犬囊状动脉瘤模型的制作

本文报道用“静脉囊镶嵌技术·制成犬的囊状动脉瘤模型。18个模型(6个单侧型,6个分叉型,6个末梢型)造型后2周经IA DSA检查。本模型在分型、血流动力学改变方面与人类囊状脑动脉瘤类似。不同类型的动脉瘤模型既有相同的血流动力学特征,又有各自的特点,这与动脉瘤与载瘤动脉的角度有关。我们认为该模型可应用于研究动脉瘤的血流动力学与血管内栓塞治疗。     

Mechanical properties vary for different regions of the finger extensor apparatus

The extensor apparatus, an aponeurosis that covers the dorsal side of each finger, transmits force from a number of musculotendons to the phalanges. Multiple tendons integrate directly into the structure at different sites and the extensor apparatus attaches to the phalanges at multiple points. Thus, prediction of the force distribution within the extensor apparatus, or hood, and the transmission to the phalanges is challenging, especially as knowledge of the underlying mechanical properties of the tissue is limited. We undertook quantification of some of these properties through material testing of cadaver specimens. We punched samples at specified locations from 19 extensor hood specimens. Material testing was performed to failure for each sample with a custom material testing device. Testing revealed significant differences in ultimate load, ultimate strain, thickness, and tangent modulus along the length of the extensor hood. Specifically, thickness, ultimate load, and ultimate strain were greater in the more proximal sections of the extensor hood, while the tangent modulus was greater in the more distal sections. The variations in mechanical properties within the hood may impact prediction of force transmission and, thus, should be considered when modeling the action of the extensor apparatus. Across the extensor hood, tangent modulus values were substantially smaller than values reported for other soft tissues, such as the Achilles tendon and knee ligaments, while ultimate strains were much greater. Thus, the tissue in the extensor apparatus seems to have greater elasticity, which should be modeled accordingly.     

Mechanical properties of calcified exoskeleton from the neotropical millipede, Nyssodesmus python

The calcified exoskeleton of millipedes plays a crucial role in resisting large forces developed during burrowing locomotion. I measured morphological and mechanical properties of cuticle from the neotropical forest floor millipede, Nyssodesmus python (Diplopoda: Polydesmidae), which ranges in body mass from 2 to 7 g. Scaling of thickness of the cuticle with respect to body mass followed predictions of geometric similarity. Both fracture strength and Young's modulus increased with body mass in females but not in males. In spite of their smaller size, male millipedes were still stronger, on average, than female millipedes. Mean fracture strength of millipede cuticle was 124 MPa, and Young's modulus was 17 GPa. Both of these values exceed measurements from typical insect cuticle, suggesting that calcium salts may play a role in stiffening and strengthening the millipede exoskeleton. Because of the high density of calcified millipede cuticle (1660 kg/m³), stiffness and strength relative to body weight remain comparable to values for other insect cuticles. These results corroborate a previous hypothesis that absolute not specific strength and stiffness have been selective factors in the evolution of millipede cuticle, and that bulkiness of the exoskeleton has been minimized through the deposition of calcium salts.     

临床护理路径对囊性动脉瘤介入手术患者的应用研究

目的:应用临床护理路径,提高囊性动脉瘤介入手术患者的护理质量。方法:采用病例对照研究随机选择囊性动脉瘤患者60例。其中病例组30例,对照组30例,在相同治疗条件下病例组使用临床护理路径干预,对照组予以常规护理。结果:病例组使用临床护理路径后,与对照组相比平均住院日缩短P0.05,住院费用减少P0.05,患者满意度提高P0.05。结论:临床护理路径对囊性动脉瘤患者介入手术的干预效果有效,值得临床护理应用。     

临床护理路径对囊性动脉瘤介入手术患者的应用研究

目的：应用临床护理路径,提高囊性动脉瘤介入手术患者的护理质量。方法：采用病例对照研究随机选择囊性动脉瘤患者60例。其中病例组30例,对照组30例,在相同治疗条件下病例组使用临床护理路径干预,对照组予以常规护理。结果：病例组使用临床护理路径后,与对照组相比平均住院日缩短P〈0．05,住院费用减少P〈0．05,患者满意度提高P〈0．05。结论：临床护理路径对囊性动脉瘤患者介入手术的干预效果有效,值得临床护理应用。     

Mechanical Behavior of Bamboo,and Its Biomimetic Composites and Structural Members:A Systematic Review

