Synthesis of poly(ethylene glycol)-silk fibroin conjugates and surface interaction between L-929 cells and the conjugates

Poly(ethylene glycol) (PEG)-silk fibroin (SF) conjugates (PEG2-SF) were prepared by the chemical modification of solubilized SF with 2,4-bis[O-methoxypoly(ethylene glycol)]-6-chloro-s-triazine (actPEG2) in borate buffer at 37 °C. The IR spectra and DSC curves of PEG2-SF and SF suggested the introduction of PEG into SF by the modification and the β-sheet structure of both SF and PEG2-SF induced by the treatment with methanol aqueous solutions. The content of the PEG component in PEG2-SF was evaluated to be 67% by weight from the melting enthalpy change of PEG observed on the DSC thermogram of PEG2-SF. Water content and contact angle measurements of SF before and after the modification indicated that the hydrophilicity of the PEG2-SF surface increased compared with that of SF. The attachment and growth of fibroblast cells (L-929) on the matrix of PEG2-SF were studied by a cell culture method. PEG2-SF exhibited very low cell attachment and growth, though SF exhibited high cell attachment and growth. The filopodium of the cells attached to PEG2-SF could not be found, and the cells aggregated to form masses in scanning electron microscopy images. These results could be explained in terms of the increased hydrophilicity of the PEG2-SF surface.