Fragmentation Of Lamellae Research Articles

Abstract 251: Selective Deletion of Smad4 in Smooth Muscle Cells Causes Thoracic Aortic Aneurysm in Mice

TGFβ signaling have been implicated in the onset of thoracic aortic aneurysms (TAA). Recently, it has been described that mutations in SMAD4, an intracellular transducer required in the TGFβ canonical pathway, present aortic disease in humans. Although transgenic models recapitulating mutations of TGFβ pathway have been studied, Smad4 role in the onset of TAA has never been explored. Smad4 homozygotes mice are embryonically lethal, thus, we postnatally targeted the gene, using a tamoxifen (TAM)-inducible Cre recombinase under the smooth muscle myosin heavy chain promoter. Activation by TAM suppressed Smad4 in aorta SMCs of Smadf/f;Myh11-CreERT2 mice. We found that, most of these mice died 4/6 months later from hemothorax due to rupture of thoracic aorta, while untreated mice survived. Echocardiography showed a progressive dilation of aorta and TAA formation. Histology revealed progressive fragmentation of elastic lamellae with increased inflammatory infiltrates at sites of disarrangement, rich in macrophages. At the molecular level, we found that lack of Smad4 was followed by increased levels of PSmad2 and PSmad1/5/8 early after TAM, suggesting an enhancement of TGFβ receptors activity, a condition that could increase non-canonical TGFβ signaling, the canonical one being depressed. We actually found a significant increase in one of the non-canonical TGFβ signaling, i.e. the p65 subunit of NFkB, a protein complex controlling DNA transcription and involved in regulating responses to different stress stimuli, including cytokines. Given the particular relevance that the latter molecules may have in TAA, we tested expression of some of them, finding a selective IL-1β upregulation, produced and stored in cells as an inactive precursor and released in its active form by caspase-1 cleavage. In turn, caspase-1 requires NLRP3 inflammasome, a multiprotein platform that assembles in response to infection and tissue damage and is responsible for activation of inflammatory caspases. Therefore, we also tested NLRP3 mRNA levels and found them to be significantly upregulated. We demonstrated for the first time that selective Smad4 deletion in the SMC of adult mice is sufficient to induce ultrastructural damage and immune reaction culminating in the onset of TAA.

The structural evolution of high-density polyethylene during crazing in liquid medium

Atomic force microscopy (AFM) was employed to study structural transformations occurring in high-density polyethylene (HDPE) during deformation in a liquid medium by crazing mechanism. Processing of the obtained images yielded the parameters of HDPE structure at different tensile strains. It was shown that crazing causes the development of a fibrillar–porous structure in the interlamellar space, the fragmentation of lamellae, and the displacement of lamella fragments relative to each other. Moreover, the deformation is accompanied by the separation of lamellae and the long period increases in the proportion to the tensile strain. The scheme of HDPE deformation upon crazing in liquid medium was constructed based on the AFM images.

Investigation on the recovery performance of olefin block copolymer/hexadecane form stable phase change materials with shape memory properties

In this work, recovery performance of a novel sort of form stable phase change materials (FSPCMs) with simultaneously shape memory properties was investigated systematically. The FSPCMs comprising hexadecane as latent heat storage material and olefin block copolymer (OBC) as supporting material were prepared by simple swelling preparation method. This kind of difunctional materials exhibits fantastic shape memory properties with mass fraction of hexadecane reaching 70wt%, which indicates excellent energy storage ability as well. It is found that the recovery performance under 50% strain is obviously better than that under higher strains for all the specimens investigated, while surprisingly, the composite with 70wt% hexadecane exhibits better recovery performance than pure OBC as well as the composite with 30wt% hexadecane at strains of 100 and 200%. The structural change brought by incorporation of hexadecane was explored with in situ two-dimensional X-ray scattering measurements. According to experiment results, we find that the recovery performance is closely correlated to change of long period, indicating the irreversible deformation of the difunctional materials may originate from lamellar fragmentation of OBC, while addition of massive hexadecane is beneficial to restrain lamellar fragmentation and thus improves the recovery performance. We believe this exploration may shed light on comprehending the relationship between structural change and shape memory performance, thus contributing to adjusting the properties of the difunctional materials and expanding their potential applications.

