Characterization of heparin-based hydrogel networks

Synthetic heparin-based hydrogels show promise as tissue engineering scaffolds for clinical applications in wound healing, tissue regeneration, and drug delivery. These bioactive materials are designed to mimic the characteristics of the natural extracellular matrix and therefore have the ability to elicit desired cell responses via specifically engineered signals, including the incorporation of cell-attachment domains, cell-degradable cross-linkers, and growth factors. The aim of this work is to rationally engineer hydrogel properties, including gel stiffness, binding ligand density, growth factor loading, and cell-mediated degradation, for optimal biological responses in the applications mentioned above. This study of hydrogel development and characterization gives insight into how hydrogel composition affects the final properties of the resulting materials.;The extensive use of the glycosaminoglycan heparin in the design of emerging biomaterials has made the physical characterization of this heterogeneous biomacromolecule increasingly important. We first examined heparin solutions 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. We found two populations present in these solutions consisting of heparin monomers and an associated species. The associated species was removed through filtration with 100 and 220 nm pore size filters, but was still present upon filtration with 450 nm pore size filters. The apparent aggregation was enhanced by increasing the molecule's negative charge through fractionation, supporting the hypothesis that polyelectrolyte interactions are the cause of the association of these similarly charged, rod-like 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.;In the development of chemically assembled hydrogels, an understanding of how chemical composition affects hydrogel formation and the resulting physical properties is necessary. To this end, heparin-based hydrogel properties were characterized through bulk rheology to create comprehensive hydrogel formation maps that lay out the effects of polymer concentration and cross-linker molar ratio on hydrogel compliance. In this work, maleimide-functionalized high molecular weight heparin (HMWH) served as the polysaccharide backbone. The network was cross-linked through the addition of either thiol-terminated linear poly(ethylene glycol) (PEG) or a matrix metalloproteinase-target peptide. The resulting hydrogels have shown promise as both growth factor delivery agents and cell scaffolds. We further investigated the effect of cross-linker length and flexibility on hydrogel stiffness and gelation kinetics by forming the network with different molecular weight linear PEGs (2,000 and 10,000) and a cell-degradable peptide, holding heparin composition constant. Finally, the extent of reaction in the hydrogels was estimated using the theory of rubber elasticity.;Overall, this work has progressed the understanding of how heparin-based hydrogels assemble and how their molecular composition affects hydrogel formation kinetics and final compliance. This information provides another useful tool in the engineering of these synthetic materials for biomedical applications.