Biological Effects of Low-Dose Radiation Therapy: From Mechanistic Aspects to Translational Approaches and Challenges.

A scaffold design method for femoral defects incorporating Haversian system-inspired architecture: Performance comparison of circumferential and radial canal arrangements.

Osteocytes provide essential functions for the maintenance of healthy bone tissue. They are embedded in lacunar pores within the mineralised bone matrix and communicate through interconnected dendritic cell processes that are housed in canalicular channels constituting the osteocyte lacunocanalicular network (LCN). Ageing is associated with increased fracture risk and bone fragility, particularly in elderly women. Despite the LCN playing a critical role in bone remodelling, characteristics of the network in bone tissue of different individual age and mineral content is thus far largely unexplored. Confocal laser scanning microscopy was used to image the fluorescent-stained LCN of cortical osteons in iliac crest bone specimens from female donors with mean age 60 years (n = 6) and 94 years (n = 6) in 3D. Quantitative backscattered electron imaging was also used to assess osteonal mineral content to compare LCN structure in highly and lowly mineralised osteons. Network defects were identified in one-third of osteons, which were further investigated using focussed ion beam scanning electron microscopy. Assessment of the LCN revealed no influence of individual age on the canalicular density, the volume of the lacunae or the degree of the lacunae, whereas canalicular density is inversely correlated with osteonal mineral content. An increase in the volume of non-mineralised matrix is demonstrated in defective regions that are prevalent in all individuals. While relative osteon age, as characterised by mineral content, influences the density of the canaliculi in the LCN, there is no influence of the age of the individual women over 60 years. STATEMENT OF SIGNIFICANCE: Osteocytes play a central and ongoing role in bone health throughout the lifespan: they orchestrate bone remodelling by regulating osteoclastic bone resorption and osteoblastic bone deposition, as well as controlling subsequent bone mineralisation. Deterioration of the osteocyte lacunocanalicular network may contribute to the decline in bone quality observed with age. Consequently, we studied this communication system in 3D in bone from middle-aged to elderly donors. Unexpectedly, individual age had no influence on network characteristics, but the density of the network was decreased in older osteons. Furthermore, we observed network defects that are surprisingly common at all ages investigated. The size of these defects increases with age, suggesting a possible link to the concurrent reduction in bone quality.

Injectable natural Tremella-derived hydrogel for reversing ferroptosis-mediated osteoporotic microenvironment imbalance and promoting osteoregeneration.

To achieve bone regeneration in critical size defects, filling of the defect either with autologous bone or with a biodegradable bone substitute material possessing osteoconductivity and osteoinductivity is required. Biomimetically mineralized collagen is a nanocomposite material that closely resembles the natural bone matrix in composition and structure and has proven potential for filling bone defects. Since the mineral phase hydroxyapatite can bind proteins, the aim of the present study was to explore this biomaterial as a delivery system for the osteoinductive factor bone morphogenetic protein-2 (BMP-2) and to investigate the dependence of BMP-2 release on the mineral content. Three-dimensional scaffolds with varying mineral content were prepared by blending biomimetically mineralized collagen and non-mineralized collagen suspensions, followed by freeze-drying and chemical crosslinking. While the average pore size decreased, the stiffness of the scaffolds increased with increasing mineral content; all scaffold variants exhibited a fundamentally elastic behavior. After loading, the release of BMP-2 was investigated over 28 days. A significant influence of the mineral content on the release kinetics of BMP-2 was observed-the higher the mineral content, the stronger the retention of BMP-2 in the scaffolds. In contrast, the release of the vascular growth factor-A (VEGF-A), which was examined for comparison, was hardly influenced by the mineral content, indicating a low retention of VEGF-A by binding to the mineral phase. In summary, adjustment of the mineral content opens up the possibility of controlling the release of BMP-2 in a customized manner, but this is not transferable to VEGF-A.

Fisetin modulates fluoride induced osteochondral toxicity in zebrafish larvae.

