Effects of titanium nanotubes on the osseointegration, cell differentiation, mineralisation and antibacterial properties of orthopaedic implant surfaces

Abstract

The development and pre-clinical evaluation of nano-texturised, biomimetic, surfaces of titanium (Ti) implants treated with titanium dioxide (TiO₂) nanotube arrays is reviewed. In vitro and in vivo evaluations show that TiO₂ nanotubes on Ti surfaces positively affect the osseointegration, cell differentiation, mineralisation, and anti-microbial properties. This surface treatment can be superimposed onto existing macro and micro porous Ti implants creating a surface texture that also interacts with cells at the nano level. Histology and mechanical pull-out testing of specimens in rabbits indicate that TiO₂ nanotubes improves bone bonding nine-fold (p = 0.008). The rate of mineralisation associated with TiO₂ nanotube surfaces is about three times that of non-treated Ti surfaces. In addition to improved osseointegration properties, TiO₂ nanotubes reduce the initial adhesion and colonisation of Staphylococcus epidermidis Collectively, the properties of Ti implant surfaces enhanced with TiO₂ nanotubes show great promise. Cite this article: Bone Joint J 2018;100-B(1 Supple A):9-16.

Keywords: Antimicrobial; Mineralisation; Nano-texturing; Nanotubes; Osseointegration; Titanium dioxide.

Fig. 1

Graphic illustration of the increased surface area provided by nano-texturising. Adapted with permission from the National Nanotechnology Coordination Office ITRI, Inc.

Fig. 2

Titanium alloy tibial tray incorporating macro fixation with pegs and keels; micro fixation with additive manufactured micrometer scale porosity, and nano-scale texturing throughout the porosity with anodised titanium dioxide nanotubes. Image courtesy of Optimotion Implants, LLC, Orlando, Florida. Macro (mm scale); Micro (μm scale); Nano (nm scale).

Fig. 3

Mesenchymal stem cells at 24 hours. Upper row (left to right): scanning electron microscope micrographs of human mesenchymal stem cells (hMSCs) on flat Ti and 30 nm, 50 nm, 70 nm and 100 nm diameter Ti dioxide (TiO₂) nanotube surfaces after two hours of culture. Lower row (left to right): fluorescent images of hMSCs on flat Ti and 30 nm, 50 nm, 70 nm, and 100 nm diameter TiO₂ nanotube surfaces showing increase in cell elongation with increasing nanotube diameter.

Fig. 4

Scanning electron microscope micrographs of osteoblasts (which appear dark) on (left to right) flat titanium (Ti) and 30 nm, 50 nm, 70 nm, 100 nm diameter Ti dioxide (TiO₂)nanotube surfaces after 24 hours of incubation. The arrows indicate strikingly long cellular extensions across the substrate on the 100 nm nanotubes. Red brackets show increased cellular elongation on the larger ~70 nm to 100 nm diameter nanotubes. Flat and more rounded cells are shown on Ti and 30 nm to 50 nm TiO₂ nanotube surfaces.

Fig. 5

Results of tensile pull-out tests for titanium dioxide (TiO₂) nanotube versus TiO₂ micro-texturised, grit blasted disk implants (*p-value = 0.008).

Fig. 6

Haematoxylin and eosin stained ground sections with thickness of 25 μm to 50 μm showing direct contact (DC) or non-direct contact (NC) with bone on (top) titanium (Ti) micro-texturised grit blasted implant and (bottom) Ti dioxide nano-texturised nanotube implant. Bone marrow (BM), old bone (OB), and new bone (NB) are indicated.

Fig. 7

Scanning electron microscope micrographs of osteoblast formation on cobalt/chrome (CoCr) implant (a), and on CoCr implant with titanium coating and titanium dioxide nanotubes after 24 hours (b). Both images are 10 μm. The yellow arrows show the location of cellular extension.

Fig. 8

Atomic percentage of phosphorus and calcium as a function of time, on titanium (Ti), tantalum (Ta), titanium dioxide (TiO₂) nanotubes (NT), and TiO₂ NT coated with Ta.