The inflation response of the posterior bovine sclera

An in vitro inflation test method was developed to characterize the mechanical behavior of the bovine posterior sclera. The method used digital image correlation to provide a spatially resolved, full-field deformation map of the surface of the posterior sclera in response to controlled pressurization. A series of experiments were performed in the range of 2–6 kPa (15–45 mmHg) to characterize the load–unload displacement response at various pressure rates and the time-dependent displacement response at different applied pressures. The magnitude of the displacement was largest in the peripapillary region, mainly between the apex and the optic nerve head. Further, the results showed that bovine scleral tissue exhibited nonlinear and viscoelastic behavior characterized by a rate-dependent displacement response, hysteresis during unloading and creep. The creep rate was insensitive to the applied pressure, suggesting that the tissue can be modeled as a quasilinear viscoelastic material in the physiological pressure range of 2–6 kPa.     

Pure epidural cavernous hemangioma of the cervical spine that presented with an acute sensory deficit caused by hemorrhage

Pure epidural cavernous hemangioma of the spine without vertebral involvement is rare. Due to the slow growth of this lesion, the most common symptoms are chronic pain, myelopathy, and radiculopathy. In our case, the patient complained of an acute onset sensory deficit of the C4 dermatome. An MRI revealed an epidural mass with an acute hematoma. Here, we report a case of a pure epidural cavernous hemangioma that presented with acute neurologic symptoms caused by intralesional hemorrhage and an acute epidural hematoma, which were demonstrated on the patient's MRI.     

Inverse Parameter Fitting of Biological Tissues: A Response Surface Approach

In this paper, we present the application of a semi-global inverse method for determining material parameters of biological tissues. The approach is based on the successive response surface method, and is illustrated by fitting constitutive parameters to two nonlinear anisotropic constitutive equations, one for aortic sinus and aortic wall, the other for aortic valve tissue. Material test data for the aortic sinus consisted of two independent orthogonal uniaxial tests. Material test data for the aortic valve was obtained from a dynamic inflation test. In each case, a numerical simulation of the experiment was performed and predictions were compared to the real data. For the uniaxial test simulation, the experimental targets were force at a measured displacement. For the inflation test, the experimental targets were the three-dimensional coordinates of material markers at a given pressure. For both sets of tissues, predictions with converged parameters showed excellent agreement with the data, and we found that the method was able to consistently identify model parameters. We believe the method will find wide application in biomedical material characterization and in diagnostic imaging.     

负压吸附式角膜夹持器设计与吸附参数仿真研究

目的 提出一种通过负压将角膜吸附提升至合适缝合深度的高度后进行缝合的方案,并对吸附参数进行仿真研究。方法 根据手术要求,设计负压吸附式角膜夹持器。建立不同长度、深度及位置的直型伤口角膜的吸附仿真模型,针对6种负压条件,利用流固耦合分析对负压吸附角膜过程进行仿真,求解角膜变形、应力及吸附力。在PDMS薄膜上测量6种负压条件所产生的吸附力,并与仿真结果对比分析。同时在离体猪眼球上进行吸附实验,评估所设计角膜夹持器的操作安全性。结果 -70～-40 kPa负压下,所有仿真模型角膜最大变形均大于角膜缝合深度要求的伤口最大提升高度。最大变形随负压减小而增大。所有仿真模型角膜最大应力均小于角膜基质破坏强度(5 MPa)。吸附力仿真值相对实验值比较吻合。负压高于-70 kPa时所设计夹持器进行吸附操作时角膜未出现破裂。结论 该角膜夹持器在-70～-40 kPa负压下能实现角膜缝合深度要求,且可通过改变负压精确调控缝合深度,高于-70 kPa时进行吸附操作不损伤角膜组织。在该角膜夹持器辅助下,医生可使用直针完成角膜缝合操作,降低临床操作的难度。     

Frequency-dependent viscoelastic parameters of mouse brain tissue estimated by MR elastography