Clinical Outcomes of Anorganic Bone Matrix Combined With a P-15 Osteogenic Cell-Binding Peptide (ABM/P-15) in One- and Two-Level Transforaminal Lumbar Interbody Fusion (TLIF): A Propensity-Matched Comparison

Background and Objectives: Reduced bone quality due to osteoporosis significantly complicates oral rehabilitation and bone regeneration therapies. While Vitamin D (Vit. D3) is crucial for osteogenesis, systemic administration often lacks local efficacy. This study aimed to evaluate the osteoregenerative potential of a novel Chitosan-based nanostructured scaffold (NS) loaded with Vit. D3, underlining its efficacy in vitro and in an ovariectomized (OVX) rat model of osteoporosis. Materials and Methods: Chitosan NSs were fabricated with varying Vit. D3 concentrations. In vitro assessments included cytotoxicity (MTT assay), cell viability (Alamar Blue), and mineralization (Alizarin Red) using human dental follicle stem cells. In vivo, 30 Wistar rats were ovariectomized to induce osteoporosis (confirmed by biomarkers Osteocalcin and β-CTX) and were divided into three groups (n = 10). Bilateral maxillary bone defects were treated with (1) a Control (clot only), (2) a Hemostatic Sponge with Vit. D3 (HS/Vit. D3), or (3) an NS loaded with Vit. D3 (NS/Vit. D3-6.25 ng/mL). Histological and morphometric analyses were performed at 4 and 8 weeks. Results: In vitro, the NS loaded with 6.25 ng/mL Vit. D3 demonstrated superior cytocompatibility, achieving a cell viability of 117.77% at 72 h and significantly enhanced calcium nodule deposition compared to controls. In vivo, a total of 44 defect sites were analyzed following the exclusion of compromised samples (Control: 16 sites; HS/Vit. D3: 16 sites; NS/Vit. D3: 12 sites). The NS/Vit. D3-6.25 ng/mL group exhibited the highest degree of mature bone formation and vascularization (p < 0.05) compared to the Control and HS/Vit. D3 groups. While cellular activity (osteoblasts/osteocytes) was initially higher in the HS/Vit. D3 group, the NS/Vit. D3-6.25 ng/mL group achieved superior structural integration and scaffold replacement by mature bone tissue over time. Conclusions: The novel Vit. D3-loaded Chitosan NS effectively promotes bone regeneration in osteoporotic conditions. It supports osteogenic differentiation in vitro and enhances bone matrix maturation in vivo, suggesting its potential as a bioactive scaffold for regenerative dentistry.

The rising number of spinal fusion procedures has increased the demand for effective bone graft substitutes. Although recombinant human bone morphogenetic protein-2 is clinically used for its osteoinductive properties, dose-dependent complications limit its broader application. Demineralized bone matrix (DBM) and bioactive glass (BAG) are alternative materials, but their comparative and combined osteogenic potential remains unclear. This study evaluated the in vitro osteoinductive activity of BMP-2, DBM, BAG, and a composite nano-BAG + DBM formulation. An in vitro C2C12 alkaline phosphatase (ALP) assay was used to assess osteogenic differentiation following exposure to BMP-2 (50 ng/mL) and test materials at 20 and 50 mg/mL. Gel-based formulations were standardized to 1 g total weight and included the following: nano-BAG + DBM (33:33:33 of cortical DBM, 45S5 BAG, and porcine gelatin; marketed as NanoFuse DBM), BAG + Gel (50:50 BAG and gelatin), and DBM + Gel (50:50 DBM and gelatin). Wet/frozen DBM (100% DBM) served as the native reference. ALP activity was measured at 410 nm and normalized to total protein content. Wet/frozen DBM exhibited the highest ALP activity (>94.420 units/mg protein), followed by nano-BAG + DBM at 50 mg/mL, which exceeded the assay's upper detection limit (>92.473 units/mg). DBM + Gel showed moderate activity, while BAG + Gel and the negative control showed minimal induction. BMP-2 at 50 ng/mL demonstrated lower activity (31.700 units/mg) than nano-BAG + DBM. NanoFuse DBM demonstrated dose-dependent osteoinductive activity and may offer a safer, more efficient alternative to BMP-2 and traditional grafts in spinal fusion, trauma, and joint reconstruction. NanoFuse DBM demonstrated dose-dependent osteoinductive activity and outperformed DBM, BAG, and BMP-2 at the tested dose. These findings support its potential as a bone graft substitute in spinal fusion and other orthopedic applications where improved biological performance and safety are critical. Further research is needed to optimize BMP-2 dosing and evaluate NanoFuse DBM's in vivo efficacy.

