Development and validation of a weight-bearing finite element model for total knee replacement

Total knee arthroplasty (TKA) is a successful procedure for osteoarthritis. However, some patients (19%) do have pain after surgery. A finite element model was developed based on boundary conditions of a knee rig. A 3D-model of an anatomical full leg was generated from magnetic resonance image data and a total knee prosthesis was implanted without patella resurfacing. In the finite element model, a restarting procedure was programmed in order to hold the ground reaction force constant with an adapted quadriceps muscle force during a squat from 20° to 105° of flexion. Knee rig experimental data were used to validate the numerical model in the patellofemoral and femorotibial joint. Furthermore, sensitivity analyses of Young’s modulus of the patella cartilage, posterior cruciate ligament (PCL) stiffness, and patella tendon origin were performed. Pearson’s correlations for retropatellar contact area, pressure, patella flexion, and femorotibial ap-movement were near to 1. Lowest root mean square error for retropatellar pressure, patella flexion, and femorotibial ap-movement were found for the baseline model setup with Young’s modulus of 5 MPa for patella cartilage, a downscaled PCL stiffness of 25% compared to the literature given value and an anatomical origin of the patella tendon. The results of the conducted finite element model are comparable with the experimental results. Therefore, the finite element model developed in this study can be used for further clinical investigations and will help to better understand the clinical aspects after TKA with an unresurfaced patella.     

Thermocline deepening and mixing alter zooplankton phenology,biomass and body size in a whole‐lake experiment

相似文献   

A Refined Open State of the Glycine Receptor Obtained via Molecular Dynamics Simulations

1. Download : Download high-res image (389KB)
2. Download : Download full-size image

     

Excitability of oxytocin neurons in paraventricular nucleus is regulated by voltage-gated potassium channels Kv4.2 and Kv4.3

Oxytocin is produced by neurons in the paraventricular nucleus (PVN) and the supraoptic nucleus in the hypothalamus. Various ion channels are considered to regulate the excitability of oxytocin neurons and its secretion. A-type currents of voltage-gated potassium channels (Kv channels), generated by Kv4.2/4.3 channels, are known to be involved in the regulation of neuron excitability. However, it is unclear whether the Kv4.2/4.3 channels participate in the regulation of excitability in PVN oxytocin neurons. Here, we investigated the contribution of the Kv4.2/4.3 channels to PVN oxytocin neuron excitability. By using transgenic rat brain slices with the oxytocin-monomeric red fluorescent protein 1 fusion transgene, we examined the excitability of oxytocin neurons by electrophysiological technique. In some oxytocin neurons, the application of Kv4.2/4.3 channel blocker increased firing frequency and membrane potential with extended action potential half-width. Our present study indicates the contribution of Kv4.2/4.3 channels to PVN oxytocin neuron excitability regulation.

Abbreviation: PVN, paraventricular nucleus; Oxt-mRFP1, Oxt-monometric red fluorescent protein 1; PaTx-1, Phrixotoxin-1; TEA, Tetraethylammonium Chloride; TTX, tetrodotoxin; aCSF, artificial cerebrospinal fluid;PBS, phosphate buffered saline 3v, third ventricle.     

Vanadate‐Based Materials for Li‐Ion Batteries: The Search for Anodes for Practical Applications

While the practical application of electrode materials depends intensively on the Li⁺ ion storage mechanisms correlating ultimately with the coulombic efficiency, reversible capacity, and morphology variation of electrode material upon cycling, only intercalation‐type electrode materials have proven viable for commercialization up to now. This paper reviews the promising anode materials of metal vanadates (M_xV_yO_z, M = Co, Cu, Mn, Fe, Zn, Ni, Li) that have high capacity, low cost, and abundant resource, and also discusses the related Li⁺ ion storage mechanism. It is concluded that most of these (M_xV_yO_z, M = Co, Cu, Mn, Fe, Zn, Ni) exhibit irreversible redox reactions upon lithiation/delithiation accompanied by large volume expansion, which is not favorable for industrial applications. In particular, Li₃VO₄ with specific intercalation Li⁺ ion storage mechanism and compatible merits of safety and energy density exhibits great potential for practical application. This review systematically summarizes the latest progress in Li₃VO₄ research, including the representative fabrication approaches for advanced morphology and state‐of‐the‐art technologies to boost performance and the morphology variation associated with Li⁺ ion storage mechanisms. Furthermore, an outlook on where breakthroughs for Li₃VO₄ may be most likely achieved will be provided.     

