Poly(α-hydroxy esters) are a class of biocompatible resorbable polyesters including poly(lactic acid) (PLA) and poly(glycolic acid) (PGA) that are FDA-approved for clinical use. Preliminary tissue culture studies have demonstrated that these poly(α-hydroxy esters) support bone tissue development both in vitro and in vivo, but biocompatibility issues still exist. Tissue scaffolds fabricated from these materials by current methods have biocompatibility limitations because they are chemically and topographically inert to cells. The chemical composition of these scaffolds does not influence cell behavior (i.e. proliferation, differentiation) and their surface topography is on a scale length larger than a cell, which is too large to affect cell adhesion or orientation. It is hypothesized that poly(α-hydroxy ester) tissue scaffolds can be made more bioactive by (1) incorporating poly(ethylene glycol) (PEG) into the polymer interface to promote osteoblastic differentiation and (2) controlling topography to direct cell behavior. The novel processing technique of electrospinning allows the fabrication of nanofiber scaffolds with topographical features the size of focal adhesion contacts capable of influencing cell behavior. Thus, the overall objective of this research project is to characterize electrospun PEG-PLA diblock copolymers as substrates for bone tissue engineering. To accomplish this, PEG-PLLA and PEG-PDLLA diblock copolymers were synthesized with target molecular weights of 42,000 g/mol (PEG:2000, PLLA or PDLLA:40,000). Next, these two polymers and commercially available PLLA and PDLLA were electrospun to form scaffolds with fibers of diameters 0.14 to 2.1 μm. Finally, cell culture studies were performed to characterize cell morphology, proliferation, and osteoblastic differentiation. Results indicate electrospun fiber scaffolds limit cell spreading and persist in cell culture for two weeks. Analysis of cells cultured over 14 days revealed that there were no differences in cell density between polymers with and without PEG. Cell density increased with fiber diameter, indicating that fiber diameter affects cell adhesion and proliferation and suggesting that cells may migrate into scaffolds with large diameter fibers. In contrast to cell density, ALP activity, an indicator of osteoblastic differentiation, was unaffected by fiber diameter. / Master of Science