The Influence of Center of Rotation on the Assessment of Trabecular Bone Densitometric and Structural Properties

The center of rotation is a physical location in the microCT scanner, defined by the axis of rotation of the sample stage. This physical location is always well defined during calibration of the instrument and fitted by an appropriate algorithm. However, in real images of limited contrast and with X-ray photon noise, this algorithm exhibits poorer precision and the optimum center of rotation cannot be always acquired. Thus, adjustment by operator is necessary to determine whether the center of rotation was correct, in order that the structural information of the sample can be correctly interpreted. In this paper, the effect of center of rotation on the assessment of densitometric and structural properties of trabecular bone was firstly evaluated. Twenty female Sprague–Dawley rats of 7-month-old were randomly assigned to ovariectomized (OVX) and SHAM-operated (SHAM) groups. The left tibiae were harvested at 3 weeks postoperatively. High resolution microCT was used to identify the densitometric and microstructural properties of trabeculae in the proximal ends of tibia. After CT scanning, the best artificial center of rotation for each scan was obtained. Bone parameters analyses were performed on the centers at different places away from the best artificial center of ±0.2, ±0.5, ±1.0, ±1.5, and ±2.0 pixels, respectively. The general linear model (GLM) repeated measures procedure was used to investigate the difference in the parameters between the two groups (OVX vs. SHAM) and the possible effects of center displacements. A significant difference between OVX and SHAM groups was found in all parameters (p < 0.05) except Tb.Th, DA, and BS/BV. TBMD, DA, BS/BV, and Conn.D were decreased while BV/TV and Tb.Th were increased with the center deflection. Variations of these parameters were acceptable when the displacements were limited within ±1.5 pixels for tBMD, BV/TV, DA, and Conn.D, and ±1.0 pixels for Tb.Th and BS/BV. These changes were similar in both OVX and SHAM groups. The changing curves of bone parameters vs. centers could be well fitted by quadric regression models, by which the real center could be acquired, and thus the precision of microCT analysis would be improved. There were some inevitable differences between the best artificial and real centers.     

珍珠、珍珠层的显微结构与鉴别

本文对海水、淡水的珍珠、珍珠层显微结构进行了研究,并与外形类似品的显微结构与粉末作了详细比较,并列表和附图。     

Technical Considerations for Microstructural Analysis of Human Trabecular Bone from Specimens Excised from Various Skeletal Sites

The purpose of this study was to test the effect of repositioning, systematic displacements of the region of interest (ROI), and acquisition parameters (scan mode and integration time) on quantitative analysis of human trabecular bone microstructure at various skeletal sites, using microcomputed tomographic (CT) technology. We investigated 28 cylindrical specimens of human trabecular bone (length 14 mm, diameter 8 mm) from four skeletal sites (femoral neck, greater trochanter, second lumbar vertebra, and distal radius). These specimens were selected from over 200 CT measurements, in order to cover a large range of bone volume fraction (BV/TV) observed at each site. Cylindrical ROIs (length 6 mm, diameter 6 mm) were examined twice at an isotropic resolution of 26 m, 8 weeks apart. In addition, comparative analyses were performed for displacements of the volumes of interest (VOIs) by 1, 2, 3, and 4 mm (83.4%, 66.6%, 50%, and 33.3% overlap), respectively. Eventually, comparative measurements were obtained at different resolution scan modes and integration times. The results show that CT measurements are highly reproducible (range of the root mean square coefficient variation % (RMS CV%) = 0.64% to 1.29% for BV/TV at different sites). Displacements of the VOI of up to 4 mm generally led to non significant systematic differences in mean values of <10%. When comparing various combinations of resolution scan modes and integration times, the use of an integration time of 100 ms was found to be preferable for determining microstructural parameters from human samples with this CT scanner.     

Bone mineral change during experimental heating: an X-ray scattering investigation

The effects of heating and burning on bone mineral have previously been studied using techniques such as X-ray diffraction (XRD) with the aim of discerning a characteristic signature of crystal change. This would enable a better understanding of alteration to bone mineral during heating, which would in turn impact on the preparation and use of natural bone hydroxyapatite as a biomaterial resource. In addition, this knowledge could prove invaluable in the investigation of burned human remains from forensic and archaeological contexts in cremation and funerary practice. Here we describe a complementary method, small-angle X-ray scattering (SAXS), to determine more accurately the changes to bone crystallite size and shape during an experimental heating regimen. Samples were subjected to controlled heating at 500°C, 700°C, or 900°C for 15 or 45 min. Our results show bone crystallites begin to alter in the first 15 min of heating to 500°C or above. They then appear to stabilise to a temperature-specific thickness and shape with prolonged heating. While the samples heated to lower temperatures or for shorter periods produce XRD traces showing little alteration to the apatite, corresponding information obtained from SAXS shows an early, subtle change in crystal parameters.     

