Bioactive Hydrogel Substrates: Probing Leukocyte Receptor–Ligand Interactions in Parallel Plate Flow Chamber Studies

The binding of activated integrins on the surface of leukocytes facilitates the adhesion of leukocytes to vascular endothelium during inflammation. Interactions between selectins and their ligands mediate rolling, and are believed to play an important role in leukocyte adhesion, though the minimal recognition motif required for physiologic interactions is not known. We have developed a novel system using poly(ethylene glycol) (PEG) hydrogels modified with either integrin-binding peptide sequences or the selectin ligand sialyl Lewis X (SLe(X)) within a parallel plate flow chamber to examine the dynamics of leukocyte adhesion to specific ligands. The adhesive peptide sequences arginine–glycine–aspartic acid–serine (RGDS) and leucine–aspartic acid–valine (LDV) as well as sialyl Lewis X were bound to the surface of photopolymerized PEG diacrylate hydrogels. Leukocytes perfused over these gels in a parallel plate flow chamber at physiological shear rates demonstrate both rolling and firm adhesion, depending on the identity and concentration of ligand bound to the hydrogel substrate. This new system provides a unique polymer-based model for the study of interactions between leukocytes and endothelium as well as a platform to develop improved scaffolds for cardiovascular tissue engineering

Biocompatible copolymers for localized cardiovascular drug delivery and tissue engineering

The integration of bioactive and biomimetic signals into materials for drug delivery and tissue engineering serves to improve cellular responses and therefore healing by more closely resembling the natural cellular microenvironment. The materials developed in this thesis show promise in delivering therapeutic doses of nitric oxide (NO) to physiological systems and provide novel surfaces for the study of cell adhesion and spatial organization. NO has several biological functions that make it an ideal candidate therapeutic agent for the prevention of the occlusive scarring of blood vessels following treatment of coronary artery disease through procedures such as balloon angioplasty and bypass grafting. The present work incorporates NO donors into polymeric biomaterials, resulting in copolymers that release NO over controllable time frames depending on material design. These NO-generating polymers have proven effective in significantly reducing platelet adhesion and smooth muscle cell proliferation in vitro. Endothelial cells exposed to these materials displayed enhanced proliferation, which is essential in restoring vessel function. Local, sustained release of NO from perivascularly-applied hydrogels reduced unwanted neointimal formation by approximately 90% in an experimental balloon angioplasty model. Novel NO releasing dendrimers have been synthesized to establish the potential for injectible NO therapy and can be targeted to sites of active vascular disease. NO-releasing polyurethane has been synthesized as a candidate material for vascular grafts. The superior mechanical properties of polyurethane combined with the inhibition of platelet adhesion by NO promise increased patency in small diameter vascular prostheses. Bioactive poly(ethylene glycol) (PEG) hydrogels have also been synthesized with covalently bound cell adhesion moieties to elucidate the mechanisms of immune cell adhesion to the vascular wall under shear. Leukocytes perfused over the surfaces of these hydrogels in a parallel plate flow chamber display rolling and adhesion properties like those seen on vascular endothelium in vivo. This work also presents a system of patterning bioactive regions onto hydrogels using transparency masks. This system allows the formation of complex patterns of cell-adhesive regions that closely mimic in vivo cellular arrangement. The intrinsic biocompatibility of PEG and the decreased thrombogenicity that NO affords make these materials ideal for incorporation into blood contacting devices

Peptide-modified polyurethane compositions and associated methods

Peptide-modified polyurethanes comprising the reaction product of an isocyanate, a chain extender, and a peptide are provided. Also provided processes for making a peptide-modified polyurethane comprising: providing an isocyanate; providing a chain extender; providing a peptide; and allowing the isocyanate, chain extender, and peptide to react thereby forming the peptide-modified polyurethane, as well as methods for treating a subject comprising: providing a peptide-modified polyurethane that comprises the reaction product of an isocyanate, a chain extender, and a peptide; and administering the peptide-modified polyurethane to the subject

Bioactive Polyurethane–Poly(ethylene Glycol) Diacrylate Hydrogels for Applications in Tissue Engineering

Polyurethanes (PUs) are a highly adaptable class of biomaterials that are among some of the most researched materials for various biomedical applications. However, engineered tissue scaffolds composed of PU have not found their way into clinical application, mainly due to the difficulty of balancing the control of material properties with the desired cellular response. A simple method for the synthesis of tunable bioactive poly(ethylene glycol) diacrylate (PEGDA) hydrogels containing photocurable PU is described. These hydrogels may be modified with PEGylated peptides or proteins to impart variable biological functions, and the mechanical properties of the hydrogels can be tuned based on the ratios of PU and PEGDA. Studies with human cells revealed that PU–PEG blended hydrogels support cell adhesion and viability when cell adhesion peptides are crosslinked within the hydrogel matrix. These hydrogels represent a unique and highly tailorable system for synthesizing PU-based synthetic extracellular matrices for tissue engineering applications