Anisotropic Organization Research Articles

Fiber alignment and coculture with fibroblasts improves the differentiated phenotype of murine embryonic stem cell‐derived cardiomyocytes for cardiac tissue engineering

Embryonic stem cells (ESCs) are an important source of cardiomyocytes for regenerating injured myocardium. The successful use of ESC-derived cardiomyocytes in cardiac tissue engineering requires an understanding of the important scaffold properties and culture conditions to promote cell attachment, differentiation, organization, and contractile function. The goal of this work was to investigate how scaffold architecture and coculture with fibroblasts influences the differentiated phenotype of murine ESC-derived cardiomyocytes (mESCDCs). Electrospinning was used to process an elastomeric biodegradable polyurethane (PU) into aligned or unaligned fibrous scaffolds. Bioreactor produced mESCDCs were seeded onto the PU scaffolds either on their own or after pre-seeding the scaffolds with mouse embryonic fibroblasts (MEFs). Viable mESCDCs attached to the PU scaffolds and were functionally contractile in all conditions tested. Importantly, the aligned scaffolds led to the anisotropic organization of rod-shaped cells, improved sarcomere organization, and increased mESCDC aspect ratio (length-to-diameter ratio) when compared to cells on the unaligned scaffolds. In addition, pre-seeding the scaffolds with MEFs improved mESCDC sarcomere formation compared to mESCDCs cultured alone. These results suggest that both fiber alignment and pre-treatment of scaffolds with fibroblasts improve the differentiation of mESCDCs and are important parameters for developing engineered myocardial tissue constructs using ESC-derived cardiac cells.

The structure of chain end-grafted nanoparticle/homopolymer nanocomposites

The morphological structure of mixtures of homopolymers with inorganic nanoparticles, onto which polymer chain ends are grafted, is described herein. In the bulk, at very low grafting densities, Σ, the morphology of these polymer nanocomposites (PNCs) is largely determined by the attractive enthalpic interactions between the nanoparticle cores, mediated by entropic interactions with the grafted polymer chains. These competing interactions have been shown to be responsible for the anisotropic organization of the nanoparticles within polymer hosts. At high grafting densities, however, even in cases where the host chains and the grafted chains are of identical chemical structure, the entropic brush layer/free host chain interactions are dominant, leading to miscibility (isotropic dispersion of the nanoparticles within the polymer host) or to microscopic and macroscopic phase separation. In the limit of very small nanoparticles, radii R ≈ 1 nm, the brush/melt interactions are not important yet the nanoparticles exhibit a high tendency toward miscibility within homopolymer hosts. This paper begins with a discussion of the bulk morphology of PNCs in order to provide a context for the subsequent description of the morphological structure of thin film brush coated nanoparticle–homopolymer mixtures. A fundamental difference between these bulk and thin film PNCs is that a preferential attraction of grafted nanoparticles to interfaces renders thin film PNCs thermodynamically less stable than their bulk analogs. Morphological phase diagrams, which delineate regimes where the PNCs are miscible, incompatible or partially miscible, are parameterized in terms of the nanoparticle curvature, the chain grafting density, the grafting chain degree of polymerization, N, that of the free host chains, P, and the thermodynamic (Flory–Huggins) interaction parameter, χ, between the host and grafted chains.

Anisotropic Porous Biodegradable Scaffolds for Musculoskeletal Tissue Engineering

It has been generally accepted that tissue engineered constructs should closely resemble the in-vivo mechanical and structural properties of the tissues they are intended to replace. However, most scaffolds produced so far were isotropic porous scaffolds with non-characterized mechanical properties, different from those of the native healthy tissue. Tissues that are formed into these scaffolds are initially formed in the isotropic porous structure and since most tissues have significant anisotropic extracellular matrix components and concomitant mechanical properties, the formed tissues have no structural and functional relationships with the native tissues. The complete regeneration of tissues requires a second differentiation step after resorption of the isotropic scaffold. It is doubtful if the required plasticity for this remains present in already final differentiated tissue. It would be much more efficacious if the newly formed tissues in the scaffold could differentiate directly into the anisotropic organization of the native tissues. Therefore, anisotropic scaffolds that enable such a direct differentiation might be extremely helpful to realize this goal. Up to now, anisotropic scaffolds have been fabricated using modified conventional techniques, solid free-form fabrication techniques, and a few alternative methods. In this review we present the current status and discuss the procedures that are currently being used for anisotropic scaffold fabrication.

