Inorganic phosphate as a signaling molecule in osteoblast differentiation

Effects of inorganic phosphate on stem cells isolated from human exfoliated deciduous teeth

Calcium phosphate-based materials (CaP) are introduced as potential dental pulp capping materials for deciduous teeth. The present study investigated the influence of inorganic phosphate (Pi) on regulating stem cells isolated from human exfoliated deciduous teeth (SHED). SHEDs were treated with Pi. Cell cycle progression and apoptosis were examined using flow cytometry analysis. Osteo/odontogenic and adipogenic differentiation were analyzed using alizarin red S and oil red O staining, respectively. The mRNA expression profile was investigated using a high-throughput RNA sequencing technique. Pi increased the late apoptotic cell population while cell cycle progression was not altered. Pi upregulated osteo/odontoblastic gene expression and enhanced calcium deposition. Pi-induced mineralization was reversed by pretreatment of cells with Foscarnet, or p38 inhibitor. Pi treatment inhibited adipogenic differentiation as determined by decreased PPARγ expression and reduced intracellular lipid accumulation. Bioinformatic analysis of gene expression profiles demonstrated several involved pathways, including PI3K/AKT, MAPK, EGFR, and VEGF signaling. In conclusion, Pi enhanced osteo/odontogenic but inhibited adipogenic differentiation in SHED.

Structural basis for inositol pyrophosphate gating of the phosphate channel XPR1

Precise regulation of intracellular phosphate (Pi) is critical for cellular function, with XPR1 serving as the sole Pi exporter in humans. The mechanism of Pi efflux, activated by inositol pyrophosphates (PP-IPs), has remained unclear. This study presents cryo-electron microscopy structures of XPR1 in multiple conformations, revealing a transmembrane pathway for Pi export and a dual-binding activation pattern by PP-IPs. A canonical binding site is located at the dimeric interface of SPX domains, and a second site, biased toward PP-IPs, is found between the transmembrane and SPX domains. By integrating structural studies with electrophysiological analyses, we characterize XPR1 as an IPs/PP-IPs-activated phosphate channel. The interplay among its TMDs, SPX domains, and IPs/PP-IPs orchestrates the conformational transition between its closed and open states.

The Role of Bovine Amniotic Membrane and Hydroxyapatite for the Ridge Preservation

Ridge preservation is an important technique for maintaining the dimensions of the alveolar bone following tooth extraction, which is crucial for successful tooth rehabilitation. The combination of bovine amniotic membrane and hydroxyapatite has shown promise as a scaffold material containing growth factors that can stimulate osteogenic-related factors such as bone morphogenetic protein 2 (BMP2), Runt-related transcription factor 2 (RUNX2), and osteocalcin. This stimulation leads to collagen production and osteoblast proliferation, resulting in new bone formation. In this study, bovine amniotic membrane-hydroxyapatite (BAM-HA) composites were prepared using three different ratios of bovine amniotic membrane and hydroxyapatite (2 : 3, 3 : 7, 7 : 13). Thirty Sprague-Dawley rats had their first incisors extracted, and different types of BAM-HA were applied for ridge preservation. The control group received no treatment, while the positive control group was given xenograft. After 14 and 28 days, the animals were sacrificed, and immunohistochemical analysis was performed to evaluate the expression of BMP2, RUNX2, and osteocalcin. Additionally, a histological examination was conducted to analyse collagen thickness and osteoblast cell proliferation. The results demonstrated that the application of BAM-HA significantly increased collagen density, osteoblast cell proliferation, and the expression of BMP2, RUNX2, and osteoclacin compared to the control group (p < 0.05) on both days 14 and 28. Furthermore, increasing the hydroxyapatite content in the composite was found to enhance collagen thickness, osteoblast cell proliferation, and the expression of osteogenic-related factors. These preliminary findings suggest that the combination of BAM-HA can be used for ridge preservation to prevent further bone resorption following tooth extraction.

In Vitro and In Vivo Biological Properties of Calcium Silicophosphate-Based Bone Grafts: Silicocarnotite and Nagelschmidtite

Accidents, trauma, bone defects, and oncological processes significantly impact patients' health and quality of life. While calcium phosphates and bioactive glasses are commonly used as bone fillers to facilitate bone regeneration in orthopedics and traumatology, they exhibit certain disadvantages compared to calcium silicophosphate phases. This study evaluates the in vitro cytocompatibility and in vivo osteogenic properties of two-third-generation ceramic phases: silicocarnotite (SC) and nagelschmidtite (Nagel). These phases were synthesized via a solid-state reaction and characterized using X-ray diffraction and scanning electron microscopy. In vitro behavior was assessed through bioactivity tests, cell viability, proliferation, and inflammatory profiles by detecting cytokines and reactive oxygen species. Osteogenic properties were evaluated by detecting bone-associated proteins in MG-G3, hFOB1.19, and MC3T3-E1 cell lines after 3, 7, and 14 days. 45S5 Bioactive glass (BG), hydroxyapatite (HAp), and osteogenic medium were employed as control standards for bone formation. SC and Nagel phases exhibited higher viability percentages as well as osteoconductive and osteoinductive behavior. Finally, SC and Nagel bone grafts were implanted in a Wistar rat model to assess their in vivo ability to induce bone formation, demonstrating complete osseointegration after 12 weeks. Histological evaluation revealed osteocytes forming osteons and the presence of blood vessels, particularly in rats implanted with Nagel. Given their favorable biological performance, SC and Nagel emerge as promising candidates for bone grafts in orthopedics, traumatology, and maxillofacial surgery.

Amino acid surface modified bioglass: A candidate biomaterial for bone tissue engineering1

Bioglasses are solid materials consisted of sodium oxide, calcium oxide, silicon dioxide and phosphorus in various proportions and have used in bone tissue engineering. There have been ongoing efforts to improve the surface properties of bioglasses to increase biocompatibility and performance. The aim of the present study is to modify the bioglass surface with an amino acid mixture consisting of arginine, aspartic acid, phenylalanine, cysteine, histidine and lysine, to characterize the surface, and to evaluate the performance and biocompatibility in vitro and in vivo. The untreated bioglass, bioglass kept in simulated body fluid (SBF), and modified bioglass were used in further evaluation. After confirmation of the surface modification with FT-IR analyses and SEM analyses, MC3T3-E1 preosteoblasts adhesion on the surface was also revealed by SEM. The modified bioglass had significantly higher ALP activity in colorimetric measurement, rate of calcium accumulations in Alizarin red s staining, lower rate of cell death in Annexin-V/PI staining to determine apoptosis and necrosis. Having higher cell viability rate in MTT test and absence of genotoxicity in micronucleus test (OECD 487), the modified bioglass was further confirmed for biocompatibility in vitro. The results of the rat tibial defect model revealed that the all bioglass treatments had a significantly better bone healing score compared to the untreated negative control. However, the modified bioglass exhibited significantly better bone healing efforts especially during the first and the second months compared to the other bioglass treatment treatments. As a result, the amino acid surface modification of bioglasses improves the surface biocompatibility and osteogenic performance that makes the amino acid modified bioglass a better candidate for bone tissue engineering. RESEARCH HIGHLIGHTS: Bioglass surface modification with amino acids contributes to bioglass-tissue interaction with an improved cell attachment. Modified bioglass increases in vitro Alp activity and calcium accumulation, and also positively affects cell behavior by supporting cell adaptation. Bioglass exerts osteogenic potential in vivo especially during early bone healing.

Unveiling the role of hydroxyapatite and hydroxyapatite/silver composite in osteoblast-like cell mineralization: An exploration through their viscoelastic properties

Mechanical properties are becoming fundamental for advancing the comprehension of cellular processes. This study addresses the relationship between viscoelastic properties and the cellular mineralization process. Osteoblast-like cells treated with an osteogenic medium were employed for this purpose. Additionally, the study explores the impact of hydroxyapatite (HA) and hydroxyapatite/silver (HA/Ag) composite on this process. AFM relaxation experiments were conducted to extract viscoelastic parameters using the Fractional Zener (FZ) and Fractional Kelvin (FK) models. Our findings revealed that the main phases of mineralization are associated with alterations in the viscoelastic properties of osteoblast-like cells. Furthermore, HA and HA/Ag treatments significantly influenced changes in the viscoelastic properties of these cells. In particular, the HA/Ag treatment demonstrated a marked enhancement in cell fluidity, suggesting a possible role of silver in accelerating the mineralization process. Moreover, the study underscores the independence observed between fluidity and stiffness, indicating that modifications in one parameter may not necessarily correspond to changes in the other. These findings shed light on the factors involved in the cellular mineralization process and emphasize the importance of using viscoelastic properties to discern the impact of treatments on cells.

