Stent implantation represents a major step forward since the introduction of coronary angioplasty. As indications continue to expand, better understanding of the early and late biocompatibility issues appears critical. Persisting challenges to the use of intracoronary stents include the prevention of early thrombus formation and late neointima development. Different metals and designs have been evaluated in animal models and subsequently in patients. Polymer coatings have been proposed to improve the biocompatibility of metallic stents or to serve as matrix for drug delivery and they are currently undergoing clinical studies. The promises of a biodegradable stent have not yet been fulfilled although encouraging results have recently been reported. Continuous low dose-rate brachytherapy combining the scaffolding effect of the stent with localized radiation therapy has witnessed the development and early clinical testing of radioactive stents. The combined efforts of basic scientists and clinicians will undoubtedly contribute to the improvement of stent biocompatibility in the future.

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Ammonia plasma generated by electrical discharge at low pressure was employed for the surface modification of PTFE and ePTFE. A new chemistry at the plasma treated surfaces is reported. X-ray photoelectron spectroscopy studies showed the incorporation of C-N, C-O, C = O etc functional groups on the plasma treated surfaces. Human endothelial cells derived from umbilical veins (HUEC) were used to seed the plasma treated PTFE and ePTFE surfaces to assess the attachment and growth. Enhanced attachment and growth of HUEC was observed on the plasma treated surfaces. In addition, the performance of these surfaces in this respect was found to be considerably superior to human collagen or human fibronectin or collagen-fibronectin coated PTFE. HUEC attachment and growth on these plasma treated surfaces was further enhanced by immobilizing collagen or fibronectin or collagen-fibronectin. Ammonia plasma treated and untreated ePTFE vascular graft samples were seeded with 3.6 X 10(4) cells/sample. At 24 hrs after seeding, HUEC cell attachment was studied. Although, HUEC attachment on collagen or fibronectin coated ePTFE was improved, but there was no significant difference between the number of cells attached to these surfaces when compared with those adhered to plasma treated ePTFE without collagen or fibronectin coating. Collagen or fibronectin coated plasma treated surfaces showed better performance over their respective controls.

The failure rates of synthetic vascular grafts, when placed in low blood flow environments in humans, are not acceptable. Thus, endothelial cell (EC) seeding technology of vascular grafts was developed to prepare prostheses lined with a human monolayer expressing optimal thromboresistant properties. In a clinical setting, endothelialization of a graft can be achieved using higher cell seeding densities, or by creating a surface on which EC can adhere and grow to confluence. But, human endothelial cells show little or no proliferation on the currently available graft materials. In this study, surface modification of PTFE and ePTFE by ammonia plasma treatment was carried out to enhance its interactions with ECM protein, EC growth factors, and with EC harvested from human umbilical vein (HUVEC), and from human saphenous veins (HSVEC). Our data shows that various vascular graft materials generated from ammonia plasma treated PTFE and ePTFE exhibited statistically significant improvements in HUVEC and HSVEC growth when compared to their respective controls (p values < 0.001). Growth of HSVEC on ammonia plasma treated ePTFE without ECM protein coating was also found to be statistically significant in comparison to that on fibronectin coated ePTFE (p < 0.001). The final HSVEC cell densities found on various ePTFE surfaces prepared from ammonia plasma treated ePTFE, suggests that transplantation of HSVEC monolayers on vascular prostheses can be established within clinically relevant times. Ammonia plasma treatment process provides an unique opportunity to surface modify prosthetic materials of various construct to transplant mammalian cells including those that have undergone ex vivo gene transfer, and to deliver angiogenic molecules to a target area for tissue development.