Dual biofunctional polymer modifications to address endothelialization and smooth muscle cell integration of ePTFE vascular grafts.

Expanded polytetrafluoroethylene (ePTFE) grafts were coated on the luminal surface with a cell-adhesive fluorosurfactant (FSP) polymer to promote endothelialization, followed by ethanol hydration to degas the pores and subsequent cell-adhesive, enzymatically degradable poly(ethylene glycol)-based hydrogel incorporation into the graft interstices to accommodate potential smooth muscle cell integration in the graft wall. The FSP coating on ePTFE was stable as demonstrated by a significantly reduced receding water contact angle on FSP-coated ePTFE (14.5 ± 6.

In vivo evaluation of biomimetic fluorosurfactant polymer-coated expanded polytetrafluoroethylene vascular grafts in a porcine carotid artery bypass model.

Objective: The objective of this study was to evaluate the potential for biomimetic self-assembling fluorosurfactant polymer (FSP) coatings incorporating heptamaltose (M7-FSP) to block nonspecific protein adsorption, the cell adhesive RGD peptide (RGD-FSP), or the endothelial cell-selective CRRETAWAC peptide (cRRE-FSP) to improve patency and endothelialization in small-diameter expanded polytetrafluoroethylene (ePTFE) vascular graft implants.

Methods: ePTFE vascular grafts (4 mm in diameter, 5 cm in length) were coated with M7-FSP, RGD-FSP, or cRRE-FSP by dissolving FSPs in distilled water and flowing solution through the graft lumen for 24 hours. Coatings were confirmed by receding water contact angle measurements on the lumen surface.

Photoinitiator-free synthesis of endothelial cell-adhesive and enzymatically degradable hydrogels.

We report on a photoinitiator-free synthetic method of incorporating bioactivity into poly(ethylene glycol) (PEG) hydrogels in order to control physical properties, enzymatic biodegradability and cell-specific adhesiveness of the polymer network, while eliminating the need for UV-mediated photopolymerization. To accomplish this, hydrogel networks were polymerized using Michael addition with four-arm PEG acrylate (10 kDa), using a collagenase-sensitive peptide (CSP) as a crosslinker, and introducing an endothelial cell-adhesive peptide either terminally (RGD) or attached to the crosslinking peptide sequence (CSP-RGD). The efficiency of the Michael addition reactions were determined by nuclear magnetic resonance and Ellman's assay.

Extracellular matrix-mimetic poly(ethylene glycol) hydrogels engineered to regulate smooth muscle cell proliferation in 3-D.

The goal of this project is to engineer a defined, synthetic poly(ethylene glycol) (PEG) hydrogel as a model system to investigate smooth muscle cell (SMC) proliferation in three-dimensions (3-D). To mimic the properties of extracellular matrix, both cell-adhesive peptide (GRGDSP) and matrix metalloproteinase (MMP) sensitive peptide (VPMSMRGG or GPQGIAGQ) were incorporated into the PEG macromer chain. Copolymerization of the biomimetic macromers results in the formation of bioactive hydrogels with the dual properties of cell adhesion and proteolytic degradation.

Cross-reactivity of cell-selective CRRETAWAC peptide with human and porcine endothelial cells.

We report on the cross-reactivity of the cell adhesive peptide CRRETAWAC between human and porcine endothelial cells (ECs). CRRETAWAC is a phage display derived peptide which has been shown to bind the α5 β1 receptor on human ECs, but does not bind platelets and thus could be incorporated into a coating for cardiovascular biomaterials that resists platelet adhesion and thrombosis, while allowing for endothelialization. To determine the cross-reactivity of the peptide, attachment and growth of human and porcine ECs on CRRETAWAC fluorosurfactant polymer (FSP) coated surfaces was explored.

Biomimetic-engineered poly (ethylene glycol) hydrogel for smooth muscle cell migration.

We report on a biomimetic scaffold as a model system to evaluate smooth muscle cell (SMC) migration in three dimensions. To accomplish this, bio-inert poly (ethylene glycol) (PEG)-based hydrogels were designed as the scaffold substrate. To mimic properties of the extracellular matrix, cell-adhesive peptide (GRGDSP) derived from fibronectin and collagenase-sensitive peptide (GPQGIAGQ) derived from collagen type I were incorporated into the PEG macromer chain.

Targeted delivery of vancomycin to Staphylococcus epidermidis biofilms using a fibrinogen-derived peptide.

This study reports on the use of a fibrinogen-derived peptide for the specific targeting and delivery of vancomycin to Staphylococcus epidermidis biofilms. One method by which S. epidermidis initially adheres to biomaterials uses the plasma protein fibrinogen as an intermediary, where the S.

Endothelial cell attachment and shear response on biomimetic polymer-coated vascular grafts.

Endothelial cell (EC) adhesion, shear retention, morphology, and hemostatic gene expression on fibronectin (FN) and RGD fluorosurfactant polymer (FSP)-coated expanded polytetrafluoroethylene grafts were investigated using an in vitro perfusion system. ECs were sodded on both types of grafts and exposed to 8 dyn/cm(2) of shear stress. After 24 h, the EC retention on RGD-FSP-coated grafts was 59 ± 14%, which is statistically higher than the 36 ± 11% retention measured on FN grafts (p < 0.

