Abstract
It is very important to fix implant to bone. Bioactive materials as hydroxyapatite or glass-ceramics have bone-bonding ability. Hydroxyapatite-coating is applied to cementless THA or TKA. I and coworkers investigated bone-bonding mechanism of bioactive material and found that bone-like apatite formation play key role for bonding. If the surface of metal is changed to form apatite on it in body, the inert metal changes into bone-bonding material. We developed alkaline and heat treatment of titanium to change titanium to bone –bonding material as follows. At first, titanium is dipped in 5N NaOH solution for 24 hours, at second the metal is washed in pure water and finally it is sintered in 500 degree C for 2 hours. The treated surface has bioactivity, bone bonding ability like hydroxyapatite. The advantage of this treatment over hydroxyapatite-coating procedure is to treat the porous surface without any change of pore figures. As to hydroxyapatite-coating procedure, pore of the small diameter is filled with hydroxyapatite and pore figures are change. We applied this alkaline and heat treatment to cementless THA and its good results of more than ten years was reported.
Porous titanium can be changed to bioactive material by alkaline and heat treatment. This bioactive porous titanium was found to have a property of material-induced osteoinduction, that is, the bone formation in pore of porous titanium implanted in canine back muscle. They can be used for bone substitute for big bone defect. We used two procedures to make porous titanium, sintering of titanium powder with spacer particle of ammonium sulfate and selective lazar melting. The latter procedure can produce any type of pore structure of titanium. Selective laser melting was employed to fabricate porous Ti implants (diameter 3.3 mm, length 15 mm) with a channel structure comprising four longitudinal square channels, representing pores, of different diagonal widths, 500, 600, 900, and 1200 micrometer. These were then subjected to chemical and heat treatments to induce bioactivity. Significant osteoinduction was observed in widths 500 and 600 micrometer, with the highest observed osteoinduction occurring at 5 mm from the end of the implants. A distance of 5 mm probably provides a favorable balance between blood circulation and fluid movement.
New bioactive bone cement is another topic of the application of bioactive titanium in this lecture. The bone cement contains barium sulphate for radiocontrast. We developed a procedure to replace barium sulphate with bioactive titanium powder. This new bone cement has not only better biocompatibility than conventional cement but also bone bonding ability. It is potent material for the fixation of implant to bone. I will speak the evaluation of this cement using canine model of THA.
