Expression of cell adhesion receptors in human osteoblasts cultured on biofunctionalized poly-(ε-caprolactone) surfaces

This study was aimed to investigate whether the activation of poly-(ε-caprolactone) (PCL) surface by low-energy irradiation and/or the biofunctionalization by absorption of arginine–glycine–aspartic sequences (RGD), can modify the expression of integrins closely related to the osteoblast activity. For this purpose, we analysed the physicochemical changes induced by irradiation and RGD immobilization, the consequences on cell adhesion and spreading, and the effects on integrin expression. PCL irradiated with 5×1015He+/cm2 (10 keV energy) (irr-PCL) showed an altered surface layer with a partial loss of carboxyl species and the formation of carbonyl groups. Moreover, irr-PCL showed a small smoothening effect and a less polar character in comparison to the pristine ones. The RGD immobilization was observed only on irr-PCL (surface coverage: 7.0 pmol/cm2). Human osteoblasts (hOB) were cultured on untreated PCL (ut-PCL), ut-PCL+RGD, irr-PCL, and irr-PCL+RGD. After 24 h, ut-PCL hindered the cell adhesion, while a discrete layer of hOB with a good cytoskeleton organization was detected on irr-PCL and irr-PCL+RGD. Before seeding, the single hOB suspension expressed α1, α2, α3, α5, β1, and αVβ3; after 24 h, cells cultured on tissue-plastic expressed high levels of β1 and αVβ3, while α1 showed a low intensity and α2, α3, and α5 were negative. β1 and αVβ3 were selected to evaluate the interaction between cells and PCL samples. The β1 expression was higher in hOB cultured on irr-PCL than on the other samples. A significant increase in αVβ3 expression was observed only in irr-PCL+RGD, and confirmed by the gene expression analysis. In conclusion, ion irradiation and RGD adsorption on PCL surfaces modulate the expression of integrin involved in hOB growth and function, indicating the effectiveness of biomimetic surfaces in promoting cell adhesion. Ultimately, the study of integrin expression may suggest proper changes to the surface structure in order to improve the osteoconductivity of selected materials.