Bioinspired matrices assembled by polysaccharide-protein interactions

Bioinspired matrices assembled on the basis of noncovalent interactions between proteins and polysaccharides have been proved suitable to deliver therapeutically relevant proteins or DNAs. Our initial efforts were dedicated to the relationship between mechanical properties of hydrogels assembled based on specific interactions between low molecular weight heparin (LMWH) and heparin binding peptides (HBPs) such as HIP, ATIII, and PF4ZIP peptides. The measured differences in affinity and kinetics for LMWH-HBP binding likely lead to observed differences in the phase separation behavior of the poly (ethylene glycol) (PEG)-LMWH/PEG-HIP hydrogels versus the PEG-LMWH/PEG-ATIII hydrogels. More attention has been given to the PF4ZIP peptide employed for the noncovalent assembly of heparinized hydrogels. Multifunctional star PEG-PF4ZIP bioconjugates complexed with star PEG-LMWH form hydrogels that exhibit increasing elastic moduli with increasing mole ratio of PEG-PF4ZIP. The viscoelastic properties of the hydrogels can be controlled via alterations in the ratio between LMWH and PF4ZIP peptide, and comparisons with other PEG-LMWH/PEG-HBP hydrogels suggest the importance of both LMWH/HBP binding kinetics and the binding capacity of LMWH in determining rheological properties in these hydrogels. Characterization of the PEG-LMWH/PEG-PF4ZIP hydrogels suggests that useful moduli for soft tissue engineering applications are obtained at physiological temperatures and after applying high shear. Furthermore, in the basic fibroblast growth factor (bFGF) release, bFGF/vascular endothelial growth factor (VEGF) co-release, and hydrogel erosion results, the combination of growth factor (GF) release profiles and hydrogel erosion profiles suggests that GF delivery from the assembled hydrogels is mainly an erosion-controlled process that may permit co-release of GF with PEG-LMWH and may therefore also improve the bioactivity of GF delivered from these matrices. Hydrogels with such engineered mechanical properties and biological activities may find expanded use in controlled delivery of therapeutics and in other biological applications.; In addition to the multivalent PEG-HBPs, a growth factor with two LMWH-binding sites, VEGF, was also employed to physically crosslink PEG-unfractionated LMWH based on protein-polysaccharide interactions, and the assembled networks can be selectively eroded in the presence of the growth factor receptors. The VEGF released from these hydrogels is bioactive and able to increase proliferation of VEGF-responsive cell lines. A receptor-mediated hydrogel erosion and protein delivery are suggested from the release of VEGF crosslinks in response to cell surface KDR. Employing similar approaches, other therapeutically important difunctional proteins or synthetic peptides can also act as crosslinks of environmentally-responsive systems and be delivered in a targeted manner.; The multivalent PEG-HBPs are also capable of binding both heparin and plasmid DNA sufficiently well to make them valuable for serving as DNA delivery vectors. Transfection studies suggest the PEG-HBPs possess significant transfection efficiency. Apart from the highly toxic PEG-ATIII vector, increased heparin affinity of PEG-HBPs correlated well with increased cellular uptake and increased transfection efficiency. In general, cell surface binding and cellular uptake, mediated by heparan sulfate, play a key role in the transfection pathway. Given that the structures and components of PEG-HBPs can be accurately tuned, the multivalent PEG-HBPs may find broader applications in gene delivery.