Abstract
Bioactive coatings have the potential to improve the bony integration of mechanically loaded orthopedic ceramic implants. Using the concept of mimicking the natural bone surface, four different coatings of varying thickness on a zirconia toughened alumina (ZTA) ceramic implant were investigated regarding their osseointegration in a drill-hole model in sheep. The hypothesis that a bioactive coating of ZTA ceramics would facilitate cancellous bone integration was investigated. The bioactive coatings consisted of either a layer of covalently bound multi phosphonate molecules (chemical modification = CM), a nano hydoxyapatite coating (HA), or two different bioactive glass (BG) coatings in micrometer thickness, forming a hydroxyl-carbonate apatite layer on the implant surface in vivo (dip-coated 45S5 = DipBG; sol-gel 70S30C = SGBG). Coated surfaces were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. After 12 weeks, osseointegration was evaluated via mechanical push-out testing and histology. HA enhanced the maximum push-out force (HA: mean 3573.85 ± 1119.91 N; SGBG: mean 1691.57 ± 986.76 N; p = 0.046), adhesive shear strength (HA: mean 9.82 ± 2.89 MPA; SGBG: mean 4.57 ± 2.65 MPA; p = 0.025), and energy release rate (HA: mean 3821.95 ± 1474.13 J/mm2; SGBG: mean 1558.47 ± 923.47 J/mm2; p = 0.032) compared to SGBG. The implant-bone interfacial stiffness increased by CM compared to SGBG coating (CM: mean 6258.06 ± 603.80 N/mm; SGBG: mean 3565.57 ± 1705.31 n/mm; p = 0.038). Reduced mechanical osseointegration of SGBG coated implants could be explained histologically by a foreign body reaction surrounding the implants.
Highlights
Bioactive coatings have the potential to improve the bony integration of mechanically loaded orthopedic ceramic implants
We hypothesized that the specific surface modification via bioactive coating in various thicknesses would improve the biological integration of textured zirconia toughened alumina (ZTA) ceramic implants into trabecular bone
CM and hydoxyapatite coating (HA) coating did not affect the textured surface structure on a micrometer scale in comparison to a NC sample (Fig. 1C–K), while the two thicker bioactive glass (BG) coatings modified the textured surface by partial filling of the ceramic pores (Fig. 1L–Q)
Summary
Bioactive coatings have the potential to improve the bony integration of mechanically loaded orthopedic ceramic implants. Using the concept of mimicking the natural bone surface, four different coatings of varying thickness on a zirconia toughened alumina (ZTA) ceramic implant were investigated regarding their osseointegration in a drill-hole model in sheep. Four bioactive coatings, mimicking the natural bone surface, were investigated for the first time on a rough textured cylindrical ZTA ceramic implant for their ability to enhance the biological and mechanical integration into cancellous bone. We hypothesized that the specific surface modification via bioactive coating in various thicknesses would improve the biological integration of textured ZTA ceramic implants into trabecular bone. To prove this hypothesis, a large animal model with drill hole defects in the epi-metaphyseal region of long bones was used. Implant integration was analyzed in a biomechanical push out test, histomorphometrical analyses, and descriptive histological evaluation of the bone implant interface 12 weeks after surgery
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