14. TITANIUM DIOXIDE NANOTUBES ENHANCE BONE BONDING IN VIVO

Department: Bioengineering
Faculty Advisor(s): Sungho Jin | David Gough

Primary Student
Name: Garrett Cale Smith
Email: gcsmith@ucsd.edu
Phone: 858-736-4400
Grad Year: 2010

Abstract
RESEARCH PREMISE: Currently, the average lifespan of an orthopedic implant is 10-15 years which fails to meet the active lifestyle needs of the baby boomer population [1]. Optimizing bone-implant integration (osseointegration) traditionally involves modifying surface chemistry and/or surface topography to improve bone bonding. It is becoming increasingly apparent in the literature that implant surface topography engineered at the nanoscale may induce greater bone cell (osteoblast) response compared with implants with microscale surface roughness (gritblasted) [2]. In a previous study, we explored the effect of titanium dioxide (TiO2) nanotubes on in vitro osteoblast behavior. TiO2 nanotubes accelerated osteoblast adhesion by approximately 300-400% compared with non-modified TiO2 surfaces [3]. Our hypothesis is that nanotubes resemble the organic and inorganic nanophase properties. In this study, we compared the in vivo bone bonding strength of TiO2 nanotube implants with TiO2 gritblasted implants.

RESULTS: Vertically aligned yet laterally spaced TiO2 nanotubes were fabricated on Ti disc implants (diameter = 5mm, height 2.5mm) by electrochemical anodization which produced nanotubes with an inner diameter of ~70 nm, outer diameter of ~100 nm, and height of 250 nm. TiO2 gritblasted implants were fabricated with a roughness diameter of ~5 um and ~2 um depth. In vivo bone-implant bonding was evaluated by a method described by Rønold et. al. in a rabbit tibia model [4]. The implants were placed directly onto the tibia and positioned with a bracket. After four weeks of implantation, the tensile test results indicated that the fracture force needed to remove the nanotube implant from the rabbit tibia was significantly greater (10.8 N ± 3.1 N and 1.2 N ± 2.7 N respectively, p=0.008) than for the gritblasted implant. Histological analysis of ground-sections confirmed greater bone-implant contact area, new bone formation, and calcium and phosphorus levels on the nanotube surfaces. CLINICAL SIGNIFICANCE: New cross-disciplinary approaches are needed for engineering titanium implants that last the lifetime of the patient. TiO2 nanotubes exhibit new types of interactions between implant and cells because the surface area is markedly increased and the surface resembles the nanophase constituents of bone. As nanotubes can be produced on any titanium implant and are resistant to abrasion, this surface may function as a novel osseointegrative biomaterial for improved bone bonding in load-bearing implants.

REFERENCES: 1. Sunfeldt, Acta Orthopaedica 77(2); 177-197, 2006 2. Khang, Biomaterials 29(8):970-83 3. Oh, J Biomed Mater Res 78A, 97, 2006 3. Rønold, Biomaterials 23, 2201,2002

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