Controlling the surface density of heparin in active coatings is important in providing anticoagulation while preventing bleeding. An approach based on tuning the degree of hydrolysis of poly(2-ethyl-2-oxazoline) (PEOX) is presented to control the surface density of heparin in layer-by-layer (LbL) assembled films. Multilayers are prepared at pH 5 in 0.5 M aqueous NaCl solutions by electrostatic interactions between negatively charged heparin and the positively charged amine groups in hydrolyzed PEOX. Characterization of the multilayers by quartz crystal microbalance with dissipation (QCM-D), toluidine blue (TBO) assay and X-ray Photoelectron Spectroscopy (XPS) all shows that the amount of heparin deposited increases with the degree of hydrolysis. While non-hydrolyzed PEOX/heparin multilayers do not grow, the average deposited mass per area per bilayer as determined by QCM-D measurements increases with the degree of hydrolysis. At 50% hydrolysis, TBO assay gives a heparin surface density of 1.03 μg/cm2 and atomic % of sulfur as determined by XPS leveled off at 14%. These results show the potential of acidic hydrolysis of PEOX combined with LbL assembly of heparin as a reproducible method for controlling the surface density of heparin in anticoagulant coatings.
