丝素蛋白纤维/聚N-异丙基丙烯酰胺复合水凝胶的性能

以丝素蛋白纤维为填充材料,采用自由基聚合的方法制备复合聚N-异丙基丙烯酰胺(PNIPPAm)水凝胶,研究复合水凝胶的黏弹性能、溶胀性能和反复溶胀收缩性能。结果表明：丝素蛋白纤维的加入改善了复合水凝胶的力学性能,其平衡溶胀率不仅与温度有关,而且与丝素蛋白纤维的含量有关。此外,处在表面的丝素蛋白纤维与水凝胶之间存在间隙,在反复溶胀-收缩过程中可以作为输水通道,有利于水分子进出,提高了PNIPPAm水凝胶对温度的响应速率并使其溶胀-收缩重复性更好。     

犬肝脏撞击伤后血液粘弹性变化的实验研究

目的　探讨犬肝脏损伤后血液粘弹性变化的特点及其临床意义。方法　通过建立肝脏损伤动物模型 ,分别在伤前及伤后 1、4、8小时 4个时相点各抽血 3ml,置于肝素抗凝管 ,在实验当日 2 4小时内全部送检并完成测定 ,并按血液粘弹性计算的方法得出结果。结果　犬肝损伤后 1小时 ,血液粘性分量 (η’)、弹性分量 (η”)即开始升高 ,与伤前比较差异显著或非常显著 (P <0 .0 1 ,P <0 .0 5 ) ,在伤后 4小时到达峰值 ,显著高于伤前和伤后 1小时 (P <0 .0 1 ,P <0 .0 5 ) ,伤后 8小时 η’、η”曲线出现下降趋势。 结论　在犬肝损伤后的抗休克救治中 ,在积极输血扩容的同时 ,还应采取降低血液粘度 ,增加血液流动性的措施 ,以达到改善末稍血循环 ,从而有效纠正组织缺血缺氧的不良状况。     

粘弹性胶束压裂液的流变动力学研究

研究了粘弹性胶束清洁压裂液(VES-60)的流变动力学，首次建立了粘弹性胶束的流变动力学模型和方程，并用于描述粘弹性胶束压裂液的形成过程。结果表明：流变动力学模型能够确切描述粘弹性胶束的形成过程，模型计算值和实验值吻合良好，模型参数物理意义明确、合理。     

The Effect of Evolving Damage on the Finite Strain Response of Inelastic and Viscoelastic Composites

A finite strain micromechanical model is generalized in order to incorporate the effect of evolving damage in the metallic and polymeric phases of unidirectional composites. As a result, it is possible to predict the response of composites with ductile and brittle phases undergoing large coupled inelastic-damage and viscoelastic-damage deformations, respectively. For inelastic composites, both finite strain elastoplastic (time-independent) and viscoplastic (time-dependent) behaviors are considered. The ductile phase exhibits initially a hyperelastic behavior which is followed by an inelastic one, and its analysis is based on the multiplicative split of its deformation gradient into elastic and inelastic parts. The embedded damage mechanisms and their evolutions are based on Gurson’s (which is suitable for the modeling of porous materials) and Lemaitre’s finite strain models. Similarly, the polymeric phase exhibits large viscoelastic deformations in which the damage evolves according to a suitable evolution law that depends on the amount of accumulated deformation. Evolving damage in hyperelastic materials can be analyzed as a special case by neglecting the viscous effects. The micromechanical analysis is based on the homogenization technique for periodic multiphase materials, which establishes the strong form of the Lagrangian equilibrium equations. These equations are implemented together with the interfacial and periodic boundary conditions, in conjunction with the current tangent tensor of the phase. As a result, the instantaneous strain concentration tensor that relates the local deformation gradient of the phase to the externally applied deformation gradient is established. This provides also the instantaneous effective stiffness tangent tensor of the composite as well as its current response. Results are given that exhibit the effect of damage on the initial yield surfaces, response and possible failure of the composite.     

Continuous and stepwise cystometry through suprapubic catheters—effect of infusion pattern and infusion rate on the cystometrogram of the normal human bladder

Summary. Continuous cystometry at two filling rates (50 and 100 ml min^-1) and stepwise cystometry (successive rapid volume infusions followed by bladder wall relaxation) were performed in 12 healthy subjects. Suprapubic catheters were used for infusion and recording of perivesical and intravesical pressures. The continuous cystometrograms obtained at filling rates of 50 and 100 ml min^-1, respectively, did not differ with respect to desire to void, transmural pressure increase or bladder capacity. Stepwise cystometry allowed the bladders to be filled to a slightly larger volume than during continuous cystometry, but with comparatively lower transmural pressures only at very large distension of the bladder. There was considerable inter-individual variation in transmural pressure at both continuous and stepwise cystometry. Stepwise cystometry did not appear to provide any important additional information about pressure-volume relationship in the normal human bladder than could be obtained at routine clinical cystometry.     