Viscoelastic properties of mouse brain tissue were estimated non-invasively, in vivo, using magnetic resonance elastography (MRE) at 4.7 T to measure the dispersive properties of induced shear waves. Key features of this study include (i) the development and application of a novel MR-compatible actuation system which transmits vibratory motion into the brain through an incisor bar, and (ii) the investigation of the mechanical properties of brain tissue over a 1200 Hz bandwidth from 600-1800 Hz. Displacement fields due to propagating shear waves were measured during continuous, harmonic excitation of the skull. This protocol enabled characterization of the true steady-state patterns of shear wave propagation. Analysis of displacement fields obtained at different frequencies indicates that the viscoelastic properties of mouse brain tissue depend strongly on frequency. The average storage modulus (G') increased from approximately 1.6 to 8 kPa over this range; average loss modulus (G″) increased from approximately 1 to 3 kPa. Both moduli were well approximated by a power-law relationship over this frequency range. MRE may be a valuable addition to studies of disease in murine models, and to pre-clinical evaluations of therapies. Quantitative measurements of the viscoelastic parameters of brain tissue at high frequencies are also valuable for modeling and simulation of traumatic brain injury.     

外伤后脑血肿对颅内压分布的力学分析研究

目的　根据患者CT和颅内压数据,建立外伤性脑损伤的有限元模型,分析脑血肿对颅内压产生的压力响应。 方法　采用成人头部有限元模型（GHBMC）与气体分子动力学分析脑血肿膨胀与颅内压增高的关系,提取并折叠血肿,置入有限元模型中相对应的位置,根据CT图像和颅内压值,加入肿胀曲线,进行模拟计算,得到各个部分的脑组织压力分布云图、脑组织应变的分布云图,计算脑疝多发区域的脑组织压力差。 结果　有限元模型中的压力值、中线偏离量与临床病人脑室型探头压力、CT图像中线的吻合度较好,误差率分别为4%和2%。模拟结果显示,在左侧颞枕叶矢状位上,左侧基底节区血肿病例大脑镰下方、小脑幕切迹后部压力差不显著,分别为1400 Pa和1320 Pa。但幕上颞叶压力明显大于小脑小叶的压力,分别为2504 Pa和1360 Pa。小脑前叶与后环池的压力无明显差异。左侧脑血肿患者小脑幕比右侧脑血肿患者具有更大的等效应变。 结论　左侧患者额颞基底节区的血肿更有可能导致小脑幕切迹疝。而右侧患者的脑血肿导致的压力被小脑幕的应变代偿,脑疝风险因此下降。通过本研究计算脑疝易形成区域的压力差,可更好地理解血肿造成的颅内压分布对激发脑损伤的影响,为损伤的预后提供力学依据。     

外伤后脑血肿对颅内压分布的力学分析研究

目的　根据患者CT和颅内压数据，建立外伤性脑损伤的有限元模型，分析脑血肿对颅内压产生的压力响应。 方法　采用成人头部有限元模型（GHBMC）与气体分子动力学分析脑血肿膨胀与颅内压增高的关系，提取并折叠血肿，置入有限元模型中相对应的位置，根据CT图像和颅内压值，加入肿胀曲线，进行模拟计算，得到各个部分的脑组织压力分布云图、脑组织应变的分布云图，计算脑疝多发区域的脑组织压力差。 结果　有限元模型中的压力值、中线偏离量与临床病人脑室型探头压力、CT图像中线的吻合度较好，误差率分别为4%和2%。模拟结果显示，在左侧颞枕叶矢状位上，左侧基底节区血肿病例大脑镰下方、小脑幕切迹后部压力差不显著，分别为1400 Pa和1320 Pa。但幕上颞叶压力明显大于小脑小叶的压力，分别为2504 Pa和1360 Pa。小脑前叶与后环池的压力无明显差异。左侧脑血肿患者小脑幕比右侧脑血肿患者具有更大的等效应变。 结论　左侧患者额颞基底节区的血肿更有可能导致小脑幕切迹疝。而右侧患者的脑血肿导致的压力被小脑幕的应变代偿，脑疝风险因此下降。通过本研究计算脑疝易形成区域的压力差，可更好地理解血肿造成的颅内压分布对激发脑损伤的影响，为损伤的预后提供力学依据。     

