兔眼角膜生物力学特性的年龄相关性

目的 利用兔眼角膜条的单轴拉伸实验数据,研究角膜生物力学特性与年龄的相关性。 方法 分别取3月龄和7~8月龄兔眼角膜条,实施单轴拉伸实验,获得实验数据;用指数模型和幂模型对应力 应变数据进行分析;用黏弹性力学模型对应力松弛数据进行分析。结果 兔眼角膜条呈现非线性黏弹性特征。在实验误差允许的范围内,不同月龄兔眼角膜条的非线性应力-应变关系差别不明显,7~8月龄兔眼角膜的切线模量略偏大,但其应力衰减得明显快。不同的拉伸速率对3月龄兔眼角膜条非线性应力-应变关系的影响不明显,但快速拉伸后的角膜条应力衰减明显变快。结论 兔眼角膜随月龄增加会轻微变硬,而角膜的松弛特性随月龄变化明显。     

人密质骨的撞击实验研究

本文用分离式Hopkinson杆（SHBM）（应变率为7001/s)对人的密度骨进行撞击实验研究,得出了应力-时间、应变-时间、应变率-时间及应力-应变等曲线。用一维波传播理论分析实验数据。结果表明即使在高应变率下,人的密质骨也具有非线性粘弹性材料的特性,据此可得人密质骨的冲击特性可用三参数粘弹性力学模型描述,同时得出了高应变率下,人的密质骨也具有非线性粘弹性材料的特性。据此可得人密质骨的冲击特性可用三参数粘弹性力学模型描述,同时得出院高应变率下人密度骨的极限应力和残余应变值。     

狗颞颌关节盘的流变特性研究

本文把狗的颞颌关节盘分成前、中、后三个区域作单向拉伸、应力松弛及循环加载实验,得出了在不同区域,试件在不同阶跃应变作用下的瞬时弹性响应及平衡模量,应用拟线性粘弹性理论分析实验结果,得出该关节盘软骨不同区域的弹性响应及归一化松弛函数,从而得到它在不同区域一维拉伸时的本构方程。实验表明,理论分析与实验结果吻合较好。     

老龄化自发性高血压模型大鼠与SD大鼠左冠状动脉的应力松弛特性

背景：目前多数研究为正常人尸体和动物动脉血管的应力松弛特性,而老龄化自发性高血压模型大鼠与SD大鼠左冠状动脉应力松弛特性的研究鲜有报道。 目的：对比分析老龄自发性高血压模型大鼠与SD大鼠左冠状动脉应力松弛特性,为高血压致血管损伤修复提供应力松弛指标。 方法：对四五个月龄正常SD雄性大鼠左冠状动脉和老龄自发性高血压模型大鼠左冠状动脉各10个试样在日本岛津电子万能试验机上进行应力松弛实验,模拟人体温在(36.5±0.1) ℃的温度场下以0.05%/s的应变增加速度对试样施加应变,设定时间为7 200 s。采集100个数据,采用归一化分析的方法计算两组试样的归一化应力松弛方程。 结果与结论：两组试样应力松弛曲线是以对数关系变化的,SD组试样7 200 s应变上升量大于自发性高血压模型组,差异有显著性意义(P < 0.05)。可见正常SD大鼠左冠状动脉和老龄自发性高血压模型大鼠左冠状动脉具有不同的应力松弛特性。     

正常与病态股骨头应力松弛特性的对比分析

比较正常股骨头和股骨头坏死后股骨头应力松弛性质,为人工关节研究和髋关节置换术提供应力松弛参数。在日本岛津电子万能试验机上对正常与病态股骨头各8个试样进行应力松弛实验。模拟人体温在36.5℃的温度场下进行实验,以5%/s的应变增加速度对标本施加应变,设定时间为7 200 s,采集100个实验数据。采用三参数模型计算应力松弛方程。观察应力松弛曲线和7 200 s应力松弛量。股骨头在最初600 s变化较快,之后应力缓慢下降,正常组7 200 s应力松弛量为0.31 MPa,病态组7 200 s应力松弛量为0.22 MPa,病态组7 200 s应力松弛量显著低于正常组(P<0.05)。股骨头坏死后打乱了松质骨头骨小梁的正常排列,骨量丢失,从而对应力松弛特性造成影响。应力松弛数据可以定量地说明坏死股骨头应力松弛特性差。     

