6 research outputs found
A OTRIBOLOGICAL I VESTIGATIO OF THE ROLE OF PROTEOGLYCA S I BIOLUBRICATIO
ABSTRACT Articular joints in human body are uniquely efficient lubrication systems. While the cartilage surfaces slide past each other under physiological working conditions (pressure of tens of atmospheres and shear rates up to 10 6 -10 7 Hz), the friction coefficient (µ) achieves extremely low values (down to 0.001) never successfully reached by mechanical prosthetic devices. Friction studies on polymer brushes attached to surfaces have recently demonstrated (17) their ability to reduce friction between the rubbing surfaces to extremely low values by means of the hydrated ions and the charges on the polymer chains. We propose that the extremely efficient lubrication observed in living joints arises from the presence of a brush-like phase of charged macromolecules at the surface of the cartilage superficial zone: hydration layers which surround the charges on the cartilage macromolecules might provide a lubricating ball-bearing-like effect as demonstrated for the synthetic polyelectrolytes (17). In this work macromolecules of the cartilage superficial zone (aggrecans) are extracted from human femoral heads and purified using well developed biochemical techniques (20). The extracted molecules are then characterized with atomic force microscope (AFM). By means of a surface force balance (SFB) normal and shear interactions between mica surfaces coated with these molecules are examined focusing on the frictional forces between such surfaces at normal stresses similar to those in human joints
Articular cartilage proteoglycans as boundary lubricants: Structure and frictional interaction of surface-attached hyaluronan and hyaluronan-aggrecan complexes
Normal and Shear Interactions between Hyaluronan–Aggrecan Complexes Mimicking Possible Boundary Lubricants in Articular Cartilage in Synovial Joints
Using a surface force balance, normal and shear interactions
have
been measured between two atomically smooth surfaces coated with hyaluronan
(HA), and with HA/aggrecan (Agg) complexes stabilized by cartilage
link protein (LP). Such HA/Agg/LP complexes are the most abundant
mobile macromolecular species permeating articular cartilage in synovial
joints and have been conjectured to be present as boundary lubricants
at its surface. The aim of the present study is to gain insight into
the extremely efficient lubrication when two cartilage surfaces slide
past each other in healthy joints, and in particular to elucidate
the possible role in this of the HA/Agg/LP complexes. Within the range
of our parameters, our results reveal that the HA/Agg/LP macromolecular
surface complexes are much better boundary lubricants than HA alone,
likely because of the higher level of hydration, due to the higher
charge density, of the HA/Agg/LP layers with respect to the HA alone.
However, the friction coefficients (μ) associated with the mutual
interactions and sliding of opposing HA/Agg/LP layers (μ ≈
0.01 up to pressure <i>P</i> of ca. 12 atm, increasing sharply
at higher <i>P</i>) suggest that such complexes by themselves
cannot account for the remarkable boundary lubrication observed in
mammalian joints (up to <i>P</i> > 50 atm)