Bone-implant interface in a rabbit femur model in vivo: nanoscopic mineralization patterns by atomic force microscopy

Bone-implant interface is characterized by a complex array of cells and macromolecules in a mineralizing matrix forming a micromechanical environment that transmits biomechanical stresses. The biomechanical properties of the bone-implant interface are unknown. Here we examined the bone-implant interface in a submicron length scale with atomic force microscopy (AFM). three screw-type titanium implants (8×4.1 mm: length×diameter) were placed in the femur in each of three, eight-week-old, NZW rabbits by following conventional clinical implant procedures. A four-week duration was given for the implants to osseointegrate. Upon block implant harvest, a diamond knife was used to transect the bone-implant block at a level that was 4 mm from the coronal surface of the fixture with a resulting size of approximately 5 mm volume. The bone-implant interface was then subjected to nanoindentation with atomic force microscopy to obtain force spectroscopy images every 60 microns from the implant surface up to 420 microns outwards in four directions that were separated by 90° angles. The average microelastic moduli demonstrated a gradient distribution, lowest from the implant surface (0.78±0.01 MPa) and increasing outbound up to 420 microns (1.70±0.06 MPa). These data suggest that mineralization in the bone-implant interface proceeds inbound towards the implant surface.