Temperature dependent photoluminescence of organic semiconductors with varying backbone conformation

We present photoluminescence studies as a function of temperature from a series of conjugated polymers and a conjugated molecule with distinctly different backbone conformations. The organic materials investigated here are: planar methylated ladder type poly para-phenylene, semi-planar polyfluorene, and non-planar para hexaphenyl. In the longer-chain polymers the photoluminescence transition energies blue shift with increasing temperatures. The conjugated molecules, on the other hand, red shift their transition energies with increasing temperatures. Empirical models that explain the temperature dependence of the band gap energies in inorganic semiconductors can be extended to explain the temperature dependence of the transition energies in conjugated molecules.Comment: 8 pages, 9 figure

Micro-Environmental Mechanical Stress Controls Tumor Spheroid Size and Morphology by Suppressing Proliferation and Inducing Apoptosis in Cancer Cells

Compressive mechanical stress produced during growth in a confining matrix limits the size of tumor spheroids, but little is known about the dynamics of stress accumulation, how the stress affects cancer cell phenotype, or the molecular pathways involved.We co-embedded single cancer cells with fluorescent micro-beads in agarose gels and, using confocal microscopy, recorded the 3D distribution of micro-beads surrounding growing spheroids. The change in micro-bead density was then converted to strain in the gel, from which we estimated the spatial distribution of compressive stress around the spheroids. We found a strong correlation between the peri-spheroid solid stress distribution and spheroid shape, a result of the suppression of cell proliferation and induction of apoptotic cell death in regions of high mechanical stress. By compressing spheroids consisting of cancer cells overexpressing anti-apoptotic genes, we demonstrate that mechanical stress-induced apoptosis occurs via the mitochondrial pathway.Our results provide detailed, quantitative insight into the role of micro-environmental mechanical stress in tumor spheroid growth dynamics, and suggest how tumors grow in confined locations where the level of solid stress becomes high. An important implication is that apoptosis via the mitochondrial pathway, induced by compressive stress, may be involved in tumor dormancy, in which tumor growth is held in check by a balance of apoptosis and proliferation

Reactive Processing Of Polyaniline In A Banbury Mixer

Polyaniline (PAni) was doped with several concentrations of dodecylbenzenesulfonic acid (DBSA) and processed in a double screw conrotatory Banbury type mixer coupled to a torque reomether. With the conditions studied, some samples were cured and reached a high torque. Depending on the hardening of PAni(DBSA) it was possible to make films in a roll mill. Polymer was characterized by DSC analysis were Tg transitions can be seen in the curves for thermally processed conductive PAni. Conductivity values were independent of DBSA concentrations.1021-310121013Laska, J., Izak, P., Pron, A., (1996) J. Appl. Polym. Sci., 61, p. 1339Prón, A., Luzny, W., Laska, J., (1996) Synth. Met., 80, p. 191Davies, S.J., Ryan, T.G., Wilde, C.J., Beyer, G., (1995) Synth. Met., 69, p. 209Gazotti, W.A., De Paoli, M.-A., (1996) Synth. Met., 80, p. 263Titelman, G.I., Zilberman, M., Siegmann, A., Haba, Y., Narkis, M., (1997) J. Appl. Polym. Sci., 66, p. 219

Using Poly(o-methoxyaniline) As Thermal Stabilizer For Polymers

Conductive polymer blends are generally prepared to obtain conductive materials with plastic characteristics. To be used in large scale, thermal stability at the working temperature of usual processing methods used in the plastic industry is required for these mixtures. In this work we studied the effect of adding poly(o-methoxyaniline) doped with p-toluene sulfonic acid to different processable polymers which present liberation of acids during their thermal degradation.1021-312071208Prón, A., Österholm, J.E., Smith, P., Heeger, A.J., Laska, J., Zagórska, M., (1993) Synth. Met., 55-57, p. 3520Laska, J., Izak, P., Prón, A., (1996) J. Appl. Polym. Sci., 61, p. 1339Cao, Y., Smith, P., Heeger, A.J., (1993) Synth. Met., 55-57, p. 3514De Paoli, M.-A., Waltman, R.J., Diaz, A.F., Bargon, J., (1984) J. Chem. Soc. Chem. Commun., p. 1015De Paoli, M.-A., (1997) Handbook of Organic Conductive Molecules and Polymers, 2, p. 773. , H.S. Nalwa (ed.), Nalwa, H. S. (ed.), John Wiley & Sons, New YorkGazotti, W.A., De Paoli, M.-A., (1996) Synth. Met., 80, p. 26

