[Show abstract][Hide abstract] ABSTRACT: An essential component of functional articular cartilage tissue engineering is a mechano-active scaffold, which responds to applied compression stress and causes little permanent deformation. As the first paper of a series on mechano-active scaffold-based cartilage tissue engineering, this study focused on mechanical responses to various modes of loading of compression forces and subsequent selection of mechano-active scaffolds from the biomechanical viewpoint. Scaffolds made of elastomeric microporous poly(L-lactide-co-epsilon-caprolactone) (PLCL) with open-cell structured pores (300 approximately 500 microm) and with different porosities ranging from 71 to 86% were used. The PLCL sponges and rabbit articular cartilage tissue were subjected to compression/unloading tests (0.1 and 0.005 Hz) at 5 kPa, and stress relaxation tests at 10, 30, and 50% strain. The measurements of the maximum strain under loading and residual strain under unloading for compression tests and the maximum stress and equilibrium stress in the stress relaxation test showed that the lower the porosity, the closer the mechanical properties are to those of native cartilage tissue. Among the PLCL sponges, the sponge with 71% porosity appears to be a suitable cartilage scaffold.
[Show abstract][Hide abstract] ABSTRACT: To fabricate a "mechano-active" tubular scaffold of nonwoven mesh-type small-diameter artificial graft made of the synthetic durable elastomer, segmented polyurethane, the fabrication technique of electrospinning on a mandrel under a high rotation speed and transverse movement was used. Emphasis was placed on how the rotation speed of the mandrel and the fusion or welding states of fibers at contact points affect the compliance (ease of intraluminal pressure-dependent circumferential inflation) and Young's modulus determined by uniaxial stretching in the longitudinal and circumferential directions. The results showed that a high rotation speed is attributed to exhibit isotropic mechanical properties in the entire range of applied strain but reduces the compliance, and a high fusion state, which is produced using a mixed solvent with a high content of high-boiling-point solvent, reduces the compliance but is expected to exhibit high durability in a continuously loaded pulsatile stress field in an arterial circulatory system.
Journal of Biomedical Materials Research Part A 04/2005; 73(1):125-31. DOI:10.1002/jbm.a.30260 · 3.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Articular cartilage has biphasic property based on high water content. It is generally believed that the proteoglycan supports the compressive load, but the detailed loading mechanism has not yet been clarified. In this study, first we observed the changes in compressive stress and strain of articular cartilage under constant total compressive deflection. We evaluated the changes in modulus of elasticity, which was estimated from the stress-strain relation in equilibrium state. To examine the role of proteoglycan in compressed articular cartilage, we compared the time-dependent viscoelastic behaviors in both the intact cartilage and the cartilage treated with chondoroitinase ABC under constant total compressive deformation. We could confirm that the peak stress after compression and the modulus of elasticity at equilibrium were reduced after the digestion of proteoglycan. Next, we observed the changes in local strain in both articular cartilage specimens with and without chondroitinase treatment by monitoring the position of stained chondrocyte in the confocal laser scanning microscope. These visualized images indicated that the local strain changed time-dependently and depth-dependently. The digested cartilage showed the quicker change in movement and larger thinning in surface layer than the intact cartilage. These results indicate that the proteoglycan contributes to the compressive load-carrying capacity and controls the permeability.
JSME International Journal Series C 12/2004; 47(4):1049-1055. DOI:10.1299/jsmec.47.1049 · 0.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The natural synovial joints have excellent tribological performance known as very low friction and very low wear for various daily activities in human life. These functions are likely to be supported by the adaptive multimode lubrication mechanism, in which the various lubrication modes such as elastohydrodynamic lubrication, weeping, boundary and gel film lubrication appear to operate to protect articular cartilage, depending on the severity of the rubbing conditions. In this paper, various protective roles of synovial fluid, cartilage surface layer, extracellular matrix and chondrocyte to severe loading are described. In the first part, the protective mechanism by adsorbed films and underlying gel films was described on the basis of the frictional behaviors of articular cartilage against articular cartilage or glass. It was discussed that the replenishment of gel film removed during severe rubbing is likely to be controlled by supply of proteoglycan from the extracellular matrix, where the chondrocyte plays the main role in the metabolism. In the second part, the time-dependent local deformation of biphasic articular cartilage under constant total compressive strain condition was evaluated in the finite element analyses. The importance of clarification of actual stress-strain in chondrocyte was indicated in relation to the tribological property of articular cartilage.
JSME International Journal Series C 06/2003; 46(2):594-603. DOI:10.1299/jsmec.46.594 · 0.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: It is well accepted that articular cartilage adapts to changing mechanical environments. As the rubbing condition is getting severe, the articular cartilage will be worn, resulting in osteoarthritis, but little is known about the mechanism to osteoarthritis. It is important to clear the stress-strain state of cartilage and in chondrocytes under repeated cartilage deformation to know how osteoarthritis gets to start and progress. The purpose of this study is to investigate an influence of chondrocytes on stress-strain state of articular cartilage and an influence of position of chondrocyte on its depth-dependent deformation. FEM analyses predict time-dependent stress-strain state of articular cartilage because of fluid exudation, but material properties of chondrocytes do not affect the behavior of articular cartilage so much. The deformation of chondrocyte is depth-dependent and the largest time-dependent deformation behavior occurs in the surface layer. These results may clear how the transduction of mechanical stimuli concern about metabolism of articular cartilage via chondrocytes.
Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A 02/2003; 69(678):487-493. DOI:10.1299/kikaia.69.487
[Show abstract][Hide abstract] ABSTRACT: Human joints are capable of functioning effectively with low friction and without failure throughout human life under circumstances where both articular cartilage as bearing material and synovial fluids as lubricants fulfill their normal functions. It is