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PubMed2002

Importance of the superficial tissue layer for the indentation stiffness of articular cartilage.

Indentation testing is a widely used technique for nondestructive mechanical analysis of articular cartilage. Although cartilage shows an inhomogeneous, layered structure with anisotropic mechanical properties, most theoretical indentation models assume material homogeneity and isotropy. In the present study, quantitative polarized light microscopy (PLM) measurements from canine cartilage were utilized to characterize thickness and structure of the superficial, collageneous tissue layer as well as to reveal its relation to experimental indentation measurements. In addition to experimental analyses, a layered, transversely isotropic finite element (FE) model was developed and the effect of superficial (tangential) tissue layer with high elastic modulus in the direction parallel to articular surface on the indentation response was studied. The experimental indentation stiffness was positively correlated with the relative thickness of the superficial cartilage layer. Also the optical retardation, which reflects the degree of parallel organization of collagen fibrils as well as collagen content, was related to indentation stiffness. FE results indicated effective stiffening of articular cartilage under indentation due to high transverse modulus of the superficial layer. The present results suggest that indentation testing is an efficient technique for the characterization of the superficial degeneration of articular cartilage.

Animals↗
PubMed2006

Developmental competence of transported in-vitro matured macaque oocytes.

This study examines in-vitro maturation (IVM) in a non-human primate model, Macaca fascicularis. The animals had hormonal injections and laparoscopic oocyte retrieval (OR)) at 12- and 24- h after human chorionic gonadotrophin (HCG). The immature oocytes were placed in tightly capped tubes containing pre-equilibrated IVM medium and transported for 5 h in a dry portable 37 degrees C incubator without CO2 supplement. Meiotic spindle was observed at 36-38- h post-HCG by polarized microscopy in 72 and 84.5% of mature oocytes collected at 12- and 24- h post-HCG oocyte retrieval intervals respectively. However, abnormal spindle formations were detected in some IVM oocytes by confocal microscopy. The IVM oocytes were also randomly selected for (i) intracytoplasmic injection with frozen-thawed epididymal M. fascicularis spermatozoa and (ii) nuclear transfer (NT) with fresh M. fascicularis cumulus cells. Embryonic development of sperm-injected embryos was not affected by the 12- and 24- h post-HCG oocyte retrieval intervals (22.5 versus 27.9% respectively). However, embryonic development of NT embryos was significantly affected by the 12- h post-HCG oocyte retrieval interval (4.5 versus 31.7% respectively; P < 0.01). In conclusion, IVM of monkey oocytes in a dry portable incubator for 5 h did not affect the maturation rate. However, the ability of primate oocytes to develop after somatic cell nuclear transfer was affected by oocyte retrieval time post-HCG.

Animals↗
PubMed1989

Early ossification within the human fetal otic capsule: morphological and microanalytical findings.

Besides the use of conventional techniques such as light and polarization microscopy, the present paper proposes the combined use of transmission electron microscopy, secondary and backscattered electron imaging, energy dispersive X-ray analysis and computed tomography for the diagnostic evaluation of ear pathology in the human fetus. These methods were used to revisit the primary calcification front of the fetal otic capsule between 16 and 23 weeks gestational age. Ultramicroscopic evaluation demonstrates similar fetal bone formation to that found in other bones of the human fetus. The formation of the endosteal and periosteal layers is a typical example of early intra-membranous ossification. The enchondral layer is made up of fibrillar bone, laid down around the calcified cartilage remnants. Microchemical analysis indicates a significantly higher Ca/P ratio in the endochondral layer with respect to the endosteum and periosteum. The consequences of a lower Ca/P ratio in the endosteal layer are discussed in view of calcium homeostasis and inner ear function.

Ear Cartilage↗
PubMed1985

Molecular motions and thermotropic phase behavior of cholesteryl esters with triolein.

