Gentamicin coating of nanotubular anodized titanium implant reduces implant-related osteomyelitis and enhances bone biocompatibility in rabbits

Abstract

Titanium and titanium alloy are widely used as orthopedic implants for their favorable mechanical properties and satisfactory biocompatibility. The aim of the present study was to investigate the antibacterial effect and bone cell biocompatibility of a novel implant made with nanotubular anodized titanium coated with gentamicin (NTATi-G) through in vivo study in rabbits. The animals were divided into four groups, each receiving different kinds of implants, that is, NTATi-G, titanium coated with gentamicin (Ti-G), nanotubular anodized titanium uncoated with gentamicin (NTATi) and titanium uncoated with gentamicin (Ti). The results showed that NTATi-G implant prevented implant-related osteomyelitis and enhanced bone biocompatibility in vivo. Moreover, the body temperature of rabbits in NTATi-G and Ti-G groups was lower than those in Ti groups, while the weight of rabbits in NTATi-G and Ti-G groups was heavier than those in NTATi and Ti groups, respectively. White blood cell counts in NTATi-G group were lower than NTATi and Ti groups. Features of myelitis were observed by X-ray films in the NTATi and Ti groups, but not in the NTATi-G and Ti-G groups. The radiographic scores, which assessed pathology and histopathology in bone tissues, were significantly lower in the NTATi-G and Ti-G groups than those in the NTATi and Ti groups, respectively (P<0.05). Meanwhile, explants and bone tissue culture demonstrated significantly less bacterial growth in the NTATi-G and Ti-G groups than in the NTATi and Ti groups, respectively (P<0.01). The bone volume in NTATi-G group was greater than Ti-G group, and little bone formation was seen in NTATi and Ti groups.

Keywords: antibiotic; gentamicin; infection; nanotubular anodized titanium; titanium implant.

Figure 1

Change patterns of the body temperature, weight and WBC in rabbits of all four groups from day 0 to day 42. (A) The body temperature increased gradually from day 1 to day 3, decreased gradually from day 3 to day 14 and remained stable from day 14 to day 42. The body temperature of NTATi-G and Ti-G groups was lower than Ti groups on day 3 (P<0.05), and no significant difference was found among four groups from day 3 to day 42. (B) The weight of rabbits decreased from day 1 to day 3 and reached the lowest on day 3. Rabbits in NTATi-G and Ti-G groups were heavier on day 3 than NTATi and Ti groups (P<0.05). The weight increased gradually afterward, and there was no difference among four groups from day 3 to day 42. (C) The WBC in NTATi and Ti groups increased gradually from day 1 to day 3 and decreased gradually from day 3 to day 42, whereas in NTATi-G and Ti-G group, WBC increased gradually from day 1 to day 7 and decreased gradually from day 7 to day 42. Besides, the WBC count in NTATi-G was significantly less than in NTATi and Ti groups on days 3, 35 and 42 (P<0.05), and WBC count in Ti-G group was less than in NTATi and Ti groups on days 3, 21 and 42 (P<0.05). Abbreviations: WBC, white blood cell; NTATi-G, nanotubular anodized titanium coated with gentamicin; Ti-G, titanium coated with gentamicin; NTATi, nanotubular anodized titanium uncoated with gentamicin; Ti, titanium uncoated with gentamicin.

Figure 2

Representative radiographs of four experimental groups on days 1, 21 and 42. Periosteal reaction, osteolysis, soft tissue swelling and deformity were observed in NTATi and Ti groups on day 21 and became more obvious on day 42 after surgery; meanwhile, spontaneous fracture and sequestrum formation were not observed in these groups. We did not observe obvious radiography signs of osteomyelitis on day 21, but slight periosteal reaction, osteolysis or soft tissue swelling was observed in some rabbits on day 42 in NTATi-G and Ti-G groups after surgery. Abbreviations: NTATi-G, nanotubular anodized titanium coated with gentamicin; Ti-G, titanium coated with gentamicin; NTATi, nanotubular anodized titanium uncoated with gentamicin; Ti, titanium uncoated with gentamicin.

Figure 3

Results of microbiological evaluation in four groups on day 42. (A) Bacterial colony formation of implants on agar plates. (B) Bacterial colony formation of bone tissues on agar plates. Abbreviations: NTATi-G, nanotubular anodized titanium coated with gentamicin; Ti-G, titanium coated with gentamicin; NTATi, nanotubular anodized titanium uncoated with gentamicin; Ti, titanium uncoated with gentamicin.

Figure 4

Photomicrographs of longitudinal sections from proximal tibiae, with toluidine blue staining. The bone volume (black arrowheads) in NTATi-G group was greater than Ti-G group; meanwhile, there was little bone formation in NTATi and Ti groups. Typical signs of infections (red arrows) were observed in NTATi and Ti histological slices, while NTATi-G and Ti-G groups showed no signs of apparent bone infection. Abbreviations: NTATi-G, nanotubular anodized titanium coated with gentamicin; Ti-G, titanium coated with gentamicin; NTATi, nanotubular anodized titanium uncoated with gentamicin; Ti, titanium uncoated with gentamicin.

Figure 5

Photomicrographs of longitudinal sections from the proximal tibiae, with hematoxylin and eosin staining. Column A (A1–D1), overview of signs of osteomyelitis in the proximal metaphysis. Magnification, ×20. Column B (A2–D2), moderate-to-severe inflammation with massive enlargement and destruction of the bone tissue (black arrow) and chronic inflammatory cells (red arrows) in the NTATi and Ti groups and mild inflammation in the NTATi-G and Ti-G groups. Magnification, ×40. Column C (A3–D3), moderate-to-severe inflammation with intramedullary abscesses and acute or chronic inflammatory cells (red arrows) around necrotic bony trabeculae (black arrow) and fibrosis (yellow arrows) in the NTATi and Ti groups, and mild inflammation in the NTATi-G and Ti-G groups. Magnification, ×100. Abbreviations: NTATi-G, nanotubular anodized titanium coated with gentamicin; Ti-G, titanium coated with gentamicin; NTATi, nanotubular anodized titanium uncoated with gentamicin; Ti, titanium uncoated with gentamicin.