HEPARIN-CONTAINING BLOCK-COPOLYMERS .1. SURFACE CHARACTERIZATION

Newly synthesized heparin-containing block copolymers, consisting of a hydrophobic block of polystyrene (PS), a hydrophilic spacer-block of poly(ethylene oxide) (PEO) and covalently bound heparin (Hep) as bioac tive block, were coated on aluminium, glass, polydimethylsiloxane (PDM S), PS or Biomer substrates. Surfaces of coated materials were charact erized by transmission electron microscopy (TEM), contact angle measur ements and X-ray photoelectron spectroscopy for chemical analysis (XPS ). It was demonstrated by TEM that thin films of PS-PEO and PS-PEO-Hep block copolymers consisted of heterogeneous microphase separated stru ctures. Using sessile-drop and Wilhelmy plate dynamic contact angle me asurements, insight was provided into the hydrophilicity of the surfac es of the coatings. Measurements with hydrated coatings of PS-PEO and PS-PEO-Hep block copolymers revealed that the surfaces became more hyd rophilic during immersion in water, due to relaxation/reorientation, o r swelling of PEO or PEO-Hep domains, respectively. XPS results for PS , PEO, heparin and PS-PEO as powder agreed well with qualitative and q uantitative predictions. XPS results for films of PS-PEO and PS-PEO-He p block copolymers showed enrichments of PEO in the top layers of the coatings. This effect was more pronounced for hydrated surfaces. Only small amounts of heparin were detected at the surface of coatings of P S-PEO-Hep block copolymers.