幼儿不同跑步着地方式的生物力学特征

文题释义：跑：跑是双脚交替接触地面的周期性运动，但跑有一个双脚都离开地面的腾空期。幼儿在 1 岁多开始学习跑步，最初是走跑结合的移动方式，由于身体发育不完善，下肢力量弱，平衡能力差，容易摔倒；到 2.5岁，幼儿跑步的腾空阶段明显；到 6岁，早期跑步的特点基本消失。 着地方式：指的是人体在跑步着地阶段足部接触地面的方式，一般分为3种方式：分别为足跟着地(fore foot strike)，跟骨先接触地面；全足着地(mid foot strike)，全脚掌着地，即足跟与前足同时接触地面；前足着地(rear foot strike)：前足部首先接触地面。 背景：成年人跑步着地方式一直是国内外学者研究的重点，而幼儿跑步的着地方式也是不容忽视的内容。 目的：运用生物力学方法探究幼儿在跑步过程中，不同着地方式下的运动学和动力学指标的差异，为幼儿正确的跑步着地方式提供科学依据。 方法：在北京市海淀区某公立幼儿园中随机抽取幼儿74名，按年龄分为3岁组、4岁组、5岁组，采用BTS红外动作捕捉系统、Kistler三维测力台和VIXTA录像解析系统同步采集幼儿跑步过程中不同着地方式下的运动学、动力学数据；运用Anybody 5.2仿真建模软件计算下肢肌肉力量指标。试验前向受试者父母详细解释并签署知情同意书，试验方案符合北京师范大学的相关伦理要求。 结果与结论：①3岁组全足着地的比例最高，足跟着地的比例最低，5岁组全足着地的比例最低，足跟着地的比例最高；前足着地者的蹬伸时间大于足跟着地(P < 0.01)和全足着地(P < 0.05)；②着地时刻，踝屈曲角度足跟着地者大于前足着地(P < 0.01)和全足着地者(P < 0.05)，全足着地者大于前足着地(P < 0.05)；前足着地者髋内收-外展角度、最大髋内收-外展角、髋内-收外展的关节变化量及最大膝内收-外展角速度大于足跟着地(P < 0.01)和全足着地者(P < 0.05)；前足着地者的踝屈伸最小值大于足跟着地者(P < 0.05)，而最大髋内收-外展角速度小于足跟着地者(P < 0.05)；③足跟着地和全足着地者的腓骨短肌、腓骨长肌、第三腓骨肌的肌力大于前足着地者(P < 0.05)，前足着地者的股中间肌、股外侧肌下束、股外侧肌上束、股内侧肌下束、股内侧肌上束、股内侧肌中束肌力均大于足跟着地(P < 0.01)和全足着地者(P < 0.05)；④结果提示：在3-6岁阶段，幼儿多采用足跟或全足着地模式进行奔跑，以满足自己在跑步过程的稳定性，随着年龄的增长，逐渐出现前足着地方式的跑步模式；前足着地能够动用更多髋关节和膝关节额状面的运动来维持人体运动中的稳定，足跟着地和全足着地能够动用更多的小腿前侧和后侧的肌力，而前足着地动用更多的大腿前侧肌力。 ORCID: 0000-0002-8337-3931(赵盼超) 中国组织工程研究杂志出版内容重点：组织构建；骨细胞；软骨细胞；细胞培养；成纤维细胞；血管内皮细胞；骨质疏松；组织工程     

Effect of Enamel Prism Decussation and Chemical Composition on the Biomechanical Behavior of Dental Tissue: A Theoretical Approach to Determine the Loading Conditions to Which Modern Human Teeth are Adapted

This theoretical study explored whether the directions of loads to which modern human molars are commonly subjected to are reflected in the biomechanical behavior of the tissue itself. A detailed finite element model of a piece of decussating enamel (M³ paracone) was created, taking into account differences in crystal orientation between the prism head and the interprismatic matrix, and was tested under differently angled mediolateral loads (i.e., mimicking various stages of the chewing cycle). Second, although teeth are highly mineralized, they also contain organic material and water, while in modern humans, there are systematic differences in chemical composition from the outer enamel surface to the dentinoenamel junction. To test the biomechanical effects of this gradient in mineralization a second set of models with gradually changing properties was created and subjected to the same loads. Chemically heterogeneous enamel yielded overall lower stress levels than homogenous enamel, especially at extreme loading angles. However, the general trends regarding the increase in tensile stresses at more oblique angles, and the number of nodes exhibiting tension, were comparable between the different set‐ups. The findings support suggestions that (a) the biomechanical behavior of dental tissue is the combined result of micromorphology and chemical composition and (b) that the range of loading directions, to which teeth are normally subjected to, can be inferred from dental microanatomy. For (palaeo)biological applications, the findings suggest that the absolute strength of teeth (e.g., bite force) cannot be predicted with certainty, whereas kinematic parameters of the masticatory apparatus can. Anat Rec, 2007. © 2008 Wiley‐Liss, Inc.     

