A comparison of seven methods to analyze heparin in biomaterials: quantification, location, and anticoagulant activity.

Glycosaminoglycans, like heparin, are frequently incorporated in biomaterials because of their capacity to bind and store growth factors and because of their hydrating properties. Heparin is also often used in biomaterials for its anticoagulant activity. Analysis of biomaterial-bound heparin is challenging because most assays are based on heparin in solution. In this study, seven different methods were probed to analyze heparin covalently attached to collagen scaffolds. For each method, the basic mechanism and the advantages and disadvantages are given. An analysis by the factor Xa assay and the Farndale assay clearly indicated that the amount of immobilized heparin cannot be determined correctly when the scaffold is intact. Scaffolds had to be proteolytically digested or acid treated to obtain reliable measurements. Methods used to quantify the amount of bound heparin included a hexosamine assay, an uronic acid assay, a Farndale assay, agarose gel electrophoresis, and immuno-dot blot analysis. Location and semiquantification of heparin were accomplished by immunofluorescence. Although all assays had their advantages and disadvantages, the hexosamine assay turned out to be the most robust and is recommended as the preferred assay to quantify the amount of heparin bound to scaffolds. It is applicable to all scaffolds that are acid hydrolyzable. This study may allow researchers in the field to select the most appropriate method to analyze glycosaminoglycans in biomaterials.