Interlamellar Zones Research Articles

A Microstructure-Based Mechanistic Approach to Detect Degeneration Effects on Potential Damage Zones and Morphology of Young and Old Human Intervertebral Discs.

There is an increasing demand to develop predictive medicine through the creation of predictive models and digital twins of the different body organs. To obtain accurate predictions, real local microstructure, morphology changes and their accompanying physiological degenerative effects must be taken into account. In this article, we present a numerical model to estimate the long-term aging effect on the human intervertebral disc response by means of a microstructure-based mechanistic approach. It allows to monitor in-silico the variations in disc geometry and local mechanical fields induced by age-dependent long-term microstructure changes. Both lamellar and interlamellar zones of the disc annulus fibrosus are constitutively represented by considering the main underlying microstructure features in terms of proteoglycans network viscoelasticity, collagen network elasticity (along with content and orientation) and chemical-induced fluid transfer. With age,anoticeable increase in shear strain is especially observed in the posterior and lateral posterior regions of the annulus which is in correlation with the high vulnerability of elderly people to back problems and posterior disc hernia. Important insights about the relation between age-dependent microstructure features, disc mechanics and disc damage are revealed using the present approach. These numerical observations are hardly obtainable using current experimental technologies whichmakes our numerical tool useful for patient-specific long-term predictions.

Quantifying Nanoparticle Ordering Induced by Polymer Crystallization.

It has recently been established that polymer crystallization can preferentially place nanoparticles (NPs) into the amorphous domains of a lamellar semicrystalline morphology. The phenomenology of this process is clear: when the time for NP diffusion is shorter than the crystal growth time, then the NPs are rejected by the growing crystals and placed in the amorphous domains. However, since there is no quantitative characterization of this ordered NP state, we develop a correlation function analysis for small-angle X-ray scattering data, inspired by classical methods used for enunciating the local morphology of lamellar semicrystalline polymers. We show that when the spherulitic growth rate is slower than NP diffusion, then all the NPs are expelled from the crystals. As we increase the crystallization temperature, Tc, the long period characterizing the periodically repeating crystal-amorphous polymer structure, rcc, increases. This results in a smaller number of amorphous domains per unit volume-the number of NPs per amorphous domain thus increases. While the scattering contrast between the pure silica and the polymer is constant, these arguments predict that the apparent contrast between the NP-rich and the polymer-rich domains scale linearly with rcc, as we confirm from our experiments. These facts allow us to posit that the NPs become more efficiently packed in the interlamellar zone with increasing Tc until they form a fully filled monolayer. Above this temperature, NP multilayers form within each of the NP-rich domains. Our analysis approach, therefore, describes NP ordering that is achieved when driven by polymer crystallization.

A microstructure-based model for a full lamellar-interlamellar displacement and shear strain mapping inside human intervertebral disc core

The determinant role of the annulus fibrosus interlamellar zones in the intervertebral disc transversal and volumetric responses and hence on their corresponding three-dimensional conducts have been only revealed and appreciated recently. Their consideration in disc modeling strategies has been proven to be essential for the reproduction of correct local strain and displacement fields inside the disc especially in the unconstrained directions of the disc. In addition, these zones are known to be the starting areas of annulus fibrosus circumferential tears and disc delamination failure mode, which is often judged as one of the most dangerous disc failure modes that could evolve with time leading to disc hernia. For this latter reason, the main goal of the current contribution is to incorporate physically for the first time, the interlamellar zones, at the scale of a complete human lumbar intervertebral disc, in order to allow a correct local vision and replication of the different lamellar-interlamellar interactions and an identification of the interlamellar critical zones. By means of a fully tridimensional chemo-viscoelastic constitutive model, which we implemented into a finite element code, the physical, mechanical and chemical contribution of the interlamellar zones is added to the disc. The chemical-induced volumetric response is accounted by the model for both the interlamellar zones and the lamellae using experimentally-based fluid kinetics. Computational simulations are performed and critically discussed upon different simple and complex physiological movements. The disc core and the interlamellar zones are numerically accessed, allowing the observation of the displacement and shear strain fields that are compared to direct MRI experiments from the literature. Important conclusions about the correct lamellar-interlamellar-nucleus interactions are provided thanks to the developed model. The critical interlamellar spots with the highest delamination potentials are defined, analyzed and related to the local kinetics and microstructure.

