Factors XI (70 kDa) and XII (80 kDa) are integral elements in the intrinsic contact coagulation pathway along with prekallikrein (85 kDa) and the high-molecular-weight kininogen(120 kDa). In this study, PCL membranes showed minimal adsorption of factor XI, indicating that the membranes might introduce minor procoagulant activity. Similar results were obtained previously for poly(acrylic acid) modified TiO2 nanoparticles and polyethylene oxide surfaces . The intensity remained unchanged following the addition of UTX. Despite the minor presence of factor XI here, the total absence of kininogen, prekallikrein, and factor XII strongly suggests that the contact activation pathway is inhibited for these PCL fibers.