Disruption of Staphylococcus epidermidis biofilm formation using a targeted cationic peptide.

This study reports the use of a targeted cationic peptide with the ability to disrupt Staphylococcus epidermidis biofilm formation. Complications due to nosocomial infections of implanted medical devices pose a significant health risk to patients, with Staphylococcus epidermidis often implicated in the case of blood-contacting biomaterials. S.

Biomimetic poly(ethylene glycol)-based hydrogels as scaffolds for inducing endothelial adhesion and capillary-like network formation.

The extracellular matrix (ECM) is an attractive model for designing synthetic scaffolds with a desirable environment for tissue engineering. Here, we report on the synthesis of ECM-mimetic poly(ethylene glycol) (PEG) hydrogels for inducing endothelial cell (EC) adhesion and capillary-like network formation. A collagen type I-derived peptide GPQGIAGQ (GIA)-containing PEGDA (GIA-PEGDA) was synthesized with the collagenase-sensitive GIA sequence attached in the middle of the PEGDA chain, which was then copolymerized with RGD capped-PEG monoacrylate (RGD-PEGMA) to form biomimetic hydrogels.

Design properties of hydrogel tissue-engineering scaffolds.

This article summarizes the recent progress in the design and synthesis of hydrogels as tissue-engineering scaffolds. Hydrogels are attractive scaffolding materials owing to their highly swollen network structure, ability to encapsulate cells and bioactive molecules, and efficient mass transfer. Various polymers, including natural, synthetic and natural/synthetic hybrid polymers, have been used to make hydrogels via chemical or physical crosslinking.

Hemocompatibility of silicon-based substrates for biomedical implant applications.

Silicon membranes with highly uniform nanopore sizes fabricated using microelectromechanical systems (MEMS) technology allow for the development of miniaturized implants such as those needed for renal replacement therapies. However, the blood compatibility of silicon has thus far been an unresolved issue in the use of these substrates in implantable biomedical devices. We report the results of hemocompatibility studies using bare silicon, polysilicon, and modified silicon substrates.

Anti-biofouling Sulfobetaine Polymer Thin Films on Silicon and Silicon Nanopore Membranes.

Silicon nanopore membranes (SNM) with monodisperse pore size distributions have potential applications in bioartificial kidneys. A protein resistant thin film coating on the SNM is required to minimize biofouling and, hence, enhance the performance efficiency of SNM. In this work, a zwitterionic polymer, poly(sulfobetaine methacrylate) (polySBMA), was used to coat silicon and SNM substrates via a surface initiated atom transfer radical polymerization method.

Molecular regulation of contractile smooth muscle cell phenotype: implications for vascular tissue engineering.

The molecular regulation of smooth muscle cell (SMC) behavior is reviewed, with particular emphasis on stimuli that promote the contractile phenotype. SMCs can shift reversibly along a continuum from a quiescent, contractile phenotype to a synthetic phenotype, which is characterized by proliferation and extracellular matrix (ECM) synthesis. This phenotypic plasticity can be harnessed for tissue engineering.

Effect of neutrophil adhesion on the mechanical properties of lung microvascular endothelial cells.

Neutrophil adhesion to pulmonary microvascular endothelial cells (ECs) initiates intracellular signaling, resulting in remodeling of F-actin cytoskeletal structure of ECs. The present study determined the mechanical properties of ECs and the changes induced by neutrophil adhesion by atomic force microscopy. The elastic moduli of ECs were compared before neutrophils were present, as soon as neutrophil adhesion was detected, and 1 minute later.

In vitro and in vivo platelet targeting by cyclic RGD-modified liposomes.

Cell-selective delivery using ligand-decorated nanoparticles is a promising modality for treating cancer and vascular diseases. We are developing liposome nanoparticles surface-modified by RGD peptide ligands having targeting specificity to integrin GPIIb-IIIa. This integrin is upregulated and stimulated into a ligand-binding conformation on the surface activated platelets.

The effects of heparin releasing hydrogels on vascular smooth muscle cell phenotype.

Poly(ethylene glycol) diacrylate (PEGDA) hydrogel scaffolds were engineered to promote contractile smooth muscle cell (SMC) phenotype via controlled release of heparin. The scaffold design was evaluated by quantifying the effects of free heparin on SMC phenotype, engineering hydrogels to provide controlled release of heparin, and synthesizing cell-adhesive, heparin releasing hydrogels to promote contractile SMC phenotype. Heparin inhibited SMC proliferation and up-regulated expression of contractile SMC phenotype markers, including smooth muscle alpha-actin, calponin, and SM-22alpha, in a dose-dependent fashion (6 microg/ml to 3.

The influence of RGD-bearing hydrogels on the re-expression of contractile vascular smooth muscle cell phenotype.

