Movement of interstitial water through loaded articular cartilage

Water transport through articular cartilage and across the articular surface is a major factor controlling the amount and rate of tissue deformation. To study water movement concentration profiles within the tissue were determined using radiotracer techniques. Water movement was spatially and temporally mapped for unloaded, undeformed tissue, after cyclic and dead weight creep, and for recovery following dead weight creep using a uniaxial confined compression configuration to produce one-dimensional fluid movement. In unloaded tissue diffusion rapidly exchanged water by 15 minutes while the gross efflux of fluid during cyclic and dead weight creep compression effectively inhibited any external water influx. During recovery fluid inhibition was restricted when a small surface load was present, and only after complete removal of all surface traction was a large fluid efflux found. The compression and/or collapse of the uppermost surface layer of the tissue is believed responsible for controlling tissue fluid transport and mechanical response.

In vitro contact stress distributions in the natural human hip

Time variant distributions of intra-articular contact stress were assembled from direct measurement in seventeen grossly normal fresh cadaveric hips. Local stresses were sensed by arrays of 24 compliant miniature transducers inset superficially in the femoral head cartilage. Local contact stress magnitude was usually found to rise nearly linearly with applied joint loads in excess of about 1000 N. The sites of maximum local stress were found to underlie the general region of the acetabular dome. For a resultant joint load of 2700 N, the spatial mean contact stress and peak local contact stress averaged 2.92 MN m-2 and 8.80 MN m-2, respectively, for the 68 loading cycles analyzed. The full contact stress patterns were irregular and complex, but most commonly the general feature was a central band or 'ridge' of pressure elevation, oriented in an approximately anterior-to-posterior direction.

Abnormal softening in articular cartilage: its relationship to the collagen framework

Abnormal softening in articular cartilage is related to the presence of collagen fibers strongly aligned in a radial direction. In this paper, a morphologic model is proposed that provides a mechanism by which these radial arrays can develop passively from the more random, 3-dimensional network of fibers observed in normal articular cartilage.

The Role of Surface Chemistry in Filter Feeding by Zooplankton

Surface chemistry of both particles and animals is important in filter feeding at low Reynolds number. Daphnia magna, fed mixtures of three sizes of polystyrene particles, retained particles that were smaller than the mesh size of the animals (1.0 micrometer) at greater efficiencies than predicted by a sieving model. Retention efficiency of the smallest particles (0.5 micrometer) was increased when negative surface charge on the particles was neutralized, and retention was decreased when a nonionic surfactant was, added to reduce wettability.