Optimization of Plasma Treatment, Manipulative Variables and Coating Composition for the Controlled Filling and Coating of a Microstructured Reservoir Stent

The object of the study was to fill and coat the microcavities of a drug eluting stent using a batch dipping process. 316L coronary stents, which were coated with a $0.25μm$ layer of $TiNOx$ were used as substrates. The stents’ surface was dimpled with $0.21μl$ microcavities separated by distances of $17–28μm$ depending on location. The experiment consisted of (1) optimizing the procedures to fill the microcavities with a solution of therapeutic agent and (2) covering the filled microcavities with a protective “lid” that shielded the solution during stent insertion in the arteries and then controlled its release into the surrounding tissue. The filling solution was a water-propanol mix containing 20% L-arginine. The coating solution was comprised of poly-ethylene-glycol (PEG-8000) and dexamethasone. The filling quality was investigated after altering the following variables: plasma surface activation (type of gas, pressure, power, and duration), water-propanol percentage ratio of the filling solution, lifting speed from the bath, and effect of ultrasonic vibration (monofrequency versus multifrequency). The surface coating was evaluated by altering the PEG-8000-dexamethasone percentage ratio and recording the effects on coating thickness and structure, on elution rate, and on wear resistance. The optimized process is presented in detail.