Nobuhiko Yui

In vitro and in vivo studies on antithrombogenicity of poly(propylene oxide) segmented nylon 610 in relation to its crystalline-amorphous micpostructure

In vitro and in vivo antithrombogenicity of poly(propylene oxide) segmented nylon 610 was investigated. For the in vitro simulation of thrombosis on copolymer surfaces, a modified microsphere column method evaluated the thrombosis time of the copolymer column. For the in vivo evaluation of the antithrombogenicity of copolymer surfaces, small diameter tubing, precoated with copolymer, was implanted in rabbits as an arteriovenous shunt to determine the time of patency for the copolymer tubing. In both the in vitro and in vivo tests, the copolymer having a particular size and distribution of crystalline and amorphous microphases on its surface exhibited excellent antithrombogenicity; the copolymer with a long period of approximately 12 nm and a crystallite thickness of 6.5 nm suppressed the activation process of adhering platelets to show thromboresistant property. This paper emphasizes the importance of controlling the crystalline-amorphous microstructure for the antithrombogenicity of polymer surfaces with a semicrystalline microstructure.

Reversibility of granulocyte adhesion using polyamine-grafted nylon-6 as a new column substrate for granulocyte separation

Reversibility of leucocytes adhered onto the surface of polyamine-grafted nylon-6 was investigated to estimate its feasibility as a new column substrate for granulocyte separation from whole blood. Polyamine-grafted nylon-6 was synthesized by a radical polymerization of 2-diethylaminoethyl methacrylate monomer onto nylon-6. The surfaces of these graft copolymers were found to show a microphase-separated structure composed of island-like phases of cationic polyamine and continuous phases of nonionic nylon-6. Interaction between leucocytes and these copolymer surfaces was studied by passing rabbit heparinized blood through a column packed with glass beads precoated with these copolymers. Columns of these copolymers showed a selective adhesion of granulocytes among leucocyte populations. Also, the adhering granulocytes were able to be recovered from the column by a gentle elution procedure. From these results, it was concluded that polyamine-grafted nylon-6 having a microphase-separated structure is suitable for use as a column substrate in granulocyte separation from whole blood.

Evaluation of cytoplasmic free calcium levels in platelets interacting with polymer surfaces

A quantitative evaluation of platelet activation on polymer surfaces was demonstrated, i.e., direct measurement of cytoplasmic free calcium concentration in platelets in contact with polystyrene latex particles and our designed nonthrombogenic polymer (polyether-segmented nylon 610) was examined by monitoring a change in the fluorescence intensity ratio of the intracellularly-trapped fluorescent indicator dye, Fura 2. An increase in the cytoplasmic free calcium level in platelets interacting with polymer surfaces was observed, and this increase was found to be strongly reduced both by the adsorption of plasma protein on polymer surface and by modifying the surface microstructure of polymer itself. This result indicates that the activation of platelets interacting with polymer surfaces can be eliminated by the design of a surface microstructure composed of crystalline and amorphous phases, and adjustment of the state of the protein layer constructed on the surface.

Changes in Platelet Metabolism in Contact with Hydrophilic Copolymer Surfaces

The metabolism of platelets in contact with poly(acrylamide-co-methacrylic acid) (PAAmMAc) particles was evaluated in terms of changes in cytoplasmic free calcium levels ([Ca2+]i), aderosine triphosphate (ATP) release, and membrane fluidity. PAAmMAc particles induced little increase in [Ca2+]i in platelets. However, PAAmMAc particle-treated platelets demonstrated a smaller response to thrombin, to calcium ionophore A23187, and to polystyrene (PSt) particles, suggesting that PAAmMAc surfaces may regulate [Ca2+]i and ATP release by altering platelet metabolism. Sodium azide-treated platelets showed an increase in [Ca2+]i when contacting PAAmMAc particles, supporting the idea that PAAmMAc surfaces could regulate platelet function. Fluorescence polarization measurements revealed that PAAmMAc particles increased membrane fluidity in platelets, which effect may be due to physicochemical interaction with PAAmMAc surfaces.

In vitro and ex vivo studies of the antithrombogenicity of polyether-segmented nylon 610 of crystalline-amorphous microstructure

The interaction of platelets with polypropylene oxide-segmented nylon 610 surfaces was investigated by two distinct approaches. First, an in vitro simulation test of thrombosis on copolymer surfaces was performed by continuous flow of recalcified platelet-rich plasma through polymer columns to clarify the relation between platelet activation and thrombosis on these surfaces. Second, an ex vivo test of the polymers was carried out using an arteriovenous shunt in rabbits to estimate the number and adhesiveness of circulating platelets in a living body with an implanted shunt. The results obtained suggest that a copolymer surface with a microstructure composed of crystalline and amorphous phases minimizes the activation of adsorbed platelets, resulting in excellent thromboresistance.

Blood compatibility of polyacrylonitrile containing ethyleneoxide and dimethylamino side chains

Polyacrylonitrile copolymer containing ethyleneoxide (EO) and dimethylamino (DA) side chains was synthesized. For the copolymer, the relation between adhesion of platelets on the copolymer surface and the DA content of the copolymer was examined by a “column method,” whereby a platelet suspension was passed through a column of glass beads precoated with the copolymer.