用激光测速法研究稳定黏附的白细胞与血液流动的相互作用

提出了血液流动与牢固黏附的白细胞之间相互作用的理论模型,根据计算流体动力学方法推导血流作用下白细胞表面应力、压力分布,以及由于黏附的白细胞对血流阻力的影响.在此基础上,用激光测速法对上述模型进行实验研究.结果表明,血流阻力、压力梯度随血流雷诺数、白细胞直径的增大而增大;细胞表面的应力重新分布,但最大剪应力总是位于细胞表面的顶点.我们认为细胞表面应力分布的不均一可能对白细胞的形态与功能变化有重要作用.     

黏附于血管壁表面的白细胞在稳定剪切流动下发生变形的生物力学模型

白细胞与血管表面的黏附是重要的生物医学工程问题，引起了学者们的广泛研究。我们用复合液滴来模拟黏附于血管表面的白细胞，根据二维计算流体动力方法研究了流体切应力作用下白细胞黏附引起的压力分布。同时，通过引入“变形指数”的概念，研究稳定剪切流动下白细胞变形的生物力学特性，数值结果表明：（1）随着初始接触角，毛细血管数，外界流场雷诺数的增大，细胞的变形也增大，而细胞浆比细胞核更易于变形，表明细胞核更能耐受切流动；（2）当切应力增大到一定值时，细胞不能进一步变形，变形指数达到峰值；（3）压力分布曲线表明，在细胞的下游形成一个高压区，提供促使细胞受力达到平衡的升力，从而阻止了细胞的进一步变形，我们关于细胞核变形的结果有助于理解白细胞如何将外界流体作用力（如切应力）等力学信号向核内转导的生物力学机理。     

剪切流动下内皮细胞变形的模拟

血液流动和内皮的耦合是重要的生物医学问题 ,引起了学者们的广泛的兴趣。目前已知内皮细胞能感知流场的剪切应力而改变其形态和功能。由于剪切应力被认为是引起内皮细胞重建的始发信号 ,所以了解内皮细胞与流动应力之间的相互作用机制是十分重要的。我们建立了一个理论模型来模拟内皮细胞与流场应力之间的相互作用。根据二维计算流体动力学方法研究了内皮细胞应力、压力的分布以及内皮细胞在剪切应力作用下的变形情况。结果表明 :( 1)内皮细胞的变形随 α(对应于流体作用于细胞表面的切应力 )的变化而变化。当 α>0 .0 2 1时 ,细胞的变形随 α的增大而显著增大 ;( 2 )流动引起了细胞表面应力和压力分布的不均匀 ,从而导致了细胞的变形。但内皮细胞的最大应力总是位于细胞的顶点。同时 ,我们用流室系统提供剪切流动 ,测量了不同剪切应力作用下培养的人主动脉内皮细胞的变形。所得到的实验结果与上述数值模拟结果是吻合的。本文结果提示 ,由于剪切流动引起细胞表面应力和压力分布的不均一 ,可能在细胞激活和细胞功能的调节 (如细胞骨架的调节 ,粘附分子的表达与分布等 )机制上具有特殊的作用。本研究为综合应用动力学方程来建立内皮细胞模型提供了工作框架     

用复合液滴模型研究稳定剪切流动下黏附于血管表面白细胞的变形

变形作用是黏附于血管表面的白细胞响应外界流体作用的重要特征，然而，尚不清楚白细胞的细胞核是否伴随细胞而发生变形。我们用复合液滴模拟黏附于血管表面的白细胞，根据二维计算流体动力学方法研究稳定剪切流动下白细咆及其细咆核发生变形的生物力学机制。结果表明：(1)外界流场雷诺数是引起细咆变形的重要原因。随着雷诺数的增大，细胞变形也增大；(2)细胞核随细胞的变形而发生了变形，但细胞的变形指数总是大于其细胞核，表明细胞核更能耐受剪切流动；(3)当雷诺数增大到一定值时，细胞和细胞核都不能进一步变形，变形指数达到峰值；(4)压力分布曲线表明，在细胞的下游形成一个高压区，提供促使细胞受力达到平衡的升力，从而阻止了细胞的进一步变形：因此，具有高粘性的细胞核在细胞的变形过程中发挥特殊作用。     