Intracranial Pressure Response to Non-Penetrating Ballistic Impact: An Experimental Study Using a Pig Physical Head Model and Live Pigs

This study was conducted to characterize the intracranial pressure response to non-penetrating ballistic impact using a "scalp-skull-brain" pig physical head model and live pigs. Forty-eight ballistic tests targeting the physical head model and anesthetized pigs protected by aramid plates were conducted with standard 9 mm bullets at low (279-297 m/s), moderate (350-372 m/s), and high (409-436 m/s) velocities. Intracranial pressure responses were recorded with pressure sensors embedded in similar brain locations in the physical head model and the anesthetized pigs. Three parameters of intracranial pressure were determined from the measured data: intracranial maximum pressure (P_max), intracranial maximum pressure impulse (PI_max), and the duration of the first positive phase (PPD). The intracranial pressure waves exhibited blast-like characteristics for both the physical model and l live pigs. Of all three parameters, P_max is most sensitive to impact velocity, with means of 126 kPa (219 kPa), 178 kPa (474 kPa), and 241 kPa (751 kPa) for the physical model (live pigs) for low, moderate, and high impact velocities, respectively. The mean PPD becomes increasingly short as the impact velocity increases, whereas PI_max shows the opposite trend. Although the pressure parameters of the physical model were much lower than those of the live pigs, good correlations between the physical model and the live pigs for the three pressure parameters, especially P_max, were found using linear regression. This investigation suggests that P_max is a preferred parameter for predicting the severity of the brain injury resulting from behind armor blunt trauma (BABT).     

The effect of devitalized trabecular bone on the formation of osteochondral tissue-engineered constructs

In the current study, evidence is presented demonstrating that devitalized trabecular bone has an inhibitory effect on in vitro chondral tissue development when used as a base material for the tissue-engineering of osteochondral constructs for cartilage repair. Chondrocyte-seeded agarose hydrogel constructs were cultured alone or attached to an underlying bony base in a chemically defined medium formulation that has been shown to yield engineered cartilaginous tissue with native Young's modulus (E(Y)) and glycosaminoglycan (GAG) content. By day 42 in culture the incorporation of a bony base significantly reduced these properties (E(Y)=87+/-12kPa, GAG=1.9+/-0.8%ww) compared to the gel-alone group (E(Y)=642+/-97kPa, GAG=4.6+/-1.4%ww). Similarly, the mechanical and biochemical properties of chondrocyte-seeded agarose constructs were inhibited when co-cultured adjacent to bone (unattached), suggesting that soluble factors rather than direct cell-bone interactions mediate the chondro-inhibitory bone effects. Altering the method of bone preparation, including demineralization, or the timing of bone introduction in co-culture did not ameliorate the effects. In contrast, osteochondral constructs with native cartilage properties (E(Y)=730+/-65kPa, GAG=5.2+/-0.9%ww) were achieved when a porous tantalum metal base material was adopted instead of bone. This work suggests that devitalized bone may not be a suitable substrate for long-term cultivation of osteochondral grafts.     

Short-term fatigue testing can predict medium-term pericardium behaviour

The medium-term fatigue behaviour of calf pericardium (similar to the one used to manufacture cardiac bioprostheses valve leaflets) has been studied. 96 samples were tested under fatigue subjecting them to biaxial stress at 1 Hz frequency for 5000 cycles, in 4 series of 24 samples, at several supra-physiological mean pressures and pressure amplitudes. Short-term damage parameters such as the accumulated energy consumption in 10 cycles (E10) and medium-term ones after 5000 cycles like total energy consumption (Et) and maximum displacement of the membrane (Dt) have been evaluated. E10 showed exponential growing tendency with pressure and linear tendency with pressure amplitude when only one parameter curve was plotted. Similar results were found when analysing Et and Dt. Linear correlation models were established between E10 and Et and E10 and Dt. Similar results were achieved in the four series, with excellent determination coefficients. The results confirm that the fatigue behaviour from the very first cycles of the test can predict the medium-term behaviour of the tissue by means of measurement of suitable damage markers. The tendencies observed between the parameters seem to show that the results could have been the same ones if the test had been performed at physiological pressures and amplitudes. This work opens the door to a non-destructive test of the tissue prior to employ it to manufacture valve leaflets.     

