Measurement of thermal conductivity of bovine cortical bone

The thermal conductivity of cortical bone was characterized experimentally. Specimens were taken from the mid-diaphysis of bovine femora, and the rate of heat transfer was measured in three orthogonal directions. The conductivity was found to be 0.58±0.018 W/mK in the longitudinal direction, 0.53±0.030 W/mK in the circumferential direction, and 0.54±0.020 W/mK in the radial direction. Because the directional differences are small, it is concluded that bovine cortical bone can be treated as thermally isotropic.     

Interfacial fracture toughness between bovine cortical bone and cements

To evaluate the bonding strength of the interfaces within the cemented arthroplasty system, various mechanical tests have been used. Conventional push-out and pull-out tests cannot reveal the actual bonding property of the interface because of the significant influence of surface roughness on the measured adhesion and the failure to account for the mismatch of elastic modulus across the interface. An alternative fracture mechanics approach, which considers the mix of opening and shear modes of the crack tip loading associated with the testing system and the elastic mismatch of materials across the interface, was used to evaluate the bonding ability of various cements. The four-point bend interfacial delamination test by Charalambides et al. (J. Appl. Mech. 56 (1989) 77; Mech. Mater. 8 (1990) 269) was used to quantify the bonding ability of cements. This method is arguably more suitable since the applied loading mode is comparable to the nature of loading within the prosthetic system, which is primarily bending. The bovine bone specimens were polished to mirror finish to eliminate bonding by mechanical interlocking. The results revealed minimal bonding for the conventional bone cement (PMMA) whereas substantial bonding was evident for the glass-ionomer cements tested. However, only the conventional glass-ionomer cements showed evidence of bonding on testing, while the resin-modified glass-ionomer cement (poly-HEMA) did not. The latter appeared to debond before testing because of excessive expansion stresses associated with swelling in water.     

A comparative study of different beta-whitlockite ceramics in rabbit cortical bone with regard to their biodegradation behaviour

Different beta-whitlockite ceramic cylinders of standard size were implanted in the tibiae of rabbits to study the influence of micropores and chemistry on the biodegradation rate. The materials were evaluated by radiography and light microscopy. Surface chemistry was varied by the addition of impurities, while different applied pressures before sintering and different sintering temperatures gave rise to different micropores. Both factors influenced the biodegradation rate.     

A comparative study of pneumatization of Temporal bone

Introduction

The present review is based on the study of various classifications of pneumatization of temporal bone and their comparison. The air cells are classified based on their location in the temporal bone in a radiograph or based on their interpretation by a radiologist or otolaryngologist with the help of different reference structures.

Differences in mitochondrial movement and morphology in young and mature primary cortical neurons in culture

Mitochondria have many roles critical to the function of neurons including the generation of ATP and regulation of intracellular Ca2+. Mitochondrial movement is highly dynamic in neurons and is thought to direct mitochondria to specific cellular regions of increased need and to transport damaged or old mitochondria to autophagosomes. Morphology also varies between individual mitochondria and is modulated by fusion and fission proteins such as mitofusin-1 and dynamin-related protein-1, respectively. Although mitochondrial movement and morphology are thought to be modulated to best meet cellular demands, few regulatory signals have been identified. In this study, we examined how the different cellular environments of synaptically immature and mature rat cortical neurons affect mitochondrial movement, morphology, distribution and function. In younger cells, mitochondria were more mobile, were shorter, occupied a smaller percentage of neuronal processes, and expressed greater mitofusin-1 and lower dynamin-related protein-1 protein levels compared with older cells. However, the number of mitochondria per mum of neuronal process, mitochondrial membrane potential and the amount of basally sequestered mitochondrial Ca2+ were similar. Our results suggest that while mitochondria in young neurons are functionally similar to mature neurons, their enhanced motility may permit faster energy dispersal for cellular demands, such as synaptogenesis. As cells mature, mitochondria in the processes may then elongate and reduce their motility for long-term support of synaptic structures.     