Interlamellar-induced time-dependent response of intervertebral disc annulus: A microstructure-based chemo-viscoelastic model

The annulus fibrosus of the intervertebral disc exhibits an unusual transversal behavior for which a constitutive representation that considers as well regional effect, chemical sensitivity and time-dependency has not yet been developed, and it is hence the aim of the present contribution. A physically-based model is proposed by introducing a free energy function that takes into account the actual disc annulus structure in relation with the surrounding biochemical environment. The response is assumed to be dominated by the viscoelastic contribution of the extracellular matrix, the elastic contribution of the oriented collagen fibers and the osmo-induced volumetric contribution of the internal fluid content variation. The regional dependence of the disc annulus response due to variation in fibers content/orientation allows a micromechanical treatment of the soft tissue. A finite element model of the annulus specimen is designed while taking into consideration the ‘interlamellar’ ground substance zone between lamellae of the layered soft tissue. The kinetics is designed using full-field strain measurements performed on specimens extracted from two disc annulus regions and tested under different osmotic conditions. The time-dependency of the tissue response is reported on stress-free volumetric changes, on hysteretic stress and transversal strains during quasi-static stretching at different strain-rates and on their temporal changes during an interrupted stretching. Considering the effective contributions of the internal fluid transfer and the extracellular matrix viscosity, the microstructure-based chemo-mechanical model is found able to successfully reproduce the significant features of the macro-response and the unusual transversal behavior including the strong regional dependency from inner to outer parts of the disc: Poisson's ratio lesser than 0 (auxetic) in lamellae plane, higher than 0.5 in fibers plane, and their temporal changes towards usual values (between 0 and 0.5) at chemo-mechanical equilibrium. The underlying time-dependent mechanisms occurring in the tissue are analyzed via the local numerical fields and important insights about the effective role of the interlamellar zone are revealed for the different disc localizations. Statement of significanceThe structural complexity of the annulus fibrosus has only been appreciated through recent experimental contributions and a constitutive representation that considers as well regional effect, chemical sensitivity and time-dependency of the unusual transversal behavior has not yet been developed. Here, a microstructure-based chemo-viscoelastic model is developed to highlight the interlamellar-induced time-dependent response by means of a two-scale strategy. The model provides important insights about the origin of the time-dependent phenomena in disc annulus along with regional dependency, essential for understanding disc functionality.

A chemo-mechanical model for osmo-inelastic effects in the annulus fibrosus.

The annulus fibrosus exhibits complex osmotic and inelastic effects responsible for unusual transversal behavior with a Poisson's ratio higher than 0.5 in fibers plane and negative (i.e., auxetic) in lamellae plane. In this paper, we present a new chemo-mechanical approach for the intrinsic osmo-inelastic response of the annulus fibrosus in relation to the microstructure of the layered reinforced soft tissue, the biochemical environment and the mechanical loading conditions. The constitutive model introduces the coupling between the deformation-induced inelastic stress in the tangled extracellular matrix and the stress-free swelling due to internal fluid content variation by osmosis. The proposed formulation is implemented into a finite element code, and numerical simulations on annulus specimens, including explicitly lamellae and interlamellar zones, are presented. To illustrate the capability of the approach to capture experimental observations quantitatively, the simulated results are compared to experimental results obtained by monitoring the full-field strain in annulus specimens using digital image correlation method. Some material constants are found by matching the free swelling in a water bath with different salt concentrations, and others are found by matching tensile results in terms of loading-unloading stress-stretch curve and transversal behavior. The constitutive model is found to successfully capture the variations in osmolarity and strain-rate conditions (both statistically significant, p < 0.05) on the intrinsic response and the auxeticity. The stress/strain patterns in the model simulation provide valuable insights into the role of the interlamellar zone in the osmo-inelastic mechanisms.

