High Molecular Weight Systems Research Articles

Impact of molecular weight on polyelectrolyte multilayer assembly and surface properties

Polyelectrolyte multilayers (PEMs) are a versatile category of materials due to their ability to modify surface properties for applications ranging from protective coatings to improved cell adhesion. Polyelectrolyte choice, including its structure and molecular weight (MW), is known to greatly influence PEM assembly and surface properties. In this work, poly(acrylic acid)/poly-l-lysine PEMs using three pairs of MWs (1.8k/15–30k, 100k/120k, and 250k/275k) were studied to determine the effects of their MWs on PEM assembly, topography and surface energy. PEMs assembly was monitored in a quartz crystal microbalance with dissipation, resulting in masses of 3.90 ± 0.87 µg/cm2, 10.80 ± 4.189 µg/cm2, and 30.04 ± 13.68 µg/cm2 for 10 bilayers of low, medium, and high MW pairs, respectively. The low MW PEM was more rigid. Low and high MW PEMs exhibited higher roughness than medium MW, caused by polyelectrolyte stripping. Surface energy remained constant with bilayer count in the low and high MW PEMs, but steadily increased in the medium MW PEM. Differences between medium MW PEMs from low and high MW systems indicate that, while PEM properties change with MW, they are not monotonically correlated and are instead related to changes in internal charge distributions and the resultant stripping that may occur.

Effect of poly-hydroxy aliphatic ester polymer type on amoxycillin release from cylindrical compacts

The objective of the work was to investigate the effects of a range of poly-hydroxy aliphatic esters (poly-lactide (PLA) and poly-lactide-co-glycolide (PLGA)) of different molecular weight and composition on the release and stability of the amphoteric drug amoxycillin. The effect of this amphoteric drug on the extent and kinetics of polymer degradation was also investigated. The polymers were used to prepare drug-free and drug-loaded cylindrical discs. Drug release profiles were determined while changes in polymer composition were monitored by weight loss and molecular weight change. The extent of drug release was highly dependant on polymer molecular weight and composition, with earlier complete release occurring with the lower molecular weight and lower lactide containing polymers. A larger proportion of drug was released by polymer degradation control with the higher lactide containing polymer. The proportion of drug released intact was influenced by the polymer molecular weight, with a greater proportion of intact drug being released from the higher molecular weight systems. The inclusion of amoxycillin influenced polymer degradation and resulted in slower polymer hydrolysis. Model parameters obtained for polymer degradation indicated that this retardation effect increased with increasing lactide content of the polymer. The results suggest that small amounts of amoxycillin or its degradation products may bind or cross link with the polymers, thus retarding their degradation.