In vivo biocompatibility and mechanical study of novel bone-bioactive materials for prosthetic implantation

Two epoxy materials with or without adhesively bonded hydroxyapatite (HA) c oatings were studied for their biocompatibility and mechanical pushout stre ngth using in vivo implantation in the rabbit lower femur for a duration of 10 days to 6 months. Both were two-part epoxies cured at room temperature for 24 h, with material 1 (Ampreg 26; SP Systems Limited, Cowes, UK) postcu red at 110 degrees C (T-g similar to 80 degrees C) and Material 2 (CG5052; Ciba Geigy Limited, Cambridge, UK) at 125 degrees C (T-g similar to 120 deg rees C). Implantation in dead rabbit bone was performed to provide mechanic al baseline levels. Polymethylmethacrylate (PMMA) and conventionally HA-coa ted titanium alloy (Ti-6Al-4V) were used as control materials. In the biolo gical study, different fluorescent dyes were used to label newly formed bon e. After 6 weeks of implantation, results from mechanical pushout tests sho wed that the interfacial shear strength (ISS) values were significantly hig her than for dead bones with each of the different implants (p < .01-.001). HA-coated material 2 showed a significantly higher ISS value than the unco ated material (p <.05) after 6 weeks' implantation. However, the ISS value for the uncoated material 2 was significantly higher than for PMMA controls (p <.05). No significant differences in the TSS values were shown between HA-coated materials 1 and 2 and Ti-6Al-4V on in vivo implantation for 6 wee ks. Failure points of the pushout test from the three HA-coated materials w ere defined by scanning electron microscopy. Specimens implanted with both HA-coated epoxies were fractured within the HA-coatings or the bone, while with HA-coated Ti-6Al-4V cracked between the coating and metal implant. The percentage of bone in contact with the implant surface was obtained by ima ge analysis which showed that there were no significant differences between different materials after short time implantation (up to 6 week). Longterm implantation of the HA-coated material 2 showed that the percentage of bon e contact had increased from 52.8 +/- 1.1% (6 week) to 80.0 +/- 0.3% (3 mon ths) (p <.01) and remained at 81.0 +/- 0.8% (6 months). Measurements of bon e mineralization rate (BMR) showed that after 3 weeks of implantation, ther e were no significant differences between PMMA and uncoated materials 1 and 2. After 6 weeks, the BMRs in animals implanted with either HA-coated mate rial 1 or 2 were significantly higher than with HA-coated Ti-6Al-4V (p <.05 -.0001 in both cases), but with HA-coated material 2 was lower than with th is material uncoated (p <.05-.001). No significant differences were found b etween the two HA-coated epoxy materials. In addition, there were always lo wer BMRs during the third week of implantation than other periods regardles s of biomaterial implanted. The study indicated that the adhesively bonded HA-coated novel epoxy materials were superior to conventional plasma-spraye d Ti-6Al-4V implants with respect to both BMR and bone integration with the implant surfaces. Adhesively bonded HA-coated epoxy materials had similar ISS values to HA-coated Ti-6Al-4V, but the former failed within the bone an d coating, while the latter showed splitting between coating and metal. (C) 1999 John Wiley & Sons, Inc.