The characterization of bovine compact bone fatigue damage using terahertz spectroscopy

Fatigue can cause cracks to propagate from the micro- to the macroscale, which results in a decrease of Young’s modulus of the bone. Non-destructive measurements of bone fatigue damage are of great importance for bone quality assessment and fracture prevention. Unfortunately, there is still a lack of effective nondestructive methods sensitive to the initial deterioration during damage accumulation, particularly in the field of orthopedics and biomechanics. In this study, terahertz spectroscopy was adopted to evaluate microscale bone damage. Specifically, the refractive index and Young’s modulus of bone samples subjected to different degrees of fatigue damage were tested at a fixed area. Both parameters are found to decrease in two stages under cycled fatigue loading, which is attributed to the initial onset and subsequent development of microdamage during fatigue loading. The change in refractive index reflects the accumulation of fatigue damage as well as the decrease in Young’s modulus.     

密质骨各向异性性质的力学实验及细观分析

目的研究牛股骨密质骨的微观结构特征与其力学行为间的关系。方法对牛股骨密质骨纵向和横向试样分别进行压缩实验;对破坏后的纵向和横向试样进行断裂路径、断裂表面微结构特征观察;基于复合材料细观力学的理论,分析密质骨中骨单元方向对骨纵向和横向弹性模量及断裂极限强度的影响。结果纵向试样的压缩弹性模量和断裂极限强度均明显大于横向试样的压缩弹性模量和断裂极限强度;纵向试样的断裂路径与加载方向近似为0°,且比较平直,而横向试样的断裂路径与加载方向近似为45°,且比较曲折;纵向试样断面中存在许多与加载方向平行的条状结构,断面较为光滑,而横向试样断面存在许多圆弧形凹坑或凸起,断面较为粗糙。结论牛股骨密质骨具有各向异性的力学性质,其各向异性力学性质与骨单元方向密切相关。     

Artificial neural network for modeling the elastic modulus of electrospun polycaprolactone/gelatin scaffolds

Scaffolds for tissue engineering (TE) require the consideration of multiple aspects, including polymeric composition and the structure and mechanical properties of the scaffolds, in order to mimic the native extracellular matrix of the tissue. Electrospun fibers are frequently utilized in TE due to their tunable physical, chemical, and mechanical properties and porosity. The mechanical properties of electrospun scaffolds made from specific polymers are highly dependent on the processing parameters, which can therefore be tuned for particular applications. Fiber diameter and orientation along with polymeric composition are the major factors that determine the elastic modulus of electrospun nano- and microfibers. Here we have developed a neural network model to investigate the simultaneous effects of composition, fiber diameter and fiber orientation of electrospun polycaprolactone/gelatin mats on the elastic modulus of the scaffolds under ambient and simulated physiological conditions. The model generated might assist bioengineers to fabricate electrospun scaffolds with defined fiber diameters, orientations and constituents, thereby replicating the mechanical properties of the native target tissue.     

Prediction of structural failure of tibial bone models under physiological loads: Effect of CT density–modulus relationships

Although finite element (FE) models can provide distinct benefits in understanding knee biomechanics, in particular the response of the knee to implants, their usefulness is limited by the modelling assumptions and input parameters. This study highlights the uncertainty of material input parameters derived from the literature and its limitation on the accuracy and usefulness of FE models of the tibia. An FE model of the intact human knee and a database of knee forces (muscles, ligaments and medial and lateral tibio-femoral contacts) were developed for walking and stair-descent activities. Ten models were constructed from ten different combinations of apparent bone density to elastic modulus material property relationships, published in the literature. Some of the published material property relationships led to predictions of bone strains in the proximal tibia which exceeded published failure criteria under loads imposed by normal activities. These relationships appear not to be applicable for the human tibia. There is a large discrepancy in proposed relationships that cover the cancellous bone density range. For FE models of the human tibia, the material relationship proposed by Morgan et al., which assumed species and anatomic site dependence, produced the most believable results for cancellous bone. In addition to casting doubt on the use of some of the published density–modulus relationships for analysis of the human proximal tibia, this study highlights the need for further experimental work to characterise the behaviour of bone with intermediate densities.     

