Zwitterions make implants safer

A pair of Florida State University researchers have received a major grant from the US National Institutes of Health (NIH) to study ways of preventing the body from developing scar tissue around biomedical devices such as coronary artery stents - a problem that affects thousands of patients each year.

Joseph Schlenoff, the Mandelkern Professor of Polymer Science, interim chairman of the department of chemistry and biochemistry at FSU, and a member of FSU's Center for Materials Research and Technology (MARTECH), is the principal investigator on a research project that will receive $1.07 million from the NIH over four years. Working with him is the project's co-principal investigator, Thomas Keller, an associate professor of biology at FSU.

Together, Schlenoff and Keller will work to develop ways of coating coronary stents, synthetic heart valves, dialysis apparatus and other biomedical devices with thin films that discourage vascular smooth muscle cells from adhering to their surfaces. Such adhesions often lead to scarring and new blockages - a process known as restenosis.

Inflammation is the body's natural response to harmful stimuli, such as pathogens, damaged cells or foreign bodies. In veins and arteries, inflammation can lead to a build-up of vascular smooth muscle cells, particularly around (and within) implanted devices such as stents - wire mesh tubes that are used to prop open damaged arteries. For some patients, this growth of muscle cells can lead to restenosis after just six months.

‘Sometimes the human body can be its own worst enemy,’ Schlenoff said. ‘For years, surgeons have used stents to reopen clogged coronary arteries - only to see the stents themselves cause new blockages in some patients as the body's natural defences attempt to 'wall off' the foreign substance. In our research project, we're looking for ways to 'camouflage' biomedical devices so that the body doesn't even know they're there.’

‘Our investigations of how cells interact with various synthetic surfaces will help us design better biocompatible coatings,’ Keller said.

To counteract the body's deleterious response to biomedical devices, Schlenoff and Keller are examining the use of neutrally charged polymers known as zwitterions. Zwitterions - like regions of cell membranes that resist cell and protein adhesion - aren't recognized by the proteins that are released by cells; therefore, the smooth muscle cells won't adhere to them.

‘By mimicking the composition of biological cell membranes, certain polymers could be all but invisible to the human body,’ Schlenoff said. ‘What we're seeking is a marriage of materials and biological cells. If we are successful at bridging the so-called 'biointerface' where synthetic materials and cells meet, then the potential applications of this technology in the fields of biomedical science and tissue engineering are tremendous.’