Characterization of a polymer-infiltrated ceramic-network material

Objectives

To characterize the microstructure and determine some mechanical properties of a polymer-infiltrated ceramic-network (PICN) material (Vita Enamic, Vita Zahnfabrik) available for CAD–CAM systems.

Methods

Specimens were fabricated to perform quantitative and qualitative analyses of the material's microstructure and to determine the fracture toughness (K_Ic), density (ρ), Poisson's ratio (ν) and Young's modulus (E). K_Ic was determined using V-notched specimens and the short beam toughness method, where bar-shaped specimens were notched and 3-point loaded to fracture. ρ was calculated using Archimedes principle, and ν and E were measured using an ultrasonic thickness gauge with a combination of a pulse generator and an oscilloscope.

Results

Microstructural analyses showed a ceramic- and a polymer-based interpenetrating network. Mean and standard deviation values for the properties evaluated were: K_Ic = 1.09 ± 0.05 MPa m^1/2, ρ = 2.09 ± 0.01 g/cm³, ν = 0.23 ± 0.002 and E = 37.95 ± 0.34 GPa.

Significance

The PICN material showed mechanical properties between porcelains and resin-based composites, reflecting its microstructural components.     

绞股蓝对高脂血症兔动脉粥样硬化超微结构和显微结构的影响

目的观察绞股蓝对高脂血症兔动脉粥样硬化(AS)超微结构和显微结构的影响。方法40只日本大耳白兔随机分为A组、B组、C组、D组,分别喂饲高脂饲料(标准饲料92.5%+2%胆固醇+2%蛋黄+3.5%猪油)+绞股蓝5 g/kg、高脂饲料+辛伐他汀5 mg/kg、高脂饲料、标准饲料。实验前和实验后6 w、9 w耳中动脉采血检测血脂:甘油三酯(TG)、胆固醇(TC)、低密度脂蛋白胆固醇(LDL-C)、高密度脂蛋白胆固醇(HDL-C)。光镜、电镜对比观察主动脉病理学形态。结果①血脂:E组饲养前后血脂比较无显著差异,A组、B组、C组饲养后TG、TC、LDL-C显著升高(P<0.05~0.01),A组、B组HDL-C显著升高(P<0.01),A组和B组TG、TC、LDL-C低于C组(P<0.05~0.01),A组和B组HDL-C高于C组(P<0.01);②病理学:A组、B组、C组、D组的斑块/内膜面积比分别为(30.91±5.21)%、(31.55±6.13)%、(59.89±8.91)%、0,A组、B组与C组间比较有显著差异(P<0.01);A组、B组、C组、D组的内膜/中膜厚度比分别为(40.13±15.56)%、(40.89±14.97)%、(70.17±12.12)%、0,A组、B组与C组间比较有显著差异(P<0.01);电镜下主动脉超微结构观察显示:C组血管内皮细胞及中膜平滑肌细胞质内大量脂滴空泡,甚至形成脂囊;A组和B组AS病变较C组轻,血管内皮细胞质内偶见小脂滴空泡,各种细胞器存在,内弹力膜存在,中层平滑肌细胞质内无脂滴空泡。结论绞股蓝能调节高脂饲料饲养兔血脂代谢,对AS显微和超微病变有明显的抑制作用。     

多载荷下带有生理限定应力的松质骨细观结构模拟

松质是骨的重要组成部分，属多胞体结构，由于构成松质骨的小梁骨尺寸较小，形状多变，因此给松质骨的研究增加了困难。本文把负反馈调节的生理特征引入骨再造模拟中，提出带有生理限定应力的骨再造自适应模型。模型具有骨再造局部适应的正反馈调节与整体控制的负反馈调节的生理调整过程，使骨结构内的应力控制在生理限定应力以下，维持骨力学环境的稳定。使用此模型在几种不同的力学环境下模拟了松质骨结构，定量地预测了松质骨细观结构与其力学环境的对应关系，同时表明了松质骨细观结构与力学环境的适应性。模拟结果与真实松质骨细观结构的典型部分相一致。     

