Induction of surface modification of polytetrafluoroethylene with proton ion beams

Cardiovascular disease is one of the leading causes of the death in the USA and developed countries. More than 570,000 artery bypass graft surgeries per USA are performed each year, though percutaneous devices have abounded in extreme cases. Based on the surgery follow-ups, large diameter expanded polytetrafluoroethylene (ePTFE) (>5 mm) are clinically employed with good results but its clinical applications in smaller vessels is still problematic due to thrombosis and neointima formation. Achievement of high patency grafts has been to some extent achieved by numerous methods of surface modification techniques, but its results are less than its initial hopes. As examples, endothelial cells coated on the luminal surface of ePTFE has demonstrated limited success after recirculation. Surface modifications of PTFE film with either argon ion beam or UV light from Xe-excimer lamp were reported to increase its interaction with vascular endothelial cell. Surface modification of poly(lactide-co-glycolide)[PLGA] is also very important in tissue engineering, in where induction of its initial high cellular adhesion and spreading is a critical step for development of tissue engineering medical products. We previously reported tissue engineering of the hybrid ePTFE scaffold by seeding smooth muscle cells and subsequently evaluation of its tissue regeneration behaviors and stabilities with circulation of pulsatile flow. To improve its tissue engineering more quickly, we here performed surface modification of ePTFE and porous PLGA scaffold and evaluated its subsequent chemical and biological properties after treating its surface with low energy ion beams. The porous ePTFE was prepared in a round shape (diameter = 1 cm) and dried after organic solvent extraction for ion beam treatment. Another porous PLGA layers (d = 1 cm, t = 1 cm with approximately 92% porosity) were fabricated and treated its surface by irradiating low energy either nitrogen or argon ion beams (1 keV, 1x1015 ions/cm2) on its surfaces. Either nitrogen or argon gas was fed to the sample surface at its different feeding rates by controlling electrical potential of the acceleration tube, ranging from 1 to 70 keV. The actual conditions of the ion beams such as ion energy and intensity were in advance determined by utilizing Stopping and Range of Ions in Matter (SRIM) software, i.e. by informing the sample conditions such as species and density of the PTFE or PLGA samples as well as its glass transition temperature. Extent of surface modification was evaluated by observing its color changes by digital camera and morphological changes by scanning electron microscopy, measuring water contract angle, and X-ray photoelectron spectroscopy. In vitro smooth muscle cell culture was performed on the sample surfaces (n=3) at a density of 200,000 cells/cm2 in DMEM media containing 10% FBS at 37 .deg. C and 5% CO2 for 4 week. Their cellular behaviors were evaluated such as its cell adhesion and spreading with cell counting kit (CCK-8) and histological staining. Surface modifications of (e)PTFE and (porous) PLGA films were successfully obtained by irradiating low energy ion beams as observed by color and chemical changes without changes in their morphologies. Cellular interaction were slightly increased on the surfaces of the beam-treated (e)PTFE and (porous) PLGA samples, but no signification changes were observed at first. However, when we changed the cell loading density and irradiation energy of the ion beam, a significant increase in cell adhesion was measured, and the amount depended on the beam irradiation energy. The highest cell adhesion was obtained on the PTFE surfaces treated at a 50 keV ion-beam energy in this study. And cellular interaction of the porous PLGA scaffolds was also increased on the surfaces of the beam-treated PLGA surface, and its tissue regeneration was improved