Modified lead hematoxylin-tartrazine yellow stain highlights changes in aortic wall after balloon angioplasty

ABSTRACTHematoxylin and eosin (H&E) has been traditionally used to highlight the morphology of elastic arteries. An alternative staining procedure, lead hematoxylin-tartrazine yellow (LHTY), will be compared with H&E to evaluate its depiction of various layers in rat aortic wall. Sliced aortic rings, from 1-year-old male Sprague–Dawley rats that had undergone balloon angioplasty, were harvested at 1 day, 7 days, and 14 days after this procedure. Stained sections of specimen rings were evaluated to determine the effects on cellular components and extracellular matrix of various sublayers in the three aortic tunics. In contrast to H&E, the LHTY staining was found to clearly differentiate sublayers of the tunica intima from the tunica media. In addition, the elastic lamellar bands in the tunica media were especially demarcated to provide greater visibility for obtaining measurable indices (such as thickness). Moreover, LHTY-stained rings clearly depicted connective tissue elements within the intervening sublayers of tunica media. The contrast provided by two dyes of LHTY enhanced the appearance of the myofibrillar texture of interlamellar zones and thickness of bands. On the other hand, the nuclei of the smooth muscle cells were somewhat more discernable using H&E staining.

Mechanical Characterization of the Lamellar Structure of Human Abdominal Aorta in the Development of Atherosclerosis: An Atomic Force Microscopy Study.

Atherosclerosis is a major risk factor for cardiovascular disease. However, mechanisms of interaction of atherosclerotic plaque development and local stiffness of the lamellar structure of the arterial wall are not well established. In the current study, the local Young's modulus of the wall and plaque components were determined for three different groups of healthy, mildly diseased and advanced atherosclerotic human abdominal aortas. Histological staining was performed to highlight the atherosclerotic plaque components and lamellar structure of the aortic media, consisting of concentric layers of elastin and interlamellar zones. The force spectroscopy mode of the atomic force microscopy was utilized to determine Young's moduli of aortic wall lamellae and plaque components at the micron level. The high variability of Young's moduli (E) at different locations of the atherosclerotic plaque such as the fibrous cap (E=15.5± 2.6kPa), calcification zone (E=103.7±19.5kPa), and lipid pool (E=3.5±1.2kPa) were observed. Reduction of elastin lamellae stiffness (18.6%), as well as stiffening of interlamellar zones (50%), were detected in the diseased portion of the medial layer of abdominal aortic wall compared to the healthy artery. Additionally, significant differences in the stiffness of both elastin lamellae and interlamellar zones were observed between the diseased wall and disease-free wall in incomplete plaques. Our results elucidate the alternation of the stiffness of different lamellae in the human abdominal aortic wall with atherosclerotic plaque development and may provide new insight on the remodeling of the aortic wall during the progression of atherosclerosis.

Tunable Multiscale Nanoparticle Ordering by Polymer Crystallization

While ∼75% of commercially utilized polymers are semicrystalline, the generally low mechanical modulus of these materials, especially for those possessing a glass transition temperature below room temperature, restricts their use for structural applications. Our focus in this paper is to address this deficiency through the controlled, multiscale assembly of nanoparticles (NPs), in particular by leveraging the kinetics of polymer crystallization. This process yields a multiscale NP structure that is templated by the lamellar semicrystalline polymer morphology and spans NPs engulfed by the growing crystals, NPs ordered into layers in the interlamellar zone [spacing of (10–100 nm)], and NPs assembled into fractal objects at the interfibrillar scale, (1–10 μm). The relative fraction of NPs in this hierarchy is readily manipulated by the crystallization speed. Adding NPs usually increases the Young’s modulus of the polymer, but the effects of multiscale ordering are nearly an order of magnitude larger than those for a state where the NPs are not ordered, i.e., randomly dispersed in the matrix. Since the material’s fracture toughness remains practically unaffected in this process, this assembly strategy allows us to create high modulus materials that retain the attractive high toughness and low density of polymers.

