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I Noh

Publications and source records attributed to I Noh.

3 recordsLinked to original sources
PubMed2000

Mechanisms of heparin transport through expanded poly(tetrafluoroethylene) vascular grafts.

Thrombosis and neointimal hyperplasia limit the utility of small-caliber artificial vascular grafts. Surface modifications and adjunctive pharmacological therapy might mediate these complications. We examined the mechanisms by which a model vasoactive compound, heparin, transverses porous graft materials and how material modifications alters this drug's transport. The effective permeance of [(3)H]heparin was measured after application of a uniform concentration of drug to either the internal or external surface of the graft and in the presence or absence of pressure-driven physiologic hydraulic flows. Transgraft permeance was equivalent to those observed in normal arteries and, while enhanced by convection, was mediated in major part by diffusion. Peclet numbers under the various conditions examined ranged from 0.05 to 1.2, indicating that diffusive forces were equal to or exceeded convective forces in governing transmural heparin motion. Heparin traversed the graft even when applied from the outer perivascular surface, against adverse hydraulic flows. Modifications of the grafts that included a yarn barrier of spun poly(tetrafluoroethylene) or chemical modification of surface tension energy altered permeances as well. A unifying model for interpretation of these data incorporates the concept of entrapped air and surface tension energy in the graft. These characterizations allow for the design of vascular grafts that are optimized for pharmacotherapy to help prolong graft patency, especially in small-caliber vascular beds.

Air↗
PubMed1998

Chemical modification and photograft polymerization upon expanded poly(tetrafluoroethylene).

Poly(tetrafluoroethylene) (PTFE) films were surface-modified by employing a reaction solution of benzophenone and sodium hydride in anhydrous dimethylformamide at a temperature of 150 degrees C for 12 h. Electron spectroscopy for chemical analysis (ESCA) showed defluorination, oxygen incorporation, and extensive unsaturation within the treated PTFE surfaces. The suitably of these reduced PTFE films as substrates for graft polymerization was initially assessed via photograft polymerization of the sodium salt of styrenesulfonic acid (SS-Na), which permitted unequivocal surface analysis by the introduction of a new atom, as well as poly(ethylene glycol) monoacrylate (PEG-Ac). All photograpt polymerization was performed employing ultraviolet irradiation with 2,2-dimethoxy-2-phenylacetophenone as an initiator. Photograft polymerization of SS-Na was verified by further reduction of fluorine atomic content and the appearance of new sulfur and sodium atomic peaks on ESCA survey spectra, and that of PEG-Ac was verified by further reduction of fluorine atomic content and increase of atomic percent ratio of O/C from ESCA survey spectra as well as appearance of a new ester peak on high resolution ESCA C 1s spectra. Dynamic water contact angles on reduced and PEG-Ac photograft polymerized films were measured and showed that the PTFE film surface became more hydrophilic after reduction (from 120 to 89 deg) and the reduced film became more hydrophilic after photograft polymerization with PEG-Ac (from 89 to 36 deg). Modification of the complete surface of expanded PTFE (ePTFE), i.e. of the lumenal, outside and pore surfaces, was performed by employing the reaction described above, except at 105 degrees C for 1 day, followed by photograft polymerization of PEG-Ac. ESCA was performed on the superficial surfaces (i.e. the lumen and exterior) as well as on cross-sections of the ePTFE to permit analysis of the pore surfaces. This analysis showed that both the initial surface reduction and subsequent photograft polymerization were successful as indicated from F/C and O/C atomic percent ratios from ESCA survey spectra, from overall peaks shapes of high resolution ESCA C 1s spectra and from generation of new ester peaks on high resolution ESCA C 1s spectra of ePTFE graft polymerized with PEG-Ac, which demonstrated an O/C atomic percent ratio close to that of PEG-Ac homopolymer. Low voltage scanning electron microscopy confirmed minimal morphological damage to the ePTFE microstructure after reduction and graft polymerization. The approach explored thus provides a means for modulation of biological interactions at ePTFE surfaces with only minimal modification of material morphology, with some surface texture appearing on a length scale of 50-100 nm.

Benzophenones↗