超声弹性成像技术评价周围性面瘫针灸疗效的临床应用价值

摘要 目的 探讨超声弹性成像技术动态评估周围性面瘫针灸治疗效果的临床应用价值。方法 选取2019年11月至2020年9月于重庆市中医院接受针灸治疗的50例周围性单侧面瘫患者为研究对象,应用超声弹性成像技术评估针灸治疗过程中6个时间点面部表情肌（额肌、降口角肌、降下唇肌）的弹性模量值,同时临床面神经功能评分评估面瘫程度。线性相关分析不同治疗时间点,患侧弹性模量值与临床面神经功能评分的相关性。结果 面瘫患者患侧表情肌（额肌、降口角肌、降下唇肌）的弹性模量值,随着针灸治疗次数增加,弹性模量值逐渐降低,6个检测时间点差异比较均具有统计学意义（P＜0.01),且治疗前7天下降速率最快;而对照组表情肌的弹性模量值无明显变化。与弹性模量值改变相一致的是,患侧面神经功能临床评分随着治疗时间增加,评分逐渐升高,治疗后7天内评分上升速率增快,差异具有统计学意义（P＜0.01）。相关性分析发现,弹性模量值与临床面神经功能评分呈负相关（r=-0.546, P＜0.001; r=-0.757, P＜0.001; r=-0.683, P＜0.001）。结论 利用超声弹性成像技术可动态评估针灸治疗前后面部表情肌群的弹性变化,与面神经功能临床评分相关,可为面瘫治疗效果评估提供重要影像学依据。     

Effect of Nano Silica on Setting Time and Physical Properties of Mineral Trioxide Aggregate

IntroductionMineral trioxide aggregate (MTA) has been widely used in all fields of endodontics. One of the major drawbacks of this material is the long setting time. MTA is primarily composed of type 1 Portland cement and bismuth oxide. In cement, nanoscale SiO₂ behaves as a filler to improve microstructure and to accelerate hydration process. The aforementioned reaction is also expected in MTA because of the same structure. Thus, the aim of this study was to evaluate the effect of addition of nano-SiO₂ to MTA on the setting time and its physical properties.MethodsTwo concentrations (8% and 10%) of nano-SiO₂ were added to the white MTA powder. After mixing with water, the setting time, compressive strength, and flexural strength were investigated and compared with pure MTA.ResultsWith the addition of 8% and 10% of nano-SiO₂ to the MTA, the setting time of both mixtures decreased significantly (P < .05). However, the compressive strength (after 1 day and 1 week) and flexural strength increased; this was not significant (P > .05). There was no significant difference between MTA mixed with 8% and 10% nano-SiO₂ in setting time, compressive strength, and flexural strength (P > .05).ConclusionsThe addition of 8% and 10% of nano-SiO₂ to MTA accelerated the hydration process, reduced the setting time, and had no adverse effect on the compressive and flexural strength of MTA.     

Ultrasonic measurement of the effects of light irradiation and presence of water on the polymerization of self‐adhesive resin cement

Self‐adhesive resin cements are useful in restorations because they reduce the number of clinical steps involved in the restoration process. This study evaluated, using ultrasonic measurements, the influence of light irradiation and the presence of water on the polymerization behavior and elastic modulus of a self‐adhesive resin cement. A self‐adhesive resin cement (RelyX Unicem 2 Automix) or a resin cement (RelyX ARC) was inserted into a transparent mold on a sample stage, and the presence of water and effect of light‐irradiation were evaluated. The transit time of a sonic wave through the cement disk was divided by the specimen thickness to obtain the sonic velocity, and longitudinal and shear waves were used to determine the elastic modulus. When the resin cements were light‐irradiated, the sonic velocity rapidly increased and plateaued at 2,500–2,700 m s^?1. When the cements were not irradiated, the rates of increase in the sonic velocity were reduced. When water was applied to the sample stage, the sonic velocity was reduced. The elastic modulus values of the specimens ranged from 9.9 to 15.9 GPa after 24 h. The polymerization behavior of self‐adhesive resin cements is affected by the polymerization mode and the presence of water.