Implantable medical devices, such as drug-eluting stents (DES) to prevent restenosis and artificial joints to promote bone integration, require incredibly precise coatings. Achieving a uniform film on these complex, 3D mesh structures is highly difficult, as they are prone to “clogging” (bridging) and “liquid pooling.” This article explains the mechanics of applying even coatings to microscopic 3D shapes and how “variable speed withdrawal” (linear dip coating) solves these challenges.<\/p>\n\n\n\n
If the coating liquid\u2019s surface tension or viscosity is too high, the liquid stretches across the gaps in the mesh like a window pane. It dries in place, permanently clogging holes that must remain open.<\/p>\n\n\n\n
Excess liquid naturally accumulates at the intersections and corners of the mesh, creating thick, localized pools. If the film thickness is uneven, the drug release rate (sustained release) inside the body will be wildly inaccurate, ruining the device’s performance.<\/p>\n\n\n\n
To form a flawless thin film on complex shapes, you must optimize both the “liquid properties” and the “equipment control.”<\/p>\n\n\n\n
To prevent clogging, you must keep the liquid’s viscosity low and optimize its surface tension so it drains smoothly through the mesh holes. Furthermore, if you pull the part out too fast, extra liquid gets dragged into the tight corners, creating large pools. By utilizing ultra-slow withdrawal speeds, you give the excess liquid enough time to naturally drain downward via gravity (leveling).<\/p>\n\n\n\n
Sometimes, pulling a complex shape at a constant speed inevitably leaves pools of liquid in specific structural pockets. The solution is “linear withdrawal” (variable speed control).<\/p>\n\n\n\n
During the withdrawal process, the machine accelerates and decelerates in real-time, matching the shape of the mesh. By intentionally changing the surface tension through speed adjustments, you can forcefully strip the liquid away from areas where it tends to pool. By combining the proper dipping angle with this variable speed control, you can form a uniform, nano-level thin film across the entire 3D structure.<\/p>\n\n\n\n
Coating stents and implants demands some of the most rigorous process control in medical manufacturing. If you are struggling to find the optimal conditions in your own lab, SDI\u2019s contract testing services allow our expert engineers to develop the perfect process for you.<\/p>\n\n\n\n
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