Three-point bending of rat femur in the mediolateral direction: introduction and validation of a novel biomechanical testing protocol

Accurate measurement of a bone surrogate flexural rigidity in three- and four-point bending

The mechanical assessment of long bones through bending is an established preclinical approach to evaluate the effectiveness of treatments for osteoporosis and fractures. Three- and four-point bending (3PB and 4PB) tests are the most common methods for mechanical characterization of long bones with Euler-Bernoulli (EB) theory to calculate of bone flexural rigidity (EI). Previous studies demonstrated that EB theory underestimates the EI of long bones due to its reliance on assumptions that are not entirely applicable to long bones. Therefore, the current study aimed to evaluate the factors that affect the percent error (PE) and bias stemming from the omission of contact and shear deflections in the EI estimation using mechanical testing and finite element analysis (FEA). The true EI of a porcine bone surrogate was used to quantify the percent error and bias of EI estimations from three deflection measurement methods and FEA, in 3PB and 4PB. The analysis confirmed that bending was the main component of total deflection, but only contributed to approximately 50 % and 65 % of the total deflection in 3PB and 4PB, respectively. The combined shear and indentation deflections accounted for the remainder of the total deflection. The FEA aligned with 3PB and 4PB tests with less than 10 % deviation. Underestimation of EI was largest with deflection measurements taken from the machine crosshead (PE 74 % in 3PB and 71 % in 4PB). However, these underestimations improved notably when indentation and shear deflections were considered (PE 42 % in 3PB and 39 % in 4PB). The deflection measurements from extensometer and digital image correlation (DIC) underestimated the EI by 66 % and 71 % in 3PB, and 57 % and 59 % in 4PB. When corrected for shear and indentation deflections, the 3PB PE reduced to 16 % and 14 %, respectively. In 4PB, PE reduced to, 10 % and 7 %, respectively, demonstrating the advantage of the 4PB test configuration over 3PB. The bias resulting from shear deflection was not consistent across deflection measurement methods; and therefore, cannot be generalized with a constant bias correction. The current study highlighted that a slight error in deflection measurement can lead to a significant inaccuracy in EI measurements. This sensitivity comes from the hyperbolic relationship between EI and deflection which not only depends on the ratio of support span to diameter of the specimen but also the test configuration and the ratio of the elastic to shear modulus of specimen. In other words, the PE from neglecting shear effects increases as the specimen EI increases. Accuracy with less than 10 % PE in EI estimations can be achieved by: 1. taking deflection measurements with extensometers, DIC, or FEA; 2. testing in 4PB instead of 3PB; and, 3. correcting for indentation and shear deflections.

Development of a subject-specific finite element analysis workflow to assess local biomechanics during segmental bone defect healing

Longitudinal estimation of local strain distributions within the regenerative niche of segmental femoral fractures is important for understanding mechanobiology principles for bone healing to design more effective rehabilitation regimens and mitigate nonunion complications. Finite element (FE) modeling is the standard for investigating these biomechanical parameters, yet most existing models lack clinical relevance due to their use of generic data and computational inefficiency. This study developed a subject-specific FE workflow aimed at accurate biomechanical predictions based on subject-specific data while addressing the limitations of previous approaches. For the experimental study, near-critical-sized segmental bone defects were created in the femurs of Wistar rats and stabilized with internal fixators before rehabilitation. Subject-specific geometries of the defect were generated from in vivo micro-CT scans, which were also used to assign material coefficients. Generalized geometries of the cortical and trabecular bone and fixator were integrated to increase computational efficiency. In addition, axial strain data from strain gauges on the fixators were used to define subject-specific boundary conditions, enabling a longitudinal study of the healing process. Sensitivity analyses revealed that incorporating subject-specific boundary conditions significantly enhanced model accuracy, a factor often overlooked in conventional approaches. The workflow was used to build six defect models to approximate compressive strains within the defect and the joint contact force. Strain distributions correlated with experimentally observed mineralization and better predicted functional bone bridging (union) compared to bone volume metrics. This efficient workflow facilitates the assessment of local biomechanics during bone healing and highlights their influence on adaptive regeneration. Further, the findings support the potential application of the subject-specific modeling workflow to guide clinical decision-making and improve therapeutic outcomes for treating bone fractures.

Effects of Moderate-Intensity Aerobic Exercise on Estrogen Levels and Bone Mineral Density in Ovariectomized Rats

OBJECTIVE

This study aimed to explore the effects of moderate-intensity aerobic exercise on estrogen levels and bone density density (BMD) in ovariectomized rats.

METHODS

The sham-operated (SHAM), ovariectomized sedentary (OVX), and ovariectomized exercise (OVX + EX) groups were established. The OVX model was established by bilateral ovariectomy. Bone metabolism indicators, structural mechanical properties of the femur, material mechanical properties of the femur, BMD and bone mineral content were assessed.

RESULTS

Compared with the OVX group, the OVX + EX group had lower levels of Ca, P, and STR-ACP, higher BGP levels, increased maximum load, elastic load, maximum stress, and elastic stress of the tibia, elevated serum E2 levels, decreased LH and FSH levels, and higher BMD (all P < 0.05).

CONCLUSION

Moderate-intensity aerobic exercise can enhance serum hormone levels, improve bone metabolism and biomechanical properties, and increase bone density in ovariectomized rats.

Self-Assembled Nanoparticles with Well-Defined Oligosaccharide Promote Osteogenesis by Regulating Golgi Stress Response

Osteoporosis, a prevalent disease characterized by low bone density and increased fracture risk, poses significant health challenges for the elderly. Current treatments offer short-term benefits but are limited by long-term efficacy and adverse effects, highlighting the need for new strategies. Chondroitin sulfate polysaccharides (CS), a major component of the bone matrix, are crucial for bone and cartilage health. However, their role in osteoporosis is understudied due to the heterogeneity of natural CS. we found reduced CS levels in osteoporosis patients and developed CS4-NP, a self-assembled tetrasaccharide nanoparticle that mimics CS's structure. CS4-NP, which efficiently delivers the active CS4, significantly improves bone mass in ovariectomized osteoporosis models. It activates the Activating Transcription Factor 4-Cystathionine gamma-Lyase signaling axis in pre-osteoblasts, enhancing osteogenesis. our findings suggest that CS4-NP, an oligosaccharide-based nanomaterial, could address the limitations of current treatments and provide a viable strategy for osteoporosis.

Impact of NaOH based perfusion-decellularization protocol on mechanical resistance of structural bone allografts

INTRODUCTION

To mitigate the post-operative complication rates associated with massive bone allografts, tissue engineering techniques have been employed to decellularize entire bones through perfusion with a sequence of solvents. Mechanical assessment was performed in order to compare conventional massive bone allografts and perfusion/decellularized massive bone allografts.

MATERIAL AND METHODS

Ten porcine femurs were included. Five were decellularized by perfusion. The remaining 5 were left untreated as the "control" group. Biomechanical testing was conducted on each bone, encompassing five different assessments: screw pull-out, 3-points bending, torsion, compression and Vickers indentation.

RESULTS

Under the experimental conditions of this study, all five destructive tested variables (maximum force until screw pull-out, maximum elongation until screw pull-out, energy to pull out the screw, fracture resistance in flexion and maximum constrain of compression) were statistically significantly superior in the control group. All seven nondestructive variables (Young's modulus in flexion, Young's modulus in shear stress, Young's modulus in compression, Elastic conventional limit in compression, lengthening to rupture in compression, resilience in compression and Vickers Hardness) showed no significant difference.

DISCUSSION

Descriptive statistical results suggest a tendency for the biomechanical characteristics of decellularized bone to decrease compared with the control group. However, statistical inferences demonstrated a slight significant superiority of the control group with destructive mechanical stresses. Nondestructive mechanical tests (within the elastic phase of Young's modulus) were not significantly different.

Ex Vivo Biomechanical Bone Testing of Pig Femur as an Experimental Model

This study investigates the mechanical behavior of femur bones under loading conditions, focusing on the transition from elastic to plastic deformation and eventual fracture. The force-displacement curves reveal distinct phases of deformation, with an initial linear relationship indicating elastic behavior, followed by deviation from linearity marking the onset of plastic deformation. Fracture occurs beyond a critical load, leading to a sharp drop in the force-displacement curve. The maximum fracture force varies among specimens and is influenced by bone geometry, size, cross-sectional area, and cortical thickness. Post-failure analysis highlights additional insights into fracture mechanics and bone material toughness. Reinforcing bones with screws enhances their strength, which is evident in the higher fracture forces observed in force-displacement diagrams. Fixation procedures following fractures further increase bone strength. Comparing specimens with and without strengthening underscores the effectiveness of reinforcement methods in improving bone mechanical properties. After analyzing the results, it is evident that femur bones with reinforcement can withstand greater loads, and they can also absorb higher impact energies while remaining in the elastic deformation range and without suffering permanent plastic damage. This study provides valuable insights into bone biomechanics and the efficacy of reinforcement techniques in enhancing bone strength and fracture resistance.

