Researchers in Canada have found that a way to make medical implants last longer makes them more biocompatible than at first thought. 

Stainless steel is often used in, for example, joint replacements, because it is cheap and corrosion resistant. Nevertheless its implants are not as long-lived in the body as those made of other materials, such as titanium or titanium alloys, so researchers have looked at modifying implant surfaces to make them more biocompatible. 

SEM image of MC3T3 preosteoblasts on a CPP-modified SS316LS surface after two days of incubation

Previously, Sasha Omanovic and coworkers at McGill University, Montreal, have shown that electrically modifying the surface of stainless steel implants can increase their lifespan. Using a form of cyclic voltammetry known as cyclic potentiodynamic passivation (CPP) the researchers can produce a film layer on the surface of stainless steel which is resistant to corrosion under physiological conditions. In their latest work, they have found the technique has further advantages. Omanovic explains that 'CPP influences the surface concentration and structure of the cell-binding protein fibronectin which leads to a healthier morphology of bone-forming cells.'

The heart disease applications are particularly important. Often after heart surgery an artery that had been widened can narrow again, a process called restenosis. For coronary stents, which are used to keep open these arteries, stainless steel is the preferred material. Omanovic suggests that CPP 'could be used to treat the surface of the stents currently in use, and thus decrease the restenosis rate and the need for re-implantation.'

Omanovic points out that fundamental challenges remain to be tackled. 'The origin of the improved protein-cell-surface interactions we report is not completely understood,' he says. 'This requires further studies, especially on the influence of the surface properties, such as charge, wettability, and topography, on fibronectin's conformation, and how this influences the interactions of various cells with the surface.'

Colin Batchelor

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