Acoustic emission from the initiation of plastic deformation of Polyethylenes during tensile tests

The acoustic emission (AE) technique has been used in the aim to detect and to observe the initiation of plasticity and damage of several Polyethylenes (PE) during tensile tests. The detection of acoustic signals originating from the deformation of the material is challenging since PE samples strongly attenuate ultrasonic waves. A weak acoustic activity has been recorded during the tests. The use of two types of PE specimens and two methodologies based on the elimination and the discrimination of spurious sources has shown that most of the AE signals truly originate from the plastic deformation of materials. We also observed that the acoustic activity increases with strain rate. Besides, some AE signals are located along the specimen length during tensile tests at high strain rate. The acoustic activity increases strongly with the crystallinity. Micro-cavities, formed before the yield point of PE samples with high crystallinity in particular, likely initiate the release of acoustic energy. In addition, some signals are collected on PE samples, which do not exhibit a formation of cavitation. Hence, the shearing of crystallites and/or the fragmentation of crystalline lamellae may also be a source of the release of acoustic energies.

Shape Evolution of Cementite during Accelerated Carbide Spheroidisation

Pearlite spheroidisation of 100CrMn6 steel was investigated. This process is well known and studied during conventional soft annealing. Presented paper describes cementite lamellae fragmentation during accelerated carbide spheroidisation. Mechanism of cementite lamellae fragmentation during conventional soft annealing depends on carbon and iron diffusion in ferrite-cementite system. On the other hand, accelerated carbide spheroidisation relies on partial pearlite austenitization and backward austenite decomposition. Aim of presented experiments was to examine shape evolution of cementite particles during transition from lamellar to globular form. Pearlite spheroidisation is normally quantified by image analysis of 2D metallographic section. Conventional metallographic observation was used for globular-lamellar particle ratio estimation. However, whole lamellae observation is necessary for spheroidisation process revelation. Ferrite matrix deep etching and cementite separation was performed to study morphological aspects of acceolerated carbide spheroidisation.

Structure Refinement of Medium Carbon Steel and Deformation Properties Respond

The work presents the results on grains refinement of steel containing 0,45 wt pct carbon resulted from severe plastic deformation (SPD). Different steel structures from prior solutioning and/or thermomechanical treatment were prepared for deformation experimental. A coarse grain ferrite-pearlite structure was achieved applying solutioning. By application of thermomechanical (TM) controlled forging process, performing multistep open die forging, the refined ferrite-pearlite mixture was prepared. Final structure refinement of steel, having different initial structure, was then accomplished applying warm Equal Channel Angular Pressing (ECAP) at 400°C. Employment of this processing route resulted in extensive deformation of ferrite grains and cementite lamellae fragmentation. Applying the highest shear stress (εef - 4) the mixed structure of subgrains and ultrafine grains was present within the ferrite phase. In pearlite grains, modification of cementite lamellae due to shearing, bending, twisting and breaking was found efficient. The coarse cementite lamellae spheroidization was more efficient in prior TM treated steel. The tensile deformation records confirmed strength increase and diversity in strain hardening behaviour.

Microstructure Development of Bearing Steel during Accelerated Carbide Spheroidisation

Carbide spheroidisation is a significant metallurgical process, which contributes to profound changes in microstructure and mechanical properties. Carbide spheroidising occurs through diffusion, which is a long-term and energy-demanding process. The holding times, sometimes up to tens of hours make soft annealing one of the most expensive heat treatment processes. The process was newly designed at the company COMTES FHT shortens carbide spheroidising several times and therefore delivers considerable time and cost savings. The heat treatment was performed using induction heating. The purpose of this annealing process is to obtain globular carbides uniformly distributed in the matrix and to achieve overall softening. The present paper explores the effect of the newly-designed thermal schedules on the cementite lamellae fragmentation, on the decrease in hardness in bearing steel grade 100CrMnSi6-4 and on processing times.