正常与病态股骨头应力松弛特性的对比分析

比较正常股骨头和股骨头坏死后股骨头应力松弛性质,为人工关节研究和髋关节置换术提供应力松弛参数。在日本岛津电子万能试验机上对正常与病态股骨头各8个试样进行应力松弛实验。模拟人体温在36.5℃的温度场下进行实验,以5%/s的应变增加速度对标本施加应变,设定时间为7 200 s,采集100个实验数据。采用三参数模型计算应力松弛方程。观察应力松弛曲线和7 200 s应力松弛量。股骨头在最初600 s变化较快,之后应力缓慢下降,正常组7 200 s应力松弛量为0.31 MPa,病态组7 200 s应力松弛量为0.22 MPa,病态组7 200 s应力松弛量显著低于正常组(P<0.05)。股骨头坏死后打乱了松质骨头骨小梁的正常排列,骨量丢失,从而对应力松弛特性造成影响。应力松弛数据可以定量地说明坏死股骨头应力松弛特性差。     

气管软骨应力松弛的实验研究

以应力松弛的试验方法研究气管软骨的应力松弛特性,为临床提供气管软骨的应力松弛特性参数。在日本岛津电子万能试验机上对10个软骨进行应力松弛实验,应力松弛实验应变增加速度为50％／min,实验温度为（36．5&#177;0．65）℃,设定实验时间7200s,采集100个实验数据,以一元线性回归分析的方法处理实验数据。结果表明：气管软骨7200s应力松弛量为0．316MPa,7200s时应力松弛曲线基本达到平衡。气管软骨应力松弛曲线是以对数关系变化的．气管软骨为非线性粘弹性材料。     

人眼巩膜归一化松弛函数探讨

本文对软组织材料——巩膜的力学性能进行描述.在单项拉伸状态下,测量了其拟弹性模量、破坏应力及相应的应变值.给出了单向拉伸状态下的应力应变曲线.同时做了常温下的应力松弛实验.测定了巩膜应力和时间相关的不同效应,给出了巩膜的归一化松弛函数和有关参数.     

人体椎间盘的一个力学模型

对人体椎间盘力学性质的深入研究,牦极大地有助于对椎间盘脱出进行治疗和预防。众所周知,椎间盘表现出粘弹性性质,椎间盘中的含水量对于控制材料的松弛特性起重要作用。本文采用从人体椎间盘中得到的试件,进行应力松弛实验。试件取自髓核和两个不同方向纤维环的外层,在不同的湿度下进行实验,得到了松弛控制曲线。根据实验数据,提出了一种定性椎间盘模型。这种模型可以考虑椎间盘的粘弹性性质,并可研究年龄,材料结构变化和含水量等对其性质的影响。结果发现:髓核     

模拟失重对雄性大鼠骨流变特性的测试

目的研究模拟失重对大鼠承重骨流变特性的影响,为航天医学提供模拟失重动物骨流变参数。方法30只Wistar雄性大鼠,随机分为正常对照组15只和头低位30°尾吊组(失重模型组)15只。实验第28天时取两组动物股骨进行压缩应力松弛、蠕变实验。结果得出了正常对照组和失重模型组大鼠股骨压缩应力松弛、蠕变数据和曲线,得出了两组大鼠股骨的归一化应力松弛函数,归一化蠕变函数与曲线,以一元线性回归分析的方法处理实验数据,得出了回归系数a、b与c、d值和归一化应力松弛函数G(t)、归一化蠕变函数J(t)表达式,还得出了两组大鼠股骨应力松弛、蠕变与时间的变化规律。结论失重模型组大鼠股骨应力松弛、蠕变量低于正常对照组。     

