Nano-scale adhesion in multilayered drug eluting stents

Area of Science:

• Biomaterials Science
• Surface Engineering
• Computational Materials Science

Background:

• Stainless steel 316L is used in drug-eluting stents but requires surface modification to prevent corrosion.
• Poly (o-chloro-p-xylylene) (Parylene C) offers inert and biocompatible coating for 316L.
• γ-methacryloxypropyltrimethoxysilane can act as an adhesion promoter for Parylene C on 316L.

Purpose of the Study:

• To quantify the work of adhesion between Parylene C/316L and silane-modified Parylene C/316L.
• To compare experimental adhesion results with atomistic simulations at room temperature.
• To investigate the effect of physiological conditions (aqueous environment, elevated temperature) on layer adhesion.

Main Methods:

• Atomic Force Microscopy (AFM) experiments to measure adhesion.
• Contact theories applied to experimental data.
• Atomistic simulations to model and predict adhesion.
• Investigation of simplified 316L models for simulation.

Main Results:

• Experimental and simulation results show good agreement for Parylene C/316L adhesion.
• Van der Waals interactions are the primary contributors to the weak affiliation between Parylene C and 316L.
• Increased temperature and aqueous environments negatively impact adhesion, with water permeation decreasing it.
• Silane treatment demonstrates a modest enhancement in adhesion between Parylene C and steel.

Conclusions:

• The adhesion between Parylene C and 316L is primarily governed by Van der Waals forces.
• Physiological conditions significantly reduce the adhesion of Parylene C coatings on 316L.
• Silane adhesion promoters offer a limited but measurable improvement in coating stability.