Drug-laden polymer coats could make medical implants more biocompatible, according to scientists in Korea.
Dong Lyun Cho and colleagues at Chonnam National University in Gwangju have developed a method of coating stents in polymer and then attaching drug molecules to the surface. Stents are narrow mesh-like metal tubes that can be inserted into the diseased parts of arteries and then expanded to hold them open and keep the blood flowing. However, being foreign objects, stents can cause abnormal cell growth and artery narrowing (restenosis). The stents can be coated with polymers to avoid this. However, for a successful result, the polymer needs to be both biocompatible and strongly fixed to the metal surface, which Cho says is difficult to acheive.
The implants hold diseased arteries open and deliver drugs
Starting from a diamine monomer, Cho's team created a strongly adhesive polymer film on the stent's surface using a two-stage plasma polymerisation process. This method uses a high-energy plasma to generate the reactive species needed to get the polymerisation started, and is an excellent way of producing thin pinhole-free films, says Cho. They then used the amino groups on the polymer surface to form amide bonds with -lipoic acid, a drug known to inhibit abnormal cell growth.
The new polymer films have high mechanical stability, says Cho, and prevent platelet aggregation in vitro. In addition, when tested on a model cell system, the new stents result in lower restenosis rates. Cho says that the key to these benefits is the -lipoic acid, since stents coated with a different anticoagulant, heparin, were not as successful at reducing restenosis. Future work, he adds, will involve investigating the long-term clinical effect of their stents.
Ketul Popat from the department of mechanical engineering at Colorado State University, Colorado, US, says that biocompatible surfaces that can prevent inflammation are critical for successful implants. Techniques such as those developed by Cho's team, he suggests, 'will be beneficial in overcoming several of the challenges that current stent technology faces.'