氧化锂含量对牙科云母微晶玻璃析晶性能的影响

目的:研究Li2O对SiO2-Al2O3-MgO-Na2O-K3O-F云母玻璃陶瓷析晶性能、显微结构和抗弯强度的影响.方法:在玻璃基础成分中添加不同含量的Li2O,由差热分析(DTA)曲线确定热处理制度,采用X射线衍射分析(XRD)、扫描电子显微镜(SEM)和三点弯曲强度测试来观测和比较晶体成分、形貌和材料的力学性能.结果:3组玻璃的核化温度为530℃,最适晶化温度随Li2O含量的增加而降低.680℃热处理1 h后,含4%Li2O的母体玻璃析出的云母晶体发育完全,抗弯强度最高(183.82±12.47)MPa.结论:添加一定量的Li2O有助于改善SiO2-Al2O3-MgO-Na2O-K2O-F系云母玻璃陶瓷的析晶性能和力学强度.     

Mitigation of hypertrophic scar contraction via an elastomeric biodegradable scaffold

Hypertrophic scar (HSc) occurs in 40–70% of patients treated for third degree burn injuries. Current burn therapies rely upon the use of bioengineered skin equivalents (BSEs), which assist in wound healing but do not prevent HSc contraction. HSc contraction leads to formation of a fixed, inelastic skin deformity. We propose that BSEs should maintain their architecture in the wound bed throughout the remodeling phase of repair to prevent HSc contraction. In this work we study a degradable, elastomeric, randomly oriented, electrospun micro-fibrous scaffold fabricated from the copolymer poly(l-lactide-co-ε-caprolactone) (PLCL). PLCL scaffolds displayed appropriate elastomeric and tensile characteristics for implantation beneath a human skin graft. In vitro analysis using human dermal fibroblasts demonstrated that PLCL scaffolds decreased myofibroblast formation as compared to an in vitro HSc contraction model. Using a validated immune-competent murine HSc contraction model, we found that HSc contraction was significantly greater in animals treated with standard of care, Integra, as compared to those treated with collagen coated-PLCL (ccPLCL) scaffolds. Finally, wounds treated with ccPLCL were significantly less stiff than control wounds at d30 in vivo. Together, these data suggest that scaffolds which persist throughout the remodeling phase of repair may represent a clinically translatable method to prevent HSc contraction.     

Controlled surface topography regulates collective 3D migration by epithelial–mesenchymal composite embryonic tissues

Cells in tissues encounter a range of physical cues as they migrate. Probing single cell and collective migratory responses to physically defined three-dimensional (3D) microenvironments and the factors that modulate those responses are critical to understanding how tissue migration is regulated during development, regeneration, and cancer. One key physical factor that regulates cell migration is topography. Most studies on surface topography and cell mechanics have been carried out with single migratory cells, yet little is known about the spreading and motility response of 3D complex multi-cellular tissues to topographical cues. Here, we examine the response to complex topographical cues of microsurgically isolated tissue explants composed of epithelial and mesenchymal cell layers from naturally 3D organized embryos of the aquatic frog Xenopus laevis. We control topography using fabricated micropost arrays (MPAs) and investigate the collective 3D migration of these multi-cellular systems in these MPAs. We find that the topography regulates both collective and individual cell migration and that dense MPAs reduce but do not eliminate tissue spreading. By modulating cell size through the cell cycle inhibitor Mitomycin C or the spacing of the MPAs we uncover how 3D topographical cues disrupt collective cell migration. We find surface topography can direct both single cell motility and tissue spreading, altering tissue-scale processes that enable efficient conversion of single cell motility into collective movement.     

Contrast-to-noise ratio analysis of microscopic diffusion anisotropy indices in q-space trajectory imaging

