Porous tantalum has been shown to be a promising orthopaedic implant material
because of its similarity to bone in both mechanical properties and its three-dimensional
porous structure. However, in some circumstances, bone quality or quantity is insufficient to
allow adequate bone ingrowth. Alendronate, one of the bisphosphonate families, affects the
activities of bone cells and enhances bone formation. In this thesis, we hypothesized that the
addition of alendronate could increase the osteoconductivity and bone-ingrowth of porous
tantalum and overcome the challenges of bone-implant gaps.
To facilitate local delivery of alendronate, a micro-porous calcium phosphate coating
was deposited onto the tantalum surface by an electrolytic deposition technique, which was
followed by alendronate adsorption. Coating structures and morphologies were confirmed by
scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy.
The presence of alendronate was confirmed by high performance liquid chromatography.
To study the effects of alendronate-immobilized calcium phosphate coating on bone
reaction to porous implants, an animal gap model, with a fixed gap of 0.6 mm between
implants and bone, was developed. Three types of surfaces, which were non-coating (Ta),
calcium phosphate coating (Ta-CaP), and alendronate-immobilized calcium phosphate
coating (Ta-CaP-AIN), were compared. Two fluorochromes were adopted to track the front
of bone formation. After four weeks of healing and following standard histology techniques,
the implants were analyzed with backscattered electron microscopy and fluorescent optical
microscopy for bone-implant interactions.
The relative volume increase of gap filling, bone ingrowth and total bone formation
were 124 % (2.24-fold), 232% (3.32-fold) and 170% (2.7-fold) respectively in Ta-CaP-ALN
compared with Ta controls. The contact length of newly formed bone on porous tantalum
was increased by 700% (8-fold) in Ta-CaP-ALN compared with Ta plugs, suggesting
enhanced osteoconductivity of Ta-CaP-ALN implants. The bone formation mechanism
analysis found that bone growth initiated on both surfaces of the Ta-CaP-ALN implants and
host bone, while little bone initiation on the Ta implant surface was detected. These
significant enhancements of Ta-CaP^ALN may have direct applications in orthopaedics. For
revision arthroplasty with insufficient bone stock, the local delivery of alendronate would
enhance biological fixation of the implant and promote the healing of bone defects.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat
