Heparin interaction with polycation immobilized surfaces

Two types of polycationic surfaces were synthesized and used as model surfaces to study the interaction of heparin with polycationic surfaces and the removal of heparin from blood. One model surface is the poly(ethylene-vinyl alcohol) (PEVAL) copolymer with covalently surface immobilized poly(L-lysine) (PLL). The other is the polyallylamine (PALA) immobilized cellulose diacetate (CA) with poly(ethylene glycol) (PEG) spacers. Both PLL and PALA immobilized surfaces have positive charges at neutral pH. PLL was immobilized on PEVAL covalently using cyanogen bromide (BrCN) as a coupling reagent. Heparin binding on the PLL grafted surface was evaluated. The amounts of heparin bound in PBS on smooth and porous PLL immobilized PEVAL surfaces were 0.52 ± 0.19 (Ig/cm2 and 1.69 ± 0.26 (Ig/cm2 (n=3), respectively. Heparin binding kinetic studies in plasma or blood showed a two step" curve, suggesting that competitive binding between heparin and proteins may exist. The bound heparin was eluted by NaOH with a recovery of 85 ± 3%, which implied that most of the heparin was tightly bound to protonated amino groups of PLL. Heparin removal ability of PLL immobilized surfaces was investigated in vitro and ex-vivo. After recirculating the heparinized blood through the PLL immobilized PEVAL surface, the anticoagulant activity of heparin in blood decreased approximately 85% of the initial value in vitro and 61% ex-vivo. To enhance heparin binding capacity, PEG spacers were grafted onto CA surfaces using 1, 3-dicyclohexylcarcodiimide (DCC) to esterify the carboxylic groups of the PEG derivative with hydroxyl groups of CA. PALA was immobilized onto CA-PEG-COOH surfaces by (3-dimethylamino-propyl)carbodiimide (EDC) . The effects of PEG spacers on heparin binding and albumin adsorption onto PALA immobilized surfaces were investigated with varying the M.W. of PEG spacers. The maximum heparin binding and minimum albumin adsorption was found at PEG M.W. 3400. This study suggests that PLL or PALA immobilized surface may be utilized for rapid and effective removal of heparin in blood for clinical use.