皮肤层在周期性载荷作用下的动态响应

根据软组织的二相混合物理论，将皮肤及皮下软组织模拟为一均匀的二相多孔弹性体，结合使用解析法和数值方法求解皮肤层在表面周期性载荷作用下的生物力学响应。     

Biaxial failure properties of planar living tissue equivalents

Quantification of the mechanical properties of living tissue equivalents (LTEs) is essential for assessing their ultimate functionality as tissue substitutes, yet their delicate nature makes failure testing problematic. For this study, we evaluated the validity of using an inflation device for quantifying the biaxial tensile failure properties of extremely delicate fibroblast-populated collagen gels (CGs) and fibrin gels (FGs). Small samples were circularly clamped and then inflated until rupture. Each sample assumed an approximately spherical shape and burst at its center indicating effective clamping. After two weeks in culture, all LTEs tested were fragile, but the FGs were significantly stronger and more extensible than the CGs (ultimate tensile strength 6.0 kPa +/- 2.0 kPa vs. 2.8 kPa +/- 0.7 kPa; failure strain 3.5 +/- 0.9 vs. 0.26 +/- 0.05, n = 4). After an additional 11 days of culture, the strength of the FGs increased significantly (26.5 kPa +/- 12.7 kPa), and the extensibility decreased (1.9 +/- 0.8, n = 3). This study demonstrates that subtle differences in the properties of LTEs can be measured using inflation methods with minimal sample handling and without having to grow the tissues into anchors or cut the specimens.     

Two-layered quasi-3D finite element model of the oesophagus

Analysis of oesophageal mechanoreceptor-dependent responses requires knowledge about the distribution of stresses and strains in the layers of the organ. A two-layered and a one-layered quasi-3D finite element model of the rat oesophagus were used for simulation. An exponential pseudo-strain energy density function was used as the constitutive equation in each model. Stress and strain distributions at the distension pressures 0.25 and 1.0 kPa were studied. The stress and strain distributions depended on the wall geometry. In the one-layered model, the stress ranged from -0.24 to 0.38 kPa at a pressure of 0.25 kPa and from -0.67 to 2.57 kPa at a pressure of 1.0 kPa. The stress in the two-layered model at the pressure of 0.25 and 1.0 kPa varied from -0.52 to 0.64 kPa and from -1.38 to 3.84 kPa. In the two-layered model, the stress was discontinuous at the interface between the muscle layer and the mucosa-submucosa layer. The maximum stress jump was 1.67 kPa at the pressure of 1.0 kPa. The present study provides a numerical simulation tool for characterising the mechanical behaviour of a multi-layered, complex geometry organ.     

硬脑膜外血肿术后硬脑膜造瘘的疗效观察

目的探讨硬脑膜外血肿清除术后,硬脑膜造瘘引流脑脊液的疗效观察。方法回顾性分析商丘市第一人民医院神经外科78例硬脑膜外血肿术后硬脑膜造瘘患者的临床资料,根据患者的意识状态及头颅CT检查结果,并对适应证选择、预后进行讨论。手术方法是将骨窗野硬脑膜切开4～5个0.5～0.8cm的小孔,并通过引流管使脑脊液流出体外。结果78例硬脑膜外血肿量在30ml以上的患者,未发生脑脊液漏。术后4～11d复查头颅CT,65例中线移位基本恢复;10例仍有脑积水存在;3例侧脑室轻度受压。结论硬脑膜外血肿术后造瘘引流脑脊液,能明显地降低术后颅内压,减轻脑组织的继发性损害,避免了去骨瓣手术,提高了患者生存质量。     

