Design and characterization of a tissue-engineered bilayer scaffold for osteochondral tissue repair.

Treatment of full-thickness cartilage defects relies on osteochondral bilayer grafts, which mimic the microenvironment and structure of the two affected tissues: articular cartilage and subchondral bone. However, the integrity and stability of the grafts are hampered by the presence of a weak interphase, generated by the layering processes of scaffold manufacturing. We describe here the design and development of a bilayer monolithic osteochondral graft, avoiding delamination of the two distinct layers but preserving the cues for selective generation of cartilage and bone. A highly porous polycaprolactone-based graft was obtained by combining solvent casting/particulate leaching techniques. Pore structure and interconnections were designed to favour in vivo vascularization only at the bony layer. Hydroxyapatite granules were added as bioactive signals at the site of bone regeneration. Unconfined compressive tests displayed optimal elastic properties and low residual deformation of the graft after unloading (< 3%). The structural integrity of the graft was successfully validated by tension fracture tests, revealing high resistance to delamination, since fractures were never displayed at the interface of the layers (n = 8). Ectopic implantation of grafts in nude mice, after seeding with bovine trabecular bone-derived mesenchymal stem cells and bovine articular chondrocytes, resulted in thick areas of mature bone surrounding ceramic granules within the bony layer, and a cartilaginous alcianophilic matrix in the chondral layer. Vascularization was mostly observed in the bony layer, with a statistically significant higher blood vessel density and mean area. Thus, the easily generated osteochondral scaffolds, since they are mechanically and biologically functional, are suitable for tissue-engineering applications for cartilage repair.

Surface morphology and mechanical properties of new-generation flowable resin composites for dental restoration.

OBJECTIVES: The purpose of this study was to characterize the surface morphology and the elastic properties of four dental restorative flowable composites currently on the market (Venus Diamond Flow, Vertise Flow, Filtex Supreme XT Flow, Surefil SDR Flow). Additionally, one adhesive system (Adhese One F) and one non-flowable composite (Venus Diamond) have also been characterized as the control materials. METHODS: Surface morphology was studied by both scanning electron and atomic force microscopy, and the elastic modulus and the hardness measured by instrumented indentation. Grain analysis was performed on the microscopic images, and statistical analysis was carried out on the results of the nanoindentation measurements. RESULTS: It was observed that Vertise, Filtek XT and Surefil SDR exhibit stiffness similar to the non-flowable Venus Diamond, whereas Venus Diamond Flow presents itself as the more compliant flowable composite, with Adhese showing intermediate stiffness. Grain analysis of the images confirmed the general rule that the mechanical properties improve with increasing filler loading, with the notable exception of Vertise Flow that shows modulus and hardness as high as 9.1±0.6 and 0.43±0.03GPa, respectively, for an estimated loading of only ∼40% by volume. SIGNIFICANCE: Whereas generally flowable composites are confirmed not to possess sufficiently strong mechanical properties for bulk restorations, exceptions can eventually be found upon appropriate laboratory screening, as presently seems to be the case for Vertise Flow. However, real practice in actual restorations and respective clinical evaluation are required for final assessment of the suggested results.

Measurements of nanoparticles of organic carbon and soot in flames and vehicle exhausts.

We measured the size distribution and UV extinction spectra of carbonaceous nanoparticles present in the size range of 1-100 nm in the exhausts of 2004 model gasoline and diesel powered vehicles and compared the results with those obtained in premixed flames. In addition to soot particles, nanoparticles of organic carbon (NOC) were measured in the emissions of these test vehicles in significant number and mass concentrations. The number and mass concentration of NOC was higher than soot in gasoline vehicle emissions. In diesel emissions, NOC had a higher number concentration than soot in terms of number concentration, but in terms of mass concentration, soot was higher than NOC. The size (1-3 nm) and extinction spectra in the UV-visible (strong in the UV and transparent in the visible) of macromolecules/nanoparticles collected in water samples from the vehicles are similar to those measured in laboratory hydrocarbon-air flames, suggesting that these nanoparticles are formed in hydrocarbon combustion reactions. We advance the hypothesis that NOC in vehicle emissions are produced by high-temperature combustion processes and not by low-temperature condensation processes.