The inorganic matrix of bone consists predominantly of calcium phosphate compounds. Among these, calcium phosphate ceramics are widely employed as bioactive materials due to their close structural resemblance to native bone tissue. Platelets, conversely, are rich in cytokines and growth factors that play critical roles in promoting osteogenesis and soft tissue repair. This biological synergy has led to the hypothesis that a combination of calcium phosphate-based biomaterials and platelet-rich fibrin (PRF) may enhance bone regeneration outcomes. Metacarpal and metatarsal fractures are frequently encountered in feline patients, accounting for approximately 3.3% of all reported fractures. Surgical intervention is typically indicated in cases involving displacement, multiple (>2) metacarpal/metatarsal fractures, or comminuted fracture patterns. This study evaluated 10 feline patients of varying breeds, sexes, and ages diagnosed with metacarpal or metatarsal fractures through comprehensive clinical and radiographic assessment. Of these, five cases (Cases 1, 4, 6, 7, and 8) presented with metacarpal fractures, while the remaining five (Cases 2, 3, 5, 9, and 10) exhibited metatarsal fractures. The therapeutic approach consisted of intramedullary fixation using Kirschner wires (K-wires), supplemented with the local application of a composite biomaterial composed of PRF and calcium phosphate-based powder directly at the fracture site. Postoperative follow-up was conducted through day 45. By this time point, all cases demonstrated weight-bearing capability on the affected limb, radiographic resolution of the fracture line, and satisfactory functional recovery. The objective of this study was to evaluate the efficacy of platelet-rich fibrin enriched with calcium phosphate-based powder in the surgical management of feline metacarpal and metatarsal fractures and to disseminate these findings for clinical application in veterinary practice.

Objective: This study evaluated outcomes following bone grafting in the foot or ankle using a natural bone matrix with porcine collagen (NBM-PC) composite. Methods: Sixty-six patients were enrolled in this prospective, single-arm, multicenter study. After signing the informed consent, all patients underwent standard-of-care treatment involving bone grafting on their foot or ankle. Patients were seen at 6 weeks, 3 months, 6 months, and 12 months after surgery. Patients also underwent a radiological examination, either radiograph, computed tomography, or magnetic resonance imaging. Results: The most common surgery was arthrodesis (n = 35), followed by skeletal deformity corrections (n = 12). At the 12-month follow-up, 53 patients were evaluated, and radiological examinations indicated a fusion rate of 85%. There was osteolysis of < 1 cm2 in 5% of patients, while six patients presented with non union or pseudoarthrosis. The most common serious adverse events were pseudoarthrosis (n = 2) and wound infection (n = 2), unrelated to the NBM. Conclusions: The radiographic fusion rate of 85% at the 12-month follow-up for this NBM is consistent with that reported for bone grafts other than void fillers. The lack of adverse events related to the use of NBM indicates it is safe and can provide an alternative to autografts in foot and ankle surgery. Level of evidence: IV; Prospective cohort study

In this study, an innovative bioreactor, named BioAxFlow, particularly suitable for tissue engineering applications, is tested. Unlike traditional bioreactors, it does not rely on mechanical components to agitate the culture medium, but on the unique fluid-dynamics behaviour induced by the geometry of the culture chamber, which ensures continuous movement of the medium, promoting the constant exposure of the cells to nutrients and growth factors. Using the human osteosarcoma cell line SAOS-2, the bioreactor’s ability to enhance cell adhesion and proliferation on polylactic acid (PLA) scaffolds, mimicking bone matrix architecture, is investigated. Cells cultured in the bioreactor showed significant improvement in cell growth and adhesion, compared to static cultures, and a more homogeneous cell distribution upon the scaffold surfaces, which is crucial for the development of functional tissue constructs. The bioreactor also preserves the osteogenic potential of SAOS-2 cells as assessed by the expression of key osteogenic markers. Additionally, it retains the tumorigenic characteristics of SAOS-2 cells, including the expression of pro-angiogenic factors and apoptosis-related genes. These results indicate that the BioAxFlow bioreactor could be an effective platform for tissue engineering and cancer research, offering a promising tool for both regenerative medicine applications and drug testing.

