In vivo evaluation of bone tissue behavior on ion implanted surfaces

The ion implantation process offers several unique advantages over other surfaces modifications techniques, in regard to ion release and material mechanical characteristics. The aim of this study was to evaluate the in vivo bone tissue response to ion implanted surfaces. Untreated and nitrogen-ion-implanted stainless steel implants were inserted in the tibia diaphysis (cortical bone) and proximal tibia epiphysis (trabecular bone) of 12 New Zealand White rabbits. The animals were divided into three groups of four animals each, which were maintained for 4, 12 and 24 weeks according to internationally accepted and standardized procedures. At sacrifice, the implants were retrieved with surrounding bone and fixed in 4% neutral buffered formaldehyde and embedded in polymethylmethacrylate (PMMA). The samples were reduced in slices and stained with hematoxylin-eosin, light-green, fuchsin acid and giemsa solution for histological evaluation; fluorescent markers were also used to assess bone apposition. Histomorphometric evaluation was used to determine the extent of bone-material contact. Results from histological and morphometrical analyses revealed active remodeling of bone around both types of implants (control and ion implanted). However, faster bone deposition was observed around the treated material (12 weeks). Both materials reached similar endpoints, as no significant differences between them were evident at 24 weeks. The results demonstrate that ion implanted stainless steel has similar, or slightly enhanced, biological compatibility in contact with bone compared to untreated material; thus it may be a useful material in biomedical applications where reduced ion release or enhanced mechanical properties (as provided by ion implantation) are required.