Quantitative comparison of ligament formulation and pre-strain in finite element analysis of the human lumbar spine

Data has been published that quantifies the nonlinear, anisotropic material behaviour and pre-strain behaviour of the anterior longitudinal, supraspinous (SSL), and interspinous ligaments of the human lumbar spine. Additionally, data has been published on localized material properties of the SSL. These results have been incrementally incorporated into a previously validated finite element model of the human lumbar spine. Results suggest that the effects of increased ligament model fidelity on bone strain energy were moderate and the effects on disc pressure were slight, and do not justify a change in modelling strategy for most clinical applications. There were significant effects on the ligament stresses of the ligaments that were directly modified, suggesting that these phenomena should be included in FE models where ligament stresses are the desired metric.     

Effect of residual stress and heterogeneity on circumferential stress in the arterial wall

Quantifying the stress distribution through the arterial wall is essential to studies of arterial growth and disease. Previous studies have shown that both residual stress, as measured by opening angle, and differing material properties for the media-intima and the adventitial layers affect the transmural circumferential stress (sigma theta) distribution. Because a lack of comprehensive data on a single species and artery has led to combinations from multiple sources, this study determined the sensitivity of sigma theta to published variations in both opening angle and layer thickness data. We fit material properties to previously published experimental data for pressure-diameter relations and opening angles of rabbit carotid artery, and predicted sigma theta through the arterial wall at physiologic conditions. Using a one-layer model, the ratio of sigma theta at the internal wall to the mean sigma theta decreased from 2.34 to 0.98 as the opening angle increased from 60 to 130 deg. In a two-layer model using a 95 deg opening angle, mean sigma theta in the adventitia increased (112 percent for 25 percent adventitia) and mean sigma theta in the media decreased (47 percent for 25 percent adventitia). These results suggest that both residual stress and wall layers have important effects on transmural stress distribution. Thus, experimental measurements of loading curves, opening angles, and wall composition from the same species and artery are needed to accurately predict the transmural stress distribution in the arterial wall.     

Heel-shoe interactions and the durability of EVA foam running-shoe midsoles

A finite element analysis (FEA) was made of the stress distribution in the heelpad and a running shoe midsole, using heelpad properties deduced from published force-deflection data, and measured foam properties. The heelpad has a lower initial shear modulus than the foam (100 vs. 1050 kPa), but a higher bulk modulus. The heelpad is more non-linear, with a higher Ogden strain energy function exponent than the foam (30 vs. 4). Measurements of plantar pressure distribution in running shoes confirmed the FEA. The peak plantar pressure increased on average by 100% after 500 km run. Scanning electron microscopy shows that structural damage (wrinkling of faces and some holes) occurred in the foam after 750 km run. Fatigue of the foam reduces heelstrike cushioning, and is a possible cause of running injuries.     

Mechanical properties of soft biological tissues

Odd published data concerning the shear mechanical properties of some soft tissues in norm and pathology are reviewed.     

Modeling mechanical stresses as a factor in the etiology of benign vocal fold lesions

Vocal fold tissue lesions such as nodules and polyps are thought to develop in response to mechanical stress that occurs during vocal fold collision. Two computational models of vocal fold collision during voice production are used to investigate this hypothesis. A one-dimensional lumped mass model, whose parameters are derived from vocal fold tissue dimensions and material properties, predicts stress perpendicular to the direction of impact (normal stress). A previously published three-dimensional finite element model that incorporates the same dimensions and properties predicts the entire stress tensor. The hypothesis is supported by predictions from the finite element model that three components of normal stress and one component of shear stress are increased during collision in the typical location of lesions (i.e. the center of the superior medial edge of the vocal fold in the middle of the vibrating and contact region). The lumped mass model predicts that mechanical stress is negatively correlated with mucosal thickness (increased by voice warm-up and hydration), is positively correlated with driving force (proportional to voice intensity), and is affected by voice production method. These relationships are consistent with clinical observations of vocal fold lesion risk factors and have implications for improving prevention and treatment of benign vocal fold lesions.     