Here we present the bone histology of Berthasaura leopoldinae MN 7821-V, a basal abelisauroid from the Late Cretaceous of Southern Brazil, and discuss the impacts of multi-element sampling in ceratosaurs, including its biological implications. Femur, tibia, and fibula from the holotype were sectioned for this study. Age was estimated using LAG retro-calculation and cyclical growth marks count. The cortex of the femur and tibia consists predominantly of parallel-fibered tissue mixed with regions of fibrolamellar bone, which suggests slow osteogenesis similar to that inferred for abelisauroids rather than ceratosaurids and most theropod dinosaurs. In contrast, the fibula is predominantly composed of a fibrolamellar complex. Whereas the femur is primarily filled by longitudinally oriented vascular canals, with a band of plexiform, the tibia is primarily of longitudinal with a reticular pattern, and the fibula is exclusively of a simple longitudinal network with primary and secondary osteons. The bone cortices are commonly interrupted by lines of arrested growth (LAG) in the femur and tibia, and LAGs plus annuli in the fibula, indicating that the bone growth was periodic. Outer circumferential layers of lamellar bone were not recorded in any of the sampled elements. In addition, the thickness of the growth zones was consistent in the femur and tibia; that, in combination with absent outer circumferential layers, suggests that MN 7821 was a subadult that did not reach sexual maturity before death. This corroborates a previous ontogenetic assessment inferred based on morphology. Inter-elemental variations in bone matrix type and growth record were observed in Berthasaura, showing that such discrepancy would impact metabolic inferences based on single bones. In addition, the particularly narrowing growth zones from the femur of MN-7821-V provided higher values of retro-calculated LAG in comparison to the tibia and fibula. Based on this histovariability observed in the different elements of Berthasaura's skeleton, our work also pointed to an underlying bias concerning LAG retro-calculation based on metric extrapolations from a single bone, which reinforces the importance of working with a multi-elemental sample.

Stress fractures are common in racehorses, with the metacarpophalangeal (MCP) joint being the most frequently affected site as it is subjected to high-magnitude and high-rate cyclic loads during training and racing. These loads lead to repeated compressive stresses, resulting in subchondral bone (SCB) sclerosis, fatigue microcracks, and matrix damage that can progress to parasagittal fractures or palmar osteochondral disease (POD). The present study developed joint-specific 3D FE models and slice-based FE models using standing CT images for three trained racehorses, each presenting distinct SCB conditions common in racehorses as identified by their CT images: (1) biaxial sclerotic condylar SCB with no visible lesions: BS, (2) focal lytic SCB with associated sclerosis in the PSG: LGL, and (3) focal lytic SCB with associated sclerosis in the condyles: BCL. Both models predicted similar overall patterns of SCB stress and strain, identifying peak tensile and compressive strains in the PSGs and condyles, while minimal strains were observed over the sagittal ridge. The 3D models predicted a larger volume of highly strained bone compared to slice-based models, particularly in the horse with biaxial sclerosis. Both 3D and slice-based FE models demonstrated strong agreement in identifying the PSG and midcondyles as high-strain regions. The sensitivity analysis showed that variations in input parameters had minimal impact on the results, indicating the robustness of slice-based models. Despite being less detailed, slice-based models were much faster and more straightforward to develop and provided stress and strain patterns comparable to 3D models. These findings suggest that slice-based models offer a valuable tool for rapid assessment of biomechanical behaviour in equine fetlock joints, particularly for identifying regions at high-risk of failure in the clinical setting.

It is essential to maintain the integrity of liner–cement–formation in the well completion and production stages. However, large liner deformations have been extensively experienced during hydraulic fracturing operations in carbonate formations. This work reveals that local collapse and burst may cause the liner to deform during hydraulic fracturing operations. The stressing and deformation of liners are investigated using numerical simulation at two levels. First, a stand-alone liner is compressed from the outside or expanded from the inside to calibrate the plastic parameters by matching the collapse and burst pressures in the liner’s technical specifications. The influence of the non-uniformity of loads and confinement on the liner’s bearing capacity is then investigated. Second, the influence of imperfections in the cement or cavities in the formation on liner deformation in a liner–cement–formation system is explored. Simulation results indicate that the hydraulic communication between the cavities, vugs, or other imperfections in formation or cementing around a liner and hydraulic fractures can introduce an uneven load on the liner, subsequently threatening the integrity of the liner–cement–formation system and causing a large deformation in the liner. This mechanism has not received much attention in the practical hydraulic fracturing operation design.