Pulsatile dynamic stiffness of cartilage-like materials and use of agarose gels to validate mechanical methods and models

Stiffness is a fundamental indicator of the functional state of articular cartilage. Reported test modes include compressive incremental strain to determine the equilibrium modulus, and sinusoidal strain to determine the dynamic modulus and stress/strain loss angle. Here, initial development is described for a method recognizing that gait is pulsatile. Agarose gels have been used by others for validation or comparison of mechanical test methods and models for cartilage and proteoglycan aggregate. Accordingly, gels ranging from 0.5 to 20% agarose were prepared. Pulsatile stiffness in both indentation and unconfined compression were closely reproducible. Stiffness as a function of agarose concentration rose exponentially, as found using other methods. Indentation stiffness was higher than for unconfined compression and ranged from approximately 2.0 kPa for 0.5% gel to approximately 3,800 kPa for 20% gel. Pulsatile dynamic stiffness appears to be a useful method, although further development is needed. Agarose gel stiffness values obtained by other methods were reviewed for comparison. Unfortunately, reported values for a given agarose concentration ranged widely (e.g. fourfold) even when test methods were similar. Causes appear to include differences in molecular weight and gel preparation time-temperature regimens. Also, agarose is hygroscopic, leading to unintended variations in gel composition. Agarose gels are problematic materials for validation or comparison of cartilage mechanical test methods and models

Cartilage tissue engineering by expanded goat articular chondrocytes

In this study we investigated whether expanded goat chondrocytes have the capacity to generate cartilaginous tissues with biochemical and biomechanical properties improving with time in culture. Goat chondrocytes were expanded in monolayer with or without combinations of FGF-2, TGF-beta1, and PDGFbb, and the postexpansion chondrogenic capacity assessed in pellet cultures. Expanded chondrocytes were also cultured for up to 6 weeks in HYAFF-M nonwoven meshes or Polyactive foams, and the resulting cartilaginous tissues were assessed histologically, biochemically, and biomechanically. Supplementation of the expansion medium with FGF-2 increased the proliferation rate of goat chondrocytes and enhanced their postexpansion chondrogenic capacity. FGF-2-expanded chondrocytes seeded in HYAFF-M or Polyactive scaffolds formed cartilaginous tissues with wet weight, glycosaminoglycan, and collagen content, increasing from 2 days to 6 weeks culture (up to respectively 2-, 8-, and 41-fold). Equilibrium and dynamic stiffness measured in HYAFF M-based constructs also increased with time, up to, respectively, 1.3- and 16-fold. This study demonstrates the feasibility to engineer goat cartilaginous tissues at different stages of development by varying culture time, and thus opens the possibility to test the effect of maturation stage of engineered cartilage on the outcome of cartilage repair in orthotopic goat models

The influence of keto defects on photoexcitation dynamics in polyfluorene

The optical properties of two differently substituted types of polyfluorenes, 9-monoalkylated PF (mono-PF) and 9,9-dialkylated PF (bi-PF) where studied by means of photo-induced absorption (PIA) and ultrafast pump and probe measurements. The photo-induced absorption was complemented by measurements on a fluorene-fluorenone copolymer, which can be seen as a model substance for the polyfluorenes containing keto-defect sites. By differential transmission measurements we show that for the 9-monoalkylated PF measurements the singlet and triplet signal is strongly reduced compared to the 9,9-dialkylated PF. Instead, the polaron signal becomes the dominant feature. © 2003 Elsevier B.V. All rights reserved