Elastic Buckling of Bionic Cylindrical Shells Based on Bamboo

High load-bearing efficiency is one of the advantages of biological structures after the evolution of billions of years.Biomimicking from nature may offer the potential for lightweight design. In the viewpoint of mechanics properties, the culm of bamboo comprises of two types of cells and the number of the vascular bundles takes a gradient of distribution. A three-point bending test was carried out to measure the elastic modulus. Results show that the elastic modulus of bamboo decreases gradually from the periphery towards the centre. Based on the structural characteristics of bamboo, a bionic cylindrical structure was designed to mimic the gradient distribution of vascular bundles and parenchyma cells. The buckling resistance of the bionic structure was compared with that of a traditional shell of equal mass under axial pressure by finite element simulations. Results show that the load-bearing capacity of bionic shell is increased by 124.8%. The buckling mode of bionic structure is global buckling while that of the conventional shell is local buckling.     

Prediction of femoral head collapse in osteonecrosis

The femoral head deteriorates in osteonecrosis. As a consequence of that, the cortical shell of the femoral head can buckle into the cancellous bone supporting it. In order to examine the buckling scenario we performed numerical analysis of a realistic femoral head model. The analysis included a solution of the hip contact problem, which provided the contact pressure distribution, and subsequent buckling simulation based on the given contact pressure. The contact problem was solved iteratively by approximating the cartilage by a discrete set of unilateral linear springs. The buckling calculations were based on a finite element mesh with brick elements for the cancellous bone and shell elements for the cortical shell. Results of 144 simulations for a variety of geometrical, material, and loading parameters strengthen the buckling scenario. They, particularly, show that the normal cancellous bone serves as a strong supporting foundation for the cortical shell and prevents it from buckling. However, under the development of osteonecrosis the deteriorating cancellous bone is unable to prevent the cortical shell from buckling and the critical pressure decreases with the decreasing Young modulus of the cancellous bone. The local buckling of the cortical shell seems to be the driving force of the progressive fracturing of the femoral head leading to its entire collapse. The buckling analysis provides an additional criterion of the femoral head collapse, the critical contact pressure. The buckling scenario also suggests a new argument in speculating on the femoral head reinforcement. If the entire collapse of the femoral head starts with the buckling of the cortical shell then it is reasonable to place the reinforcement as close to the cortical shell as possible.     

磁共振成像技术在毛竹幼竹显微结构和水分含量表征中的应用

竹子节部对竹秆的中空结构以及竹秆快速高生长起着关键作用,研究竹子解剖结构有助于认识竹子生长机制。本研究利用核磁共振成像(MRI)无创、高分辨率和准确的技术优势,对毛竹幼竹去笋箨梢部进行横切面高精度核磁共振成像扫描,使用MATLAB软件对 MRI进行灰度值采集,分析节部、近节部和节间水分分布差异。结果表明: 无数维管束在毛竹幼竹节隔以及近节隔内腔反复扭曲和水平转动,组成了一个错综复杂和高度连接的网络结构,通过分轴向载荷来保护重要组织免受机械应力,同时实现水分和营养物质的横向运输,这是毛竹在短时间内快速完成高生长的重要基础。MRI信号值(亮度值)表明,幼竹维管束的水分含量远远高于周围的基本组织。节间平均水分含量和像素点间含水量标准差显著高于节部,近节部居中。MRI技术可以在未来竹子解剖学和生理生化学研究中发挥作用。     

开花红哺鸡竹叶片的显微结构与光响应参数研究

为阐释竹子开花过程中的生理功能变化,探寻竹子花后复壮更新的途径,本研究选取红哺鸡竹(Phyllostachys iridescens)竹林换叶后出现开花征兆的竹株异形叶和外观正常叶,并以未开花竹株正常叶为对照,进行了叶片结构观察和光响应测定。结果发现:红哺鸡竹从营养生长向生殖生长转变的过程中,叶片的发育有变小变薄的特征,相邻维管束距离增大,维管束横切面积和气孔密度有显著变小的趋势(p0.05)。开花竹异形叶的叶片厚度、上表皮厚度、维管束横切面积和气孔密度是未开花竹正常叶的71.59%、87.40%、77.79%和73.56%,相邻维管束距离增加了19.34%,这种结构的变化相应地导致了开花竹叶片光合和蒸腾作用的显著降低(p0.05)。开花竹异形叶的光响应参数,如光饱和点、表观量子效率和最大光合速率是未开花竹正常叶的67%、40.5%和8.27%,分别为900、0.015、1.22μmol·m-2·s-1;光补偿点比未开花竹正常叶高出208.5%,达85.11μmol·m-2·s-1,而开花竹外观正常叶的光响应参数介于两者之间。开花竹株的叶片结构弱化和随之产生的生理功能异化可能是多年生竹子无法像树木那样连年开花、持续生长的重要原因之一。     