模拟腰椎后路间盘摘除植骨与置融合器术T12-S1腰段脊柱粘弹性实验研究

根据国人腰椎的特点，设计研制了一种纯钛腰椎置入融合器，并进行生物力学测试，方法是取18具新鲜成年男性T12－S1腰椎标本,测定完整腰椎（正常组）模拟后路间盘摘除植骨组（对照1组）和模拟后路间盘摘除置入融合器组（对照2组）T12－S1段腰椎 的应力松弛和蠕变－时间曲线及数据。用回归分析的方法处理实验数据，得出了归一化应力松弛函数、蠕变函数及曲线，对后路间盘摘除植骨与置入纯钛融合器对 脊柱稳定性的影响进行分析讨论。     

周期性牵张椎间盘纤维环细胞肌动蛋白骨架的重排

BACKGROUND: When the intervertebral disc is under stress, the hydraulic pressure generated inside the nucleus pulposus makes the annulus fibrosus extend outward and expand, and the annulus collagen fibers are stretched so that the extracellular matrix of annulus fibrosus cells is also under the pressure. In the intervertebral disc, aggrecan is the main component of proteoglycans, matrix metalloproteinase-2 is a major enzyme for extracellular matrix degradation, and tissue inhibitor of metalloproteinase is a multifunctional specific inhibition factor for matrix metalloproteinase activity. There is a mutual regulation between the latter two to keep the homeostasis between them. OBJECTIVE: To investigate the mechanism of cyclic tensile strain in the metabolism of intervertebral disc annulus matrix. METHODS: Rat anulus fibrosus cells were subjected to 2% or 10% cyclic tensile strain at 1.0 Hz for 2 and 12 hours using Flexcell4000 tension system. Then cells were collected and cultured in conditioned medium for gene and protein detection. Real-time quantitative PCR was used to detect mRNA expression of aggrecan, matrix metalloproteinases-2 and tissue inhibitor of metalloproteinase-2. Gelatin zymography was used to detect matrix metalloproteinases-2 activity. RESULTS AND CONCLUSION: The use of 2% cyclic tensile strain had no obvious effect on the stress fiber of actin cytoskeleton, whereas actin cytoskeleton was depolymerized in response to 10% cyclic tensile strain. The 2% cyclic tensile strain raised the expression of Aggrecan at 12 hours; whereas raised the matrix metalloproteinases-2 and tissue inhibitor of metalloproteinase-2 at 2 hours, both of which were in homeostasis; matrix metalloproteinases-2 activity had no significant changes. 10% cyclic tensile strain had no effect on the mRNA expression of Aggrecan. No matter stretching 2 or 12 hours, the matrix metalloproteinases-2 was up-regulated, and the tissue inhibitor of metalloproteinase-2 was down-regulated, both of which were not in balance. Moreover, the matrix metalloproteinases-2 activity was not significantly changed. These findings indicate that the mRNA expressions of Aggrecan, matrix metalloproteinases-2 and tissue inhibitor of metalloproteinase-2 alter in response to cyclic tensile strain in rat anulus fibrosus cells, and the tensile strain induces different mechano-responses in the actin cytoskeleton.      

腰椎4、5间盘纤维环纤维层力学性能的实验研究

测试成人腰椎间盘纤维环纤维层的力学性能。用显微外科技术将纤维环逐层分离,每层纤维平均分成8个测点,每层每测点处按纤维走向切取5个试件,长度l=15~20mm,宽b=1~1.5mm,厚t=0.1~0.5mm。进行拉伸实验测得应力-应变曲线,并给出拟合曲线及方程,得出弹性模量、破坏应变、破坏应力、测点处的力学性能参数和方程。测试结果表明:各测点处,沿径向,由外向内弹性模量皆随层数的增加,不断变小;每层纤维弹性模量由前侧向后侧逐渐变小;破坏应力由外层向内层线性递减;破坏应变外部9层随层数增加略有提高,9层以后基本上为一常数(0.34±0.14)。可见,腰椎间盘纤维环纤维具有特殊的力学性能,与其功能相适应,与腰椎疾病的发生有密切的关系。     

A three-dimensional nonlinear finite element analysis of the mechanical behavior of tissue engineered intervertebral discs under complex loads

