Biomimetic Hydroxyapatite Coated Titanium Screws Demonstrate Rapid Implant Stabilization and Safe Removal In-Vivo

Abstract

The early fixation of bone screws after surgical implantation still remains a challenge in the field\rof traumatology. Whilst hydroxyapatite (HA) coatings are known to enhance the fixation of implants;\rtheir removal at a later time-point may be problematic. An HA coating has been developed\rto demonstrate that both implant fixation and safe removal are feasible in the same design. Accordingly\rthe aim of this study was to compare the In-Vivo performance of thin biomimetic HA coated\rtitanium screws to uncoated counterparts used as control after bilateral implantation in the femoral\rcondyle of 36 New Zealand White Rabbits. The screws were analysed macroscopically, by\rhistology, micro-CT and biomechanically at both two and six weeks post-implantation. The HA\rcoated screws demonstrated excellent biocompatibility. At two weeks the HA coated screws demonstrated\ra significant increase in removal torque values as well as a strong trend towards higher\rpull-out forces. In addition histology confirmed a higher degree of osseointegration and direct\rbone to implant contact. At six weeks no difference in pull-out force and removal torque could be\rdetected. SEM images confirmed the absence of any residual HA coating indicating a fast coating\rdegradation In-Vivo. The low level of removal torque after full osseointegration at 6 weeks supports\rthe feasibility of safe and easy removal of the implant. The HA coating under study appears to offer a unique characteristic of enhanced fixation with a minimal increase in removal torque\rafter full osseointegration. This may be of value in clinical applications where it is necessary to\rassure both screw fixation and later removal.