Improved blood compatibility of drawn polyamide sheets

Membrane thickness is an important variable in membrane scaffolds: Influence of chitosan membrane structure on the behavior of cells

Cell and tissue responses to polymeric materials are orchestrated in part by the conformations of adsorbed plasma proteins. Thus, the chemical properties of a polymer membrane that govern protein adsorption behavior can play an important role in determining the biological properties of tissue engineered scaffolds derived from that polymer. In this study, we explored the role of membrane thickness as a factor influencing cell adhesion and proliferation on chitosan membranes with and without covalently attached glycosaminoglycans. Rat mesenchymal stem cells (MSCs) cultured on chitosan membranes of various thicknesses demonstrated significantly improved cell adhesion, spreading and proliferation as membrane thickness was increased. Rat hepatocytes displayed increased spreading on the substrate with increasing membrane thickness, similar to MSCs. Increased thickness reduced the overall crystallinity of the membrane, and the data indicate that the improved cellular responses were likely due to enhanced adsorption of serum vitronectin, presumably due to reduced membrane crystallinity. These results demonstrate that membrane thickness is an important design variable that can be manipulated in chitosan-based scaffolds to achieve enhanced cell spreading, proliferation and function.

Branched chitosans II: Effects of branching on degradation, protein adsorption and cell growth properties

The demand for biodegradable implant materials has fueled interest in chitosan as a biomaterial. In previous work, branched chitosans were synthesized and structurally characterized. In this study the biological properties of branched chitosans were explored. Branched chitosans were synthesized by grafting low molecular weight chitosan chains (1.6, 16 and 80 kDa) to high molecular weight (600 kDa) linear chitosans via reductive amination. Films of the branched materials were evaluated with regard to: lysozyme-mediated degradation; protein adsorption; cell adhesion and proliferation. Branched chitosan with a 1.6 kDa branch length exhibited higher degradation rates than either linear or higher branch length materials. Branched chitosans also exhibited reduced adsorption of bovine serum albumin that was more pronounced with thicker films. Branched chitosans supported proliferation of rat endothelial cells, but growth rates were significantly lower than on linear chitosan. The results of this study demonstrate that control of many aspects of chitosan's physical and biological properties can be achieved by changes in molecular architecture.

Mechanistic aspects of blood-contacting properties of polypropylene surfaces--from the viewpoint of macromolecular entanglement and hydrophobic interaction via water molecules

Polypropylene surfaces with a particular crystalline-amorphous microstructure have been demonstrated to reduce protein adsorption and platelet activation. Such blood-contacting properties may be affected by the crystalline-amorphous microstructure of the surfaces, although wettability such as dynamic contact angles and surface free energy components were almost constant, being independent from the variation in the microstructure. In order to clarify the mechanistic aspects on their blood-contacting properties, the physicochemical properties of the surfaces were evaluated for a series of compression-molded polypropylene sheets in terms of the work of adhesion and the structure of sorbed water. The work of adhesion of the compression-molded sheets increased with decreasing surface layer crystallinity, presumably due to macromolecular entanglement with a polymeric glue used. The work of adhesion involving macromolecular entanglement may occur between proteins and the surfaces. Thus, a decrease in the surface layer crystallinity is considered to cause an increase in the protein adsorption. The structure of water sorbed into the sheets changed--it was more gaseous (isolated) at the surfaces with a higher crystallinity. This suggests that the hydrophobic interaction via water molecules increased with surface layer crystallinity, resulting in increasing protein adsorption and denaturation. Thus, it is considered that both macromolecular entanglement and hydrophobic interaction are important on the mechanistic aspects of blood-contacting properties of polypropylene surfaces. In order to confirm this hypothesis, the evaluation of the physicochemical properties and blood-contacting properties was also performed on a series of uniaxially drawn polypropylene films. A decrease in the work of adhesion and the hydrophobic interaction at the surfaces was observed with increasing draw ratio, and the protein adsorption and platelet activation were effectively prevented with increasing draw ratio. This result supports our hypothesis. Therefore, it is concluded that the excellent blood-contacting properties of polypropylene surfaces can be achieved by reducing the macromolecular entanglement and the hydrophobic interaction with proteins.

Blood compatibility of polypropylene surfaces in relation to the crystalline-amorphous microstructure

Blood-contacting properties of polypropylene surfaces with different crystalline states at the surface layer were examined in terms of plasma protein adsorption and changes in cytoplasmic free Ca2+ levels in platelets. Though the wettability of polypropylene surfaces was almost constantly independent from the surface layer crystallinity and interlamellar spacing, an increase in adhesiveness was observed with decreasing surface layer crystallinity and interlamellar spacing. It is suggested that the surface properties of the sheets varied in relation to the crystalline-amorphous microstructure. Minimum magnitudes in albumin and fibrinogen adsorption were observed on the polypropylene surface with a particular surface layer crystallinity (c. 55 wt%). A decrease in interlamellar spacing resulted in enhancing albumin adsorption and diminishing fibrinogen adsorption. Transient phenomena in plasma protein adsorption were observed on their surfaces with a plasma concentration. It is considered that the polypropylene surface with a particular crystalline-amorphous microstructure reduces the denaturation of adsorbed proteins. An increase in cytoplasmic free Ca2+ levels in platelets was prevented at the polypropylene surface with a surface layer crystallinity of 55 wt%: the particular crystalline-amorphous microstructure of such apolar surfaces as polypropylenes acts to reduce platelet activation. Thus, it is concluded that the blood compatibility of polypropylene surfaces is greatly improved by controlling a crystalline-amorphous microstructure at the surface layer.