骨的显微损伤及其对骨力学性能的影响

骨的显微损伤是由于反复受载所致的仅能在显微镜下观察到的骨基质的损伤,往往表现为各种形态的显微裂纹或弥散性损伤。通过特殊染色和标记可对显微损伤进行组织学观察和定量分析,并根据其形态和与骨单位的位置关系进行分类。显微损伤往往伴有骨强度的降低和骨脆性的增加,裂纹的长度及其位置是影响骨力学性能的决定因素。显微损伤的积累最终会导致骨的疲劳骨折。     

The influence of age on adaptive bone formation and bone resorption

Bone is a tissue with enormous adaptive capacity, balancing resorption and formation processes. It is known that mechanical loading shifts this balance towards an increased formation, leading to enhanced bone mass and mechanical performance. What is not known is how this adaptive response to mechanical loading changes with age. Using dynamic micro-tomography, we show that structural adaptive changes of trabecular bone within the tibia of living mice subjected to two weeks of in vivo cyclic loading are altered by aging. Comparisons of 10, 26 and 78 weeks old animals reveal that the adaptive capacity diminishes. Strikingly, adaptation was asymmetric in that loading increases formation more than it reduces resorption. This asymmetry further shifts the (re)modeling balance towards a net bone loss with age. Loading results in a major increase in the surface area of mineralizing bone. Interestingly, the resorption thickness is independent of loading in trabecular bone in all age groups. This data suggests that during youth, mechanical stimulation induces the recruitment of bone modeling cells whereas in old age, only bone forming cells are affected. These findings provide mechanistic insights into the processes that guide skeletal aging in mice as well as in other mammals.     

Controlling stem cell-mediated bone regeneration through tailored mechanical properties of collagen scaffolds

Mechanical properties of the extracellular matrix (ECM) play an essential role in cell fate determination. To study the role of mechanical properties of ECM in stem cell-mediated bone regeneration, we used a 3D in vivo ossicle model that recapitulates endochondral bone formation. Three-dimensional gelatin scaffolds with distinct stiffness were developed using 1-Ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC) mediated zero-length crosslinking. The mechanical strength of the scaffolds was significantly increased by EDC treatment, while the microstructure of the scaffold was preserved. Cell behavior on the scaffolds with different mechanical properties was evaluated in vitro and in vivo. EDC-treated scaffolds promoted early chondrogenic differentiation, while it promoted both chondrogenic and osteogenic differentiation at later time points. Both micro-computed tomography and histologic data demonstrated that EDC-treatment significantly increased trabecular bone formation by transplanted cells transduced with AdBMP. Moreover, significantly increased chondrogenesis was observed in the EDC-treated scaffolds. Based on both in vitro and in vivo data, we conclude that the high mechanical strength of 3D scaffolds promoted stem cell mediated bone regeneration by promoting endochondral ossification. These data suggest a new method for harnessing stem cells for bone regeneration in vivo by tailoring the mechanical properties of 3D scaffolds.     

Soluble silica inhibits osteoclast formation and bone resorption in vitro

Several studies have suggested that silicon (Si) may be essential for the normal development of connective tissue and the skeleton. Positive effects of Si from the diet as well as from Si-containing biomaterials, such as bioactive glass 45S5 (BG), have been demonstrated. Studies have reported that Si stimulates osteoblast proliferation and differentiation. However, the effects of Si on osteoclasts have not been directly addressed. The purpose of the present in vitro study was to clarify if Si has regulatory effects on osteoclast formation and bone resorption. The effects of BG, BG dissolution extracts and Si containing cell culture medium were investigated in a mouse calvarial bone resorption assay and osteoclast formation assays (mouse bone marrow cultures and RAW264.7 cell cultures). We conclude from our results that Si causes significant inhibition of osteoclast phenotypic gene expressions, osteoclast formation and bone resorption in vitro. In conclusion, the present study suggests that Si has a dual nature in bone metabolism with stimulatory effects on osteoblasts and inhibitory effects on osteoclasts. This suggested property of Si might be interesting to further explore in future biomaterials for treatments of bone defects in patients.     

