Mechanical stability, corrosion performance and bioresponse of amorphous diamond-like carbon for medical stents and guidewires

Diamond-ike carbon (DLC) coatings have been investigated with respect to biocompatibility, mechanical stability under biofluid exposure, corrosion resistance and the impact of the fabrication or operation of catheter guidewires and stents upon coating integrity. High mechanical tensile and compressive forces, during guidewire winding or stent expansion, pose severe limitations on the use of DLC-coated stainless steel. Doping with silicon and the use of an a-Si:H interlayer can help minimise the risk of adhesion failure or film cracking. The incorporation of Si increased the hydrogen content and the estimated sp3 fraction but reduced the film hardness. Silicon-doped a-C:H coatings exhibit significantly improved corrosion barrier properties, with over two orders of magnitude increase in the charge transfer resistance. Immersion in biofluid, however, reduced the interfacial adhesion strength by up to 75%. Human microvascular endothelial cell attachment was enhanced while platelet attachment was reduced on Si-doped compared to undoped a-C:H. The macrophage response to non-hydrogenated tetragonal (t-aC) carbon show that these coatings stimulate less inflammatory activity than uncoated materials and produce comparable responses to already existing polyurethane coatings.