Collagen, a key extracellular matrix (ECM) protein of bone, provides connective tissues with strength and cohesion through its unique triple-helical structure, whose disruption is linked to numerous diseases and aging. The nanoscale organization of collagen within native bone ECM remains poorly understood. In this study, we employ high-resolution fast magic-angle spinning (MAS) solid-state NMR (ssNMR) spectroscopy to investigate collagen structure directly within the native bone matrix. Using two-dimensional (2D) 1H-detected 13C-1H double cross-polarization experiments at 70 kHz MAS, we detect signals from low-abundance residues and uncover previously unresolved inter-residue correlations in the aliphatic region. These proximities suggest potential π-interactions between aromatic residues and anionic or imino acids within the triple helix. Such interactions could provide additional stabilizing forces that are frequently overlooked in hydrogen bond-centered structural models. Our results reveal previously missing insights into the chemico-physical basis of collagen structural stabilization in the native ECM, laying the foundation for understanding disease-related structural changes and guiding the design of biomimetic materials to advance tissue engineering.

Cancer-related bone metastasis represents a dynamic and multifaceted process driven by reciprocal interactions between malignant cells and the specialized bone microenvironment. Within this setting, the immune system exerts a pivotal influence, modulating both the progression of metastasis and the remodeling of bone tissue. The metastatic bone niche is frequently characterized by a state of immune dysregulation, in which chronic inflammation and immunosuppressive signaling pathways coexist. This interplay results in an environment that impairs effective antitumor immunity while simultaneously facilitating tumor cell colonization, survival, and osteolytic activity. A defining feature of bone metastasis is its tendency to establish an immunologically cold microenvironment, typified by low infiltration of cytotoxic T cells and reduced expression of immune-activating cytokines. However, this does not imply an absence of immune activity. Rather, certain immune cell subsets, such as regulatory T cells, myeloid-derived suppressor cells (MDSCs), and alternatively activated macrophages, accumulate within the metastatic site, where they secrete factors that suppress adaptive immune responses and support tumor-associated osteoclast activation. Through these mechanisms, cancer cells effectively hijack immune regulatory pathways to evade immune surveillance and promote bone destruction. On the other hand, systemic inflammation and cytokine storms are central players in the complex network governing bone metastatic progression. They create a pro-tumor, osteolytic environment by recruiting immunosuppressive cells, fueling osteoclast activity, promoting tumor cell survival and dissemination, and destabilizing the bone matrix. These inflammatory processes are intertwined with immune evasion mechanisms, tissue remodeling, and dormancy-reactivation cycles, collectively accelerating the metastatic cascade in bone. Targeting these inflammatory pathways represents a critical strategy to alter the course of metastatic disease and improve therapeutic outcomes.

Inadequate control of inflammation and insufficient vascularization remain major challenges in repair of bone defects. Here, we developed a multifunctional nanoflower, Au NPs@ZIF-8/Ga, by loading gallic acid (Ga) into a nanoflower-like structure consisting of gold nanoparticles (Au NPs) core and zeolitic imidazolate framework-8 (ZIF-8) shell, to synergistically exert anti-inflammatory, pro-angiogenic, and osteogenic effects. The hollow architectures of the synthesized Au NPs@ZIF-8/Ga nanoflowers were characterized by transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and nitrogen adsorption-desorption analysis. In vitro studies demonstrated that Au NPs@ZIF-8/Ga reduced secretion of pro-inflammatory cytokines in macrophages via suppressing NF-κB pathway activation, while concurrently promoted endothelial cell migration, and tube formation. Yet, Au NPs@ZIF-8/Ga enhanced osteogenic differentiation of MC3T3-E1 cells, as evidenced by the upregulated expression of bone formation related genes runt-related transcription factor 2 (RUNX2) and osteocalcin (OCN), as well as increased alkaline phosphatase (ALP) activity and bone matrix mineralization. In vivo studies showed that Au NPs@ZIF-8/Ga promoted early resolution of inflammation, neovascularization and robust new bone formation in a rat model with critical-sized calvarial defects, as confirmed by Micro-computed tomography (micro-CT) and histological analyses. Collectively, this work presents a versatile nanoplatform for reducing inflammation in early stage while subsequently promoting angiogenesis and osteogenesis, thereby offering a promising therapeutic strategy for bone regeneration under inflammatory conditions.

