Many types of bioactive bone cement have been developed to overcome the disadvantages of polymethyl-methacrylate (PMMA) bone cement, especially its lack of bone-bonding ability, which occasionally leads to aseptic loosening of prostheses used for arthroplasty. Earlier, we showed that bioactive bone cements containing either nano-sized or micron-sized titania (TiO2) particles had excellent in vivo osteoconductivity.

However, anatase phase titania particles contained in these bioactive bone cements raise concerns about their safety in vivo. We developed pure rutile micron-sized titania particles. because rutile is the only stable phase, whereas anatase is metastable.

In this study, polymethylmethacrylate (PMMA)-based bone cement containing pure rutile micron-sized titania (TiO2) particles were developed, and their mechanical properties and osteoconductivity are evaluated. The three types of bioactive bone cement were T10, T20, and T30, which contained 10, 20, and 30wt% TiO2, respectively.

Commercially available PMMA cement (PMMAc) was used as a control. Hardened cylindrical cement sample (φ2.5mm*10mm) was inserted manually on rabbit femur vertically. Push out test was performed for evaluation of bonding strength. For mechanical testing, the flexural strength, flexural modulus, and compressive strength were measured.

Results of this study revealed that polymethylmeth-acrylate (PMMA)-based bone cement containing pure rutile micron-sized titania particles has outstanding osteoconductivity in vivo, and their mechanical properties were exceeded that of commercially available PMMA cement. Interfacial shear strength of T10, T20 and T30 were 17.1~24.0MPa each at 12 weeks, and were significantly higher than PMMAc. In general, the interfacial bonding strength of bone cement depends mainly on its interdigitation with cancellous tissue, which is accomplished by the pressurized injection of the cement in paste form. On the other hand, we inserted the hardened specimens into oversized holes on rabbit femur in this study, because we intended to examine the osteoconductive and bone-bonding potentials of each material. The flexural strength, flexural modulus, and compressive strength were equivalent to or exceeded that of PMMAc.

These results show that bone cement containing pure rutile micron-sized titania particles is a promising material applied to prosthesis fixation as well as vertebroplasty.

Titanium alloys such as Ti-6Al-4V and Ti-6Al-7Nb have been widely used as orthopedic implants such as artificial hip joint, because of their high mechanical strengths and good biocompatibilities. Recently, new kinds of titanium-based alloys free from elements such as V and Al, which are suspicious for cytotoxicities, are being developed. Ti-15Zr-4Ta-4Nb (Ti-15-4-4) is one of such alloys and shows high mechanical strength and corrosion resistance which are comparable to those of the Ti-6Al-4V alloy. In the present study, chemical treatments for providing bone-bonding ability to this alloy were investigated. Apatite-forming ability in a simulated body fluid (SBF) was used as an indication of the bone-bonding ability.

Ti-15-4-4 alloy plates 10×10×1 mm3 in size were soaked in 5M-NaOH solution at 60 °C for 24 h, soaked in 100mM-CaCl2 solution at 40 °C for 24 h, heated at 600 °C for 1 h and then soaked in hot water at 80 °C for 24 h. Surface structural changes of the alloy with these treatments were analyzed by a field emission scanning electron microscope (FE-SEM) attached with an energy-dispersive X-ray spectrometer (EDX), Thin-film X-ray diffraction (TF-XRD) and Fourier transform confocal laser Raman spectroscopy (FT-Raman). Scratch resistance of surface layer of the alloy was measured by a thin-film scratch tester. Apatite-forming ability of the specimens was examined by soaking them in SBF for 3 days. Long-term stability of the apatite-forming ability was examined after keeping the specimens in an incubator with relative humidity of 95 % at 80 °C for 1 week.

A sodium hydrogen titanate layer about 500 nm in thickness was formed on the surface of the alloy by the NaOH treatment. This specimen formed some amounts of apatite in SBF within 3 days, but its scratch resistance was as low as less than 10 mN. When the NaOH-treated specimen was subsequently heat treated, the sodium hydrogen titanate transformed into sodium titanate to give scratch resistance as high as 92 mN, but lost its apatite-forming ability.

When the NaOH-treated specimen was soaked in CaCl2 solution, the sodium hydrogen titanate was isomorphously transformed into calcium hydrogen titanate. Thus treated specimen increased its apatite-forming ability, but its scratch resistance was still low. When the NaOH- and CaCl2-treated specimen was subsequently heat treated, the calcium hydrogen titanate transformed into calcium titanate to give scratch resistance as high as 169 mN. However, its apatite-forming ability was lost. Thus treated specimen was then soaked in hot water. As a result, its apatite-forming ability remarkably increased without decreasing scratch resistance. It showed high apatite-forming ability even after a long-term-stability test.

The NaOH-, CaCl2-, heat- and hot-water-treated Ti-15-4-4 alloy is believed to be promising materials for artificial joints, because of its high apatite-forming ability with long-term stability as well as high scratch resistance.

In cementless fixation system, surface character becomes important factor. Alkali and heat treatments on titanium metal has been proved to show strong bonding to bone and higher ongrowth rate. In this study we examined the effect of alkali and heat treatments on titanium rod in rabbit femur intramedurally model, in consideration of cementless hip stem. The implant had a 5mm in diameter and 25 mm in length. The implants were and half of them were immersed in 5 mol/L sodium hydroxide solution and heated at 600 åé for one hour (AH implant), and the other half were untreated (CL implant). The implants were implanted into the distal femur of the rabbits, AH implant into left femur and CL implants into right. The bone-implant interfaces were evaluated at 3, 6, and 12 weeks after implantations.

Pull-out tests showed that AH implants significantly higher bonding strength to bone than CL implants at each week after operations. At 12 weeks mean pull-out load of AH implants was 411.7 N and that of CL implants 72.2 N. As postoperative time elapsed, histological examination revealed that new bone form on the surface of the both types of the implants, but significantly more bone contacted directly on the surface of AH implants. At 12 weeks AH implant was covered by the newly formed bone about 56% of the whole surface of the implants and CL implants was about 19%.

In conclusion, alkali- and heat-treated titanium offers strong bone-bonding and high affinity to bone instead of conventional mechanical interlocking mechanism. Alkali and heat treatments on titanium may be applicable to the surface treatment for cementless joint replacement implant.