The phase behavior of cholesteryl esters with triglyceride has been characterized by differential scanning calorimetry (DSC), light microscopy, and polarizing light microscopy (PLM). Temperature-dependent molecular motions determined by 13C NMR spectroscopy were correlated with thermotropic phase behavior. Two systems, cholesteryl oleate (CO) and a 3/1 w/w mixture of cholesteryl linoleate (CL) and CO, were examined in the presence of small amounts of triolein (TO). Both systems exhibited metastable cholesteric and smectic (or only smectic) phases. Increasing amounts of TO progressively lowered the liquid-crystalline phase transition temperatures and eventually abolished the cholesteric phase, but at differing amounts of TO for the two systems (between 4% and 5% with CL/CO and between 7% and 10% with CO). DSC and PLM showed a progressive broadening of the phase transitions as well as an overlapping of the temperature ranges of the cholesteric and smectic phases. At greater than or equal to 4% TO, a separate isotropic liquid phase coexisted with liquid-crystalline phases. 13C NMR spectroscopy was used to monitor the molecular motions of the cholesteryl ester steroid ring and acyl chain in liquid and liquid-crystalline phases. In the liquid phase, no significant changes in fatty acyl motions, as reflected in spin-lattice relaxation time (T1) and nuclear Overhauser enhancement (NOE) values, were found on addition of TO. The line width (v 1/2) of the steroid ring resonances increased markedly near (1-5 degrees C above) the isotropic liquid----liquid-crystal phase transition temperature (TLC). However, the C3/C6 v 1/2 ratio at 1 degree C above TLC was greater for mixtures exhibiting an isotropic----cholesteric transition than for mixtures exhibiting an isotropic----smectic transition. Rotational correlation times calculated for motions about the long molecular axis and the nonunique axis showed (i) that the ring motions became more anisotropic as TLC was approached and (ii) that the motions were more anisotropic at TLC + 1 degree C for systems exhibiting a cholesteric phase than for systems exhibiting only a smectic phase. 13C line widths in spectra of the cholesteryl ester liquid-crystalline phases suggested that TO perturbed the cholesteryl ester intermolecular interactions and increased the rates of cholesteryl ester molecular motions relative to neat esters.

Calorimetry, Differential Scanning↗
PubMed2003

In vitro characterization of lactoferrin aggregation and amyloid formation.

Lactoferrin has previously been identified in amyloid deposits in the cornea, seminal vesicles, and brain. We report in this paper a highly amyloidogenic region of lactoferrin (sequence of NAGDVAFV). This region was initially identified by sequence comparison with medin, a 5.5 kDa amyloidogenic fragment derived from lactadherin. Subsequent characterization revealed that this peptide forms amyloid fibrils at pH 7.4 when incubated at 37 degrees C. Furthermore, although full-length lactoferrin does not by itself form amyloid fibrils, the protein does bind to the peptide fibrils as revealed by an increase in thioflavin T fluorescence and the presence of enlarged fibrils by transmission electron microscopy and polarized light microscopy. The binding of lactoferrin is a selective interaction with the NAGDVAFV fibrils. Lactoferrin does not bind to insulin or lysozyme fibrils, and the NAGDVAFV fibrils do not bind to soluble insulin or lysozyme. The lactoferrin appears to coat the peptide fibril surface to form mixed peptide/protein fibrils, but again there is no evidence for the formation of lactoferrin-only fibrils. This interaction, therefore, seems to involve selective binding rather than conventional seeding of fibril formation. We suggest that such a process could be generally important in the formation of amyloid fibrils in vivo since the identification of both full-length protein and protein fragments is common in ex vivo amyloid deposits.

Amino Acid Sequence↗
PubMed2001

Poly(oxazolines)s with tapered minidendritic side groups. The simplest cylindrical models to investigate the formation of two-dimensional and three-dimensional order by direct visualization.

The synthesis of 2-[3,4-bis(n-alkan-1-yloxy)phenyl]-2-oxazolines with alkan = octan, decan, dodecan, and tridecan is presented. Their living cationic ring opening polymerization produces cylindrical macromolecules that self-organize in a hexagonal columnar two-dimensional phase. The structural analysis of these polymers was carried out by a combination of techniques including differential scanning calorimetry, thermal optical polarized microscopy, X-ray diffraction, transmission electron microscopy, electron diffraction, scanning force microscopy, and atomic force microscopy (AFM). The diameter of these cylindrical macromolecules ranges from 33 to 44 A, and therefore they represent the simplest cylindrical macromolecules that can be directly visualized by AFM on a surface. Preliminary experiments have demonstrated the use of these cylindrical macromolecules as models to investigate the creation of two-dimensional and three-dimensional order via direct visualization and thus they represent the simplest nonbiological systems that mimic the role played by the complexes of nucleic acids with proteins in structural analysis by direct visualization.

