The present invention provides bioconjugates comprising a sulfated polysaccharide such as alginate sulfate and hyaluron sulfate and at least one bioactive polypeptide capable of binding a sulfate group of said sulfated polysaccharide. The bioactive polypeptide can be a heparin-binding polypeptide or a positively-charged polypeptide and is preferably a peptide growth factor or a cytokine. The bioconjugates serve as delivery systems for sustained release of the bioactive polypeptides. Also provided are pharmaceutical compositions comprising the bioconjugates or comprising the sulfated polysaccharides.