Mineral matrix deposition of MC3T3-E1 pre-osteoblastic cells exposed to silicocarnotite and nagelschmidtite bioceramics: In vitro comparison to hydroxyapatite

This work presents the effect of the silicocarnotite (SC) and nagelschmidtite (Nagel) phases on in vitro osteogenesis. The known hydroxyapatite of biological origin (BHAp) was used as a standard of osteoconductive characteristics. The evaluation was carried out in conventional and osteogenic media for comparative purposes to assess the osteogenic ability of the bioceramics. First, the effect of the material on cell viability at 24 h, 7 and 14 days of incubation was evaluated. In addition, cell morphology and attachment on dense bioceramic surfaces were observed by fluorescence microscopy. Specifically, alkaline phosphatase (ALP) activity was evaluated as an osteogenic marker of the early stages of bone cell differentiation. Mineralized extracellular matrix was observed by calcium phosphate deposits and extracellular vesicle formation. Furthermore, cell phenotype determination was confirmed by scanning electron microscope. The results provided relevant information on the cell attachment, proliferation, and osteogenic differentiation processes after 7 and 14 days of incubation. Finally, it was demonstrated that SC and Nagel phases promote cell proliferation and differentiation, while the Nagel phase exhibited a superior osteoconductive behavior and could promote MC3T3-E1 cell differentiation to a higher extent than SC and BHAp, which was reflected in a higher number of deposits in a shorter period for both conventional and osteogenic media.

In vitro cytotoxicity of magnetic-fluorescent bioactive glasses on SaOS-2, MC3T3-E1, BJ fibroblast cells, their hemolytic activity, and sorafenib release behavior

In the study, the fabrication of superparamagnetic-fluorescent bioactive glasses in the form of the particle, nanofiber, and 3D scaffolds was performed by including maghemite (γ-Fe2O3) nanoparticles and photoluminescent rare earth element ions (Eu3+, Gd3+, and Yb3+) using sol-gel, electrospinning, and robocasting techniques, respectively. The in vitro cytotoxicity of the magnetic-fluorescent bioactive glasses on osteosarcoma SaOS-2, pre-osteoblast MC3T3-E1, and BJ fibroblast cells, as well as their hemolytic activity and sorafenib tosylate loading and release behavior, were investigated. The cytotoxicity of the bioactive glass samples was tested using the MTT assay. Additionally, the alkaline phosphatase activity of the studied glasses was examined as a function of time. The mineralization behavior of the pre-osteoblast cell-seeded glass samples was analyzed using Alizarin red S staining. Results revealed that the in vitro cytotoxicity of the studied bioactive glasses in the form of particles and nanofibers depended on the sample concentration, whereas in the case of the 3D scaffolds, no cytotoxic response was observed on the osteosarcoma, pre-osteoblast, and fibroblast cells. Similarly, particle and nanofiber-based glass samples induced dose-dependent hemolysis on red blood cells. Drug loading rates were much lower for the 3D scaffolds compared to the particle and nanofiber-based samples. Drug release rates ranged from 25 % to 90 %, depending on the bioactive glass morphology and the pH of the release medium. It was concluded that the studied bioactive glasses have the potential to be used in tissue engineering applications and cancer therapy.

Direct coupled electrical stimulation towards improved osteogenic differentiation of human mesenchymal stem/stromal cells: a comparative study of different protocols

Electrical stimulation (ES) has been described as a promising tool for bone tissue engineering, being known to promote vital cellular processes such as cell proliferation, migration, and differentiation. Despite the high variability of applied protocol parameters, direct coupled electric fields have been successfully applied to promote osteogenic and osteoinductive processes in vitro and in vivo. Our work aims to study the viability, proliferation, and osteogenic differentiation of human bone marrow-derived mesenchymal stem/stromal cells when subjected to five different ES protocols. The protocols were specifically selected to understand the biological effects of different parts of the generated waveform for typical direct-coupled stimuli. In vitro culture studies evidenced variations in cell responses with different electric field magnitudes (numerically predicted) and exposure protocols, mainly regarding tissue mineralization (calcium contents) and osteogenic marker gene expression while maintaining high cell viability and regular morphology. Overall, our results highlight the importance of numerical guided experiments to optimize ES parameters towards improved in vitro osteogenesis protocols.

Osteogenic assessment of leukocyte platelet-rich fibrin and injectable platelet-rich fibrin in the human osteosarcoma MG - 63 cell line in chronic periodontitis patients: An in vitro study

Background

The burgeoning interest in implant and regenerative dental care has led to a notable upsurge in the utilization of regenerative modalities. The intent of the present investigation was to evaluate the osteogenic ability of two different concentrated platelet groups at various concentrations in the human osteosarcoma MG-63 cell line.

Materials and Methods

Blood samples from 21 volunteers with chronic periodontitis were collected which were then centrifuged in accordance with the protocols of Choukroun et al. and Miron et al. to produce leukocyte- and platelet-rich fibrin (L-PRF) and injectable platelet-rich fibrin (I-PRF), respectively. Following MG-63 cell culture, the osteogenic ability of 0, 4%, and 20% concentrations of both L-PRF and I-PRF were determined using the real-time polymerase chain reaction assay.

Results

The results showed that 20% I-PRF (1.52 ± 0.24) and 4% L-PRF (1.42 ± 0.37) had the highest amount of bone morphogenetic protein 2 and osteocalcin, respectively.

Conclusion

I-PRF appears to promote the initial differentiation of cells.

β-TCP from 3D-printed composite scaffolds acts as an effective phosphate source during osteogenic differentiation of human mesenchymal stromal cells

Introduction: Human bone marrow-derived mesenchymal stromal cells (hBM-MSCs) are often combined with calcium phosphate (CaP)-based 3D-printed scaffolds with the goal of creating a bone substitute that can repair segmental bone defects. In vitro, the induction of osteogenic differentiation traditionally requires, among other supplements, the addition of β-glycerophosphate (BGP), which acts as a phosphate source. The aim of this study is to investigate whether phosphate contained within the 3D-printed scaffolds can effectively be used as a phosphate source during hBM-MSC in vitro osteogenesis. Methods: hBM-MSCs are cultured on 3D-printed discs composed of poly (lactic-co-glycolic acid) (PLGA) and β-tricalcium phosphate (β-TCP) for 28 days under osteogenic conditions, with and without the supplementation of BGP. The effects of BGP removal on various cellular parameters, including cell metabolic activity, alkaline phosphatase (ALP) presence and activity, proliferation, osteogenic gene expression, levels of free phosphate in the media and mineralisation, are assessed. Results: The removal of exogenous BGP increases cell metabolic activity, ALP activity, proliferation, and gene expression of matrix-related (COL1A1, IBSP, SPP1), transcriptional (SP7, RUNX2/SOX9, PPARγ) and phosphate-related (ALPL, ENPP1, ANKH, PHOSPHO1) markers in a donor dependent manner. BGP removal leads to decreased free phosphate concentration in the media and maintained of mineral deposition staining. Discussion: Our findings demonstrate the detrimental impact of exogenous BGP on hBM-MSCs cultured on a phosphate-based material and propose β-TCP embedded within 3D-printed scaffold as a sufficient phosphate source for hBM-MSCs during osteogenesis. The presented study provides novel insights into the interaction of hBM-MSCs with 3D-printed CaP based materials, an essential aspect for the advancement of bone tissue engineering strategies aimed at repairing segmental defects.

Bioactive Materials for Bone Regeneration: Biomolecules and Delivery Systems

Novel tissue regeneration strategies are constantly being developed worldwide. Research on bone regeneration is noteworthy, as many promising new approaches have been documented with novel strategies currently under investigation. Innovative biomaterials that allow the coordinated and well-controlled repair of bone fractures and bone loss are being designed to reduce the need for autologous or allogeneic bone grafts eventually. The current engineering technologies permit the construction of synthetic, complex, biomimetic biomaterials with properties nearly as good as those of natural bone with good biocompatibility. To ensure that all these requirements meet, bioactive molecules are coupled to structural scaffolding constituents to form a final product with the desired physical, chemical, and biological properties. Bioactive molecules that have been used to promote bone regeneration include protein growth factors, peptides, amino acids, hormones, lipids, and flavonoids. Various strategies have been adapted to investigate the coupling of bioactive molecules with scaffolding materials to sustain activity and allow controlled release. The current manuscript is a thorough survey of the strategies that have been exploited for the delivery of biomolecules for bone regeneration purposes, from choosing the bioactive molecule to selecting the optimal strategy to synthesize the scaffold and assessing the advantages and disadvantages of various delivery strategies.