牛膝关节软骨的力学承载特性及其有限元仿真分析

目的分析软骨的压缩变形行为和液相力学承载特性的关系。方法利用压痕实验测定牛膝关节软骨在不同压头直径、不同载荷下的压缩变形位移,建立有限元模型模拟关节软骨内部液相流动及承载特性。结果模拟压缩位移与实验结果最大相对误差为1.73%,在相同载荷作用下,随着压头直径的增大,软骨的弹性模量与渗透系数随之增大;在相同压头直径作用下,随着载荷的增大,软骨的弹性模量与渗透系数随之减小。载荷作用在软骨上,软骨内部液相主要在软骨内流动,随着载荷的持续,液相逐渐向软骨外流动。软骨表面的孔隙压力、轴向应力、径向应力由于液相的流动呈非线性变化。结论软骨表面的液相流动、孔隙压力及应力分布等影响软骨表面的承载特性;在不同压头、不同载荷下,软骨的承载特性有较大差异。     

电场作用下多细胞膜电场应力分布

目的:在电场作用下,多细胞相对位置对电场应力分布的影响。方法:对于单细胞,通过求解满足边界条件的拉普拉斯方程,对于多细胞利用电磁场仿真软件ANSYS-Maxwell求解细胞内外电场分布。用麦克斯韦应力张量法分析细胞电场应力分布。结果:与单个细胞相比,电场作用于3个细胞时,细胞表面电场应力分布仍具有一定的对称性,细胞间距变化时,细胞间感应强度也相应发生变化。在细胞间距足够大的情况下,各细胞间的相互影响非常小,可以将其近似为单细胞模型处理。结论:细胞数目和细胞间距都会影响细胞表面电场应力的分布情况,细胞在电场作用下发生的形变与细胞表面所受电场应力有关。     

白细胞与内皮细胞的粘附模型及其生物力学基础

白细胞与内皮细胞的粘附问题，是目前国际上的前沿性生物医学课题。分子生物学、细胞生物学和生物力学新方法、新技术不断出现，使白细胞与内皮细胞粘附问题的研究不断深入和创新。一方面，以分子生物学为基础的白细胞和内皮细胞粘附分子的研究，揭示了白细胞与内皮细胞相互作用的分子基础，另一方面，以生物力学方法为基础建立了白细胞与内皮细胞的粘附模型的提出，为研究白细胞－内皮细胞粘附引起的血流阻力、压力梯度、速度分布、应力分布、流场扰动等变化规律开辟了全新的方法；而基于液滴模型建立的白细胞复合液滴模型珠提出，为探讨白细胞－内皮细胞之间在不同初始接触面积、接触角、受体与配体的结合数等方面对白细胞的变形性、流变学特性的影响以及相邻白细胞、内皮细胞之间力的传递规律开辟了新途径。本旨在对这一领域的最新成果作一扼要介绍。     

数值模拟不同充气压力对支架术后颈动脉力学环境的影响

目的研究支架介入在不同充气压力下对病变血管壁力学环境的影响。方法使用高分辨率磁共振成像(MRI)获得含有脂质斑块和钙化斑块的颈动脉模型,通过有限元软件构建体内血管-支架两者之间相互作用的力学模型,数值模拟分析不同充气压力(909、1 212和1 515 kPa)作用下血管壁及斑块的Von Mises应力分布。结果随着充气压力的增大,血管壁与支架接触内表面的Von Mises应力逐渐增大。在高充气压力作用下支架撑开后,脂质斑块区域会产生严重的应力集中现象;而在不同充气压力作用下,钙化斑块区域Von Mises应力分布差异很小。结论较大充气压力作用下支架撑开后将给血管壁和脂质斑块带来较大伤害,可能会引发支架后期失效。研究结果可为支架术充气压力的选择以及支架植入后斑块稳定性的预估提供临床参考。     