Konjac Oligosaccharides Alleviated Ovariectomy-Induced Bone Loss through Gut Microbiota Modulation and Treg/Th17 Regulation

Oligosaccharides from the plant Amorphophallus konjac were potentially effective in menopausal osteoporosis due to their prebiotic attributes. The present work mainly studied the regulation of konjac oligosaccharides (KOS) on menopausal bone loss. Experiments were carried out in ovariectomized (OVX) rats, and various contents of KOS were correlated with diet. After 3 months of treatment, the degree of osteoporosis was determined by bone mineral density and femoral microarchitecture. The research data showed that the 8% dietary KOS significantly alleviated bone loss in OVX rats, as it promoted the bone trabecular number by 134.2% and enhanced the bone bending stiffness by 103.1%. From the perspective of the gut-bone axis, KOS promoted gut barrier repair and decreased pro-inflammatory cytokines. Besides, KOS promoted the growth of Bifidobacterium longum and restored Treg/Th17 balance in bone marrow. The two aspects contributed to decreased osteoclastogenic activity and thus inhibited inflammation-related bone loss. This work extended current knowledge of prebiotic inhibition on bone loss and provide an alternative strategy for osteoporosis prevention.

Mechanical bone strength decreases considerably after microwave ablation-Ex-vivo and in-vivo analysis in sheep long bones

BACKGROUND

Bone metastases are on the rise due to longer survival of cancer patients. Local tumor control is required for pain relief. Microwave ablation (MWA) is a technique for minimally invasive local tumor treatment. Tumor tissue is destroyed by application of local hyperthermia to induce necrosis. Given the most common setting of palliative care, it is generally considered beneficial for patients to start mobilizing directly following treatment. No data on mechanical strength in long bones after MWA have been published so far.

MATERIALS AND METHODS

In- and ex-vivo experiments on sheep tibias were performed with MWA in various combinations of settings for time and power. During the in-vivo part sheep were sacrificed one or six weeks after ablation. Mechanical strength was examined with a three-point bending test for ablations in the diaphysis and with an indentation test for ablations in the metaphysis.

RESULTS

MWA does not decrease mechanical strength in the diaphysis. In the metaphysis strength decreased up to 50% six weeks after ablation, which was not seen directly after ablation.

CONCLUSION

MWA appears to decrease mechanical strength in long bone metaphysis up to 50% after six weeks, however strength remains sufficient for direct mobilization. The time before normal strength is regained after the remodeling phase is not known.

The accordion technique enhances bone regeneration via angiogenesis factor in a rat distraction osteogenesis model

Objective: The purpose of this study was to observe the effect of the accordion technique (AT) during the distraction phase on chondrogenesis and bone regeneration in a rat femoral distraction osteogenesis (DO) model, and investigate its potential mechanism for reducing the total treatment time of DO. Methods: Fifty-four male Sprague-Dawley (SD) rats that were specific-pathogen-free (SPF) were subjected to DO surgery on the right femur. The distraction rate was 0.5 mm/day for 10 days, following a latency period of 5 days. Rats were randomly divided into Control (no AT, n = 18), Group LA (low amplitude with AT, n = 18), and Group HA (high amplitude with AT, n = 18) according to different AT protocols in the distraction phase. Rats were respectively euthanized by anesthesia overdose at 2, 4 and 6 weeks of the consolidation phase, and the femurs were harvested. Digital radiography, micro-computed tomography (micro-CT), biomechanical tests, and histomorphological analysis were used to assess the quality of regenerated bone in the distraction area. Results: Digital radiographic, micro-CT, biomechanical tests, and histological analysis revealed an increase in early-stage callus formation (p < 0.05) and improved blood supply to the callus tissue in Group LA, as compared to both the Control and Group HA. The enhanced differentiation of fibrous and cartilaginous tissue into bone tissue was also observed in Group LA, leading to improved strength and stiffness (p < 0.05) of the regenerated bone at 6 weeks of the consolidation phase. The angiogenic (hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF), p < 0.05) and osteogenic (runt-related transcription factor 2 (RUNX2), osteocalcin (OCN) and osteopontin (OPN), p < 0.05) biomarkers were higher expressed in Group LA at 2 and 4 weeks of consolidation phase, whereas decreased at 6 weeks of consolidation phase. Conclusion: The application of AT with low amplitude during the distraction phase can enhance chondrogenesis and bone regeneration by activating the angiogenesis factor pathway and upregulating the expression of osteogenic-related biomarkers such as HIF-1α, VEGF, RUNX2, OCN, and OPN.

Fracture Healing in Elderly Mice and the Effect of an Additional Severe Blood Loss: A Radiographic and Biomechanical Murine Study

Femoral fractures and severe bleeding frequently occur in old patients showing a delayed healing. As there are no studies investigating the combined effect of high age and severe blood loss on fracture healing, this was examined radiographically and biomechanically in this study. Therefore, young and old male mice were randomly assigned to three operation groups. In the fracture group (Fx), external fixator and osteotomy were applied to the femur. The combined trauma group (THFx) additionally received a pressure-controlled hemorrhage. Sham animals were only implanted with arterial catheter and external fixator. Sacrifice was performed after three weeks and bone healing was evaluated radiologically via µCT, as well as biomechanically using a three-point bending test. A decreased share of callus/total bone volume was observed in old mice with blood loss compared to old Fx. Hemorrhagic shock also reduced the trabecular number in old mice compared to Fx and young THFx. Moreover, a lower elastic limit in old Sham mice without fracture was revealed. Fracture combined with a high loss of blood further reduced the elastic limit in old mice compared to isolated Fx in old animals. In conclusion, this study showed that severe blood loss has a higher negative effect in old mice compared to young ones.

Decellularized vascularized bone grafts as therapeutic solution for bone reconstruction: A mechanical evaluation

INTRODUCTION

Large bone defects are challenging for surgeons. Available reimplanted bone substitutes can't properly restore optimal function along and long term osteointegration of the bone graft. Bone substitute based on the perfusion-decellularization technique seem to be interesting in order to overcome these limitations. We present here an evaluation of the biomechanics of the bones thus obtained.

MATERIAL AND METHODS

Two decellularization protocols were chosen for this study. One using Sodium Dodecyl Sulfate (SDS) (D1) and one using NaOH and H2O2 (D2). The decellularization was performed on porcine forearms. We then carried out compression, three-point bending, indentation and screw pull-out tests on each sample. Once these tests were completed, we compared the results obtained between the different decellularization protocols and with samples left native.

RESULTS

The difference in the means was similar between the tests performed on bones decellularized with the SDS protocol and native bones for pull-out test: +1.4% (CI95% [-10.5%- 12.4%]) of mean differences when comparing Native vs D1, compression -14.9% (CI95% [-42.7%- 12.5%]), 3-point bending -5.7% (CI95% [-22.5%- 11.1%]) and indentation -10.8% (CI95% [-19.5%- 4.6%]). Bones decellularized with the NaOH protocol showed different results from those obtained with the SDS protocol or native bones during the pull-out screw +40.7% (CI95% [24.3%- 57%]) for Native vs D2 protocol and 3-point bending tests +39.2% (CI95% [13.7%- 64.6%]) for Native vs D2 protocol. The other tests, compression and indentation, gave similar results for all our samples.

CONCLUSION

Vascularized decellularized grafts seem to be an interesting means for bone reconstruction. Our study shows that the decellularization method affects the mechanical results of our specimens. Some methods seem to limit these alterations and could be used in the future for bone decellularization.

