The objective of the present investigation is to systematically evaluate the role of polymer crystallinity on osteoblast adhesion, proliferation, osteogenic gene expression and bioactive protein adsorption using a series of polycaprolactone- co-glycolide) PCL-PGA) polymers. Five compositions of pure PCL and PGA, and PCL-PGA intermediate copolymeric compositions in ratios of 25:75, 35:65 and 45:55, were selected. These polymers were fabricated into thin films by compression molding. The samples were characterized using scanning electro microscopy SEM) for surface morphology, differential scanning caloriometry DSC) for crystallinity, contact angle measurement for hydrophobicity CA), and atomic force microscopy AFM) for nanotopography. The PCL-PGA films demonstrated similar morphology, hydrophobicity and nanotopography whereas they differed significantly in crystallinity. Cell adhesion and proliferation, as well as osteogenic gene expression were evaluated with osteoblasts HEPM 1486) on PCL-PGA surfaces. Recombinant human growth and differentiation factor 5 rhGDF-5) and Fibronectin Fn) were adsorbed from single protein solutions using depletion method and quantified using bicinchoninic acid BCA) protein and radiolabelling assay. The protein-adsorbed surface nanotopography was analyzed using AFM. In the cellular responses experiments, amorphous/flexible PCL-PGA 35:65 supports osteoblast growth and promotes osteogenic gene expression significantly better than the crystalline PCL and PGA. These studies demonstrated that crystallinity and rigidity played major roles in determining cell responses with PCL-PGA polymers. Protein adsorption study results indicate that rhGDF-5 adsorbed to a higher extent on PCL surfaces and least on PGA surfaces. Reduced rhGDF-5 a more hydrophilic and flexible protein form adsorbed significantly in greater amounts on all PCL-PGA substrates, demonstrating that the conformation and hydrophibicity of rhGDF-5 played a major role in its adsorption to PCL-PGA surfaces. Fn, a 450 kDa protein, contains multiple binding motifs with varied hydrophobicity. Binding motifs of Fn fragments strongly impacted their adsorption to PCL-PGA surfaces. The adsorption of Fn 70 kDa fragment on PCL-PGA polymers was found to favor binding to PCL material with the greatest adsorption on pure PCL surfaces, similar to the full length of Fn molecule. Collectively, these studies demonstrate that Fn 70 kda) played a major role in full-length Fn adsorption to PCL-PGA substrates.