关键词： Cu-Ag nanocomposite   Nanoindentation   Inclusion   MD simulation   Dislocations density  

摘要： In this work, we study the effect of silver inclusions on the mechanical behavior of Cu-Ag nanocomposites during nanoindentation using Molecular Dynamics Simulations. Pure Cu and Cu matrices containing Ag inclusions of different sizes, located at various depths under the surface, are investigated. The results of simulations show that the presence of silver inclusion influences the strength of the material. Indeed, the hardness of Cu substrate containing an Ag inclusion is lower than that of pure Cu. In addition, for a given inclusion radius, the hardness decreases with decreasing inclusion depth beneath the indenter. Furthermore, our results also showed that, at a fixed inclusion depth, hardness increases as the inclusion radius decreases and the maximum hardness value is obtained for an inclusion radius and depth of 17.5 A and 60 A, respectively.

关键词： Lignocelluloses   Peach stone   Mechanical treatment   Modification   Copper   Biosorption kinetics  

摘要： In this paper, the character of structural changes induced by different mechanical treatments to Prunus persica stones (PSs), and its subsequent effect on biosorption kinetics of Cu(II) were investigated. PSs were processed in vibratory disk mill (PS-V) and ultra-centrifugal mill (PS-C) and characterized by XRD, BET, SEM and FTIR spectroscopy. It was shown that PS-V was smaller and more reactive with less crystallinity index and hydrogen bond intensity compared to PS-C. In opposite, surface area of the PS-C was bigger than that of the PS-V. The total pore volume was about threefold, while the volume of micro pores was 9.29 times higher in PS-Cs than in PS-Vs. The kinetics of Cu(II) biosorption by both PSs was tested through various kinetic models: pseudo-first and pseudo-second order rate equations, Elovich equation, Boyd model, Weber-Morris and Urano-Tachikawa intraparticle diffusion model. For both sample types, Cu(II) biosorption occurred through combination of intraparticle and film diffusion mechanism, while kinetic results were best described by the pseudo-second order kinetic model. At the same time, the results indicated that together with kinetic rate the biosorption capacity of PS-C (21.20 mg g(-1)) was higher than that of PS-V (16.30 mg g(-1)). Mechanical activation like crushing and grinding will change material particle size, specific surface area and porosity, as well as its crystallinity. However, this paper elucidates that such physical structural changes will impact on heavy metal ions removal efficiency. This investigation suggests that the type of size reduction in lignocellulosic biosorbent preparation plays a very important role in overall biosorption performance, so it should be carefully considered every time when the mechanical treatment of material is necessary to be applied. (C) 2016 The Authors. Published by Elsevier B.V.

关键词： Cardiac arrest   Cardiopulmonary resuscitation   Transesophageal echocardiography   External cardiac massage  

摘要： Aim: Early onset of adequate chest compression is mandatory for cardiopulmonary resuscitation (CPR) following cardiac arrest. Transmission of forces from chest strain to the heart may be variable between manual and mechanical chest compressions. Furthermore, automated mechanical chest devices can deliver an active decompression, thus improving the venous return to the heart. This pilot study investigated the kinetics of cardiac deformation during these two CPR methods. Methods: Transesophageal echocardiographic analysis of the right ventricular wall behind the sternum during CPR was assessed during manual and mechanical chest compression in adult patients admitted to the emergency department for out-of-hospital cardiac arrest. Results: 9 patients had manual and 11 mechanical chest compression. Mechanical chest compression was characterized by greater right ventricular lateral wall displacement [with a median (IQR) of 3.7 (3.12-4.27) vs. 2.53 (2.27-2.6) cm, p < 0.0001], and lower rising time [123 (102-169) vs. 187 (164-215) ms, p = 0.002], relaxing time [109 (102-127) vs. 211 (133-252) ms, p = 0.0003], compression rate [100.6 (99.6-102.2) vs. 131.9 (125.4-151.4) bpm, p < 0.0001], with compression-decompression time ratio of [1.04 (0.86-1.1) vs. 0.86 (0.78-0.96), p = 0.046]. Conclusion: Mechanical compared to manual chest compression delivered a more rapid compression and decompression of the cardiac structures at an adequate rate, with broader inward-outward movement of the ventricular walls suggesting greater emptying and filling of the ventricles. Transesophageal echocardiography may be a useful tool to assess the adequacy of chest compression without CPR interruption.

