$476 Journal of Biomechanics 2006, Vol. 39 (Suppl 1) Poster Presentations

first validated by comparing theoretical strain maps generated from numerically distorted images. Results: The texture correlation algorithm was sensitive to the grid size superimposed on the original image, but remained insensitive to parameters related to the size of the mask, which was searched by the algorithm in the final image. Experimental growth plate strain distributions were non-uniform in all six specimens and mostly compressive. The strain distributions differed among histomorphological zones, which was most obvious in specimens with regular growth plate shape: higher compressive strains (4 to 8 times higher than the applied 5% strain) were located mainly in regions overlapping the reserve and hypertrophic zones with lower compressive strains in the proliferative zone. Transverse and shear strains showed no particular patterns. Conclusion: To our knowledge, this is the first study that documents the non- uniform mechanical behavior of compressed growth plate across its histological zones. Further investigation is required to establish the significance of non- uniform strain fields during growth in vivo.

References [1] Hunziker, 1989. [2] Ballock, 2003. [3] Stokes, 1994. [4] Frost, 1990. [5] Cohen, 1994. [6] Fujii, 2000. [7] Bay, 1995. [8] Wang, 2002.

5657 We-Th, no. 2 (P56) An experimental investigation of boundary lubrication mechanism with protein and lipid in synovial joint using total internal reflection fluorescence microscopy Y. Sawae, T. Murakami. Faculty of Engineering, Kyushu University, Fukuoka, Japan

It is well recognized that articular cartilage has impressive lubrication ability and gives low friction and wear characteristics to natural synovial joints. Many studies have been conducted to investigate the lubrication mechanism of articular cartilage and some of them have suggested that phospholipid thin film covers cartilage surface and plays an important role as a boundary lubrication film protecting cartilage surface and keeping joint friction low even if elasto hydrodynamic lubrication film hardly separate cartilage surfaces. On the other hand, some experimental results have indicated that serum proteins contained in synovia is also contributing to reduce friction between cartilage surfaces. Therefore, it may be considered that there are some interactions between the phospholipid surface film and protein molecules contained in synovia establishing a sophisticated boundary lubrication mechanism in natural synovial joints. In this study, phospholipid film was prepared on cover glasses by Langmuir- Blodgett (LB) method and used as a model of the cartilage lipid surface film, and the interaction between protein molecules and the phospholipid film was examined by using total internal reflection fluorescence microscopy (TIRFM). A friction test between articular cartilage specimen and the prepared phospholipid film was also conducted to examine the boundary lubrication ability of the lipid film and protein molecules, and the relationship between the observed protein-lipid interaction and frictional behaviour was considered. As a result, the behaviour of protein molecules adsorbing to the phospholipid film was clearly observed by using TIRFM, and characteristics of the interaction between protein and the phospholipid film was significantly affected by the pH and composition change in the protein solution. The friction coefficient between articular cartilage and the phospholipid layer was also affected by the pH and composition of the lubricant, and it might be linked to the difference in the protein adsorption behaviour.

4661 We-Th, no. 3 (P56) Dynamic viscoelastic response of articular cartilage under shear and compressive loading following enzymatic treatment S. Miyata 1 , T. Tateishi 2, K. Furukawa 3, T. Ushida 4. 1Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, Fukuoka, Japan, 2National Institute for Material Science, Tsukuba, Japan, 3Graduate School of Engineering, University of Tokyo, Tokyo, Japan, 4 Graduate School of Medicine, University of Tokyo, Tokyo, Japan

For understanding of degenerating mechanism of articular cartilage in such as osteoarthritis (CA) or improvement of mechanical functions of tissue- engineered cartilage, it is important to explore structure-function relationship of articular cartilage. To understand this relationship, various configurations of its compressive and shear stiffness have been investigated following the enzymatic degradation. The objective of this study was to quantify the role of the matrix components, especially those of collagen and proteoglycan (PG), on the dynamic compressive and the shear viscoelastic response of articular

