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PubMed1996

Improved blood compatibility of segmented polyurethanes by polymeric additives having phospholipid polar groups. I. Molecular design of polymeric additives and their functions.

To improve the blood compatibility of a segmented polyurethane (SPU), 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer was blended with the SPU. The MPC was copolymerized with cyclohexyl methacrylate (CHMA) or 2-ethylhexyl methacrylate (EHMA), and the MPC polymers obtained could be dissolved in the same solvent as the SPU (Tecoflex 60). The blended membranes composed of SPU and MPC polymers were prepared by a solvent evaporation method. A small amount of MPC polymer in the blended membrane leached out after immersion in water for 10 days. The X-ray photo electron spectra indicated that the MPC moieties were located at the surface of the SPU membrane blended with poly(MPC-co-CHMA). On the other hand, the poly-(MPC-co-EHMA) was located homogeneously in the SPU membrane. The mechanical properties of the SPU membrane, as determined by tensile stress-strain measurements, changed very little even after addition of the MPC polymers. Blood compatibility of the blended membrane was evaluated by blood-cell adhesion on the surface when the membranes were placed in contact with rabbit whole blood or platelet-rich plasma. The addition of MPC polymer in the SPU membrane dramatically reduced cell adhesion. It is concluded that the blending of the MPC polymer in the SPU membrane is an effective method for imparting nonthrombogenicity.

Animals↗
PubMed2002

Influence of polymerization conditions on the hydrolytic degradation of poly(DL-lactide) polymerized in the presence of stannous octoate or zinc-metal.

Laboratory- and pilot-scale racemic polylactides (PLA50) were synthesized in the presence of stannous octoate (SnOct2) or zinc-metal as initiators in the absence of alcohol. The resulting polymers were processed by compression molding or injection molding depending on the batch scale. The hydrolytic degradation of compression-molded samples selected to be comparable was investigated first in order to show the influence of the initiator system. Differences in water uptake were found between PLA50-Zn (zinc-metal initiation) and PLA50-Sn (SnOct2 initiation). PLA50-Zn being much more hydrophilic. PLA50-Sn exhibited a slower molecular weight decrease and delayed onsets of weight loss, release of acidity and stereocomplex formation, with respect to PLA-Zn. The concentration in residual tin in PLA50-Sn increased from 306 to 795 ppm during aging. In the case of PLA50-Zn the residual metal remains constant at ca. 40 ppm. In a second series of experiments, high molecular weight PLA50 different in characteristics and in initiator, synthesized under pilot-scale, were compared. The effects of the initiator on the degradation of the polymers well agreed with laboratory-scale findings, differences in hydrophobicity being enlarged by the up scaling. PLA50-Sn polymers appeared much more degradation resistant than PLA50-Zn ones. Contributions of the other characteristics (e.g. molecular weight, purity, stereoregularity, processing) were shown to be important as well.

Absorption↗