The use of tissue-engineering method holds great promise for treating degenerative disc disease [Gan JC, Ducheyne P, Vresilovic E, Shapiro IM. J Biomed Mater Res 2000; 51(4): 596-604]. This concept typically implies that nucleus pulposus (NP) cells are seeded on a scaffold, while the NP tissue is regenerated. Such hybrid implant is inserted into the host intervertebral disc. Because the success of a tissue engineering approach depends on maintenance or restoration of the mechanical function of the intervertebral disc, it is useful to study the initial mechanical performance of the disc after implantation of the hybrid. A three-dimensional finite element model (FEM) of the L2-L3 disc-vertebrae unit has been analyzed. The model took into account the material nonlinearities and it imposed different and complex loading conditions. In this study, we validated the model by comparison of its predictions with several sets of experimental data; we determined the optimal Young's modulus as well as the failure strength for the tissue-engineered scaffold under different loading conditions; and we analyzed the effects of implanted scaffold on the mechanical behavior of the intervertebral disc. The results of this study suggest that a well-designed tissue-engineered scaffold preferably has a modulus in the range of 5-10 MPa and a compressive strength exceeding 1.67 MPa. Implanted scaffolds with such properties can then achieve the goal of restoring the disc height and distributing stress under different loading conditions.     

起床过程中腰椎应力动力学响应

目的揭示起床过程中腰椎间盘的应力响应特征。方法根据实验数据,建立并验证考虑材料非线性和各向异性属性的全腰椎有限元模型,在此基础上模拟并计算人体从仰卧、起身、左转到坐在床沿完整过程中腰椎主要结构的应力分布和动态变化情况。结果起床过程中腰椎间盘纤维环、髓核及终板的应力大小和分布不断变化,各节段的应力集中在背侧,L4~5上最大,应力峰值出现在当躯干从仰卧起转过35°~62°之时,分别是坐稳时的3倍、仰卧时的17倍。结论 L4~5椎间盘后侧是损伤和退变高发区,在日常活动中实际承受的应力可能要比以往按静态测算的应力更高,影响范围也更大。动力学模拟能更全面深入地了解腰椎间盘的负载特点,为防治相关腰椎疾病提供科学依据。     

人眼角膜黏弹性实验研究

对正常国人6具新鲜尸体8个眼角膜标本进行单向拉伸实验和拉伸应力松弛、蠕变实验。得出了人眼角膜拉伸最大载荷、伸长比、张应力、应变、拟弹性模量。还得出了人眼角膜的应力松弛、蠕变数据和曲线。对应力松弛、蠕变实验数据进行归一化处理,得出了归一化应力松弛函数、蠕变函数及曲线。对应力松弛、蠕变实验数据进行回归分析,得出了回归系数。对人眼角膜应力、应变数据以多项式,用最小二乘法进行拟合,得出了其应力应变关系公式及曲线,建立了人眼角膜的松弛函数k(λ,t)=G(t)T(e)λ的表达式,得出了一些重要结论。     

A stimulation unit for the application of mechanical strain on tissue engineered anulus fibrosus cells: a new system to induce extracellular matrix synthesis by anulus fibrosus cells dependent on cyclic mechanical strain

A bioreactor system consisting of a multifunctional stimulation unit and common 6-well culture plate is introduced to activate extracellular matrix synthesis in intervertebral disc cells due to cyclic mechanical strain. The developed stimulation unit is sterilizable and reusable. It is viable for cultivation and mechanical stimulation of cartilage tissue and tissue engineered cell matrix constructs in combination with the common 6-well culture plate. The custom made device allows long-term cultivations in batch- or continuous operation mode. Manual handling and thereby the risk of contamination is reduced. Sampling, changing the medium, and addition of supplements are easily performed from the connected conditioning vessel. This bioreactor system enables stimulation of different samples independently during one run. For the work presented here anulus fibrosus cells from pigs were taken and immobilized in agarose to obtain three-dimensional cell matrix constructs. Over a period of 14 days the constructs were subjected to 10% compression under cyclic mechanical pressure with a frequency of 0.1 Hz. Afterwards the constructs were biochemically examined for hydroxyproline and sulphated glycosaminoglycanes. These proven constituents of extracellular matrix were found to be released depending on the applied compressive strain.     

