Crosslinking-Dependent Drug Kinetics in Hydrogels for Ophthalmic Delivery.

Drug-diffusion kinetics in 2-hydroxyethyl methacrylate hydrogels were studied as a function of the crosslinking density and porosity. By varying the concentration of the crosslinker, tetraethylene glycol dimethacrylate, we demonstrated how the release of Timolol maleate could be optimized to allow for efficient drug delivery. FTIR and spectrophotometry supplied optical inferences into the functional groups present. By studying the swelling and degradation of hydrogels, supplemented with drug-release kinetics studies, the relationship between these two tenets could be formulated.

Comparing Percolation and Alignment of Cellulose Nanocrystals for the Reinforcement of Polyurethane Nanocomposites.

The reinforcement of polymer nanocomposites can be achieved through alignment or percolation of cellulose nanocrystals (CNCs). Here, we compare the efficacy of these reinforcement mechanisms in thermoplastic polyurethane (PU) elastomer nanocomposites containing thermally stable cotton CNCs. CNC alignment was achieved by melt spinning nanocomposite fibers, while a percolating CNC network was generated by solvent casting nanocomposite films with CNC contents up to 20 wt %. While in films both the CNCs and the PU matrix were entirely isotropic at all concentrations as confirmed by wide-angle X-ray scattering and birefringence analysis, the CNCs in the fibers exhibited a preferential orientation, which improved with increasing CNC concentration. Increasing the CNC concentration in the fibers reduces, however, the alignment of the PU chains, resulting in an entirely isotropic PU matrix at high CNC contents. The mechanical properties of films and fibers were evaluated using stress-strain measurements. Nanocomposite fibers with low CNC content exhibited superior stiffness, extensibility, and strength compared to the films, while the films displayed superior mechanical properties at high CNC concentrations. These findings are rationalized using common semiempirical models describing the reinforcing effects of CNC alignment in fibers (Halpin-Tsai) and CNC percolation in films (percolation model). The formation of a percolating CNC network leads to a stronger reinforcement than CNC alignment, as the reinforcing effect of the latter is limited by the comparably low aspect ratio of CNCs extracted from cotton. As a consequence, above the percolation threshold for cotton CNCs, isotropic nanocomposite PU films show a higher stiffness than aligned nanocomposite PU fibers.

Conflict Processes and Transitions in Parent and Peer Relationships: Implications for Autonomy and Regulation.

Relational components of three attributes often regarded as individual variables (conflict, autonomy, and self-regulation) were examined in two studies. In Study 1, mothers and their 10- through 12-, 13- through 15-, or 16- through 17-year-old offspring reported expected times of transition to 47 adultlike behaviors (behavioral autonomy) and rated the importance of delaying each transition. Discrepancies from mothers' expectancies were found to be greatest for 13- through 15-year-olds. In Study 2, characteristics and correlates of conflict across different types of relationships were assessed. Sixth-grade and eighth-grade Hispanic American adolescents reported significant differentiation among relationships with mothers, fathers, and friends in frequency of conflict, conflict resolution strategies and sequelae, and correlates of adolescents'psychosocial competence. Variations suggest that multiple relationships may be involved in the development of autonomy and self-regulation during childhood and adolescence.