Wnt10b-overexpressing umbilical cord mesenchymal stem cells promote fracture healing via accelerated cartilage callus to bone remodeling

The aim of this study was to investigate whether HUCMSCs^Wnt10b could promote long bone fracture healing. Commercially-available HUCMSCs^Emp (human umbilical cord mesenchymal stem cells transfected with empty vector) in hydrogel, HUCMSCs^Wnt10b in hydrogel and HUCMSCs^Wnt10b with the Wnt signaling pathway inhibitor IWR-1 were transplanted into the fracture site in a rat model of femoral fracture. We found that transplantation of HUCMSCs^Wnt10b significantly accelerated bone healing in a rat model of femoral fracture. Meanwhile, three-point bending test proved that the mechanical properties of the bone at the fracture site in the HUCMSC^Wnt10b treatment group were significantly better than those of the other treatment groups. To understand the cellular mechanism, we explored the viability of periosteal stem cells (PSCs), as they contribute the greatest number of osteoblast lineage cells to the callus. In line with in vivo data, we found that conditioned medium from HUCMSCs^Wnt10b enhanced the migration and osteogenic differentiation of PSCs. Furthermore, conditioned medium from HUCMSCs^Wnt10b also induced endothelial cells to form capillary-like structures in a tube formation assay, which was blocked by SU5416, an angiogenesis inhibitor, suggesting that enhanced vessel formation and growth also contribute to accelerated hard callus formation. In summary, our study demonstrates that HUCMSCs^Wnt10b promote fracture healing via accelerated hard callus formation, possibly due to enhanced osteogenic differentiation of PSCs and vessel growth. Therefore, HUCMSCs^Wnt10b may be a promising treatment for long bone fractures.

Antiepileptic Stiripentol May Influence Bones

Bone structure abnormalities are increasingly observed in patients chronically treated with antiepileptic drugs (AEDs). The majority of the available data concern older conventional AEDs, while the amount of information regarding newer AEDs, including stiripentol, is limited. The aim of the study was to assess the effect of stiripentol on bones. For 24 weeks, male Wistar rats, received 0.9% sodium chloride (control group) or stiripentol (200 mg/kg/day) (STP group). In the 16th week of the study, we detected lower serum PINP levels in the STP group compared to the control group. In the 24th week, a statistically significant lower 1,25-dihydroxyvitamin D3 level, higher inorganic phosphate level and higher neutrophil gelatinase-associated lipocalin (NGAL) levels in serum were found in the STP group compared to the control. Micro X-ray computed tomography of the tibias demonstrated lower bone volume fraction, lower trabecular thickness, higher trabecular pattern factor and a higher structure model index in the stiripentol group. Considering the results of this experiment on rats which suggests that long-term administration of stiripentol may impair the cancellous bone microarchitecture, further prospective human studies seem to be justified. However, monitoring plasma vitamin D, calcium, inorganic phosphate and kidney function in patients on long-term stiripentol therapy may be suggested.

Biomechanical properties of the bone during implant placement

Background

In this research the biomechanical properties of a bone model was examined. Porcine ribs are used as experimental model. The objective of this research was to investigate and compare the biomechanical properties of the bone model before and after implant placement.

Methods

The bone samples were divided in three groups, Group 1 where ALL-ON-FOUR protocol was used during pre-drilling and placing the implants, Group 2 where ALL-ON-FOUR protocol was used during pre-drilling, and implants were not placed, and Group 3 consisting of intact bones served as a control group. Static and dynamic loading was applied for examining the model samples. Kruskal–Wallis statistical test and as a post-hoc test Mann–Whitney U test was performed to analyze experimental results.

Results

According to the results of the static loading, there was no significant difference between the implanted and original ribs, however, the toughness values of the bones decreased largely on account of predrilling the bones. The analysis of dynamic fatigue measurements by Kruskal–Wallis test showed significant differences between the intact and predrilled bones.

Conclusion

The pre-drilled bone was much weaker in both static and dynamic tests than the natural or implanted specimens. According to the results of the dynamic tests and after a certain loading cycle the implanted samples behaved the same way as the control samples, which suggests that implantation have stabilized the skeletal bone structure.

Is the 0.2%-Strain-Offset Approach Appropriate for Calculating the Yield Stress of Cortical Bone?

The 0.2% strain offset approach is mostly used to calculate the yield stress and serves as an efficient method for cross-lab comparisons of measured material properties. However, it is difficult to accurately determine the yield of the bone. Especially when computational models require accurate material parameters, clarification of the yield point is needed. We tested 24 cortical specimens harvested from six bovine femora in three-point bending mode, and 11 bovine femoral cortical specimens in the tensile mode. The Young's modulus and yield stress for each specimen derived from the specimen-specific finite element (FE) optimization method was regarded as the most ideal constitutive parameter. Then, the strain offset optimization method was used to find the strain offset closest to the ideal yield stress for the 24 specimens. The results showed that the 0 strain offsets underestimated (- 25%) the yield stress in bending and tensile tests, while the 0.2% strain offsets overestimated the yield stress (+ 65%) in three-point bending tests. Instead, the yield stress determined by 0.007 and 0.05% strain offset for bending and tensile loading respectively, can effectively characterize the biomechanical responses of the bone, thereby helping to build an accurate FE model.

Influence of bone defect position and span in 3-point bending tests: experimental and finite element analysis

Three-point bending test is the most common mechanical test used for quantifying the biomechanical quality of bone tissue and bone healing in small animals. However, there is a lack of standardization for evaluation of bone repair by cortical perforation. The aim of this study was to determine the influence of bone defect position in the proximal metaphysis of rat tibias during load application and different span configuration on the three-point bending test outcomes. Cortical defects with 1.6 mm diameter were created at a standardized location on the medial surface of 60 tibias of male Wistar rats. The animals were euthanized 7 days after surgery. Five specimens were used to create 3D models for finite element analysis using high-resolution micro-CT images. Two spans (6 and 10mm) and three positions of the bone defect in relation to the load application (upward, frontal and downward) were evaluated experimentally (n = 10) and in finite element analysis (n = 5). Maximum load (N) and stiffness (N/mm) were statistically analyzed with 2-way ANOVA and Tukey test (α = 0.05). The results demonstrated that span and orientation of the bone defect significantly influenced the fracture pattern, stress distribution and force versus displacement relation. Therefore, reliable outcome can be achieved creating the bone defect at 8 mm from the extremity of the proximal epiphysis; placing a 10 mm distance span and downward facing defect position to allow a better distribution of stress and more fracture patterns that reached the bone defect target area with less intra-group variability.

The Effect of the Supplementation of a Diet Low in Calcium and Phosphorus with Either Sheep Milk or Cow Milk on the Physical and Mechanical Characteristics of Bone using A Rat Model

This study assessed the effect of cow milk (CM) and sheep milk (SM) consumption on the micro-structure, mechanical function, and mineral composition of rat femora in a male weanling rat model. Male weanling rats were fed a basal diet with a 50% reduction in calcium and phosphorus content (low Ca/P-diet) supplemented with either SM or CM. Rats were fed for 28 days, after which the femora were harvested and stored. The femora were analyzed by μ-CT, three-point bending, and inductively coupled plasma-mass spectrometry (ICP-MS). The addition of either milk to the low Ca/P-diet significantly increased (p < 0.05) trabecular bone volume, trabecular bone surface density, trabecular number, cortical bone volume, and maximum force, when compared to rats that consumed only the low Ca/P-diet. The consumption of either milk resulted in a significant decrease (p < 0.05) in trabecular pattern factor, and cortical bone surface to volume ratio when compared to rats that consumed only the low Ca/P-diet. The results were achieved with a lower consumption of SM compared to that of CM (p < 0.05). This work indicates that SM and CM can help overcome the effects on bone of a restriction in calcium and phosphorus intake.

Three-dimensional microstructures of the intracortical canals in the animal model of osteoporosis

Osteoporosis is a major disease in aged women, increasing the risk for fractures accompanied by changes in the microarchitecture. The aim of this study was to investigate the three-dimensional (3D) histomorphology of femur diaphysis in the animal model for postmenopausal osteoporosis. The cortical bone of femur diaphysis of the rat was serially sectioned at a thickness of 5 mm and evaluated age-associated changes of the intracortical (osteonal) canal networks three-dimensionally. Cortical microstructures of 10-month old rats were not affected by ovariectomy. Intracortical canal networks were radial toward endosteal aspect and frequently interconnected across the neighboring canals with short arciform and irregular canals reminiscent for resorption spaces in ovarectomized 16-month old rats, contrary to intact canals in 16-month old control rat. Increased proportion of the periosteal circumference lamella and deformed endosteal regions with rare cortical canals hampered reconstructive histomorphology in ovarectomized rats of 26 month age. We have shown that 3D reconstruction of rat femur of the aged model over 16-month old is suitable methods that evaluate and microstructural change of the intracortical canals and cortical bone porosity by estrogen depletion.