Stretching temperature and direction dependency of uniaxial deformation mechanism in overstretched polyethylene

ABSTRACTIn order to elucidate microscopic deformation behavior at different locations in isotropic semicrystalline polymers, the structural evolution of a preoriented high‐density polyethylene sample during tensile deformation at different temperatures and along different directions with respect to the preorientation was investigated by means of combined in situ synchrotron small‐angle X‐ray scattering (SAXS) and wide‐angle X‐ray diffraction (WAXD) techniques. For samples stretched along preorientation, two situations were found: (1) at 30 °C, the sample broke after a moderate deformation, which is accomplished by the slippage of the microfibrils; (2) at 80 and 100 °C, fragmentation of original lamellae followed by recrystallization process was observed resulting in new lamellar crystals of different thickness depending on stretching temperature. For samples stretched perpendicular or 45° with respect to the preorientation, the samples always end up with a new oriented lamellar structure with the normal along the stretching direction via a stress‐induced fragmentation and recrystallization route. The thickness of the final achieved lamellae depends only on stretching temperature in this case. Compared to samples stretched along the preorientation direction, samples stretched perpendicular and 45° with respect to the preorientation direction showed at least several times of maxima achievable stress before macroscopic failure possibly due to the favorable occurrence and development of microdefects in those lamellar stacks with their normal parallel to the stretching direction. This result might have significant consequence in designing optimal procedure to produce high performance polyethylene products from solid state. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 716–726

Role of surfactant on inducing specific microdomains of block copolymer: An example case from polystyrene-b-poly(ethylene-co-1-butene)-b-polystyrene (SEBS) electrospun thermoplastic-elastomer fiber containing polyethylene glycol lauryl ether (PGLE)

The present work demonstrates a simple approach to control microdomains in thermoplastic elastomer by using surfactants based on a good example of polystyrene-b-poly(ethylene-co-1-butene)-b-polystyrene triblock copolymer (SEBS) containing polyethylene glycol lauryl ether (PGLE) electrospun fibers. The interaction between PGLE and the phenyl group of PS in SEBS chain is a key factor to allow PGLE functioning in changing morphology of the SEBS micro-fibers. In general, SEBS electrospun fibers show distorted and fragmented lamellae. By adding only 1 wt% of PGLE in SEBS, the PGLE retards the microdomain distortion as well as initiates isotropic lamellar orientation. When fiber stretching force reached a certain level, the fragmented lamellar of SEBS-PGLE is initiated, and at that time, the tensile strength of the fibers increases significantly.

Lethal chlorophyll change resulting in a light-violet colour in winter rye (Secale cereale L.) seedlings

This paper describes a lethal chlorophyll change characterized by light-violet seedlings, obtained after self-fertilization of a dwarf winter rye form from Jeleniec. The manner of inheritance of this mutation has been established. Genetic analysis of green and light-violet plant segregating frequences in inbred generations S<sub>3</sub> and S<sub>4</sub> has showed that the obtained split ratio approximates the theoretical ratio 3:1. This proves that the feature in question is determined by the recessive gene cl<sub>3</sub>. The gene cl<sub>3</sub> is lethal as it results in the death of the seedlings 4 weeks after germination. In contrast to the membrane system characteristic for the chloroplasts, the mesophyll cells of mutants (light-violet in colour) contained plastids devoid of granal and intergranal thylakoids. Only fragments of lamellae, vesicles or light areas were present in the granular matrix of these plastids.

Grain Refinement and Deformation Behaviour of Medium Carbon Steel Processed by ECAP

The work presents the results on grains refinement of steel containing 0,45 wt pct carbon resulted from severe plastic deformation (SPD). Different steel structures from prior solutioning and/or thermomechanical treatment were prepared for deformation experimental. A coarse grain ferrite-pearlite structure was achieved applying solutioning. By application of thermomechanical (TM) controlled forging process, performing multistep open die forging, the refined ferrite-pearlite mixture was prepared. Final structure refinement of steel, having different initial structure, was then accomplished applying warm Equal Channel Angular Pressing (ECAP) at 400°C. Employment of this processing route resulted in extensive deformation of ferrite grains and cementite lamellae fragmentation. Applying the highest shear stress (εef - 4) the mixed structure of subgrains and ultrafine grains was present within the ferrite phase. In pearlite grains, modification of cementite lamellae due to shearing, bending, twisting and breaking was found efficient. The coarse cementite lamellae spheroidization was more efficient in prior TM treated steel. The tensile deformation records confirmed strength increase and diversity in strain hardening behaviour.

