Bone regeneration for replacing and repairing damaged and defective bones in the human body has attracted much attention over the last decade. In this research, highly porous polyetheretherketone (PEEK)/hydroxyapatite (HA) bionanocomposite scaffolds reinforced with carbon fiber (CF) and carbon nanotubes (CNTs) were fabricated, and their structural, mechanical, and biological properties were studied in detail. Salt porogen (200–500 µm size) leaching methods were adapted to produce porous PEEK structures with controlled pore size and distribution, facilitating greater cellular infiltration and biological integration of PEEK composites within patient tissue. In biological tests, nanocomposites proved to be non-toxic and have very good cell viability. In addition, bone marrow cell growth was observed, and PEEK/HA biocomposites with carbon particles showed increased cell attachment over the neat PEEK/HA composites. In cell viability tests, bionanocomposites with 0.5 wt% CNTs established good attachment of cells on disks compared to neat PEEK/HA biocomposites. A similar performance was seen in culture tests of bone marrow cells (osteoblasts and osteoclasts). The 0.5 wt% CF for osteoblasts and 1 wt% CNTs for osteoclasts showed higher cell attachment. The addition of carbon-based nanomaterials into PEEK/HA has been identified as an effective approach to improve cell attachment as well as mechanical and biological properties. With confirmed cell attachment and sustained viability and proliferation of the fabricated PEEK/HA/CNTs, CF bionanocomposites were confirmed to possess excellent biocompatibility and will have potential uses in bone scaffolding and other biomedical applications.

No abstract

In addition, the model shows that the most active region for the stratosphere-mesosphere mass exchange is at the summer polar stratopause. The active exchange is driven by a strong summer mesospheric drag force through the "downward control" principle.

No abstract

A series of coordinated investigations of polar stratospheric chemistry, radiation, and dynamics has resolved and generated many questions regarding ozone depletion in the Earth's atmosphere. Photodissociation plays a key role, and the radiation field models utilized have often been singled out as possible sources of uncertainty. Mean intensities (source functions) are compared for three independent models: discrete-ordinate, integral equation, and Monte Carlo simulation. It was found that the results differ by < 10% for clear, cloudy, and aerosol conditions over an altitude range of 0-50 km, wavelength interval of 175-800 nm and a wide range of solar zenith angles. It is shown that in the presence of Pinatubolike aerosol concentrations, twilight photodissociation rates within an aerosol layer centered at 20 km can be reduced by more than an order of magnitude, whereas for solar zenith angles <60 ø, photodissociation rate changes are a few percent or less. Assessment of the effects of the aerosols on twilight stratospheric chemistry within the aerosol layer shows that radiation field perturbations on the homogeneous photochemistry are small and that heterogeneous processes are the major source of the altered photochemistry. 7135 7136 ANDERSON ET AL.' TWILIGHT PHOTOCHEMISTRY ET AL.: TWILIGHT PHOTOCHEMISTRY 7137 ET AL.: TWILIGHT PHOTOCHEMISTRY 7139