The role of heparin self-association in the gelation of heparin-functionalized polymers.

The extensive use of the glycosaminoglycan (GAG) heparin in the design of emerging biomaterials has made the physical characterization of this heterogeneous biomacromolecule increasingly important. In this work, heparin solutions are characterized via dynamic light scattering to investigate heparin's self-association, since this behavior was recently hypothesized to play a role in the gelation of heparin-functionalized polymer hydrogels. Samples of either low molecular weight heparin or high molecular weight heparin were filtered using membranes with 100, 220, or 450 nm average pore sizes. The 100 and 220 nm filters produce a single population of monomers with a diameter range of 3-10nm in the intensity-weighted size distribution. However, the 450 nm filters reveal a second population of associated heparin. Increasing the solution concentration of high molecular weight heparin (HMWH) from 2.5 to 10 wt% causes the magnitude of the smaller population to decrease, while the diameter of the larger associated species approximately doubles. HMWH from different manufacturers displays varying degrees of association. Therefore, weaker associating HMWH can potentially be identified to control heparin self-interactions. Finally, fractionated, N-deacetylated low molecular weight heparin (LMWH) is compared to unmodified LMWH. The chemically modified heparin exhibits a heightened degree of association, suggesting an enhanced self-interaction. The increased negative charge of LMWH in the fractionated sample likely enhances polyelectrolyte interactions proposed to drive the association of these similarly charged polysaccharides. A more detailed understanding of heparin-heparin interactions will assist in the design of new scaffold materials with controlled release profiles, in the clinical use of heparin as an anticoagulant, and in investigations of interactions of other like-charged biomacromolecules.