Mapping the 3D distribution of CdSe nanocrystals in highly oriented and nanostructured hybrid P3HT–CdSe films grown by directional epitaxial crystallization

Highly oriented and nanostructured hybrid thin films made of regioregular poly(3-hexylthiophene) and colloidal CdSe nanocrystals are prepared by a zone melting method using epitaxial growth on 1,3,5-trichlorobenzene oriented crystals. The structure of the films has been analyzed by X-ray diffraction using synchrotron radiation, electron diffraction and 3D electron tomography to afford a multi-scale structural and morphological description of the highly structured hybrid films. A quantitative analysis of the reconstructed volumes based on electron tomography is used to establish a 3D map of the distribution of the CdSe nanocrystals in the bulk of the films. In particular, the influence of the P3HT-CdSe ratio on the 3D structure of the hybrid layers has been analyzed. In all cases, a bi-layer structure was observed. It is made of a first layer of pure oriented semi-crystalline P3HT grown epitaxially on the TCB substrate and a second P3HT layer containing CdSe nanocrystals uniformly distributed in the amorphous interlamellar zones of the polymer. The thickness of the P3HT layer containing CdSe nanoparticles increases gradually with increasing content of NCs in the films. A growth model is proposed to explain this original transversal organization of CdSe NCs in the oriented matrix of P3HT.

Oriented and Nanostructured Polycarbonate Substrates for the Orientation of Conjugated Molecular Materials and Gold Nanoparticles

A simple method to prepare large areas of polycarbonate (PC) alignment layers with a high degree of polymer chain orientation, a periodic and oriented nanoscale pattern, and a controlled surface roughness is presented. The method involves three steps: (i) the preparation of a film of bisphenol A polycarbonate in its glassy state, (ii) the near-surface orientation of the polymer chains by rubbing, and (iii) exposure to vapors of acetone which acts as a plasticizer removing the microgrooves formed by rubbing and promotes solvent induced crystallization of PC. The resulting surface of the PC films is oriented and nanostructured, it consists of the periodic alternation of edge-on oriented crystalline lamellae and amorphous interlamellar zones with a total periodicity of ∼20 nm. The roughness of the oriented and nanostructured PC layers can be tuned by adjusting the exposure time to the solvent. The PC films exhibit a high orienting ability for various materials grown from the vapor phase, e.g., conjugated or...

Fabrication of Oriented and Periodic Hybrid Nanostructures of Regioregular Poly(3‐hexylthiophene) and CdSe Nanocrystals by Directional Epitaxial Solidification

Hybrid nanostructures of regioregular (RR) P3HT and colloidal CdSe nanocrystals (spheres and rods, see figure) have been prepared by directional epitaxial solidification. The hybrid nanostructured films involve the periodic alternation of crystalline P3HT lamellae separated by amorphous interlamellar zones harboring the confined CdSe nanocrystals. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2089/2007/c0311_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Effect of Molecular Weight on the Structure and Morphology of Oriented Thin Films of Regioregular Poly(3‐hexylthiophene) Grown by Directional Epitaxial Solidification

AbstractRegioregular head‐to‐tail (HT)‐coupled poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) with a weight‐average molecular weight (Mw) in the 7.3–69.6 kDa range is crystallized by directional epitaxial solidification in 1,3,5‐trichlorobenzene (TCB) to yield highly oriented thin films. An oriented and periodic lamellar structure consisting of crystalline lamellae separated by amorphous interlamellar zones is evidenced by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Both the overall crystallinity as well as the orientation of the crystalline lamellae decrease significantly with increasing Mw. The total lamellar periodicity is close to the length of “fully extended” chains for Mw = 7.3 kDa (polystyrene‐equivalent molecular weight, eq. PS) and it saturates to a value of ca. (25–28) ± 2 nm for Mw ≥ 18.8 kDa (eq. PS). This behavior is attributed to a transition from an oligomeric‐like system, for which P3HT chains are essentially in a fully extended all‐trans conformation and do not fold, to a semicrystalline system that involves a periodic alternation of crystalline lamellae separated by extended amorphous interlamellar zones, which harbor chain folds, chain ends, and tie molecules. For P3HT with Mw of ca. 7.3 kDa (eq. PS), epitaxial crystallization on TCB allows for the growth of both “edge‐on” and “flat‐on” oriented crystalline lamellae on the TCB substrate. The orientation of the lamellae is attributed to 1D epitaxy. Because of the large size of the “flat‐on” crystalline lamellae, a characteristic single‐crystal electron diffraction pattern corresponding to the [001] zone was obtained by selected area electron diffraction (SAED), indicating that P3HT crystallizes in a monoclinic unit cell with a = 16.0 Å, b = 7.8 Å, c = 7.8 Å, and γ = 93.5°.

