Enhanced Osseointegrative Properties of Ultra-Fine-Grained Titanium Implants Modified by Chemical Etching and Atomic Layer Deposition

An integrated approach combining severe plastic deformation (SPD), chemical etching (CE), and atomic layer deposition (ALD) was used to produce titanium implants with enhanced osseointegration. The relationship between morphology, topography, surface composition, and bioactivity of ultra-fine-grained (UFG) titanium modified by CE and ALD was studied in detail. The topography and morphology have been studied by means of atomic force microscopy, scanning electron microscopy, and the spectral ellipsometry. The composition and structure have been determined by X-ray fluorescence analysis, X-ray diffraction, and X-ray photoelectron spectroscopy. The wettability of the surfaces was examined by the contact angle measurement. The bioactivity and biocompatibility of the samples were studied in vitro and in vivo. CE of UFG titanium in basic (NH₄OH/H₂O₂) or acidic (H₂SO₄/H₂O₂) piranha solution significantly enhances the surface roughness and leads to microstructures, nanostructures, and hierarchical micro-/nanostructures on the surfaces. In vitro results demonstrate deterioration of adhesion, proliferation, and differentiation of MC3T3-E1 osteoblasts cell for CE samples as compared to the non-treated ones. Atomic layer deposition of crystalline titanium oxide onto the CE samples increased hydrophilicity, changed the surface composition, and enhanced significantly in vitro characteristics. In vivo experiments demonstrated non-toxicity of the implants. Etching in basic piranha solution with subsequent ALD significantly improved implant osseointegration as compared with the non-modified samples.