This study reports on the ability of poly(ethylene glycol) diacrylate (PEGDA) hydrogel scaffolds with pendant integrin-binding GRGDSP peptides (RGD-gels) to support the re-differentiation of cultured vascular smooth muscle cells (SMCs) toward a contractile phenotype. Human coronary artery SMCs were seeded on RGD-gels, hydrogels with other extracellular matrix derived peptides, fibronectin (FN) and laminin (LN). Differentiation was induced on RGD-gels with low serum medium containing soluble heparin, and the differentiation status was monitored by mRNA expression, protein expression, and intracellular protein organization of the contractile smooth muscle markers, smooth muscle alpha-actin, calponin, and SM-22alpha.

Biomimetic fluorocarbon surfactant polymers reduce platelet adhesion on PTFE/ePTFE surfaces.

We describe a series of fluorocarbon surfactant polymers designed as surface-modifying agents for improving the thrombogenicity of ePTFE vascular graft materials by the reduction of platelet adhesion. The surfactant polymers consist of a poly(vinyl amine) backbone with pendent dextran and perfluoroundecanoyl branches. Surface modification is accomplished by a simple dip-coating process in which surfactant polymers undergo spontaneous surface-induced adsorption and assembly on PTFE/ePTFE surface.

Design and synthesis of biomimetic hydrogel scaffolds with controlled organization of cyclic RGD peptides.

We report on the rational design and synthesis of a new type of bioactive poly(ethylene glycol) diacrylate (PEGDA) macromers, cyclic Arg-Gly-Asp (cRGD)-PEGDA, to mimic the cell-adhesive properties of extracellular matrix (ECM), aiming to create biomimetic scaffolds with controlled spatial organization of ligands and enhanced cell binding affinity for tissue engineering. To attach the cRGD peptide in the middle of PEGDA chain, a tailed cRGD peptide, c[RGDfE(SSSKK-NH2)] (1), was synthesized with c(RGDfE) linked to a tail of SSSKK. The tail consists of a spacer with three serine residues and a linker with two lysine residues for conjugating with acryloyl-PEG-NHS (5) to create cRGD-PEGDA (6).

The effects of monoacrylated poly(ethylene glycol) on the properties of poly(ethylene glycol) diacrylate hydrogels used for tissue engineering.

This study investigated the effects of poly(ethylene glycol) monoacrylate (PEGMA) on the properties of poly(ethylene glycol) diacrylate (PEGDA)-co-PEGMA hydrogel networks. The PEGMA materials utilized were similar to ligand-linked materials typically copolymerized with PEGDA for use as tissue engineering scaffolds. PEGDA (5-20% wt/wt, 6 kDa) and PEGMA (0-20% wt/wt, 0-43 mM, 5 kDa) were copolymerized by photo-initiated free radical polymerization and the mass swelling ratio and shear modulus of the resulting hydrogels were determined.

Effect of monomer structure and solvent on the growth of supramolecular nanoassemblies on a graphite surface.

The self-assembly of high aspect ratio hierarchical surface assemblies, as observed by fluid tapping mode AFM, can be achieved through careful design of the supramolecular interactions between low-molecular-weight adsorbates. Needlelike assemblies of monotopic guanine end-capped alkanes grow on a graphite surface when deposited from a water/DMSO solution. The growth of these assemblies can be monitored by AFM in real time, and the growth rate along the two different axes can be understood (through molecular modeling) in terms of the specific adsorbate-adsorbate interactions along those axes.

Platelet and endothelial adhesion on fluorosurfactant polymers designed for vascular graft modification.

A prominent failure mechanism of small diameter expanded polytetrafluoroethylene (ePTFE) vascular grafts is platelet-mediated thrombosis. We have designed a surface modification for ePTFE consisting of a self-assembling fluorosurfactant polymer (FSP) bearing biologically active ligands, including adhesive peptides and polysaccharide moieties. The goal of this biomimetic construct is to improve graft hemocompatibility by promoting rapid surface endothelialization, whereas minimizing platelet adhesion.

Changes in the hyperelastic properties of endothelial cells induced by tumor necrosis factor-alpha.

Mechanical properties of living cells can be determined using atomic force microscopy (AFM). In this study, a novel analysis was developed to determine the mechanical properties of adherent monolayers of pulmonary microvascular endothelial cells (ECs) using AFM and finite element modeling, which considers both the finite thickness of ECs and their nonlinear elastic properties, as well as the large strain induced by AFM. Comparison of this model with the more traditional Hertzian model, which assumes linear elastic behavior, small strains, and infinite cell thickness, suggests that the new analysis can predict the mechanical response of ECs during AFM indentation better than Hertz's model, especially when using force-displacement data obtained from large indentations (>100 nm).

Affinity manipulation of surface-conjugated RGD peptide to modulate binding of liposomes to activated platelets.

Platelet adhesion, activation and fibrinogen-mediated aggregation are primary events in vascular thrombosis and occlusion. An injectable delivery system that can carry thrombolytics selectively to the sites of active platelet aggregation has immense potential in minimally invasive targeted therapy of vascular occlusion. To this end we are studying liposomes surface-modified by fibrinogen-mimetic RGD motifs that can selectively target and bind integrin GPIIb-IIIa on activated platelets.