The effect of gamma irradiation on the anisotropy of bovine cortical bone

Bone is an anisotropic non-homogenous composite material composed of inorganic bone mineral embedded in an organic matrix. The mechanical behaviour of bone is governed by the volume fraction of these constituents, their mechanical properties, the degree of crystallite-collagen orientation and the bonding between phases. This study aims to evaluate the mechanical role of these constituents in the expression of anisotropy by using gamma irradiation to alter the mineralised collagen fibrils. Bovine cortical cubes were prepared, treated and mechanically tested in uniaxial compression in the axial, radial and tangential orientations. Ultimate stress, ultimate strain, energy to failure and stiffness were evaluated. This study confirmed deleterious effect of gamma irradiation on the axial compressive properties of cortical bone with a dose dependent decrease in ultimate stress of 6% (P=0.231) and 16% (P=0.001) at 15 and 25 kGy respectively. This corresponded to a 39% (P=0.058) and 30% (P=0.167) reduction in energy to failure. In the radial orientation there was also a dose dependant decrease in ultimate stress which was consistent with a statistically significant decline in ultimate strain (31% (P=0.003) and 36% (P=0.000)) and energy to failure (36% (P=0.053) and 45% (P=0.008)) at both doses. In the tangential orientation there was a significant 22% (P=0.01) and 23% (P=0.02) decrease in stiffness; though these changes did not alter ultimate stress considerably. This study provides valuable insights into the role of collagen in the radial and tangential orientation when loaded in compression; while also building on the body of work related to the use of gamma irradiation for load bearing bone allografts.     

A comparative magnetoencephalographic study of cortical activations evoked by noxious and innocuous somatosensory stimulations

We recorded somatosensory-evoked magnetic fields and potentials produced by painful intra-epidermal stimulation (ES) and non-painful transcutaneous electrical stimulation (TS) applied to the left hand in 12 healthy volunteers to compare cortical responses to noxious and innocuous somatosensory stimulations. Our results revealed that cortical processing following noxious and innocuous stimulations was strikingly similar except that the former was delayed approximately 60 ms relative to the latter, which was well explained by a difference in peripheral conduction velocity mediating noxious (Adelta fiber) and innocuous (Abeta fiber) inputs. The first cortical activity evoked by both ES and TS was in the primary somatosensory cortex (SI) in the hemisphere contralateral to the stimulated side. The following activities were in the bilateral secondary somatosensory cortex (SII), insular cortex, cingulate cortex, anterior medial temporal area and ipsilateral SI. The source locations did not differ between the two stimulus modalities except that the dipole for insular activity following ES was located more anterior to that following TS. Both ES and TS evoked vertex potentials consisting of a negativity followed by a positivity at a latency of 202 and 304 ms, and 134 and 243 ms, respectively. The time course of the vertex potential corresponded to that of the activity of the medial temporal area. Our results suggested that cortical processing was similar between noxious and innocuous stimulation in SI and SII, but different in insular cortex. Our data also implied that activities in the amygdala/hippocampal formation represented common effects of noxious and tactile stimulations.     

比较青年男子走与跑的能量消耗

背景：能量代谢是健身、减重、行军、假肢评定、医疗诊断等比较关注的热点之一。康复师与健身教练根据具体情况以及不同目的选择不同的运动方式、运动量与运动强度,有关同等运动速度不同走跑步态模式的能量消耗差异研究较少。 目的：探讨相同运动速度两种步态模式下走跑步态特征以及能耗差异,为大众健身以及运动处方的制定提供理论支持。 方法：受试者为男性健康大学生志愿者20名,使用H/P/COSMOS Gaitway跑台控制走跑运动的速度,测量走跑的步频和步长,使用气体成分分析仪VO2000间接测试人体的能量代谢。在人体第一骶椎放置两维加速度传感器采集前后方向以及垂直方向的加速度原始信号。 结果与结论：相同速度跑模式的步频明显高于走模式下的步频。随着速度的递增,行走主要依靠步频的增加,而跑动时主要依靠步长加大来维持速度。同等速度下跑的能耗明显高于行走的能耗。相同速度下跑明显大于走的人体质心垂直方向加速度均方根值。建议根据不同目的选择不同的步态模式,如需要减重健身时可选择跑模式,而在长距离行军时为了节省能量可以选择快走模式。     

