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

Abstract

Two epoxy materials with or without adhesively bonded hydroxyapatite (HA) coatings were studied for their biocompatibility and mechanical pushout strength 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) postcured at 110 degrees C (Tg approximately 80 degrees C) and Material 2 (CG5052; Ciba Geigy Limited, Cambridge, UK) at 125 degrees C (Tg approximately 120 degrees C). Implantation in dead rabbit bone was performed to provide mechanical baseline levels. Polymethylmethacrylate (PMMA) and conventionally HA-coated titanium alloy (Ti-6Al-4V) were used as control materials. In the biological study, different fluorescent dyes were used to label newly formed bone. After 6 weeks of implantation, results from mechanical pushout tests showed that the interfacial shear strength (ISS) values were significantly higher 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 uncoated 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 ISS values were shown between HA-coated materials 1 and 2 and Ti-6Al-4V on in vivo implantation for 6 weeks. Failure points of the pushout test from the three HA-coated materials were 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 image analysis which showed that there were no significant differences between different materials after short time implantation (up to 6 week). Long-term implantation of the HA-coated material 2 showed that the percentage of bone contact had increased from 52.8+/-1.1% (6 week) to 80.0+/-0.3% (3 months) (p < .01) and remained at 81.0+/-0.8% (6 months). Measurements of bone mineralization rate (BMR) showed that after 3 weeks of implantation, there were no significant differences between PMMA and uncoated materials 1 and 2. After 6 weeks, the BMRs in animals implanted with either HA-coated material 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 this material uncoated (p < .05-.001). No significant differences were found between the two HA-coated epoxy materials. In addition, there were always lower BMRs during the third week of implantation than other periods regardless of biomaterial implanted. The study indicated that the adhesively bonded HA-coated novel epoxy materials were superior to conventional plasma-sprayed Ti-6Al-4V implants with respect to both BMR and bone integration with the implant surfaces. Adhesively bonded HA-coated epoxy materials h...

The healing response to implants used in joint replacement

“…An early stage in the bone ongrowth is described by Bloebaum and colleagues in a single case dying three weeks after implantation, when 10 per cent of the surface of the HA-coated femoral component and 20 per cent of the similarly coated acetabular component showed new bone formation (Bloebaum et al, 1991). Rabbit implantation studies in our own laboratories have shown a gradual increase in bone contact over the first weeks after implantation and equilibrium being reached at 60% at 10 days to 6 weeks, with a consistent, and as yet unexplained further increase to 80% at 3 and 6 months (Zhang et al, 1999). That there was no evidence of loss of HA coating in humans over time has been reported (Coathup et al, 2001), though the general consensus seems to be that some thinning of the HA layer is seen when this is measured on retrieved prostheses and that there is loss of the coating in places so that bone, fibrous tissue or bone marrow is seen in direct contact with the underlying metal of the implant (Bauer et al, 1991;Dumbleton and Manley, 2004) (Fig.…”

Characterization methods of bone–implant-interfaces of bioresorbable and titanium implants by fracture mechanical means

“…When measuring the load-displacement-curves in pull-out tests, the movement of the crosshead of the test setup is often used to determine the displacement of the implant (Chang et al, 2003;Zhang et al, 1999). Many papers do not even mention the reference point of their measurement at all (Brånemark and Skalak, 1998).…”

Microgel particles containing methacrylic acid: pH-triggered swelling behaviour and potential for biomaterial application

“…MMA and EGDMA were selected for use within the pHresponsive microgels in this study because they have been used in bone cement and contact lenses [7,8]. There has been very little work reported in the literature for poly(MMA/MAA/ EGDMA) microgel dispersions.…”