Wireless sensor enables longitudinal monitoring of regenerative niche mechanics during rehabilitation that enhance bone repair

Mechanical loads exerted on the skeleton during activities such as walking are important regulators of bone repair, but dynamic biomechanical signals are difficult to measure inside the body. The inability to measure the mechanical environment in injured tissues is a significant barrier to developing integrative regenerative and rehabilitative strategies that can accelerate recovery from fracture, segmental bone loss, and spinal fusion. Here we engineered an implantable strain sensor platform and longitudinally measured strain across a bone defect in real-time throughout rehabilitation. The results showed that load-sharing permitted by a load-sharing fixator initially delivered a two-fold increase in deformation magnitude, subsequently increased mineralized bridging by nearly three-fold, and increased bone formation by over 60%. These data implicate a critical role for early mechanical cues on the long term healing response as strain cycle magnitude at 1 week (before appreciable healing occurred) had a significant positive correlation with the long-term bone regeneration outcomes. Furthermore, we found that sensor readings correlated with the status of healing, suggesting a role for strain sensing as an X-ray-free healing assessment platform. Therefore, non-invasive strain measurements may possess diagnostic potential to evaluate bone repair and reduce clinical reliance on current radiation-emitting imaging methods. Together, this study demonstrates a promising framework to quantitatively develop and exploit mechanical rehabilitation strategies that enhance bone repair.

Connexin 43 Channels in Osteocytes Regulate Bone Responses to Mechanical Unloading

Connexin (Cx) 43 forms gap junctions and hemichannels that mediate communication between osteocytes and adjacent cells or the extracellular environment in bone, respectively. To investigate the role of each channel type in response to mechanical unloading, two transgenic mouse models overexpressing dominant-negative Cx43 predominantly in osteocytes driven by a 10 kb dentin matrix protein 1 (Dmp1) promoter were generated. The R76W mutation resulted in gap junction inhibition and enhancement of hemichannels, whereas the Δ130-136 mutation inhibited both gap junctions and hemichannels. Both mutations led to cortical bone loss with increased endocortical osteoclast activity during unloading. Increased periosteal osteoclasts with decreased apoptotic osteocytes were observed only in R76W mice. These findings indicated that inhibiting osteocytic Cx43 channels promotes bone loss induced by unloading, mainly in the cortical area; moreover, hemichannels protect osteocytes against apoptosis and promote periosteal bone remodeling, whereas gap junctions modulate endocortical osteoclast activity in response to unloading.

Bone Health in Rats With Temporal Lobe Epilepsy in the Absence of Anti-Epileptic Drugs

Rationale: Epilepsy patients often exhibit reduced bone mineral density and are at an increased risk of bone fracture. Whether these bone abnormalities are due to the use of anti-epileptic drugs (AED’s) or the disease itself is unknown. For example, although decreased bone health in epilepsy patients is generally attributed to the use of AED’s, seizures can also trigger a number of physiological processes that have the potential to affect bone. Therefore, to assess whether bone abnormalities occur in epilepsy in the absence of AED’s, the current study investigated mechanical characteristics and trabecular bone morphology in rats with chronic temporal lobe epilepsy.

Methods: Ten-week old male Wistar rats underwent kainic acid-induced status epilepticus (SE; n = 7) or a sham procedure (n = 9). Rats were implanted with EEG recording electrodes at nine weeks post-SE, and video-EEG was continuously recorded for one week at 10- and 22-weeks post-SE to confirm that SE rats had spontaneous seizures. Open-field testing to assess locomotion was conducted at 23-weeks post-SE. At 24-weeks post-SE, rats were euthanized and tibia were extracted to determine trabecular morphology by micro-computed tomography (µCT), while femurs were used to investigate mechanical properties via 3-point bending.

Results: All post-SE rats had spontaneous seizures at 10- and 22-weeks post-SE, while none of the sham rats had seizures. µCT trabecular analysis of tibia revealed no differences in total volume, bone volume, bone volume fraction, trabecular number, or trabecular separation between post-SE or sham rats, although post-SE rats did have increased trabecular thickness. There were also no group differences in total distance travelled in the open field suggesting that activity levels did not account for the increased trabecular thickness. In addition, no differences in mechanical properties of femurs were observed between the two groups.

Conclusion: There was a lack of overt bone abnormalities in rats with chronic temporal lobe epilepsy in the absence of AED treatment. Although further studies are still needed, these findings may have important implications towards understanding the source (e.g., AED treatments) of bone abnormalities in epilepsy patients.

Calcium Alleviates Fluoride-Induced Bone Damage by Inhibiting Endoplasmic Reticulum Stress and Mitochondrial Dysfunction

Excessive fluoride mainly causes skeletal lesions. Recently, it has been reported that an appropriate level of calcium can alleviate fluorosis. However, the appropriate concentration and mechanism of calcium addition is unclear. Hence, we evaluated the histopathology and ultrastructure, DNA fragmentation, hormonal imbalances, biomechanical levels, and expression of apoptosis-related genes after treating the rats with 150 mg/L NaF and different concentrations of CaCO₃. Our results suggested that NaF induced the histopathological and ultrastructural injury, with a concomitant increase in the DNA fragmentation (P < 0.05) and serum OC (17.5 ± 0.89 pmoL/L) at 120 days. In addition, the qRT-PCR and western blotting results indicated that NaF exposure upregulated the mRNA and protein expression of Bax, Calpain, Caspase 12, Caspase 9, Caspase 7, Caspase 3, CAD, PARP, and AIF while downregulated Bcl-2 (P < 0.01) and decreased the bone ultimate load by 27.1%, the ultimate stress by 10.1%, and the ultimate deformity by 23.3% at 120 days. However, 1% CaCO₃ supplementation decreased the serum OC (14.7 ± 0.65 pmoL/L), bone F content (P < 0.01), and fracture and breakage of collagen fibers and changed the expression of endoplasmic reticulum pathway-related genes and proteins at 120 days. Further, 1% CaCO₃ supplementation increased the bone ultimate load by 20.9%, the ultimate stress by 4.89%, and the ultimate deformity by 21.6%. In summary, we conclude that 1% CaCO₃ supplementation alleviated fluoride-induced bone damage by inhibiting endoplasmic reticulum stress and mitochondrial dysfunction.

Consumption of sheep milk compared to cow milk can affect trabecular bone ultrastructure in a rat model

Cow milk has a positive effect on bone health due to the effects of its protein, fat, lipid, vitamin, and mineral components. Sheep milk contains a unique composition of all of these components. However, to the best of our knowledge the benefits of sheep milk in relation to bone development have not been studied. The aim of the present study was to determine the effects of the consumption of sheep milk in comparison to cow milk on the structural and physical characteristics of growing bone in a rat model. Newly weaned male rats were fed either cow milk, sheep milk or sheep milk diluted to the same total solids content as cow milk for 28 days in addition to a basal chow. At the end of the feeding period animals were euthanized, the femora harvested and stored. The femora were analysed by μ-CT, mechanical bending tests, and ICP-MS. Rats consuming sheep milk in the trial were found to have significantly higher trabecular bone surface density and trabecular bone surface to volume ratio (p < 0.05) when compared to the rats consuming cow milk. No significant differences were observed in the mechanical properties and the mineral composition of the bones (p > 0.05). With the exception of Rb, which was found to be present in higher concentrations in rats consuming sheep milk (p < 0.05). Our results indicate that consumption of sheep milk may positively influence the structural integrity of bone, which may result in an enhancement of bone health.

Iron overload involved in the enhancement of unloading-induced bone loss by hypomagnetic field

During deep-space exploration missions, astronauts will be exposed to abnormal space environments including microgravity and hypomagnetic field (HyMF) that is 10,000 times weaker than geomagnetic field (GMF). It is well known that microgravity in space can induce bone loss; however, it is ill-defined whether HyMF involved in this process. Herein, we aimed to investigate the combined effects of HyMF and microgravity on bone loss. A mouse model of hindlimb suspension (HLU) was adopted to simulate microgravity-induced bone loss, that was exposed to a hypomagnetic field of <300 nanotesla (nT) generated by a geomagnetic field-shielding chamber. Besides, a recent study showed that HLU induced bone loss was orchestrated by iron overload. Therefore, the changes of iron content in unloading-induced bone loss under HyMF condition were detected simultaneously. The results showed HyMF exacerbated the loss of bone mineral content (BMC), induced more detrimental effects on microstructure of cancellous bone but not cortical bone and yielded greater negative effects on biomechanical characteristics in mice femur under unloading status. Concomitantly, there was more iron accumulation in serum, liver, spleen and bone in the combined treatment group than in the separate unloading group or HyMF exposure group. These results showed that HyMF promoted additional bone loss in mice femur during mechanical unloading, and the potential mechanism may be involved in inducing iron overload of mice.

