Quantifying the contributions of implant hydrophilicity and nanotopography on bone anchorage

摘要

Introduction: There is currently no consensus on the most effective treatments for improving the anchorage of an implant and bone. Both hydrophilicity and implant surface topography have been cited as being beneficial, however, the relative contributions of hydrophilicity and implant topography to bone anchorage are not known. Methods: Eight groups of rectangular, commercially pure titanium implants (n=20; Total=560 - see Figure 1) were placed bi-cortically in rat femora for 5,9 or 14 days as well as 28 and 140 days for G1 and G5. Groups 5,6,7, and 8 were treated with discrete calcium phosphate (CaP) nanocrystals or DCD, increasing implant nanotopography, Groups 2, 4,6 and 8 were treated by exposure to ultraviolet (UV) light to increase hydrophilicity, and Groups 3,4,7, and 8 were immersed in sodium lactate (SL) which was done to maintain the effects of the UV treatment. Bone anchorage was tested using a bi-cortical pullout test and disruption force data was compiled and analyzed using the statistical software "R". Linear modeling was used to analyze data which ranged from 5-14 days for all implant groups. Curve fitting using the function F=C-D-e~(-X/T), a generalized form of the asymptotic function, was also used for analyzing the data across all 5 timepoints for G1 and G5 implants. P values ＜0.05 were considered significant. Additional implants were examined by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and water contact angle evaluation (CA). Data was compared with legacy data obtained on similarly modified acid-etched titanium alloy (Ti64) samples using a pulloff test method, Results: Curve fitting of the G1 and G5 data showed that the DCD increased the rate of bone anchorage (P＜0.05). Similarly, Groups 5-8 resulted in higher disruption values than Groups 1-4 (overall means 53.2N and 42.1N respectively; p＜0.001), greater than any changes produced by the UV and/or SL treatments. The SL treatment, however, did show a statistically significant increase in removal force at day 5 (p＜0.05). The UV treatment did not result in any significant differences. CA measurements were: G1 =94°; G2=71°; G5=93°; G6=65°, but could not be measured accurately for SL implants because their surfaces were too wettable, resulting in the water running off the implant. XPS showed an increase in Ca and P due to DCD, however this was masked by the SL in G7 and G8. Discussion: As observed previously, the addition of nanotopography accelerated osseointegration, showing that the newly developed test method did not influence results. Analysis of the 5-14 day time points demonstrated that of all treatments, only DCD resulted in a significant increase in disruption force across all time points, although the SL treatment did demonstrate increased disruption forces at 5 days. From XPS it was determined the SL left a film over the sample surface thicker than the sampling depth of 7-10nm. Simply rinsing the implant with distilled water for a short amount of time removed this layer revealing the underlying surface in SEM. Conclusion: Increased implant hydrophilicity was only observed to have an effect on implant removal forces at the earliest of examined timepoints. In contrast, increased implant nanotopography showed increased removal forces up to 14 days.