The effect of simvastatin on bone formation and ceramic resorption in a peri-implant defect model

Experimental use of statins as stimulators of bone formation suggests they may have widespread applicability in the field of orthopaedics. With their combined effects on osteoblasts and osteoclasts, statins have the potential to enhance resorption of synthetic materials and improve bone ingrowth. In this study, the effect of oral and local administration of simvastatin to a beta tricalcium phosphate (betaTCP)-filled defect around an implant was compared with recombinant human bone morphogenetic protein 2 (rhBMP2). On hundred and sixty-two Sprague-Dawley rats were assigned to treatment groups: local application of 0.1, 0.9 or 1.7 mg of simvastatin, oral simvastatin at 5, 10 or 50 mg kg(-1) day(-1) for 20 days, local delivery of 1 or 10 microg of rhBMP2, or control. At 6 weeks rhBMP2 increased serum tartrate-resistant acid phosphatase 5b levels and reduced betaTCP area fraction, particle size and number compared with control, suggesting increased osteoclast activity. There was reduced stiffness and increased mechanical strength with this treatment. Local simvastatin resulted in a decreased mineral apposition rate at 6 weeks and increased fibrous area fraction, betaTCP area fraction, particle size and number at 26 weeks. Oral simvastatin had no effect compared with control. Local application of rhBMP2 increased resorption and improved mechanical strength whereas simvastatin was detrimental to healing. Oral simvastatin was ineffective at promoting either ceramic resorption or bone formation. The effect of statins on the repair of bone defects with graft substitute materials is influenced by its bioavailability. Thus, further studies on the optimal delivery system are needed.     

骨水泥中的硫酸钡对破骨细胞的作用

目的验证骨水泥中的硫酸钡对破骨细胞形成及其生物学活性的影响。方法体外培养外周血单核细胞并加入巨噬细胞克隆集落刺激因子及核因子B激活因子配体诱导破骨细胞分化,实验组中分别加入含有或不含有硫酸钡的骨水泥颗粒。以抗酒石酸酸性磷酸酶阳性多核细胞及象牙磨片上虫蚀样骨吸收陷窝的形成昨作为检测破骨细胞形成及其骨吸收活性的检测指标,检验骨水泥中的硫酸钡对破骨细胞的影响。结果含或不含硫酸钡的骨水泥颗粒组抗酒石酸酸性磷酸酶阳性多核细胞形成均早于无骨水泥颗粒的对照组（4天vs6天）,而骨水泥颗粒中是否含有硫酸钡的两组间抗酒石酸酸性磷酸酶阳性多核细胞形成的时间无明显差异。各组间抗酒石酸酸性磷酸酶阳性多核细胞的数量无显著差异;含硫酸钡的骨水泥颗粒组象牙磨片上骨吸收陷窝的面积较不含硫酸钡的骨水泥颗粒组及阴性对照组均增大（28.26±4.98vs22.28±3.49vs14.58±2.82,〈0.05）。结论骨水泥颗粒中的硫酸钡能够促进破骨细胞分化并促进成熟破骨细胞的骨吸收活性。     

Acoustic emission and mechanical properties of trabecular bone

The mechanical properties of trabecular bone and a simple plug prosthetic system have been determined over a range of displacement from 0.1 to 5 mm/min. Acoustic emission, a technique which is capable of detecting dynamic processes within a material, was used to monitor the compression tests on the prosthetic system. It was found that the stiffness and strength of trabecular bone and the prosthetic system increased with increasing strain rate of testing. The acoustic emission results demonstrated that the improvement in mechanical behaviour at the fast strain rates was accompanied by a decrease in the extent of the failure of the trabeculae. The technique of activation analysis has been applied to the results in order to identify the rate controlling fracture mechanism. Finally, the strength of the prosthetic system was correlated with the shear and compressive strengths of trabecular bone.     

双膦酸盐药物长期应用对显微损伤和骨力学性能的影响

双膦酸盐类药物作为治疗骨质疏松的一线药物,可以通过降低骨转换来增加骨密度,防止骨折的发生,在临床已经有较长期应用。最近研究表明,双膦酸盐类药物在抑制骨重建的同时,会影响显微损伤的修复,导致显微损伤的积聚和骨质量的下降,进而降低骨的韧性,削弱骨的力学性能。已有临床报告指出,骨质疏松病人使用双膦酸盐后有可能发生非创伤性骨折。本文综述了双膦酸盐类药物对骨显微损伤和骨力学性能的影响。     

Analysis of the mechanical properties ofin vitro reconstructed epidermis: preliminary results

Human epidermis can be reconstructed in vitro and is currently used in autografts for the treatment of severe, extensive burns and pigmentation disorders. However, there are neither international standards nor a common nomenclature for engineered tissues. The paper discusses the results of a preliminary study on human cultured epidermis to assess its mechanical tensile strength, and to eventually establish mechanical evaluation criteria that will enable test and comparison of the behaviour of different engineered tissue products. To perform uniaxial tension tests a traditional testing machine was adapted, and dedicated sample holding frame and grips designed.     

