C. Nojiri et al., CAN HEPARIN IMMOBILIZED SURFACES MAINTAIN NONTHROMBOGENIC ACTIVITY DURING IN-VIVO LONG-TERM IMPLANTATION, ASAIO journal, 42(5), 1996, pp. 468-475
The authors previously demonstrated that heparin immobilized surfaces
showed excellent nonthrombogenic properties for extracorporeal membran
e oxygenation experiments as long as 168 hr. The characteristics of th
e heparin immobilized surfaces include high heparin bioactivity and pr
evention of platelet adhesion and complement activation. However, it i
s not known whether the heparin immobilized surfaces would be effectiv
e for in vivo long-term implantation. Heparin bioactivity may be lost
because of complete degradation or blocking of binding sites on hepari
n by adsorbed proteins. This study attempted to elucidate the in vivo
long-term fate of heparin immobilized surfaces. The blood contacting s
urfaces of the ventricular assist device (VAD) made from polyurethane
was modified with heparin immobilization and evaluated in a long-term
sheep left VAD (LVAD) model for as long as 3 months. After removal of
the VAD, heparin bioactivity was measured by Factor Xa assay. The bloo
d contacting surfaces were analyzed with a scanning electron microscop
e, and the adsorbed proteins on the surfaces of the diaphragm were ana
lyzed by SDS-PACE and Western blotting. The thickness of adsorbed prot
eins on the surfaces also was measured by a confocal laser microscope.
For the control ventricular assist devices, thrombus formation was ob
served within 1 month, whereas heparin immobilized VADs were able to o
perate thrombus free for periods as long as 3 months. The control surf
aces demonstrated a thick adsorbed protein layer on thin surfaces, whe
reas heparin immobilized surfaces maintained thinner adsorbed proteins
on thin surfaces. Anti Factor Xa activity of the heparinized surfaces
disappeared after 15 days, but the surfaces remained nonthrombogenic
even after heparin bioactivity was completely lost. The protein compos
ition analyzed by SDS-PACE showed an albumin dominant pattern on the h
eparinized surfaces. The band of 110 kD corresponding to C3b was detec
ted only on the control surfaces, which possibly activated complement,
and subsequently activated platelets and coagulation. Immunoblot show
ed degradation products of fibronectin and vitronectin on the control
surfaces, which probably were promoted by surface generated protease,
whereas the heparinized surfaces showed minimal degradation throughout
the experimental periods. These results suggest that the heparin moie
ty has an ability to control adsorbed proteins, thereby inhibiting thr
ombus formation during in vivo long-term implantation.