Length-dependence of flexural rigidity as a result of anisotropic elastic properties of microtubules

Unexplained length-dependence of flexural rigidity and Young's modulus of microtubules is studied using an orthotropic elastic shell model. It is showed that vibration frequencies and buckling load predicted by the accurate orthotropic shell model are much lower than that given by the approximate isotropic beam model for shorter microtubules, although the two models give almost identical results for sufficiently long microtubules. It is this inaccuracy of the isotropic beam model used by all previous researchers that leads to reported lower flexural rigidity and Young's modulus for shorter microtubules. In particular, much lower shear modulus and circumferential Young's modulus, which only weaken flexural rigidity of shorter microtubules, are responsible for the observed length-dependence of the flexural rigidity. These results confirm that longitudinal Young's modulus of microtubules is length-independent, and the observed length-dependence of the flexural rigidity and Young's modulus is a result of strongly anisotropic elastic properties of microtubules which have a length-dependent weakening effect on flexural rigidity of shorter microtubules.     

巨龙竹笋-幼竹期秆形发育的组织解剖学研究

巨龙竹（Dendrocalamus sinicus Chia et J.L.Sun）是云南特有的珍稀木本丛生竹,其秆形分为通直型和弯曲型两种变型。为了揭示巨龙竹不同秆形的组织结构特征,本文通过定点观测0~49 d的巨龙竹笋和幼竹生长发育状况,并采用石蜡切片技术对笋期0~45 d内样品的组织结构进行比较解剖学研究。结果显示：（1）巨龙竹在笋-幼竹（0~49 d）发育期,秆高生长呈"慢-快"的趋势,21~35 d时弯曲型茎秆开始显现,易于辨别;（2）5~30 d时,弯曲型茎秆中维管束的发育早于通直型;对比弯曲型茎秆内外两侧维管束,内侧维管束导管内径较小,但纤维鞘中的纤维细胞层数更多;（3）弯曲型茎秆中薄壁细胞的分化早于通直型,20 d后弯曲型茎秆中的薄壁细胞出现明显的可被番红-固绿染色的细胞核,并呈有规律的排列;弯曲型茎秆内侧薄壁细胞稍小于外侧薄壁细胞,但内侧被染色细胞核的薄壁细胞多于外侧。研究结果表明巨龙竹弯曲型茎秆性状在笋期第21~35 d内即可通过茎秆形态判别,弯曲型茎秆中维管束的发育以及薄壁细胞分化均早于通直型茎秆,同一时期弯曲型茎秆内侧细胞分裂较外侧旺盛、维管束木质化程度更高。     

巨龙竹笋-幼竹期秆形发育的组织解剖学研究

巨龙竹( Dendrocalamus sinicus Chia et J. L. Sun)是云南特有的珍稀木本丛生竹,其秆形分为通直型和弯曲型两种变型。为了揭示巨龙竹不同秆形的组织结构特征,本文通过定点观测0 ~ 49 d的巨龙竹笋和幼竹生长发育状况,并采用石蜡切片技术对笋期0 ~ 45 d内样品的组织结构进行比较解剖学研究。结果显示:(1)巨龙竹在笋-幼竹(0 ~ 49 d)发育期,秆高生长呈“慢-快”的趋势,21 ~ 35 d时弯曲型茎秆开始显现,易于辨别;(2)5 ~ 30 d时,弯曲型茎秆中维管束的发育早于通直型;对比弯曲型茎秆内外两侧维管束,内侧维管束导管内径较小,但纤维鞘中的纤维细胞层数更多;(3)弯曲型茎秆中薄壁细胞的分化早于通直型,20 d后弯曲型茎秆中的薄壁细胞出现明显的可被番红-固绿染色的细胞核,并呈有规律的排列;弯曲型茎秆内侧薄壁细胞稍小于外侧薄壁细胞,但内侧被染色细胞核的薄壁细胞多于外侧。研究结果表明巨龙竹弯曲型茎秆性状在笋期第21 ~ 35 d内即可通过茎秆形态判别,弯曲型茎秆中维管束的发育以及薄壁细胞分化均早于通直型茎秆,同一时期弯曲型茎秆内侧细胞分裂较外侧旺盛、维管束木质化程度更高。     

Elastic properties of the growth-controlling outer cell walls of maize coleoptile epidermis