A quantitative histologic study of bone turnover in young adult beagles

Thirty-six regions of trabecular bone from two 18-month-old beagles and transilial biopsies of 25 female beagles aged 28–52 months were studied following in vivo double tetracycline labeling. Turnover rate varied from about 20% per year to 200% per year among the 36 regions. It was highest in the vertebral bodies and the proximal humerus, and lowest in the proximal ulna and foot-bones. The mineral apposition rate varied from 0.35 to 1.02 μm/day, with a mean of about 0.7 μm/day, tending to be lower in areas of lower turnover. The specific surface varied from 10.9 to 23.8 mm/mm² with a mean of 17.5 mm/mm², tending to be higher in areas of high turnover. Specific surface varied only about twofold around the skeleton, while turnover varied by one order of magnitude. The average annual turnover rate for all trabecular bone in the young adult beagle is estimated at 140% per year. The accuracy of this estimate would be improved by knowing the exact mass of trabecular bone at each site. The annual turnover rate in the ilium of 25 female beagles was 134 ± 94% per year. The iliac trabecular bone turnover rate is two to three times faster in young adult female beagles than in young adult female humans. Using a human to beagle ratio of 1:2.5, the average annual turnover rate for all trabecular bone in the young adult human could be estimated at 40–55% per year. The beagle may be an appropriate model for certain experiments involving the adult bone remodeling system, because it may show a quicker response than humans to various experimental conditions and drugs, due to its faster turnover rate.     

Anisotropy in the compressive mechanical properties of bovine cortical bone and the mineral and protein constituents

The mechanical properties of fully demineralized, fully deproteinized and untreated cortical bovine femur bone were investigated by compression testing in three anatomical directions (longitudinal, radial and transverse). The weighted sum of the stress-strain curves of the treated bones was far lower than that of the untreated bone, indicating a strong molecular and/or mechanical interaction between the collagen matrix and the mineral phase. Demineralization and deproteinization of the bone demonstrated that contiguous, stand-alone structures result, showing that bone can be considered an interpenetrating composite material. Structural features of the samples from all groups were studied by optical and scanning electron microscopy. Anisotropic mechanical properties were observed: the radial direction was found to be the strongest for untreated bone, while the longitudinal one was found to be the strongest for deproteinized and demineralized bones. A possible explanation for this phenomenon is the difference in bone microstructure in the radial and longitudinal directions.     

A comparative ultrastructural study of in vivo versus in vitro fertilization of bovine oocytes

Summary Heifers were superovulated by PMSG or FSH, and oestrus was induced by prostaglandin. One group of animals was ovariectomized 19–26 h after the LH peak, the content of preovulatory follicles aspirated, and the oocytes processed for in vitro fertilization. Another group was inseminated and ova were collected from the oviducts for study of in vivo fertilization. All ova were examined ultrastructurally. The developmental rate following in vitro fertilization was delayed compared to fertilization in vivo. A high proportion of the in vitro fertilized ova showed polyspermic penetration of the zona pellucida, and supernumerary spermatozoa were found in the ooplasm of some ova. In vivo fertilization was associated with release and subsequent dispersal of the cortical granule content in the perivitelline space. In contrast to this the released granule content of the in vitro fertilized ova remained undispersed close to the oolemma. This feature may account for the high incidence of polyspermic penetration of the zona pellucida. In addition, the study provided an ultrastructural visualization of the initial contact between the equatorial segment of the spermatozoon and the microvilli of the oocyte, and the subsequent internalization of the sperm head.     

Microradiographic study of bone and tooth alterations in bovine fluorosis

Exostoses were found in the 5th rib, the cannon bone and the mandible of a 6-year-old fluorotic cow. Microradiographic alterations of lamellar bone in these skeletal items included both matrix modifications and mineralization troubles. In the incisors, the enamel was covered by a layer of cementum, and the dentine presented numerous giant tubules and accentuation of incremental lines. In the cementum, hypomineralized areas were located along the periodontal fibres.     

