Titanium (Ti) is the most widely used material for bone substitution, due to its biocompatibility and mechanical properties. However, in some cases osseointegration is not achieved, mainly due to the still high elastic modulus and the low bioactivity of Ti, ending with implant failure. Hence, modifications of Ti biomechanical properties are required to improve its osseointegration.
The aim of this study was to produce bioactive Ti foam for both improve the biological and mechanical properties of Ti and to evaluate its in vivo osseointegration properties.
In the present study, porous Ti implants were produced by powder sintering route. Samples with different porous diameter and interconnectivity channels were produced varying the concentrations of NaCl as space holder in order to select the proper conditions to achieve optimal mechanical properties. Surface bioactivation treatment was performed by a thermo-chemical treatment (incubation in 5 M NaOH at 60ºC for 24h followed by heat treatment at 600ºC for 6h) on the whole porous scaffold in order to further stimulate the generation of a suitable apatite layer on the interconnected porosity surface when implanted. . The mechanical properties of the bioactive Ti foam were evaluated by static (compression) and dynamic (fatigue) mechanical tests. Non-activated Ti foam was used as control. The bioactive and non-activated Ti foams were implanted in a critical-size defect drilled in the tibiae of 16 adult female New Zealand rabbits. Histological evaluation was performed 4 and 12 weeks after implantation. The osseointegration was evaluated on SEM micrographs by determining the BIC contact and the bone penetration (ingrowth).
Materials with 55% interconnected porosity were the ones fitting best mechanical properties similar to healthy bone. Due to the presence of interconnections between macropores of 170 µm in diameter, this formulation was expected to promote bone ingrowth through cell colonization as well as allow neovascularisation. This condition was thus used for the in vivo study. Bone ingrowth was observed inside all the implants analyzed on macroporous and through interconnected porosity as well as BIC was successfully achieved at the scaffold surface. In addition, successfully bone colonization of inner region of all specimens suggests a good osteoconductive capability of the designed interconnected porous structure. Bioactive foams showed better results than non treated ones, suggesting that bioactivation of Ti foams induce their osteoconduction capabilities as well as osseointegration.