One-Pot Covalent Grafting of Gelatin on Poly(Vinyl Alcohol) Hydrogel to Enhance Endothelialization and Hemocompatibility for Synthetic Vascular Graft Applications

Abstract

Cardiovascular diseases remain the leading cause of death worldwide. Patency rates of clinically utilized small diameter synthetic vascular grafts, such as Dacron and expanded polytetrafluoroethylene (ePTFE), to treat cardiovascular disease are inadequate because of the lack of endothelialization. Sodium trimetaphosphate (STMP) cross-linked poly­(vinyl alcohol) (PVA) could be potentially employed as blood-compatible small diameter vascular graft for the treatment of cardiovascular disease. However, PVA severely lacks cell adhesion properties, and the efforts to endothelialize STMP-PVA have been insufficient to produce a functioning endothelium. To this end, we developed a one-pot method to conjugate cell-adhesive protein via hydroxyl-to-amine coupling using carbonyldiimidazole by targeting residual hydroxyl groups on cross-linked STMP-PVA hydrogel. Primary human umbilical vascular endothelial cells (HUVECs) demonstrated significantly improved cells adhesion, viability, and spreading on modified PVA. Cells formed a confluent endothelial monolayer, and expressed vinculin focal adhesions, cell–cell junction protein zonula occludens 1 (ZO1), and vascular endothelial cadherin (VE-Cadherin). Extensive characterization of the blood-compatibility was performed on modified PVA hydrogel by examining platelet activation, platelet microparticle formation, platelet CD61 and CD62P expression, and thrombin generation, which showed that the modified PVA was blood-compatible. Additionally, grafts were tested under whole, flowing blood without any anticoagulants in a nonhuman primate, arteriovenous shunt model. No differences were seen in platelet or fibrin accumulation between the modified-PVA, unmodified PVA, or clinical, ePTFE controls. This study presents a significant step in the modification of PVA for the development of next generation in situ endothelialized synthetic vascular grafts.

Covalently Crosslinked Hydrogels via Step‐Growth Reactions: Crosslinking Chemistries, Polymers, and Clinical Impact

“…[ 29 ] Later, crosslinking chemistries with native chemical ligation, [ 107 ] oxime and hydrazone ligation, [ 107 ] and thiol–ene chemistry [ 119 ] have been harnessed for creating PVA hydrogels in a rapid and biocompatible manner, suitable for use as injectables and in situ formed hydrogels. As with PEG, the lack of cell‐adhesion ability can be surmounted by attaching cell‐adhesion peptides or proteins [ 453,456 ] or crosslinking with other natural polymers, [ 457 ] making PVA hydrogels useful for cell‐encapsulation and tissue regeneration.…”

“…In vivo tests in a rat model further demonstrated its good hemocompatibility. One major limitation of such PVA hydrogels is the lack of endothelialization, which was addressed later by attaching cyclic RGD peptide [ 466 ] or gelatin [ 456 ] on the surface of PVA devices. The ability to allow cell adhesion and spreading, and the absence of thrombotic complications represents a major step toward future preclinical and clinical studies with PVA hydrogels.…”

Quantifying Physical Thrombus Characteristics on Cardiovascular Biomaterials Using MicroCT

“…The luminal surfaces of plasma modification samples were subjected to NH 3 plasma modification using a variation of the radio frequency glow discharge treatment in the presence of NH 3 , as described previously [ 16 , 22 ]. The PVA for the gelatin-modified samples were activated using CDI with the goal of conjugating a gelatin protein, as described previously [ 18 ]. Additionally, unmodified PVA samples were subjected to terminal sterilization using ethylene oxide (EtO) and gamma radiation after cross-linking and before implantation, as described previously [ 19 ].…”

“…The luminal surfaces were then modified using a variety of techniques, including biochemical and topographical modifications, and assessed for thrombogenesis and hemocompatibility in the ex vivo shunt whole blood test. Specific modifications included integration of the peptide sequence Gly-Phe-Pro-Gly-Glu-Arg (GFPGER), plasma modification, addition of gelatin with a carbonyldiimidazole (CDI) covalent linker, and sterilization, and their preparation methods are described in greater detail in previous publications [16][17][18][19]. Samples, which were modified by the integration of GFPGER, a peptide subsequence of type I collagen, had GFPGER mixed with the STMP in the PVA manufacturing process [17].…”

“…Specifically, ePTFE served as a clinical control; collagen-coated ePTFE acted as a positive, thrombogenic control; and poly(vinyl alcohol) (PVA) served as a preclinical, non-thrombogenic, hydrogel material. Several surface modifications of the PVA, which were previously evaluated for their hemocompatibility and endothelialization potential [16][17][18][19], were used in this work to assess and validate the measurement of the physical properties of the thrombus. Advanced image software analysis was then used to quantify the luminal volume (the inverse of thrombus volume) and the intra-thrombus variability.…”