A new t-PA releasing concept based on protein–protein displacement

A new tissue plasminogen activator (t-PA) releasing concept based on a unique protein-displacement triggering mechanism is reported. This concept takes advantage of the fact that plasminogen has higher affinity than t-PA for surface bound lysine. t-PA bound to lysine-modified materials through specific interactions is thus displaced from the surface (released) by plasminogen when in contact with plasma. The concept was investigated using a lysine-modified polyurethane (PU) material in the form of fibrous mats fabricated by electrospinning. The mats are of high surface area to volume ratio and are effectively porous due to fiber entanglement. They were successively modified with poly(2-hydroxyethyl methacrylate) (PHEMA) and lysine, such that the ε-amino and carboxyl groups were free (ε-lysine). These materials were shown to be significantly resistant to nonspecific protein adsorption and to take up large amounts of t-PA through specific interactions with lysine residues. The role of plasminogen-mediated displacement in t-PA release was fully confirmed, and efficient clot lysis by the t-PA loaded materials was demonstrated in an in vitro plasma assay. Release of t-PA by plasminogen displacement endows the t-PA-loaded materials with dual mechanisms for clot-lysis, i.e. by t-PA released from the material to generate plasmin in the fluid phase and by plasmin generated on the surface.