Influence of Prior Warm Deformation on Cementite Spheroidization Process in a Low-Alloy Medium Carbon Steel

Warm deformations have been applied to a low-alloy medium carbon steel (AISI 5140) to promote faster spheroidization during soft annealing treatments. The application of warm deformation leads to the fragmentation of cementite lamellae and the formation of defects on both cementite and the matrix. This induces faster lamellae break-up according to a boundary splitting mechanism, which is responsible for the improved spheroidization after annealing. The substructure developed in the matrix enhances pipe diffusion through the sub-boundaries, which helps the lamellae terminations to coarsen and causes lamellae fast splitting and finally yields a coarse cementite particle distribution. When deforming up to e = 0.3, almost fully spheroidized microstructures are obtained after annealing at 993 K (720 °C), independently of the initial pearlite features. By means of the EBSD technique, it has been observed that the applied warm deformation, in addition to enhancing the degree of spheroidization, allows a much finer microstructure to be formed after annealing. Grain refinement takes place as a consequence of a continuous recrystallization process, which is directly related to cementite spheroidization in the long term.

Two Sides of MGP Null Arterial Disease: CHONDROGENIC LESIONS DEPENDENT ON TRANSGLUTAMINASE 2 AND ELASTIN FRAGMENTATION ASSOCIATED WITH INDUCTION OF ADIPSIN

Mutations in matrix Gla protein (MGP) have been correlated with vascular calcification. In the mouse model, MGP null vascular disease presents as calcifying cartilaginous lesions and mineral deposition along elastin lamellae (elastocalcinosis). Here we examined the mechanisms underlying both of these manifestations. Genetic ablation of enzyme transglutaminase 2 (TG2) in Mgp(-/-) mice dramatically reduced the size of cartilaginous lesions in the aortic media, attenuated calcium accrual more than 2-fold, and doubled longevity as compared with control Mgp(-/-) animals. Nonetheless, the Mgp(-/-);Tgm2(-/-) mice still died prematurely as compared with wild-type and retained the elastocalcinosis phenotype. This pathology in Mgp(-/-) animals was developmentally preceded by extensive fragmentation of elastic lamellae and associated with elevated serine elastase activity in aortic tissue and vascular smooth muscle cells. Systematic gene expression analysis followed by an immunoprecipitation study identified adipsin as the major elastase that is induced in the Mgp(-/-) vascular smooth muscle even in the TG2 null background. These results reveal a central role for TG2 in chondrogenic transformation of vascular smooth muscle and implicate adipsin in elastin fragmentation and ensuing elastocalcinosis. The importance of elastin calcification in MGP null vascular disease is highlighted by significant residual vascular calcification and mortality in Mgp(-/-);Tgm2(-/-) mice with reduced cartilaginous lesions. Our studies identify two potential therapeutic targets in vascular calcification associated with MGP dysfunction and emphasize the need for a comprehensive approach to this multifaceted disorder.

Effect of Equal Channel Angular Pressing on Lamellar Microstructures in Nickel Aluminum Bronze

A lamellar nickel aluminum bronze has been processed by equal channel angular pressing (ECAP) and its microstructure investigated. The orientation, spacing, and morphology of the lamellae after ECAP were observed to be dependent on the orientation of the lamellae before ECAP with respect to the shear plane. Two distinct microstructures were produced following a single ECAP pass. The most common type consisted of fragmented lamellae with a reduced lamellar spacing, inclined between >0 deg and 45 deg and <180 deg, with exceptions at 0/180 deg and 45 deg. A model describing the evolution of lamellar microstructures subjected to a single ECAP pass has been proposed.

