Effect of Compaction Temperature on Consolidation of Amorphous Copolymers with Different Glass Transition Temperatures

Purpose. The purpose of this study was to relate the combination of glass transition temperature (T _g) and temperature of measurement with the mechanical and compaction properties of some test materials. Methods. Copolymers with different T _gs were synthesised by free radical copolymerisation of methyl methacrylate with lauryl methacrylate. Elastic moduli were measured by dynamic mechanical analysis at different strain rates and temperatures. Compaction experiments were performed at different compaction speeds and temperatures. Results. The difference between temperature of measurement and T _g appears to determine both elastic modulus and yield strength completely. They both decrease with decreasing difference between temperature of measurement and Tg and increase with strain rate. At temperatures of measurement higher than the T _g, the elastic modulus is extremely low because the materials behave as rubbers. Consequently, the amount of energy stored during compaction decreases when the compaction temperature approaches the T _g and increases with strain rate. When the compaction temperature is higher than the T _g, the amount of stored energy is extremely large. The compaction experiments show that the final tablet porosity is completely determined by stress relaxation phenomena. Consequently, the final tablet porosity follows exactly the same relation as that of stored energy. Conclusions. The final tablet porosity is unequivocally determined by the amount of stored energy. This implies that tablet production at a temperature of about 20 K under the glass transition temperature of the material yields tablets with minimum porosity.     

The viscoelastic behaviour of the ureter during elongation

Summary The viscoelastic behaviour of segments of ureters from dogs and guinea pigs has been studied by an ergometer. Elongation of the ureter produces a force, which may be ten times greater than the force of ureteric contractions, and which is proportional to the rate and magnitude of the stretch. Elongations of sufficient length and rate induce spontaneous contractions, the amplitude of which is proportional to the extent of the stretch after some cycles of elongation and shortening. The ureter shows hysteresis so that the loops of the force-length diagrams run in a clockwise direction. However, strain cycles of less than 4% L_O, and less than 0.07 Hz, provoke counterclockwise loops. The loops of the force-length diagram of the contractions also slope in a counterclockwise direction. The ureter behaves like a plasto-elastic body and adapts to strain. The plastic element is at least partly due to the musculature, since the deformation is reduced by continous stimulation of the ureter.     

拇展肌与拇收肌移位吻接术前、后黏弹性实验研究

研究了正常拇展肌、拇收肌拉伸黏弹性力学性质和模拟拇外翻拇展肌、拇收肌移位吻接术后拇展肌和拇收肌的拉伸黏弹性力学性质.取20个足标本,解剖后暴露拇展肌与拇收肌,得出拉伸应力松弛、蠕变等数据.对断裂后的拇收肌和拇展肌模拟临床手术进行移位吻接,对10个拇展肌和10个拇收肌标本做腱与腱吻接,另各取10个拇收肌、拇展肌标本做了腱与骨膜吻接.对吻接后的标本进行拉伸实验,得出了吻接术后各组拉伸应力松弛、蠕变曲线.以回归分析的方法处理实验数据,得出了归一化应力松弛、蠕变曲线及归一化应力松弛函数和归一换化蠕变函数.     

骨质疏松动物模型治疗的黏弹性实验研究

研究了正常大鼠去势所致骨质疏松大鼠和以电针、灸法、雌激素、电针加雌激素、灸法加雌激素治疗组大鼠骨的压缩、应力松弛、蠕变等力学性质.选用280～320g,4～5月龄Wistar雌性大鼠50只,随机分为正常对照组8只,骨质疏松模型组7只,电针治疗组7只,灸法治疗组7只,雌激素治疗组7只,电针加雌激素治疗组7只,灸法加雌激素治疗组7只,对实验组大鼠于0周摘除其卵巢.各组大鼠饲养40周后,以腹主动脉放血法处死大鼠.取大鼠胫骨进行压缩应力松弛、蠕变实验,得出各组大鼠胫骨应力松弛、蠕变数据和曲线,以三参数模型进行处理,拟合应力松弛、蠕变曲线,得出了各组应力松弛、蠕变方程.结果表明,正常组和治疗组7200s应力松弛量和蠕变量大于模型组(P＜0.05).     

实验性兔动脉粥样硬化进程中全血粘弹性的变化及其临床意义

经喂饲胆固醇饲料成功地复制了兔主动脉粥样硬化模型，并显示了ＡＳ脂纹期及ＡＳ纤维 杰斑块期的改变。在ＡＳ进程中呈现：１．血清总胆固醇浓度明显升高。２．红细胞膜钠泵活性渐降低；３．红细胞膜收缩蛋白相对含量下降４．全血粘弹性在ＡＳ晚期明显增高。     