A new acellular vascular prosthesis as a scaffold for host tissue regeneration

OBJECTIVE: In situ tissue engineering using acellular xenografts is a new approach to autologous tissue regeneration. In the present study, we analyzed a new regeneration scaffold comprised of xenogenic acellular vessels in a dog model. DESIGN OF STUDY AND RESULTS: Xenogenic vascular conduits of porcine carotid arteries were acellularized by a 48-hour detergent incubation to extract all the cell components of the graft. The acellularisation procedure resulted in a complete removal of all cells. After this procedure, heparinization was performed sequentially to induce antithrombogenicity in the graft. The burst pressure of the graft was tested. The bursting pressure of the fresh vessels was 2.83 +/- 0.56 x 10(3) mmHg (377 +/- 75kPa, n = 6). After detergent treatment, the bursting pressure of the grafts was 2.50 +/- 0.48 x 10(3) mmHg (334 +/- 63 kPa, n = 6); after heparinization, it was 3.44 +/- 0.38 x 10(3) mmHg (459 +/- 51 kPa, n = 5). In vivo function was tested in a dog model by transplantation to the abdominal artery. By 18 weeks, endothelial cells were aligned as in normal, healthy artery over the surface of the entire graft. Fibroblasts and macrophages had infiltrated the graft from both inside and outside. The neointima contained normal layers of smooth muscle cells, which were identified by anti alpha-smooth muscle fiber antigen staining. CONCLUSIONS: The acellular heparinized xenograft has sufficient mechanical properties and was successfully replaced with host tissue, and is thus a promising new type of vascular prosthesis.     

Low-frequency viscoelastic properties of canine femoral artery in vivo.

Mechanical properties of the canine femoral artery in vivo are measured as a function of frequency (0.0025--0.1 Hz) and as a function of mean pressure (10--16 kPa). Sinusoidal pressure variations are generated with a servo-controlled occluder system. The absolute value of the Young's modulus increases with mean pressure (E = 0.63 X 10(5) exp(0.211P)-N.m-2) at 0.05 Hz; where P is pressure. At heart rate frequencies (average value 2.22 Hz) this relation is: E = 1.25 X 10(5) exp(0.175P) N.m-2. The phase angle of the Young's modulus is independent of pressure at both frequencies. At 0.05 Hz we found: phi = 0.189 - 0.00788 P radians and at 2.22 Hz: phi = 0.0723 + 0.000428 P. The slope of both lines is not significantly different from zero slope (alpha = 0.05). Frequency dependence is studied at a constant pressure level (Pr, average value 14.3 kPa) just below the animals' mean pressure levels (average value 15.9 kPa). The frequency behavior of the elastic modulus is fitted with a function with two poles and two zeros (poles at 0.003 and 0.038 Hz; zeros at 0.0022 and 0.03 Hz).     

Biomechanical and biochemical characteristics of a human fibroblast-produced and remodeled matrix

We report on a culture method for the rapid production of a strong and thick natural matrix by human cells for tissue engineering applications. Dermal fibroblasts were cultured for three weeks at high density on porous substrates in serum-containing or chemically defined media. The mechanical and biochemical properties of the resulting cell-derived matrix (CDM) were compared to those of standard fibroblast-populated collagen and fibrin gels and native human skin. We found that the ultimate tensile strength of CDM cultured in our chemically defined media (313+/-8.7 kPa) is significantly greater than for collagen gels (168+/-39.3 kPa), fibrin gels (133+/-8.0 kPa) and CDM cultured with serum (223+/-9.0 kPa), but less than native skin (713+/-55.2 kPa). In addition to the biomechanics, this *CDM is also biochemically more similar to native skin than the collagen and fibrin gels in terms of all parameters measured. As *CDM is produced by human cells in a chemically defined culture medium and is mechanically robust, it may be a viable living tissue equivalent for many connective tissue replacement applications requiring initial mechanical stability yet a high degree of biocompatibility.     

