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Due to the important structural and signaling roles of elastin in vascular stability, engineered human vascular tissues must incorporate elastin. However, despite considerable progress toward engineering of elastin-containing vascular tissues from animal cells, currently engineered vascular tissues using human cells largely lack elastin. In this study, we evaluated the effect of scaffold topography (two dimensional [2D] vs. three dimensional [3D]) on elastogenesis in adult human coronary artery smooth muscle cells (HCASMCs). We report that elastin gene expression by HCASMCs was increased by twofold after 4 days of culture in porous 3D polyurethane scaffolds. Transforming growth factor β1 (TGF-β1) further increased elastin gene expression in 3D cultures but not in 2D cultures. To evaluate if gene expression is translated into elastin synthesis, both 2D and 3D cultures were analyzed using Western blots. We show that only HCASMCs in 3D scaffolds produced elastin, suggesting that scaffold geometry itself is an important cue for elastogenesis. Moreover, TGF-β1 enhanced elastin synthesis in 3D, but had no effect on cells grown on 2D surfaces. TGF-β1, known to induce vascular smooth muscle cells (VSMC) differentiation, upregulated contractile VSMC marker proteins smooth muscle-α-actin and calponin in cells on 2D surfaces. Interestingly, in 3D scaffolds, TGF-β1 failed to upregulate these differentiation marker proteins for at least 7 days, but did so in cells cultured for 14 days, whereas elastin synthesis was not affected. To our knowledge this study is the first to successfully demonstrate that adult human VSMC can produce elastin when seeded on 3D scaffolds and to directly compare the effect of scaffold topography on elastin synthesis. Knowledge about the conditions required to regulate the phenotype of human VSMCs is paramount to engineer elastin-containing autologous human vascular substitutes.

One strategy in vascular tissue engineering is the design of hybrid vascular substitutes where vascular cells infiltrate biostable porous scaffolds that provides favorable environment for guided cell repopulation and acts as a mechanically supporting layer after the tissue regeneration process. The aim of the present work was to study the interaction of human coronary artery smooth muscle cells (HCASMC) with 3D porous polyurethane scaffolds. We therefore fabricated porous and highly interconnected 3D polyurethane scaffolds that can promote HCASMC attachment, proliferation, and migration. SEM and microCT studies of the fabricated scaffolds showed that the current scaffolds had highly open and interconnected pore structures, with an average porosity of 84%. HCASMC interaction on polyurethane films revealed that cells adhere and express specific marker proteins (vinculin and h-caldesmon). This expression was further enhanced by coating the polyurethane with Matrigel. On uncoated 3D scaffolds, dense spherical aggregates of cells were often encountered with little adhesion of individual cells alongside the struts of the scaffold, independent of the porogens used. In contrast, when cultured on Matrigel-coated scaffolds, cell numbers quickly increased after 14 days and spread along the entire scaffold. At the upper scaffold surface, elongated cells were seen adhering to one another and also to the scaffold surface. These cells were elongated, aligned in parallel and contained abundant F-actin bundles suggesting a differentiated contractile phenotype. Deep into the scaffold, cells were encountered that formed actin-rich lamellipodial extensions spreading along the strut and lacked stress fibers, suggesting active cell migration along the substrate.

Successful tissue engineering of vascular grafts largely depends on synthetic scaffolds that support the survival, proliferation, and differentiation of seeded cells. To investigate the utility of polyurethanes for vascular tissue engineering, three-dimensional porous polyurethane scaffolds with highly interconnected pore structures were fabricated by a pressure differential/particulate leaching technique. Ammonium chloride and paraffin porogens were prepared to fabricate the scaffolds. Grinding of ammonium chloride resulted in particulates with uniform particle sizes but irregular shapes. Paraffin particulates made by a dispersion method, on the other hand, had spherical shapes and uniform particle sizes. Polyurethane scaffolds fabricated from these particulates had open faced, highly interconnected channels that could allow cellular infiltration and nutrient delivery. Human coronary artery smooth muscle and endothelial cell interactions with polyurethane surfaces revealed these biomaterials to maintain the contractile phenotype of human coronary artery smooth muscle cells and the formation of endothelial monolayers. During longer culture times, surface modification with cell adhesive extracellular matrix (ECM) protein promoted vascular cell proliferation, maintenance of the differentiated phenotype and endothelial monolayer integrity. Our results suggest that these polyurethanes, in conjunction with cell adhesive ECM proteins, could also support vascular cells in three-dimensional bioreactor-based culture conditions., (Copyright 2007 Wiley Periodicals, Inc.)