Hydroxyapatite-filled osteoinductive and piezoelectric nanofibers for bone tissue engineering

Osteoporotic-related fractures are among the leading causes of chronic disease morbidity in Europe and in the US. While a significant percentage of fractures can be repaired naturally, in delayed-union and non-union fractures surgical intervention is necessary for proper bone regeneration. Given the current lack of optimized clinical techniques to adequately address this issue, bone tissue engineering (BTE) strategies focusing on the development of scaffolds for temporarily replacing damaged bone and supporting its regeneration process have been gaining interest. The piezoelectric properties of bone, which have an important role in tissue homeostasis and regeneration, have been frequently neglected in the design of BTE scaffolds. Therefore, in this study, we developed novel hydroxyapatite (HAp)-filled osteoinductive and piezoelectric poly(vinylidene fluoride-co-tetrafluoroethylene) (PVDF-TrFE) nanofibers via electrospinning capable of replicating the tissue's fibrous extracellular matrix (ECM) composition and native piezoelectric properties. The developed PVDF-TrFE/HAp nanofibers had biomimetic collagen fibril-like diameters, as well as enhanced piezoelectric and surface properties, which translated into a better capacity to assist the mineralization process and cell proliferation. The biological cues provided by the HAp nanoparticles enhanced the osteogenic differentiation of seeded human mesenchymal stem/stromal cells (MSCs) as observed by the increased ALP activity, cell-secreted calcium deposition and osteogenic gene expression levels observed for the HAp-containing fibers. Overall, our findings describe the potential of combining PVDF-TrFE and HAp for developing electroactive and osteoinductive nanofibers capable of supporting bone tissue regeneration.

Dentoalveolar Alterations in an Adenine-Induced Chronic Kidney Disease Mouse Model

Chronic kidney disease (CKD) is characterized by kidney damage and loss of renal function. CKD mineral and bone disorder (CKD-MBD) describes the dysregulation of mineral homeostasis, including hyperphosphatemia and elevated parathyroid hormone (PTH) secretion, skeletal abnormalities, and vascular calcification. CKD-MBD impacts the oral cavity, with effects including salivary gland dysfunction, enamel hypoplasia and damage, increased dentin formation, decreased pulp volume, pulp calcifications, and altered jaw bones, contributing to clinical manifestations of periodontal disease and tooth loss. Underlying mechanisms are not fully understood, and CKD mouse models commonly require invasive procedures with high rates of infection and mortality. We aimed to characterize the dentoalveolar effects of an adenine diet (AD)-induced CKD (AD-CKD) mouse model. Eight-week-old C57BL/6J mice were provided either a normal phosphorus diet control (CTR) or adenine and high-phosphorus diet CKD to induce kidney failure. Mice were euthanized at 15 weeks old, and mandibles were collected for micro-computed tomography and histology. CKD mice exhibited kidney failure, hyperphosphatemia, and hyperparathyroidism in association with porous cortical bone in femurs. CKD mice showed a 30% decrease in molar enamel volume compared to CTR mice. Enamel wear was associated with reduced ductal components, ectopic calcifications, and altered osteopontin (OPN) deposition in submandibular salivary glands of CKD mice. Molar cusps in CKD mice were flattened, exposing dentin. Molar dentin/cementum volume increased 7% in CKD mice and pulp volume decreased. Histology revealed excessive reactionary dentin and altered pulp-dentin extracellular matrix proteins, including increased OPN. Mandibular bone volume fraction decreased 12% and bone mineral density decreased 9% in CKD versus CTR mice. Alveolar bone in CKD mice exhibited increased tissue-nonspecific alkaline phosphatase localization, OPN deposition, and greater osteoclast numbers. AD-CKD recapitulated key aspects reported in CKD patients and revealed new insights into CKD-associated oral defects. This model has potential for studying mechanisms of dentoalveolar defects or therapeutic interventions. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Modulating Temporospatial Phosphate Equilibrium by Nanoparticulate Mineralized Collagen Materials Induces Osteogenesis via PiT-1 and PiT-2

The temporospatial equilibrium of phosphate contributes to physiological bone development and fracture healing, yet optimal control of phosphate content has not been explored in skeletal regenerative materials. Nanoparticulate mineralized collagen glycosaminoglycan (MC-GAG) is a synthetic, tunable material that promotes in vivo skull regeneration. In this work, the effects of MC-GAG phosphate content on the surrounding microenvironment and osteoprogenitor differentiation are investigated. This study finds that MC-GAG exhibits a temporal relationship with soluble phosphate with elution early in culture shifting to absorption with or without differentiating primary bone marrow-derived human mesenchymal stem cells (hMSCs). The intrinsic phosphate content of MC-GAG is sufficient to stimulate osteogenic differentiation of hMSCs in basal growth media without the addition of exogenous phosphate in a manner that can be severely reduced, but not eliminated, by knockdown of the sodium phosphate transporters PiT-1 or PiT-2. The contributions of PiT-1 and PiT-2 to MC-GAG-mediated osteogenesis are nonredundant but also nonadditive, suggestive that the heterodimeric form is essential to its activity. These findings indicate that the mineral content of MC-GAG alters phosphate concentrations within a local microenvironment resulting in osteogenic differentiation of progenitor cells via both PiT-1 and PiT-2.

Role of Berberine Thermosensitive Hydrogel in Periodontitis via PI3K/AKT Pathway In Vitro

Periodontitis is a long-term inflammatory illness and a leading contributor to tooth loss in humans. Due to the influence of the anatomic parameters of teeth, such as root bifurcation lesions and the depth of the periodontal pocket, basic periodontal treatment on its own often does not completely obliterate flora microorganisms. As a consequence, topical medication has become a significant supplement in the treatment of chronic periodontitis. Berberine (BBR) has various pharmacological effects, such as hypoglycemic, antitumor, antiarrhythmic, anti-inflammatory, etc. The target of our project is to develop a safe and non-toxic carrier that can effectively release berberine, which can significantly reduce periodontal tissue inflammation, and to investigate whether berberine thermosensitive hydrogel can exert anti-inflammatory and osteogenic effects by modulating phosphatifylinositol-3-kinase/Protein Kinase B (PI3K/AKT) signaling pathway. Consequently, firstly berberine temperature-sensitive hydrogel was prepared, and its characterizations showed that the mixed solution gelated within 3 min under 37 °C with a hole diameter of 10-130 µm, and the accumulation of berberine release amounted to 89.99% at 21 days. CCK-8 and live-dead cell staining results indicated that this hydrogel was not biotoxic, and it is also presumed that the optimum concentration of berberine is 5 µM, which was selected for subsequent experiments. Real-time polymerase chain reaction (qRT-PCR) and Western blotting (WB)results demonstrated that inflammatory factors, as well as protein levels, were significantly reduced in the berberine-loaded hydrogel group, and LY294002 (PI3K inhibitor) could enhance this effect (p < 0.05). In the berberine-loaded hydrogel group, osteogenesis-related factor levels and protein profiles were visibly increased, along with an increase in alkaline phosphatase expression, which was inhibited by LY294002 (p < 0.05). Therefore, berberine thermosensitive hydrogel may be an effective treatment for periodontitis, and it may exert anti-inflammatory and osteogenic effects through the PI3K/AKT signaling pathway.

Micropatterned photothermal double-layer periosteum with angiogenesis-neurogenesis coupling effect for bone regeneration

The abundant neurovascular network in the periosteal fibrous layer is essential for regulating bone homeostasis and repairing bone defects. However, the majority of the current studies only focus on the structure or function, and most of them merely involve osteogenesis and angiogenesis, lacking an in-depth study of periosteal neurogenesis. In this study, a photothermal double-layer biomimetic periosteum with neurovascular coupling was proposed. The outer layer of biomimetic periosteum is a conventional electrospinning membrane to prevent soft tissue invasion, and the inner layer is an oriented nanofiber membrane to promote cell recruitment and angiogenesis. From the perspective of functional bionics, based on the whitlockite (WH) similar to bone composition, we doped Nd (the trivalent form of neodymium element) in it as the inducing element of photothermal response to prepare photothermal whitlockite (Nd@WH). The sustained release of Mg²⁺ in Nd@WH can effectively promote the up-regulation of nerve growth factor (NGF) and vascular endothelial growth factor (VEGF). The release of Ca²⁺ and PO₄ ^3- ions and photothermal osteogenesis jointly promote bone regeneration. Under the combined effect of structure and function, the formation of nerves, blood vessels, and related collagens greatly simulates the microenvironment of extracellular matrix and periosteum regeneration and ultimately promotes bone regeneration. In this study, physical and chemical characterization proved that the bionic periosteum has good flexibility and operability. The in vitro cell experiment and in vivo calvarial defect model verified that PPCL/Nd@WH biomimetic periosteum had excellent bone tissue regeneration function compared with other groups. Finally, PPCL/Nd@WH provides a new idea for the design of bionic periosteum.

The extracellular matrix of human bone marrow adipocytes and glucose concentration differentially alter mineralization quality without impairing osteoblastogenesis

Bone marrow adipocytes (BMAds) accrue in various states of osteoporosis and interfere with bone remodeling through the secretion of various factors. However, involvement of the extracellular matrix (ECM) produced by BMAds in the impairment of bone marrow mesenchymal stromal cell (BM-MSC) osteoblastogenesis has received little attention. In type 2 diabetes (T2D), skeletal fragility is associated with several changes in bone quality that are incompletely understood, and BMAd quantity increases in relationship to poor glycemic control. Considering their altered phenotype in this pathophysiological context, we aimed to determine the contribution of the ECM of mature BMAds to osteoblastogenesis and mineralization quality in the context of chronic hyperglycemia.

