Push-out testing and histological evaluation of glass reinforced hydroxyapatite composites implanted in the tibia of rabbits M. A. Lopes, 1,2 J. D. Santos, 1,2 F. J. Monteiro, 1,2 C. Ohtsuki, 3 A. Osaka, 3 S. Kaneko, 4 H. Inoue 4 1 Laborato ´rio de Biomateriais, Instituto de Engenharia Biome ´dica (INEB), Rua do Campo Alegre, 823, 4150-180, Porto, Portugal 2 Departamento de Engenharia Metalu ´ rgica e Materiais, Universidade do Porto, Faculdade de Engenharia da Universidade do Porto (FEUP), Rua dos Bragas, 4099 PORTO CODEX, Portugal 3 Biomaterials Laboratory, Faculty of Engineering, Okayama University, Tsushima, Okayama-shi 700-8530, Japan 4 Department of Orthopaedic Surgery, Okayama University Medical School, Shikata-cho, Okayama-shi 700-8558, Japan Received 6 July 1999; revised 23 May 2000; accepted 21 June 2000 Abstract: In vitro and in vivo bioactivity studies were per- formed to assess the biocompatibility of CaO-P 2 O 5 glass- reinforced hydroxyapatite (GR-HA) composites. The ability to form an apatite layer by soaking in simulated body fluid (SBF) was examined and surfaces were characterized using FTIR reflection and thin-film X-ray diffraction analyses. Qualitative histology, histomorphometric measurements, and push-out testing were performed in a rabbit model for characterizing bone/implant bonding. Under the in vitro conditions using SBF, an apatite layer could not be formed on GR-HA composites within 8 weeks. Results of push-out testing showed bonding between the composites and bone, ranging from 130–145 N after 2 weeks of implantation. After the longest implantation period, 16 weeks, the GR-HA com- posite prepared with the higher content of CaO-P 2 O 5 glass showed the highest bonding force, 606 ± 45 N, compared to 459 ± 30 N for sintered HA. Development of immature bone and modifications in the turnover of a more mature bone on the surface of GR-HA composites were similar to those on sintered HA. © 2000 John Wiley & Sons, Inc. J Biomed Mater Res 54: 463–469, 2001 Key words: in vivo evaluation; glass-reinforced hydroxyapa- tite composites; in vitro bioactivity; push-out testing; histo- logical studies INTRODUCTION For decades, calcium phosphate ceramics have re- ceived attention in the clinical field as orthopedic and dental materials because of their ability to bond to living tissue. 1 Their clinical advantages are due to both biodegradable and osteoconductive characteristics, 2 although the properties are dependent on their struc- ture, such as chemical stoichiometry, crystallinity, and surface morphology. To improve properties of calcium phosphate mate- rials for clinical use, Santos and his colleagues have proposed fabrication of ceramic composites with a method of sintering hydroxyapatite (HA) with a small amount of CaO-P 2 O 5 glass. 3 The glass-reinforced hy- droxyapatite (GR-HA) recently developed has been physicochemically and mechanically characterised. 3–6 Both biaxial bending strength and toughness of GR- HA composites were higher than those of sintered HA ceramics. The superior mechanical characteristics (compared to sintered HA ceramics) of GR-HA com- posites was achieved by reduction in porosity as well as by the presence of - and -tricalcium phosphate (TCP) secondary phases in the microstructure of GR- HA composites. These crystalline phases and their presence in the microstructure depended on the amount of CaO-P 2 O 5 glass added and the sintering temperature, which affected the transformation of the HA matrix phase. In vitro biological performance of the GR-HA composites was also evaluated by an assay measuring their response to osteoblast-like human cells under in vitro conditions. 7 Results of the in vitro evaluation showed an initial delay in cell proliferation compared to sintered HA ceramics, which was later recovered, and a slight down-regulation in the expres- Correspondence to: J.D. Santos Contract grant sponsor: Canon Foundation; contract grant number: PBICT/CTM/1890/95 Contract grant sponsor: Fundac ¸a ˜o para a Cie ˆncia e Tecno- logia; contract grant number: FMRH/BD/1355/94 © 2000 John Wiley & Sons, Inc.