Analysis of the mechanical properties ofin vitro reconstructed epidermis: preliminary results

Human epidermis can be reconstructed in vitro and is currently used in autografts for the treatment of severe, extensive burns and pigmentation disorders. However, there are neither international standards nor a common nomenclature for engineered tissues. The paper discusses the results of a preliminary study on human cultured epidermis to assess its mechanical tensile strength, and to eventually establish mechanical evaluation criteria that will enable test and comparison of the behaviour of different engineered tissue products. To perform uniaxial tension tests a traditional testing machine was adapted, and dedicated sample holding frame and grips designed.     

应力松驰接骨板对固定段骨结构及力学性能影响的实验 …

目的：了解应力松驰接骨板固定对固定段骨形态结构及力学性能的影响。方法：分别将应力松驰接骨板（实验组）和坚硬接骨板（对照组）固定于兔胫骨干中段,采用ＣＴ扫描及ＣＴ值测定和力学测试,观察固定段骨结构及力学性能的变化。结果：固定后８～１２周,两组板下皮质骨厚度均逐渐变薄,伴ＣＴ值和固定骨段力学强度下降,以对照组为明显。２４～２６周,实验组板上皮质骨厚度、ＣＴ值和固定骨段力学强度逐渐恢复,接近正常;而对照     

多孔生物陶瓷与PVA水凝胶复合材料的制备与力学性能分析

目的将多孔生物陶瓷和聚乙烯醇(PVA)水凝胶交联成为一个仿生软骨-硬关节双层结构,并对该结构的微观形貌和力学性能进行分析。方法以羟基磷灰石(HA)为基体,采用添加碳酸氢铵(NH4HCO3)晶粒造孔的方式制备不同孔隙率的多孔羟基磷灰石生物陶瓷,以聚乙烯醇(PVA)为主要原料,环氧丙烷为交联剂,在多孔生物陶瓷表面及基体内交联制备出PVA水凝胶形成双层结构,对试样的断口形貌进行表征,对试样的拉伸强度和剪切强度等性能进行测试分析。结果交联的PVA水凝胶可以渗入到生物陶瓷基体表层以下的孔隙中,并且陶瓷基体和PVA水凝胶有很好的结合。随着多孔生物陶瓷孔隙率的增大,试样的最大拉伸和剪切负载均增大,平均孔隙率为70%试样的最大拉伸和剪切负载分别为153.61 N和64.46 N;而相应的拉伸和剪切强度略有下降,平均孔隙率为30%试样对应的最大拉伸和剪切强度分别为2.12 MPa和1.13 MPa。两者的失效形式均是因为裂纹的扩展,断口的微观形貌表明,断裂面存在明显的裂纹和内部缺陷,同时可观察出裂纹源和扩展方向。结论考虑到多孔生物陶瓷基体的强度,平均孔隙率为50%的多孔生物陶瓷的渗入效果适中,试样的拉伸强度和剪切强度、多孔生物陶瓷基体的压缩强度也有一定的保证,选择孔隙率为50%的试样较为合适。     

Material properties of trabecular bone structures

Abstract: The transplantation of human allograft for restoration and filling of cortical bone defects is well known. Our aim was an experimental investigation of the mechanical stability of the often used femoral head spongiosa depending on the caliber and extent of the allograft. To evaluate the orientation of the trabecular structures of the femoral head and relate this data to its mechanical properties, morphometric studies were combined with mechanical tests of cancellous bone specimens. The mechanical examination of the allograft was done following the compression test according to DIN 50106. We examined 36 human unfixed hip joint spongiosa cylinders with a height of 11 mm and a diameter of 24 mm. We took three specimens from each femoral head. We compressed the allograft at a constant velocity of 0.017 mm/sec. We calculated the maximum compression strength, the yield point and the Young’s modulus. We also examined 12 parallelepipedic specimens with (17 × 17 × 51 mm) for morphometric analysis and loading in the direction of the primary compressive group (PCG), as well as perpendicular loading and at an angle of 45°. We found divergent mechanical stabilities. None of the femoral heads showed comparable compressive strength. There was no position dependency of the strength of the samples. No relation between optical appearance and strength was found. We found a value for the lower compressive strength, which can be used for calculation as a basic value for safe constructions. Furthermore we tested the well known dependence of strength on the direction of the trabecular structure. We found a strong relationship between strength and load direction on the preferred direction of the trabecular structure. The sole recommendation resulting from our investigations is to rely on the lowest compressive strength for all preoperative planning. Relying on higher compressive strength by using the theoretical predicted areas of higher strength is hazardous since we found no correlation between position of sampling and strength. The size of our samples is important, because of the fact that different sizes of the samples might cause different failure mechanisms in the samples. The preparation of the femoral head spongiosa should be done according to the primary compressive group of the trabecular structure.     

