Medical coating on implants prevents thrombus formation
Friday, 13 April 2012
Using a special form of the chemical vapour deposition, the so-called plasma enhanced chemical vapour deposition (PECVD), the researchers are able to produce biocompatible coatings with a thickness of just a few nanometres.
It depends on various conditions, whether implants are well-tolerated in the human body and long-lasting. The risk of thrombosis increases through undamped cell growth on implants, often resulting in a second operation after a short time with further risks for the patient. Materials researchers from Leibniz-Institute Saarbruecken developed a protective coating, which prevents thrombus formation on stents and heart valves.
On the one hand, the coating increases the adherence of desirable endothelial cells so that such implants take root particularly well in the body. On the other hand, the coating reduces the attachment of non-desirable smooth muscle cells. The new coating prevents the formation of plaques or aggressive cell growth.
"The special application technique from the gas phase allows not only the deposition of stents", explains Cenk Aktas, head of the program division CVD/Biosurfaces. "We are working on a way to change this method and the composition of the coating so that we are also able to use them for heart valves or other implants on metal base, such as titanium", says the materials scientist.
The procedure allows the surface of the implant to be structured by laser and then to be implemented in a plasma chamber filled with a special gaseous mixture. By ignition of the plasma, aluminium oxide or silicon oxide is deposited from the gas phase onto the surface of the implants, both as solid material. Using this procedure, the thickness of the coating is 30 nanometres. The coating is much more uniform than those made by other procedures, such as dip-coating.
For first tests, the researchers use an artificial pump system outside the human body. Human blood or blood substitutes circle through an artificial heart valve. Two coatings are added to the heart valve: a magnetic coating serves as a sensor in order to signalise how good or bad the heart valve closes. The protective coating is deposited over the magnetic layer in order to prevent the deposition of blood components. If there are many deposits on the heart valve, it closes badly. If there are no deposits on it, the heart valve closes well – the results are various magnetic signals measured in an external sensor. "With this combination, we can exactly determine which protective coating allows the heart valve to work longest", says the project leader Aktas. The protective coating on the heart valve consists of adamantine carbonate. With a thickness of 100 millionth of a millimetre, the test system is mechanically comparable with the artificial heart valves existing so far.
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