Successful tissue repair and regeneration relies on the design of new biomaterials that can mediate cell interaction without inflicting undesirable responses. Novel physically crosslinked polyurethane-block-poly(vinyl pyrrolidone) hydrogel biomaterials were synthesized by the macroiniferter controlled radical polymerization method. The structures of the hydrogels were studied by FT-IR and (1)H NMR. Hydrogels with EWC up to 37 wt.-% were prepared. The presence of the PVP block significantly increased the hard-segment glass transition temperature. Vascular smooth muscle cell attachment and spreading on the hydrogels indicated that these materials have a potential for use as scaffolds in tissue engineering.

Protein adsorption and platelet adhesion properties of polyurethane biomaterials are important considerations for blood-contacting applications. Although the presence of ionic groups on the surface of biomaterials is believed to influence their blood response, their exact role is not known. The objective of this work was to study the protein adsorption and platelet adhesion properties of ion-containing polyurethane biomaterials. Thus, we prepared polyurethanes that contained ions either on the soft segment or hard segment and investigated their in vitro protein adsorption and platelet adhesion. The presence of ions increased the amount of adsorbed proteins and adhered platelets on the synthesized polyurethanes. Whereas albumin and lysozyme adsorption were independent of the location of the ions (soft vs. hard segments), fibrinogen adsorption was strongly dependent on the location of the ions. Platelet adhesion, on the other hand, was found to be less dependent on the location of the ions within the polyurethane structure. This is the first evidence to unequivocally demonstrate the exact role of ions on protein adsorption and platelet adhesion. Taken together, our study suggests that in the absence of known biocompatible chains such as polyethyleneoxide, ion-containing polyurethanes do not demonstrate improved blood compatibility. Therefore, we conclude that ion incorporation into polyurethanes may not be a viable approach to design polyurethane biomaterials for blood-contacting applications.

Physically crosslinked hydrogels based on poly(2-hydroxyethyl methacrylate) (PHEMA) and polyurethane macroiniferter (PUMI) were prepared. The synthesis of polyurethane-block-poly(2-hydroxyethyl methacrylate) (PU-b-PHEMA) was verified by spectroscopic analyses. Due to the low fibronectin adsorption from culture media, cell attachment on PU-b-PHEMA surface was poor compared with the PUMI control. To improve the cell affinity of PU-b-PHEMA, fibronectin was conjugated via surface hydroxyl groups. These biomimetic PU-b-PHEMA hydrogel surfaces were tested for tissue engineering applications. A short-term cell culture study revealed that, compared with the unmodified PU-b-PHEMA, fibronectin-conjugated PU-b-PHEMA hydrogel showed more uniform and dense cell attachment and spreading, indicating a potential use for tissue engineering applications. [ABSTRACT FROM PUBLISHER]