DXA predictions of human femoral mechanical properties depend on the load configuration

The aim of this study was to evaluate the ability of dual energy X-rays absorptiometry (DXA) areal bone mineral density (aBMD) measured in different regions of the proximal part of the human femur for predicting the mechanical properties of matched proximal femora tested in two different loading configurations.36 pairs of fresh frozen femora were DXA scanned and tested until failure in two loading configurations: a fall on the side or a one-legged standing. The ability of the DXA output from four different regions of the proximal femur in predicting the femoral mechanical properties was measured and compared for the two loading scenarios.The femoral neck DXA BMD was best correlated to the femoral ultimate force for both configurations and predicted significantly better femoral failure load (R² = 0.80 vs. R² = 0.66, P < 0.05) when simulating a side than when simulating a standing configuration. Conversely, the work to failure was predicted similarly for both loading configurations (R² = 0.54 vs. R² = 0.53, P > 0.05).Therefore, neck BMD should be considered as one of the key factors for discriminating femoral fracture risk in vivo. Moreover, the better predictive ability of neck BMD for femoral strength if tested in a fall compared to a one-legged stance configuration suggests that DXA's clinical relevance may not be as high for spontaneous femoral fractures than for fractures associated to a fall.     

Local suppression of pro-inflammatory cytokines and the effects in BMP-2-induced bone regeneration

The objective of this study is to investigate the effect of local inflammation suppression on the bone regeneration. Gelatin hydrogels incorporating mixed immunosuppressive triptolide-micelles and bone morphogenic protein-2 (BMP-2) were prepared. The controlled release of both the triptolide and BMP-2 from the hydrogels was observed under in vitro and in vivo conditions. When either J774.1 macrophage-like or MC3T3-E1 osteoblastic cells were cultured in the hydrogels incorporating mixed 2.5, 5 or 10 mg of triptolide-micelles and BMP-2, the expression level of pro- and anti-inflammatory cytokines including interleukin (IL)-6 and IL-10 was down-regulated, but the alkaline phosphatase (ALP) activity was promoted compared with those of hydrogels incorporating BMP-2 without triptolide-micelles. When implanted into a critical-sized bone defect of rats, the hydrogels incorporating mixed 2.5 or 5 mg of triptolide-micelles and BMP-2 showed significantly lower number of neutrophils, lymphocytes, macrophages or dendritic and mast cells infiltrated into the defect, and lower expression level of IL-6, TNF-α, and IL-10 than those incorporating BMP-2 without triptolide-micelles. The reduced local inflammation responses at the defects implanted with the hydrogels incorporating mixed 2.5 or 5 mg of triptolide-micelles and BMP-2 subsequently enhanced the bone regeneration thereat. It is concluded that the proper local modulation of inflammation responses is a promising way to achieve the enhanced bone regeneration.     

The effect of dose on rhBMP-2 signaling,delivered via collagen sponge,on osteoclast activation and in vivo bone resorption