股骨颈骨折空心钉内固定手术参数的优化分析

闭合复位空心钉内固定手术是目前治疗股骨颈骨折的常用方法,采用有限元方法对空心钉内固定手术进行力学综合分析,根据股骨近端力学实验的结果,建立股骨近端有限元分析模型,对可能影响手术效果的患者体重、骨折线角度、空心钉布局与角度等几个参数进行分组分析,提取骨折面、钉子的应力应变分析结果,获得了216组不同手术参数组合的情况下,影响术后愈合与承载能力的骨折端面的错位位移、钉孔底部应变、钉子最大应力、股骨最大应变四个参数,并进行综合分析比较,找到一组符合生物力学规律的内固定治疗参数,并应用于医疗机器人手术参数规划及手术效果的评价系统。     

Stress analysis between implant prostheses with different moduli and surrounding bones北大核心

背景:应力遮挡效应会导致植入假体修复骨缺损手术失败,其主要原因是由于植入假体的弹性模量大于骨组织弹性模量。目的:分析植入假体弹性模量对应力分布的影响,寻求消除应力遮挡现象的方法。方法:通过CT扫描的方式获取实验犬与人体骨组织的模型,分别对其优化后进行梯度赋值,建立较为可靠的骨骼力学模型,并与植入假体组合后进行有限元仿真。首先,通过对比格犬骨骼模型和人体骨骼模型及其对应的植入假体进行有限元仿真,模拟了不同弹性模量对植入假体修复术后的应力和位移分布情况;其次,分析了较小弹性模量差仍会形成应力遮挡现象的原因,建立了骨骼模型及植入假体模型,确立了材料属性赋予方法;最后,验证了该模型及材料属性赋予方法的可行性,并通过随机选取受力点的方式,定量分析植入假体弹性模量与骨骼弹性模量之间的关系对应力遮挡形成的影响。结果与结论:通过梯度赋值法建立与骨骼力学性质更加接近的实验犬骨骼模型和人体骨骼模型,该方法重建的力学模型与真实骨骼的力学性质更为接近;通过有限元仿真力学测试证明,不同弹性模量植入假体对假体本身与周围骨骼间相对位移的影响较小;另外量化弹性模量对假体植入骨骼后对应力分布的影响,可为后续的相关研究提供帮助。     

腹主动脉瘤应力模型的建立及其应用

本研究用螺旋CT扫描腹主动脉瘤获得的断层图像合成腹主动脉瘤几何模型，通过设定瘤壁组织生物力学参数和边界条件，使用有限元分析的方法分析腹主动脉瘤瘤壁的应力分布。结果标明，本例腹主动脉瘤应力峰值位于远端分叉部位，瘤体应力峰值位于后壁，均小于瘤壁的承受极限。本研究所得结果对腹主动脉瘤应力模型有助于分析个体化腹主动脉瘤的破裂部位和生长方向，对研究疾病进程提供依据。     

兔眼虹膜组织力学特性的实验研究

利用我们创建的将兔眼蝉孔水密缝合后，模拟眼内前后房压强差，对虹膜整体进行加压的实验方法，对兔眼虹膜的力学特性进行了实验研究。结果表明：兔眼虹膜是典型的粘弹性物质；面积模量与前后方压强差之间基本成线性关系。实验结果可为青光眼致盲机制解释和瞳孔阻滞力的估算提供参考。     

搭桥、分流手术中分流管端侧交接缝合处的受力分析

本文对搭桥分流术中分流管端侧交接缝合处受力进行了分析，发现分流管向的张力随分流管面积与动脉管面积的比值增大而增大，并且在流量比为０．３时该张力有最小值。夹角的影响不大，但不可忽略。考虑到缝合材料等其它因素，还需建立对缝合线密度等因素的要求。     

Tensile properties of fresh human calcaneal (Achilles) tendons

The purpose of this study was to measure the tensile properties of fresh human calcaneal (Achilles) tendons. Twenty fresh cadaveric (age range = 57-93 years) bone-Achilles tendon complexes were harvested within 24 hr postmortem. The calcaneus together with 15 cm of the Achilles tendon extending proximally from the insertion on the calcaneus was clamped and biomechanically tested. Each tendon was firmly fixed in clamps in an MTS Systems Corporation MTS testing machine and tension was applied at a displacement rate of 8 cm per minute until the tendon failed. The tensile force and tensile strain (as measured using an extensometer) were recorded and plotted using onboard software. The narrow age range of our donors prevented any meaningful correlation between age and tensile properties; however, the results showed that: 1) the average ultimate tensile strength (UTS) of the human Achilles tendon was 1189 N (range = 360-1,965), 2) there was a correlation between left and right legs for UTS, 3) there was a correlation between left and right legs in regard to cross sectional area, and 4) there was no correlation between UTS and cross-sectional area.     

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??Objective    To study the stress distribution and displacement of the Chinese standard artificial temporomandibular joint. Methods    ANSA??Hypermesh and Abaqus softwares were used to establish finite element model of condylar defect??which was reconstructed separately by Chinese and Biomet standard artificial temporomandibular joint. The stress distribution and displacement of the jaw and Chinese and Biomet standard artificial temporomandibular joints were analyzed by loading maximal bite force on the model. Results    The maximum stress of four kinds of Chinese standard prostheses were 54MPa??79MPa??64MPa and 72MPa??while maximum stress of Biomet standard prosthesis was 78MPa.The stress of the jaw was under 20MPa in each model??and the displacement of prosthesis and jaw was under 0.05mm. The maximum stress of Chinese standard prosthesis occurred at the first posterior screw hole??whereas for Biomet standard prosthesis it was located at the neck of the condyle. Conclusion    The stress is distributed uniformly in Chinese standard prostheses?? which can avoid prosthesis fracture and bone absorption caused by excessive stress.