Enhanced Osseointegration of Endoprostheses Using Selective Laser Sintered Porous Titanium Alloy Combined With Solution Deposited Coatings

Massive endoprostheses are used for the reconstruction of bone defects following removal of malignant bone tumours. Aseptic loosening is a major cause of failure of endoprostheses and accounts for 25% of revisions. The main hypothesis of this thesis was that a novel porous selective laser sintered (SLS) Ti6Al4V collar augmented with electrochemically deposited hydroxyapatite coatings will enhance osseointegration. A radiological study that evaluated the effect of chemotherapy on the osseointegration of massive endoprostheses in bone tumour patients showed significantly increased loosening at 3 years in patients who received chemotherapy and that osseointegration to the implant collar was protective against signs of radiographic loosening. This study highlighted the importance of increasing osseointegration of these implants. An experimental study investigated the osseointegration of SLS Ti6Al4V collars in an ovine midshaft implant over a 6 month period. SLS porous collars provided a greater area for bone contact (p<0.001) and greater osseointegration (p<0.001), with bone directly permeating into the porous structure. Electrochemically deposited hydroxyapatite (EHA), silicate-substituted hydroxyapatite (ESiHA) and strontium-substituted hydroxyapatite (ESrHA) were developed enabling the inner pores of SLS structure to be coated. ESiHA (1.63 Si wt%) and ESrHA (4.08 Sr wt%) coatings were optimised and both crystalline and amorphous phases were found with significant dissolution of Si from ESiHA (p=0.002). No significant differences were found when stem cell proliferation and osteogenic differentiation were compared between coatings. In an ovine defect model, investigation of these coatings on SLS implants of two different pose sizes (1125μm and 550μm) showed increased osseointegration with electrochemically coated implants (p<0.001). Osseointegration was greatest with the EHA coating on the smaller pore size (p<0.05). 2 In conclusion, the hypothesis can be accepted and novel electrochemically coated laser sintered porous collars may provide a viable alternative ingrowth region to enhance the osseointegration of massive bone tumour endoprostheses