纳米压痕法用于人下颌骨弹性模量的测量

目的:对既往文献中所采用的纳米压痕技术进行横向比较并推荐出制作时间短、对实验结果影响较小的实验项目。方法:获取一具人新鲜尸体下颌骨,应用推荐的实验方法指导试件制备、纳米压痕及结果分析,设定压入载荷分别为1、2、3、4、5mN,最大载荷保持时间为0、10、30、60s,分析测出的颌骨弹性模量(E),对载荷—深度曲线进行初步解析。结果:在人下颌骨的纳米压痕测试时,当压入载荷为3～5mN、最大载荷保持时间为10s及以上,所得测试结果对弹性模量值的影响较小。结论:本文确定了颌骨测试时推荐使用的压入载荷大小及最大载荷的保持时间,并应用纳米压痕测试法测试得到人下颌骨磨牙区皮质骨的平均弹性模量(E)值为18GPa。     

Rheological characterization of human fibrin and fibrin-agarose oral mucosa substitutes generated by tissue engineering

In regenerative medicine, the generation of biocompatible substitutes of tissues by in vitro tissue engineering must fulfil certain requirements. In the case of human oral mucosa, the rheological properties of tissues deserve special attention because of their influence in the acoustics and biomechanics of voice production. This work is devoted to the rheological characterization of substitutes of the connective tissue of the human oral mucosa. Two substitutes, composed of fibrin and fibrin-agarose, were prepared in cell culture for periods in the range 1-21 days. The time evolution of the rheological properties of both substitutes was studied by two different experimental procedures: steady-state and oscillatory measurements. The former allows the plastic behaviour of the substitutes to be characterized by estimating their yield stress; the latter is employed to quantify their viscoelastic responses by obtaining the elastic (G') and viscous (G') moduli. The results demonstrate that both substitutes are characterized by a predominant elastic response, in which G' (order 100 Pa) is roughly one order of magnitude larger than G' (order 10 Pa). But the most relevant insight is the stability, throughout the 21 days of culture time, of the rheological quantities in the case of fibrin-agarose, whereas the fibrin substitute shows a significant hardening. This result provides evidence that the addition to fibrin of a small amount of agarose allows the rheological stability of the oral mucosa substitute to be maintained. This feature, together with its viscoelastic similitude with native tissues, makes this biomaterial appropriate for potential use as a scaffold in regenerative therapies of human oral mucosa.     

Rheological Characterization of an Acetaminophen Jelly

The aim of this study was to prepare an inclusion complex of acetaminophen and β-cyclodextrin (molar ratio of 1:1). A jelly with inclusion complexes formed by kneading was prepared. The formation of inclusion complexes was assessed by powder X-ray diffraction patterns and Fourier transform-infrared spectroscopy. Jellies were prepared with xanthan gum, gelatin, and κ-carrageenan. The concentration of each jelling agent was 0.5, 1.0, and 1.5% w/v. Viscoelasticity and dissolution characteristics were determined and osmometry was performed. PGWater^™, a commercial jelly for fluid replacement, served as a reference for viscoelastic characteristics and dissolution. Powder X-ray diffraction measurement revealed a different diffraction pattern for the kneading than for acetaminophen and β-cyclodextrin. Fourier transform-infrared spectroscopy revealed an absorption peak (at around 1655 cm⁻¹) due to the carbonyl group and benzene ring (at around 1610 cm⁻¹) of acetaminophen. In contrast, the kneaded mixture (1:1) had a shift in the absorption peak due to the carbonyl group (at around 1650 cm⁻¹) in acetaminophen''s molecular structure, and the formation of an inclusion complex was noted. The viscosity of xanthan gum-1.0, gelatin-1.5, and carrageenan-0.5 resembled the viscoelasticity of PGWater^™. The acetaminophen in gelatin-1.0 and carrageenan-0.5 had dissolution behavior similar to that of commercial acetaminophen preparations. The osmolality of jellies prepared in different concentrations ranged from about 20-50 mOsm/kg. Results suggested that carrageenan-0.5 could serve as a useful jelly vehicle for acetaminophen.     

基于正交频率脉冲编码激励的软组织粘弹性定量测量

高频剪切波对粘性参数的准确估计非常重要。为了提高高频剪切波的检测能力,并研究其对粘弹性参数估计的影响,本研究探讨了基于正交频率脉冲激励的超声振动计方法。通过构造具有特定频谱特性的正交频率波形,经稀疏采样之后激励组织振动,可以增强剪切波的高频分量。以新鲜猪肝为对象进行离体实验。选择二进制编码和两种正交频率编码脉冲激励组织振动,然后分别运用激光振动计和超声对不同编码激励方式产生的剪切波进行检测。激光振动计实验证明了该方法可以有效增强剪切波的高频分量,而从超声实验结果上看,与二进制编码激励方式的结果相比,当只用100～400 Hz剪切波速度拟合求解时,三码片与六码片的正交频率脉冲激励所估计得到的剪切弹性和剪切粘性的相对偏差分别为2.3%和4.1%,13.6%和11.5%;而当将所有频率剪切波速度用于拟合求解时,三码片与六码片的正交频率脉冲激励所估计得到的剪切弹性和剪切粘性的相对偏差分别为10.6%和3.5%,5.4%和11.8%。实验结果表明,正交频率编码激励方式可以降低激励峰值声强,并提高系统对高频剪切波的检测能力;另一方面,高频剪切波对粘弹性估计值具有影响,但其影响方式还不确定,需要进一步研究。