Biocompatibility of poly(L-lactide) films modified with poly(ethylene imine) and polyelectrolyte multilayers

Poly(L-lactide) (PLLA) films were modified with poly(ethylene imine) (PEI) either by adsorption or covalent binding to prepare the material for immobilization of polyelectrolyte multilayers (PEM). Two different PEI, low- and high-molecular-weight (LMW or HMW, respectively) PEI, were used. The PEI modification efficiency was monitored via surface amino group density, water contact angle and X-ray photoelectron spectroscopy (XPS) measurements. Covalent binding of HMW PEI by a two-step-activation method produced the highest amino group density and the lowest water contact angle. On the other hand, the adsorption method resulted in moderate amounts of immobilized PEI on the surface. Subsequently sulphated hyaluronan and chitosan were used to form PEM on PLLA that was covalently modified with HMW PEI. Regular formation of PEM was achieved, which was demonstrated by change of water contact angles and mass increase measured with quartz crystal microbalance. An osteoblast-like cell line, MG 63, was used to test the effects of modifications on biocompatibility. Contrarily to earlier reports showing that particularly HMW PEI had certain cytotoxicity, it was found that all modifications including PEM resulted in a better biocompatibility than plain PLLA indicated by a more spread phenotype of cells, their increased growth and metabolic activity.