Human BM-MSCs were differentiated for 21 days in adipogenic medium containing either a normoglycemic (LG, 5.5 mM) or a high glucose concentration (HG, 25 mM). The ECM laid down by BMAds were devitalized through cell removal to examine their impact on the proliferation and differentiation of BM-MSCs toward osteoblastogenesis in LG and HG conditions. Compared to control plates, both adipocyte ECMs promoted cell adhesion and proliferation. As shown by the unmodified RUNX2 and osteocalcin mRNA levels, BM-MSC commitment in osteoblastogenesis was hampered by neither the hyperglycemic condition nor the adipocyte matrices. However, adipocyte ECMs or HG condition altered the mineralization phase with perturbed expression levels of type 1 collagen, MGP and osteopontin. Despite higher ALP activity, mineralization levels per cell were decreased for osteoblasts grown on adipocyte ECMs compared to controls. Raman spectrometry revealed that culturing on adipocyte matrices specifically prevents type-B carbonate substitution and favors collagen crosslinking, in contrast to exposure to HG concentration alone. Moreover, the mineral to organic ratio was disrupted according to the presence of adipocyte ECM and the glucose concentration used for adipocyte or osteoblast culture. HG concentration and adipocyte ECM lead to different defects in mineralization quality, recapitulating contradictory changes reported in T2D osteoporosis.

Our study shows that ECMs from BMAds do not impair osteoblastogenesis but alter both the quantity and quality of mineralization partly in a glucose concentration-dependent manner. This finding sheds light on the involvement of BMAds, which should be considered in the compromised bone quality of T2D and osteoporosis patients more generally.

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Glucose level alters the Extracellular Matrix composition of Bone Marrow adipocytes.

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Osteoblastogenesis on adipocyte ECMs is unaltered but produced less mineral amount.

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The quality of the mineral is altered differently by adipocyte ECMs or glucose levels.

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The presence of BM adipocytes should be valued in damaged osteoporosis bone quality.

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.

Between a rock and a hard place: Regulation of mineralization in the periodontium

The periodontium supports and attaches teeth via mineralized and nonmineralized tissues. It consists of two, unique mineralized tissues, cementum and alveolar bone. In between these tissues, lies an unmineralized, fibrous periodontal ligament (PDL), which distributes occlusal forces, nourishes and invests teeth, and harbors progenitor cells for dentoalveolar repair. Many unanswered questions remain regarding periodontal biology. This review will focus on recent research providing insights into one enduring mystery: the precise regulation of the hard-soft tissue borders in the periodontium which define the interfaces of the cementum-PDL-alveolar bone structure. We will focus on advances in understanding the molecular mechanisms that maintain the unmineralized PDL "between a rock and a hard place" by regulating the mineralization of cementum and alveolar bone.

Sustained local ionic homeostatic imbalance caused by calcification modulates inflammation to trigger heterotopic ossification

Heterotopic ossification (HO) is a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues. Despite being a frequent complication of orthopedic and trauma surgery, brain and spinal injury, the etiology of HO is poorly understood. The aim of this study is to evaluate the hypothesis that a sustained local ionic homeostatic imbalance (SLIHI) created by mineral formation during tissue calcification modulates inflammation to trigger HO. This evaluation also considers the role SLIHI could play for the design of cell-free, drug-free osteoinductive bone graft substitutes. The evaluation contains five main sections. The first section defines relevant concepts in the context of HO and provides a summary of proposed causes of HO. The second section starts with a detailed analysis of the occurrence and involvement of calcification in HO. It is followed by an explanation of the causes of calcification and its consequences. This allows to speculate on the potential chemical modulators of inflammation and triggers of HO. The end of this second section is devoted to in vitro mineralization tests used to predict the ectopic potential of materials. The third section reviews the biological cascade of events occurring during pathological and material-induced HO, and attempts to propose a quantitative timeline of HO formation. The fourth section looks at potential ways to control HO formation, either acting on SLIHI or on inflammation. Chemical, physical, and drug-based approaches are considered. Finally, the evaluation finishes with a critical assessment of the definition of osteoinduction. STATEMENT OF SIGNIFICANCE: The ability to regenerate bone in a spatially controlled and reproducible manner is an essential prerequisite for the treatment of large bone defects. As such, understanding the mechanism leading to heterotopic ossification (HO), a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues, would be very useful. Unfortunately, the mechanism(s) behind HO is(are) poorly understood. The present study reviews the literature on HO and based on it, proposes that HO can be caused by a combination of inflammation and calcification. This mechanism helps to better understand current strategies to prevent and treat HO. It also shows new opportunities to improve the treatment of bone defects in orthopedic and dental procedures.

A new perspective on the function of Tissue Non-Specific Alkaline Phosphatase: from bone mineralization to intra-cellular lipid accumulation

Tissue-nonspecific alkaline phosphatase (TNAP) is one of four isozymes, which include germ cell, placental and intestinal alkaline phosphatases. The TNAP isozyme has 3 isoforms (liver, bone and kidney) which differ by tissue expression and glycosylation pattern. Despite a long history of investigation, the exact function of TNAP in many tissues is largely unknown. Only the bone isoform has been well characterised during mineralization where the enzyme hydrolyses pyrophosphate to inorganic phosphate, which combines with calcium to form hydroxyapatite crystals deposited as new bone. The inorganic phosphate also increases gene expression of proteins that support tissue mineralization. Recent studies have shown that TNAP is expressed in preadipocytes from several species, and that inhibition of TNAP activity causes attenuation of intracellular lipid accumulation in these and other lipid-storing cells. The mechanism by which TNAP stimulates lipid accumulation is not known; however, proteins that are important for controlling phosphate levels in bone are also expressed in adipocytes. This review examines the evidence that inorganic phosphate generated by TNAP promotes transcription that enhances the expression of the regulators of lipid storage and consequently, that TNAP has a major function of lipid metabolism.

Hydrogen phosphate selectively induces MDA MB 231 triple negative breast cancer cell death in vitro

Phosphate ions are the most abundant anions inside the cells, and they are increasingly gaining attention as key modulators of cellular function and gene expression. However, little is known about the effect of inorganic phosphate ions on cancer cells, particularly breast cancer cells. Here, we investigated the toxicity of different phosphate compounds to triple-negative human breast cancer cells, particularly, MDA-MB-231, and compared it to that of human monocytes, THP-1. We found that, unlike dihydrogen phosphate (H₂PO₄⁻), hydrogen phosphate (HPO₄²⁻) at 20 mM or lower concentrations induced breast cancer cell death more than immune cell death, mainly via apoptosis. We correlate this effect to the fact that phosphate in the form of HPO₄²⁻ raises pH levels to alkaline levels which are not optimum for transport of phosphate into cancer cells. The results in this study highlight the importance of further exploring hydrogen phosphate (HPO₄²⁻) as a potential therapeutic for the treatment of breast cancer.

Cytocompatibility and Bioactive Ion Release Profiles of Phosphoserine Bone Adhesive: Bridge from In Vitro to In Vivo

One major challenge when developing new biomaterials is translating in vitro testing to in vivo models. We have recently shown that a single formulation of a bone tissue adhesive, phosphoserine modified cement (PMC), is safe and resorbable in vivo. Herein, we screened many new adhesive formulations, for cytocompatibility and bioactive ion release, with three cell lines: MDPC23 odontoblasts, MC3T3 preosteoblasts, and L929 fibroblasts. Most formulations were cytocompatible by indirect contact testing (ISO 10993-12). Formulations with larger amounts of phosphoserine (>50%) had delayed setting times, greater ion release, and cytotoxicity in vitro. The trends in ion release from the adhesive that were cured for 24 h (standard for in vitro) were similar to release from the adhesives cured only for 5−10 min (standard for in vivo), suggesting that we may be able to predict the material behavior in vivo, using in vitro methods. Adhesives containing calcium phosphate and silicate were both cytocompatible for seven days in direct contact with cell monolayers, and ion release increased the alkaline phosphatase (ALP) activity in odontoblasts, but not pre-osteoblasts. This is the first study evaluating how PMC formulation affects osteogenic cell differentiation (ALP), cytocompatibility, and ion release, using in situ curing conditions similar to conditions in vivo.