壁冠状动脉血流动力学体外模拟

目的 研究心肌桥压迫对壁冠状动脉内血流、正压力、周向应力、切应力的影响。方法 对原有的壁冠状动脉模拟装置进行较大改进,使其测量的血流动力学参数从单一应力（正应力）扩展到多种应力,以便更全面准确地模拟在正压力、周向应力、切应力共同作用下的真实血流动力学环境,从而综合考虑在多种应力共同作用下血流动力学规律与壁冠状动脉粥样硬化之间的关联。结果 壁冠状动脉模拟装置实验结果表明,应力的异常主要位于壁冠状动脉近端,随着心肌桥压迫程度加剧,近端的应力平均值与波动值明显增大,正应力平均值升高27.8%,波动值升高139%。结论 心肌桥压迫造成壁冠状动脉近端血流动力学发生异常,对认识冠脉粥样硬化发病的血流动力学机理具有重要意义,对于心肌桥的病理影响及治疗具有潜在的临床价值。     

颅内动脉瘤径颈比对瘤体与分支血管血流动力学影响的数值模拟研究

动脉瘤的血流动力学是影响其生长与破裂的重要因素,尤其是形态学参数径颈比(aspect ratio,AR,瘤体长径/瘤颈宽度)对其血流动力学影响较大。本研究使用基于计算流体力学(computational fluid dynamics,CFD)技术的ANSYS 16.0软件包,数值仿真分析了不同径颈比对颅内动脉瘤瘤体与分支血管血流动力学的影响,为临床上制定合理的形态学与血流动力学指标来筛选高危的动脉瘤患者,并进行积极的干预治疗提供一定的理论依据。通过使用空间直角坐标系建立径颈比为3.33、2.5、2、1.67、1.43、1.25的理想颅内动脉瘤几何模型,分析和比较了包括血液流场与涡量分布、流速与流量、壁面压力、壁面切应力(wall shear stress,WSS)、瘤颈近远侧端与分支血管剪切应变率(shear strain rate,SSR)在内的血流动力学参数。数值模拟结果给出了动脉瘤与分支血管内的流线图、涡核图、压力分布云图、WSS分布云图以及随X轴变化的流速与压力峰值分布曲线。分析得出,径颈比决定瘤内血流模式,径颈比减小,瘤顶的流速与SSR增大,瘤壁上的压力与WSS增大,分支血管壁上的压力增大,且WSS/SSR瘤颈远侧端>WSS/SSR瘤颈近侧端>WSS/SSR分支血管中心,涡核区域由瘤体远侧壁增大至覆盖整个动脉瘤,但对分支血管内血流的阻碍作用减小。     

Flow-mediated cell stress induction in adherent leukocytes is accompanied by modulation of morphology and phagocytic function

Leukocytes adherent to the surfaces of both vascular biomaterials and normal blood vessels experience blood flow induced shear stress. The goal of the reported studies was to investigate the effect of fluid flow on the morphology, phagocytic function and stress response induction in adherent immune cells. Shear approximating arterial, venous and intermediate levels were applied onto glass-adherent IC21 macrophages in a temperature-controlled parallel plate flow system. The results indicate that fluid flow induces a shear-dependent physiological stress response in adherent macrophages and that significant morphological changes accompany macrophage responses to shear stress. In addition, arterial flow conditions induce not only significant cell polarisation, but also enhanced phagocytic ingestion in glass-adherent IC21 macrophages. These findings suggest that blood flow induced shear stress may not only be consequent to adherent leukocyte activation, but may also be integral to the regulation of adherent leukocyte behaviour in vivo.     

Flow-mediated cell stress induction in adherent leukocytes is accompanied by modulation of morphology and phagocytic function

Leukocytes adherent to the surfaces of both vascular biomaterials and normal blood vessels experience blood flow induced shear stress. The goal of the reported studies was to investigate the effect of fluid flow on the morphology, phagocytic function and stress response induction in adherent immune cells. Shear approximating arterial, venous and intermediate levels were applied onto glass-adherent IC21 macrophages in a temperature-controlled parallel plate flow system. The results indicate that fluid flow induces a shear-dependent physiological stress response in adherent macrophages and that significant morphological changes accompany macrophage responses to shear stress. In addition, arterial flow conditions induce not only significant cell polarisation, but also enhanced phagocytic ingestion in glass-adherent IC21 macrophages. These findings suggest that blood flow induced shear stress may not only be consequent to adherent leukocyte activation, but may also be integral to the regulation of adherent leukocyte behaviour in vivo.     