Polarized light emission from aligned luminescent liquid crystal films based on 4,7-disubstituted-2,1,3-benzothiadiazoles

The physical properties of a series of light emitting liquid crystal compounds based on 4,7-disubstituted-2,1,3-benzothiadiazoles were investigated in thin solid films. The films were produced on glass plates via spin-coating and then heated to give their liquid crystal mesophases leading to an anisotropic organization of the molecules inside the films after subsequent cooling down to the room temperature. An important finding was that the induced film anisotropy exhibited photo-emission of polarized light. The absorption and fluorescence spectra of the heated films had significant differences compared to the non-heated ones and interesting differences in the organization of the molecules were observed when the films were deposited on anisotropic substrates. Optical microscopy and atomic force microscopy (AFM) measurements were performed to investigate the texture and morphology of the films.

CAMP‐dependent protein kinase A and the dynamics of epithelial cell surface domains: Moving membranes to keep in shape

Cyclic adenosine monophosphate (cAMP) and cAMP-dependent protein kinase A (PKA) are evolutionary conserved molecules with a well-established position in the complex network of signal transduction pathways. cAMP/PKA-mediated signaling pathways are implicated in many biological processes that cooperate in organ development including the motility, survival, proliferation and differentiation of epithelial cells. Cell surface polarity, here defined as the anisotropic organisation of cellular membranes, is a critical parameter for most of these processes. Changes in the activity of cAMP/PKA elicit a variety of effects on intracellular membrane dynamics, including membrane sorting and trafficking. One of the most intriguing aspects of cAMP/PKA signaling is its evolutionary conserved abundance on the one hand and its precise spatial-temporal actions on the other. Here, we review recent developments with regard to the role of cAMP/PKA in the regulation of intracellular membrane trafficking in relation to the dynamics of epithelial surface domains.

Auto-organization modulation of tetrasubstituted tetrathiafulvalenes (TTF) in silica based hybrid materials

The effect of the interactions generated by the spacer group between the TTF core and the four triethoxysilane groups on the auto-organization of the organic bridging moieties in hybrid materials obtained by sol–gel chemistry has been investigated. The silica-based hybrid solids are highly polycondensed. They present different scales of organization (nanometric and micrometric) that are independent one from each other and are governed by the different parameters which control the kinetics of polycondensation. Their anisotropic organization is function of the interaction forces induced by the spacer, van der Waals, hydrogen bonding or both, during the hydrolytic condensation process.

Hydrophobic induced supramolecular self-organization of tetrahedral units based on van der Waals interactions

Nanostructured hybrid materials were prepared by sol–gel hydrolysis–polycondensation of tetrakis(4-trisisopropoxysilylphenyl)germane PGe and tetrakis(4-trisisopropoxysilylphenyl) tin PSn which present a tetrahedral germanium or tin central atom. Both precursors presented twelve directions for solid formation oriented regularly on the four directions of the tetrahedron. Their organization was evaluated by X-ray diffraction studies (nanometric scale) and birefringence measurements (micrometric scale). It has been shown that the organization of these solids was influenced by the experimental parameters. The intensities of birefringence lay in the same range (1.6 × 10−3 to 2.1 × 10−3) for all the gels XGe and XSn. Regular parallel rectangular chunks were observed in all cases. The orientation of the optical axis was found perpendicular to the edges of the chunks in all cases. The existence of such optical axes regularly oriented towards the edges of the chunks corresponded to an anisotropic organization at the micrometric scale. The results presented here strengthen the fact that the auto-organization observed in nanostructured organic–inorganic hybrid materials occurs during the formation of Si–O–Si bonds, which transforms intermolecular interactions into intramolecular ones corresponding to the weak van der Waals-type interactions existing between the organic units. The role of hydrophilic–hydrophobic interactions is discussed.

