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Drug-laden polymer coats could increase biocompatibility of medical implants |
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Drug-laden polymer coats could make medical implants more biocompatible, according to scientists in Korea. A team at Chonnam National University has 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 narrowing of artery. A coating of polymers helps to avoid this successfully, provided the polymer is both biocompatible and strongly fixed to the metal surface. Starting from a diamine monomer, the 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. The amino groups on the polymer surface are used to form amide bonds with -lipoic acid, a drug known to inhibit abnormal cell growth. The new polymer films have high mechanical stability, and prevent platelet aggregation in vitro. In addition, when tested on a model cell system, the new stents result in lower restenosis rates. 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 will involve investigating the long-term clinical effect of their stents.
Brain implants that can more clearly record signals from surrounding neurons in rats have been created by scientists at the University of Michigan (Ann Arbor) that could eventually lead to more-effective treatment of neurological disorders such as Parkinson�s disease and paralysis. Neural electrodes must work for periods ranging from hours to years. When they are implanted, the brain first reacts to an acute injury with an inflammatory response. Then the brain settles into a wound-healing, or chronic, response. During this secondary phase, the brain tissue starts to encapsulate the electrode, cutting it off from communication with surrounding neurons. To prevent this phenomenon, the new brain implants are coated with nanotubes made of poly(3,4-ethylenedioxythiophene)�PEDOT�a biocompatible and electrically conductive polymer that has been shown to record neural signals better than conventional metal electrodes. PEDOT nanotubes in the coating enable the electrodes to operate with less electrical resistance than current metal electrode sites, which means they can communicate more clearly with individual neurons. U-M researchers have found that PEDOT nanotubes increase high-quality unit activity (a signal-to-noise ratio >4) by about 30% over uncoated sites. They have also discovered that based on in vivo impedance data, PEDOT nanotubes might be used as a novel method for biosensing to indicate the transition between acute and chronic responses in brain tissue. In the experiment, the researchers implanted two neural microelectrodes in the brains of three rats. PEDOT nanotubes were fabricated on the surface of every other recording site by using a nanofiber templating method. Over the course of seven weeks, researchers monitored the electrical impedance of the recording sites and measured the quality of recording signals. These electrodes enable neuroprosthetic devices, which hold the promise to return functionality to individuals with spinal cord injuries and neurodegenerative diseases. However, robust and reliable chronic application of neural electrodes remains a challenge. Conducting polymers are biocompatible and have both electronic and ionic conductivity, therefore, these materials are good candidates for biomedical applications such as neural interfaces, biosensors, and drug delivery systems. |
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