Calorimetry, Differential Scanning↗
PubMed2001

Poly(oxazoline)s with tapered minidendritic side groups as models for the design of synthetic macromolecules with tertiary structure. A demonstration of the limitations of living polymerization in the design of 3-D structures based on single polymer chains.

The synthesis and living cationic ring-opening polymerization of 2-[3,4-bis(n-alkan-1-yloxy)phenyl]-2-oxazolines with alkan being tetradecan and pentadecan, i.e., (3,4)nG1-Oxz with n = 14 and 15, is described. The structural analysis of the resulting polymers with well-defined molecular weights and narrow molecular weight distribution was carried out by a combination of techniques, including differential scanning calorimetry (DSC), thermal optical polarized microscopy (TOPM), and X-ray diffraction (XRD). At low molecular weights both polymers self-assemble into spherical supramolecules that self-organize into a Pm3n 3-D lattice while at high molecular weights they form cylindrical macromolecules that self-organize into a p6mm 2-D hexagonal columnar lattice. Both polymers exhibit a 3-D shape change as a function of their degree of polymerization as was reported for the first time in a previous publication from our laboratory (Percec, V.; Ahn, C.-H; Ungar, G.; Yeardley, D. J. P.; Möller, M.; Sheiko, S. S. Nature (London) 1998, 391, 161). Since these polymers can be obtained via a living polymerization, a detailed mechanistic investigation of the influence of the degree of polymerization and molecular weight distribution on the formation of a 3-D spherical macromolecule from a single polymer chain, i.e., a tertiary structure, was possible. The experimental results have demonstrated that the synthesis of nonbiological macromolecules exhibiting tertiary structure is possible in at most a few percent of all macromolecules via living polymerization. This is the case even when macromolecules with very narrow molecular weight distributions and well-defined molecular weights are used. Therefore, the design of synthetic macromolecules with tertiary structure requires not only chains with well-defined molecular weight but also, in particular, macromolecules with no distribution of their chain length.

Calorimetry, Differential Scanning↗
PubMedDate not supplied

Influence of in vitro hydrolytic degradation on the morphology and crystallization behavior of poly(p-dioxanone).

We have studied the hydrolytic degradation of high molecular weight poly(p-dioxanone), PPDX, sutures. The samples were degraded either in distilled water or in a phosphate buffer at 37 degrees C, and the starting viscosity-average molecular weight was 130 kg/mol. The hydrolytic degradation of PPDX occurs in an approximate two stage process where the amorphous regions of the sample are attacked faster than the crystalline regions of the sample. The changes experienced by the samples as degradation proceeded were successfully monitored by viscosimetry, differential scanning calorimetry (DSC), weight loss, pH changes, and scanning electron microscopy (SEM). Polarized optical microscopy (POM) observations performed on PPDX films revealed that PPDX crystallizes in spherulites whose detailed morphology depends on the supercooling employed during isothermal crystallization. Changes in the spherulitic morphology as molecular weight is reduced are only pronounced when the molecular weight is equal or lower than 8 kg/mol. The dependence of lamellar thickness as a function of isothermal crystallization temperature was examined by atomic force microscopy (AFM) in thin films of PPDX together with melting point data obtained by DSC. Through the use of the Thomson-Gibbs equation, we obtained a value of 166 erg/cm2 for the fold surface free energy of PPDX. This value is in the same range as those obtained previously for similar linear polyesters. The lamellar thickness, as well as the melting point, was found to have a small decreasing dependence with the molecular weight of the samples.

Biocompatible Materials↗
PubMedDate not supplied

Preparation and crystallization kinetics of new structurally well-defined star-shaped biodegradable poly(L-lactide)s initiated with diverse natural sugar alcohols.

