颅脑模型减速撞击过程中脑组织受力特点的研究

目的 研究颅脑减速撞击过程中脑组织关键部位受力的特点（受拉或受压）。方法 制作含气泡的透明颅脑物理模型,并将其固定在竖式颅脑减速撞击实验台上。将移动平台放置在400 mm的高度,自由下落并撞击固定台面,同时采用高速摄像记录整个减速撞击过程,并用序列图片分析软件对气泡长、短轴（分别位于垂直于撞击方向及撞击方向）的轴长变化进行分析。结果 撞击点处的气泡在短轴方向上的轴长变化大于长轴方向上的轴长变化,对冲点处的气泡在短轴方向上的轴长变化小于长轴方向上的轴长变化。结论 实验结果表明撞击点处的气泡所受到的作用力主要为压力且来自于短轴方向,即撞击方向;对冲点处的气泡所受到的作用力主要为拉力且来自于长轴方向,即撞击方向的垂直方向。该研究对于研究颅脑减速撞击致伤的力学机制及其诊断和防护具有重要意义。     

颅脑对冲伤的监护进展

重型颅脑损伤是一种严重的创伤类型,发生率较高据统计我国城市中伤死病例的60%为颅脑损伤。Miller等报告颅脑对冲伤死亡率为35%左右〔1,2〕。国内外对颅枕部对冲伤的预防、急救、监护都很重视。国内对于脑损伤后的系列变化进行了探索,特别注重伤后的监护,从而大大提高了颅脑损伤的救治率,现就目前颅脑对冲伤的监护体系作一综述。1　颅脑对冲伤的发病机制颅枕对冲损伤大多是在受撞击处的对侧,如枕部着地者的额叶、颞叶的前方脑组织可发生脑挫裂伤(对冲伤所致),而枕部脑组织常可无损伤或损伤轻(击伤所致)。对冲伤的形成,是由于颅骨和脑组织在…     

一种用于动物肝脏减速撞击伤机制研究的装置及实验探讨

目的：构建一种减速撞击装置,对小动物肝脏减速撞击过程中的受力方式进行研究,以便对汽车交通事故中驾乘人员可能存在的肝脏损伤特点进行分析。方法：通过肝脏自身的粘性将其置放于一可移动撞击平台上．此外．无其它约束。之后,使肝脏随同移动平台从一定的高度自由下落并撞击一固定台面。通过对撞击前后的肝脏照片情况进行比对．可以明确肝脏的损伤方式进而确定肝脏的受力方式。结果：在肝脏的减速撞击过程中．在对冲部位出现了明显的撕裂伤,该部位的伤情也是整个肝脏最严重的伤情所在位置。此外,在肝脏的撞击部位未见明显的撕裂伤。提示,在肝脏的减速撞击过程中,其对冲部位受到了相对较大的拉伸应力的作用。讨论：一般而言,生物体软组织的抗拉伸致伤的性能较弱,而其抗压缩致伤的性能相对较好。因此,在肝脏的减速撞击过程中,其对冲部位在较大的拉伸应力的作用下易于损伤并且往往是最严重的损伤发生的部位。结论：该装置可以很方便地应用于肝脏减速撞击损伤机制的研究。在交通事故中,组织器官对冲部位潜在的撕裂伤产生的可能性往往是最大的,这部分组织需要得到更多更有效的保护。因此在后续的研究中,这种损伤的生物力学机制研究应是重点之一。     

诊断相关条件下的声空化

在适当的条件下,超声通过对组织内微气泡的国外医学生物医学工程分姗作用将会产生意义深远的生物效应.在低极生物体的实验中,已有许多明显的例证。为了确定空化现像对哺乳动物的作用,我们需要更好地了解其基本物理过程,掌握更多的有关哺乳动物组织内存在适当空化核的资料.目前所能得到的有限资料表明,超声对气饱有两类性质不同的作用方式,一类是连续波辐照,激发气泡反复振荡,以此来影响组织结构,这类作用会导致细胞间芝徽流和细胞膜应力,当应力足够大     

人头颅受撞击作用的力学分析

本文提出了一个由双层线性粘弹性固体球壳充以线性粘弹性流体所形成的人头颅力学模型,考虑了头颅的外皮层在受撞击时的作用。用粘弹性动力学对应原理,导出了波的传播方程。分析结果表明:1.脑区最大正压位于撞击点,而最大负压出现在对侧点;2.分析结果证实了脑在撞击荷载作用下的空化损伤理论;3.皮层对于提高头颅的刚度、衰减冲击能量、缓解撞击引起的脑损伤具有重要作用。     