关键词： HDPE   Dynamic oscillatory shear flow   Molecular dynamics simulation   Processing-structure-property relationship  

摘要： Dynamic oscillation shear flow-induced crystallization has been proved to be an effective approach to achieving high-performance semi-crystalline polymer (SCP) in recent years. In this study, a loop push-pull oscillatory molding (LOPPM) technology with controlled shear intensity was employed to investigate the processing-structure-property relationship in semi-crystalline high-density polyethylene (HDPE). The results of SEM, SAXS, and WAXD showed that the crystal structure of the samples changed significantly from skin to core layer such as refined spherulites and oriented shish-kebabs. The tensile strength, Young's modulus, and impact toughness firstly increased and then decreased with the enhanced shear flow field, exhibiting optimal shear intensity for mechanical properties. In particular, the tensile strength, Young's modulus, bending strength, bending modulus, and impact strength of HDPE sample under the optimal external shear intensity (LOPPM-M) were 176.2%, 124.5%, 129.2%, 243.6%, and 207.8% higher than those values of the conventional injection molding sample (CIM) respectively. Additionally, molecular dynamics simulations were adopted to explore the processing-structure relationship and the results showed good correspondence with the experimental findings. The strengthening-toughening mechanism and crystal evolution process were further discussed. Overall, this study provides valuable guidance for designing and fabricating SCP with tunable properties.

关键词： Antimicrobial materials   Polymerization   Dental adhesives   S. mutans   Biofilm  

摘要： Objectives: Quaternary ammonium (QA) methacrylate monomers have been extensively investigated and demonstrate excellent antibacterial properties. However, the presence of ester bonds makes them prone to degradation in the oral cavity. In this study, ester-free QA monomers based on meth-acrylamides were synthesized and screened for polymerization kinetics, mechanical properties and antibacterial effects. Materials and methods: Tertiary quaternary ammonium acrylamides (AM) and methacrylamides (MAM) with alkyl side chain lengths of 9 and 14 carbons (C9 and C14) were synthesized and incorporated at 10 wt% into experimental composites based on BisGMA:TEGDMA (1:1), camphorquinone/ethyl-4dimethylaminobenzoate (0.2/0.8 wt%) and 70 wt% barium glass fillers. Analogous methacrylate versions (MA) were used as controls. Degree of conversion (DC) and rate of polymerization (RP) during photoactivation (800 mW/cm(2)) were followed in real-time with near-IR. Flexural Strength (FS) and Modulus (E) were measured on 2 x 2 x 25 mm bars in 3-point bending after 24 h dry storage and 7-day storage in water at 37 degrees C. Antimicrobial properties and biofilm adhesion (fouling) were evaluated by bioluminescence (Luciferase Assay) and biofilm removal by water spray microjet impingement test, respectively. Cytotoxicity was assessed by MTT assay on dental pulp stem cells (DPSC). Data were analyzed with one-way ANOVA/Tukey's test (alpha = 0.05). Results: DC was similar for all groups tested (similar to 70%). Both MAMs and C14-AM presented significantly lower RP. Under dry conditions, FS (110-120 MPa) and E (8-9 GPa) were similar for all groups. After water storage, all materials presented FS/E similar to the control, except for C14-AM (for FS) and C14-MAM (for E), which were lower. All C14 versions were strongly antibacterial, decreasing the titer counts of biofilm by more than two orders of magnitude in comparison to the control. C9 monomers did not present significant antibacterial nor antif