Improving results in rat fracture models: enhancing the efficacy of biomechanical testing by a modification of the experimental setup

Background

Animal fracture models, primarily performed in rats, are crucial to investigate normal and pathological bone healing. However, results of biomechanical testing representing a major outcome measure show high standard deviations often precluding statistical significance. Therefore, the aim of our study was a systematical examination of biomechanical characteristics of rat femurs during three-point bending. Furthermore, we tried to reduce variation of results by individually adapting the span of bearing and loading areas to the bone’s length.

Methods

We examined 40 paired femurs of male Wistar-rats by DXA (BMD and BMC of the whole femur) and pQCT-scans at the levels of bearing and loading areas of the subsequent biomechanical three-point bending test. Individual adjustment of bearing and loading bars was done respecting the length of each specimen. Subgroups of light (< 400 g, n = 22) and heavy (> 400 g, n = 18) animals were formed and analysed separately. We furthermore compared the results of the individualised bending-setting to 20 femurs tested with a fix span of 15 mm.

Results

Femurs showed a length range of 34 to 46 mm. The failure loads ranged from 116 to 251 N (mean 175.4 ± 45.2 N; heavy animals mean 221 ± 18.9 N; light animals mean 138.1 ± 16.4 N) and stiffness ranged from 185 N/mm to 426 N/mm (mean 315.6 ± 63 N/mm; heavy animals mean 358.1 ± 34.64 N/mm; light animals mean 280.8 ± 59.85 N/mm). The correlation of densitometric techniques and failure loads was high (DXA R² = 0.89 and pQCT R² = 0.88). In comparison to femurs tested with a fix span, individual adaptation of biomechanical testing homogenized our data significantly. Most notably, the standard deviation of failure loads (221 ± 18.95 N individualized setting vs. 205.5 ± 30.36 N fixed) and stiffness (358.1 ± 34.64 N/mm individualized setting vs. 498.5 ± 104.8 N/mm fixed) was reduced by at least one third.

Conclusions

Total variation observed in any trait reflects biological and methodological variation. Precision of the method hence affects the statistical power of the study. By simply adapting the setting of the biomechanical testing, interindividual variation could be reduced, which improves the precision of the method significantly.

Electronic supplementary material

The online version of this article (10.1186/s12891-018-2155-y) contains supplementary material, which is available to authorized users.

Healing potential of nanohydroxyapatite, gelatin, and fibrin-platelet glue combination as tissue engineered scaffolds in radial bone defects of rats

Different biomaterials have been used in orthopedic surgery. Evaluation of biomaterials for bone healing promotion has been a wide area of research of the orthopedic field. Sixty critical size defects of 5 mm long were bilaterally created in the radial diaphysis of 30 rats. The animals were randomly divided into six equal groups as empty defect, autograft, nanohydroxyapatite (nHA), Gelatin (Gel)-nHA, fibrin-platelet glue (FPG)-nHA, and Gel-FPG-nHA groups (n = 10 in each group). Radiographs of each forelimb were taken postoperatively on the 1st day and then at the 28th and 56th days post injury. After 56 days, the rats were euthanized and their harvested healing bone samples were evaluated by histopathology, scanning electron microscopy, and biomechanical testing. All the treated defects demonstrated significantly superior new bone formation, remodeling, and bone tissue volume. Moreover, the defects treated with FPG-nHA showed significantly higher ultimate load, yield load, and stiffness. The Gel-FPG-nHA moderately improved bone regeneration that was not close to the autograft in some parameters, whereas FPG-nHA significantly improved bone healing closely comparable with the autograft group in most parameters. In conclusion, although all the nHA-containing scaffolds had some beneficial effects on bone regeneration, the FPG-nHA scaffold was more effective in improving the structural and functional properties of the newly formed bone and was more osteoinductive than the Gel and was comparable to the autograft. Therefore, the FPG can be regarded as a promising option to be used in conjunction with mineral scaffolds for bone tissue engineering.

Cortical bone adaptation and mineral mobilization in the subterranean mammal Bathyergus suillus (Rodentia: Bathyergidae): effects of age and sex

The patterns of bone modeling and mineral mobilization (skeletal homeostasis) among mammals other than humans and laboratory rodents are still poorly known. In this study we assessed the pattern of bone formation and bone resorption in the femur of a wild population of Cape dune molerats, Bathyergus suillus (n = 41) (Bathyergidae), a solitary subterranean mammal with a marked extended longevity among rodents, and which also lives in a naturally deficient state of vitamin D. In order to determine ontogenetic and sex effects on histomorphometric parameters of transversal undecalcified bone sections, two-way ANOVA, linear mixed-effects model and regression statistical analyses were performed. During ontogeny, B. suillus increased their cross sectional area, cortical area and cortical thickness, and most importantly, they showed scarce endosteal bone resorption which resulted in a retained medullary cavity size during ontogeny. This resulted in a positively imbalanced bone modeling, where bone formation considerably surpasses bone loss by almost 100-fold in adulthood. This differs markedly from other terrestrial mammals with relatively thin cortical walls. Regarding bone loss and remodeling, three main processes involving intracortical resorption were observed: modeling-related bone loss in early postnatal growth; secondary osteon formation occurring in both sexes; and subendosteal secondary reconstruction observed only in females. The latter is accompanied by females having six-fold more relative bone loss than males, which is evidenced by the development of enlarged resorption cavities (RCs) distributed circumferentially around the medullary cavity. Males have smaller, more circular and randomly distributed RCs. In general, our data indicate no age-related decline in mineral content in B. suillus, and provides strong support for a pattern of sexual dimorphism in skeletal homeostasis, similar to that occurring in humans and other mammals, with females losing more bone throughout aging as compared to males due to reproductive factors. Interestingly as well, despite the high mechanical loads experienced during burrow construction, bone remodeling in B. suillus is kept at very low levels throughout their lifespan, and dense Haversian tissue never forms. This study represents the first comprehensive assessment of skeletal homeostasis in a subterranean mammal, and it enables a better understanding of the complex processes governing the acquisition and maintenance of bone properties in this species with extraordinary fossorial adaptations.

Combining electrical stimulation and tissue engineering to treat large bone defects in a rat model

Bone Tissue engineering (BTE) has recently been introduced as an alternative to conventional treatments for large non-healing bone defects. BTE approaches mimic autologous bone grafts, by combining cells, scaffold, and growth factors, and have the added benefit of being able to manipulate these constituents to optimize healing. Electrical stimulation (ES) has long been used to successfully treat non-healing fractures and has recently been shown to stimulate bone cells to migrate, proliferate, align, differentiate, and adhere to bio compatible scaffolds, all cell behaviors that could improve BTE treatment outcomes. With the above in mind we performed in vitro experiments and demonstrated that exposing Mesenchymal Stem Cells (MSC) + scaffold to ES for 3 weeks resulted in significant increases in osteogenic differentiation. Then in in vivo experiments, for the first time, we demonstrated that exposing BTE treated rat femur large defects to ES for 8 weeks, caused improved healing, as indicated by increased bone formation, strength, vessel density, and osteogenic gene expression. Our results demonstrate that ES significantly increases osteogenic differentiation in vitro and that this effect is translated into improved healing in vivo. These findings support the use of ES to help BTE treatments achieve their full therapeutic potential.