The effect of comonomer content on structure and property relationship of propylene-1-octene copolymer during uniaxial stretching

The structure and property relationships of propylene-1-octene random copolymer having different octene comonomer concentrations were investigated. In specific, the crystal structure evolution in these copolymers during uniaxial stretching at 60 °C was characterized by in-situ synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) techniques. With high octene content, the copolymer behaved like an elastomer with small elastic modulus and yield stress, low crystallinity and low crystal orientation under stretching. Furthermore, step-cycle tensile test showed that the copolymer with high octene content had a high recovery ratio. With low octene content, the copolymer behaved like a plastomer with large elastic modulus and yield stress, high crystallinity and high crystal orientation under stretching. From 2D SAXS results, it was found that in low octene content sample, lamellar fragmentation occurred resulting in a significant decrease in lamellar lateral size. In contrast, in high octene content sample, stress might be mainly concentrated on the amorphous matrix, leading to an inter-lamellar slip and a small decrease in lamellar lateral size. Schematic structural changes of propylene-1-octene copolymer under tensile deformation were illustrated to explain the different elasticity behavior in these copolymers.

Prior Structure Modification on Grain Refinement and Deformation Behavior of Medium Carbon Steel Processed by ECAP

The present work, deals with grain refinement of medium carbon steel AISI 1045 (0.45% C), having different initial ferrite–pearlite microstructure resulted from thermal and thermomechanical treatment (TM). The purpose of TM steel processing was to refine ferrite and modify pearlite lamellae structure. The final grain refinement of steel structure was then accomplished during warm Equal Channel Angular Pressing (ECAP) at 400°C. Employment of this processing route, in dependence of the applied effective strain ϵef, resulted in extensive deformation of ferrite grains and cementite lamellae fragmentation. When applying higher shear stress (ϵef = 4) the mixed structure of subgrains and ultrafine grains was formed within ferrite phase, regardless the initial steel structure morphology. In pearlite grains, modification of cementite lamellae due to shearing, bending, twisting, and breaking was found efficient as straining increased. Processes of dynamic polygonization and recrystallization in deformed structure also contributed to submicrocrystalline grains formation in deformed structure. Comparing results the course of lamellae cementite spheroidization was then more efficient in prior TM treated steel. The tensile deformation results confirmed the strength increase, however deformation behavior and strain hardening generally for different initial structural conditions of steel, showed diversity.

Formation of nanostructure and nano-hardness characterization on the meso-scale workpiece by a novel laser indirect shock forming method

The meso-scale workpiece with greatly enhanced mechanical properties is potential to be widely used in the electronics productions and micro-electro mechanical systems. In this study, it demonstrates that the meso-scale cup-shape workpiece with good geometry can be obtained by a novel laser indirect shock forming method. After the forming process, the mechanical properties and microstructures of the formed workpiece were characterized. By transmission electron microscope observation, it was found that a mixed refined microstructure consisting of nano-scale twins embedded in nano-sized grains was produced at the center of the formed sample. Formation of these nanograins could be mainly attributed to two mechanisms: twin-twin intersections and twin∕matrix lamellae fragmentation. By nanoindentation tests, it reveals that the hardness of the sample has increased greatly after laser shock forming and the hardness increases with the laser energy. The elevated hardness originates from a considerable number of nano-scale twins and nanograins, which possess a pretty high strength due to the significant effects of grain boundary strengthening and twin boundary strengthening.

Uniaxial Tensile Deformation of Poly(ε-caprolactone) Studied with SAXS and WAXS Techniques Using Synchrotron Radiation

The structural evolution of poly(ε-caprolactone) (PCL) during uniaxial tensile deformation at 25 °C was examined using small- and wide-angle X-ray scatterings (SAXS and WAXS) techniques with simultaneous stress and strain (S–S) curves. A high-energy X-ray beam at the recently upgraded Pohang synchrotron radiation source revealed the complete lamellar deformation behavior of PCL. Slope-based division of the S–S curves indicated three distinct regions of elastic (region I), yielding (region II) and plastic deformations (region III). In region I, which showed elastic deformation, the WAXS patterns were isotropic, whereas the SAXS patterns became oblate due to elongation of the amorphous chains along the draw direction. In region II, which showed yielding deformation, the WAXS patterns showed a slight orientation, whereas the SAXS patterns exhibited a change from oblate to four-point and to six-point patterns due to the simultaneous fragmentation and melting of the chain-folded lamellae (leading to the four-point pattern) and the subsequent formation of chain-extended lamellae (adding another two maxima along the meridian). In region III, the WAXS patterns revealed the development of the orientation of PCL crystals, whereas SAXS patterns exhibited a two-point pattern. The newly formed chain-extended lamellae in regions II and III might produce network junctions that can transfer an applied force to the PCL crystals for increased orientation. The six-point pattern in region II for PCL was not observed or reported in the past during the uniaxial tensile deformation experiment. This might be due to fast acquisition of the X-ray patterns during mechanical drawing using synchrotron radiation.

