Hydrolytically labile poly(ethylene glycol)-based hydrogels are fabricated via a Michael-type addition reaction between unsaturated acrylate moieties and nucleophilic thiols. Although these gels offer the advantage of selective, in situ polymerization and potential as biocompatible matrixes for cell and protein encapsulation, a thorough understanding of the complex structure-property relationships that control the macroscopic behaviors of these cross-linked networks before and during hydrolytic degradation does not exist. Therefore, in this work, a novel theoretical model is presented to describe the formation and hydrolytic degradation of the step-polymerized gels. The model accounts for variations in hydrolysis kinetics as well as structural effects such as precursor functionality and the presence of primary cycles or other structural nonidealities that lower the cross-linking efficiency of the networks. Comparison of model predictions and experimental data validate this methodology for optimizing biomaterial design and reveal that structural nonidealities play a key role in determining the degradation behavior of real cross-linked systems. Decreasing precursor concentration and functionality during network formation generate high concentrations of network nonidealities that ultimately lead to higher initial swelling ratios and faster apparent rates of degradation.

The major objective of this research was to modify PLA film surfaces with the ultimate aim of making a bioactive surface that will show faster degradation. The PLA film was solvent-cast, and the film surfaces were grafted with poly(acrylic acid) (PAA) and poly(acrylamide) (PAAm) using a UV-induced photopolymerization process. The film surface resulting from each reaction step was analyzed using ATR−FTIR spectroscopy and contact angle measurements. Results showed that PAA was grafted from PLA film surfaces in 2 or 3 h, while PAAm was grafted in 3 or 5 h depending on the method of activation. Films grafted with PAA and PAAm exhibited improved wettability. The neat and surface-modified films were incubated in different pH solutions, viz., pH = 4, 7, and 10, for specified time periods. The films resulting from each treatment were analyzed using atomic force microscopy (AFM). The molecular weights of the incubated films were measured using chloroform-based GPC. Results established that faster degradation of the PLA film when incubated in different pH solutions was achieved for PLA-g-PAA films; however, control studies revealed that the major contribution to the observed degradation was due to the entangled PAA chains resulting from acrylic acid monomer that migrated into the film bulk and not due to the surface-grafted layers.