FIB patterning of stainless steel for the development of nano-structured stent surfaces for cardiovascular applications

Stent implantation is a percutaneous interventional procedure that mitigates vessel stenosis, providing mechanical support within the artery and as such a very valuable tool in the fight against coronary artery disease. However, stenting causes physical damage to the arterial wall. It is well accepted that a valuable route to reduce in-stent re-stenosis can be based on promoting cell response to nano-structured stainless steel (SS) surfaces such as by patterning nano-pits in SS. In this regard patterning by focused ion beam (FIB) milling offers several advantages for flexible prototyping. On the other hand FIB patterning of polycrystalline metals is greatly influenced by channelling effects and redeposition. Correlative microscopy methods present an opportunity to study such effects comprehensively and derive structure–property understanding that is important for developing improved patterning. In this chapter we present a FIB patterning protocol for nano-structuring features (concaves) ordered in rectangular arrays on pre-polished 316L stainless steel surfaces. An investigation based on correlative microscopy approach of the size, shape and depth of the developed arrays in relation to the crystal orientation of the underlying SS domains is presented. The correlative microscopy protocol is based on cross-correlation of top-view scanning electron microscopy, electron backscattering diffraction, atomic force microscopy and cross-sectional (serial) sectioning. Various FIB tests were performed, aiming at improved productivity by preserving nano-size accuracy of the patterned process. The optimal FIB patterning conditions for achieving reasonably high throughput (patterned rate of about 0.03 mm2/h) and nano-size accuracy in dimensions and shapes of the features are discussed as well

Directional nanotopographic gradients: a high-throughput screening platform for cell contact guidance

A novel approach was developed using PDMS-substrates with surface-aligned nanotopography gradients, varying unidirectional in amplitude and wavelength, for studying cell behavior with regard to adhesion and alignment. The gradients target more surface feature parameters simultaneously and provide more information with fewer experiments and are therefore vastly superior with respect to individual topography substrates. Cellular adhesion experiments on non-gradient aligned nanowrinkled surfaces displayed a linear relationship of osteoblast cell adhesion with respect to topography aspect ratio. Additionally, an aspect ratio of 0.25 was found to be most efficient for cell alignment. Modification of the surface preparation method allowed us to develop an approach for creating surface nanotopography gradients which innovatively provided a superior data collection with fewer experiments showing that 1) low amplitude with small wavenumber is best for osteoblast cell adhesion 2) indeed higher aspect ratios are favorable for alignment however only with features between 80-180 nm in amplitude and 450-750 nm in wavelength with a clear transition between adhesion and alignment efficiency and 3) disproved a linear relationship of cell adhesion towards aspect ratio as was found for single feature substrate analysis