超声－微气泡介导的基因转染研究进展

能否成功高效地转染靶基因对于基因治疗的效果具有决定性的影响。微气泡是具有稳定的封装壳,直径为微米量级的小气泡,已作为超声造影剂被广泛应用。微气泡在超声脉冲的作用下可以在靶区释放其携带的基因并使之转染,同时超声脉冲产生的热效应和空化效应能提高转染率。若将微气泡与磁性纳米颗粒结合,还可以进一步提高转染率和转染精度,是一种理想、安全的基因载体。本文综述了由超声－微气泡介导的基因转染在近5年的主要研究成果。对影响转染率的主要因素如微气泡种类、超声辐照条件、基因及受体类型等方面做了详细的论述,并对微气泡介导基因转染过程中的安全性、长效性和差异性等问题进行了讨论。     

高强度聚焦超声"切除"肿瘤过程中的空化效应

随着高强度聚焦超声(HIFU)在多种肿瘤治疗中的广泛应用,对其生物学效应的研究也不断深入.空化效应是超声的主要生物学效应之一.本文对近年来众学者在HIFU治疗肿瘤过程中关于空化效应是否存在、产生空化效应的条件以及对空化效应的评价等问题进行了较为全面的阐述.     

超声空化消融治疗术的研究进展

超声相关的消融治疗包括超声引导下的微创介入消融术（射频和微波热消融、冷冻消融、酒精消融等）和超声波直接作用的无创消融治疗术（高强度聚焦超声、超声空化消融术等）。近年来,以超声热学效应为主要治疗机制的高强度聚焦超声（HIFU）作为一种无创性消融术发展迅速,已在临床得到广泛应用[1-3]。超声空化效应最初被认为是难以控制的不利因素,现逐渐演变为超声治疗学研究的热点方向之一。超声空化消融术是近几年发展起来的新技术,是利用超声作用于机体内在的微气泡（内源性）或输入的微泡（外源性）发生强烈的空化效应,毁损机体组织、血管从而实现了直接消融治疗的目的,与HIFU不同的是,超声热效应在其治疗中的作用很小或可忽略。目前,应用超声空化效应进行消融治疗主要为组织毁损术和血管毁损术,动物实验显示在肿瘤治疗、溶解血栓、创伤止血等方面具有较好的效果[4-10]。本文对超声空化消融术的研究进展进行综述。     

信号与图像处理 多普勒超声对流动血液中微栓塞的时域检测

流动血液中的小堆积元和气泡称为微栓塞,用多普勒超声可以对其进行检测。在本研究中,中脑动脉中一定体积的血液受脉冲恒频超声波信号的作用,微栓塞在采样体积中移动,产生多普勒漂移暂态反射。目前的检测方法是采用短时傅立叶变换(STFT)在反射信号中寻找这些暂态反射。由于栓子通过多普勒采样体积的时间与栓子的速度成反比(多普勒频移),所以理论上讲,要想获得最佳结果,合适的滤波检测器应该用小波变换而不是短时傅立叶变换。但对多普勒漂移信号的进一步测试表明通常会由于栓子在多普勒采样体积内移动的加速度或负加速度而表现出线性调频脉…     

颅脑组织材料参数对儿童头部冲击响应的影响

目的针对目前对儿童颅脑组织材料参数的不确定性,研究直接冲击载荷条件下颅脑组织材料参数对儿童头部冲击响应的影响。方法应用已验证的3岁儿童头部有限元模型进行冲击仿真实验,采用正交实验设计和方差分析对儿童颅脑组织材料进行参数分析。结果颅骨弹性模量对儿童头部冲击响应具有显著性影响,随着颅骨弹性模量的增加,头部撞击侧颅内压力显著减小(P=0.000),对撞侧颅内压力显著增大(P=0.000),颅骨最大Von Mises应力显著增大(P=0.000)。脑组织的线性黏弹性材料参数对儿童头部冲击响应同样具有显著性影响,随着脑组织短效剪切模量的增加,脑组织最大主应变显著减小(P=0.000),脑组织最大剪应力则显著增加(P=0.000)。结论参数分析结果可为今后儿童头部有限元模型的材料选取提供参考依据,进而提升模型在预测临床上无法通过脑CT影像确诊的脑震荡等脑损伤时的准确性。     

