, and MBCP + DPSCs + melatonin preconditioning in four-created calvarial bone defects by using micro-computed tomographic, histological, histomorphometric, and immunohistochemical analyses after 4 and 8 weeks of healing.

Results

In vitro experiments revealed that melatonin (1, 10, and 100 μM) significantly and concentration-dependently promoted proliferation, surface marker expression (CD 146), ALP activity and extracellular calcium deposition, and osteogenic gene expression of DPSCs (p < 0.05). Melatonin activated the protein expression of ALP, OCN, and RUNX-2 and inhibited COX-2/NF-κB expression. Furthermore, the phosphorylation of mitogen-activated protein kinase (MAPK) p38/ERK signaling was significantly increased in DPSCs treated with 100 μM melatonin, and their inhibitors significantly decreased osteogenic differentiation. In vivo experiments demonstrated that bone defects implanted with MBCP bone-grafting materials and melatonin-preconditioned DPSCs exhibited significantly greater bone volume fraction, trabecular bone structural modeling, new bone formation, and osteogenesis-related protein expression than the other three groups at 4 and 8 weeks postoperatively (p < 0.05).

Conclusions

These results suggest that melatonin promotes the proliferation and osteogenic differentiation of DPSCs by regulating COX-2/NF-κB and p38/ERK MAPK signaling pathways. Preconditioning DPSCs with melatonin before transplantation can efficiently enhance MSCs function and regenerative capacities.

The Impact of the Extracellular Matrix Environment on Sost Expression by the MLO-Y4 Osteocyte Cell Line

Bone is a dynamic organ that can adapt its structure to meet the demands of its biochemical and biophysical environment. Osteocytes form a sensory network throughout the tissue and orchestrate tissue adaptation via the release of soluble factors such as a sclerostin. Osteocyte physiology has traditionally been challenging to investigate due to the uniquely mineralized extracellular matrix (ECM) of bone leading to the development of osteocyte cell lines. Importantly, the most widely researched and utilized osteocyte cell line: the MLO-Y4, is limited by its inability to express sclerostin (Sost gene) in typical in-vitro culture. We theorised that culture in an environment closer to the in vivo osteocyte environment could impact on Sost expression. Therefore, this study investigated the role of composition and dimensionality in directing Sost expression in MLO-Y4 cells using collagen-based ECM analogues. A significant outcome of this study is that MLO-Y4 cells, when cultured on a hydroxyapatite (HA)-containing two-dimensional (2D) film analogue, expressed Sost. Moreover, three-dimensional (3D) culture within HA-containing collagen scaffolds significantly enhanced Sost expression, demonstrating the impact of ECM composition and dimensionality on MLO-Y4 behaviour. Importantly, in this bone mimetic ECM environment, Sost expression was found to be comparable to physiological levels. Lastly, MLO-Y4 cells cultured in these novel conditions responded accordingly to fluid flow stimulation with a decrease in expression. This study therefore presents a novel culture system for the MLO-Y4 osteocyte cell line, ensuring the expression of an important osteocyte specific gene, Sost, overcoming a major limitation of this model.

In vivo study of bovine hydroxyapatite-gelatin-hydroxypropyl methylcellulose with alendronate as injectable bone substitute composite in osteoporotic animal model

The injectable bone substitute (IBS) is a self-setting local drug delivery system that adjusts the shape of the bone gap in the fracture. This study aimed to examine the effectiveness of IBS composites of bovine hydroxyapatite (BHA) and alendronate (Ale) in accelerating bone growth in osteoporotic rats. IBS was made by mixing BHA with gelatin 5%, hydroxypropyl methylcellulose (HPMC) 2%, and Ale 10%. The physical properties of IBS were viscosity, injectability, and density tests. Twenty-four female Wistar rats were divided into four groups. After 8 weeks, 2 mm gap was made in the right femur of all rats and filled with IBS. The healing process was observed after 6 weeks with X-ray imaging and H and E staining. The obtained results showed viscosity, injectability, and density value of IBS from 30.4 to 39.4 dPa.s, 98.22%-98.64%, and 0.6325-0.8409 g/cm³, respectively. X-ray imaging and histology results proved the condition of osteoporosis in rats with ovariectomy. The addition of BHA-Gel-HPMC-Ale significantly affected the number of osteoblasts, osteocytes, and osteoclasts (P < 0.05). After 45 days of observation, the addition of BHA-Gel-HPMC-Ale showed the highest mean number of osteoblasts, osteocytes, and osteoclasts, which were 25.00 ± 3.00, 64.33 ± 11.15, and 5.67 ± 0.58 compared to BHA-Gel-HPMC and positive control groups. The BHA-Gel-HPMC-Ale IBS has the potential to reverse osteoporosis. Nevertheless, the underlying potential of these biomaterials to reverse osteoporosis needs further research.