Living Synthetic Vascular Grafts with Renewable Endothelium
Project Abstract:
A functioning vascular access is necessary for hemodialysis Arteriovenous polytetrafluoroethylene PTFE dialysis grafts remain the most common form of hemodialysis vascular access in the US because they are relatively easy to apply and available offtheshelf However they have extremely high failure rates due to thrombosis stenosis and infection It was reported that the primary graft survival time from graft placement to the first intervention was only 23 at 1 year and 4 at 2 years Thus there is a critical clinical need for vascular grafts that can maintain superior patency PTFE grafts possess no regenerative or growth potential and the major cause of their high failure rate is the lack of functional endothelium There is great need to develop technology that enables generation of selfrenewable living endothelium on the luminal surface of synthetic vascular grafts Various biomacromolecules have been applied to coat the vascular grafts to recruit circulating endothelial cells EC andor endothelial progenitor cells EPCs from the blood stream to facilitate endothelialization However most of these large proteins are not structurally stable making chemical manipulation and product shippingstorage technically challenging A molecule that has high binding affinity and specificity to ECs and EPCs is needed OneBead OneCompound OBOC combinatorial library technology is an ultrahigh throughput screening method based on synthetic chemistry Recently using primary arteryderived ECs and bloodderived EPCs as living probes to screen OBOC peptide libraries we have identified LXW7 a highaffinity binding ligand against the avb3 integrin on the surface of EPCsECs LXW7 binds strongly to primary EPCsECs but weakly to platelets and does not bind to THP1 monocytes Furthermore because i 4 out of 8 amino acids are Damino acids and ii it is cyclic LXW7 is highly proteolytically stable a critical requirement for in vivo application To test the ability of LXW7 to promote endothelialization of synthetic grafts we evaluated polymerbased small diameter vascular grafts functionalized with LXW7 via Click chemistry in a rat carotid artery bypass model We found that LXW7modified grafts showed significantly higher patency rate than the control grafts After 6 weeks postimplantation mature ECs were present throughout the whole length of the LXW7modified grafts while only a limited number of ECs were identified in the middle segment of the control grafts confirming that LXW7 coating generates a living endothelium on the luminal surface of synthetic vascular grafts In this study we propose to establish LXW7 as a potent ligand to modify the surface of vascular grafts to achieve improved in situ endothelialization The routinely used PTFE vascular graft is used as a model for the study We propose to adapt the chemical vapor deposition CVD polymerization protocol to introduce alkyne functional groups to the graft surface via alkynefunctionalized parylene and then covalently ligate LXW7linkerazide via Click chemistry Parylene is chosen as the coating material because it possesses excellent mechanical properties in terms of flexibility and longlasting in vivo adherence to the implant surface and the FDA has already approved Parylenes as Class VI polymers for coating medical devices due to their biocompatibility We will perform in vitro experiments to confirm the functions including stability cell type specificity thrombogenicity and hemocompatibility of the LXW7modified grafts We will further test our prototype in an established pig arteriovenous graft model to determine device patency thrombosis and neointimal hyperplasia and extent of endothelial ingrowth Successful completion of this project will provide valuable basis for the development of LXW7based surface modification for improved endothelialization to a wide range of intravascular devices including cardiac valves and catheters
