Endothelialization promotes thromboresistance in blood-contacting devices, but biomaterial designs often overlook sex differences in endothelialization processes. In this study, we elucidated sex differences in endothelial cell-material interactions through investigation of the integrin-ligand interplay with biomaterial substrates and the corollary effects on cell adhesion and spreading. First, integrin expression of human coronary artery endothelial cells (HCAECs) was characterized for age-matched donors (3 male, 3 female). Sex-based differences in integrin expression were identified, with notably higher 2{beta}1, 5{beta}1, and V{beta}3 expression in female cells and higher 1{beta}1 expression in male cells. On polyethylene glycol (PEG)-based hydrogel incorporating collagen or gelatin, female cells showed increased attachment on stiff substrates as compared to male HCAECs, likely driven by increased 2{beta}1, 5{beta}1, and V{beta}3 expression in female cells. Collectively, these results demonstrate sex-biased endothelial cell responses to bioactive hydrogels mediated by integrin interactions and highlight the importance of incorporating biological sex as a design variable in the development of blood-contacting biomaterials.