Abstract: One important advantage offered by polymeric iniferters is the possibility that polycondensation polymers could be further reacted with vinyl monomers to produce novel block copolymers with interesting properties. The objective of this work was the kinetic investigation of polyurethane-block-poly(methyl methacrylate) (PU-b-PMMA) using dithiocarbamate (DC)-based polyurethane macroiniferter (PUMI) at different concentrations. It is shown that the copolymerization reactions followed the first order dependency. A linear increase of molecular weight with monomer conversion demonstrated that the copolymerization followed the mechanism of controlled radical polymerization. The rate of polymerization (Rp ) at specific reaction time increased as the PUMI concentration increased from 0.34×10−3 mol/L to 2.74×10−3 mol/L, pass through a maxima, and decreased as PUMI concentration was increased beyond 2.74×10−3 mol/L. The thermogravimetric analysis showed that both PUMI and PU-b-PMMA degraded in three distinctive stages but the PU-b-PMMA is thermally more stable than the PUMI especially at lower temperatures. Thus, a combination of polycondensation and free radical photopolymerization methods, as demonstrated in this study, could be used to synthesize polyurethane-based block copolymers with tailored chain lengths of different blocks suitable for biomedical applications. [Copyright &y& Elsevier]

Protein adsorption and platelet adhesion properties of polyurethane biomaterials are important considerations for blood-contacting applications. Although the presence of ionic groups on the surface of biomaterials is believed to influence their blood response, their exact role is not known. The objective of this work was to study the protein adsorption and platelet adhesion properties of ion-containing polyurethane biomaterials. Thus, we prepared polyurethanes that contained ions either on the soft segment or hard segment and investigated their in vitro protein adsorption and platelet adhesion. The presence of ions increased the amount of adsorbed proteins and adhered platelets on the synthesized polyurethanes. Whereas albumin and lysozyme adsorption were independent of the location of the ions (soft vs. hard segments), fibrinogen adsorption was strongly dependent on the location of the ions. Platelet adhesion, on the other hand, was found to be less dependent on the location of the ions within the polyurethane structure. This is the first evidence to unequivocally demonstrate the exact role of ions on protein adsorption and platelet adhesion. Taken together, our study suggests that in the absence of known biocompatible chains such as polyethyleneoxide, ion-containing polyurethanes do not demonstrate improved blood compatibility. Therefore, we conclude that ion incorporation into polyurethanes may not be a viable approach to design polyurethane biomaterials for blood-contacting applications. [ABSTRACT FROM AUTHOR]

Abstract: Nano-particle segmented polyurethane anionomer dispersions with ions either on the soft segment or on the hard segment were synthesised using 2,2-bis(hydroxymethyl) propionic acid and 5-sodiosulfo-1,3-benzenedicarboxylic acid as ionic centre. The resulting polyurethane dispersions were characterized for their particle size, reduced viscosity and hydrolytic stability in the presence of the aqueous phase during storage. At similar ionic contents, the polyurethanes that contain ionic groups on their soft segment had smaller particle sizes than those that contain ionic groups on the hard segment due to the effectiveness of the sulphonate ionic groups incorporated in the former. The reduced viscosity of the anionomers in dimethylformamide (DMF) showed typical polyelectrolyte effect that can be eliminated by the addition of LiBr. The hydrolysis study conducted over 2-years indicated that polyurethanes in which the ions were located on the hard segment had better hydrolytic stability in aqueous environment than those with ions located on the soft segment. We attributed this due to the fact that unsolvated hydrophobic polyester segments were packed in the interior of the particles while the strongly hydrated urethane segments with mutually repelling carboxylate ions were situated on the outside surface of the particles. The polyester groups prone to hydrolytic attack were thus protected against hydrolysis as effectively as in the dry solid form. [Copyright &y& Elsevier]

Abstract: Segmented polyurethanes are important polymers for a number of industrial and technological applications. The purpose of this work was to synthesize polybutadiene-based polyurethanes and subsequently graft carboxylate and sulfonate side chains via thiol-ene reaction. Spectroscopic investigations showed that grafting yielded good conversion for the vinyl unsaturation of the polybutadiene soft segment. DSC and tensile testing revealed that grafted polyurethanes had a better segmental compatibility and superior mechanical properties than the control polyurethane without grafting. The carboxylic side chains of the soft segment were responsible for the observed improved mechanical properties. Initial protein adsorption tests on these polymers were found to be higher than the control surface. The polyurethanes of the current study could be used for biomedical applications where protein attachment to the surface is needed for specific cell adhesion and tissue repair. [Copyright &y& Elsevier]