Suppressing Lithium Dendrite Growth via Sinusoidal Ripple Current Produced by Triboelectric Nanogenerators

Lithium metal as an ultimate anode material of future rechargeable batteries may furnish the highest energy density for its pairing cathode, although preventing the growth of lithium dendrites in liquid electrolytes is a major challenge. This work reports that stable lithium metal anodes can be achieved by charging with high‐frequency sinusoidal ripple current generated by rotating triboelectric nanogenerators (R‐TENGs). Compared with constant DC current charging, sinusoidal ripple current charging by R‐TENG improves the uniformity of lithium deposition during cycling test. Consequently, symmetric Li/Li cells exhibit lower overpotential and better cycling stability. In addition, full cells assembled with lithium metal anodes and LiFePO₄ cathodes show considerably improved capacity retention when charged by R‐TENG's sinusoidal ripple current (99.5%) compared to constant current (78.7%) after 200 cycles. The charging strategy device in this work provides a promising direction toward improving the cycle life of Li metal batteries. In addition, the combination of R‐TENGs with Li metal batteries offers an encouraging solution for achieving stable energy supply in self‐powered systems.     

落叶松人工林土壤热传导季节变化及其与环境因子的关系

以2003—2005年落叶松人工林土壤热状况的实际监测数据为基础,研究了其土壤热传导特性及其与环境因子的关系.结果表明：落叶松人工林不同年份、不同地点土壤热通量的季节变化十分明显,4—8月为正值,9月至次年3月的绝大部分时间为负值,其年收支基本处于平衡状态.土壤热通量和土壤热导率（k）受净辐射影响显著,并存在时间延迟效应,冬季为4～5 h,夏季为2～3 h.基于实测的土壤热通量和土壤温度差计算得到的k值早春季节显著高于其他季节（P<0.05）,而其他月份不存在显著差异(P>0.05).使用我国大多数气象观测站积累的土壤温差数据和 k值进行土壤热通量季节变化估计时,早春季节（3—5月）可能会产生较大的误差.     

Voltage-dependence of contraction in streptozotocin-induced diabetic myocytes

Cardiac contractile dysfunction is frequently reported in human patients and experimental animals with type-1 diabetes mellitus. The aim of this study was to investigate the voltage-dependence of contraction in ventricular myocytes from the streptozotocin (STZ)-induced diabetic rat. STZ-induced diabetes was characterised by hyperglycaemia and hypoinsulinaemia. Other characteristics included reduced body and heart weight and raised blood osmolarity. Isolated ventricular myocytes were patched in whole cell, voltage-clamp mode after correcting for membrane capacitance and series resistance. From a holding membrane potential of –40 mV, test pulses were applied at potentials between –30 and +50 mV in 10 mV increments. L-type Ca²⁺ current (I _Ca,L) density and contraction were measured simultaneously using a video-edge detection system. Membrane capacitance was not significantly altered between control and STZ-induced diabetic myocytes. The I _Ca,L density was significantly (p < 0.05) reduced throughout voltage ranges (–10 mV to +10 mV) in myocytes from STZ-treated rats compared to age-matched controls. Moreover, the amplitude of contraction was significantly reduced (p < 0.05) in myocytes from STZ-treated rats at all test potentials between –20 mV and +30 mV. However, in electrically field-stimulated (1 Hz) myocytes, the amplitude of contraction was not altered by STZ-treatment. It is suggested that in field-stimulated myocytes taken from STZ-induced diabetic hearts, prolonged action potential duration may promote increased Ca²⁺ influx via the sodium-calcium exchanger (NCX), which may compensate for a reduction in Ca²⁺ trigger through L-type-Ca²⁺-channels and lead to normalised contraction. (Mol Cell Biochem 261: 235–243, 2004)     

Ligand binding induces a conformational change in ifnar1 that is propagated to its membrane-proximal domain

The type I interferon (IFN) receptor plays a key role in innate immunity against viral and bacterial infections. Here, we show by intramolecular Förster resonance energy transfer spectroscopy that ligand binding induces substantial conformational changes in the ectodomain of ifnar1 (ifnar1-EC). Binding of IFNα2 and IFNβ induce very similar conformations of ifnar1, which were confirmed by single-particle electron microscopy analysis of the ternary complexes formed by IFNα2 or IFNβ with the two receptor subunits ifnar1-EC and ifnar2-EC. Photo-induced electron-transfer-based fluorescence quenching and single-molecule fluorescence lifetime measurements revealed that the ligand-induced conformational change in the membrane-distal domains of ifnar1-EC is propagated to its membrane-proximal domain, which is not involved in ligand recognition but is essential for signal activation. Temperature-dependent ligand binding studies as well as stopped-flow fluorescence experiments corroborated a multistep conformational change in ifnar1 upon ligand binding. Our results thus suggest that the relatively intricate architecture of the type I IFN receptor complex is designed to propagate the ligand binding event to and possibly even across the membrane by conformational changes.