填充剂对凝胶贴膏基质流变学特性的影响

目的:粘弹性是凝胶贴膏基质的一个基本性质,粘弹性可通过测量凝胶贴膏的流变特性来确定。通过研究不同填充剂对凝胶贴膏基质的流变学特性的影响,为筛选基质处方提供参考。方法:利用旋转流变仪测定不同填充剂基质配方的流变学性质,包括复数模量(G~*),弹性模量(G')和粘性模量(G″),研究不同填充剂对基质流变学特性的影响,同时对比不同填充剂基质的黏附性,建立用流变学筛选填充剂基质的方法。结果:不同填充剂随着质量分数的增加,G'和G″均增加,尤其是微粉硅胶,其质量分数由1%增加到5%时,G'和G″分别增加了99%和130%。结论:凝胶贴膏基质的流变学可为凝胶贴膏处方的筛选提供借鉴。     

Brain elastic behavior in experimental brain compression: Influence of steroid therapy

This paper describes the pathways for lithium transport across the axonal membrane of squid. We were able to show that the membrane of this classical neuronal preparation possesses the lithium transport mechanisms previously identified in red blood cells. It is now possible to predict that the lithium treatment-induced changes in choline and lithium transport that have been observed in red blood cells of manic depressive patients also occur in nerve membrane.     

软组织粘弹性准线性理论在模拟血管材料中的应用

本文应用软组织粘弹性准线性理论来建立一种模拟血管材料的本构方程,分析指出了方程中应以加载曲线的拟弹性应力作为弹性响应T(e)(γ)的近似,以保证本构关系的唯一性;归一化松弛函数可选择适当的连续松弛谱函数,使理论结果与生物软组织对频率的不敏感性相容。根据一维拉伸试验的结果,对理论方程中的参数加以拟合,其结果是令人满意的,并与动物血管的参数进行比较,表明该材料作为模拟血管是适宜的。     

Anisotropic tensile viscoelastic properties of vascular graft materials tested at low strain rates

Mechanical matching of vascular grafts and host vessels has been suggested to be important in determining graft patency rates. In this context, we have examined the anisotropic viscoelastic properties of natural vessels and some synthetic replacements using low strain rate tensile testing of circumferential and longitudinal strips. The canine iliac artery and iliac vein were compared with 6 mm diameter woven and knitted Dacron® grafts, expanded polytetrafluoroethylene (PTFE) grafts, and helically constructed prototype Polyurethane grafts at wrap angles of 45, 60 and 75°. A thick-walled pressure vessel analysis was used to approximate physiological stress levels, and SEM was used to correlate anisotropic properties with graft wall structure.     

Effects of SIN-1 on peripheral hemodynamics and viscoelastic properties of aorta in anesthetized rabbits

Summary In closed-chest, non-barbiturate-anesthetized rabbits, we have used a computer-based parameter estimation method to evaluate the effects of a slow intravenous infusion of SIN-1 (15 g/kg/min for 20 minutes) upon hemodynamic, geometric, viscoelastic, and energetic characteristics of the hindlimb arterial bed from the measurement of abdominal aortic diameter, blood flow, and blood pressure. To evaluate intrinsic effects of SIN-1 upon arterial wall characteristics, a moderate arterial bleeding (3 ml/kg) was performed to achieve a-10% lowering of arterial pressure, i.e., to reach an equivalent blood pressure reference threshold in the absence of the drug. The SIN-1 IV infusion induced a marked blood pressure lowering (–10.0±2.1%), resulting from a relaxing action on smooth muscle vasculature both in capacitive and resistive components of the hindlimb vascular tree, thereby eliciting a lowering in periphral resistance (–22.8±3.1%) and an increased blood flow (+11.7±3.6%). SIN-1 enhanced vascular compliance (+28.0±2.2%) and lowered vascular input impedance (–31.2±8.9%), as confirmed by modulus and phase spectra. SIN-1 IV infusion contrasted bleeding effects by increasing blood flow and maintaining constant or increasing aortic diameter, both of them being lowered by bleeding. The relaxing effect elicited by SIN-1 was further demonstrated by changes in viscoelastic characteristics, and it was further associated with a decreasing energetic demand as well. The present results demonstrated that SIN-1, administered as a slow IV infusion, exhibits vasodilating properties by acting both on capacitive and resistive vessels of the systemic circulation.Part of the data in this paper was presented at the Second Cardiovascular Pharmacotherapy International Symposium in San Francisco, CA, U.S.A., October 1987. SIN-1 was kindly supplied by Hoechst Laboratories, Paris, France     

Human umbilical cord blood-derived stem cells and brain-derived neurotrophic factor protect injured optic nerve：viscoelasticity characterization

