Study of nanoscale structures in hydrated biomaterials using small-angle neutron scattering

Distribution of water in three classes of biomedically relevant and degradable polymers was investigated using small-angle neutron scattering. In semicrystalline polymers, such as poly(lactic acid) and poly(glycolic acid), water was found to diffuse preferentially into the non-crystalline regions. In amorphous polymers, such as poly(D,L-lactic acid) and poly(lactic-co-glycolic acid), the scattering after 7 days of incubation was attributed to water in microvoids that form following the hydrolytic degradation of the polymer. In amorphous copolymers containing hydrophobic segments (desaminotyrosyl-tyrosine ethyl ester) and hydrophilic blocks (poly(ethylene glycol) (PEG)), a sequence of distinct regimes of hydration were observed: homogeneous distribution (similar to 10 angstrom length scales) at <13 wt.% PEG (similar to 1 water per EG), clusters of hydrated domains (similar to 50 angstrom radius) separated at 24 wt.% PEG (1-2 water per EG), uniformly distributed hydrated domains at 41 wt.% PEG (similar to 4 water per EG) and phase inversion at >50 wt.% PEG (>6 water per EG). Increasing the PEG content increased the number of these domains with only a small decrease in distance between the domains. These discrete domains appeared to coalesce to form submicron droplets at similar to 60 degrees C, above the melting temperature of crystalline PEG. The significance of such observations on the evolution of micrometer-size channels that form during hydrolytic erosion is discussed. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.