Strain-rate-dependent non-linear tensile properties of the superficial zone of articular cartilage

Aim of the study: The tensile properties of articular cartilage play an important role in the compressive behavior and integrity of the tissue. The stress-strain relationship of cartilage in compression was observed previously to depend on the strain-rate. This strain-rate dependence has been thought to originate mainly from fluid pressurization. However, it was not clear to what extent the tensile properties of cartilage contribute to the strain-rate dependence in compressive behavior of cartilage. The aim of the present study was to quantify the strain-rate dependent stress-strain relationship and hysteresis of articular cartilage in tension.

Methods: Uniaxial tensile tests were performed to examine the strain-rate dependent non-linear tensile properties of the superficial zone of bovine knee cartilage. Tensile specimens were oriented in the fiber direction indicated by the India ink method. Seven strain-rates were used in the measurement ranging from 0.1 to 80%/s, which corresponded to nearly static to impact joint loadings.

Results: The experimental data showed substantial strain-rate and strain-magnitude dependent load response: for a given strain-magnitude, the tensile stress could vary by a factor of 1.95 while the modulus by a factor of 1.58 with strain-rate; for a given strain-rate, the modulus at 15% strain could be over four times the initial modulus at no strain. The energy loss in cartilage tension upon unloading exhibited a complex variation with the strain-rate.

Conclusion: The strain-rate dependence of cartilage in tension observed from the present study is relatively weaker than that in compression observed previously, but is considerable to contribute to the strain-rate dependent load response in compression.     

健康儿童血液粘弹特性的研究

本文采用Low Shear-30流变测定仪研究健康儿童211例的血液粘弹特性,测定指标共10项,确立了小儿正常值。从不同年龄分析,新生儿期呈血高粘滞状态;此外整个儿童时期呈血低粘滞状态。从不同性别分析,10岁以下小儿各指标参数无男女差异;10岁以上小儿开始出现性别差异。以上血液流变学变化与儿童时期的生长发育、解剖生理特点是相适应的。     

Three-dimensional finite-element model of the human temporomandibular joint disc during prolonged clenching

In the temporomandibular joint (TMJ), overloading induced by prolonged clenching appears to be important in the cascade of events leading to disc displacement. In this study, the effect of disc displacement on joint stresses during prolonged clenching was studied. For this purpose, finite-element models of the TMJ, with and without disc displacement, were used. Muscle forces were used as a loading condition for stress analysis during a time-period of 10 min. The TMJ disc and connective tissue were characterized as a linear viscoelastic material. In the asymptomatic model, large stresses were found in the central and lateral part of the disc through clenching. In the retrodiscal tissue, stress relaxation occurred during the first 2 min of clenching. In the symptomatic model, large stresses were observed in the posterior part of the disc and in the retrodiscal tissue, and the stress level was kept constant through clenching. This indicates that during prolonged clenching the disc functions well in the asymptomatic joint, meanwhile the retrodiscal tissue in the symptomatic joint is subject to excessive stress. As this structure is less suitable for bearing large stresses, tissue damage may occur. In addition, storage of excessive strain energy might lead to breakage of the tissue.     

An alcohol-free tissue conditioner--a laboratory evaluation

OBJECTIVES: An alcohol-free tissue conditioner based on a n-butyl methacrylate/i-butyl methacrylate copolymer has recently been developed. The purpose of the present study was to compare some key properties of the new tissue conditioner with those of poly(ethyl methacrylate)-based conventional materials containing ethyl alcohol. The effect of a coating, which consisted of poly(ethyl methacrylate) and methyl methacrylate, was also evaluated. METHODS: The new alcohol-free tissue conditioner (Fictioner) and three tissue conditioners containing ethyl alcohol (FITT, Hydro-Cast, SR-Ivoseal) were evaluated. The coated alcohol-free material was also used. Gelation characteristics, dynamic viscoelastic properties and compatibility with dental stones were measured using a displacement rheometer, dynamic viscoelastometer and profilometer, respectively. In addition, weight changes during immersion in water were determined. RESULTS: The working time and gelation time of the alcohol-free tissue conditioner were similar to those of the conventional materials. This alcohol-free material had significantly lower shear storage modulus and shear loss modulus, and higher loss tangent (P<0.05) than FITT and SR-Ivoseal at 0.01 and 1 Hz. The alcohol-free material maintained its inherent viscoelastic properties and exhibited only a slight change in weight during 14 days of water immersion when compared to the conventional materials. The application of the coating significantly reduced the loss of the initial viscoelastic properties and surface quality during the test periods. CONCLUSIONS: The coated alcohol-free tissue conditioner would be superior to the conventional materials containing ethyl alcohol in view of viscoelastic properties after gelation, compatibility with dental stones and durability.     

非线性粘弹性方程的EQrot1非协调有限元分析

针对非线性粘弹性方程,在半离散和全离散格式下给出EQrot1非协调有限元逼近.由于该单元的相容误差(O(h2)阶)比插值误差(O(h)阶)高一阶,可得到在H1模意义下的O(h2)阶超逼近结果,并利用插值后处理技术导出整体超收敛.进而,基于该单元的渐近展开式,构造新的插值后处理算子和外推格式,给出O(h4)阶的外推结果.最后,运用与以往文献不同的方法得到全离散逼近格式的最优误差估计.