Surface analysis of (Ti,Mg)N coated bone fixation devices following the rabbit femur surgery.

BACKGROUND: Magnesium (Mg) enhances the bone regeneration, mineralization and attachment at the tissue/biomaterial interface. OBJECTIVE: In this study, the effect of Mg on mineralization/osseointegration was determined using (Ti,Mg)N thin film coated Ti6Al4V based plates and screws in vivo. METHODS: TiN and (Ti,Mg)N coated Ti6Al4V plates and screws were prepared using arc-PVD technique and used to fix rabbit femur fractures for 6 weeks. Then, mineralization/osseointegration was assessed by surface analysis including cell attachment, mineralization, and hydroxyapatite deposition on concave and convex sides of the plates along with the attachment between the screw and the bone. RESULTS: According to Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analyses; cell attachment and mineralization were higher on the concave sides of the plates from both groups in comparison to the convex sides. However, mineralization was significantly higher on Mg-containing ones. The mean gray value indicating mineralized area after von Kossa staining was found as 0.48 ± 0.01 and 0.41 ± 0.04 on Mg containing and free ones respectively. Similarly, Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD) analyses showed that hydroxyapatite growth was abundant on the Mg-containing and concave sides of the plates. Enhanced mineralization and strong attachment to bone were also detected in EDS and SEM analyses of Mg-containing screws. CONCLUSION: These findings indicated that (Ti,Mg)N coatings can be used to increase attachment at the implant tissue interface due to accelerated mineralization, cell attachment, and hydroxyapatite growth.

Assessment of bone healing using (Ti,Mg)N thin film coated plates and screws: Rabbit femur model.

Magnesium (Mg) based implants such as plates and screws are often preferred to treat bone defects because of the positive effects of magnesium in bone growth and healing. Their low corrosion resistance, however, leads to fast degradation and consequently failure before healing was completed. Previously, we developed Mg doped titanium nitrate (TiN) thin film coatings to address these limitations and demonstrated that <10 at% Mg doping led to enhanced mineralization in vitro. In the present study, in vivo performance of (Ti,Mg)N coated Ti6Al4V based plates and screws were studied in the rabbit model. Bone fractures were formed on femurs of 16 rabbits and then fixed with either (Ti,Mg)N coated (n = 8) or standard TiN coated (n = 8) plates and screws. X-ray imaging and µCT analyses showed enhanced bone regeneration on fracture sites fixed with (Ti,Mg)N coated plates in comparison with the Mg free ones. Bone mineral density, bone volume, and callus volume were also found to be 11.4, 23.4, and 42.8% higher, respectively, in accordance with µCT results. Furthermore, while TiN coatings promoted only primary bone regeneration, (Ti,Mg)N led to secondary bone regeneration in 6 weeks. These results indicated that Mg presence in the coatings accelerated bone regeneration in the fracture site. (Ti,Mg)N coating can be used as a practical method to increase the efficiency of existing bone fixation devices of varying geometry.