Bamboo is a typical biological material widely growing in nature with excellent physical and mechanical properties.It is lightweight with high strength and toughness.The naturally optimized bamboo structure,which has inspired global material scientists and engineers for decades,is significantly important for the bionic design of novel structural materials with ultra-light,ultra-strong,or ultra-tough and comprehensive properties.Typical literature on innovative composite materials and structural members inspired by bamboo are reviewed in this paper,and the research progress and prospects in this field are expounded in three parts.First,the structural characteristics of the bamboo wall layer along the thickness and height direc-tions are described in terms of chemical composition,gradient structure,pore structure,and hollow structure with variable cross-section.Second,this paper summarizes the research progress on new composite materials and structural components by applying bamboo's structural features from the perspective of sustainability,designability,and customization.Finally,given the limitations of current research,the biomimetic scientific research on bamboo's structural characteristics is prospected from the interpretation of bamboo structure,new bamboo-like materials,and structural design optimization perspectives,providing a reference for future research on biomimetic aspects of biomass.     

Three-dimensional Orthotropic Viscoelastic Finite Element Model of a Human Ligament

Ligaments undergo finite strain displaying hyperelastic behaviour as the initially tangled fibrils present straighten out, combined with viscoelastic behaviour (strain rate sensitivity). In the present study the anterior cruciate ligament of the human knee joint is modelled in three dimensions to gain an understanding of the stress distribution over the ligament due to motion imposed on the ends, determined from experimental studies. A three dimensional, finite strain material model of ligaments has recently been proposed by Pioletti in Ref. [2]. It is attractive as it separates out elastic stress from that due to the present strain rate and that due to the past history of deformation. However, it treats the ligament as isotropic and incompressible. While the second assumption is reasonable, the first is clearly untrue. In the present study an alternative model of the elastic behaviour due to Bonet and Burton (Ref. [4]) is generalized. Bonet and Burton consider finite strain with constant modulii for the fibres and for the matrix of a transversely isotropic composite. In the present work, the fibre modulus is first made to increase exponentially from zero with an invariant that provides a measure of the stretch in the fibre direction. At 12% strain in the fibre direction, a new reference state is then adopted, after which the material modulus is made constant, as in Bonet and Burton's model. The strain rate dependence can be added, either using Pioletti's isotropic approximation, or by making the effect depend on the strain rate in the fibre direction only.

A solid model of a ligament is constructed, based on experimentally measured sections, and the deformation predicted using explicit integration in time. This approach simplifies the coding of the material model, but has a limitation due to the detrimental effect on stability of integration of the substantial damping implied by the nonlinear dependence of stress on strain rate. At present, an artificially high density is being used to provide stability, while the dynamics are being removed from the solution using artificial viscosity. The result is a quasi-static solution incorporating the effect of strain rate. Alternate approaches to material modelling and integration are discussed, that may result in a better model.     

Age-dependent material properties of the porcine cerebrum: effect on pediatric inertial head injury criteria

During growth and development, the immature central nervous system undergoes rapid alterations in constituents and structure. We hypothesize that these alterations are accompanied by changes in the mechanical properties of brain tissue which, in turn, influence the response of the brain to traumatic inertial loads. Samples of frontal cerebrum from neonatal (2–3 days) and adult pigs were harvested and tested within 3 h post-mortem. The complex shear modulus of the samples was measured in a custom-designed oscillatory shear testing device at engineering shear strain amplitudes of 2.5% or 5% from 20–200 Hz, at 25°C and 100% humidity. In this range, the elastic and viscous components of the complex shear modulus increased significantly with the development of the cerebral region of the brain. Using an idealized model of the developing head, the age-dependent material properties of brain tissue were shown to affect the mechanical response of the brain to inertial loading. This study is a first step toward developing head injury tolerance criteria specifically for the pediatric population.     

Mechanical phenotyping of stem cells

Elasticity and visco-elasticity are mechanical properties of cells which directly reflect cellular composition, internal structure (cytoskeleton), and external interactions (cell-cell and/or cell-surface). A variety of techniques involving probing, pulling, or deforming cells have been used to characterize these mechanical properties. With continuing advances in the technology, it may be possible to establish mechanical phenotypes that can be used to identify cells at specific points of differentiation and dedifferentiation with direct applications to regenerative medicine, therapeutics, and diagnostics.     