Salivary phosphate as a biomarker for human diseases

Phosphate is a common ingredient of the daily consumed foods and is absorbed in the intestine and is excreted in the urine through the kidney to maintain the homeostatic balance. For adults, the Recommended Dietary Allowance (RDA) for phosphorus is around 700 mg/day. The change in dietary habits resulted in far more phosphate consumption (almost double) than the RDA, contributing to increased cardiovascular diseases, kidney diseases, and tumor formation. Due to a lack of clinical appreciation for the long-term consequences of chronic phosphate burden on non-communicable disorders, it is rapidly becoming a global health concern. The possible association between dysregulated phosphate metabolism and obesity is not studied in-depth, mainly because such an association is believed to be nonexistent. However, in the animal model of obesity, serum phosphate level was higher than their non-obese controls. In a similar observation line, significantly higher salivary phosphate levels were detected in obese children compared to normal-weight children. Of clinical importance, despite the significant increase of salivary phosphate levels in obese children, the plasma phosphate levels did not change in samples collected from the same group of children. Such disparity between plasma and saliva raised the possibility that human salivary phosphate levels may be an early biomarker of childhood obesity.

Uni-Directionally Oriented Fibro-Porous PLLA/Fibrin Bio-Hybrid Scaffold: Mechano-Morphological and Cell Studies

In this study, we report a biohybrid oriented fibrous scaffold based on nanofibers of poly(l-lactic acid) (PLLA)/fibrin produced by electrospinning and subsequent post-treatment. Induced hydrolytic degradation of the fibers in 0.25 M NaOH solution for various time periods followed by the immobilization of fibrin on the hydrolyzed fiber surfaces was shown to significantly affect the mechanical properties, with the tensile strength (40.6 MPa ± 1.3) and strain at failure (38% ± 4.5) attaining a value within the range of human ligaments and ligament-replacement grafts. Unidirectional electrospinning with a mandrel rotational velocity of 26.4 m/s produced highly aligned fibers with an average diameter of 760 ± 96 nm. After a 20-min hydrolysis treatment in NaOH solution, this was further reduced to an average of 457 ± 89 nm, which is within the range of collagen bundles found in ligament tissue. Based on the results presented herein, the authors hypothesize that a combination of fiber orientation/alignment and immobilization of fibrin can result in the mechanical and morphological modification of PLLA tissue scaffolds for ligament-replacement grafts. Further, it was found that treatment with NaOH enhanced the osteogenic differentiation of hMSCs and the additional inclusion of fibrin further enhanced osteogenic differentiation, as demonstrated by decreased proliferative rates and increased ALP activity.

Biomimetic Composite Coatings for Activation of Titanium Implant Surfaces: Methodological Approach and In Vivo Enhanced Osseointegration

Innovative nanomaterials are required for the coatings of titanium (Ti) implants to ensure the activation of Ti surfaces for improved osseointegration, enhanced bone fracture healing and bone regeneration. This paper presents a systematic investigation of biomimetic composite (BC) coatings on Ti implant surfaces in a rat model of a diaphyseal femoral fracture. Methodological approaches of surface modification of the Ti implants via the usual joining methods (e.g., grit blasting and acid etching) and advanced physicochemical coating via a self-assembled dip-coating method were used. The biomimetic procedure used multi-substituted hydroxyapatite (ms-HAP) HAP-1.5 wt% Mg-0.2 wt% Zn-0.2 wt% Si nanoparticles (NPs), which were functionalized using collagen type 1 molecules (COL), resulting in ms-HAP/COL (core/shell) NPs that were embedded into a polylactic acid (PLA) matrix and finally covered with COL layers, obtaining the ms-HAP/COL@PLA/COL composite. To assess the osseointegration issue, first, the thickness, surface morphology and roughness of the BC coating on the Ti implants were determined using AFM and SEM. The BC-coated Ti implants and uncoated Ti implants were then used in Wistar albino rats with a diaphyseal femoral fracture, both in the absence and the presence of high-frequency pulsed electromagnetic shortwave (HF-PESW) stimulation. This study was performed using a bone marker serum concentration and histological and computer tomography (micro-CT) analysis at 2 and 8 weeks after surgical implantation. The implant osseointegration was evaluated through the bone–implant contact (BIC). The bone–implant interface was investigated using FE-SEM images and EDX spectra of the retrieved surgical implants at 8 weeks in the four animal groups. The obtained results showed significantly higher bone–implants contact and bone volume per tissue volume, as well as a greater amount of newly formed bone, in the BC-coated Ti implants than in the uncoated Ti implants. Direct bone–implant contact was also confirmed via histological examination. The results of this study confirmed that these biomimetic composite coatings on Ti implants were essential for a significant enhancement of osseointegration of BC-coated Ti implants and bone regeneration. This research provides a novel strategy for the treatment of bone fractures with possible orthopedic applications.

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

Bone defects and periodontal disease are pathological conditions that may become neglected diseases if not treated properly. Hydroxyapatite (HA), along with tricalcium phosphate and bioglass ceramic, is a biomaterial widely applied to orthopedic and dental uses. The in vivo performance of HA is determined by the interaction between HA particles with bone cells, particularly the bone mineralizing cells osteoblasts. It has been reported that HA-induced osteoblastic differentiation by increasing the expression of osteogenic transcription factors. However, the pathway involved and the events that occur in the cell membrane have not been well understood and remain controversial. Advances in gene editing and the discovery of pharmacologic inhibitors assist researchers to better understand osteoblastic differentiation. This review summarizes the involvement of extracellular signal-regulated kinase (ERK), p38, Wnt, and bone morphogenetic protein 2 (BMP2) in osteoblastic cellular regulation induced by HA. These advances enhance the current understanding of the molecular mechanism of HA as a biomaterial. Moreover, they provide a better strategy for the design of HA to be utilized in bone engineering.

Poly-ε-caprolactone/Whitlockite Electrospun Bionic Membrane with an Osteogenic-Angiogenic Coupling Effect for Periosteal Regeneration

The periosteum is rich in vascular networks, osteoprogenitor cells, and stem cells and plays an important role in bone defect repair. However, existing artificial periosteum materials still have difficulty in meeting clinical requirements, such as good mechanical properties and bionic structure construction, osteogenic differentiation, and vascularization capabilities. Here, a poly-ε-caprolactone (PCL)/whitlockite (WH, 5, 10, 15 wt %) artificial periosteum with different doping amounts was prepared by electrospinning technology. According to the results of in vitro mineralization experiments, the rapid ion release from WH promotes the deposition of mineralized hydroxyapatite. Inductively coupled plasma-optical emission spectroscopy, in vitro angiogenesis, and cell migration experiments showed that the bionic periosteum of the 15% WH group had the best release rate of Mg²⁺ and the best ability to promote the human umbilical vein endothelial cell angiogenesis and migration. In addition, this group promoted collagen formation and calcium deposition. Finally, the subcutaneous implantation model was used to verify the biocompatibility and angiogenesis ability of the proposed membrane in vivo. Overall, this biomimetic PCL/WH nanofiber membrane combines the positive osteogenic differentiation ability and angiogenic ability of calcium phosphate materials and thus has good application prospects in the field of periosteal repair in the future.

Hydroxyapatite-modified micro/nanostructured titania surfaces with different crystalline phases for osteoblast regulation

Surface structures and physicochemical properties critically influence osseointegration of titanium (Ti) implants. Previous studies have shown that the surface with both micro- and nanoscale roughness may provide multiple features comparable to cell dimensions and thus efficiently regulate cell-material interaction. However, less attention has been made to further optimize the physicochemical properties (e.g., crystalline phase) and to further improve the bioactivity of micro/nanostructured surfaces. Herein, micro/nanostructured titania surfaces with different crystalline phases (amorphous, anatase and anatase/rutile) were prepared and hydroxyapatite (HA) nanorods were deposited onto the as-prepared surfaces by a spin-assisted layer-by-layer assembly method without greatly altering the initial multi-scale morphology and wettability. The effects of crystalline phase, chemical composition and wettability on osteoblast response were investigated. It is noted that all the micro/nanostructured surfaces with/without HA modification presented superamphiphilic. The activities of MC3T3-E1 cells suggested that the proliferation trend on the micro/nanostructured surfaces was greatly influenced by different crystalline phases, and the highest proliferation rate was obtained on the anatase/rutile surface, followed by the anatase; but the cell differentiation and extracellular matrix mineralization were almost the same among them. After ultrathin HA modification on the micro/nanostructured surfaces with different crystalline phases, it exhibited similar proliferation trend as the original surfaces; however, the cell differentiation and extracellular matrix mineralization were significantly improved. The results indicate that the introduction of ultrathin HA to the micro/nanostructured surfaces with optimized crystalline phase benefits cell proliferation, differentiation and maturation, which suggests a favorable biomimetic microenvironment and provides the potential for enhanced implant osseointegration in vivo.