Regional variations in the density and arrangement of elastic fibres in the anulus fibrosus of the human lumbar disc

Elastic fibres are critical components of the extracellular matrix in dynamic biological structures that undergo extension and recoil. Their presence has been demonstrated in the anulus fibrosus of the human lumbar intervertebral disc; however, a detailed regional analysis of their density and arrangement has not been undertaken, limiting our understanding of their structural and functional roles. In this investigation we have quantitatively described regional variations in elastic fibre density in the anulus fibrosus of the human L3-L4 intervertebral disc using histochemistry and light microscopy. Additionally, a multiplanar comparison of patterns of elastic fibre distribution in the intralamellar and interlamellar zones was undertaken. Novel imaging techniques were developed to facilitate the visualization of elastic fibres otherwise masked by dense surrounding matrix. Elastic fibre density was found to be significantly higher in the lamellae of the posterolateral region of the anulus than the anterolateral, and significantly higher in the outer regions than the inner, suggesting that elastic fibre density in each region of the anulus is commensurate with the magnitude of the tensile deformations experienced in bending and torsion. Elastic fibre arrangments in intralamellar and interlamellar zones were shown to be architecturally distinct, suggesting that they perform multiple functional roles within the anulus matrix structural hierarchy.

Relaxations in semicrystalline polyethyleneterephthalate using thermally stimulated currents

Relaxation processes at temperatures above 20 °C in semicrystalline polyethylene-terephthalate have been studied using thermally stimulated depolarization currents (TSDC). The discharge curve shows three relaxation peaks (αc, ρc and ρ*) whose positions and intensities depend on the polarization conditions and the crystallinity. Relaxations αc and ρc are heteropolar, while ρ* may be homopolar or heteropolar according to the polarization temperature used. The effect of the crystallinity on these relaxations has been analysed by the thermal steps stimulation (TSS) method applied to an amorphous sample. Results show that αc is fundamentally a dipolar relaxation associated with the amorphous interlamellar zone. The relaxation ρc is associated with the release of a free charge trapped in the amorphous regions, and ρ* is a Maxwell–Wagner–Sillars relaxation associated with crystalline – amorphous interphases. For polarization temperatures above 150 °C, two relaxations are observed only as a consequence of overlapping ρC and ρ* relaxations. © 1998 Chapman & Hall

Melting behavior of poly(ether ether ketone) in its blends with poly(ether imide)

AbstractWe detail the melting behavior of poly(ether ether ketone) (PEEK) and investigate its melting behavior in miscible blends with poly(ether imide) (PEI). The determination of the equilibrium melting point (Tm0) of PEEK is discussed by considering its inhomogeneous morphology. Tm0 is obtained by a long extrapolation of a Hoffman–Weeks plot to 384°C. Hindrance of PEEK crystal reorganization induced by PEI during heating is observed over the blend composition investigated (20–75 wt % PEEK). This behavior is correlated with the incorporation of PEI in the interlamellar zones of PEEK crystals. The interaction parameter χ of PEEK/PEI blends is estimated by the equilibrium melting point depression. This gives the interaction density B = −1.2 cal/cm3, and x = −0.40 at 400°C. © 1993 John Wiley &amp; Sons, Inc.

Phase behavior of poly(butylene terephthalate)/polyarylate blends

The amorphous phase behavior of poly(butylene terephthalate) (PBT)/polyarylate (based on bisphenol A and a 75/25 mole ration of isophtalic andterephtalic acids) (PAr) (blends) primilary using dielectric spectroscopy. SAXS experiments show clearly that the PAr resides in the interlamellar zones. Two dielectric relaxations associated with long-range motion for blends in which PBT has crystallized were observed. Following from recent research on order-disorder interphases in crystalline blends, the low-temperature transition was tentatively assigned to the presence of a crystal-amorphous interphase and the high-temperature relaxation to an unconstrained (mixed) amorphous phase

Influence of structural and morphological factors on the mechanical properties of the polyethylenes