Evaluation of leukocyte adhesion on polyurethanes: the effects of shear stress and blood proteins

Leukocytes are a central cell type in directing host inflammatory and immune processes; thus, its response to biomaterials is extremely important in understanding material-host interaction. Blood contacting biomaterials may activate the complement cascade, thus promote leukocyte adhesion and activation to the biomaterial surface. We hypothesize that the extent of complement-mediated leukocyte activation is modulated by the material chemical formulation and the presence of fluid shear stress. Medical-grade polyurethanes with or without 4,4'-butyldiene bis(6-tert-butyl-m-cresol) antioxidant additives and a rotating disk system were utilized to study cell adhesion under a well-characterized shear stress field. Radioimmunoassay and ELISA were employed to assess the extent of complement activity. The results showed that adherent leukocyte densities decreased with increasing shear stress and that leukocyte adhesion was decreased significantly further by the presence of the antioxidant in the polyurethanes. Cell adhesion under flow conditions was abolished when complement C3 protein was depleted from the test medium. An increase in complement Factor H adsorption was observed at high shear region; however, no change in the complete complement activation was observed in the presence of shear stress as indicated by the protein S-terminal complement complex level. Based on these results, oligopeptides designed from C3a, C5a, and fibronectin were grafted onto a cell-nonadhesive polymer surface to probe the molecular mechanisms of leukocyte adhesion as mediated by protein-receptor complexation. The results showed that C3a-derived peptides mediated higher adherent macrophage density when compared to that mediated by C5a- and fibronectin-derived peptides.     

Platelet and leukocyte activation and design consequences for thoracic artificial lungs

Blood contact with the prosthetic surfaces of artificial lungs causes extensive activation of molecular and cellular mediators of coagulation and inflammation that can lead to patient morbidity and mortality. To determine the effects of artificial lung fiber bundle shear stress and surface area on blood activation, porcine blood was recirculated for 4 hours through circuits containing mock artificial lungs with bundle shear stresses of 11.6, 7.3, and 3.9 dynes/cm2 and surface areas of 5.2, 3.5, and 1.7 cm2/ml of circuit volume. Blood from these circuits was assayed for platelet and leukocyte counts, soluble P-selectin concentrations, and lactoferrin concentrations to determine the level of platelet and leukocyte adherence to the circuit, platelet activation, and leukocyte activation, respectively. Neither platelet nor leukocyte counts were significantly affected by shear stress or surface area. P-selectin and lactoferrin concentrations were significantly greater at a fiber bundle shear stress of 11.6 dynes/ cm2. P-selectin and lactoferrin concentrations were significantly greater at a fiber bundle surface area of 5.2 cm2/ml of circuit volume. Artificial lungs, therefore, should be designed with average bundle shear stresses < 11.6 dynes/cm2 and with surface areas < 5.2 cm2/ml of circuit volume. Current thoracic artificial lungs meet both these requirements.     

Cell adhesion on gaseous plasma modified poly-(L-lactide) surface under shear stress field

A series of gases were used for plasma treatment of poly-(L-lactide) (PLLA) under various conditions such as atmosphere, electric power, pressure and time. The NH(3) was preferably selected for modifying the surface of PLLA because it can obtain appropriate hydrophilicity and surface energy with high polar component compared to other gases. Subsequently, cells were seeded onto NH(3) modified surface and exposed to 29.5N/m(2) of shear stress field by means of a parallel plate flow chamber in order to get good insight into the influence of N-containing incorporation on cell retention, cell morphology, and cell shape factor. The results showed that cell retention on the modified PLLA was much higher than that on the unmodified one. The NH(3) plasma modified PLLA with high cell affinity and resistance to shear stress was gained. Surface hydrophilicity, surface energy with high polar component and N-containing groups may play an important role in enhancing cell resistance to shear stress. It revealed that the parallel plate flow chamber is an effective device for evaluating the effects of surface modification on the cell affinity of a material.     