The shape-effect of calcium phosphate nanoparticle based films on their osteogenic properties

Calcium phosphates (CaPs) in the form of hydroxyapatite (HA) have been extensively studied in the context of bone regeneration due to their chemical similarity to natural bone mineral. While HA is known to promote osteogenic differentiation, the structural properties of the ceramic have been shown to affect the extent of this effect; several studies have suggested that nanostructured HA can improve the bioactivity. However, the role shape plays in the osteogenic potential is more elusive. Here we studied the effect of HA nanoparticle shape on the ability to induce osteogenesis in human mesenchymal stromal cells (hMSCs) by developing nanoparticle films using needle-, rice- and spherical-shaped HA. We showed that the HA films made from all three shapes of nanoparticles induced increased levels of osteogenic markers (i.e. runt-related transcription factor 2 (RUNX2), bone morphogenetic protein 2 (BMP2), alkaline phosphatase (ALP), osteopontin (OPN), osteocalcin (OCN) on protein and gene level in comparison to hMSCs cultured on cover glass slides. Furthermore, their expression levels and profiles differed significantly as a function of nanoparticle shape. We also showed that nanoparticle films were more efficient in inducing osteogenic gene expression in hMSCs compared to adding nanoparticles to hMSCs in culture media. Finally, we demonstrated that hMSC morphology upon adhesion to the HA nanoparticle films is dependent on nanoparticle shape, with hMSCs exhibiting a more spread morphology on needle-shaped nanoparticle films compared to hMSCs seeded on rice- and spherical-shaped nanoparticle films. Our data suggests that HA nanoparticle films are efficient in inducing hMSC osteogenesis in basic cell culture conditions and that nanoparticle shape plays a vital role in cell adhesion and morphology and extent of induction of osteogenic differentiation.

The Signalling Effects of Photobiomodulation on Osteoblast Proliferation, Maturation and Differentiation: A Review

Proliferation of osteoblasts is essential for maturation and mineralization of bone matrix. Ossification, the natural phase of bone-forming and hardening is a carefully regulated phase where deregulation of this process may result in insufficient or excessive bone mineralization or ectopic calcification. Osteoblasts can also be differentiated into osteocytes, populating short interconnecting passages within the bone matrix. Over the past few decades, we have seen a significant improvement in awareness and techniques using photobiomodulation (PBM) to stimulate cell function. One of the applications of PBM is the promotion of osteoblast proliferation and maturation. PBM research results on osteoblasts showed increased mitochondrial ATP production, increased osteoblast activity and proliferation, increased and pro-osteoblast expression in the presence of red and NIR radiation. Osteocyte differentiation was also accomplished using blue and green light, showing that different light parameters have various signalling effects. The current review addresses osteoblast function and control, a new understanding of PBM on osteoblasts and its therapeutic impact using various parameters to optimize osteoblast function that may be clinically important. Graphical Abstract.

MC3T3 E1 cell response to mineralized nanofiber shish kebab structures

Block copolymers (BCPs) are of growing interest because of their extensive utility in tissue engineering, particularly in biomimetic approaches where multifunctionality is critical. We synthesized polycaprolactone-polyacrylic acid (PCL-b-PAA) BCP and crystallized it onto PCL nanofibers, making BCP nanofiber shish kebab (BCP NFSK) structures. When mineralized in 2× simulated body fluid, BCP NFSK mimic the structure of mineralized collagen fibrils. We hypothesized that the addition of a calcium phosphate layer of graded roughness on the nano-structure of the nanofiber shish kebabs would enhance preosteoblast alkaline phosphatase (ALP) activity, which has been shown to be a critical component in bone matrix formation. The objectives in the study were to investigate the effect of mineralization on cell proliferation and ALP activity, and to also investigate the effect of BCP NFSK periodicity, a structural feature describing the distance between PCL-b-PAA crystals on the nanofiber core, on cell proliferation, and ALP activity. ALP activity of cells cultured on the mineralized BCP NFSK template was significantly higher than the nonmineralized BCP NFSK templates. Interestingly, no statistical difference was observed in ALP activity when the periodic varied, indicating that surface chemistry seemed to play a larger role than the surface roughness.

Mesoporous bioactive glass composition effects on degradation and bioactivity

Mesoporous bioactive glasses (MBGs) are promising materials for regenerative medicine, due to their favorable properties including bioactivity and degradability. These key properties, but also their surface area, pore structure and pore volume are strongly dependent on synthesis parameters and glass stoichiometry. However, to date no systematic study on MBG properties covering a broad range of possible compositions exists.

Here, 24 MBG compositions in the SiO₂–CaO–P₂O₅ system were synthesized by varying SiO₂ (60–90 mol %), CaO and P₂O₅ content (both 0 to 40 mol-%), while other synthesis parameters were kept constant. Mesopore characteristics, degradability and bioactivity were analysed.

The results showed that, within the tested range of compositions, mesopore formation required a molar SiO₂ content above 60% but was independent of CaO and P₂O₅ content. While mesopore size did not depend on glass stoichiometry, mesopore arrangement was influenced by the SiO₂ content. Specific surface area and pore volume were slightly altered by the SiO₂ content. All materials were degradable; however, degradation as well as bioactivity, i.e. the ability to form a CaP mineral on the surface, depended on stoichiometry. Major differences were found in early surface reactions in simulated body fluid: where some MBGs induced direct hydroxyapatite crystallization, high release of calcium in others resulted in calcite formation.

In summary, degradation and bioactivity, both key parameters of MBGs, can be controlled by glass stoichiometry over a broad range while leaving the unique structural parameters of MBGs relatively unaffected. This allows targeted selection of material compositions for specific regenerative medicine applications.

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Mesoporous bioactive glasses can be obtained over a broad range of compositions.

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In the SiO₂/CaO/P₂O₅ system up to 15 mol-% P₂O₅ allow ordered porosity.

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In SiO₂/P₂O₅ glasses, up to 30 mol-% P₂O₅ are possible.

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Bioactivity and degradation can be tailored by controlling stoichiometry.

Bioglass/carbonate apatite/collagen composite scaffold dissolution products promote human osteoblast differentiation

OssiMend® Bioactive (Collagen Matrix Inc., NJ) is a three-component porous composite bone graft device of 45S5 Bioglass/carbonate apatite/collagen. Our in vitro studies showed that conditioned media of the dissolution products of OssiMend Bioactive stimulated primary human osteoblasts to form mineralized bone-like nodules in vitro in one week, in basal culture media (no osteogenic supplements). Osteoblast differentiation was followed by gene expression analysis and a mineralization assay. In contrast, the dissolution products from commercial OssiMend (Bioglass-free carbonate apatite/collagen scaffolds), or from 45S5 Bioglass particulate alone, did not induce the mineralization of the extracellular matrix, but did induce osteoblast differentiation to mature osteoblasts, evidenced by the strong upregulation of BGLAP and IBSP mRNA levels. The calcium ions and soluble silicon species released from 45S5 Bioglass particles and additional phosphorus release from OssiMend mediated the osteostimulatory effects. Medium conditioned with OssiMend Bioactive dissolution had a much higher concentration of phosphorus and silicon than media conditioned with OssiMend and 45S5 Bioglass alone. While OssiMend and OssiMend Bioactive led to calcium precipitation in cell culture media, OssiMend Bioactive produced a higher concentration of soluble silicon than 45S5 Bioglass and higher dissolution of phosphorus than OssiMend. These in vitro results suggest that adding 45S5 Bioglass to OssiMend produces a synergistic osteostimulation effect on primary human osteoblasts. In summary, dissolution products of a Bioglass/carbonate apatite/collagen composite scaffold (OssiMend® Bioactive) stimulate human osteoblast differentiation and mineralization of extracellular matrix in vitro without any osteogenic supplements. The mineralization was faster than for dissolution products of ordinary Bioglass.

Modulating phosphate consumption, a novel therapeutic approach for the control of cancer cell proliferation and tumorigenesis

Phosphorus, often in the form of inorganic phosphate (Pi), is critical to cellular function on many levels; it is required as an integral component of kinase signaling, in the formation and function of DNA and lipids, and energy metabolism in the form of ATP. Accordingly, crucial aspects of cell mitosis - such as DNA synthesis and ATP energy generation - elevate the cellular requirement for Pi, with rapidly dividing cells consuming increased levels. Mechanisms to sense, respond, acquire, accumulate, and potentially seek Pi have evolved to support highly proliferative cellular states such as injury and malignant transformation. As such, manipulating Pi availability to target rapidly dividing cells presents a novel strategy to reduce or prevent unrestrained cell growth. Currently, limited knowledge exists regarding how modulating Pi consumption by pre-cancerous cells might influence the initiation of aberrant growth during malignant transformation, and if reducing the bioavailability or suppressing Pi consumption by malignant cells could alter tumorigenesis. The concept of targeting Pi-regulated pathways and/or consumption by pre-cancerous or tumor cells represents a novel approach to cancer prevention and control, although current data remains insufficient as to rigorously assess the therapeutic value and physiological relevance of this strategy. With this review, we present a critical evaluation of the paradox of how an element critical to essential cellular functions can, when available in excess, influence and promote a cancer phenotype. Further, we conjecture how Pi manipulation could be utilized as a therapeutic intervention, either systemically or at the cell level, to ultimately suppress or treat cancer initiation and/or progression.