A Surface–Regional and Freeze–Thaw Characterization of the Porcine Temporomandibular Joint Disc

The temporomandibular joint (TMJ) disc is a central element in several TMJ disorders. Tissue-engineered TMJ disc replacements may alleviate discomfort associated with TMJ disorders; however, prior to developing a replacement, a thorough understanding of the native disc must be attained. Toward this end, we developed an unconfined compression, incremental stress relaxation viscoelastic model which simultaneously incorporates the strain increment magnitude and total deformation in the stress relaxation solution. This multiple strain step model was fit to stress relaxation data from (i) 80 test sites from eight porcine TMJ discs for the purposes of a surface–regional characterization and (ii) 30 test sites from five porcine TMJ discs for the purposes of a freeze–thaw characterization. The model estimated viscoelastic parameters accurately and surface–regional variations were detected throughout the TMJ disc. Regionally, the medial and anterior regions have the largest relaxation moduli, and the posterior and anterior regions have the largest instantaneous moduli. The inferior surface was found to have higher instantaneous modulus values than the superior surface. Furthermore, material properties were retained over five freeze–thaw cycles. The results of this study allow for the creation of design and validation criteria for future engineering efforts and shed light on the disc’s role in TMJ function and dysfunction.     

Regional variations in the viscoelastic compressive properties of the temporomandibular joint disc and implications toward tissue engineering

Evidence from experimental and finite element studies have shown that the temporomandibular joint disc is heavily loaded during normal physiological function. Several studies have been carried out to investigate the response of the disc to tensile and static compressive forces. However, there is limited information that elucidates the dynamic characteristics of the disc under in vivo loading conditions. These investigations assessed the effect of physiologically relevant applied strain amplitudes and frequencies to determine regional mechanical properties of the disc. Cyclic tests on porcine TMJ discs were carried out over a period of 15 cycles, and the resultant compressive moduli and energy dissipation properties of the disc were reported. Results showed that modulus values were more dependent on strain amplitude than on frequency, and modulus values exhibited a strong regional variation. Clear hysteresis loops were evident in each set of testing parameters, and the only statistically significant regional variation in energy dissipation was between the central and medial regions. From these investigations, a more detailed understanding of the spatial mechanical properties of the TMJ disc has been achieved under physiologically relevant loading conditions. Combined with studies on other loading modalities of the disc, these results will serve as a benchmark for future TMJ disc tissue engineering endeavors.     

Assessing viscoelastic properties of chitosan scaffolds and validation with cyclical tests

We evaluated and modeled the viscoelastic characteristics of chitosan and chitosan-gelatin scaffolds prepared using a freeze-drying technique. Chitosan and chitosan-gelatin solutions (0.5 and 2 wt.%) were frozen at -80°C and freeze-dried. Using the scaffolds, uniaxial tensile properties were evaluated under physiological conditions (hydrated in phosphate buffered saline at 37°C) at a cross-head speed of 0.17 mms(-1) (10 mm min(-1)). From the break strain, the limit of strain per ramp was calculated to be 5% and the samples were stretched at a strain rate of 2.5%s(-1). The ramp-and-hold type of stress-relaxation test was performed for five successive stages. Chitosan and chitosan-gelatin showed nearly 90% relaxation of stress after each stage. The relaxation behavior was independent of the concentration of chitosan and gelatin. Also, changes in the microstructure of the tested samples were evaluated using an inverted microscope. The micrographs acquired after relaxation experiments showed orientation of pores, suggesting the retention of the stretched state even after many hours of relaxation. Based on these observations, two models (i) containing a hyper-elastic spring (containing two parameters) and (ii) retaining pseudo-components (containing three parameters) were developed in Visual Basic Applications accessed through MS Excel. The models were used to fit the experimental stress-relaxation data and the parameters obtained from modeling were used to predict their respective cyclic behaviors, which were compared with cyclical experimental results. These results showed that the model could be used to predict the cyclical behavior under the tested strain rates. The model predictions were also tested using cyclic properties at a lower strain rate of 0.0867%s(-1) (5%min(-1)) for 0.5 wt.% scaffolds but the model could not predict cyclical behavior at a very slow rate. In summary, the pseudo-component modeling approach can be used to model the sequential strain-and-hold stage and predict cyclical properties for the same strain rate.