A covalently interconnected phosphazene-silicate network: Synthesis and surface functionalization

A sol-gel precursor was prepared by the reaction of poly[bis(2-(2-hydroxy-ethoxy)ethoxy)phosphazene] (1) with 3-isocyanatopropyltriethoxysilane. It was then sol-gel polymerized to produce a covalently interconnected phosphazene-silicate network with urethane functionalities. Isocyanato groups were introduced on the surface of the network through coupling by allophanate formation between hexamethylene diisocyanate and urethane functionalities on the gel surface. Heparin was immobilized on the surface of the network by reacting hydroxyl or amino groups of heparin with the surface isocyanato groups. The activity of the immobilized heparin was 4.0 % that of free heparin.