Nanoscale characterization of bone–implant interface and biomechanical modulation of bone ingrowth

Bone–implant interface is characterized by an array of cells and macromolecules. This study investigated the nanomechancial properties of bone–implant interface using atomic force microscopy in vitro, and the mechanical modulation of implant bone ingrowth in vivo using bone histomorphometry. Upon harvest of screw-type titanium implants placed in vivo in the rabbit maxilla and proximal femur for 4 weeks, nanoindentation was performed in the bone–implant interface at 60-μm intervals radially from the implant surface. The average Youngʹs Moduli (E) of the maxillary bone–implant interface was 1.13 ± 0.27 MPa, lacking significant differences at all intervals. In contrast, an increasing gradient of E was observed radially from the femur bone–implant interface: 0.87 ± 0.25 MPa to 2.24 ± 0.69 MPa, representing significant differences among several 60-μm intervals. In a separate experiment, bone healing was allowed for 6 weeks for proximal femur implants. The right femoral implant received axial cyclic loading at 200 mN and 1 Hz for 10 min/d over 12 days, whereas the left femoral implant served as control. Cyclic loading induced significantly higher bone volume, osteoblast numbers per endocortical bone surface, mineral apposition rate, and bone formation rate than controls. These data demonstrate nanoscale and microscale characterizations of bone–implant interface, and mechanical modulation of bone ingrowth surrounding titanium implants.