Tomokazu Hattori

Mechanical strength of calcium phosphate cement in vivo and in vitro.

Two different kinds of calcium phosphate cement were developed for implant fixation: cement A comprised of alpha-tricalcium phosphate (alpha-TCP) 95% and dicalcium phosphate dihydrate (DCPD) 5%, and cement B comprised of alpha-tricalcium phosphate 90% and dicalcium phosphate dihydrate 10%. The compression strength and pullout force of the new materials were tested both in vitro and in vivo. Microscopic observations were performed on the interface between bone and cement. Cement A showed a greater mechanical strength than cement B. The results suggest the clinical possibility of this calcium phosphate cement, which could be used as a material for enhancing implant fixation.

Bioactive calcium phosphate invert glass-ceramic coating on β-type Ti-29Nb-13Ta-4.6Zr alloy

A fine, strong coating consisting of a bioactive calcium phosphate invert glass-ceramic can be prepared easily by reaction of the glassy phase with an oxide layer formed on a new beta-type titanium alloy, Ti-29Nb-13Ta-4.6Zr, when the metal, on which the mother glass powders with a composition of 60CaO-30P(2)O(5)-7Na(2)O-3TiO(2) in mol% are placed, is heated at 800 degrees C in air. A compositionally gradient layer is developed on the titanium alloy during the heating. Tensile bonding strength of the coating to the metal is significantly higher than those of the coatings to conventional metals such as Ti-6Al-4V alloy or pure titanium. The oxidized layer on Ti-29Nb-13Ta-4.6Zr alloy is relatively thinner than that on Ti-6Al-4V alloy even with heat treatment in air; large tensile stresses are not generated in the layer.

Biomechanics in orthopedics

New aspects of orthopaedic biomechanics - fracture, ligament, spine, hip joint, knee joint, gait, biomaterials modern trends of orthopaedic biomechanics in Japan - fracture, spine, hip joint, knee joint, gait analysis, miscellaneous.

Enhancing Effect of Autoclaving on Bioactivity of ß-Titanium Alloy Coated with Calcium Phosphate Glass-Ceramic

60CaO-30P2O5-7Na2O-3TiO2 (mol%) glass-ceramic can be strongly joined with a new β-type Ti-29Nb-13Ta-4.6Zr alloy. In the present work apatite-forming ability in simulated body fluid of the glass-ceramic-coated titanium alloy was enhanced by autoclaving in water at 120°C for 1 h; surface of the autoclaved coating was completely covered with apatite after 10 days of soaking. In vivo tests showed that the glass-ceramic-coated titanium alloy after autoclaving in water makes a strong bond to natural bone.

Current Trends in Gait Analysis: Advanced Techniques for Data Acquisition and Analysis

For kinematic gait measurement, a video device was developed using television techniques and optoreflective markers, and a personalcomputer-based three-dimensional system was completed using direct linear transformation (DLT) method for three-dimensional calibration. Accuracy of the three-dimensional system was examined, and root mean square (RMS) errors of 3.3 mm, 2.6 mm, 1.4 mm in the X, Y, and Z axes were obtained with a camera angle of 60° and camera distance of 3 m. For kinetic measurement, a twin long force plate system was developed, which can measure the triaxial force components for several steps. The frequency response of the long force plate was investigated, and a finite impulse response (FIR) filter with a cutoff frequency of 10 Hz was designed and applied for an automatic data analysis program. Basic knowledge on gait analysis expressly stated in the program allowed detection of gait events and particular peak values, and calculation of time factors and stride dimensions. This kinetic measurement system was used on 95 normal female subjects, and mean values and standard ranges of those parameters were obtained in each age group.

Mechanical and Biological Biocompatibilityof Novel β-Type Ti-Mn Alloys for Biomedical Applications

Mechanical biocompatibility, including tensile properties and Young’s modulus, of -type Ti-Mn alloys,namely, Ti-10Mn and Ti-14Mn, fabricated by the metal injection molding method were investigated. Thebone formability (biological biocompatibility) of a Ti-Mn alloy, namely, Ti-12Mn, fabricated by thearc-melting method was evaluated by means of an animal test. The tensile strength of sintered Ti-10Mn andTi-14Mn achieve a maximum value of 860 and 886 MPa, respectively. The Ti-14Mn specimen sintered at1273 K shows the lowest Young’s modulus (76 GPa) among all sintered Ti-10Mn and Ti-14Mn specimens.The tensile strength of Ti-Mn alloys is almost equal to that of Ti64 ELI; further, their Young’s modulus islower than that of Ti-6Al-4V ELI. The relative bone contact ratio of Ti-12Mn increases from 11% to 29%with increasing implantation time from 12 weeks to 52 weeks. Moreover, the relative bone contact ratio ofTi-12Mn and CP-Ti is almost constant for all implantation times.

A review of surface modification of a novel low modulus β-type titanium alloy for biomedical applications

Ti-29Nb-13Ta-4.6Zr (TNTZ) is a novel β-type titanium alloy that has great potential use in biomedical implants because of its relatively low Young’s modulus (around 60 GPa), which minimise bone atrophy due to stress shielding. However, the biocompatibility and bio-functionality of TNTZ is poor. Therefore, a bioactive ceramic surface modification or soft-tissue-compatible polymer surface modification is advantageous for enhancing the biological properties of TNTZ. The bio-functionality of TNTZ itself, and that modified with a coating hydroxyapatite (HAp) using alkali treatment, electrochemical treatment, and dip-coating treatment with calcium phosphate glass ceramic or metal organic chemical vapour deposition (MOCVD) is assessed. In addition, modification of TNTZ with soft-tissue-compatible segmented polyurethane (SPU) using different silane coupling agents is described. The bonding strength of the bioactive ceramic and soft-tissue compatible polymer with the TNTZ is assessed with respect to variations in surface roughness.

