Surface characterization of functionalized polylactide through the coatingwith heterobifunctional poly(ethylene glycol)/polylactide block copolymers

An AB-type block copolymer composed of alpha -acetalpoly(ethylene glycol) ( PEG) as the hydrophilic segment and polylactide (PLA) as the hydrophobic se gment was synthesized and utilized to construct a functionalized PEG layer possessing a reactive aldehyde group at the free end of the tethered PEG ch ain by simple coating on polylactide substrates. Detailed characterization of the functionalized PEGylated surfaces was done from the physicochemical (contact angle and zeta potential) as well as the biological (protein adsor ption) point of view to highlight their potential utility as biofunctional interfaces. The amount of protein adsorption was inversely correlated with the degree of water structuring around the PEG molecules, which facilitates the formation of a strongly bound water film to increase the surface hydra tion. For these surfaces investigated, the extent of surface hydration was more important in determining the materials biocompatibility rather than th e actual PEG molecular weight, as evidenced by an extremely low receding co ntact angle directly related to the adhesive energy of a water molecule. Fu rthermore, the contact angle relaxation less than a few minutes proved to b e determinant for the receding contact angle and resultant hysteresis, caus ed by rearrangement of the hydrophilic PEG component. Aldehyde groups were confirmed to be present at the tethered PEG chain end using an electron spi n resonance probe and can be derivatized with bioactive molecules with amin o or hydrazide functionality. The functionalized PEG layer thus prepared on a biodegradable polylactide surface has both nonfouling and ligand-binding properties and may have promising utility as engineered biomaterials inclu ding tissue engineering scaffolds.