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排序方式: 共有8134条查询结果,搜索用时 15 毫秒
41.
Dynamic Mechanical Conditioning of Collagen-Gel Blood Vessel Constructs Induces Remodeling In Vitro 总被引:11,自引:0,他引:11
Dynamic mechanical conditioning is investigated as a means of improving the mechanical properties of tissue-engineered blood vessel constructs composed of living cells embedded in a collagen-gel scaffold. This approach attempts to elicit a unique response from the embedded cells so as to reorganize their surrounding matrix, thus improving the overall mechanical stability of the constructs. Mechanical conditioning, in the form of cyclic strain, was applied to the tubular constructs at a frequency of 1 Hz for 4 and 8 days. The response to conditioning thus evinced involved increased contraction and mechanical strength, as compared to statically cultured controls. Significant increases in ultimate stress and material modulus were seen over an 8 day culture period. Accompanying morphological changes showed increased circumferential orientation in response to the cyclic stimulus. We conclude that dynamic mechanical conditioning during tissue culture leads to an improvement in the properties of tissue-engineered blood vessel constructs in terms of mechanical strength and histological organization. This concept, in conjunction with a proper biochemical environment, could present a better model for engineering vascular constructs. © 2000 Biomedical Engineering Society.
PAC00: 8719Rr, 8714Ee, 8718-h, 8768+z 相似文献
42.
N. A. T. Lusamvuku P. Aubineau R. Sercombe 《Medical & biological engineering & computing》1980,18(5):643-649
A new method is described for simultaneous measurements of electrical and mechanical activity in an intact segment of a small
artery (outside diameter 0·3–0·5 mm). A 7–9 mm segment of rabbit middle-cerebral artery was ligated on a Teflon tube connected
to a perfusion circuit. The presence of a plug in the tube, flanked by two orifices, forced the physiological solution to
flow in the annular space between the tube and the artery wall. Physiological pressures could thus be attained at low rates
of flow, and the pressure, measured upstream, was significantly modifed by the slightest constriction or dilatation of the
vascular segment. Electrical recording with glass microelectrodes was performed on a short immobilised portion of the artery.
The artery and tube were bathed in a physiological solution at 38°C, but perfusing and incubating solutions did not mix. Spontaneous
electrical and mechanical activity of middle cerebral arteries is described, together with modifications induced by vasoactive
agents. 相似文献
43.
Drawn gelatin films with improved mechanical properties 总被引:4,自引:0,他引:4
Chain anisotropic distribution in gelatin films has been obtained by uniaxial stretching at constant relative humidity, followed by air drying and successive cross-linking with glutaraldehyde. The drawn samples have been characterized by mechanical tests, differential scanning calorimetry and scanning electron microscopy. The Young’s modulus, E, and the stress at break, σb, increase linearly with the draw ratio and reach values which are about five times those characteristic of undrawn samples. Furthermore, on stretching the alignment of the gelatin strands along the direction of deformation increases while the thickness of the layers decreases significantly. The renaturation level, that is the fraction of gelatin in a collagen-like structure, has been calculated as the ratio between the melting enthalpy of gelatin samples and that of tendon collagen. The results indicate that the improvement of mechanical properties achieved by drawn gelatin is closely related to the renaturation level. The experimental approach utilized to induce segmental orientation in gelatin films, allows to obtain anisotropic materials with improved mechanical properties in the direction of deformation, and can be usefully applied in the preparation of biomaterials. 相似文献
44.