Microhardness and microstructure of deciduous enamel with different types of amelogenesis imperfecta

Amelogenesis imperfecta (AI) is an inherited tooth disorder with widely varying phenotypes. The aim of this study was to determine the microhardness and microstructure characteristics of the enamel in AI teeth. The AI phenotypes examined were hypoplastic (pitted and smooth form), hypomaturated, and hypocalcified. Six AI patients were diagnosed according to clinical characteristics. The microhardness of the enamel was measured on axial cuts of AI teeth acquired from the patients. The measurements were done on several sites from the enamel surface towards the dentine-enamel junction using the Vickers scale. Values of microhardness were compared to corresponding control teeth. The microstructure of AI enamel types was evaluated using scanning electron microscopy. The values of microhardness in pitted hypoplastic AI samples were, on average, lower compared to the control enamel and dropped markedly towards the dentine-enamel junction. The smooth hypoplastic enamel was not only extremely thin but also much softer than control enamel. The values for hypomaturated AI fluctuated, but the palatal sites were markedly softer than in the control tooth. Hypocalcified enamel was the softest, with values resembling those of dentin. Microstructural changes varied from altered orientation of enamel prisms in pitted hypoplastic AI to lack of normal prismatic structure and severe porosity in hypocalcified AI. The present results suggest different microhardness profiles and microstructures in each phenotype. Variations among phenotypes are expected with larger case selection in this genetically heterogeneous disease.     

A novel combinatorial approach for understanding microstructural evolution and its relationship to mechanical properties in metallic biomaterials

The new generation of metallic biomaterials for prosthesis implantation (orthopedic and dental) typically have a Ti base with fully biocompatible alloying additions such as Nb, Ta, Zr, Mo, Fe and Sn. While the binary Ti-Ta and the ternary Ti-Nb-Ta systems are promising, the large composition space afforded by these systems offers tremendous scope in terms of alloy design via optimization of alloy composition and thermomechanical treatment. In the present paper a novel combinatorial approach has been developed for rapidly exploring the microstructural evolution and microstructure-microhardness (or elastic modulus) relationships in these systems. Using directed laser deposition, compositionally graded alloy samples have been fabricated and subsequently heat-treated to affect different microstructures in terms of the volume fraction and distribution of the alpha phase in the beta matrix as a function of composition. Subsequently, composition-specific indentation-based hardness and modulus information has been obtained from these graded samples, and the resulting data have been used to develop relationships between the composition, microstructure and mechanical properties. Such rapid combinatorial assessments can be very useful in optimizing not only the alloy composition but also the desired microstructure for achieving the best combination of properties for specific orthopedic or dental applications.     

形态学与形态计量学观察大豆异黄酮对前列腺增生大鼠的作用

目的观察与分析斑马鱼肝脏的显微和超微结构。方法光镜和透射电镜观察组织切片。结果斑马鱼肝脏没有典型的门管区,静脉和胆管随机地分布在肝实质中,很难观察到动脉。肝板由两层并列的肝细胞排列成双层板状结构,以中央静脉为中心呈放射状分布,在肝板（肝细胞索）之间是血窦,肝细胞索呈弯曲、分支和吻合状态,肝细胞核大而圆,核仁分区明显,核孔数目多,且密度大,呈现细胞代谢活跃旺盛的形态。胞质中粗面内质网（RER）既有管状结构也有扁平囊状结构,扁平囊状结构的RER呈区域化的层层排列,可达二十余层。线粒体成群分布,并且与RER紧密接触,为RER合成蛋白质提供能量。电镜观察发现当细胞质富含线粒体、RER、核糖体时,核孔的数目多,细胞质内出现一定量的溶酶体,糖原在细胞质内有少量的聚集。当细胞质内有大量的糖原分布时,则核孔的数目较少,且细胞嚣也较少。胆管系统在肝脏内呈树枝状分布,胆小管包括细胞内胆小管和细胞间胆小管,细胞内胆小管腔内的微绒毛明显多于细胞间胆小管。本文也对内皮细胞、贮脂细胞、红细胞和淋巴细胞进行了描述。并对斑马鱼肝脏的结构与其他硬骨鱼类进行了比较。结论斑马鱼肝细胞排列方式与其他硬骨鱼类有一定差异,也与前人的报道并不完全相同,这种差异和不同与动物种类和研究方法有一定关系。肝细胞的超微结构特征,在形态学角度证明了其活跃的合成和代谢功能。     