In vitro squeeze-flow phenomena at the instant of mechanical valve closure

Cavitation bubble formation associated with mechanical valve closure has been investigated in vitro, and the region of bubble formation has been correlated with large negative pressure transients. The region of cavitation bubbles forms in valve designs where leaflets interact with seat stops. It has been postulated that the fluid is squeezed between the leaflet and the seat stop and radially propelled at high velocities, resulting in further pressure reduction below the vapor pressure of fluid and initiating cavitation bubble formation. We conducted in vitro experiments to visualize and detect the presence of squeeze-flow phenomena associated with valve closure of mechanical heart valves. The closing dynamics were studied by simulating a single closing event of the leaflet with the valve mounted at the mitral position. Squeeze flow was detected at the instant of valve closure, when the valve leaflet interacts with the valve seat stop. The use of a high-speed video camera at 1000 frames per second with strobe light at 16000 pulses per second enabled the visualization of cavitation bubbles and its radial motion from the valve's seat stop due to the squeeze-flow effect. Vapor cavitation bubbles were observed to collapse within 0.5 ms after inception. In mechanical valves without seat stops in the major orifice region, bubbles of duration longer than that of the cavitation bubbles were observed. These microbubbles were present for 4 s before collapsing and are believed to be air bubbles whose presence in vivo has been detected with ultrasound imaging.     

Prevention of air bubble formation in a microfluidic perfusion cell culture system using a microscale bubble trap

Formation of air bubbles is a serious obstacle to a successful operation of a long-term microfluidic systems using cell culture. We developed a microscale bubble trap that can be integrated with a microfluidic device to prevent air bubbles from entering the device. It consists of two PDMS (polydimethyldisiloxane) layers, a top layer providing barriers for blocking bubbles and a bottom layer providing alternative fluidic paths. Rather than relying solely on the buoyancy of air bubbles, bubbles are physically trapped and prevented from entering a microfluidic device. Two different modes of a bubble trap were fabricated, an independent module that is connected to the main microfluidic system by tubes, and a bubble trap integrated with a main system. The bubble trap was tested for the efficiency of bubble capture, and for potential effects a bubble trap may have on fluid flow pattern. The bubble trap was able to efficiently trap air bubbles of up to 10 μl volume, and the presence of captured air bubbles did not cause alterations in the flow pattern. The performance of the bubble trap in a long-term cell culture with medium recirculation was examined by culturing a hepatoma cell line in a microfluidic cell culture device. This bubble trap can be useful for enhancing the consistency of microfluidic perfusion cell culture operation.     

Quantitative ultrasound method to detect and monitor laser-induced cavitation bubbles

An ultrasound technique to measure the spatial and temporal behavior of the laser-induced cavitation bubble is introduced. The cavitation bubbles were formed in water and in gels using a nanosecond pulsed Nd:YAG laser operating at 532 nm. A focused, single-element, 25-MHz ultrasound transducer was employed both to detect the acoustic emission generated by plasma expansion and to acoustically probe the bubble at different stages of its evolution. The arrival time of the passive acoustic emission was used to estimate the location of the cavitation bubble's origin and the time of flight of the ultrasound pulse-echo signal was used to define its spatial extent. The results of ultrasound estimations of the bubble size were compared and found to be in agreement with both the direct optical measurements of the stationary bubble and the theoretical estimates of bubble dynamics derived from the well-known Rayleigh model of a cavity collapse. The results of this study indicate that the proposed quantitative ultrasound technique, capable of detecting and accurately measuring laser-induced cavitation bubbles in water and in a tissue-like medium, could be used in various biomedical and clinical applications.     

Mechanical Performance of Cranial Bone in Impact Protection of Woodpecker Brain:A Finite Element Study

Human head impact injuries caused by a sudden impact force are very common in aviation lifesaving,car crash accident,war or sports activities. Yet,an intriguing example of nature is woodpecker which is free from head injury even it drums trunk continually at a speed of about 6-7 m/s and a deceleration of about 1000 g.Woodpecker must have special characteristics to attenuate repetitive impact force to sustain rapid pecking without brain injury. In this study,the effect of mechanical property of cranial bone on the brain during impact was investigated using the finite element(FE)approach. It was demonstrated that the pressure,Von-Mises stresses and shear stress at the same point on the posterior of woodpecker's brain were decreased greatly compared with hoopoe and lark. It was stated that the higher strength of woodpecker's cranial bone might play an important role for preventing woodpecker's head injury.     