Biomechanopharmacology in Evaluation of Herbs of Activating Blood Circulation to Remove Blood Stasis

Herbs of activating blood circulation to remove blood stasis （ABCRBS） are a category of over 10% in the modern Chinese Pharmacopoeia. A new borderline discipline, biomechanopharmacology, is shaping by the efforts of applying biomechanics in pharmacological studies of ABCRBS herbs. Biomechanics is involved in modeling of blood stasis syndrome （BSS） with mechanical force induced injury and model evaluation by shear stress monitoring for blood coagulation. Investigations showed that tetramethylpyrazine （TMP） contained in Ligusticum chuanxiong Hort and diallyl trisulfide （DT） extracted from garlic demonstrated inhibiting characteristics on vWF mediated platelet activation and thrombus formation occurring under high shear rates. The effect of TMP on shear-induced platelet aggregation might be due to inhibition of calcium channel activity since it showed significant inhibition on intracellular level of calcium demonstrated by laser confocal microscope. The combined effects of TMP and shear stress on rat cerebral microvascular endothelial cell （rCMEC） were investigated by various doses of TMP incorporated with different levels of shear stress generated by a rotational coneplate rheometer. The results indicated that apoptosis of rCMECs could be restrained by a combination of medial level of shear stress with a suitable dose of TMP. To study the influences of shear stress, pressure and TMP on angiogenesis of vascular endothelial cell, cultured rCMEC was pretreated in a flow chamber with independent adjustment for levels of shear stress and pressure, and then 3D cultured on Matrigel. The results indicate that combined effects of shear stress, pressure and TMP may influence angiogenesis significantly. We believe that research on interactions among blood shear stress, secretion of endothelial cell, and pharmacodynamics will be an interesting area of biomechanopharmacology. Herbs of ABCRBS and their extracts for protecting endothelial cells to maintain their normal functions are expected.     

Panning of multiple subsets of leukocytes on antibody-decorated poly(ethylene) glycol-coated glass slides

The antibody (Ab) array format provides a unique opportunity to pan and characterize multiple leukocyte subsets in parallel. However, the questions of reproducibility and robustness of leukocyte panning on Ab arrays need to be answered for this technology to become an immunophenotyping tool. The present study sought to address several of these questions, including: (1) purity of leukocyte subsets captured on Ab regions, (2) dynamics of leukocyte binding, (3) elimination of non-specific cell adhesion, and (4) standardization of cell washing conditions. Abs for CD4 T-cells, CD8 T-cells, CD36 monocytes, and CD16b neutrophils were dispensed onto standard glass slides containing a thin film of poly(ethylene glycol) (PEG) hydrogel. PEG gel coating was highly effective in eliminated non-specific cell adhesion on the surface. Incubation of the Ab arrays with red blood cell (RBC) depleted whole blood resulting in antigen-specific panning of leukocyte subsets on the respective Ab domains. A flow through chamber was employed to determine optimal shear stress conditions for removal of non-specifically attached cells. The purity of the four subsets remaining on the surface after washing was determined by Wright staining and immunofluorescence, and was found to be as follows: CD4 T-cells (99.2+/-0.3%), CD8 T-cells (98.7+/-0.3%), CD36 monocytes (97.2+/-0.9%), and CD16b neutrophils (99.1+/-0.6%). In conclusion, the methods described in this study allow to separate whole blood into pure leukocyte subsets with minimal sample preparation and handling. These approaches will be valuable in the future development of Ab arrays as tools for quantitative immunophenotyping of leukocytes.     

二维脉动流场中内皮细胞表面切应力分布的数值模拟

本文对三种生理相关的正弦入口速度波形的脉动流场内,VEC表面的切应力分布进行了有限差分方法的数值模拟。结果表明：（1）脉动流场与稳态流场中内皮细胞表面的流场分布完全不同,脉动流场中内皮细胞表面的切应力变化幅度远大于稳态流场中的值。（2）同一时刻,每个VEC上的切应力分布是不均匀的,细胞形状影响其表面的切应力分布。（3）在脉动周期的不同时刻,细胞表面的切应力分布也是不均匀的,切应力分布随时间的变化波形与入口波形相类似,但相位有所超前,（4）细胞的伸长主要取决于EC表面的最大平均应力大小。（5）本章的计算结果可以用于Helmilinger实验现象的解释。