Processing of nanotubes on NiTi-shape memory alloys and their modification with photografted anti-adhesive polymer brushes. Towards smart implant surfaces

Abstract

Implants based on NiTi shape memory alloys may be overgrown with cells which is undesirable in traumatology and stenting. The processing of a self-organized nanotube (NT) layer and its functionalization with a polymer that resists protein and cell adhesion can help solving this issue. The necessary mechanical strength of the layer should arise from its 3D structure and inorganic-organic nanocomposite character. The self-organized NT layer is obtained via potentiostatic anodization of NiTi alloy sheets. Differential scanning calorimetry measurements show that the anodization process barely affects the transformation behavior of NiTi. Structural characterization reveals that the NT layer mainly consists of TiO2 after heat treatment at temperatures ≥450 °C. The functionalization of the NT layer is conducted via the photografting of a biocompatible, anti-adhesive zwitter-ionic polymer using soft UV light. The polymer layer is shown to cover the surface and the nanotube walls. Further, the high adhesion and mechanical strength of the functionalized anodic films together with their in vitro biocompatibility are demonstrated. Samples structured in functionalized and non-functionalized stripes show that the functionalized stripes are endowed with a high resistance to protein and bacteria adhesion. The results show that with the proposed surface design the aims set are attained.