The bone ingrowth potential of trabecular-like implant surfaces produced by either selective laser melting (SLM) or electron beam melting (EBM), with or without a biomimetic calciumphosphate coating, was examined in goats. For histological analysis and histomorphometry of bone ingrowth depth and bone implant contact specimens were implanted in the femoral condyle of goats. For mechanical push out tests to analyse mechanical implant fixation specimens were implanted in the iliac crest. The follow up periods were 4 (7 goats) and 15 weeks (7 goats). Both the SLM and EBM produced trabecular-like structures showed a variable bone ingrowth after 4 weeks. After 15 weeks good bone ingrowth was found in both implant types. Irrespective to the follow up period, and the presence of a coating, no histological differences in tissue reaction around SLM and EBM produced specimens was found. Histological no coating was detected at 4 and 15 weeks follow up. At both follow up periods the mechanical push out strength at the bone implant interface was significantly lower for the coated SLM specimens compared to the uncoated SLM specimens. The expected better ingrowth characteristics and mechanical fixation strength induced by the coating were not found. The lower mechanical strength of the coated specimens produced by SLM is a remarkable result, which might be influenced by the gross morphology of the specimens or the coating characteristics, indicating that further research is necessary.

BackgroundElectron beam melting (E-beam) is a new technology to produce 3-dimensional surface topographies for cementless orthopedic implants.MethodsThe friction coefficients of two newly developed E-beam produced surface topographies were in vitro compared with sandblasted E-beam and titanium plasma sprayed controls. Bone ingrowth (direct bone–implant contact) was determined by implanting the samples in the femoral condyles of 6 goats for a period of 6 weeks.ResultsFriction coefficients of the new structures were comparable to the titanium plasma sprayed control. The direct bone–implant contact was 23.9 and 24.5% for the new surface structures. Bone–implant contact of the sandblasted and titanium plasma sprayed control was 18.2 and 25.5%, respectively.ConclusionsThe frictional and bone ingrowth properties of the E-beam produced surface structures are similar to the plasma-sprayed control. However, since the maximal bone ingrowth had not been reached for the E-beam structures during the relatively short-term period, longer-term follow-up studies are needed to assess whether the E-beam structures lead to a better long-term performance than surfaces currently in use, such as titanium plasma spray coating.

The bone ingrowth potential of biomimetic hydroxyapatite and brushite coatings applied on porous E-beam structure was examined in goats and compared to a similar uncoated porous structure and a conventional titanium plasma spray coating. Specimens were implanted in the iliac crest of goats for a period of 3 (4 goats) or 15 weeks (8 goats). Mechanical implant fixation generated by bone ingrowth was analyzed by a push out test. Histomorphometry was performed to assess the bone ingrowth depth and bone implant contact. The uncoated and hydroxyapatite-coated cubic structure had significantly higher mechanical strength at the interface compared to the Ti plasma spray coating at 15 weeks of implantation. Bone ingrowth depth was significantly larger for the hydroxyapatite- and brushite-coated structures compared to the uncoated structure. In conclusion, the porous E-beam surface structure showed higher bone ingrowth potential compared to a conventional implant surface after 15 weeks of implantation. Addition of a calcium phosphate coating to the E-beam structure enhanced bone ingrowth significantly. Furthermore, the calcium phosphate coating appears to work as an accelerator for bone ingrowth.

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