In vivo evaluation of bone tissue behavior on ion implanted surfaces

The ion implantation process offers several unique advantages over other su rfaces modifications techniques, in regard to ion release and material mech anical characteristics. The aim of this study was to evaluate the in vivo b one tissue response to ion implanted surfaces. Untreated and nitrogen-ion-i mplanted stainless steel implants were inserted in the tibia diaphysis (cor tical bone) and proximal tibia epiphysis (trabecular bone) of 12 New Zealan d White rabbits. The animals were divided into three groups of four animals each, which were maintained for 4, 12 and 24 weeks according to internatio nally accepted and standardized procedures. At sacrifice, the implants were retrieved with surrounding bone and fixed in 4% neutral buffered formaldeh yde and embedded in polymethylmethacrylate (PMMA). The samples were reducte d in slices and stained with hematoxylin-eosin, light-green, fuchsin acid a nd giemsa solution for histological evaluation; fluorescent markers were al so used to assess bone apposition. Histomorphometric evaluation was used to determine the extent of bone-material contact. Results from histological a nd morphometrical analyses revealed active remodeling of bone around both t ypes of implants (control and ion implanted). However, faster bone depositi on was observed around the treated material (12 weeks). Both materials reac hed similar endpoints, as no significant differences between them were evid ent at 24 weeks. The results demonstrate that ion implanted stainless steel has similar, or slightly enhanced, biological compatibility in contact wit h bone compared to untreated material; thus it may be a useful material in biomedical applications where reduced ion release or enhanced mechanical pr operties (as provided by ion implantation) are required. (C) 2001 Kluwer Ac ademic Publishers.