次氯酸钠和氢氧化钙对牙本质弹性模量和挠曲强度的影响

目的 :评估 5 %次氯酸钠 (NaOCl)溶液和饱和氢氧化钙 [Ca(OH) 2 ]溶液对牙本质弹性模量和挠曲强度的影响 ,以进一步了解根管治疗过程中药物对牙齿机械性能的影响。方法 :取新鲜拔除的完整前磨牙制成标准规格牙本质条 ,经 5 %NaOCl和饱和Ca(OH) 2 溶液处理 ,三点加荷系统测定其弹性模量和挠曲强度。结果 :5 %NaOCl使牙本质弹性模量和挠曲强度显著降低 ;饱和Ca(OH) 2 溶液使牙本质挠曲强度显著降低 ,对弹性模量无显著影响 ;5 %NaOCl处理后再用饱和Ca(OH) 2 溶液处理对牙本质弹性模量和挠曲强度无进一步影响。结论 :5 %NaOCl和饱和Ca(OH) 2 溶液对牙本质的机械性能有一定影响     

兔胫骨应力性骨折过程中的生物力学研究

目的 探讨兔应力性骨折发生过程中胫骨生物力学指标的变化与应力性骨折发生的关系.方法 将36只雄性大耳白兔随机分为6组,进行跑跳训练,根据制定的分组训练时间,于训练任务完成后的第7、14、21、28、35天分别处死动物.光镜下观察胫骨病理变化;生物力学机上行胫骨三点弯曲生物力学测试,描记载荷-变形曲线,并根据该曲线及相应参数分析胫骨生物力学性能.结果 实验组动物训练第2、3、4、5周后最大载荷与对照组动物相比之差异均有统计学意义(P＜0.05).实验组动物第1、2、3、4、5周后载荷与变形量之比与对照组动物相比之差异均有统计学意义(P＜0.05),最大应力和弹性模量与对照组动物相比之差异则均无统计学意义(P＞0.05).结论 应力性骨折的发生是一个由骨细胞直接参与的破骨细胞性重吸收大于成骨细胞性骨形成的生理过程;胫骨结构力学性能的改变是由胶原纤维紊乱、骨皮质厚度降低等所造成,从而导致应力性骨折的发生.     

In vivo measurement of the shear modulus of the human vocal fold: interim results from eight patients

The shear modulus of the vocal fold is an essential parameter required to enhance our understanding of how the vocal fold operates, to develop mathematical models of phonatation, and to provide benchmarks to quantify the effectiveness of surgical procedures. The authors announced the successful deployment of an instrument to measure vocal fold elasticity in vivo last year, and now present the data taken from eight patients in vivo. The shear modulus was measured at the mid-membranous point, in a transverse direction with respect to the axis drawn between the anterior commissure and vocal process. The range of mean shear modulus results is 701–2,225 Pa, with a mean value of 1,371 Pa.     

The application of percolation theory to the compaction of pharmaceutical powders

Based on the concepts of percolation theory the compaction process is interpreted as a site-bond percolation phenomenon. The combination of the Heckel equation with an equation derived earlier yields a simple relationship between the tensile strength σ_t, or the deformation hardness P and the relative density. This mathematical model is identical with the fundamental law of percolation theory i.e., X = s(p − p_c)^q with X= system property equivalent to tensile strength or deformation hardness, S = scaling factor, p = site occupation or bond formation probability corresponding to the relative density p,p_c = percolation threshold and critical exponent q = 1 according to percolation on a Bethe lattice. In the case of the tensile strength σ_t and the deformation hardness p, two percolation thresholds p_c(1) and p_c(2) corresponding to p_c(1) and p_c(2) could be identified. The relative density p_c(1) which is close to the relative poured or relative tapped density can be interpreted as a bond percolation threshold. The particles are bonded by weak interparticulate forces and form only loose compacts as used for filling of capsules. The relative density p_c(2) is the relative density where the first stable pharmaceutical compact is achieved which can no longer be disintegrated mechanically into its primary particles. It is of special interest that the above equation is also valid for the elastic modulus with the only percolation threshold p_c(1) = p_c(1).     