Bone-targeting parathyroid hormone conjugates outperform unmodified PTH in the anabolic treatment of osteoporosis in rats

Synthetic parathyroid hormone (PTH) is clinically indicated for the treatment of osteoporosis, through its anabolic effects on parathyroid hormone receptors (PTHRs), located on osteoblast cells. However, the bioavailability of PTH for bone cells is restricted by the short half-life of PTH and the widespread distribution of PTHRs in non-skeletal tissues. To impart affinity for mineralized bone surfaces, bisphosphonate (BP)-mediated PTH analogues were synthesized, characterized, and evaluated in vitro and in vivo. The successful synthesis of PTH-PEG-BP was identified on MALDI-ToF mass spectra; bone-targeting potential was evaluated by hydroxyapatite binding test; and receptor bioactivity was assessed in UMR-106 (rat osteosarcoma) cells that constitutively express PTHRs. Therapeutic efficacy was evaluated using ovariectomized rats that remained untreated for 8 weeks to allow development of osteopenia. Those rats then received daily subcutaneous injections of PTH-PEG-BP, thiol-BP vehicle, or unmodified PTH, and compared to sham-operated healthy rats at 0, 4, 8, 12, and 16 weeks. In vivo micro-CT was conducted on the proximal tibial metaphysis to measure microstructural bone parameters, and new bone formation was detected using dynamic labeling. Bone strength was assessed using three-point bending mechanical testing. Our study determined that PTH-PEG-BP conjugates significantly enhanced PTH targeting to the bone matrix while retaining full PTH bioactivity. Moreover, PTH-PEG-BP conjugates significantly increased trabecular bone quality, anabolic bone formation, and improved bone strength over systemically administered PTH alone. We highlight the promise of a novel class of bone-targeting anabolic compound for the treatment of osteoporosis and related bone disorders.

Whole bone testing in small animals: systematic characterization of the mechanical properties of different rodent bones available for rat fracture models

Objectives

Rat fracture models are extensively used to characterize normal and pathological bone healing. Despite, systematic research on inter- and intra-individual differences of common rat bones examined is surprisingly not available. Thus, we studied the biomechanical behaviour and radiological characteristics of the humerus, the tibia and the femur of the male Wistar rat—all of which are potentially available in the experimental situation—to identify useful or detrimental biomechanical properties of each bone and to facilitate sample size calculations.

Methods

40 paired femura, tibiae and humeri of male Wistar rats (10–38 weeks, weight between 240 and 720 g) were analysed by DXA, pQCT scan and three-point-bending. Bearing and loading bars of the biomechanical setup were adapted percentually to the bone’s length. Subgroups of light (skeletal immature) rats under 400 g (N = 11, 22 specimens of each bone) and heavy (mature) rats over 400 g (N = 9, 18 specimens of each bone) were formed and evaluated separately.

Results

Radiologically, neither significant differences between left and right bones, nor a specific side preference was evident. Mean side differences of the BMC were relatively small (1–3% measured by DXA and 2.5–5% by pQCT). Over all, bone mineral content (BMC) assessed by DXA and pQCT (TOT CNT, CORT CNT) showed high correlations between each other (BMC vs. TOT and CORT CNT: R² = 0.94–0.99). The load–displacement diagram showed a typical, reproducible curve for each type of bone. Tibiae were the longest bones (mean 41.8 ± 4.12 mm) followed by femurs (mean 38.9 ± 4.12 mm) and humeri (mean 29.88 ± 3.33 mm). Failure loads and stiffness ranged from 175.4 ± 45.23 N / 315.6 ± 63.00 N/mm for the femurs, 124.6 ± 41.13 N / 260.5 ± 59.97 N/mm for the humeri to 117.1 ± 33.94 N / 143.8 ± 36.99 N/mm for the tibiae. Smallest interindividual differences were observed in failure loads of the femurs (CV% 8.6) and tibiae (CV% 10.7) of heavy animals, light animals showed good consistency in failure loads of the humeri (CV% 7.7). Most consistent results of both sides (left vs. right) in failure loads were provided by the femurs of light animals (mean difference 4.0 ± 2.8%); concerning stiffness, humeri of heavy animals were most consistent (mean difference of 6.2 ± 5%). In general, the failure loads showed strong correlations to the BMC (R² = 0.85–0.88) whereas stiffness correlated only moderate, except for the humerus (BMC vs. stiffness: R² = 0.79).

Discussion

Altogether, the rat’s femur of mature specimens showed the most accurate and consistent radiological and biomechanical results. In synopsis with the common experimental use enabling comparison among different studies, this bone offers ideal biomechanical conditions for three point bending experiments. This can be explained by the combination of a superior aspect ratio and a round and long, straight morphology, which satisfies the beam criteria more than other bones tested.

Electronic supplementary material

The online version of this article (10.1186/s40001-018-0307-z) contains supplementary material, which is available to authorized users.

Preparative expression and purification of a nacreous protein N16 and testing its effect on osteoporosis rat model

N16, a nacreous protein isolated from Pinctada martensii, is related to nacreous layer formation. Our previous study indicated that N16 showed dual regulatory effects by inducing osteoblast biomineralization as well as inhibiting osteoclast formation. In order to obtain large quantity of N16 for animal experiment and clinical trial, a fermentation and preparative purification method was established. The N16 cDNA was cloned to a BL21(DE3)plysE-pET32a vector and grown in a 20 L fermenter. The medium, temperature, pH and dissolved oxygen (DO) were optimized. N16 was expressed in inclusion bodies. It was denatured and refolded in 8 M urea buffer and purified to 97% purity by passing through a gel filtration column. The glucocorticoid induced osteoporosis (GIO) rat model was used to investigate the anti-osteoporosis activity of N16 in vivo. Results showed that the decrease of the bone mineral density (BMD) and the ultimate load was significantly relieved after N16 treatment. N16 displayed dual regulatory effects by promoting osteogenesis as well as inhibiting bone resorption in vivo. Our work will contribute to further clinical studies on N16 for osteoporosis treatment.

The effects of gelatin, fibrin-platelet glue and their combination on healing of the experimental critical bone defect in a rat model: radiological, histological, scanning ultrastructural and biomechanical evaluation

Fibrin-platelet glue (FPG) is a blood derivative, in which platelets and fibrinogen are concentrated in a small plasma volume, by differential centrifugation and precipitation. It can form a three-dimensional and biocompatible fibrin scaffold with a myriad of growth factors and proteins that are released progressively to the local environment and contribute to the accelerated postoperative bone healing. Gelatin (Gel) is a derivative of collagen and can promote cell adhesion and proliferation due to its unique sequence of amino acids, so it is suitable for bone tissue applications. This study examined the effects of Gel, FPG and their combinations as bone scaffold on the healing of surgically created critical-size defects in rat radius. Fifty critical size defects of 5 mm long were bilaterally created in the radial diaphysis of 25 rats. The animals were randomly divided into five equal groups as empty defect, autograft, Gel, FPG and Gel-FPG groups (n = 10 in each group). Radiographs of each forelimb were taken postoperatively on the 1st day and then at the 28th and 56th days post injury to evaluate bone formation, union and remodeling of the defect. After 56 days, the rats were euthanized and their harvested healing bone samples were evaluated by histopathology, scanning electron microscopy (SEM) and biomechanical testing. The results of present study showed that the Gel alone did not significantly affect bone healing and regeneration; however, the Gel treated defects promoted healing more than those that were left untreated (negative control). Furthermore, the FPG-enhanced grafts provided a good scaffold containing numerous growth factors for proliferation of osteoinduction and was effective in improving the structural and functional properties of the newly formed bone more than that of the untreated and also the Gel treated groups. Incorporation of Gel into the FPG scaffold improved healing potential of the FPG scaffold; however, it was still inferior to the autograft (positive control). Although the Gel-FPG scaffolds had best effectiveness during bone regeneration, it still needs to be further enhanced by incorporation of the ceramic and osteoinductive biomaterials.

Experimental Traumatic Brain Injury Induces Bone Loss in Rats

Few studies have investigated the influence of traumatic brain injury (TBI) on bone homeostasis; however, pathophysiological mechanisms involved in TBI have potential to be detrimental to bone. The current study assessed the effect of experimental TBI in rats on the quantity and quality of two different weight-bearing bones, the femur and humerus. Rats were randomly assigned into either sham or lateral fluid percussion injury (FPI) groups. Open-field testing to assess locomotion was conducted at 1, 4, and 12 weeks post-injury, with the rats killed at 1 and 12 weeks post-injury. Bones were analyzed using peripheral quantitative computed tomography (pQCT), histomorphometric analysis, and three-point bending. pQCT analysis revealed that at 1 and 12 weeks post-injury, the distal metaphyseal region of femora from FPI rats had reduced cortical content (10% decrease at 1 week, 8% decrease at 12 weeks; p < 0.01) and cortical thickness (10% decrease at 1 week, 11% decrease at 12 weeks p < 0.001). There was also a 23% reduction in trabecular bone volume ratio at 1 week post-injury and a 27% reduction at 12 weeks post-injury in FPI rats compared to sham (p < 0.001). There were no differences in bone quantity and mechanical properties of the femoral midshaft between sham and TBI animals. There were no differences in locomotor outcomes, which suggested that post-TBI changes in bone were not attributed to immobility. Taken together, these findings indicate that this rat model of TBI was detrimental to bone and suggests a link between TBI and altered bone remodeling.