Aspiration-assisted bioprinting of co-cultured osteogenic spheroids for bone tissue engineering

Conventional top-down approaches in tissue engineering involving cell seeding on scaffolds have been widely used in bone engineering applications. However, scaffold-based bone tissue constructs have had limited clinical translation due to constrains in supporting scaffolds, minimal flexibility in tuning scaffold degradation, and low achievable cell seeding density as compared with native bone tissue. Here, we demonstrate a pragmatic and scalable bottom-up method, inspired from embryonic developmental biology, to build three-dimensional (3D) scaffold-free constructs using spheroids as building blocks. Human umbilical vein endothelial cells (HUVECs) were introduced to human mesenchymal stem cells (hMSCs) (hMSC/HUVEC) and spheroids were fabricated by an aggregate culture system. Bone tissue was generated by induction of osteogenic differentiation in hMSC/HUVEC spheroids for 10 days, with enhanced osteogenic differentiation and cell viability in the core of the spheroids compared to hMSC-only spheroids. Aspiration-assisted bioprinting (AAB) is a new bioprinting technique which allows precise positioning of spheroids (11% with respect to the spheroid diameter) by employing aspiration to lift individual spheroids and bioprint them onto a hydrogel. AAB facilitated bioprinting of scaffold-free bone tissue constructs using the pre-differentiated hMSC/HUVEC spheroids. These constructs demonstrated negligible changes in their shape for two days after bioprinting owing to the reduced proliferative potential of differentiated stem cells. Bioprinted bone tissues showed interconnectivity with actin-filament formation and high expression of osteogenic and endothelial-specific gene factors. This study thus presents a viable approach for 3D bioprinting of complex-shaped geometries using spheroids as building blocks, which can be used for various applications including but not limited to, tissue engineering, organ-on-a-chip and microfluidic devices, drug screening and, disease modeling.

Bone morphogenetic protein-2 delivery from polyelectrolyte multilayers enhances osteogenic activity on nanostructured titania

Incomplete osseointegration is primary cause of failure for orthopedic implants. New biomaterials that present stable signals promoting osteogenesis could reduce failure rates of orthopedic implants. In this study bone morphogenetic protein-2 (BMP-2) was delivered from titania nanotubes (Nt) modified with chitosan/heparin polyelectrolyte multilayers (PEMs). The surfaces were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. BMP-2 release from the surfaces was measured in vitro for up to 28 days. After an initial burst release of BMP-2 during the first 2 days, most of the BMP-2 remained on the surface. To determine the osteogenic properties of these surfaces, they were seeded with rat bone marrow cells; alkaline phosphatase (ALP) activity, total protein, calcium deposition, and osteocalcin were measured up to 4 weeks in vitro. When compared to Nt surfaces, the surfaces with BMP-2 induce greater osteocalcin and calcium deposition. PEMs provide sustained presentation of BMP-2, from a biomimetic surface. This enhances the osteogenic properties of the surface without requiring supraphysiologic growth factor dose. This growth factor delivery strategy could be used to improve bone healing outcomes and reduce complications for recipients of orthopedic implants.

Restriction of Dietary Phosphate Ameliorates Skeletal Abnormalities in a Mouse Model for Craniometaphyseal Dysplasia

Craniometaphyseal dysplasia (CMD), a rare genetic bone disorder, is characterized by lifelong progressive thickening of craniofacial bones and metaphyseal flaring of long bones. The autosomal dominant form of CMD is caused by mutations in the progressive ankylosis gene ANKH (mouse ortholog Ank), encoding a pyrophosphate (PPi) transporter. We previously reported reduced formation and function of osteoblasts and osteoclasts in a knockin (KI) mouse model for CMD (Ank^KI/KI) and in CMD patients. We also showed rapid protein degradation of mutant ANK/ANKH. Mutant ANK protein displays reduced PPi transport, which may alter the inorganic phosphate (Pi) and PPi ratio, an important regulatory mechanism for bone mineralization. Here we investigate whether reducing dietary Pi intake can ameliorate the CMD-like skeletal phenotype by comparing male and female Ank^+/+ and Ank^KI/KI mice exposed to a low (0.3%) and normal (0.7%) Pi diet for 13 weeks from birth. Serum Pi and calcium (Ca) levels were not significantly changed by diet, whereas PTH and 25-hydroxy vitamin D (25-OHD) were decreased by low Pi diet but only in male Ank^+/+ mice. Importantly, the 0.3% Pi diet significantly ameliorated mandibular hyperostosis in both sexes of Ank^KI/KI mice. A tendency of decreased femoral trabeculation was observed in male and female Ank^+/+ mice as well as in male Ank^KI/KI mice fed with the 0.3% Pi diet. In contrast, in female Ank^KI/KI mice the 0.3% Pi diet resulted in increased metaphyseal trabeculation. This was also the only group that showed increased bone formation rate. Low Pi diet led to increased osteoclast numbers and increased bone resorption in all mice. We conclude that lowering but not depleting dietary Pi delays the development of craniofacial hyperostosis in CMD mice without severely compromising serum levels of Pi, Ca, PTH, and 25-OHD. These findings may have implications for better clinical care of patients with CMD. © 2020 American Society for Bone and Mineral Research.

High phosphate actively induces cytotoxicity by rewiring pro-survival and pro-apoptotic signaling networks in HEK293 and HeLa cells

Inorganic phosphate (Pi) is an essential nutrient for human health. Due to the changes in our dietary pattern, dietary Pi overload engenders systemic phosphotoxicity, including excessive Pi-related vascular calcification and chronic tissue injury. The molecular mechanisms of the seemingly distinct phenotypes remain elusive. In this study, we investigated Pi-mediated cellular response in HEK293 and HeLa cells. We found that abnormally high Pi directly mediates diverse cellular toxicity in a dose-dependent manner. Up to 10 mM extracellular Pi promotes cell proliferation by activating AKT signaling cascades and augmenting cell cycle progression. By introducing additional Pi, higher than the concentration of 40 mM, we observed significant cell damage caused by the interwoven Pi-related biological processes. Elevated Pi activates mitogen-activated protein kinase (MAPK) signaling, encompassing extracellular signal-regulated kinase 1/2 (ERK1/2), p38 and Jun amino-terminal kinase (JNK), which consequently potentiates Pi triggered lethal epithelial-mesenchymal transition (EMT). Synergistically, high Pi-caused endoplasmic reticulum (ER) stress also contributes to apparent apoptosis. To counteract, Pi-activated AKT signaling promotes cell survival by activating the mammalian target of rapamycin (mTOR) signaling and blocking ER stress. Pharmacologically or genetically abrogating Pi transport, the impact of high Pi-induced cytotoxicity could be reduced. Taken together, abnormally high extracellular Pi results in a broad spectrum of toxicity by rewiring complicated signaling networks that control cell growth, cell death, and homeostasis.

Fabrication and Characterization of Silk Fibroin Microfiber-Incorporated Bone Marrow Stem Cell Spheroids to Promote Cell-Cell Interaction and Osteogenesis

In this study, silk fibroin microfiber (mSF) was applied to assist spheroid assemblies of rBMSCs (rabbit bone marrow stem cells) (S/B). Alkaline hydrolysis was induced with different times and conditions to manufacture the various sizes of mSF. The mSF was incorporated in the rBMSC with different amounts to optimize proper content for spheroid assembly. The formation of the S/B was confirmed under optical microscopy and SEM. Proliferation and viability were characterized by CCK-8 and live/dead staining. Osteogenesis was analyzed with ALP (alkaline phosphatase) activity studies and real-time polymerase chain reaction. The S/B was successfully produced and displayed uniformly distributed cells and mSF with the presence of a gap in the structure. Proliferation and viability of the S/B significantly increased when compared to rBMSC spheroids (B), which is potentially due to the enhanced transportation of oxygen and nutrients to the cells located in the core region. Additionally, ALP activity and osteogenic markers were significantly upregulated in the optimized S/B under osteogenic media conditions. Overall, a hybrid-spheroid system with a simple 3D cell culture platform provides a potential approach for engineering therapeutic stem cells.

Injectable thermosensitive chitosan/gelatin-based hydrogel carried erythropoietin to effectively enhance maxillary sinus floor augmentation in vivo

OBJECTIVE

Maxillary sinus floor augmentation (MSFA) is commonly used to increase the alveolar bone height in the posterior maxilla before implant placement. In the present study, we evaluated if the injectable thermosensitive chitosan/β-sodium glycerophosphate disodium salt hydrate/gelatin (CS/GP/GA) hydrogel carried erythropoietin (EPO) could enhance the new bone formation for MSFA in vivo.