This study presents syntheses, structural characterization, and crystallization kinetic investigation of new structurally well-defined star-shaped poly(l-lactide)s (PLLAs). First, a series of new 3- to 6-arm star-shaped PLLAs were synthesized through SnOct(2) catalyzed ring-opening polymerization of (l)-lactide with natural sugar alcohols of glycerol, erythritol, xylitol, and sorbitol as the favorable initiators. Subsequently, their chemical structures were characterized by means of GPC, NMR, and viscometer with respect to the star-shaped structures, demonstrating the well-defined arm structures as evidenced on the g(1/2)/g' values, where g and g' denote the ratios of mean-square radius of gyration and intrinsic viscosity of a star-shaped polymer to those of a linear structural reference with similar absolute molecular weight. Furthermore, spherulite morphologies and growth rates were studied by a polarized microscopy (POM) for the synthesized star-shaped PLLAs with different molecular weights, and it was found that the more arms of a star-shaped PLLA finally resulted in a lower spherulite growth rate. With regard to the crystallization kinetics of these star-shaped PLLAs, isothermal and nonisothermal crystallization were examined by differential scanning calorimeter (DSC). It was found that Avrami exponent n values of isothermal crystallization were almost independent of the isothermal crystallization temperature T(c) for different series of star-shaped PLLAs. In contrast, the values of Avrami exponent n were observed to strongly depend on the star-shaped structures with different arms, implying their distinct nucleation mechanisms, and the more arms of a star-shaped PLLA led to a slower isothermal crystallization rate. On the basis of a modified Avrami equation, new light was shed on the nonisothermal crystallization kinetics for the star-shaped PLLAs, and the activation energies were found to vary from 146.86 kJ/mol for the linear PLLA EG-3 to 221.23 kJ/mol of the star-shaped S-3, demonstrating much decreased crystallizabilities of star-shaped PLLAs with more arms.

Biodegradation, Environmental↗
PubMed2003

Synthesis and mesogenic properties of binuclear copper(II) complexes derived from salicylaldimine Schiff bases.

The synthesis and mesomorphic (liquid crystal) properties of new binuclear dihalocopper(II) complexes derived from N- and ring-substituted salicylaldimine Schiff bases are reported, together with the mesomorphic properties of their monomeric precursor complexes. With just N-substituents both the dichlorodicopper(II) binuclear complexes and their mononuclear analogues are waxy solids with melting points that increase with their N-chain length. However, with both N- and ring-substituents in the 4-positions, the mononuclear and binuclear complexes are each liquid crystalline or mesogenic, except in case of the mononuclear complexes where the N-substituent is straight chain alkyl. The other mononuclear complexes exhibit a variety of liquid crystal phases: smectic A, C, and E (SA, SC, and SE, respectively). The liquid crystal phase SA is observed in the binuclears with shorter chain N-substituents p-R-O-C6H4- and shorter chain ring-substituents. The chain lengths were increased until the phase behavior expanded to a further form SC in the case of an N-substituent p-C14H29O-C6H4- and a -OC12H25 ring substituent. This points the way toward achieving multiphase behavior with these binuclear systems. The Cu-Br analogues of the binuclear complexes behave similarly but with significant qualitative differences, specifically lower mesophase stability and higher melting temperatures. The structures of the nonmesogenic binuclears ([Cu(N-dodecylSal)X]2, X=Cl, Br) were determined with the aid of X-ray crystallography. These are prototypes for the structures of the binuclear complexes and especially for the shape of the central Cu2O2 X2 core in the binuclears: distorted planar coordination about the copper with distortion toward tetrahedral measured by a characteristic twist angle tau (0 degrees planar; 90 degrees tetrahedral). The binuclear complexes also show magnetic coupling which can be used to estimate the geometry. For [Cu(N-dodecylSal)X]2 tau>36 degrees, which corresponds to weaker coupling than observed in the mesogenic binuclears where a stronger magnetic coupling indicates a geometry closer to planar (tau=25 degrees). The mesophases were characterized by differential scanning calorimetry (DSC) analysis and optical polarized microscopy.

Journal Article↗
PubMed2002

The interplay of bent-shape, lateral dipole and chirality in thiophene based di-, tri-, and tetracatenar liquid crystals.

A range of mesogenic molecules varying in both bend angle and strength of lateral dipole were synthesized, and their phase behavior was characterized by polarizing microscopy, thermal analysis, X-ray diffraction, and electrooptical measurements. We find the general destabilization of the liquid crystallinity caused by strong lateral dipolar groups and the bent molecular shape are off-set in mesomorphic tetracatenars, which display stable nematic, smectic, columnar, and cubic mesophases. The broad mesomorphism of the tetracatenars containing lateral dipoles and their incompatibility with chiral induction are explained by considering that loosely correlated dimers exist within the mesophases. Chiral mesophases of derivatives with strong lateral dipoles were achieved by attaching fewer or different side chains to each end of the mesogen.

