Heparin incorporating liposomes as a delivery system of heparin from PET-covered metallic stents: Effect on haemocompatibility

We investigate the possibility of coating polymer-covered stents with heparin-encapsulating liposomes for improving their haemocompatibility. Thin-film hydration (for multilamellar vesicles, MLV), and the dehydration–rehydration vesicle (DRV) methods are used for preparation of low-molecular weight heparin (LMWH)-encapsulating liposomes with varying lipid compositions. Liposomes are characterized for LMWH encapsulation and retention. For measurement of LMWH, a chromogenic technique is adjusted. For evaluation of heparin release from vesicles in platelet poor plasma (PPP) coagulation time is measured in presence of liposomal samples. Results reveal that LMWH encapsulation in liposomes is higher in DRV, however compositions with high encapsulation are leaky during buffer incubation. Most liposomes release LMWH slowly during plasma incubation (retention after 24 h ranges between 74% and 95%). Concerning the haemocompatibility of polyethylene terephthlate-covered stents after coating with LMWH-encapsulating liposomes, there is a marked increase (higher for DRV-coated stents compared to MLV) in plasma recalcification time compared to the control (plain blood) and reference (non-coated stent), which increases with blood–material contact time. This is probably due to LMWH release, demonstrating that encapsulated LMWH retains its biological functionality. Interestingly, the DRV-coated stents retained a high plasma recalcification time and a large number of liposomes on the stents (as proven by SEM studies) even after extensive washing (high shear conditions), proving that this method may be functional under high flow applying in vivo conditions.