Phosphate Binding with Sevelamer Preserves Mechanical Competence of Bone Despite Acidosis in Advanced Experimental Renal Insufficiency

Introduction

Phosphate binding with sevelamer can ameliorate detrimental histomorphometric changes of bone in chronic renal insufficiency (CRI). Here we explored the effects of sevelamer-HCl treatment on bone strength and structure in experimental CRI.

Methods

Forty-eight 8-week-old rats were assigned to surgical 5/6 nephrectomy (CRI) or renal decapsulation (Sham). After 14 weeks of disease progression, the rats were allocated to untreated and sevelamer-treated (3% in chow) groups for 9 weeks. Then the animals were sacrificed, plasma samples collected, and femora excised for structural analysis (biomechanical testing, quantitative computed tomography).

Results

Sevelamer-HCl significantly reduced blood pH, and final creatinine clearance in the CRI groups ranged 30%-50% of that in the Sham group. Final plasma phosphate increased 2.4- to 2.9-fold, and parathyroid hormone 13- to 21-fold in CRI rats, with no difference between sevelamer-treated and untreated animals. In the femoral midshaft, CRI reduced cortical bone mineral density (-3%) and breaking load (-15%) (p<0.05 for all versus Sham), while sevelamer increased bone mineral density (+2%) and prevented the deleterious changes in bone. In the femoral neck, CRI reduced bone mineral density (-11%) and breaking load (-10%), while sevelamer prevented the decrease in bone mineral density (+6%) so that breaking load did not differ from controls.

Conclusions

In this model of stage 3–4 CRI, sevelamer-HCl treatment ameliorated the decreases in femoral midshaft and neck mineral density, and restored bone strength despite prevailing acidosis. Therefore, treatment with sevelamer can efficiently preserve mechanical competence of bone in CRI.

Melatonin can Ameliorate Radiation-Induced Oxidative Stress and Inflammation-Related Deterioration of Bone Quality in Rat Femur

The aim of the present study was to evaluate the radioprotective effects of melatonin on the biomechanical properties of bone in comparison to amifostine (WR-2721). Forty Sprague Dawley rats were divided equally into 5 groups namely; control (C), irradiation (R; single dose of 50 Gy), irradiation + WR-2721 (R + WR-2721; irradiation + 200 mg/kg WR-2721) radiation + melatonin 25 mg/kg (R + M25; irradiation + 25 mg/kg melatonin), and radiation + melatonin 50 mg/kg (R + M50; irradiation + 50 mg/kg melatonin). In order to measure extrinsic (organ-level mechanical properties of bone; the ultimate strength, deformation, stiffness, energy absorption capacity) and intrinsic (tissue-level mechanical properties of bone; ultimate stress, ultimate strain, elastic modulus, toughness) features of the bone, a three-point bending (TPB) test was performed for biomechanical evaluation. In addition, a bone mineral density (BMD) test was carried out. The BMD and extrinsic properties of the diaphyseal femur were found to be significantly higher in the R + M25 group than in group R (p < 0.05). A significant increase was observed in R + M50 (p < 0.05) in comparison to group R in the cross-sectional area of the femoral shaft and elastic modulus parameter. The protective effect of melatonin was similar to that of WR-2721. Thus, biomechanical quality of irradiated bone can be ameliorated by free radical scavenger melatonin.

A new, low cost, locking plate for the long-term fixation of a critical size bone defect in the ratfemur: in vivo performance, biomechanical and finite element analysis

BACKGROUND

The optimum fixation device for the critical size bone defect is not established yet.

OBJECTIVE

A reliable, feasible and low-cost fixation device for the long-term maintenance of a critical bone defect.

METHODS

A custom-made plate made of poly-methyl-methacrylate was used for the fixation of a critical defect of rats' femurs. The screws were securely fixing both on the plate and the bone. A three point bending test, aimed to resemble the in vivo loading pattern, a Finite Element Analysis and a 24-week in vivo monitoring of the integrity of the plate fixation were utilized.

RESULTS

The plate has linear and reproducible behavior. It presents no discontinuities in the stress field of the fixation. Its properties are attributed to the material and the locking principle. It fails beyond the level of magnitude of the normal ambulatory loads. In vivo, 100% of the plates maintained the bone defect intact up to 12 weeks and 85% of them at 24 weeks.

CONCLUSION

This novel locking plate shows optimal biomechanical performance and reliability with high long-term in vivo survival rate. It is fully implantable, inexpensive and easily manufactured. It can be qualified for long term critical defect fixation in bone regeneration studies.

Comparative study of two types of herbal capsules with different Epimedium species for the prevention of ovariectomised-induced osteoporosis in rats

Background/Objective

Epimedii Folium is the most important osteogenic herb formulated for the traditional Chinese Medicine Xian Ling Gu Bao (XLGB) capsule. The present study compared XLGB capsules containing two different Epimedium species, i.e., either Epimedium pubescens (XEP) or Epimedium koreanum (XEK), with the focus being on the chemical constituents and antiosteoporotic efficacy.

Methods

Ultra performance liquid chromatography was used to demonstrate the different chemical constituents. Biomechanical tests, histological, and cytological evaluation were performed to characterise and compare the bone mineral density, bone strength, microstructure of bone tissue, and biological activity between XEP and XEK using an established ovariectomised (OVX) rat model.

Results

Six flavonoids with different contents between XEK and XEP were identified. As compared with the OVX group, significantly higher bone mineral density, elastic-modulus, and compressive strength were found in both the XEK group and XEP group (p < 0.05 for all, n = 8). Histomorphometric data presented significantly higher osteoblast surface ratio and osteoid area accompanied by significantly lower values of erosion surface and adiopocytes area in two treatment groups (p < 0.05, n = 6). XLGB Fufang with either XEK or XEP all showed significant preventive effects in OVX-induced osteoporosis and deterioration of bone mechanical properties.

Conclusion

The significance of the current preclinical experimental study was that these two Epimedium species used for formulating XLGB capsules were equally effective for the prevention of oestrogen-depletion induced osteoporosis.

Development of Injectable Citrate-Based Bioadhesive Bone Implants

Injectable bone implants have been widely used in bone tissue repairs including the treatment of comminuted bone fractures (CBF). However, most injectable bone implants are not suitable for the treatment of CBF due to their weak tissue adhesion strengths and minimal osteoinduction. Citrate has been recently reported to promote bone formation through enhanced bioceramic integration and osteoinductivity. Herein, a novel injectable citrate-based mussel-inspired bioadhesive hydroxyapatite (iCMBA/HA) bone substitute was developed for CBF treatment. iCMBA/HA can be set within 2-4 minutes and the as-prepared (wet) iCMBA/HA possess low swelling ratios, compressive mechanical strengths of up to 3.2±0.27 MPa, complete degradation in 30 days, suitable biocompatibility, and osteoinductivity. This is also the first time to demonstrate that citrate supplementation in osteogenic medium and citrate released from iCMBA/HA degradation can promote the mineralization of osteoblastic committed human mesenchymal stem cells (hMSCs). In vivo evaluation of iCMBA/HA in a rabbit comminuted radial fracture model showed significantly increased bone formation with markedly enhanced three-point bending strength compared to the negative control. Neovascularization and bone ingrowth as well as highly organized bone formation were also observed showing the potential of iCMBA/HA in treating CBF.

Osteoprotective effect of geraniin against ovariectomy-induced bone loss in rats

In the present study, we investigated the antiosteoporotic effect of geraniin on osteoporosis induced by OVX in rats. The analysis of biochemical parameters showed that geraniin could significantly increase serum calcium, estradiol and calcitonin levels, and decrease serum ALP, tartrate-resistant acid phosphatase, serum crosslinked C-terminal telopeptide of type I collagen, and urinary deoxypyridinoline/creatinine ratio levels, respectively. Geraniin was also found to prevent OVX-induced bone loss in bone mineral density and bone mineral content, to elevate femur weight and bone calcium content, and to enhance the bone mechanical properties as compared with OVX group. In addition, geraniin was demonstrated to improve the histomorphological parameters of OVX-induced bone loss, including bone trabecular number, thickness, and separation. These results indicated that geraniin have a protective effect against OVX-induced rat osteoporosis.

