Effects of hydrophobicity and mat thickness on release from hydrogel-electrospun fiber mat composites

Poly(ethylene glycol) (PEG)-based hydrogel-electrospun fiber mat (EFM) composites are a promising new controlled release system for hydrophilic drugs, providing longer and more linear release characteristics accompanied by a smaller initial burst than traditional hydrogel systems. However, the effect of EFM properties on release characteristics has not yet been examined. Here, we investigated the influence of EFM thickness and hydrophobicity on swelling and release behavior using bovine serum albumin as a model hydrophilic protein. EFMs investigated were comprised of poly(ε-caprolactone) (PCL) at thicknesses of 300, 800, or 1100 μm. Hydrophobicity was adjusted through surface modification: fluorinated PCL, core/shell PCL/PEGPCL, and acrylic acid (AAc)-treated PCL EFMs were examined. EFMs comprised of the external composite surface, forming a sandwich around PEG-poly(lactic acid) (PEGPLA) hydrogels, and significantly restrained hydrogel swelling in the radial direction while increasing swelling in the axial direction. Incorporation of EFMs also reduced initial hydrophilic protein release rates and extended the duration of release. Increased EFM thickness and hydrophobicity were equally correlated with longer and more linear release profiles. Increased thickness most likely increases the diffusional path length, whereas increased hydrophobicity hinders hydrophilic drug diffusion. These composites form a promising new class of tunable release materials having properties superior to those of unmodified hydrogels.