Poly(ethylene oxide) (PEO) is a neutral, highly biocompatible, and pharmacologically inactive water-soluble polymer [1]. The physicochemical incorporation of PEO into biodegradable poly(Llactic acid) (PLLA)-based drug delivery implant systems would be expected to improve the interfacial biocompatibility of these polymeric devices. Blend matrices of PEO and relatively hydrophobic PLLA or PEO-b-PLLA block copolymers should improve the three dimensional stability and the biological activity of watersoluble macromolecular drugs such as proteins or enzymes in the delivery systems, which are incorporated in the matrix [2] for two reasons: first, if surface-segregated PEO in the aqueous environment provides a diffusive hydrophilic layer [3] facilitating the interaction between cells and polymeric biodevices, and secondly, if hydrophilic PEO segments in the bulk protect water-soluble drugs from hydrophobic polymers in the form [4] of a micelle or encapsulation.
Two model systems of PEO-containing polymer systems are considered in the present study as candidates for seeding proteinbased drugs into a PLLA matrix. One approach is to use PLLA blend matrices with PEO-b-poly(propylene oxide) (PPO)-b-PEO triblock copolymers (Pluronics 1 , BASF Corp.), Pluronics 1 exhibit a wide range of hydrophilicity/hydrophobicity as a function of PEO/PPO ratio [5]. The blend concept is based on the assumption that blends can exhibit advantageous physicomechanical properties that each individual polymer does not have [6,7]. The other model system involves PLLA-b-PEO diblock and PLLA-b-PEO-b-PLLA triblock copolymers [8]. Recently, these nonionic amphiphilic block copolymers have been studied as a new biodegradable hydrogel in the application of injectable drug delivery systems due to the novel thermosensitive sol-gel transition [4,9,10]. The chemistry in bulk of two polymer systems above has been extensively studied. However, few attempts have been made for the surface char-