AbstractForce‐length relations at ambient temperature have been determined for a set of polyethylenes which represent a wide range in molecular weight and molecular constitution. Taking advantage of previous work from this laboratory, samples have been prepared in such a manner that the important independent structural variables can be identified and isolated and their influence on the different aspects of the deformation process assessed. Partial melting‐recrystallization processes appear to play an important role. For the linear polymers there is a direct influence of molecular weight. The influence of molecular weight manifests itself in the structure of the interlamellar zone which has a major influence on the initial modulus as well as the ultimate properties. Copolymers and branched copolymers display quite different behavior. The most striking difference is the invariance of the ultimate properties with molecular weight, branching, and level of crystallinity. From the set of experimental results that are presented the molecular factors involved in the deformation process can be sorted out. It becomes quite evident that all of the basic structural regions, characteristic of semicrystalline polymers, contribute to the observations. Focus solely on the changes in the crystallite, in analogy to the deformation of small‐molecule crystalline systems, is inadequate in the case of crystalline polymers.

The porosity of deferrated montmorillonites: ethanol and methylbromide sorption

AbstractComparative porosity studies based on nitrogen sorption isotherms were carried out on six freeze-dried Na-montmorillonites (Moosburg, Camp Berteau, Marnia, Greek Yellow, Greek White, Wyoming bentonite), untreated and deferrated with dithionite/citrate. Mesopore analysis was carried out using the ‘parallel-plate model’; for supermicropores the ‘MP’ method was used. Most of the surface area was located in the supermicropores (width 7–15 Å). Higher total surface areas of the deferrated clays resulted from a much higher supermicroporous surface area, while the mesopore surface was similar or smaller. The lower the charge density of a subfraction of deferrated Wyoming (Na-)bentonite, the lower the vapour pressure at which the interlamellar sorption of ethanol occurred. The results predict an expansion on contact with the first traces of ethanol at 298 K for a Na-smectite with a charge density ξ = 0·11 e/(Si,Al)4O10 unit. Compared with ethanol, methylbromide showed a weaker interaction with Na-smectite. At p/p0 = 0·4 only 18 % of the interlamellar zones of low-charged Laponite were penetrated; one third of the supermicropores of this smectite were not accessible to CH3Br.

Visualization by STEM annular DF of intralamellar shear in polyethylene

Thin films of polyethylene (PE) with high orientation have recently been prepared by “melt-drawing”. This process produces long crystalline lamellae normal to the draw direction and with the chain axis [00ℓ] parallel to the draw direction (Figure 1).Thin films were prepared from a 0.5% solution of high density PE (Marlex 6003, Mw=2×l05) in xylene, which was drawn from a glass slide at 125°C. The films were annealed on glycerol at 125°C for two hours, then were placed on specially fabricated soft copper deformation grids. In-situ deformation was performed in a tensile deformation stage of a JE0L 100CX STEM. The initial gauge length was 0.5mm, with a strain rate of 0.1min−1.Figure 1 shows a bright field (BF) CTEM image of an annealed film. Crystals properly oriented for diffraction appear black, while non-Bragg-oriented lamellar crystals are grey. The interlamellar zones (amorphous regions) appear as bright areas for underfocus conditions since innerpotential of the crystalline phase is approximately one volt larger than that of the amorphous phase. The bright white “ghosts” are diffraction images displaced by defocus from their corresponding main beam images in the direction of the appropriate diffraction vector.

Lamellar and interlamellar structure in melt‐crystallized polyethylene. II. Lamellar spacing, interlamellar thickness, interlamellar density, and stacking disorder

AbstractMeasurements of the small‐angle scattering power and the degree of crystallinity in melt‐crystallized high‐density polyethylene have been used to evaluate the “amorphous” density in situ by the relation, where V is the irradiated volume and ḡ(S) is the “slit‐smeared” absolute intensity. The amorphous density is a function of sample history and is always higher than the extrapolated melt density. After slit‐height correction, and within the experimental error, the ratio of the two observed long periods is 2:1 at all temperatures (25‐‐126°C). The lamellar thickness and the average interlamellar spacing are obtained from the degree of crystallinity and the first corrected long period. At increasing temperatures between 25°C and 110°C, the lamellae become thinner while the interlamellar zone expands by almost half. Over this range the changes are reversible with temperature. Above 110°C, both the lamellae and the interlamellar region expand with temperature. The thickening is partially reversible upon recooling. Other results obtained include measurements of stacking disorder and of microstructural changes with crystallization temperature and with time at ambient temperature.