果园生草对中国果园土壤肥力和生产力影响的整合分析

果园生草是维持土壤基础肥力、改善土壤生态环境、推动果树产业可持续发展的有效措施之一。但是,有关生草对果园土壤养分含量的定量改变,及其对果园果实产量和品质的提升机制并不清楚。本研究采用Meta分析,共搜集了1990—2020年间发表的62篇文献,定量分析土层深度、生草种植年限和生草植物种类对果园土壤理化性质和果实产量及品质的影响,探究果园生草对中国果园可持续生产的影响。结果表明: 1990—2020年间,与不生草果园相比,果园生草土壤有机质、碱解氮、速效磷含量可分别提高18%、11%、27%,土壤容重降低20%;当气温低于10 ℃时,果园生草可使土壤温度增加23%;当气温高于10 ℃时,果园生草可使土壤温度平均降低8%左右。与一年生草相比,果园连续多年生草,无论是自然生草,还是人工生草,都显著提升了果园土壤质量、产量和果实品质(如可溶性固形物)。因此,果园长期生草对中国果园可持续生产具有深远意义。     

Influence of chondroitin sulfate on collagen gel structure and mechanical properties at physiologically relevant levels

The ability to alter collagen organization could lead to more physiologically relevant scaffolds for tissue engineering. This study examined collagen organization in the presence of polysaccharide and the resulting effects on viscoelastic properties. Fibrillogenesis in the presence of chondroitin sulfate (CS) resulted in changes in the collagen network organization with an increase in void space present. The increased void space caused by CS addition correlated with a decreased stiffness of the collagen gel. These changes occurred with physiologically relevant ratios of collagen to CS, at physiological pH and ionic strength, and without a decrease in the amount of collagen incorporated into fibrils. The addition of dextran, an uncharged polysaccharide, yielded no change in network void space or mechanical properties. Changes in fibril diameter caused by CS or dextran were not correlated with mechanical properties. The results of this study demonstrate that collagen organization can be modified by the addition of GAG, leading to altered matrix mechanical properties. (c) 2008 Wiley Periodicals, Inc. Biopolymers 89: 841-851, 2008.This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com.     

Multiscale, structure-based modeling for the elastic mechanical behavior of arterial walls

Passive elastic behavior of arterial wall remains difficult to model. Although phenomenological and structural models exist, the question of how the three-dimensional network structure of the collagen in the artery determines its mechanical properties is still open. A model is presented that incorporates a collagen network as well as the noncollagenous material that comprise the artery. The collagen architecture is represented as a network of interconnected fibers, and a neo-Hookean constitutive equation is used to describe the contribution of the noncollagenous matrix. The model is multiscale in that volume-averaging theory is applied to the collagen network, and it is structural in that parameters of the microstructure of the collagen network were considered instead of a macroscopic constitutive law. The computational results provided a good fit to published experimental data for decellularized porcine carotid arteries. The model predicted increased circumferential compliance for increased axial stretch, consistent with previously published reports, and a relatively small sensitivity to open angle. Even at large extensions, the model predicted that the noncollagenous matrix would be in compression, preventing collapse of the collagen network. The incorporation of fiber-fiber interactions led to an accurate model of artery wall behavior with relatively few parameters. The counterintuitive result that the noncollagenous component is in compression during extension and inflation of the tissue suggests that the collagen is important even at small strains, with the noncollagenous components supporting the network, but not resisting the load directly. More accurate representation of the microstructure of the artery wall is needed to explore this issue further.     

Fracture mechanics of the cell wall of Chara corallina

Previous mechanical studies using algae have concentrated on cell extension and growth using creep-type experiments, but there appears to be no published study of their failure properties. The mechanical strength of single large internode cell walls (up to 2 mm diameter and 100 mm in length) of the charophyte (giant alga) Chara corallina was determined by dissecting cells to give sheets of cell wall, which were then notched and fractured under tension. Tensile tests, using a range of notch sizes, were conducted on cell walls of varying age and maturity to establish their notch sensitivity and to investigate the propagation of cracks in plant cell walls. The thickness and stiffness of the walls increased with age whereas their strength was little affected. The strength of unnotched walls was estimated as 47 ± 13 MPa, comparable to that of some grasses but an order of magnitude higher than that published for model bacterial cellulose composite walls. The strength was notch-sensitive and the critical stress intensity factor K _1c was estimated to be 0.63 ± 0.19 MNm^−3/2, comparable to published values for grasses. Received: 4 April 2000 / Accepted: 21 July 2000     

Water kefir: Factors affecting grain growth and health-promoting properties of the fermented beverage

