[In vivo osteogenic evaluation of titanium implants with strontium loaded nanotubes]

Objective: To evaluate the in vivo osteogenic activity of titanium implants with strontium loaded TiO₂ nanotubes (NTSr). Methods: The strontium loaded titanium nanotubes were formed on pure titanium implants through anodization and hydrothermal treatment, and the unmodified titanium (Control) and sheer TiO₂ nanotubes (NT) were set to be control groups and treatment group. Inductively coupled plasma mass spectrometry (ICP-MS) was used to evaluate the Sr release at 28 days. Field emission scanning electron microscopes (FE-SEM) was used to view the micro-topography, atomic force microscope was used to exam the surface roughness, and nano-indenter was used to evaluate the hardness of three groups (n=3). Three groups of implant samples were inserted into the distal femoral metaphysis of New Zealand rabbits (n=4 at each time point). After 4 weeks and 12 weeks, samples were harvested. Micro-CT scanning, immunofluorescent and histological examinations were carried out. Results: The strontium ions could be released slowly for at least 28 days [the Sr concentration at 28 Day was (2.6±1.5) ng/ml]. NTSr coating exhibited a nanoscale tube array (the diameter was about 70 nm), and the surface roughness of implant was increased with the nanobube coating [Control (34.8±5.3) nm, NT (66.2±4.3) nm, NTSr (85.7±10.6) nm, F=37.59, P<0.001]. The surface roughness (Ra) of NT and NTSr groups was higher than the control group (P<0.05). Comparing to Control implants, NTSr implants exhibited a better osteogenic ability [the bone volume/total volume (BV/TV) value was Control (24.7±1.1)% vs. NTSr (37.7±1.9)% at 4 weeks (P<0.05), and Control (40.7±0.9)% vs. NTSr (51.9±2.1)% at 12 weeks (P<0.05)]. The fluorescent examination revealed that NTSr coating can also accelerated the generation of new bone tissue (bone tissue area% labelled by alizarin red at day 7 was Control (19.2±2.9)% vs. NT (35.4±3.7)% vs. NTSr (40.9±0.9)% (F=42.74, P<0.01). The results in the NT and NTSr group were statistically higher than that in the control group (P<0.05). Conclusions: The strontium loaded TiO₂ nanotubes can enhance new bone formation around titanium implants.