METHODS

EPO-CS/GP/GA hydrogel was prepared by ionic crosslinking. Then, characteristics of EPO-CS/GP/GA were evaluated by morphology, injectable property and pH on the gelling time (GT). The release profile of EPO was evaluated by enzyme linked immunosorbent assay (ELISA), and effects of EPO on proliferation and osteoblastic differentiation of bone marrow stromal cells (BMSC) were analyzed by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) and reverse transcription quantitative real-time PCR (RT-qPCR), respectively. Finally, EPO-CS/GP/GA was injected into the maxillary sinus floor of the rabbit to test the potential application for MSFA.

RESULTS

Results showed that GT was decreased with the increase of pH value. The GT was 110±15s at pH 7.0. SEM images showed that the CS/GP/GA hydrogel had a sponge network structure. Results from ELISA assay revealed that the cumulative release of EPO from the EPO-CS/GP/GA hydrogel reached 67% at 4h, and 94% at 15 days. MTT assay showed that EPO within EPO-CS/GP/GA hydrogel could significantly promote proliferation of BMSCs compared to control group (p<0.001) . Results of RT-qPCR assays demonstrated that the expression of Sp7, Runx2, Col I and Alp were significantly increased from EPO-CS/GP/GA group compared to control group on day 14 (p<0.001). Importantly, EPO-CS/GP/GA hydrogel could significantly induce bone formation (81.98mm³) compared with control group (43.11mm³) after 12 weeks post-implantation in vivo. The calculation of thickness of mesenchymal condensation indicated that thickness of mesenchymal condensation was significantly increased from EPO-CS/GP/GA group (∼121.4μm) compared to control group (∼37μm) resulting in enhancing intramembranous ossification.

SIGNIFICANCE

The EPO-CS/GP/GA hydrogel provides a novel strategy for MSFA with a minimally invasive way.

Ex vivo investigations on bioinspired electrospun membranes as potential biomaterials for bone regeneration

OBJECTIVES

To assess the surface characteristics and composition that may enhance osteoblasts viability on novel electrospun composite membranes (organic polymer/silicon dioxide nanoparticles).

METHODS

Membranes are composed by a novel polymer blend, the mixture of two hydrophilic copolymers 2-hydroxyethylmethacrylate-co-methylmethacrylate and 2-hydroxyethylacrylate-co-methylacrylate, and they are doped with silicon dioxide nanoparticles. Then the membranes were functionalized with zinc or doxycycline. The membranes were morphologically characterized by atomic force and scanning electron microscopy (FESEM), and mechanically probed using a nanoindenter. Biomimetic calcium phosphate precipitation on polymeric tissues was assessed. Cell viability tests were performed using human osteosarcoma cells. Cells morphology was also studied by FESEM. Data were analyzed by ANOVA, Student-Newman-Keuls and Student t tests (p < 0.05).

RESULTS

Silica doping of membranes enhanced bioactivity and increased mechanical properties. Membranes morphology and mechanical properties were similar to those of trabecular bone. Zinc and doxycycline doping did not exert changes but it increased novel membranes bioactivity. Membranes were found to permit osteoblasts proliferation. Silica-doping favored cells proliferation and spreading. As soon as 24 h after the seeding, cells in silica-doped membranes were firmly attached to experimental tissues trough filopodia, connected to each other. The cells produced collagen and minerals onto the surfaces.

CONCLUSIONS

Silica nanoparticles enhanced surface properties and osteoblasts viability on electrospun membranes.

CLINICAL SIGNIFICANCE

The ability of silica-doped matrices to promote precipitation of calcium phosphate, together with their mechanical properties, observed non-toxicity, stimulating effect on osteoblasts and its surface chemistry allowing covalent binding of proteins, offer a potential strategy for bone regeneration applications.

In vitro bioactivity of AH plus with the addition of nano-magnesium hydroxide

Background

AH Plus (AH) has been widely used as a root canal sealer in the endodontic field due to its superior physicochemical properties. However, clinical application of AH is limited due to its weak bioactivity.

Methods

In this study, we have developed an AH cement containing nano-magnesium hydroxide (NMH) as an additive to enhance the bioactivity of AH. The NMH can neutralize pH and facilitate bone formation. The objective of this study was to evaluate the effects of NMH and modified AH on osteoblasts behavior in vitro. The CCK-8, alkaline phosphatase (ALP) staining, and real-time polymerase chain reaction (PCR) assays were used to assess the proliferation and differentiation of MC3T3-E1 cells, respectively. The adhesion and spreading of MC3T3-E1 cells were investigated in vitro by scanning electron microscopy (SEM). Meanwhile, the flow and magnesium ion release of the modified AH was also concerned.

Results

In vitro cell assays further showed that the addition of NMH into AH cement, which was denoted as modified AH (especially AH+3%NMH), could effectively improve the proliferation and osteogenic differentiation of MC3T3-E1 cells.

Conclusions

Taken all together, we believe that the modified AH samples (especially AH+3%NMH) have outstanding biocompatibility and osteogenic properties and may have great potential in endodontic field.

Enhanced Osseointegration Capability of Poly(ether ether ketone) via Combined Phosphate and Calcium Surface-Functionalization

Biomedical applications of poly(ether ether ketone) (PEEK) are hindered by its inherent bioinertness and lack of osseointegration capability. In the present study, to enhance osteogenic activity and, hence, the osseointegration capability of PEEK, we proposed a strategy of combined phosphate and calcium surface-functionalization, in which ozone-gas treatment and wet chemistry were used for introduction of hydroxyl groups and modification of phosphate and/or calcium, respectively. Surface functionalization significantly elevated the surface hydrophilicity without changing the surface roughness or topography. The cell study demonstrated that immobilization of phosphate or calcium increased the osteogenesis of rat mesenchymal stem cells compared with bare PEEK, including cell proliferation, alkaline phosphatase activity, and bone-like nodule formation. Interestingly, further enhancement was observed for samples co-immobilized with phosphate and calcium. Furthermore, in the animal study, phosphate and calcium co-functionalized PEEK demonstrated significantly enhanced osseointegration, as revealed by a greater direct bone-to-implant contact ratio and bond strength between the bone and implant than unfunctionalized and phosphate-functionalized PEEK, which paves the way for the orthopedic and dental application of PEEK.

Calcium Polyphosphate Nanoparticles Act as an Effective Inorganic Phosphate Source during Osteogenic Differentiation of Human Mesenchymal Stem Cells

The ability of bone-marrow-derived mesenchymal stem/stromal cells (BM-MSCs) to differentiate into osteoblasts makes them the ideal candidate for cell-based therapies targeting bone-diseases. Polyphosphate (polyP) is increasingly being studied as a potential inorganic source of phosphate for extracellular matrix mineralisation. The aim of this study is to investigate whether polyP can effectively be used as a phosphate source during the in vitro osteogenic differentiation of human BM-MSCs. Human BM-MSCs are cultivated under osteogenic conditions for 28 days with phosphate provided in the form of organic β-glycerolphosphate (BGP) or calcium-polyP nanoparticles (polyP-NP). Mineralisation is demonstrated using Alizarin red staining, cellular ATP content, and free phosphate levels are measured in both the cells and the medium. The effects of BGP or polyP-NP on alkaline phosphatase (ALP) activity and gene expression of a range of osteogenic-related markers are also assessed. PolyP-NP supplementation displays comparable effects to the classical BGP-containing osteogenic media in terms of mineralisation, ALP activity and expression of osteogenesis-associated genes. This study shows that polyP-NP act as an effective source of phosphate during mineralisation of BM-MSC. These results open new possibilities with BM-MSC-based approaches for bone repair to be achieved through doping of conventional biomaterials with polyP-NP.

Tissue non-specific alkaline phosphatase mediates the accumulation of cholesterol esters in the murine Y1 adrenal cortex cell line

BACKGROUND

Cholesterol esters (CEs) accumulate in the cells of the adrenal cortex and are used for the synthesis of steroid hormones. The full molecular pathways involved in mediating the accumulation of CEs within the adrenal cortex are yet to be elucidated. Tissue non-specific alkaline phosphatase (TNAP) is needed for intracellular lipid accumulation of triglycerides in adipocytes and is also expressed in the cortical cells of the adrenal gland. Therefore we aimed to determine if TNAP is needed for the accumulation of CEs within the murine Y1 adrenal cortex cell line.

METHODS

Y1 cells were induced to accumulate lipids. Lipid accumulation and TNAP activity and expression were determined throughout intracellular lipid accumulation. The location of TNAP within the cell was determined through immunohistochemical analysis. Lipid accumulation in the cells was associated with a rise in TNAP activity and TNAP was localised to lipid droplets within the Y1 cells. Inhibition of TNAP with a specific inhibitor (levamisole) resulted in the cessation of CE accumulation.

DISCUSSION AND CONCLUSIONS

These data demonstrate that TNAP plays a role in the control of lipid accumulation in this adrenal cortex cell line. Therefore, in both triglyceride and CE storing cell types TNAP would seem to be essential for intra-cellular lipid storage.