A route to anionic hydrophilic films of copolymers of l-leucine, l-aspartic acid and l-aspartic acid esters

A series of copolymers of l-leucine and β-benzyl-l-aspartate [Leu/Asp(OBz)] covering the range 30–70 mol % of l-leucine, was synthesized by the N-carboxyanhydride (NCA) method. The copolymers were characterized by elemental analysis, infra-red spectroscopy and viscometry. For all compositions high molecular weight copolymers were prepared with excellent film-forming properties. Tercopolymers of l-leucine, β-benzyl-l-aspartate and β-methyl-l-aspartate [Leu/Asp(OBz)/Asp(OMe)] were obtained after an ester interchange reaction (conversion 85–95%) with the original copolymer systems. These tercopolymers were characterized by elemental analysis and i.r. spectroscopy. Films of the tercopolymers, cast from organic solvents, could be converted into hydrophilic films by saponification of the methyl ester groups using alkaline water/organic solvent media. The hydrophilic films, which will be further investigated for their use as haemodialysis membranes were characterized by potentiometric titration and i.r. spectroscopy

Elastic modulus in the crystalline region of poly(p-phenylene terephthalamide)

Fibres from aromatic polyamides have a much higher Young's modulus than fibres from aliphatic polyamides. In order to contribute to the explanation of this observed difference we looked at one of the ultimate properties, the elastic modulus in the crystalline region in the chain direction (Ecr). We carried out measurements on a bundle of filaments of PRD 49 fibre, which we identified by i.r. and X-ray analyses as poly(p-phenylene terephthalamide). With the X-ray technique we determined the lattice extensions under loading and from these data the Ecr was calculated. The Ecr was found to be 20 × 1011 dyne/cm2 which is in good agreement with the calculated Ecr, but not very different from that of nylon-6,6. The Young's modulus was found to be 11 × 1011 dyne/cm2

Thermal bulk polymerization of cholesteryl acrylate

The thermal bulk polymerization of cholesteryl acrylate was carried out in the solid phase, the mesomorphic phase, and the liquid phase to study the effect of monomer ordering on polymerization rate and polymer properties. The rate increased with decreasing ordering (or enhanced mobility) of the monomer. Formation of inhibitive by-products during the polymerization limited conversions to 35%. The sedimentation constant S0 = 6.2 S was the same for the polymers obtained in the three phases. The weight-average molecular weight (w) was 480,000 as determined by ultracentrifugation. Poly-(cholesteryl acrylate) formed in bulk is randomly coiled when dissolved in tetrahydrofuran. The thermal properties of the monomer are given

Biodegradability and tissue reaction of random copolymers of L-leucine, L-aspartic acid, and L-aspartic acid esters

A series of copoly(α-amino acids) with varying percentages of hydrophilic (l-aspartic acid) and hydrophobic monomers (l-leucine, ß-methyl-l-aspartate, and ß-benzyl-l-aspartate) were implanted subcutaneously in rats and the macroscopic degradation behavior was studied. Three groups of materials (A, B, C) with different ranges of hydrophilicity were distinguished: A) hydrophobic materials showed no degradation after 12 weeks; B) more hydrophilic materials revealed a gradual reduction in size of the samples, but were still present after 12 weeks; and C) hydrophilic copolymers disappeared within 24 hr. \ud The tissue reactions caused by the materials of group A resembled that of silicone rubber, whereas those of group B showed a more cellular reaction

Interaction of cultured human endothelial cells with polymeric surfaces of different wettabilities

The in vitro interaction of human endothelial cells (HEC) and polymers with different wettabilities in culture medium containing serum was investigated. Optimal adhesion of HEC generally occurred onto moderately wettable polymers. Within a series of cellulose type of polymers the cell adhesion increased with increasing contact angle of the polymer surfaces. Proliferation of HEC occurred when adhesion was followed by progressive flattening of the cells.\ud \ud Our results suggest that moderately wettable polymers exhibit a serum and/or cellular protein adsorption pattern that is favourable for growth of HEC

Adhesion of endothelial cells and adsorption of serum proteins on gas plasma-treated polytetrafluoroethylene

From in vitro experiments it is known that human endothelial cells show poor adhesion to hydrophobic polymers. The hydrophobicity of vascular prostheses manufactured from Teflon® or Dacron® may be the reason why endothelialization of these grafts does not occur after implantation in humans. We modified films of polytetrafluoroethylene (Teflon®) by nitrogen plasma and oxygen plasma treatments to make the surfaces more hydrophilic. Depending on the plasma exposure time, modified polytetrafluoroethylene surfaces showed water-contact angles of 15–58°, versus 96° for unmodified polytetrafluoroethylene. ESCA measurements revealed incorporation of both nitrogen- and oxygen-containing groups into the polytetrafluoroethylene surfaces, dependent on the plasma composition and exposure time. The thickness of the modified surface layer was ~1 nm. The adhesion of cultured human endothelial cells from 20% human serum-containing culture medium to modified polytetrafluoroethylene surfaces with contact angles of 20–45° led to the formation of a monolayer of cells, which was similar to the one formed on tissue culture polystyrene, the reference surface. This was not the case when endothelial cells were seeded upon unmodified polytetrafluoroethylene. Surface-modified expanded polytetrafluoroethylene prosthesis material (GORE TEX® soft tissue) also showed adhesion of endothelial cells comparable to cell adhesion to the reference surface. The amounts of serum proteins, including fibronectin, adsorbed from serumcontaining medium to modified polytetrafluoroethylene surfaces were larger than those adsorbed to unmodified polytetrafluoroethylene. Moreover, the modified surfaces probably allow the exchange of adsorbed serum proteins with cellular fibronectin