Tetrahydrofuran (co)polymers as potential materials for vascular prostheses

Polyethers were studied as potential materials for vascular prostheses. By crosslinking poly(tetramethylene oxide) (PTMO) with poly(ethylene oxide) (PEO), hydrophilic networks were obtained containing PTMO as well as PEO. Attempts were made to reduce the crystallinity and melting point of PTMO because of the required elastomeric behaviour at body temperature. Compared to non-crosslinked PTMO, crosslinking in the melt resulted in a decrease in the melting point from 43·7 to 38·7°C and a decrease of the crystallinity from 46 to 28%. By copolymerizing tetrahydrofuran with oxetane or dimethyloxetane, melting points below 38°C were obtained, together with crystallinities lower than 20%

The mineralogy of newly formed dust in active galactic nuclei

The tori around active galactic nuclei (AGN) are potential formation sites for large amounts of dust, and they may help resolve the so-called dust budget crisis at high redshift. We investigate the dust composition in 53 of the 87 Palomar Green (PG) quasars showing the 9.7 micron silicate feature in emission. By simultaneously fitting the mid-infrared spectroscopic features and the underlying continuum, we estimate the mass fraction in various amorphous and crystalline dust species. We find that the dust consists predominantly of alumina and amorphous silicates, with a small fraction in crystalline form. The mean crystallinity is 8 +/- 6%, with more than half of the crystallinities greater than 5%, well above the upper limit determined for the Galaxy. Higher values of crystallinity are found for higher oxide fractions and for more luminous sources.Comment: 24 pages, 9 figures, accepted for publication in Planetary and Space Scienc

Biodegradability and biocompatibility of copoly(butylene sebacate-co-terephthalate)s

In the present study poly (butylene sebacate-co-terephthalate)s having different compositions were synthesized with a high yield and a random distribution by thermal transesterification of poly (butylene sebacate) and poly (butylene terephthalate) homopolymers. The copolymer with the highest comonomer ratio was the least crystalline sample, although the melting peaks corresponding to both, sebacate and terephthalate-rich phases were still observable in calorimetric heating runs. This copolymer was associated with interesting thermal and mechanical properties, as the maximum melting point was higher than 100 °C and the storage modulus was also high (i.e. 1.1 × 109 N/m2 and 1.7 108 N/m2 were determined just before and after the main glass transition temperature of -12 °C). As all studied samples were thermally stable up to temperatures clearly higher than the fusion temperature, they could be easily processed. Increasing the terephthalate content of the copolymers resulted in higher hydrophobicity, which had a minor influence on cell adhesion and proliferation of both fibroblast-like and epithelial-like cells. Hydrolytic and enzymatic degradability were assessed and the effect of composition and crystallinity on the degradation rate was investigated. Molecular weight measurements during exposure to a hydrolytic media indicated a first order kinetic mechanism during the initial stages of degradation before reaching a limiting molecular size, which was indicative of solubilization. The most amorphous sample appears as a highly promising biodegradable material since it showed a significant weight loss during exposure to all selected degradation media, but also exhibited good performance and properties that were comparable to those characteristic of polyethylenePeer ReviewedPostprint (author's final draft

Mechanical Properties Transformation on Zr54Al17Co29 Bulk Metallic Glass by Partial Crystallization

Study on biomaterials is recently essential for rapid development of medical application and Zr54Al17Co29 BMGbecomes promising candidate due to the lack of toxic elements. Partial crystallization by isothermal annealing at SCL region was used to variate the crystallinities of BMG. The structural and thermal properties of as cast and partially crystallized samples were confirmed by XRD and DSC test, while microvickers and compression test were further utilized to investigate their mechanical properties. By the higher crystallinity, the hardness could be slightly increased in range 540 ± 5 to 575 ± 5 Hv. As-cast sample shows the yield strength and plastic strain of 2130 ± 75 MPa and 2.2 ± 1.6%. The yield strength is increased by the presence of 10% nanocrystal, afterwards, fall and raise phenomena are obtained with further crystallinity. However, with higher crystallinity, the plasticity is significantly degraded and no more plastic strain observed at sample with 50% of crystallinity. Both the presence of nanocrystalline phase and free volume annihilation are the reason of mechanical properties change on the Zr-based BMG