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。     

门静脉高压症猪肝动脉的生物力学特性

目的：建立猪门静脉高压症模型,探讨门静脉高压症对肝动脉的生物力学特性的影响。方法：猪以四氯化碳、苯巴比妥、乙醇,配合高脂、低蛋白、低胆碱饮食进行混合饲养。通过脾静脉插管测压,取肝动脉在生物软组织力学试验机上测定其压力-直径关系,计算机图像分析测量肝动脉两端血管环的张开角及其几何形态学指标。结果：实验组门静脉压(4．17±1．03)kPa明显大于对照组(1．51±0．79)kPa,肝动脉的各向同性增量弹性模量、血管容积弹性模量和血管压力-应变模量均随压力的上升而增大,在相同压力下明显大于对照组。肝动脉的顺应性显著低于对照组,而张开角显著增加。结论：门静脉高压症时,肝动脉的生物力学特性发生了显著变化。     

微机控制的韧带动态力学特性测试系统

本系统是为自动测试人体韧带或类似组织的动态力学特性试验而研制的。在试验时,受控的加载过程和数据采集过程同时进行。系统向韧带试件提供一个快速的匀速可控的拉伸载荷,模拟人体剧烈运动的实况,同时实时采集力和变形的数据。系统还提供对所采集数据的分析手段,从而得到力、变形、应力、应变、弹性模量和变形能等参数之间的关系,并可以图形和文字形式输出。系统亦可将各数据文件转换为其它应用软件包可接受的形式,以便利用标准商品软件包的数据和图象处理能力。系统采用菜单提示的人机对话方式进行监控。     

Mechanical and Cellular Changes During Compaction of a Collagen-Sponge-Based Corneal Stromal Equivalent

The need for corneas suitable for transplantation, combined with the decreasing supply, has fueled interest in the development of a corneal replacement. In this study, a collagen-sponge-based stromal equivalent, consisting of human corneal fibroblasts cultured on a type I collagen sponge, was maintained in culture for up to 21 days and characterized with respect to mechanical properties and cellular behavior. The Young's modulus of the stromal equivalent varied from 95 to 370 Pa, and its permeability varied from 5.3 x 10(-8) - 4.2 x 10(-7) m4 N(-1) s(-1). The greatest changes occurred during the first few days in culture, but the mechanical properties continued to change during the entire 21 days. Cell traction stress, determined from sponge compaction and DNA count, decreased during the compaction process with the maximum traction value the initial value of 6.6 +/- 2.9 x 10(-3) Pacm3 cell(-1). Microarray data showed that the expression level of fibronectin, decorin sulfate, collagenase, and gelatinase A was upregulated at day 14 in the sponge. This suggested that the repair fibroblast phenotype was being expressed by the fibroblasts. Additional analysis suggested that a subpopulation of cells expressed the myofibroblast phenotype.     

聚氯乙烯／聚丙烯酸丁酯／白泥纳米复合材料的研究

通过多步交换反应及扩散－聚合的方法,使聚丙烯酸丁酯被嵌入到改性层状结构的白泥层间,得到白泥－聚丙烯酸丁酯纳米复合物的微米粒子;然后将聚氯乙烯与白泥－聚丙烯酸丁酯进行熔融共混,制得具有一一特性的有机－无机纳米复合材料,并对复合材料的缺口冲击强度及动态力学性能进行了研究,结果表明,白泥－聚丙烯酸酯含量为5．0wt％时,复合材料的力学性能最佳;聚氯乙烯与高含量的白泥－聚丙烯酸丁酯（分别为25．0wt%和50．0wt%）形成的复合材料,在聚氯乙烯的玻璃化转变温度之前,储能模量出现先降低而后增加的过程。     

干牛骨拉伸弹性模量沿径向的分布

本文研究了干牛胫骨骨干密质骨部分沿生长轴方向的拉伸弹性模量沿径向的分布，发现此弹性模量沿径向呈非均匀分布，内外两侧的弹性模量值低于中间部分；提出了一种骨内疲劳裂纹的分布假设，并据此对测试结果进行了初步性的分析。