Degradation mechanisms of biodegradable poly(DL-lactide-co-glycolide)1000 diacrylate network as studied by proton solid-state flow NMR relaxometry

Degradation mechanisms of biodegradable photo-polymerised poly(DL-lactide-co-glycolide)1000 diacrylate {[(DL-LA/GA)DA]} matrices or films were studied by proton solid-state NMR relaxometry. A flow NMR unit cell was developed for this purpose. The (DL-LA/GA)DA-network was degraded in PBS buffer solution of pH = 7.4. A real-time proton NMR method provided information about the staged break down of the network during continuous circulation of the buffer solution through the NMR tube. The current study shows that degradation of the network proceeds in three stages: 1 - extraction of a sol fraction that causes substantial immobilization of the material, 2 - scissions of network chains producing network defects without formation of extractable products, and 3 - finally, chain scissions that cause formation of a sol fraction and complete degradation of the material. It was shown that the [(DL-LA/GA)DA-network was composed of rigid and viscoelastic domains on all stages of degradation. This heterogeneity could be due to heterogeneous spatial distribution of network junctions in the initial network and/or nano-scale phase separation of polyacrylate chains that form multifunctional network junctions and poly(lactide-co-glicolide) network chains. A combination of bulk and surface erosion both on nano- and macroscopic scales could explain the observed degradation mechanisms. it is shown that knowledge of weight loss upon hydrolytic degradation is not sufficient for understanding degradation mechanisms in the relation to functional properties of this type of hydrogels.