Journal Article↗
PubMed2003

A novel biaxial smectic liquid crystalline phase formed by rodlike molecules with a 1,3-diazaazulene skeleton.

Novel rodlike liquid crystalline (LC) materials incorporating the nonbenzenoid aromatic 1,3-diazaazulene unit have been synthesized and investigated by polarizing microscopy, differential scanning calorimetry, and X-ray diffraction of oriented samples. Some representatives form, in addition to conventional SmC phases, a novel biaxial smectic LC phase, in which the rotation of the molecules around their long axes is greatly restricted. Attractive face-to-face interactions of the flat aromatic units lead to columnar aggregates which are organized in layers. As there is no positional correlation between adjacent layers, these mesophases are related to lamellar columnar phases formed by some disklike and boardlike molecules. Such LC materials may be promising candidates in the field of organic semiconductors, photoconduction, and other applications.

Journal Article↗
PubMed2005

Thermotropic uniaxial and biaxial nematic and smectic phases in bent-core mesogens.

Two azo substituted achiral bent-core mesogens have been synthesized. Optical polarizing microscopy and synchrotron X-ray scattering studies of both compounds reveal the existence of the thermotropic uniaxial and biaxial nematic and three smectic phases at different temperatures in these single component small molecule systems. The transition from the uniaxial to biaxial nematic phase is confirmed to be second order. The transitions from the biaxial nematic to the underlying smectic phase and between the smectic phases have barely discernible heat capacity signatures and thus are also second order.

Journal Article↗
PubMed2003

Effect of sucrose ester addition on nucleation and growth behavior of milk fat-sunflower oil blends.

The effects of addition of the sucrose esters (SE) P-1670, P-170, and S-170 to a high-melting fraction of milk fat (HMF) and its blends with sunflower oil (SFO) on nucleation and growth were studied by laser polarized light turbidimetry and polarized light microscopy (PLM). The three SE delayed nucleation of HMF at the temperatures selected. P-1670 did not modify average crystal size after 3 h at crystallization temperature (T(c)) or crystal size distribution and modified crystallization kinetics only slightly. P-170 and S-170, however, markedly diminished crystal size and narrowed crystal size distribution. Activation free energies of nucleation at equivalent supercooling, calculated using the Fisher-Turnbull equation, significantly increased with addition of SE. According to these results, among the mechanisms described in the literature for fats or emulsions, the cocrystallization hypothesis is the one that better described the effects of sucrose esters on crystallization behavior in these systems.

Animals↗
PubMed2004

In situ synthesis of hexakis(alkoxy)diquinoxalino[2,3-a:2',3'-c]phenazines: mesogenic phase transition of the electron-deficient discotic compounds.

2,3,8,9,14,15-Hexakis(alkoxy)diquinoxalino[2,3-a:2',3'-c]phenazines with alkyl side chains varying from 6 to 12 carbon atoms were readily synthesized by the condensation of hexaketocyclohexane with the respective 1,2-bisalkoxy-4,5-diaminobenzene. Polarization microscopy and DSC studies showed all these compounds to exhibit a very wide mesophase range of over 150 degrees C. An interesting D(hd) to D(rd) transition was observed for the octyl derivative 3b, as determined by X-ray diffraction measurements. The hexyl derivative showed three reduction potentials, suggesting that the HATN core maintained its electron-deficient characteristic and considered suitable as an n-doped discotic-liquid crystalline material. Incorporation of six alkoxy chains did not override the electron deficiency of the HATN core.

Journal Article↗
PubMed2006

Liquid crystal and crystal structure of octahomotetraoxacalix[4]arenes.

Octahomotetraoxacalix[4]arenes bearing long alkyl chains on their lower rim were prepared. Ester 4a existed in a 1,2-alternate conformation in its crystal structure, which was examined by single-crystal X-ray diffraction analysis. To prepare liquid crystalline materials possessing calixarene moieties by self-assembling, carboxylic acid derivatives 5 were synthesized. Among them, 5c, the octadecyloxy derivative, showed smectic liquid crystal phase. Homooxacalixarenes 5 also formed liquid crystal phases with longer layer distances when two equivalent moles of 1,2-ethylenediamine were added as a linker. These phases were investigated with X-ray diffraction, differential scanning calorimetry, and polarized optical microscopy.

Calixarenes↗