The effects of tensile stress and temperature on cell wall elasticity have been investigated in the outer cell walls of coleoptile epidermis of 4- and 6-day-old Zea mays L. seedlings. The change in tensile stress from 6 to 40 MPa caused the increase in cell wall elastic modulus from 0.4 to 3 GPa. Lowering the temperature from 30 to 4 °C resulted in instantaneous and reversible cell wall elongation of 0.3–0.5 ‰. At a given temperature and stress level, the wall elastic modulus of 6-day-old seedlings tended to be 30 % higher than that of 4-day-old plants. The relationship between cell wall elasticity and mechanical stress indicated that the stress distribution within the cell wall is highly uneven. The analysis of the effect of temperature on cell wall elastic strain showed that structural differences between crystalline and amorphous load-bearing polymers were not the only cause of the uneven stress distribution. Based on the results obtained by Hejnowicz and Borowska-Wykr?t (Planta 220:465–473, 2005), we suggested that the uneven stress distribution is partially related to the stress gradient between inner and outer layers of the cell wall.     

Particle Erosion Resistance of Bionic Samples Inspired from Skin Structure of Desert Lizard, Laudakin stoliczkana

In order to improve the particle erosion resistance of engineering surfaces,this paper proposed a bionic sample which is inspired from the skin structure of desert lizard,Laudakin stoliczkana.The bionic sample consists of a hard shell (aluminum) and a soft core (silicone rubber) which form a two-layer composite structure.The sand blast tests indicated that the bionic sample has better particle erosion resistance.In steady erosion period,the weight loss per unit time of the bionic sample is about 10％ smaller than the contrast sample.The anti-erosion mechanism of the bionic sample was studied by single particle impact test.The results show that,after the impact,the kinetic energy of the particle is reduced by 56.5％ on the bionic sample which is higher than that on the contrast sample (31.2％).That means the bionic sample can partly convert the kinetic energy of the particle into the deformation energy of the silicone rubber layer,thus the erosion is reduced.     

Micro- and macrorheological properties of actin networks effectively cross-linked by depletion forces

The structure and rheology of cytoskeletal networks are regulated by actin binding proteins. Aside from these specific interactions, depletion forces can also alter the properties of cytoskeletal networks. Here we demonstrate that the addition of poly(ethylene glycol) (PEG) as a depletion agent results not only in severe structural changes, but also in alterations in mechanical properties of actin solutions. In the plateau of the elastic modulus two regimes can be distinguished by micro and macrorheological methods. In the first, the elastic modulus increases only slightly with increasing depletion agent, whereas above a critical concentration c*, a strong increase of cPEG6k3.5 is observed in a distinct second regime. Microrheological data and electron microscopy images show a homogenous network of actin filaments in the first regime, whereas at higher PEG concentrations a network of actin bundles is observed. The concentration dependence of the plateau modulus G0, the shift in entanglement time taue, and the nonlinear response indicate that below c* the network becomes effectively cross-linked, whereas above c* G0(cPEG6k) is primarily determined by the network of bundles that exhibits a linearly increasing bundle thickness.     

核桃果皮的发育解剖学研究

核桃果皮的发育过程可分为３个阶段,发育时期：中、内三层果皮的界线不清,维管束处于发育初期;发育中期：随着中果皮最外侧两层石细胞的出现和薄壁组织细胞体积的迅速扩大以及维管束轮数的增加,使三层果皮具较明显的界面,发育后期：中果皮的维管束递增到４－５轮,     

Buckling Behavior of Individual and Bundled Microtubules

As the major structural constituent of the cytoskeleton, microtubules (MTs) serve a variety of biological functions that range from facilitating organelle transport to maintaining the mechanical integrity of the cell. Neuronal MTs exhibit a distinct configuration, hexagonally packed bundles of MT filaments, interconnected by MT-associated protein (MAP) tau. Building on our previous work on mechanical response of axonal MT bundles under uniaxial tension, this study is focused on exploring the compression scenarios. Intracellular MTs carry a large fraction of the compressive loads sensed by the cell and therefore, like any other column-like structure, are prone to substantial bending and buckling. Various biological activities, e.g., actomyosin contractility and many pathological conditions are driven or followed by bending, looping, and buckling of MT filaments. The coarse-grained model previously developed in our lab has been used to study the mechanical behavior of individual and bundled in vivo MT filaments under uniaxial compression. Both configurations show tip-localized, decaying, and short-wavelength buckling. This behavior highlights the role of the surrounding cytoplasm and MAP tau on MT buckling behavior, which allows MT filaments to bear much larger compressive forces. It is observed that MAP tau interconnections improve this effect by a factor of two. The enhanced ability of MT bundles to damp buckling waves relative to individual MT filaments, may be interpreted as a self-defense mechanism because it helps axonal MTs to endure harsher environments while maintaining their function. The results indicate that MT filaments in a bundle do not buckle simultaneously implying that the applied stress is not equally shared among the MT filaments, that is a consequence of the nonuniform distribution of MAP tau proteins along the bundle length. Furthermore, from a pathological perspective, it is observed that axonal MT bundles are more vulnerable to failure in compression than tension.     