Nowadays, the interest in the consumption of healthy foods has increased as well as the homemade preparation of artisanal fermented product. Water kefir is an ancient drink of uncertain origin, which has been passed down from generation to generation and is currently consumed practically all over the world. Considering the recent and extensive updates published on sugary kefir, this work aims to shed light on the scientific works that have been published so far in relation to this complex ecosystem. We focused our review evaluating the factors that affect the beverage microbial and chemical composition that are responsible for the health attribute of water kefir as well as the grain growth. The microbial ecosystem that constitutes the grains and the fermented consumed beverage can vary according to the fermentation conditions (time and temperature) and especially with the use of different substrates (source of sugars, additives as fruits and molasses). In this sense, the populations of microorganisms in the beverage as well as the metabolites that they produce varies and in consequence their health properties. Otherwise, the knowledge of the variables affecting grain growth are also discussed for its relevance in maintenance of the starter biomass as well as the use of dextran for technological application.     

放牧对草原土壤的影响

介绍了放牧对草原土壤物理性质 (容重、渗透率 )、化学性质 (有机质、N素 )和微生物的影响。由于草原土壤系统本身的复杂性、滞后性和弹性 ,放牧对土壤性质的影响不尽相同。一般而言 ,随放牧强度的增大 ,动物践踏作用的增强 ,土壤孔隙分布的空间格局发生变化 ,土壤的总孔隙减少 ,特别是大孔隙 (>5 0μm)和较大中等孔隙 (9～ 5 0μm)减少 ,使土壤容重增加 ,土壤的渗透阻力加大 ,土壤的保水和持水能力下降。但在有机质含量很低的沙质土壤中 ,超载过牧 ,造成有机质含量降低 ,土壤的团粒结构减少 ,稳定性团聚体减少 ,土壤结构遭到破坏 ,使得土壤容重反而降低。土壤有机质和放牧之间存在复杂的相互关系 ,土壤有机质对放牧的响应受多种因素的影响 ,这些因素包括植被和土壤的初始状况 ;环境因素 ,特别是水分和温度 ;放牧历史 (强度、频率、持续时间和动物类型 )。同时 ,土壤有机质含量低的土壤比含量高的土壤更易受放牧的影响 ,而使有机质发生变化。土壤微生物量碳是最具活性的土壤碳库 ,对环境的变化敏感 ,能较早地指示生态系统功能的变化。当考虑时间尺度时 ,高强度放牧对土壤肥力有负面的影响 ,短期内 ,由于加速了养分的循环效率 ,产生有利的影响 ,但长期无管理的超载放牧必然造成系统物质 (资源 )输入和输     

Prospects for the replenishment of a feed protein deficit in aquaculture

The study of the properties of the PepT1 proton-dependent oligopeptide transport system in the fish intestine is a promising direction to solve the problem of the replacement of dietary proteins in aquaculture. At the same time, some publications provide direct evidence for the close relationship of the processes of oligopeptide absorption in the fish gut with the parameters of plastic metabolism in various organs and tissues, especially in the early stages of ontogeny. The published data suggest that the food value of synthetic oligopeptides for fish may be increased by including amino acids that are growth limiting for a given tissue in the early stages of ontogeny of a fish species. Finding the parameters of the affinity of individual substrates (oligopeptides) to the PepT1 transport system in fish will contribute to solving this problem in aquaculture.     

The Current Understanding of the Properties of Liquid Water: A Possible Alternative Solution

Biophysics - Based on information extracted from the published literature, we analyze the current state of knowledge on the properties of liquid water. There is a discrepancy between the efforts...     

Glycine N-methyltransferases: a comparison of the crystal structures and kinetic properties of recombinant human, mouse and rat enzymes

Glycine N-methyltransferases (GNMTs) from three mammalian sources were compared with respect to their crystal structures and kinetic parameters. The crystal structure for the rat enzyme was published previously. Human and mouse GNMT were expressed in Escherichia coli in order to determine their crystal structures. Mouse GNMT was crystallized in two crystal forms, a monoclinic form and a tetragonal form. Comparison of the three structures reveals subtle differences, which may relate to the different kinetic properties of the enzymes. The flexible character of several loops surrounding the active site, along with an analysis of the active site boundaries, indicates that the observed conformations of human and mouse GNMTs are more open than that of the rat enzyme. There is an increase in kcat when going from rat to mouse to human, suggesting a correlation with the increased flexibility of some structural elements of the respective enzymes.     