Pietro E. di Prampero Urs Boutellier Anouk Marguerat 《Pflügers Archiv : European journal of physiology》1988,412(5):455-461
Mechanical work, ATP, ADP, PC, free creatine and lactate concentrations were determined on IAA poisoned frog sartorii tetanically stimulated in humidified N, at 10°C in isotonic conditions (0.25 or 0.45 P0). Tetanus duration was 0.35 s, number of tetani was varied from 0 (rest) to 25 (exhaustion). The mechanical work performed per mole ATP+PC split (W
P
*
) amounted on the average to 16.7 kJ/mol. It was observed, however, that w
p
*
increased from about 13 to about 24 kJ/mol with decreasing ATP concentration from about 2 (resting value) to about 1 mol/g and that this decrease in ATP was associated with a decrease of the shortening (and relaxation) speed of the muscle to about 30% of the values observed on the first tetanus. It is concluded that the thermodynamic efficiency of muscle contraction, calculated from the ratio of w
P
*
(measured) to the thermodynamic affinity (free energy change) of ATP hydrolysis (estimated) increases from about 0.3 to about 0.5 with decreasing ATP concentration and shortening speed.This work was supported by the Fonds National Suisse de la Recherche Scientifique, Grants 3.332.78 and 3.364.0.82 相似文献
45.
通过电化学共沉积方法制备具有生物活性的有机高聚物/钙磷陶瓷复合膜层。用XPS、SIMS等对复合膜层的化学组分进行表征,证明少量有机高聚物可能在分子层次上掺杂形成有机高聚物/羟基磷灰石复合膜层。对电沉积HAP陶瓷膜层进行微刮痕实验表明,陶瓷膜层与金属基体的结合力得到显著改善。 相似文献
46.
Chouvarda I Maglaveras N Boufidou A Mohlas S Louridas G 《Medical & biological engineering & computing》2003,41(6):609-617
Non-stationary analysis of electrocardiograms (ECGs) using Wigner-Ville distribution is presented. Analysis was performed
on subjects with acute myocardial infarction who had undergone thrombolysis, in Holter recordings of lead V1. The distinction
between successfully and non-successfully thrombolysed patients was evaluated, based on time-frequency features of the Wigner-Ville
transformed ECGs at the sixth hour after lysis. Characteristic parameters were extracted from time-frequency areas, and linear
discriminant analysis was performed on these parameters, leading to a prediction index to distinguish the two classes. Thirteen
features were found statistically significant by t-test and were used for the classification with linear modelling. Out of
these features, four corresponded to frequencies lower than 25 Hz and higher than 50 Hz for, roughly, the QRS complex, five
features corresponded to all the frequency bands of, roughly, the ST area, and the last four features corresponded to the
T-wave. The feature-vector used in linear modelling was iteratively generated, and the iterative prediction found all 18 features
significant. The iterative method resulted in better classification than that of the standard statistical procedure (3.8%
error against 18.1% with the classic method). The evolution of the prediction index with time for the first 12 h was different
for the successfully and non-successfully thrombolysed groups. Specifically, in the successful thrombolysis group, oscillations
and variation with time were more obvious, indicating a possible difference in the dynamics of the cardiac system. 相似文献
47.
Barclay Morrison III David F. Meaney Tracy K. McIntosh 《Annals of biomedical engineering》1998,26(3):381-390
Due to the nonlinear, viscoelastic material properties of brain, its mechanical response is dependent upon its total strain history. Therefore, a low strain rate, large strain will likely produce a tissue injury unique from that due to a high strain rate, moderate strain. Due to a lack of current understanding of specific in vivo physiological injury mechanisms, a priori assumptions cannot be made that a low strain rate injury induced by currently employed in vitro injury devices is representative of clinical, nonimpact, inertial head injuries. In the present study, an in vitro system capable of mechanically injuring cultured tissue at high strain rates was designed and characterized. The design of the device was based upon existing systems in which a clamped membrane, on which cells have been cultured, is deformed. However, the present system incorporates three substantial improvements: (1) noncontact measurement of the membrane deflection during injury; (2) precise and independent control over several characteristics of the deflection; and (3) generation of mechanical insults over a wide range of strains (up to 0.65) and strain rates (up to 15s–1). Such a system will be valuable in the elucidation of the mechanisms of mechanical trauma and determination of injury tolerance criteria on a cellular level utilizing appropriate mechanical injury parameters. 相似文献
48.