Auto-organization of Nanostructured Organic−Inorganic Hybrid Xerogels Prepared by Sol−Gel Processing: The Case of a “Twisted” Allenic Precursor

Nanostructured hybrid materials prepared by sol−gel hydrolysis−polycondensation of the precursor 1,3-bis(propyltrimethoxysilyl)-1,3-diphenylallene P having a bulky rigid and twisted core with two short flexible arms exhibited a self-organization evaluated by birefringence measurements (micrometric scale) and X-ray diffraction studies (nanometric scale). These observations show that the auto-organization of hybrid materials is not limited to rigid-rod or mesogenic spacers. It appears as a more general phenomenon. The twisted geometry of the organic group induced an anisotropic organization, the morphology of which was unprecedented and different from the one observed with the linear or mesogenic hybrid materials previously studied. Moreover, the birefringence pictures were also different from those observed with liquid crystals. In some cases unprecedented wavy parallel cracks showed the extension of the organization over the millimetric scale. It is the same for the X-ray diffraction. In all the cases precedently studied the X-ray diffraction diagrams exhibit diffraction peaks related to the length of the organic spacer. We observed here signals which did not correspond to this distance, suggesting a different nanometric scale organization in the solid.

Auto-organization in sol-gel type polycondensation: a door to the nanosciences.

Silica-based hybrid organic-inorganic materials prepared by sol-gel chemistry exhibit chemical and physical properties revealing their anisotropic organization. Besides the opportunities that these phenomena open for the preparation of new materials, they also provide arguments for the chemist looking for better comprehension and control of the solid's organization.

Mechanical Considerations of the Laminated Composite Structure Modeled on the Anisotropic Organization of a Bamboo.

Mechanical Considerations of the Laminated Composite Structure Modeled on the Anisotropic Organization of a Bamboo.

Nonrelaxable Anisotropic Organization of Organic-Inorganic Hybrid Materials Induced by an Electric Field

Ein doppelbrechendes Gel entsteht bei der Polykondensation einer stark dipolaren Bis(trialkoxysilyl)-substituierten Verbindung in einem elektrischen Feld. Die Doppelbrechung ist ein Beleg für anisotrope Ordnung im Mikrometerbereich. Das Bild zeigt eine Aufnahme des Gels unter dem Polarisationsmikroskop.

Auto-organisation of hybrid organic-inorganic materials prepared by sol-gel process.

Silica-based hybrid organic-inorganic materials prepared by sol-gel chemistry exhibit chemical and physical properties revealing their anisotropic organisation. Besides the opportunities that this phenomenon opens for the preparation of new materials, it also provides arguments to the chemist looking for a better comprehension and control of the organisation of solids.

Nonrelaxable Anisotropic Organization of Organic-Inorganic Hybrid Materials Induced by an Electric Field

A birefringent gel is formed when polycondensation of a strongly dipolar bis(trialkoxysilyl) compound is performed in an electric field. The birefringence is evidence for anisotropic ordering on the micrometer scale. The picture shows an image of the gel under a polarizing light microscope.

Enthalpy Relaxation Behavior of Liquid-Crystalline Glasses of an Esterified Cholesterol Derivative and its Complex Salts with Aliphatic Amines