cartilage as well as to obtain detailed information on the specificity of the selected enzymes. The cartilage explants were harvested from humeral head of 3-6 week-old bovine. Collagenase type VII was used for the degradation of the collagen network, and chondroitinase ABC was used for the specific digestion of PGs. All the specimens were tested before and after treatment; thus each specimen served as its own control. The dynamic viscoelastic properties (dynamic modulus, loss tangent) of the specimen were measured by dynamic compressive and shear loading. In the case of the dynamic compressive response, the dynamic modulus decreased after digestion in the case of both collagenase and chondroitinase. No significant change was observed in the loss tangent in the collagenase- treated group; however it significantly increased in the chondroitinase-treated group. In the case of the dynamic shear response, the dynamic shear modulus decreased after each of these enzymatic treatments. Contrary to the com- pressive response, a significant increase in the loss tangent was observed in the collagenase-treated group; however no significant change was observed in the chondrotinase-treated group. These findings may help to elucidate the contribution of the ECM components to the dynamic viscoelastic response of articular cartilage to combine with measurements of collagen and PGs content.

6774 We-Th, no. 4 (P56) Mechanical effect of pericellar matrix formation by chondrocyte cultured in agarose-gel on the viscoelastic properties of agarose-gel matrix N. Sasaki, T. Imai, A. Fukui. Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan

Viscoelastic properties of articular cartilage have been analyzed by the interac- tion of solid phase with interstitial fluid components. Chondrocytes and pericel- luar matrix (PM) around them have long been regarded as solid components. Recent histological studies have revealed that a chondron, a metabolic unit of a chondrocyte in cartilage made of a chondrocyte and surrounding matrices, has to be regarded as an independent viscoelastic mechanical element in a cartilage. There are, however, few works focusing on the mechanical properties of chondrons. The aim of this study was to determine viscoelastic properties of chondron in order to understand the viscoelastic nature of articular cartilage. As a preliminary model system for the investigation of the viscoelasticity of articular cartilage, chondrocyte-agarose gel composite systems were prepared by dispersing chondrocytes in the gel matrix. The composite system containing chondrocytes were cultured to synthesize biologically chondron-like PM around each chondrocyte. The production of PM in the agarose gel matrix was confirmed by toluidin blue staining. Stress relaxation of the chondrocyte- agarose gel composite system was examined by an indentation method. Relaxation modulus curve after the cultivation of the composite system could be superimposable by shifting the curve before cultivation along both horizontal and vertical aces, suggesting stiffness of PM as compared with the agarose gel-matrix and a percolation of PM throughout the composite system.

4580 We-Th, no. 5 (P56) Effects on mechanical loading on solute transport in the intact, perfused equine metacarpophalangeal joint K.E Arkill, C.E Winlove. School of Physics, University of Exeter, Exeter, UK

Introduction: Articular Cartilage is avascular and the mechanism of transport of solutes such as nutrients and signal molecules through the extensive extra- cellular matrix have been investigated for many years. However, fundamental issues concerning the importance of solute exchange with the subchondral microcirculation and the effects of mechanical loads remain unresolved. To address these issues we have developed a preparation of the intact equine forelimb, perfused with fluorescent tracers under a range of loading conditions. Methods: Fresh, intact equine metacarpophalangeal joints (7-11 years old) were perfused with saline containing rhodamine B (uncharged) and Na- fluorescein (anionic), either with the limb unloaded or under a load of 1500 N. In other experiments rhodamine base was injected into the synovial cavity. Full depth plugs of cartilage were then excised and the fluorophore distribution in frozen histological sections was quantified, after correction for non-uniform illumination and tissue autofluorescence. Results: The concentration profiles showed tracer entering the calcified car- tilage from the microcirculation and the upper zones from the synovial fluid. The transport rate for Na-fluorescein was greater than for rhodamine B in both unloaded and loaded preparations. Loading produced compression of the articular surface in the loaded zone and a reduction in the distribution volume and effective diffusivity for the anionic solute. The effective diffusivity of rho- damine base entering from the articular surface was (1.6±0.3) 10 -12 m 2 s -1 in unloaded tissue and reduced to (1.1 ±0.1) 10-12 m2 s -1 under load. Conclusions: Solute exchange occurs both across the articular surface and via the subchondral microcirculation in the mature horse. Static loading re- duces transport rates. These observations have implications on the aetiology of arthritis. The intact perfused joint will be invaluable in further investigations.