Mechanical properties of anterior malleolar ligament from experimental measurement and material modeling analysis

In this paper, mechanical properties of the anterior malleolar ligament (AML) of human middle ear were studied through the uniaxial tensile, stress relaxation and failure tests. The digital image correlation (DIC) method was used to assess the boundary effect in experiments and calculate the strain on specimens. The constitutive behavior of the AML was described by a transversely isotropic hyperelastic model which consists of a first-order Ogden model augmented by a I (4)-type reinforcing term. The material parameters of the model were estimated and the viscoelasticity of the AML was illustrated by hysteresis phenomena and stress relaxation function. The mechanical strength of the AML was obtained through the failure test and the mean ultimate stress and stretch ratio were measured as 1.05 MPa and 1.51, respectively. Finally, a linear Young's modulus-stress relationship of the AML was derived based on constitutive equation of the AML within a stress range of 0-0.5 MPa.     

Differential Activation of Dual Signaling Responses by Human H1 and H2 Histamine Receptors

Abstract

Stimulation of human H₁ and H₂‐histamine receptors (HRs) primarily activates signaling pathways to increase intracellular calcium [Ca²⁺]_i and cyclic AMP (cAMP), respectively. Activation of H₂‐HR in human embryonic kidney (HEK) cells by histamine and dimaprit increases both cAMP formation and [Ca²⁺]_i, as determined by cAMP‐scintillation proximity assays and fluorescence imaging plate reader (FLIPR) assays. In HEK cells expressing relatively high levels of H₂‐HR (B_max = 26 pmol/mg protein), histamine and dimaprit are full agonists in eliciting cAMP responses with pEC₅₀ values of 9.30 and 7.72 that are 1000‐fold more potent than their respective pEC₅₀ values of 6.13 and 4.91 for increasing [Ca²⁺]_i. The agonist potencies decrease for both responses at lower H₂‐HR density (5 pmol/mg protein) and dimaprit exhibits partial agonist behavior for the [Ca²⁺]_i response. The inverse agonists ranitidine and cimetidine more potently inhibit cAMP production in the higher expressing H₂‐HR line. Histamine also activated both signaling pathways via human H₁‐HRs highly expressed (B_max = 17 pmol/mg protein) in HEK cells, with a 1000‐fold greater potency for [Ca²⁺]_i vs. cAMP responses (pEC₅₀ = 7.86 and 4.82, respectively). These studies demonstrate a markedly different potency for activation of multiple signaling pathways by H₁‐ and H₂‐HRs that may contribute to the selectivity of histamine responses in vivo.     

The evolution of tendon--morphology and material properties

Phylogenetically, tendinous tissue first appears in the invertebrate chordate Branchiostoma as myosepta. This two-dimensional array of collagen fibers is highly organized, with fibers running along two primary axes. In hagfish the first linear tendons appear and the myosepta have developed specialized regions with unidirectional fiber orientation-a linear tendon within the flat sheet of myoseptum. Tendons react to compressive load by first forming a fibrocartilaginous pad, and under severe stress, sesamoid bones. Evidence for this ability to react to load first arises in the cartilaginous fish, here documented in a tendon from the jaw of a hard-prey crushing stingray. Sesamoid bones are common in bony fish and also in tetrapods. Tendons will also calcify under tensile loads in some groups of birds, and this reaction to load is seen in no other vertebrates. We conclude that the evolutionary history of tendon gives us insight into the use of model systems for investigating tendon biology. Using mammal and fish models may be more appropriate than avian models because of the apparent evolution of a novel reaction to tensile loads in birds.     

Effect of arabinose substitution on the material properties of arabinoxylan films

This study was undertaken to investigate the effect of arabinose content on film properties. The substrate used was a rye arabinoxylan that had an Ara/Xyl ratio of 0.52 and an average number molecular weight of 305 kDa. Oxalic acid was used to attempt selective removal of the arabinose substituents on the xylan main chain. The debranching of the polymer was coupled with a decrease in molecular weight. The effect of reaction conditions on the decrease in arabinose content and loss of molecular weight was investigated. Optimal conditions were selected using an experimental design. Treatment at lower temperature for longer period of times resulted in debranching with less degradation of the main chain. As the Ara/Xyl ratio was lowered, aggregates began to form in an interval of the Ara/Xyl ratio between 0.31 and 0.23 in a water solution. Precipitation occurred below an Ara/Xyl ratio of 0.1. Thus, removal of arabinose substituents results in a gradual association of unsubstituted chains. There is a linear correlation between arabinose substitution and the moisture content of arabinoxylan at 98% RH. A decrease in arabinose content resulted in the loss of a plasticizing effect, as determined by dynamic mechanical analysis, which is correlated to water binding capacity.     

