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 Vinoy Thomas

An interdisciplinary team of researchers at the University of Alabama at Birmingham (UAB) has developed a new method designed to improve the surface characteristics of Teflon, or polytetrafluorethylene (PTFE). This method has the potential to address challenges associated with PTFE for blood-contact applications—specifically poor endothelial cell growth and the risk of blood clots.

The team’s findings were recently published in the Royal Society of Chemistry’s Journal of Materials Chemistry.

PTFE is a fluoropolymer that is widely used as a vascular graft substitute in cardiovascular and hemodialysis applications. The chemically inert nature of PTFE makes it a suitable material for implants, but only for large- and medium-diameter PTFE vascular grafts. For small-diameter PTFE vascular grafts (less than 6 mm), there are considerable risks for thrombosis (blood clotting) and a lack of endothelial cell growth and associated intimal hyperplasia.

“The best blood-compatible surface is a confluent monolayer,” said Vinoy Thomas, Ph.D., lead author, and director of the UAB Polymers & Healthcare Materials/ Devices Lab in the Department of Materials Science & Engineering. “But the highly hydrophobic nature of PTFE makes it very difficult for endothelial cells to attach and grow. Hence, there is an unmet need to modify the surface properties of PTFE to meet the requirements of small-diameter vascular grafts.”

With support from EPSCoR Funding from the National Science Foundation: Connecting the Plasma Universe to Plasma Technology in Alabama (CPU2AL), Thomas and Vineeth Vijayan, the first author and postdoctoral scholar in the team, hypothesized that a plasma-polymerized hydrophilic glass-like coating would provide an adhesive surface for endothelial cell proliferation. To create such a coating, Thomas utilized low-temperature plasma processing of soft biomaterials to form a new blood compatible coating of nanothin flexible-glass onto PTFE from plasma polymerizable organic monomeric precursors. Thomas named this process the “Organic Plasma Process.”

“This method was a facile, single-step surface modification technique which does not require any further post modification steps,” Thomas said. “The augmented PTFE surfaces demonstrate better endothelial cell adhesion and reduced platelet adhesion without changing the mechanical flexibility of the graft. Taken together, these results suggest the potential of this methodology towards potential blood-contacting vascular graft applications.”

This study was the result of a previous project, in which this same team showed the feasibility of utilizing the Atmospheric Pressure Plasma Jet (APPJ) to selectively modify the inner surface of tubular grafts. The commercial synthetic tubular grafts made of Dacron and expanded PTFE have been disappointing for small vessel (less than six millimeters) applications, with its limited patency rate.

According to the American Society of Nephrology more than 300, 000 Americans have end-stage renal disease (ESRD) and are depending on artificial dialysis to stay alive. In the context of COVID-19, there are increased cases in the number of ICU dialysis patients due to severe kidney infections and blood clots. Arterio-venous PTFE grafts are one of the options for vascular access in dialysis. Currently accounting for more than 25% of all hospitalizations in ESRD patients totaling more than $1 billion per year being spent on access related care in the US alone.

In addition to Thomas and Vijayan, the collaboration includes personnel from the UAB Department of Biomedical Engineering; the UAB College of Arts and Sciences Department of Physics; and Endomimetics, LLC, a company co-founded by BME Professor Ho-Wook Jun.