关键词： Temporomandibular joint disc   Collagen fiber   Elastin fiber   Dynamic mechanical properties   Enzymatic degradation  

摘要： The temporomandibular joint disc is a structure, characterized as heterogeneous fibrocartilage, and is composed of macromolecular biopolymers. Despite a large body of characterization studies, the contribution of matrix biopolymers on the dynamic viscoelastic behavior of the disc is poorly understood. Given the high permeability and low concentration of glycosaminoglycans in the disc, it has been suggested that poro-elastic behavior can be neglected and that the intrinsic viscoelastic nature of solid matrix plays a dominant role in governing its time dependent behavior. This study attempts to quantify the contribution of collagen and elastin fibers to the viscoelastic properties of the disc. Using collagenase and elastase, we perturbed the collagen and elastin fibrillar network in porcine temporomandibular joint discs and investigated the changes of dynamic viscoelastic properties in five different regions of the disc. Following both treatments, the storage and loss moduli of these regions were reduced dramatically up to the point that the tissue was no longer mechanically heterogeneous. However, the proportion of changes in storage and loss moduli were different for each treatment, reflected in the decrease and increase of the loss tangent for collagenase and elastase treated discs, respectively. The reduction of storage and loss moduli of the disc correlated with a decrease of biopolymer length. The present study indicates that the compositional and structural changes of collagen and elastin fibers alter the viscoelastic properties of the disc consistent with polymer dynamics.

ISBN: (纸本)9787568280648

关键词： Click chemistry   Thiol-ene   Gel   Gelation dynamics   Mechanical property  

摘要： Click chemistry is an effective tool to fabricate three-dimensional gel network in an accurate way. In this work, Pluronic F127 gels are prepared by thiol-ene click chemistry, utilizing double-bond end-capped Pluronic F127 (F127DA) and pentaerythritol tetras-mercaptopropionate (PETMP) as the starting materials and triethylamine as the catalyst. Both the mass fraction of F127DA and the initial concentration of PETMP have effects on the properties of the resulting F127 gels. The optimized F127 gel prepared under a F127DA mass fraction of 15 wt% and a PETMP concentration of 17.62 mmol/L exhibits the highest swelling ratio (10) and has the largest elongation at break (194%). When the F127DA mass fraction and PETMP concentration are fixed at 15 wt% and 48.26 mmol/L, respectively, the resulting F127 gel has a high stress of 0.25 MPa. The present example has presented a method to fabricate three-dimensional gel network in a controlled way.

关键词： Collagen fibril   Mechanical properties   Collagenase   Gelatinase   Molecular dynamics   Monte Carlo  

摘要： Loading in cartilage is supported primarily by fibrillar collagen, and damage will impair the function of the tissue, leading to pathologies such as osteoarthritis. Damage is initiated by two types of matrix metalloproteinases, collagenase and gelatinase, that cleave and denature the collagen fibrils in the tissue. Experimental and modeling studies have revealed insights into the individual contributions of these two types of MMPs, as well as the mechanical response of intact fibrils and fibrils that have experienced random surface degradation. However, no research has comprehensively examined the combined influences of collagenases and gelatinases on collagen degradation nor studied the mechanical consequences of biological degradation of collagen fibrils. Such preclinical examinations are required to gain insights into understanding, treating, and preventing degradation-related cartilage pathology. To develop these insights, we use sequential Monte Carlo and molecular dynamics simulations to probe the effect of enzymatic degradation on the structure and mechanics of a single collagen fibril. We find that the mechanical response depends on the ratio of collagenase to gelatinase-not just the amount of lost fibril mass-and we provide a possible mechanism underlying this phenomenon. Overall, by characterizing the combined influences of collagenases and gelatinases on fibril degradation and mechanics at the preclinical research stage, we gain insights that may facilitate the development of targeted interventions to prevent the damage and loss of mechanical integrity that can lead to cartilage pathology.