Finite element analysis of brain contusion: An indirect impact study

The mechanism of brain contusion has been investigated using a series of three-dimensional (3D) finite element analyses. A head injury model was used to simulate forward and backward rotation around the upper cervical vertebra. Intracranial pressure and shear stress responses were calculated and compared. The results obtained with this model support the predictions of cavitation theory that a pressure gradient develops in the brain during indirect impact. Contrecoup pressure-time histories in the parasagittal plane demonstrated that an indirect impact induced a smaller intracranial pressure (−53.7 kPa for backward rotation, and −65.5 kPa for forward rotation) than that caused by a direct impact. In addition, negative pressures induced by indirect impact to the head were not high enough to form cavitation bubbles, which can damage the brain tissue. Simulations predicted that a decrease in skull deformation had a large effect in reducing the intracranial pressure. However, the areas of high shear stress concentration were consistent with those of clinical observations. The findings of this study suggest that shear strain theory appears to better account for the clinical findings in head injury when the head is subjected to an indirect impact.     

自动紧急制动对公交车内儿童乘员颅脑损伤影响

目的 研究自动紧急制动(autonomous emergency braking,AEB)对公交车内儿童乘员的颅脑损伤影响。 方法 使用 Prescan 软件搭建公交车 AEB 测试场景,通过仿真得到 60 km/ h 初速度下公交车 AEB 制动工况下的减速度曲线。 基于已经验证的公交车模型和具有详细解剖学头部结构的 6 岁儿童混合有限元模型,选取车内儿童乘员典型的 4 个乘坐位置,使用 LS-DYNA 软件对公交车有、无 AEB 制动工况下儿童乘员头部损伤进行仿真。 以儿童乘员头部损伤指标 HIC15 、大脑灰质处压力、脑组织 von Mises 应力及剪切应力等生物力学响应为损伤评价指标,对儿童乘员的颅脑损伤进行分析。 结果 各组仿真试验中,位置 1 和 2 前方设置挡板时,儿童乘员大脑灰质处压力超过其损伤阈值,其余各位置儿童乘员的各项损伤指标均远小于对应的损伤阈值。 结论 AEB 能有效降低公交车内儿童乘员头部碰撞损伤,公交车内位置 3 处的儿童容易发生碰撞损伤风险,位置 1、2 处设置广告牌挡板会增加儿童乘员的颅脑损伤风险。     

An analysis of contact stiffness between a finger and an object when wearing an air-cushioned glove: the effects of the air pressure

Air-cushioned gloves have the advantages of lighter weight, lower cost, and unique mechanical performance, compared to gloves made of conventional engineering materials. The goal of this study is to analyze the contact interaction between fingers and object when wearing an air-cushioned glove. The contact interactions between the the fingertip and air bubbles, which is considered as a cell of a typical air-cushioned glove, has been analyzed theoretically. Two-dimensional finite element models were developed for the analysis. The fingertip model was assumed to be composed of skin layers, subcutaneous tissue, bone, and nail. The air bubbles were modeled as air sealed in the container of nonelastic membrane. We simulated two common scenarios: a fingertip in contact with one single air bubble and with two air cushion bubbles simultaneously. Our simulation results indicated that the internal air pressure can modulate the fingertip-object contact characteristics. The contact stiffness reaches a minimum when the initial air pressure is equal to 1.3 and 1.05 times of the atmosphere pressure for the single air bubble and the double air bubble contact, respectively. Furthermore, the simulation results indicate that the double air bubble contact will result in smaller volumetric tissue strain than the single air bubble contact for the same force.     

基于有限元法的人类头部损伤生物力学的模拟分析

根据正常头部螺旋CT扫描影像，通过对CT扫描影像的图像处理，利用计算机辅助工程技术，采用单元网格划分和三维重构技术，开发、建立了三维的人类头部有限元计算模型。应用本模型模拟颅脑在直接碰撞中的生物力学问题。计算模型比较真实地反映了头颅实际碰撞实验中的物理反应，比较忠实地再现了某些实验的结果，如头部撞击合力和脑压力/强等。同时，脑压力，强的分布再次证实了经典的撞击压-对撞压产生理论。本研究的计算模型可为进一步的头部损伤生物力学研究提供一种新的工具。