A novel technique is described to conjugate macromolecular heparin complexes to cell surfaces. The method is based on the dual properties of avidin-expressing binding sites for both biotin and a macromolecular complex of heparin. A quartz crystal microbalance with dissipation monitoring (QCM-D) revealed sequential binding of biotin, avidin, and heparin complexes. Large particle flow cytometry confirmed functional integrity. Confocal microscopy of the heparinized islets showed evenly distributed fluorescence. An in vitro Chandler loop model demonstrated that the biocompatibility of the new method is comparable to the previous method used on artificial materials with regard to coagulation and antithrombin uptake. The technique presented allows human islets of Langerhans to successfully be covered with functional heparin as a means to reduce instant blood-mediated inflammatory reactions induced by the innate immune system.