Freeze-thaw treatment effects on the dynamic mechanical properties of articular cartilage

BACKGROUND: As a relatively non-regenerative tissue, articular cartilage has been targeted for cryopreservation as a method of mitigating a lack of donor tissue availability for transplant surgeries. In addition, subzero storage of articular cartilage has long been used in biomedical studies using various storage temperatures. The current investigation studies the potential for freeze-thaw to affect the mechanical properties of articular cartilage through direct comparison of various subzero storage temperatures. METHODS: Both subzero storage temperature as well as freezing rate were compared using control samples (4°C) and samples stored at either -20°C or -80°C as well as samples first snap frozen in liquid nitrogen (-196°C) prior to storage at -80°C. All samples were thawed at 37.5°C to testing temperature (22°C). Complex stiffness and hysteresis characterized load resistance and damping properties using a non-destructive, low force magnitude, dynamic indentation protocol spanning a broad loading rate range to identify the dynamic viscoelastic properties of cartilage. RESULTS: Stiffness levels remained unchanged with exposure to the various subzero temperatures. Hysteresis increased in samples snap frozen at -196°C and stored at -80°C, though remained unchanged with exposure to the other storage temperatures. CONCLUSIONS: Mechanical changes shown are likely due to ice lens creation, where frost heave effects may have caused collagen damage. That storage to -20°C and -80°C did not alter the mechanical properties of articular cartilage shows that when combined with a rapid thawing protocol to 37.5°C, the tissue may successfully be stored at subzero temperatures

Doped ZnO Thin Films Properties/Spray Pyrolysis Technique

International audienceIn this contribution, the effect of different dopants (Al, Sn, and Cu) on the structure, texture and optical properties of ZnO thin films was investigated. Al-doped ZnO (AZO), Sn-doped ZnO (TZO) and Cu-doped ZnO (CZO) thin films are synthesized by chemical spray pyrolysis technique on glass substrates. The so-obtained films crystallized in hexagonal wurtzite polycrystalline structure. The pole figures show that all the thin films have (0002) as the preferred orientation along the c-axis with the highest level was obtained in TZO thin film. The morphology film was significantly affected by the doping type. The transmittance spectra of all the films point out highly transparent in the visible range with an average transmittance higher than 80% for TZO and AZO films but with an average transmittance equal to about 70% for CZO film. Furthermore, the optical bandgap values were determined by the Tauc's law and were found to be 3.30 eV, 3.28 eV and 3.27 eV for AZO, TZO, and CZO thin films, respectively. The Urbach energy of the films was also calculated

Efficient inverted polymer solar cells employing favourable molecular orientation

The improvement in the power conversion efficiency is a critical issue for polymer-based bulk-heterojunction solar cells (PSCs). Here, we show that high efficiencies of ~10% can be obtained by using a crystalline polymer, PNTz4T, in single-junction inverted cells with the thick active layer measuring ca. 300 nm. The improved performance is likely due to the large population of the polymer crystallites with the face-on orientation and the “favourable” distribution of edge-on and face-on crystallites along the film thickness, as revealed by in-depth studies of the blend films using grazing incidence wide angle X-ray diffraction, which results in the reduction of charge recombination and the efficient charge transport. These results underscore the great promise of PSCs, and raise hopes of achieving even higher efficiencies by materials development and control of molecular ordering