Abstract 86: Apo(a) Inhibits Plasminogen-Dependent Abdominal Aortic Aneurysm Formation in Transgenic Mice

Abdominal Aortic Aneurysm (AAA) is a lethal disorder found primarily in adults over 65. Unlike coronary heart disease, the incidence of AAA is rapidly increasing, and currently there is no nonsurgical treatment. AAA is a chronic inflammatory disease that includes early leukocyte infiltration, destruction of the elastic lamina and extracellular matrix, expansion of the aorta, and eventually fatal aorta rupture. Components of the plasminogen (Plg) and MMP pathways that mediate leukocyte infiltration are prominent in AAA. The goal of this study is to investigate regulators of these pathways in AAA, namely the inhibition Plg by apo(a). In AAA patients, the association of elevated Lp(a) and progression of AAA is controversial. Apolipoprotein(a) [apo(a)], a component of lipoprotein(a) [Lp(a)], has a high homology to Plg, and interferes with Plg functions in vitro. In our previous studies apo(a), independent of Plg, inhibited neutrophil recruitment in a peritonitis model of inflammation, and in Plg deficient mice macrophage infiltration was impaired in CaCl2 induced AAA formation. Our hypothesis is that apo(a) inhibits AAA formation by reducing neutrophil or macrophage infiltration by interfering with Plg. To test our hypothesis, the CaCl2 induced AAA model was performed in 5 strains of mice: WT; Plg-/-; apo(a)tg; apo(a)tg:Plg-/-; and Lp(a)tg mice (6-14 mice analyzed per genotype). Three weeks after injury, the WT aorta diameter increased from 0.54 to 0.88mm (62%). The diameter changed in WT 0.31±0.11mm, apo(a)tg 0.06±0.02mm, apo(a):Plg -/- 0.39±0.07mm and Lp(a) 0.08±0.07mm. The dilation was significantly lower in apo(a) and Lp(a) mice compared to WT (P&lt;0.001). The H&amp;E, Trichrome and EVG stain showed elevated leukocyte infiltration in WT and apo(a):Plg -/- injured aorta, accompanied by thining of the media layer and elastic lamellae fragmentation. In contrast, the aorta of apo(a) mice remained preserved. Neutrophils and macrophages were decreased in apo(a) mice compared to WT(P&lt;0.05). In apo(a):Plg -/- mice, only neutrophil infiltration was decreased not macrophages. These results suggest that inhibition of neutrophils in apo(a) mice is independent of Plg, but reduced macrophage infiltration in apo(a) mice is Plg-dependent during AAA formation.

Memory effect of the molecular topology of lamellar polyethylene on the strain-induced fibrillar structure

The fibrillar structure that develops upon drawing of semi-crystalline polymers has been investigated at room temperature by means of in situ SAXS for a series of ethylene copolymers crystallized through various thermal treatments. The long period of the microfibrils for any given material proved to be only dependent on the experimental conditions of the drawing. This suggested the occurrence of a destruction and reconstruction of the semi-crystalline structure via fragmentation accompanied with melting–recrystallization. However, the diameter of the microfibrils proved to keep the memory of the lamellar microstructure via a correlation with the content of interphase at the crystal-amorphous boundary. A physical explanation is proposed for these apparently antagonist findings. The memory of the lamellar semi-crystalline microstructure is completely erased in the microfibrils owing to the melting–recrystallization process. In contrast, the diameter of the fibrils keeps the memory of the chain topology to which a major role is ascribed in the strain-induced fragmentation of the crystalline lamellae.