A cholesteryl hydrogen phthalate (CHP) and its complex salts with normal aliphatic amines (Cn-amines) are capable of forming a glassy liquid-crystalline phase, where an anisotropic organization of their fluid mesophase is frozen in an uncrystallized solid state. Differential scanning calorimetry (DSC) measurements were conducted for these glassy materials to examine an enthalpy relxation phenomenon, occurring when they were annealed adequately at temperatures lower than the glass transition temperature. The enthalpy relaxation behavior, monitored as evolution of a DSC endothermic peak, was analyzed in terms of a Kohlrausch-Williams-Watts type of stretched exponential equation, and the overall relaxation time τ and a parameter β chracterizing the distribution of the relaxation mode were evaluated. It turned out that the τ values obtained for CHP/Cn-amine salts were rather smaller than those for CHP per se, and β became close to unity when CHP was complexed with the Cn-amines through ionic interaction, the latter component employed having 12, 16, and 18 carbons. The activation energy for the relaxation process of the CHP/Cn-amine samples was considerably small, compared with that in the case of CHP alone, and tended to decrease with an increase in the carbon number of the amine component. An attempt was also made to estimate the fragility of these samples as glass.

Anisotropic organization of the rat superior paraolivary nucleus.

In rodents, the superior paraolivary nucleus (SPON) is one of the major nuclei of the superior olivary complex that innervate the inferior colliculus. To analyze the intrinsic organization of the SPON and to gain further insight into its relationship with the inferior colliculus, the neuroanatomical tracers biotinylated dextran and horseradish peroxidase were unilaterally injected into different regions of the central nucleus of the inferior colliculus of adult albino rats. Both tracers resulted in retrograde labeling of SPON cell bodies. In addition, biotinylated dextran rendered excellent filling of dendritic and axonal processes within the nucleus. Our results confirm that the projection from the SPON to the central nucleus of the inferior colliculus is nearly exclusively ipsilateral and strictly topographic. Furthermore, our data show that virtually all SPON neurons participate in this projection. The labeling with biotinylated dextran reveals that typical SPON neurons are medium to large multipolar cells with four to seven thick, long, scarcely branched and smooth dendrites that extend over long distances within a nearly parasagittal plane and intermingle with similarly oriented axonal plexuses. Some of the neurons located ventrally within the nucleus possess dendrites that extend ventrally beyond the limits of the SPON to penetrate into the underlying ventral nucleus of the trapezoid body. The parallel arrangement of flattened dendritic and axonal fields within the SPON is reminiscent of the fibrodendritic laminae found in other mammalian auditory nuclei. This fact and the available data about the connectivity of the nucleus stress the similarities between the SPON and the principal nuclei of the superior olivary complex.

Corticostriatal Projections from Rat Barrel Cortex Have an Anisotropic Organization that Correlates with Vibrissal Whisking Behavior

To elucidate the detailed organization of corticostriatal projections from rodent somatosensory cortex, the anterograde tracers biotinylated dextran amine (BDA) and fluoro-ruby (FR) were injected into separate parts of the whisker "barrel" representation. In one group of rats, the two tracers were injected into different barrel columns residing in the same row; in the other group of rats, the tracers were deposited into barrel columns residing in different rows. Reconstructions of labeled axonal varicosities in the neostriatum and ventrobasal thalamus were analyzed quantitatively to compare the extent of overlapping projections to these subcortical structures. For both groups of animals, corticostriatal projections terminated in densely packed clusters that occupied curved lamellar-shaped regions along the dorsolateral edge of the neostriatum. When the tracers were injected into different whisker barrel rows, the distribution of BDA- and FR-labeled terminals in the neostriatum followed a crude somatotopic organization in which the amount of overlap was approximately the same as in the ventrobasal thalamus. When both tracers were injected into the same whisker barrel row, however, the amount of corticostriatal overlap was significantly higher than the amount of overlap observed in the ventrobasal thalamus. These results indicate that corticostriatal projections from whisker barrel cortex have an anisotropic organization that correlates with the pattern of vibrissal movements during whisking behavior.