Holocellulase Activity from <Emphasis Type="Italic">Schizophyllum commune</Emphasis> Grown on Bamboo: A Comparison with Different Substrates

The natural biodiversity that is found in tropical areas offers countless biotechnological opportunities; especially if we take in account that many biomolecules from several microorganisms have supported for many years, different industrial applications in areas such as pharmacology, agro-industry, bioprocess, environmental technology, and bioconversion. In order to find new lignocellulolytic enzymes and evaluate bamboo fibers as substrate, Schizophyllum commune a fungus with broad distribution was isolated and grown during 15 days in liquid culture medium containing 1% lignocellulosic fibers from bamboo, banana stem, and sugarcane bagasse. The enzymatic activity of xylanase, mannanase, polygalacturonase, CMCase, FPase, and avicelase were evaluated. Sugarcane bagasse and banana stem showed to induce higher hollocellulase activity when compared with bamboo as the main carbon source. The physical mechanism that the fungus uses to degrade bamboo was observed not only in fibers naturally infected but also in healthy fibers that were treated and untreated with enzyme solution. SEM analysis showed the structural disruption and invasion of the vascular bundles, parenchyma cells, and parenchymatous tissues as a consequence of the presence of this fungus and the catalytic action of its enzymes into the plant tissue.     

Type-I IFN signaling is required for the induction of antigen-specific CD8(+) T cell responses by adenovirus vector vaccine in the gut-mucosa

Microtubules in living cells are very important component for various cellular functions as well as to maintain the cell shape. Mechanical properties of microtubules play a vital role in their functions and structure. To understand the mechanical properties of microtubules in living cells, we developed an orthotropic-Pasternak model and investigated the vibrational behavior when microtubules are embedded in surrounding elastic medium. We considered microtubules as orthotropic elastic shell and its surrounding elastic matrix as Pasternak foundation. We found that due to mechanical coupling of microtubules with elastic medium, the flexural vibration is increased with the stiffening of elastic medium. We noticed that foundation modulus (H) and shear modulus (G) have more effect on radial vibrational mode as compared to longitudinal vibrational mode and torsional vibrational mode.     

A quantitative model of cellular elasticity based on tensegrity

A tensegrity structure composed of six struts interconnected with 24 elastic cables is used as a quantitative model of the steady-state elastic response of cells, with the struts and cables representing microtubules and actin filaments, respectively. The model is stretched uniaxially and the Young's modulus (E0) is obtained from the initial slope of the stress versus strain curve of an equivalent continuum. It is found that E0 is directly proportional to the pre-existing tension in the cables (or compression in the struts) and inversely proportional to the cable (or strut) length square. This relationship is used to predict the upper and lower bounds of E0 of cells, assuming that the cable tension equals the yield force of actin (approximately 400 pN) for the upper bound, and that the strut compression equals the critical buckling force of microtubules for the lower bound. The cable (or strut) length is determined from the assumption that model dimensions match the diameter of probes used in standard mechanical tests on cells. Predicted values are compared to reported data for the Young's modulus of various cells. If the probe diameter is greater than or equal to 3 microns, these data are closer to the lower bound than to the upper bound. This, in turn, suggests that microtubules of the CSK carry initial compression that exceeds their critical buckling force (order of 10(0)-10(1) pN), but is much smaller than the yield force of actin. If the probe diameter is less than or equal to 2 microns, experimental data fall outside the region defined by the upper and lower bounds.     

