Nano-scale adhesion in multilayered drug eluting stents

Using stainless steel 316L for drug-eluting stents needs specific surface finishing due to corrosion phenomena that take place on the metal surface upon prolonged contact with human tissue. Poly (o-chloro-p  -xylylene) (Parylene C) is one of the inert and biocompatible materials that are used for 316L coating with γγ-methacryloxypropyltrimethoxysilanemethacryloxypropyltrimethoxysilane as an adhesion promoter. In this study, a combination of atomic force microscopy experiments and contact theories have been used to quantify the work of adhesion between parylene C/316L and silane added parylene C/316L. An atomistic simulation has been used, first, to investigate and compare the adhesion at the room temperature with the experiments and then, to investigate the effect of aqueous environment with higher temperature, inside the body, on the adhesion between layers in the structure of drug eluting stent. The simulation results of simplified model for 316L are in good agreement with the experimental results and suggest that the week affiliation between this polymer and 316L is mainly due to Van der Waals interactions. The effect of temperature on the adhesion is found to be regressive and as the water molecules permeate the polymer the adhesion decreases. They also imply that the effect of silane on the adhesion between parylene C and steel is modest.

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► Chromite can be used to simulate the stainless steel interfacial structure.
► Van der Waals energy of parylene C/316L interface decreases in the presence of water.
► Van der Waals energy of silane-parylene C/316L interface decreases in the presence of water.
► The adhesion between parylene C/316L decreases as the temperature increases.
► The adhesion energies of silane-parylene C/316L decreases at body temperatures.