Influence of bioactive glass-coating of zirconia implant surfaces on human osteoblast behavior in vitro

ObjectiveThe recently developed bioactive glass PC-XG3, which is suitable to coat zirconia implant surfaces with high adhesion strength may reduce the time of osseointegration and the marginal bone loss following implantation. The glass composition has been previously evaluated for cytotoxicity on fibroblast cells, and will now be used to evaluate the cell behavior of osteoblast cells.MethodsThree different surface morphologies were created with PC-XG3 on zirconia discs. A clinically tested zirconia implant surface as well as polished and machined zirconia served as a reference. Cell viability after 24 h, cell spreading after 30 min and 24 h and the respective morphology of human osteoblasts using scanning electron microscopy were evaluated. Additionally, the corrosive process of PC-XG3 in cell culture medium up to 7 d was measured.ResultsInitial cell behavior of human osteoblasts was not accelerated by the PC-XG3 surface when compared to zirconia. Additionally, it was found that a decreased surface roughness promoted initial cell spreading. Storage in cell culture medium resulted in the accumulation of C and N on the bioglass surface while Mg, Si, K and Ca were decreased and crack formation was observed.SignificanceSince initial spreading quality to a biomaterial is a crucial factor that will determine the subsequent cell function, proliferation, differentiation, and viability it can be assumed that a coating of zirconia implants with this bioactive glass will unlikely reduce osseointegration time.     

Formulation of ascorbic acid microemulsions with alkyl polyglycosides

Ascorbic acid microemulsions for topical application were developed. In this study, microemulsions were prepared using HLD (hydrophilic lipophilic deviation) concept to optimise the formulation. From this optimal formulation, the realisation of dilution ternary diagrams leads to obtain microemulsion zones. In addition, the effects of composition variable on the physicochemical characteristics of each system were investigated. After optimisation of the microemulsion systems, ascorbic acid was loaded in the formulations. Surface tension and small angle neutron scattering were used to characterise the surface properties and the structure of the microemulsions. Bicontinuous structure microemulsions were identified, and the influence of ascorbic acid localisation at the interface leading to modifications of the microemulsion structure was pointed out. The solubilisation of ascorbic acid, the stabilisation and in vitro transdermal penetration “Frantz cells” of ascorbic acid microemulsions were studied. Three different microemulsions were envisaged. The results confirmed that these microemulsion systems present a real interest for formulation and protection of ascorbic acid. Regarding their transcutaneous penetration behaviour, the different microemulsions studied could be useful for different topical applications. A major location of ascorbic acid found in the epidermis where the decomposition of melanin occurred indicates that microemulsion could be considered as a suitable carrier system for application of ascorbic acid as a whitening agent. In addition, a good passage of the drug in the dermis could be interesting for the relative oxygen matrix damage.     

Shortcomings of DXA to assess changes in bone tissue density and microstructure induced by metabolic bone diseases in rat models

Summary  The aim of this study is to demonstrate the deficiencies of dual-energy X-ray absorptiometry (DXA), compared with quantitative computed tomography, to reflect and differentiate between changes in bone mineral density and microstructure that contribute to a well-defined finding of altered skeletal state for both osteoporosis and renal osteodystrophy induced by chronic renal insufficiency. Introduction  The aim of this study is to demonstrate the deficiencies of dual-energy X-ray absorptiometry (DXA), compared with quantitative CT, to reflect and differentiate between changes in bone mineral density and microstructure that contribute to a well-defined finding of altered skeletal state for both osteoporosis and renal osteodystrophy induced by chronic renal insufficiency. Methods  Forty-five female Sprague–Dawley rats were divided into three equal groups: control, ovariectomy, and nephrectomy. Following euthanasia, femurs were excised, divided into diaphyseal and distal metaphyseal sections, and subjected to DXA and micro-CT imaging and mechanical testing. Results  Ovariectomy does not affect the structural and mechanical properties of cortical bone material, but partial nephrectomy does adversely affect these properties. Both are verified by DXA and micro-CT imaging and mechanical testing. Meanwhile, nephrectomy does not affect trabecular bone microstructure or equivalent density, yet ovariectomy affects the trabecular microstructure. DXA is unable to detect changes in trabecular bone microstructure in relation to changes in their mechanical properties. Discussion  Dual energy X-ray absorptiometry measures the average bone mineral content in a 2D projected area and cannot differentiate whether the changes occur in the bone microstructure or equivalent bone tissue density. In contrast, micro-CT provides an accurate measurement of the changes in both equivalent bone tissue mineral density and microstructure for cancellous and cortical bone. A. Nazarian and E. Cory have contributed equally to this work.