Abstract
We used an atomic layer deposition (ALD) approach to create titanium oxide nanolayers on ultra high molecular weight polyethylene (UHMWPE) surfaces. These materials were then characterised in terms of rat osteoblast adhesion, morphology and differentiation.
UHMWPE discs produced from a machined cylinder or impact moulded discs were coated with titanium oxide by ALD. Light, atomic force microscopy and scanning electron microscopy with EDX were used to characterise the coated surfaces. These approaches showed 1-1.5 micron tooling grooves with a periodicity of 40 microns on the machined discs whilst the moulded discs exhibited nanotopographical features. The titanium oxide coating was successfully deposited on discs from both sources but was not uniform across the surfaces, with vein-like ‘creases’ clearly visible. We believe that these features are due to the thermal expansion of the UHMWPE discs during the ALD process and their subsequent cooling.
Coated and uncoated discs were seeded with osteoblasts for 24 hours, then fixed. Immunofluorescence microscopy and computer-based image processing enabled determination of osteoblast numbers, size and shape. A trend of larger average cell area was associated with the coated discs and P<0.01 for an H0 of no difference in cell area between coated and uncoated grooved discs.
Osteoblasts were also cultured on the discs in osteogenic medium to promote bone nodule formation. After a few weeks, von Kossa staining and computer-based image processing allowed calculation of surface area covered with bone nodules for each of the discs. Based on results from three of each type of disc, a significantly greater proportion of the surface area of coated discs was covered with calcified deposits compared to uncoated discs (P<0.025 for grooved discs and P<0.005 for smooth discs). On average, the coated discs had bone nodules on 1.4 times the surface area as compared to their uncoated counterparts.
The hypothesis for our study was that TiO2 coating of a polymer might better promote osteoblast interaction with the biomaterial surface leading to enhanced osteogenesis. Our preliminary data support this view and suggest that this approach could likely be exploited in the fabrication of implant materials with tailored biological activity.
