In vivo osteocompatibility of lotus-type porous nickel-free stainless steel in rats

The bone response to lotus-type porous nickel-free stainless steels implants was investigated using Sprague-Dawley rats. The implants were inserted in the femora and tibiae of rats (n = 60) and bone formation inside the pores of the implants was followed up to 12 weeks. Bone ingrowth in transverse histological sections was calculated using an image analysis program. Shear strength of the bone–implant interface was evaluated by the push-out test. Histological examination showed that bone grew into apparent direct contact with the implant surface and into the pores, which sizes were between 70–650 μm. At 12 weeks, maximum compressive shear strengths of 24 ± 1 MPa were obtained; these values are substantially higher than the typical shear strength achieved by porous-coated materials. These results clearly indicate that lotus-type porous structure allowed bone cells and tissue to invade the implant throughout superficial porous spaces, which resulted in an efficient biological fixation responsible for the mechanical stability at the implantation site.