单芽狗脊营养器官的解剖学研究

采用离析法和石蜡切片法对单芽狗脊营养器官进行形态解剖研究。结果表明：单芽狗脊叶为异面叶,上、下表皮细胞均为不规则型,仅下表皮有气孔器分布;叶柄维管束有2~6个,自叶柄基部向上至叶轴仅有2个较大的维管束;根状茎薄壁细胞之间有多个维管束散生分布,且富含丰富的淀粉粒;皮层在根的横切结构中占比较大,木质部的发育方式为外始式;单芽狗脊珠芽的发育过程分为三个阶段,珠芽原基的形成期、珠芽原基的分化期、成熟期。     

仿生技术构建小口径人造血管

目的：研究以改性猪小肠粘膜下层组织(SIS)为支架,利用仿生技术构建小口径人造血管的可行性。方法：自犬隐动脉分离出血管内皮细胞和平滑肌细胞,与胶原蛋白凝胶均匀混合,分别种植于改性SIS膜表面,制成3 mm 仿生三层人造血管为实验组;制成单层人造血管为对照组,分别植入修复15例犬双侧股动脉缺损,术后进行彩超、组织学检测和电镜检测鉴定。结果：植入12周,14个仿生人造血管保持通畅,通畅率93.3%,有血管样生物结构形成,管腔内壁有完整的内皮覆盖,管壁中层见大量平滑肌细胞;对照组通畅率60%,有少许内皮细胞覆盖。结论：仿生小口径人造血管具有良好的血液相容性,并能在体内保持良好通畅性, 修复动脉缺损效果满意。     

Elastic moduli, yield stress, and ultimate stress of cancellous bone in the canine proximal femur

Elastic moduli, yield stress and ultimate compressive stress were determined for cancellous bone from the femoral head and neck regions of the canine femur. Unconfined compression tests were performed on 5 mm cubic samples which were cut from two femurs. Elastic moduli were measured in three orthogonal directions, and the yield stress and ultimate stress were measured along the proximal-distal axis. The results from this investigation support previous assumptions that the mechanical behavior of canine cancellous bone is qualitatively similar to human cancellous bone. The canine cancellous bone was observed to be anisotropic in elastic modulus. For two thirds of the cubic specimens tested, the elastic modulus was largest in the load-bearing, proximal-distal direction. A linear relationship between yield stress and elastic modulus was observed for canine bone, as is typical of human bone. A similar linear relationship between ultimate stress and elastic modulus was observed. Thus, for canine bone as well as for human bone, failure appears to be governed by a strain level which is position independent. The yield strain of 0.0259 and ultimate strain of 0.0288 for canine bone were both less than the yield strain of 0.0395 reported for human bone.     

Use of a Digital Image Correlation Technique for Measuring the Material Properties of Beetle Wing

Beetle wings are very specialized flight organs consisting of the veins and membranes.Therefore it is necessary from abionic view to investigate the material properties of a beetle wing experimentally.In the present study,we have used a DigitalImage Correlation (DIC) technique to measure the elastic modulus of a beetle wing membrane.Specimens were prepared bycarefully cutting a beetle hind wing into 3.0 mm by 7.0 mm segments (the gage length was 5 mm).We used a scanning electronmicroscope for a precise measurement of the thickness of the beetle wing membrane.The specimen was attached to a designedfixture to induce a uniform displacement by means of a micromanipulator.We used an ARAMISTM system based on the digitalimage correlation technique to measure the corresponding displacement of a specimen.The thickness of the beetle wing variedat different points of the membrane.The elastic modulus differed in relation to the membrane arrangement showing a structuralanisotropy;the elastic modulus in the chordwise direction is approximately 2.65 GPa,which is three times larger than the elasticmodulus in the spanwise direction of 0.84 GPa.As a result,the digital image correlation-based ARAMIS system was suc-cessfully used to measure the elastic modulus of a beetle wing.In addition to membrane’s elastic modulus,we considered thePoisson’s ratio of the membrane and measured the elastic modulus of a vein using an Instron universal tensile machine.Theresult reveals the Poisson’s ratio is nearly zero and the elastic modulus of a vein is about 11 GPa.     

A microstructurally driven model for pulmonary artery tissue

A new constitutive model for elastic, proximal pulmonary artery tissue is presented here, called the total crimped fiber model. This model is based on the material and microstructural properties of the two main, passive, load-bearing components of the artery wall, elastin, and collagen. Elastin matrix proteins are modeled with an orthotropic neo-Hookean material. High stretch behavior is governed by an orthotropic crimped fiber material modeled as a planar sinusoidal linear elastic beam, which represents collagen fiber deformations. Collagen-dependent artery orthotropy is defined by a structure tensor representing the effective orientation distribution of collagen fiber bundles. Therefore, every parameter of the total crimped fiber model is correlated with either a physiologic structure or geometry or is a mechanically measured material property of the composite tissue. Further, by incorporating elastin orthotropy, this model better represents the mechanics of arterial tissue deformation. These advancements result in a microstructural total crimped fiber model of pulmonary artery tissue mechanics, which demonstrates good quality of fit and flexibility for modeling varied mechanical behaviors encountered in disease states.