Biomer/
poly(N-isopropylacrylamide)/[poly(NiPAAm)] thermosensitive
polymer blends were prepared and their application as
heparin-releasing
polymer coatings for the prevention of surface-induced
thrombosis was examined. The advantage of using poly (NiPAAm)-based coatings as
heparin-releasing
polymers is based on the unique temperature-dependent swelling of these materials. At room temperature, i.e., below the lower critical
solution temperature (LCST) of poly (NiPAAm), the
Biomer/(poly(NiPAAm) coatings are highly swollen. The high swelling enables fast loading of hydrophilic macromolecules (e.g.,
heparin) into the coating by a
solution sorption technique. At a body temperature, i.e., above the LCST of poly (NiPAAm) the coatings are in a deswollen state and the absorbed macromolecules may be slowly released from a dense coating via a diffusion controlled mechanism.
Biomer/poly(NiPAAm) coatings were obtained by blending and coprecipitation of the two linear
polymers,
Biomer and (poly(NiPAAm). The structure and water-swelling properties of the coatings were examined. Significant differences in water swelling at room temperature (RT) and 37 degrees C were observed as a result of the thermosensitivity of poly (NiPAAm). The surface structure of the coatings in dry and swollen states at RT and 37 degrees C was examined by scanning electron microscopy.
Heparin was loaded into the coatings via a
solution sorption at room temperature. Kinetic studies of
heparin loading demonstrated that maximum loading was obtained within 1 h. The in vitro (37 degrees C) release profiles were characterized by a rapid initial release due to the squeezing effect of the collapsing
polymer network, followed by a slower release phase controlled by
heparin diffusion through the dense coating. The short-term antithrombogenicity of intravenous
polyurethane catheters coated with
heparin-releasing
Biomer/poly(NiPAAm) thermosensitive coating was evaluated in a canine animal model. The results show that the
heparin release from
Biomer/poly(NiPAAm)-coated surfaces resulted in a significant reduction of
thrombus formation on test surfaces in contact with venous blood as compared to control surfaces.