Diffusion anisotropy in diffusion tensor imaging (DTI) is commonly quantified with normalized diffusion anisotropy indices (DAIs). Most often, the fractional anisotropy (FA) is used, but several alternative DAIs have been introduced in attempts to maximize the contrast-to-noise ratio (CNR) in diffusion anisotropy maps. Examples include the scaled relative anisotropy (sRA), the gamma variate anisotropy index (GV), the surface anisotropy (UA_surf), and the lattice index (LI). With the advent of multidimensional diffusion encoding it became possible to determine the presence of microscopic diffusion anisotropy in a voxel, which is theoretically independent of orientation coherence. In accordance with DTI, the microscopic anisotropy is typically quantified by the microscopic fractional anisotropy (μFA).In this work, in addition to the μFA, the four microscopic diffusion anisotropy indices (μDAIs) μsRA, μGV, μUA_surf, and μLI are defined in analogy to the respective DAIs by means of the average diffusion tensor and the covariance tensor. Simulations with three representative distributions of microscopic diffusion tensors revealed distinct CNR differences when differentiating between isotropic and microscopically anisotropic diffusion. q-Space trajectory imaging (QTI) was employed to acquire brain in-vivo maps of all indices. For this purpose, a 15 min protocol featuring linear, planar, and spherical tensor encoding was used. The resulting maps were of good quality and exhibited different contrasts, e.g. between gray and white matter. This indicates that it may be beneficial to use more than one μDAI in future investigational studies.     

骨碎补治疗去卵巢大鼠骨质疏松的实验研究

目的：观察骨碎补对去卵巢后骨质疏松大鼠骨密度、微结构和生物力学性能的影响,研究骨碎补对治疗骨质疏松的作用。方法：30只6月龄SD大鼠随机分为3组：去卵巢组（OVX）、假手术组（SHAM）和骨碎补治疗组（OVX＋D）。骨碎补治疗3个月后,检测各组大鼠的骨密度、微结构、生物力学性能的变化,并比较各组间差异。结果：OVX＋D组的的骨密度、微结构、生物力学指标与OVX组比较差异有统计学意义,与SHAM组比较差异无统计学意义。结论：骨碎补可以增加去卵巢后骨质疏松大鼠的骨密度,改善微结构,提高生物力学性能,对实验动物的骨质疏松有治疗作用。     

Cocaine facilitation of prefrontal cortex self-stimulation: a microstructural and pharmacological analysis

A novel self-stimulation methodology involving a fixed-interval (FI-5 s) schedule of reinforcement, microanalysis and threshold evaluation was used to investigate the effects of cocaine on rats lever pressing for electrical stimulation of the prefrontal cortex. Cocaine (15 mg/kg) increased medial prefrontal cortex (MPC) self-stimulation rates under FI-5 by a mean of 269% and reduced current thresholds for self-stimulation. A similar facilitation was evident with self-stimulation of the sulcal prefrontal cortex. Microanalysis showed that cocaine decreased inter-response times and post-reinforcement pauses, increased responding in the second and third quartiles of the inter-reinforcement interval (IRI) and decreased responding in the fourth IRI quartile. Schedule control of responding was still evident following cocaine despite the profound facilitation of response rates. Increased response rates were seen up to 48 h following a single dose of cocaine, suggesting sensitization of the PFC reinforcement substrate. The acute effects of cocaine on MPC self-stimulation were completely reversed by the dopamine (DA) D₁ antagonist SCH 23390 0.02 mg/kg) and the D₂ antagonist raclopride (0.3 mg/kg) but not by naloxone (0.5 mg/kg). These results are consistent with previous studies demonstrating the PFC as part of the neural substrate mediating cocaine reward. Further, these results implicate DA receptors in the reinforcing properties of both cocaine and MPC self-stimulation.     

Bidirectional changes in the consumption of food produced by β-carbolines

β-Carboline derivatives provide examples of benzodiazepine receptor ligands which span the range: full agonist-partial agonist-antagonist-partial inverse agonist-full inverse agonist. Taken together, the effects of these compounds illustrate two important principles: firstly, the bidirectionality of effects which can be achieved using benzodiazepine receptor ligands; secondly, the selectivity of effects which are produced by partial agonists. Applied to the study of feecling processes, these principles imply that both hyperphagic and anorectic effects can be generated by actions of selected ligands at benzodiazepine receptors. Furthermore, they suggest that a hyperphagic effect may occur in the absence of side-effects (e.g., sedation, muscle-relaxation), which are characteristic of classical benzodiazepines. Experimental data in support of these predictions are presented. A microstructural approach to feecling behaviour indicated that a benzodiazepine receptor agonist and an inverse agonist extend and abbreviate, respectively, the duration of individual bouts of eating. Preference for a saccharin solution was attenuated by the β-carboline inverse agonist, FG 7142, but rejection of a quinine solution was not increased. Adrenalectomy had no effect on the anorectic effect of inverse agonists.