Noh I, Goodman S L, Hubbell J A
Department of Chemical Engineering, University of Texas, Austin 78712, USA.
J Biomater Sci Polym Ed. 1998;9(5):407-26. doi: 10.1163/156856298x00532.
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.
聚四氟乙烯（PTFE）薄膜在150℃下，于含有二苯甲酮和氢化钠的无水二甲基甲酰胺反应溶液中处理12小时，进行表面改性。化学分析电子能谱（ESCA）显示，处理后的PTFE表面存在脱氟、氧掺入以及大量不饱和键。通过苯乙烯磺酸钠（SS-Na）的光接枝聚合反应，初步评估了这些还原后的PTFE薄膜作为接枝聚合底物的适用性，该反应通过引入新原子实现了明确的表面分析，同时还评估了聚乙二醇单丙烯酸酯（PEG-Ac）的适用性。所有光接枝聚合反应均以2,2 - 二甲氧基 - 2 - 苯基苯乙酮为引发剂，采用紫外线照射进行。通过ESCA扫描谱中氟原子含量的进一步降低以及新硫和钠原子峰的出现，验证了SS-Na的光接枝聚合；通过ESCA扫描谱中氟原子含量的进一步降低、O/C原子百分比的增加以及高分辨率ESCA C 1s谱上新酯峰的出现，验证了PEG-Ac的光接枝聚合。测量了还原后的以及PEG-Ac光接枝聚合后的薄膜的动态水接触角，结果表明，还原后的PTFE薄膜表面亲水性增强（从120°降至89°），而用PEG-Ac进行光接枝聚合后的还原薄膜亲水性进一步增强（从89°降至36°）。采用上述反应对膨体聚四氟乙烯（ePTFE）的整个表面，即内腔、外表面和孔隙表面进行改性，但反应温度为105℃，反应时间为1天，随后进行PEG-Ac的光接枝聚合。对ePTFE的表面（即内腔和外表面）以及横截面进行ESCA分析，以便对孔隙表面进行分析。该分析表明，从ESCA扫描谱中的F/C和O/C原子百分比、高分辨率ESCA C 1s谱的整体峰形以及与PEG-Ac接枝聚合的ePTFE的高分辨率ESCA C 1s谱上新酯峰的产生来看，初始表面还原和随后的光接枝聚合均成功，这表明O/C原子百分比接近PEG-Ac均聚物的O/C原子百分比。低电压扫描电子显微镜证实，还原和接枝聚合后ePTFE微观结构的形态损伤最小。因此，所探索的方法为调节ePTFE表面的生物相互作用提供了一种手段，且材料形态的改变最小，一些表面纹理出现在50 - 100 nm的长度尺度上。