Self-polarization and directional motility of cytoplasm

Background: Directional cell motility implies the presence of a steering mechanism and a functional asymmetry between the front and rear of the cell. How this functional asymmetry arises and is maintained during cell locomotion is, however, unclear. Lamellar fragments of fish epidermal keratocytes, which lack nuclei, microtubules and most organelles, present a simplified, perhaps minimal, system for analyzing this problem because they consist of little other than the motile machinery enclosed by a membrane and yet can move with remarkable speed and persistence.Results: We have produced two types of cellular fragments: discoid stationary fragments and polarized fragments undergoing locomotion. The organization and dynamics of the actin–myosin II system were isotropic in stationary fragments and anisotropic in the moving fragments. To investigate whether the creation of asymmetry could result in locomotion, a transient mechanical stimulus was applied to stationary fragments. The stimulus induced localized contraction and the formation of an actin–myosin II bundle at one edge of the fragment. Remarkably, stimulated fragments started to undergo locomotion and the locomotion and associated anisotropic organization of the actin–myosin II system were sustained after withdrawal of the stimulus.Conclusions: We propose a model in which lamellar cytoplasm is considered a dynamically bistable system capable of existing in a non-polarized or polarized state and interconvertible by mechanical stimulus. The model explains how the anisotropic organization of the lamellum is maintained in the process of locomotion. Polarized locomotion is sustained through a positive-feedback loop intrinsic to the actin–myosin II machinery: anisotropic organization of the machinery drives translocation, which then reinforces the asymmetry of the machinery, favoring further translocation.

Coupling and memory in liquid crystal elastomers

AbstractThe polymer backbone of a side‐chain liquid crystal polymer exhibits an anisotropic shape due to the coupling of the liquid crystal orientational order of the mesogenic side‐chains to the backbone. The magnitude and sign of this coupling may be controlled by chemical design. The introduction of chemical cross‐links in to such a system provides both a memory of the anisotropic organisation and a mechanism by which the microscopic anisotropy can be realised at a macroscopic level. We show how this anisotropic network structure yields new phenomena when electric or mechanical fields are applied.

Phase Behavior of Novel Liquid-Crystalline Salts Containing a Cholesteryl Group

Abstract The phase behavior of liquid-crystalline salts having a cholesteryl group was investigated by differential scanning calorimetry and polarized-light microscopy. Cholesteryl hydrogen succinate (CHS) and cholesteryl hydrogen phthalate (CHP) were used as a mesogenic core, and a series of normal aliphatic amines with 12 ∼ 18 carbons were used as a flexible tail. The salts were prepared as a stoichiometric 1:1 complex of a cholesterol derivative and an amine from mixed solutions in ethanol by solvent evaporation. CHS exhibited a monotropic cholesteric phase, while the salts of CHS with amines showed a mesophase in both cooling and heating cycles and it was frozen into a glassy state at temperatures below 0°C without changing the anisotropic organization. A similar state of glassy liquid crystal was noted for CHP per se and its salts with amines. The temperature range where a fluid liquid-crystalline phase appeared was mostly wider in the salt systems, when compared with the cases using the cholesterol derivatives alone. An odd-even oscillation phenomenon was perceived in the dependence of the mesophase-isotropic transition temperature and enthalpy of the salts on the carbon number of the amine component.

An English journal published by the Japanese Orthopaedic Association

Anisotropic collagen/apatite microstructure is a prominent determinant of bone tissue functionalization; in particular, bone matrix modulates its anisotropic microstructure depending on the surrounding mechanical condition. Although mechanotransduction in bones is governed by osteocyte function, the precise mechanisms linking mechanical stimuli and anisotropic formation of collagen/apatite microstructure are poorly understood. Here we developed a novel anisotropic mechano-coculture system which enables the understanding of the biological mechanisms regulating the oriented bone matrix formation, which is constructed by aligned osteoblasts. The developed model provides bone-mimetic coculture platform that enables simultaneous control of mechanical condition and osteoblast-osteocyte communication with an anisotropic culture scaffold. The engineered coculture device helps in understanding the relationship between osteocyte mechanoresponses and osteoblast arrangement, which is a significant contributor to anisotropic organization of bone tissue. Our study showed that osteocyte responses to oscillatory flow stimuli regulated osteoblast arrangement through soluble molecular interactions. Importantly, we found that prostaglandin E2 is a novel determinant for oriented collagen/apatite organization of bone matrix, through controlling osteoblast arrangement.