Cells residing in, and on, the calcified periodontal bone matrix experience numerous mechanical stimuli daily. The nature of the mechanical stimuli depends on whether the mechanical triggers are physiological, e.g., arising from masticatory forces, distributed via a healthy periodontal ligament to the alveolar bone, or represent "error-loads", e.g., arising during orthodontic tooth movement or around dental implants. Mechanosensitive osteocytes mediate osteoclast and osteoblast recruitment and activity in the presence of unloading, but "error loads" can directly activate signaling pathways in osteoblasts, thereby directing osteoblast activity and accumulating the bone mass essential for a functional masticatory system. Mitogen-activated protein kinases (MAPKs) play a pivotal role in regulating osteoblast growth, differentiation, and survival. This scoping review investigates which MAPKs are rapidly (within minutes) activated in osteoblasts in response to different types of mechanical stimuli. In the discussion, we tie the activation of MAPKs to altered osteoblast number and activity and the production of signaling factors. Using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, we identified studies linking MAPKs, osteoblasts, and mechanical stress. The review included 33 in vitro studies. The findings revealed that extracellular signal-regulated kinases ERK1/2, p38, and JNK were rapidly activated in osteoblasts in response to various mechanical stimuli. Fluid flow forces, representing shear stress such as those present during mastication or orthodontic movement, activated all three MAPK branches. Substrate stretch, applied to simulate strain from mastication, induced a broad spectrum of responses. Hydrostatic pressure, often applied to reflect compression from implant loading or mastication, triggered all known MAPK pathways within an hour. In contrast, more selective stimuli such as low-intensity pulsed ultrasound and hypotonic pressure preferentially activated ERK1/2. Regardless of the stimulus, ERK1/2 was usually, and rapidly activated within minutes. In conclusion, diverse mechanical stimuli, including shear stress, substrate strain, and hydrostatic pressure, frequently, and rapidly, upregulate ERK1/2 signaling in osteoblasts. Given ERK1/2's established role in promoting osteoblast proliferation and differentiation, this early activation may help explain the localized bone formation observed under mechanical loading during orthodontic treatment, dental implant integration, or alveolar bone remodeling.

Bone formation is a dynamic process, while the stiffness of extracellular matrix increases dynamically during bone maturation. Matrix stiffness can significantly regulate the stem cell differentiation and bone repair. It is particularly important to develop dynamic stiffness scaffolds to simulate dynamic mechanical microenvironment for bone repair. This study proposed a novel method to achieve dynamic improvement of scaffold stiffness by mineralization, which is a natural process of bone matrix dynamic stiffening. The decalcified bone matrix (DBM)/collagen (Col)/silicon-substituted hydroxyapatite (SiHA) scaffold was constructed by coating the Col/SiHA on the surface of DBM. When the scaffolds contacted with body fluid, the stiffness of scaffolds were enhanced by mineralization, increasing from 9.10 ± 4.42 kPa to 19.77 ± 9.66 kPa in the DBM/Col scaffold and from 40.54 ± 6.25 kPa to 69.40 ± 8.76 kPa in the DBM/Col/SiHA scaffold. The experimental results proved that the DBM/Col/SiHA scaffold with dynamic stiffness had good biocompatibility and could promote the osteogenic differentiation of mesenchymal stem cell. The DBM/Col/SiHA scaffold, when implanted in a rat calvarial defect model, further enhanced bone regeneration and integration, as evidenced by a bone mineral density reaching 285.592 ± 19.611 mg HA ccm-1at 12 weeks. This research may provide new insights into the application of mineralization-dependent stiffening scaffolds in bone tissue engineering.