Characterization and evaluation of silk protein hydrogels for drug delivery

The objective of this study was to characterize and evaluate the physicochemical properties and drug release profiles of hydrogels composed of silk protein (SP) polymers. SPs with a low MW (SPL, ca. 18 kDa) and a high MW (SPH, ca. 76 kDa) were used for preparing hydrogels. Both the random coil form and beta-sheet conformation simultaneously existed in the hydrogels according to Fourier-transformed IR determination. Morphologically, the hydrogels showed a sponge-like cross-linked structure produced by physical entanglement as well as chemical hydrogen and covalent bindings. The in vitro buprenorphine delivery from SPH hydrogels showed a slow-release effect, and a zero-order rate was obtained for all preparations. Drug release could be controlled by varying the SPH concentrations or incorporation of SPL into the systems. SP hydrogels showed a stronger barrier property for hydrophilic solutes than for hydrophobic solutes. The incorporation of SPH into Pluronic F-127 (PF-127) hydrogels changed the gel structure from amorphous micelles to a regularly interconnected texture with pores. Furthermore, SPH as an adjuvant polymer in PF-127 and chitosan hydrogels lowered and controlled the amount of drug released from those systems.