No abstract

This work demonstrates the production of a well-controlled, chemical gradient on the surface of graphene. By inducing a gradient of oxygen functional groups, drops of water and dimethyl-methylphosphonate (a nerve agent simulant) are "pulled" in the direction of increasing oxygen content, while fluorine gradients "push" the droplet motion in the direction of decreasing fluorine content. The direction of motion is broadly attributed to increasing/decreasing hydrophilicity, which is correlated to high/low adhesion and binding energy. Such tunability in surface chemistry provides additional capabilities in device design for applications ranging from microfluidics to chemical sensing.

Striatal 18F-6-fluorodopa (FD) uptake constants were measured by positron emission tomography in (1) normal cynomolgus monkeys and (2) a series of cynomolgus and rhesus monkeys that had received intracarotid infusions of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). After the animals were killed, the number and average size of dopaminergic neurons in the substantia nigra pars compacta were measured. Striatal levels of dopamine and its metabolites, and the striatal activities of the dopaminergic synthetic enzymes, were also determined. The striatal FD uptake constants showed highly significant positive correlations with both number and size of dopaminergic neurons, indicating atrophy of surviving neurons in MPTP-treated animals. The uptake constants also showed significant positive correlations with striatal levels of dopamine, total catecholamines, and the activities of the synthetic enzymes. Both histochemical and biochemical data on tyrosine hydroxylase suggested some contralateral enzyme loss in these MPTP-treated monkeys, as well as decreased enzyme activity in surviving neurons on the lesioned side. However, residual enzyme activities were apparently not rate limiting to striatal FD uptake. It is concluded that PET-FD measurements by positron emission tomography provide a good index of the integrity of the nigrostriatal pathway.

The phase-segregated nature of polyurethanes allows meaningful connections to be made between morphological and physical properties. We have taken advantage of this behavior by synthesizing a series of polyurethanes with varying extents of crystallinity and studying their morphologies in both the unstrained and deformed states, going from a completely amorphous soft segment to one with similar chemistry that displays a high extent of soft domain crystallization, thus enhancing phase segregation. The presence of dispersed semicrystalline regions within the continuous soft domain has been shown to provide a reinforcing effect when compared to that of a non-crystalline soft segment polyurethane. Incorporating a semicrystalline soft segment (PEO, 1000 g/mol) has been shown to improve overall sample toughness; however, if higher molecular weight PEO soft segments are employed (4600 g/mol), extensibility and, consequently, toughness are adversely affected due to an increased continuous domain modulus. In-situ deformation experiments demonstrate two very different deformation responses. In the copolymer-containing polyurethane (PEO-PPO-PEO, 1900 g/mol), the hard domains retain a tilted configuration up to strains of ∼450%, with only a small fraction of the hard segments undergoing reshuffling. The PEO1000-containing polyurethane, on the other hand, begins to demonstrate meridional scattering at strains of 200%, with it being the dominant peak by a strain of 300%. These two deformation behaviors are indicative of the two primary responses to deformation, which are shear and tensile, respectively. Frequently, a tensile mechanism points to decreased polyurethane mechanical properties, though this phenomenon is not seen in the series of interest.