Background. Ultrasound measurement of osteoarthritis cartilage thickness is not sufficiently accurate if constant sound velocity is used. The aim of this study was to investigate the applicability of estimating the sound velocity using echo reflectance from the cartilage surface. Methods. Change in measurement error of cartilage thickness was evaluated using collagenase-treated osteochondral plugs. Sound velocity was calculated from the reflectance ratio, and the reference thickness was measured using a needle method. Findings. The relative errors of thickness measurements using constant sound velocity were increased after collagenase treatment. The errors using calculated sound velocity showed no significant difference between intact and degenerated samples. Interpretation. The collagenase treatment-induced error was reduced from 7% to 2% in absolute value, suggesting the applicability of the correction method for ultrasound measurement.

Keywords

Ultrasound, Cartilage, Thickness Measurement

Paper information

Keisuke YAMADA, Ken IKEUCHI, Koji HATTORI and Naohide TOMITA, “Correction of Thickness Measurement by Ultrasound for Articular Cartilage Using Sound Velocity Estimation”, Journal of Biomechanical Science and Engineering, Vol. 5, No. 2 (2010), pp.175-184 . doi:10.1299/jbse.5.175

The possibility of pressure-induced leaching of vitamin E from inside of vitamin E-blended ultrahigh molecular weight polyethylene (UHMWPE) was investigated. UHMWPE specimens were pressed against a base plate, and leached vitamin E was dissolved in ethanol. The quantification of vitamin E in ethanol was carried out by fluorescence spectrophotometry. Vitamin E was confirmed to leach from inside of the vitamin E-blended UHMWPE specimens under compressive load, and the amount of leached vitamin E was positively correlated with the applied load.

Keywords

Medical Engineering, Artificial Knee Joint, UHMWPE, Vitamin E, Wear, Adhesion, Pressure Leaching

Paper information

Yasushi OKUBO, Shin-ichiro MORI, Koji YAMAMOTO and Naohide TOMITA, “Confirmation of Pressure-Induced Leaching of Vitamin E from inside of Ultrahigh Molecular Weight Polyethylene”, Journal of Biomechanical Science and Engineering, Vol. 5, No. 2 (2010), pp.154-162 . doi:10.1299/jbse.5.154

Accelerated ageing was conducted on UHMWPE with and without vitamin E (D, L-α tocopherol, VE). Wear performance was investigated using a knee simulator and wear debris was analysed. Aged UHMWPE with VE showed significantly lower wear volume than that of aged virgin UHMWPE and showed approximately similar wear volume as non-aged virgin UHMWPE. There were no significant differences among the materials as far as shape factor of the debris is concerned.<br /><br />

Keywords

Medical Engineering, Biomaterials, Material Testing, Wear, Bearing, UHMWPE, Vitamin E, Artificial Joint, Wear Debris, Accelerated Ageing

Paper information

Satoshi TERAMURA, Hideyuki SAKODA, Tomohiro TERAO, Kunihiko FUJIWARA, Kosuke KAWAI and Naohide TOMITA, “Reduction of Wear Volume from Accelerated Aged UHMWPE Knee Components by the Addition of Vitamin E”, Journal of Biomechanical Science and Engineering, Vol. 4, No. 4 (2009), pp.589-596 . doi:10.1299/jbse.4.589

Cartilage tissue was regenerated using fibroin sponge seeded with chondrocyte aggregates. The aggregates were formed on the sponge by micro-folding culture, where chondrocytes were cultured on a substrate containing an array of pits of 100 μm diameter. The aggregate-derived cartilage tissue showed higher safranin O staining intensity and was positive for collagen type II by immunostaining. However, its friction coefficient was higher than that of the cartilage tissue regenerated using individual cells. Moreover, the surface of this aggregate-derived cartilage tissue showed weak positive staining for collagen type I. Thus, regeneration of the aggregate-derived cartilage tissue has the possibility of forming larger amounts of extracellular matrix from a limited number of chondrocytes. However, such tissue showed relatively poor tribological function possibly because of its immature functional layer structure.