A rat model of chondrocyte death after closed intra-articular fracture

OBJECTIVE

The development of osteoarthritis after intra-articular fractures has been described for decades, although the exact mechanical and cellular changes that occur remain poorly understood. There are several animal models to study this phenomenon, but they are mechanistically different from physiologic fractures in several important ways. This article describes a novel model that recreates the kinematics present in high-energy trauma and intra-articular fractures.

METHODS

We designed a "drop tower" for the creation of intercondylar femoral fractures in rats and tested it on cadaveric rats to determine the optimal kinetic parameters. Intra-articular fractures were then created in live rats and the animals were killed at 0, 24, and 72 hours after the fracture. Cartilage samples were obtained for live/dead staining, and the relationships among fracture time, cartilage depth, and cell viability were evaluated.

RESULTS

The model reproduced intra-articular fractures very similar to those seen in high-energy trauma, although we required significantly higher energies (3600 mJ) than those reported in other fracture models (40-200 mJ). Cartilage viability decreased with time (68% immediately after the fracture and 46% at 72 hours, P = 0.02) and increased with depth from the articular surface (47% at the surface vs. 66% in the deepest layer, P = 0.001).

CONCLUSIONS

This model is a physiologically relevant reliable method for creating intra-articular fractures in rats and can produce meaningful data about the biologic changes occurring in cartilage after injury. Cell viability decreases with time postfracture and with proximity to the articular surface.

Predicting cortical bone strength from DXA and dental cone-beam CT

OBJECTIVE

This study compared the capabilities of dual-energy X-ray absorptiometry (DXA) and dental cone-beam computed tomography (CBCT) for predicting the cortical bone strength of rat femurs and tibias.

MATERIALS AND METHODS

Specimens of femurs and tibias obtained from 14 rats were first scanned with DXA to obtain the areal bone mineral density (BMD) of the midshaft cortical portion of the bones. The bones were then scanned using dental CBCT to measure the volumetric cortical bone mineral density (vCtBMD) and the cross-sectional moment of inertia (CSMI) for calculating the bone strength index (BSI). A three-point bending test was conducted to measure the fracture load of each femur and tibia. Bivariate linear Pearson analysis was used to calculate the correlation coefficients (r values) among the CBCT measurements, DXA measurements, and three-point bending parameters.

RESULTS

The correlation coefficients for the associations of the fracture load with areal BMD (measured using DXA), vCtBMD (measured using CBCT), CSMI (measured using CBCT), and BSI were 0.585 (p = 0.028) and 0.532 (p = 0.050) (for the femur and tibia, respectively), 0.638 (p = 0.014) and 0.762 (p = 0.002), 0.778 (p = 0.001) and 0.792 (p<0.001), and 0.822 (p<0.001) and 0.842 (p<0.001), respectively.

CONCLUSIONS

CBCT was found to be superior to DXA for predicting cortical bone fracture loads in rat femurs and tibias. The BSI, which is a combined index of densitometric and geometric parameters, was especially useful. Further clinical studies are needed to validate the predictive value of BSI obtained from CBCT and should include testing on human cadaver specimens.

Load/strain distribution between ulna and radius in the mouse forearm compression loading model

Finite element analysis (FEA) of the mouse forearm compression loading model is used to relate strain distributions with downstream changes in bone formation and responses of bone cells. The objective of this study was to develop two FEA models - the first one with the traditional ulna only and the second one in which both the ulna and radius are included, in order to examine the effect of the inclusion of the radius on the strain distributions in the ulna. The entire mouse forearm was scanned using microCT and images were converted into FEA tetrahedral meshes using a suite of software programs. The performance of both linear and quadratic tetrahedral elements and coarse and fine meshes were studied. A load of 2N was applied to the ulna/radius model and a 1.3N load (based on previous investigations of load sharing between the ulna and radius in rats) was applied to the ulna only model for subsequent simulations. The results showed differences in the cross sectional strain distributions and magnitude within the ulna for the combined ulna/radius model versus the ulna only model. The maximal strain in the combined model occurred about 4mm toward the distal end from the ulna mid-shaft in both models. Results from the FEA model simulations were also compared to experimentally determined strain values. We conclude that inclusion of the radius in FE models to predict strains during in vivo forearm loading increases the magnitude of the estimated ulna strains compared to those predicted from a model of the ulna alone but the distribution was similar. This has important ramifications for future studies to understand strain thresholds needed to activate bone cell responses to mechanical loading.

The effects of loading and estrogen on rat bone growth

This study evaluated the contributions of locomotive loading and estrogen to the development of diaphysis of rat femur. A randomized 2 × 2 study design was used. Altogether, 70 female Sprague-Dawley rats were used, of which 10 were euthanized at entry. Of the remaining rats, 16 served as controls, and the rest, 44, underwent a unilateral sciatic neurectomy. The effect of estrogen was removed by ovariectomizing one-half of the neurectomized rats. After 27 wk, the animals were euthanized, and the femora were excised. Irrespective of loading or estrogen, the femur length and mineral mass increased by 142 and 687%, respectively. Axial growth was not modulated either by locomotive loading or estrogen, but the loading resulted in direction-specific changes in the cross-sectional geometry. The estrogen-related gains were evident on the endocortical surface, while the loading-related gains occurred on the periosteal surface. The loading and estrogen were significantly associated with increased bone strength (21 and 15%, respectively) in the mediolateral direction, but not in the anteroposterior direction. Axial growth and accrual of bone mineral mass of the rat femur are largely independent of locomotive loading or estrogen, whereas these factors specifically account for the femur function, as either a mechanical lever or a mineral reservoir for reproduction, respectively.

Evaluation of the mechanical properties of rat bone under simulated microgravity using nanoindentation

Exposure to microgravity causes a decrease in bone mass and altered bone geometry due to the lack of weight-bearing forces on the skeleton. The mechanical properties of bone are due not only to the structure and geometry, but also to the tissue properties of the bone material itself. To study the effects of microgravity on bone tissue, the mechanical properties of tail suspension rat femurs were investigated. Twelve Sprague-Dawley rats were randomly divided into two groups, tail suspension (TS) and control (CON). On days 0 and 14, the bone mineral density (BMD) of the femurs was determined by Dual Energy X-ray Absorptiometry. After 14 days, three-point bending was used to test the mechanical properties of the whole femur and nanoindentation was used to measure the mechanical properties of the bone materials. The BMD of femurs in TS was significantly lower than that in CON. In the three-point bending testing, the breaking load, stiffness and energy absorption all decreased significantly in the TS group. In the nanoindentation tests, there was no significant difference between TS and CON in elastic modulus (E), while hardness (H) was significantly decreased and E/H significantly increased in TS. Weightlessness affects the intrinsic mechanical properties of bone at the bone material level. It is necessary to investigate further the effect of microgravity on the collagen bone matrix. Nanoindentation is a relatively new technique that is useful for investigating the above changes induced by microgravity and for assessing the efficacy of intervention.

Supraphysiological testosterone enanthate administration prevents bone loss and augments bone strength in gonadectomized male and female rats

High-dose testosterone enanthate (TE) may prevent hypogonadism-induced osteopenia. For this study, 3-mo-old male and female Fisher SAS rats underwent sham surgery, gonadectomy (GX), or GX plus 28 days TE administration (7.0 mg/wk). GX reduced serum sex hormones (i.e., testosterone, dihydrotestosterone, and estradiol) (P < 0.05) in both sexes and bone concentrations of testosterone (males only), and estradiol (females only). GX also elevated urine deoxypyridinoline/creatinine in both sexes and serum osteocalcin (females only), findings that are consistent with high-turnover osteopenia. GX reduced cancellous bone volume (CBV) and increased osteoid surfaces in tibia of both sexes. GX males also experienced reduced trabecular number and width and increased trabecular separation, whereas GX females experienced increased osteoblast and osteoid surfaces. Bone biomechanical characteristics remained unaffected by GX, except that femoral stiffness was reduced in females. In contrast, TE administration to GX rats elevated serum and bone androgens to supraphysiological concentrations in both sexes but altered neither serum nor bone estradiol in males. Additionally, TE did not prevent GX-induced reductions in serum or bone estradiol in females. TE also reduced markers of high-turnover osteopenia in both sexes. In males, TE prevented GX-induced changes in trabecular number and separation, CBV, and osteoid surfaces while diminishing osteoblast and osteoclast surfaces; however, these changes were not fully prevented in females. In both sexes, TE increased femoral length and femoral maximal strength to above that of Sham and GX animals while preventing the loss of femoral stiffness in females. In conclusion, TE administration appears protective of cancellous bone in male rats and augments cortical bone strength in both sexes.