A comparative study of attachment of human, bovine and mouse blastocysts to uterine epithelial monolayer

The in-vitro attachment of human, bovine and murine blastocyststo monolayer cultures of uterine epithelium were studied bytransmission electron microscopy. The human trophoblastic cellsintrude between uterine epithelial cells forming a multilayerduring attachment in vitro, thus resembling the intrusive typeof penetration observed in vivo. The bovine trophoblastic outgrowthresembled an epithelio-chorial attachment as the trophoblastformed an attachment plate on top of the endometrial cells withoutpenetration. In the murine attachment study, the trophoblastcells immediately displaced the uterine cells and formed contactwith the culture vessel.     

A broadband viscoelastic spectroscopic study of bovine bone: implications for fluid flow

To explore the hypothesis that mechanical excitation-induced fluid flow and/or fluid pressure are potential mechanical transduction mechanisms in bone adaptation, a complementary experimental and analytical modeling effort has been undertaken. Experimentally, viscoelastic tan properties of saturated cortical bovine bone were measured in both torsion and bending, and significant tan values in the 10⁰-10⁵Hz range were observed, although the nature of the damping is not consistent with a fluid pressure hypothesis. Analytically, micromechanically based poroelasticity models were exercised to quantify energy dissipation associated with load-induced fluid flow in large scale channels. The modeling results indicate that significant damping due to fluid flow occurs only above 1 MHz frequencies. Together, the experimental and analytical results indicate that at excitation frequencies presumed to be physiological (1–100 Hz), mechanical loading of bone generates extremely small pore fluid pressures, making the hypothesized fluid-pressure transduction mechanism upon osteocytes untenable. © 2001 Biomedical Engineering Society. PAC01: 8380Lz, 8710+e, 8385Cg     

Malignant fibrous histiocytoma of bone and osteosarcoma. A comparative light and electron microscopic study.

Malignant fibrous histiocytomas are well-described tumors of the soft tissues. Recent investigations have shown that malignant histiocytoma may also occur as a primary bone tumor. However, difficulties may arise to distinguish malignant histiocytoma of bone from other malignant bone tumors, such as osteosarcoma. In the present study, the ultrastructure of five cases of malignant fibrous histiocytoma of bone is compared with that of osteosarcoma. The results show that malignant fibrous histiocytoma is composed mainly of histiocytic cells and fibroblastic cells. In addition, xanthomatous cells, undifferentiated cells, and giant cells may be observed. By contrast, the predominant cell type in osteosarcoma is the neoplastic osteoblast, characterized by abundant rough endoplasmic reticulum. Signs of matrix calcification in the intercellular matrix between the collagen fibrils are regularly observed in osteosarcoma, but not in malignant histiocytoma. From these results it is concluded that the ultrastructure of malignant fibrous histiocytoma arising in bone is morphologically identical with the soft tissue counterpart of this tumor. The components of the tumor are derived from neoplastic histiocytes. This cytogenesis differs from that of osteosarcoma, which is derived from neoplastic osteoblasts. Therefore, from the ultrastructural point of view, malignant fibrous histiocytoma of bone should be accepted as a distinct histologic entity among bone tumors.     

A comparative study of biphasic calcium phosphate ceramics for human mesenchymal stem-cell-induced bone formation

For the repair of bone defects, a tissue engineering approach would be to combine cells capable of osteogenic (i.e. bone-forming) activity with an appropriate scaffolding material to stimulate bone regeneration and repair. Human mesenchymal stem cells (hMSCs), when combined with hydroxyapatite/beta-tricalcium phosphate (HA/TCP) ceramic scaffolds of the composition 60% HA/40% TCP (in weight %), have been shown to induce bone formation in large, long bone defects. However, full repair or function of the long bone could be limited due to the poor remodeling of the HA/TCP material. We conducted a study designed to determine the optimum ratio of HA to TCP that promoted hMSC induced bone formation yet be fully degradable. In a mouse ectopic model, by altering the composition of HA/TCP to 20% HA/80% TCP, hMSC bone induction occurred at the fastest rate in vivo over the other formulations of the more stable 100% HA, HA/TCP (76/24, 63/37, 56/44), and the fully degradable, 100% TCP. In vitro studies also demonstrated that 20/80 HA/TCP stimulated the osteogenic differentiation of hMSCs as determined by the expression of osteocalcin.     