Pulmonary clearance of inhaled [99Tcm]DTPA: effects of ventilation pattern

While a rise in lung volume is known to increase the pulmonary clearance of technetium-99m-labelled dietylene triamine pentaacetate ([99Tcm]DTPA), little interest has been focused on the effects of changes in ventilation frequency, tidal volume and airway pressure. We studied adult, anaesthetized and intubated rabbits during three ventilation patterns (VP) using pressure controlled ventilation (ServoVentilator 900C). VP was either deep slow (f = 20 min-1, tidal volume (VT) = 30 +/- 4 ml kg-1 and positive end-expiratory pressure (PEEP) = 0.2 kPa [VP 20/0.2, n = 8]) or rapid shallow (f = 80 min-1, VT = 11 +/- 2 ml kg-1 and PEEP = 0.2 or 0.4 kPa [VP 80/0.2, n = 6 and VP 80/0.4, n = 6]). The mean airway pressure was similar at VP 20/0.2 and VP 80/0.4. During administration of [99Tcm]DTPA aerosol all animals were ventilated under the same conditions (f = 40 min-1 and PEEP = 0.2 kPa). The pulmonary clearance rate expressed as the half-life time (T1/2) of [99Tcm]DTPA was at VP 80/0.2 = 113 +/- 31 min, at VP 80/0.4 = 70 +/- 24 min (P less than 0.01 compared to VP 80/0.2) and at VP 20/0.2 = 36 +/- 18 min (P less than 0.001 compared to VP 80/0.2 and P less than 0.01 compared to VP 80/0.4). We conclude that the pulmonary clearance of [99Tcm]DTPA increases (1) during rapid shallow ventilation when PEEP is increased from 0.2 to 0.4 kPa; (2) during deep slow ventilation relative to rapid shallow ventilation even when the mean airway pressure is similar.     

喷气试验中角膜生物力学效应影响因素的有限元分析

目的:研究喷气试验中眼内压、喷气压力以及巩膜材料对角膜生物力学效应的影响。方法:基于全眼三维模型及轴对称的喷气模型进行有限元分析,根据角膜前表面位移云图结果,结合曲面拟合等方法,分析角膜形态学参数变化,定量分析眼内压、喷气压力以及巩膜材料对角膜生物力学效应的影响。结果:当喷气压力峰值以及巩膜刚度一定,改变眼内压时,眼内压为24 mmHg相对于12 mmHg时的最大凹陷角膜顶端位移减少13%,角膜前表面反向曲率半径增加7.3%;眼内压以及巩膜刚度一定,改变喷气压力时,喷气压力峰值为60 kPa相对于20 kPa时的最大凹陷角膜顶端位移增加2.1倍,角膜前表面反向曲率半径减小0.68倍;眼内压以及喷气压力峰值一定,巩膜刚度为基准3倍相对于1/3倍时的最大凹陷角膜顶端位移减少26.8%。结论:角膜形变是角膜生物力学特性的反映,是由眼内压、角膜与巩膜材料以及外力作用共同决定,当其中任一参数发生变化,则影响角膜的生物力学效应。     

The effects of a functional elbow brace on medial joint stability: a case study

Medical elbow ligament sprains in athletics can be traumatic and disabling. In this case report, we outline the effect of a prototype functional elbow brace on joint stability in a female collegiate javelin thrower with an ulnar collateral ligament sprain. A valgus force to both elbows was applied using graded stress radiography (Telos GA-II/E stress device) at 0, 5, 10, and 15 kiloPascals (kPa) of pressure. The increase in gap width between the coronoid process and the medial epicondyle was measured from anteroposterior radiographs to determine medial displacement. The brace resulted in less displacement in both injured and noninjured ulnar collateral ligament; injured ulnar collateral ligament demonstrated greater displacement regardless of condition. The brace restored medial stability to the elbow joint by 49%, 38%, and 35% at 5, 10, and 15 kPa of pressure, respectively. The application of the brace may be useful in athletes with ulnar collateral ligament injuries.