Keywords

Fibroin Sponge, Cartilage, Chondrocyte, Cell Aggregate, Friction Test

Paper information

Naoyoshi KACHI, Naohide TOMITA, Koji YAMAMOTO, Riki TAKAYA and Yasushi TAMADA, “Tribological Maturation of Regenerated Cartilage was Inhibited by Using Chondrocyte Aggregates”, Journal of Biomechanical Science and Engineering, Vol. 4, No. 2 (2009), pp.174-181 . doi:10.1299/jbse.4.174

The mechanical interaction between ultrahigh molecular weight polyethylene (UHMWPE) and a Co-28Cr-6Mo alloy in water was examined in order to clarify the wear resistance mechanism of vitamin E-containing UHMWPE in knee prostheses. The sample UHMWPE was pressed and rubbed against the surface of the Co-28Cr-6Mo alloy in water by using a computer-controlled pin-on-disk wear test apparatus. The formation of a UHMWPE transfer film on the surface of the Co-28Cr-6Mo alloy was reduced by the addition of vitamin E to UHMWPE. The pull-away force between UHMWPE and the Co-28Cr-6Mo alloy was also reduced by the addition of vitamin E. These results suggest that vitamin E reduces the attraction between UHMWPE and the surface of the Co-28Cr-6Mo alloy.

Keywords

Ultrahigh Molecular Weight Polyethylene (UHMWPE), Vitamin E (dl-α-Tocopherol), Wear, Transfer Film Formation, Pull-Away Force

Paper information

Yasushi OKUBO, Shin-ichiro MORI, Koji YAMAMOTO, Daisuke HAMADA, Hiroyuki KOHNO, Kunihiko FUJIWARA, Masato HASHIMOTO, Ken IKEUCHI and Naohide TOMITA, “Mechanical Interaction between Vitamin E-Containing Ultrahigh Molecular Weight Polyethylene and Co-28Cr-6Mo Alloy in Water”, Journal of Biomechanical Science and Engineering, Vol. 4, No. 2 (2009), pp.166-173 . doi:10.1299/jbse.4.166

Ultrahigh molecular weight polyethylene (UHMWPE) is the popular material of choice for use as a bearing surface in total joint replacement (TJR). Despite an extremely low friction coefficient of UHMWPE to metals with liquid lubrication, however, wear and fatigue fractures are major problems limiting the durability of implanted UHMWPE components. Although highly crosslinked UHMWPE has been intensively studied for decades, its use in orthopedic implants has been limited to relatively low stress and multidirectional load applications, such as acetabular cups in hip joint replacements (HJR). This is mainly because highly crosslinked UHMWPE requires thermal treatment process, indispensable for eliminating the residual free radicals, which leads to a decrease in crystallinity resulting in the reduction of fatigue performance of highly crosslinked UHMWPE. By contrast, recently α-tocopherol doped UHMWPE has been viewed seriously as a novel orthopedic UHMWPE. The α-tocopherol doped UHMWPE exhibits excellent wear and fatigue performance and can be applicable to high stress and linear motion applications, such as total knee replacements (TKR). This paper comprehensively reviews recent advances in the mechanical properties and oxidation stability of medical grade UHMWPE, particularly focusing on highly crosslinked UHMWPE and α-tocopherol doped UHMWPE.

Keywords

Ultrahigh molecular weight polyethylene (UHMWPE), α-Tocopherol, Crosslinking, Oxidation stability, Oxidation index, Wear, Fatigue, Crystallinity

Paper information

Nobuyuki SHIBATA, Steven M. KURTZ and Naohide TOMITA, “Recent Advances of Mechanical Performance and Oxidation Stability in Ultrahigh Molecular Weight Polyethylene for Total Joint Replacement: Highly Crosslinked and α-Tocopherol Doped”, Journal of Biomechanical Science and Engineering, Vol. 1, No. 1 (2006), pp.107-123 . doi:10.1299/jbse.1.107