Biomedical Engineering Reference
In-Depth Information
Prolactin induces the synthesis of proteoglycans and, in combination with glucocorticoids, it
contributes to the configuration of chondrocytes inside AC and to the syntheses of type II
collagen. The average molecular weight of human SF is 3 - 4 MDa.
Important components of SF are lubricin and some proteins from blood plasma (γ-globulin
and albumin), which enhance the lubricating properties of SF (Oates , 2006). The importance
of HA and proteins for the lubricating properties of SF was also described (Swann et al.,
1985; Rinaudo et al., 2009).
In the gap between AC surfaces, synovial fluid forms a micro-layer with a thickness of ca 50
μm. It fills up all surface micro-depressions (Fig. 3. and 4. , Petrtýl et al., 2010) and in
accessible places its molecules are in contact with the macromolecules of residual SF
localized in the pores of the femoral and tibial peripheral zone of AC.
Fig. 4. Topography of the articular cartilage surface of a man (58 years of age). The AC
surface oscillates to relative heights of 2.5 μm . During fast shifts of the AC surface (due to
the effect of dynamic shifting forces/dynamic bending moments or shear stresses), the AC
surface is filled up with generated synovial gel (with less associated NaHA macromolecules)
with low viscosity
SF is a rheological material whose properties change in time (Scott, 1999 and others). As a
consequence of loading, associations of polymer chains of HA (and some proteins) arise and
rheopexic properties of SF are manifested (Oates et al., 2006). Due to its specific rheological
properties, SF ensures the lubrication of AC surfaces. The key component contributing to
lubrication is HA/NaHA. In healthy young individuals, the endogenous production of
hyaluronic acid (HA) reaches the peak values during adolescence. It declines with age. It
also decreases during arthritis and rheumatic arthritis (Bloch et al., 1963; Anadere et al.,
1979; Davies & Palfrey, 1968; Schurz & Ribitsch, 1987 and numerous other authors). Some
AC diseases originate from the disturbance of SF lubrication mechanisms and from the
defects of genetically predetermined SF properties. Therefore, the lubrication mechanisms of
AC surfaces must be characterized with respect to the rheological properties of SF.
2. Contents
The objectives of our research has been aimed on the definition of the biomechanical
properties of SF which contribute to the lubrication of the opposite surfaces of articular
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