Effects of fabrication on the mechanics,microstructure and micromechanical environment of small intestinal submucosa scaffolds for vascular tissue engineering

In small intestinal submucosa scaffolds for functional tissue engineering, the impact of scaffold fabrication parameters on success rate may be related to the mechanotransductory properties of the final microstructural organization of collagen fibers. We hypothesized that two fabrication parameters, 1) preservation (P) or removal (R) of a dense collagen layer present in SIS and 2) SIS in a final dehydrated (D) or hydrated (H) state, have an effect on scaffold void area, microstructural anisotropy (fiber alignment) and mechanical anisotropy (global mechanical compliance). We further integrated our experimental measurements in a constitutive model to explore final effects on the micromechanical environment inside the scaffold volume. Our results indicated that PH scaffolds might exhibit recurrent and large force fluctuations between layers (up to 195 pN), while fluctuations in RH scaffolds might be larger (up to 256 pN) but not as recurrent. In contrast, both PD and RD groups were estimated to produce scarcer and smaller fluctuations (not larger than 50 pN). We concluded that the hydration parameter strongly affects the micromechanics of SIS and that an adequate choice of fabrication parameters, assisted by the herein developed method, might leverage the use of SIS for functional tissue engineering applications, where forces at the cellular level are of concern in the guidance of new tissue formation.     

Integrating the Multiple Biological Causes of Human Behavior

I introduce a range of examples of different causal hypotheses about human mate selection. The hypotheses I focus on come from evolutionary psychology, fluctuating asymmetry research and chemical signaling research. I argue that a major obstacle facing an integrated biology of human behavior is the lack of a causal framework that shows how multiple proximate causal mechanisms can act together to produce components of our behavior.     

A comprehensive experimental study on material properties of human brain tissue

A comprehensive study on the biomechanical response of human brain tissue is necessary to investigate traumatic brain injury mechanisms. Published brain material property studies have been mostly performed under a specific type of loading, which is insufficient to develop accurate brain tissue constitutive equations. In addition, inconsistent or contradictory data in the literature made it impossible for computational model developers to create a single brain material model that can fit most, if not all, experimental results.     

Influence of material properties and photocatalysis on phototrophic growth in multi-year roof weathering

Phototrophic growth on roofs leads to weathering and impacts their appearance. Roof tiles with various properties are available (natural clay, engobed, varnished or coated with photocatalytic TiO₂). The aim of this study was to examine the influence of materials on the development of phototrophic biofilms. Roof tiles were weathered in six climatic regions in Germany for several years. Phototrophic biomass was periodically determined by PAM-fluorometry, image analysis, and visual evaluation. Roof tiles of natural clay were the most heavily infested, while black varnished roof tiles were hardly covered with any phototrophs. This colonisation pattern was compared to water availability on roof tiles surfaces. In contrast to rough natural clay, varnished black tiles accumulated less water, dried quickly, and were rather resistant to phototrophs. The photocatalytic coating was not effective against phototrophic growth. Materials with appropriate properties may prevent phototrophic growth without biocides through reduced water absorption capacities and by avoiding radiation protected structures.     

香椿木材解剖构造及其物理力学性质

为扩大和培育香椿资源和填补国内经济建设及人民生活对优质木材的需求,为其开发和利用提供一定的基础数据及科学的理论指导,依照GB1927-91实验方法对其木材的解剖和物理力学性质做了系统研究。结果表明：香椿纤维13年生后形态均匀,长宽比46.18,双壁厚11.00μm,纤维壁腔比0.56,腔径比0.76;导管分子平均长度383.52μm,宽度143.98μm;基本密度和气干密度分别为0.415g/cm3和0.475g/cm3,属“轻”型;差异干缩为1.93;木材的抗弯强度、抗弯弹性模量和顺纹抗压强度分别为67.85MPa、6179.82MPa和38.23MPa,综合强度106.08MPa,均属“低”级,香椿的综合品质系数为2556.1×105 Pa,为高等级材。综合分析表明香椿材质优良。