Growth and remodeling in a thick-walled artery model: effects of spatial variations in wall constituents

A mathematical model is presented for growth and remodeling of arteries. The model is a thick-walled tube composed of a constrained mixture of smooth muscle cells, elastin and collagen. Material properties and radial and axial distributions of each constituent are prescribed according to previously published data. The analysis includes stress-dependent growth and contractility of the muscle and turnover of collagen fibers. Simulations were conducted for homeostatic conditions and for the temporal response following sudden hypertension. Numerical pressure-radius relations and opening angles (residual stress) show reasonable agreement with published experimental results. In particular, for realistic material and structural properties, the model predicts measured variations in opening angles along the length of the aorta with reasonable accuracy. These results provide a better understanding of the determinants of residual stress in arteries and could lend insight into the importance of constituent distributions in both natural and tissue-engineered blood vessels.     

Polypeptides of African swine fever virus

The published data on the characteristics and properties of structural and nonstructural polypeptides of the African porcine virus are reviewed. Localization of the viral proteins in virions and infected cells, kinetics of biosynthesis, glycosylation, phosphorylation and the antigenicity of the proteins are discussed.     

Effect of biofumigation and chemical fumigation on soil microbial community structure and control of pepper Phytophthora blight

Soil biofumigation with brassica plant residues has been shown to significantly suppress soilborne pathogen. However, little published data reported the impact of biofumigation on microbial community structure in pepper (Capsicum annuum L.) production systems under field conditions. Biofumigation with rapeseed (Brassica napus ‘Dwarf Essex’) meal and chemical fumigation with dazomet were tested to control the pepper disease caused by Phytophthora capsici. BF treatment showed the lowest disease incidence among these treatments. Effects on soil bacterial and fungal communities were assessed by denaturating gradient gel electrophoresis and the results showed that the biofumigation increased bacterial diversity and decreased fungal diversity. There was a negative correlation between soil bacterial diversity and disease incidence and a positive correlation between soil fungal diversity and disease incidence. Cloning of the microbial community showed that the microbial community structures were altered by biofumigation. Soil was also evaluated for their chemical properties. Biofumigation increased soil content of total N, NO₃ ^?–N, available P and available K. A significant correlation between soil microbial community structures and soil chemical properties was found. Overall, these results indicated that biofumigation reduced disease incidence of pepper through altering soil microbial community structures.     

Analysis of Rat Hindlimb Muscle Proteins by Two-Dimensional Gels Following Spinal Cord Injury

Proteins from extensor digitorum longus (EDL), plantaris (PLN), and soleus (SOL) muscles of adult, female rats were examined by high resolution two-dimensional gel electrophoresis up to 4 weeks following spinal cord transection. The electrophoretograms were analyzed by computer imaging and densitometry. Reproducible and significant changes in the relative concentrations of several proteins in each muscle type were detected. Whereas changes involving the largest number of proteins were observed in SOL, changes in EDL and PLN were also detected. In SOL, approximately 50% of the altered proteins increased in concentration and the remaining decreased: Actin and myosin light chains LCF-1 and LCF-2 were among those proteins whose concentrations increased, whereas myosin light chains LCS-1 and LCS-2 were among those proteins whose concentrations decreased. The present findings regarding the reversal in myosin light chain composition provide biochemical support for previously published data on changes in contractile properties of muscles following spinalization. In EDL, the relative concentration of only one protein was elevated in a time-dependent manner. The concentrations of two protein species in PLN were increased following cord transection. These findings provide new biochemical markers on the effects of spinal cord on gene expression in specific hindlimb skeletal muscles.     

A method to investigate the diffusion properties of nuclear calcium

Modeling biophysical processes in general requires knowledge about underlying biological parameters. The quality of simulation results is strongly influenced by the accuracy of these parameters, hence the identification of parameter values that the model includes is a major part of simulating biophysical processes. In many cases, secondary data can be gathered by experimental setups, which are exploitable by mathematical inverse modeling techniques. Here we describe a method for parameter identification of diffusion properties of calcium in the nuclei of rat hippocampal neurons. The method is based on a Gauss-Newton method for solving a least-squares minimization problem and was formulated in such a way that it is ideally implementable in the simulation platform uG. Making use of independently published space- and time-dependent calcium imaging data, generated from laser-assisted calcium uncaging experiments, here we could identify the diffusion properties of nuclear calcium and were able to validate a previously published model that describes nuclear calcium dynamics as a diffusion process.