Research and Development of Low-Cost Titanium Alloys for Biomedical Applications

β-type titanium alloys comprising low cost elements such as Fe, Mn, Cr, Sn, Al, O and N and having low Young’s modulus are currently being developed. Examples of such alloys include Ti-10Cr-Al, Ti-Mn, Ti-Mn-Fe, Ti-Mn-Al, Ti-Cr-Al, Ti-Sn-Cr, Ti-Cr-Sn-Zr, Ti-(Cr, Mn)-Sn, and Ti-12Cr. Ti-5Fe-3Nb-3Zr belongs to that class of titanium alloys in which rare metals such as Nb, Ta, and Zr have been reduced using Fe. Ti-5Fe-3Nb-3Zr has a Young’s modulus of around 76 GPa and has greater strength than that of Ti-6Al-4V ELI for biomedical applications. The characteristics of Ti-5Fe-3Nb-3Zr and other low-cost beta-type titanium alloys with low Young’s moduli are discussed from the viewpoint of biomedical applications.

Mechanical Performance of Newly Developed Titanium and Zirconium System Alloys for Biomedical Applications

A new -type Ti alloy composed of non-toxic and allergy-free elements like Nb, Ta, and Zr, Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) proposed by present authors, has been developed in order to achieve relatively low Young’s modulus and excellent mechanical performance. On the other hand, Zr has been also paid attention as metallic biomaterial for the next generation because of good biocompatibility nearly equal to Ti or a few GPa smaller Young’s modulus as compared to one. In this study, mechanical performances such as tensile properties and Youngs modulus of TNTZ subjected to thermo-mechanical treatments or severe deformation, and the mechanical properties and biocompatibility of Zr-Nb system alloys were investigated in order to judge their potential for biomedical applications. Young’s modulus of as-solutionized TNTZ, which is around 63 GPa, is pretty similar to that of as-cold-rolled TNTZ. The Young’s moduli of hot-rolled Ti-6Al-4V ELI alloy are respective around 110 GPa. The Young’s moduli of as-solutionized and as-cold-rolled TNTZ are around a half of those, and are twice as large as that of the cortical bone. The tensile strengths of TNTZ aged after solution treatment and those aged after cold rolling decrease with an increase in the aging temperature, although the elongation shows the reverse trend. The tensile strength of as-cold-rolled TNTZ is improved drastically through severe deformation such as high pressure torsion and shows more than 1000 MPa. Zr-XNb system alloy (X: 5-30mass%) shows the smallest value of Young’s modulus (around 58 GPa) at Nb content of 20mass%. In the case of implantation of the bars made of Zr-XNb system alloys into the lateral femoral condyles of Japanese white rabbits, the tendency of contact between the cancellous bone and the bar becomes remarkably at 24 weeks after the implantation according to increasing with Nb content.

Analysis of the Endosteal Geometry of the Proximal Femur in Japanese Patients with Osteoarthritic Hips: Use in Femoral Stem Design

A study was undertaken to establish a basic design for a straight femoral stem to be used in total hip arthroplasty (THA). This stem would be fitted to the endosteal geometry of femurs in Japanese patients with advanced osteoarthritis of the hip due to congenital displacement of the hip (CDH). Using our three-dimensional computer-aided design (3D-CAD) system, we investigated the geometry of the proximal femur, based on computed tomography (CT) slices obtained from 30 femurs in patients with advanced osteoarthritis and 20 femurs in healthy controls. We found that almost 90% of the femurs in the patients with advanced osteoarthritis had a straight section in the marrow cavity, between 40 and 60 mm below the tip of the lesser trochanter. An adequate basic axis, as a standard for measuring and as a guide for reaming the marrow cavity of the femur, could be obtained by extending the connecting line of the inner center of each slice in this specific straight section. Reaming along our basic axis, simulated by the 3D-CAD system, cut off less cortical bone (79 mm3) than reaming along a conventional axis determined by connecting the center of two cross sections, one at the entry point of the marrow cavity and the other at the maximum depth of reaming (203 mm3). Excessive variations were observed in the cross-sectional geometry of the upper part of the canal of the proximal femur. It was found that, in THA, to obtain a standard straight marrow cavity with no excessive variation and under-cut, the femoral neck should be cut off less than 15 mm above the tip of the lesser trochanter, with a cutting angle of less than 20°. Two radiuses of curvature (R1, 100 mm; R2, 150 mm) were proposed to simplify the curve on the medial flare of the femoral canal between the levels of 15 mm above and 40 mm below the tip of the lesser trochanter. Two taper angles (T1, 2°; T2, 1°) were proposed, to simplify the inclination of the medial femoral canal between 40 and 80 mm below the tip of the lesser trochanter. Correlations were found between patient’s canal flare indices (CFIs) and canal widths 60 mm below the tip of the lesser trochanter in both the frontal (r = −0.6697) and sagittal (r = −0.7961) dimensions. No correlation, however, was revealed between frontal and sagittal CFIs.