While recombinant human bone morphogenetic protein (rhBMP)-2-based bone therapy presents potential osteoinductivity, it also leads concern due to transient osteoclast activation during early healing periods, ultimately limiting its clinical use. Therefore, we investigated in vivo and in vitro rhBMP-2 signaling which mediates early bone resorbing effect, depending on the dose, and attempted to inhibit this resorption phenomenon using NFAT inhibitor as a target molecule. High-dose of rhBMP-2 (20 μg/defect) enhanced osteoclast activation and the expression of bone resorption markers, compared to low dose (5 μg/defect) at one week after surgery in collagen sponge-delivered rat calvarial defect models. Interestingly, this trend was also observed in the expression of bone formation markers. In particular, rhBMP-2 upregulated RANKL expression, while it downregulated osteoprotegerin (OPG) expression, resulting in a dose-dependent increase in the ratio of RANKL to OPG. NFAT inhibitor (150 μm) treatment in vivo suppressed the high-dose effect of rhBMP-2 on both resorption and formation. In vitro results of rhBMP-2 signaling and NFAT inhibitor effects in rat mesenchymal stem cells showed similar trends as in vivo results. Microcomputer tomography-based evaluation at 4 weeks showed that combined treatment of NFAT inhibitor with 20 μg rhBMP-2 in vivo increased bone volume (BV) more than 20 μg rhBMP-2 alone, which showed little difference in BV compared to 5 μg of rhBMP-2. These results demonstrated that rhBMP-2 implantation concurrently signalized into enhanced osteoclastogenesis and osteoblastogenesis in vivo, dose-dependently. Ratio of RANKL/OPG might be an index for early bone resorbing activity of implanted rhBMP-2. A local cocktail treatment of NFAT inhibitor and high-dose rhBMP-2 might be an alternative to overcome early bone resorbing effects, thereby accelerating bone formation.     

Effects of in vitro bone formation on the mechanical properties of a trabeculated hydroxyapatite bone substitute

This study was designed to test the hypothesis that the mechanical properties of a trabecular bone substitute can be enhanced through in vitro tissue formation. Our specific objectives were to (1) determine the effects of in vitro marrow stromal cell-mediated tissue deposition upon a trabeculated hydroxyapatite scaffold on the strength and toughness of the resulting bone substitute; and (2) identify and characterize regions of newly deposited matrix and mineral. This work provides a basis for future investigations aimed at transforming a brittle hydroxyapatite scaffold into an osteoinductive, biomechanically functional implant through in vitro bone deposition. As hypothesized, the mechanical properties of the trabecular bone substitutes were significantly enhanced by in vitro tissue formation. As a result of cell seeding and a 5 week culture protocol, mean strength increased by 85% (p = 0.008) and energy to fracture increased by 130% (p = 0.003). Accompanying the enhancement of mechanical properties was the deposition of significant amounts of bone matrix and mineral. Fluorescence imaging, scanning electron microscopy, electron probe microanalysis, and nanoindentation confirmed the presence of bonelike mineral with Ca/P ratio, modulus, and hardness similar to that within human and rat trabecular bone tissue. This new mineralization was found to exist within a newly deposited parallel-fibered matrix both encasing and bridging between scaffold trabeculae. Taken as a whole, our results establish the feasibility of the production of an osteoinductive hydroxyapatite-based trabecular bone substitute with mechanical properties enhanced through in vitro bone deposition.     

Triterpenoids from Cimicifugae rhizoma, a novel class of inhibitors on bone resorption and ovariectomy-induced bone loss

OBJECTIVE: Increasing research suggested that Cimicifugae rhizoma might be protective against osteoporosis. In this study, we investigated the effects of three cycloartane-type triterpenoids isolated from Cimicifugae rhizoma, cimicidol-3-O-beta-D-xyloside (1), cimicidanol-3-O-beta-D-xyloside (2) and acetylacteol-3-O-beta-d-xyloside (3) on bone resorption in vitro and bone loss in ovariectomized (OVX) mice. METHODS: The activities of the tested compounds on bone resorption were evaluated using three assays, neonatal mouse parietal bone organ culture, osteoclast-like cells (OCLs) formation and pit formation. The effects on bone mineral density (BMD) and uterine weight were examined using OVX mice. Using LC-MS/MS method, the serum concentrations of the triterpenoids were measured in mice serum collected at 0.5, 1, 3, 6 and 12h following its oral administration. RESULTS: All of the tested compounds exerted the inhibitory effects on bone resorption in bone organ culture, suppressed both of the formation and the resorbing activity of OCLs. Furthermore, a synergistic effect was observed among those compounds. In vivo studies revealed that compounds 1-3 and the mixture of compounds 1-3 prevented the bone loss in OVX mice without affecting uterine weight, and each compound was detected in the mice serum after single oral administration. CONCLUSIONS: The triterpenoids exerted the inhibitory effects on osteoclastic bone resorption through the suppression of both OCLs formation and the resorbing activity of OCLs, and also showed a significant protective effect on BMD in OVX mice. The present results might provide a new pharmacological potential for the treatment of osteoporosis.