The optic nerve is a viscoelastic solid-like biomaterial.Its normal stress relaxation and creep properties enable the nerve to resist constant strain and protect it from injury.We hypothesized that stress relaxation and creep properties of the optic nerve change after injury.Moreover,human brain-derived neurotrophic factor or umbilical cord blood-derived stem cells may restore these changes to normal.To validate this hypothesis,a rabbit model of optic nerve injury was established using a clamp approach.At 7 days after injury,the vitreous body received a one-time injection of 50 μg human brain-derived neurotrophic factor or 1 × 106 human umbilical cord blood-derived stem cells.At 30 days after injury,stress relaxation and creep properties of the optic nerve that received treatment had recovered greatly,with pathological changes in the injured optic nerve also noticeably improved.These results suggest that human brain-derived neurotrophic factor or umbilical cord blood-derived stem cell intervention promotes viscoelasticity recovery of injured optic nerves,and thereby contributes to nerve recovery.     

Microvasculature alters the dispersion properties of shear waves – a multi‐frequency MR elastography study

Magnetic Resonance Elastography (MRE) uses macroscopic shear wave propagation to quantify mechanical properties of soft tissues. Micro‐obstacles are capable of affecting the macroscopic dispersion properties of shear waves. Since disease or therapy can change the mechanical integrity and organization of vascular structures, MRE should be able to sense these changes if blood vessels represent a source for wave scattering. To verify this, MRE was performed to quantify alteration of the shear wave speed c_s due to the presence of vascular outgrowths using an aortic ring model. Eighteen fragments of rat aorta included in a Matrigel matrix (n=6 without outgrowths, n=6 with a radial outgrowth extent of ~600µm and n=6 with ~850µm) were imaged using a 7 Tesla MR scanner (Bruker, PharmaScan). High resolution anatomical images were acquired in addition to multi‐frequency MRE (ν = 100, 115, 125, 135 and 150 Hz). Average c_s was measured within a ring of ~900µm thickness encompassing the aorta and were normalized to c_s0 of the corresponding Matrigel. The frequency dependence was fit to the power law model c_s ~ν^y. After scanning, optical microscopy was performed to visualize outgrowths. Results demonstrated that in presence of vascular outgrowths (1) normalized c_s significantly increased for the three highest frequencies (Kruskal‐Wallis test, P = 0.0002 at 125 Hz and P = 0.002 at 135 Hz and P = 0.003 at 150 Hz) but not for the two lowest (Kruskal‐Wallis test, P = 0.63 at 100 Hz and P = 0.87 at 115 Hz), and (2) normalized c_s followed a power law behavior not seen in absence of vascular outgrowths (ANOVA test, P < 0.0001). These results showed that vascular outgrowths acted as micro‐obstacles altering the dispersion relationships of propagating shear waves and that MRE could provide valuable information about microvascular changes. Copyright © 2015 John Wiley & Sons, Ltd.     

A new device for assessing changes in skin viscoelasticity using indentation and optical measurement

Background/aims: Skin is a viscoelastic material, comprised of fluidic and fibrous components. Changes in viscoelasticity can arise due to a number of conditions including dehydration, swelling (associated with injury or disease), impaired heart function, rehydration therapy, ageing, scarring, sun exposure and genetic conditions affecting connective tissue. Quantification of changes in skin viscoelasticity due to these processes is of great clinical interest in the fields of therapy monitoring, wound healing and disease screening. However, devices currently available to measure aspects of the mechanical properties of skin have limitations in ease‐of‐use, accessibility, and depth of measurement. This paper describes a new technique to follow changes in the viscoelasticity of the skin, using a novel approach to an indentation manoeuvre. The device is portable, low‐cost and easy to use while at the same time providing rich information on the mechanical response of the skin. Methods: The method proposed optically tracks the skin's recovery from an initial strain, made with a novel linear indentor, using diffuse side‐lighting and a CCD video camera. Upon indentation, the skin's elastin fibres are stretched and fluid is displaced from the compressed region. When the indentor is removed, the rate of recovery of the skin from this imprint is therefore principally dependent on its hydration and elasticity. Using the blue colour plane of the image and polarisation filtering, it is possible to examine the surface topography only, and track the decay of the imprint over time. Results: The decrease in size of the imprint over time (decay curve) recorded by the device is shown to agree with the theoretical predictions of an appropriate viscoelastic model of skin mechanical behaviour. The contributors to the response measured using the indentation device are fully characterised and evaluated using separate measurement techniques including high‐frequency ultrasound, polarisation spectroscopy and optical coherence tomography. Conclusion: The device developed is capable of tracking the viscoelastic response of skin to minimal indentation. The high precision achieved using low‐cost materials means that the device could be a viable alternative to current technologies.