A Near-Infrared Mechanically Switchable Elastomeric Film as a Dynamic Cell Culture Substrate.

Commercial static cell culture substrates can usually not change their physical properties over time, resulting in a limited representation of the variation in biomechanical cues in vivo. To overcome this limitation, approaches incorporating gold nanoparticles to act as transducers to external stimuli have been employed. In this work, gold nanorods were embedded in an elastomeric matrix and used as photothermal transducers to fabricate biocompatible light-responsive substrates. The nanocomposite films analysed by lock-in thermography and nanoindentation show a homogeneous heat distribution and a greater stiffness when irradiated with NIR light. After irradiation, the initial stiffness values were recovered. In vitro experiments performed during NIR irradiation with NIH-3T3 fibroblasts demonstrated that these films were biocompatible and cells remained viable. Cells cultured on the light stiffened nanocomposite exhibited a greater proliferation rate and stronger focal adhesion clustering, indicating increased cell-surface binding strength.

Microparticles as Additives for Increasing the Mechanical Stiffness of Polypropylene.

Composite materials of polypropylene and mineral microparticles have been generated by compounding and tested in terms of mechanical stiffness. In a first step silica, boehmite and functionalized clay microparticle powder have been mixed with the polymer in a twin-screw compounder. The elastic modulus was highest for mixtures with a microparticle concentration of 5 to 10%w/w. An increase of 25% of the elastic modulus was achieved by simple melt extrusion. In a second step, a maleic anhydride-grafted polypropylene (PP-g-MA) was used as a matrix. When measured by nanoindentation, the pure PP-g-MA matrix showed an elastic modulus twice as high as pure PP, probably because of a partial reticulation. During extrusion, amino-silane functionalized clay microparticles were added to the PP-g-MA matrix and reacted with it by building covalent amide group bonds. The resulting compound material showed an elastic modulus of more than four times the stiffness of pure PP.

Influence of the hydrogen reduction time and temperature on the morphology evolution and hematite/magnetite conversion of spindle-type hematite nanoparticles.

We report on the transformation via hydrogen reduction of spindle-type hematite nanoparticles into hematite/magnetite hybrid iron oxide particles. The transformation process consists of the reduction of nanoparticles powder in an autoclave using hydrogen gas at a fixed pressure of 11 bars. Both temperature and time of reduction are varied between 300 °C to 360 °C and 0 to 45 h. X-Ray powder diffraction data on the obtained powder and corresponding Rietveld refinement allow the amount of reduced hematite to be determined as a function of these two parameters. Kinetics parameters are measured and an estimation of the activation energy is obtained through linearization of the Arrhenius equation. While reduction is dramatically accelerated at higher temperature, the morphology of the nanoparticles only remain qualitatively unchanged at 300 °C as seen from transmission electron microscopy images. The mechanisms underlying morphology changes are still under study and seem to be closely related to reactor pressure.

Local dynamic mechanical analysis.

While new materials with tailored properties appear every day, the need of appropriate characterization tools is still an important concern. Analyses of thin films on thick substrate are often highly influenced by the substrate properties. A dynamical nanoindentation system has been designed and built through the integration of a nanoindenter head equipped with capacitive displacement sensing, scanning probe microscope with related XYZ scanning electronics and an additional transducer for sample actuation. Our Local-Dynamic Mechanical Analysis (L-DMA) setup allows for both, tip and sample modulation mode what somehow contrasts with commercially available systems. This issue allows for direct comparison between both techniques and therefore for consistent quantitative mechanical measurements. The system offers two distinctive measurement techniques, local mechanical spectroscopy and mechanical imaging modes. Bulk materials as well as thin films of ceramics and polymers have been used for testing and validating the setup. The instrument has been modeled in sample modulation mode and experimental results obtained for different materials were compared with simulation data.

Intrinsic bone tissue properties in adult rat vertebrae: modulation by dietary protein.

Bone strength depends on bone mass, geometry, microarchitecture, and intrinsic tissue quality. Whether intrinsic bone tissue properties could be influenced by changes in dietary protein is not known. To address this issue, nanoindentation tests were performed on the lateral, anterior, and posterior site of L5 vertebral bodies in adult female rats fed a normal protein containing diet and in ovariectomized (OVX) rats receiving an isocaloric low protein diet with or without isocaloric essential amino acids supplements. The tissue properties varied significantly between the different sites (anterior, posterior, lateral), suggesting possible effects of heterogeneous stress distribution on the vertebrae in vivo. Isocaloric low protein intake associated with ovariectomy led to significant decreases of indentation modulus, hardness, and dissipated energy on the posterior vertex. Axial compression tests of adjacent vertebral bodies were correlated with the indentation results. Correlations between macroscopic mechanical data obtained by axial compression of vertebral body, and intrinsic tissue properties measured by nanoindentation test suggest that postelastic behavior strongly varied with material fragility detected on the tissue level. Macroscopic stiffness however may be dominated by bone geometry changes and less by variations of intrinsic bone tissue properties. Combining parameters of tissue properties and bone mineral density was highly predictive of vertebral body ultimate strength. Besides geometry and microarchitecture, intrinsic bone tissue properties are important determinants of the mechanical competence of rat vertebrae. Changes in intrinsic tissue properties could thus contribute to the increased bone fragility found in protein undernutrition.