工程化肌腱修复肌腱缺损后力学特性的组织学基础 总被引:5,自引:0,他引:5
探讨组织工程化肌腱修复肌腱缺损后体内愈合过程中力学特性的组织学基础。取罗曼鸡肌腱细胞 ,经体外培养、扩增 ,与可降解生物材料聚羟基乙酸筛网构建工程化肌腱 ;将其植入修复 2 0只罗曼鸡第二趾深屈肌腱0 .5~ 0 .8cm缺损。术后第 2、4、6、8周取材 ,对标本进行大体、组织学及生物力学测定。植入 2、4、6、8周 ,新生肌腱在大体形态、细胞及胶原纤维排列方式上与正常肌腱相似 ,但新生肌腱的胶原纤维束并未形成较多的沿肌腱长度方向的致密结构 (“塑形”) ,导致其最大张力增加缓慢 ,到 8周时为 15 .4 0± 10 .6 3N,仅达正常肌腱的 2 3 ;8周时最大张应变为 2 2 .4 9± 10 .2 1 ,比正常肌腱大 10。结果表明 ,单纯聚羟基乙酸作支架 ,材料降解过快 ,新生肌腱失去了正常的力学刺激 ,“塑形”能力差 ,其生物力学强度低。提示 ,保持新生肌腱形成过程中正常的力学刺激对新生肌腱的“塑形”可能是至关重要的。 相似文献
49.
Milner TE 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2002,143(4):406-416
Adaptive control of wrist mechanics was investigated by means of destabilizing dynamics created by a torque motor. Subjects performed a 20 degrees movement to a 3 degrees target under the constraint that no motion should occur outside of the target zone once 800 ms had elapsed from movement onset. This constraint served as the minimum acceptable level of postural stability. The ability of subjects to modify their muscle activation patterns in order to successfully achieve this stability was investigated by creating three types of destabilizing dynamics with markedly different features: negative stiffness, negative damping, and square-wave vibration. Subjects performed sets of trials with the first type of destabilizing dynamics and were then required to adapt to the second and third. The adaptive response was quantified in terms of the rms electromyographic (EMG) activity recorded during various phases of the task. Surface EMG activity was recorded from three muscles contributing to wrist flexion and three muscles contributing to wrist extension. With negative stiffness, a significant compensatory increase in cocontraction of wrist flexor and extensor muscles was observed for slow movements, but there was little change in the muscle activity for rapid movements. With negative damping, muscle cocontraction was elevated to stabilize rapid movements, declining only gradually after the target was reached. For slow movements, cocontraction occurred only when negative damping was high. The response to square-wave vibration (10 Hz, +/-0.5 Nm), beginning at movement onset, was similar to that of negative damping, in that it resulted in elevated cocontraction. However, because the vibration persisted after the target was reached, there was no subsequent decrease in muscle activity. When the frequency was reduced to 5.5 Hz, but with the same torque impulse, cocontraction increased. This is consistent with greater mechanical instability. In summary, agonist-antagonist cocontraction was adapted to the stability of the task. This generally resulted in less of a change in muscle activity during the movement phase, when the task was performed quickly compared with slowly. On the other hand, the change in muscle activity during stabilization depended more on the nature of the instability than the movement speed. 相似文献
50.
长骨内开口效应对其力学性能影响的理论模型研究 总被引:3,自引:0,他引:3
建立一个股骨中段的外侧皮质带有矩形开口的力学模型,采用有限元方法,计算骨开口区的尺寸改变时,股骨的扭转刚度和应力分布的变化。结果表明:骨开口长度为骨外径的1倍时(1OD),对股骨扭转刚度和剪应力分布的影响较小;开口长度从2OD增至4OD时扭转刚度急剧减小,而且剪应力的最大值位于开口区中心。本结论对临床骨科的手术治疗方法和骨开口尺寸的控制提供了重要的理论依据。 相似文献