A comparative study of shear stresses in collagen-glycosaminoglycan and calcium phosphate scaffolds in bone tissue-engineering bioreactors

The increasing demand for bone grafts, combined with their limited availability and potential risks, has led to much new research in bone tissue engineering. Current strategies of bone tissue engineering commonly use cell-seeded scaffolds and flow perfusion bioreactors to stimulate the cells to produce bone tissue suitable for implantation into the patient's body. The aim of this study was to quantify and compare the wall shear stresses in two bone tissue engineering scaffold types (collagen-glycosaminoglycan (CG) and calcium phosphate) exposed to fluid flow in a perfusion bioreactor. Based on micro-computed tomography images, three-dimensional numerical computational fluid dynamics (CFD) models of the two scaffold types were developed to calculate the wall shear stresses within the scaffolds. For a given flow rate (normalized according to the cross-sectional area of the scaffolds), shear stress was 2.8 times as high in the CG as in the calcium-phosphate scaffold. This is due to the differences in scaffold geometry, particularly the pore size (CG pore size approximately 96 microm, calcium phosphate pore size approximately 350 microm). The numerically obtained results were compared with those from an analytical method that researchers use widely experimentalists to determine perfusion flow rates in bioreactors. Our CFD simulations revealed that the cells in both scaffold types were exposed to a wide range of wall shear stresses throughout the scaffolds and that the analytical method predicted shear stresses 12% to 21% greater than those predicted using the CFD method. This study demonstrated that the wall shear stresses in calcium phosphate scaffolds (745.2 mPa) are approximately 40 times as high as in CG scaffolds (19.4 mPa) when flow rates are applied that have been experimentally used to stimulate the release of prostaglandin E(2). These findings indicate the importance of using accurate computational models to estimate shear stress and determine experimental conditions in perfusion bioreactors for tissue engineering.     

The Slosson Intelligence Test and young learning-disabled children: a comparative study

Evaluated 26 children independently diagnosed as learning disabled in a counterbalanced design with the deviation IQ form of the Slosson Intelligence Test and the Wechsler Intelligence Scale for Children-Revised (WISC-R). Moderate to good correlations were obtained between the Slosson and the WISC-R Full Scale (r = .91), Verbal (r = .94) and Performance (r = .60) IQ scores. The Slosson correctly predicted functioning level to within 10 IQ points of WISC-R Full Scale scores for 88% of the Ss. These data suggest that the recent revision of the Slosson has corrected the tendency of earlier versions of this instrument to inflate the estimated IQs of young learning-disabled children.     

Skeletal alterations in hypophysectomized rats: II. A histomorphometric study on tibial cortical bone

Background: Pituitary hormones play an important role in bone growth, modeling, and remodeling. The purpose of this study is to examine the effect of hypophysectomy (HX) on tibial cortical bone with histomorphometry. Methods: Forty-Five female Sprague-Dawiey rats, at 3 months of age, were hypophysectomized or served as intact controls. They were sacrificed at 0, 2, and 5 weeks after the surgery. Cortical bone histomorphometry was performed on double-fluorescent-labeled 30-mcm-thick sections of the tibial shaft. Results: The dry weight and density of tibial diaphysis and the cortical bone area of the tibial shaft in the HX rats were significantly lower (P<0.05) than that of the age-matched intact rats, but did not differ between the HX and basal control rats. The dynamic data show that the bone formation parameters (labeled surface, mineral apposition rate, and bone formation rate) were profoundly decreased (P<0.01) on both the periosteal and endocortical surfaces in the HX rats as compared with the age-matched intact rats at the 2 and 5 weeks. However, the decrease in the labeled surface was much less on the endocortical envelope than on the periosteal envelope in the HX rats. Although no significant change was detected in the medullar size between the HX and age-matched intact rats, the eroded surface on the endocortical surface was greater (P<0.05) in the HX rats than in the intact rats at either time point. Conclusions: Hypophysectomy-suppressed, radial growth-dependent bone gain without a bone loss in the tibial shaft of the young rat. This is associated with decreased modeling-dependent bone formation. A greater eroded surface on the endosteum did not affect the marrow size at 5 weeks after hypophysectomy. © 1995 Wiley-Liss, Inc.