Surface tension of animal cartilage as it relates to friction in joints

Abstract

Measurement of the surface tension of articular cartilage and friction experiments were carried out to provide further evidence in support of a new theory regarding the mechanism of friction in joints. To determine the surface tension of cartilage, contact angle measurements were used in conjunction with the equation of state for interfacial tensions. The advancing contact angle between saline drops and articular cartilage was found to be 100 degrees +/- 5 degrees, indicating a highly hydrophobic surface. The corresponding surface tension value was calculated to be 22.5 ergs/cm2. Friction of cartilage against hydrophobic surfaces is shown to be lower than the friction of cartilage against hydrophilic surfaces. All these results further support the theory that lubrication by nonwetting drops occurs in joints and may be responsible for the exceptional friction characteristics of the joints.

The Probable Explanation for the Low Friction of Natural Joints

“…These friction tests thus confirm our hypothesis on the relationship between the wettability and friction coefficient as shown by Fig. 5 [5,14,16]. This reveals a significantly enhanced friction between (AC/AC) for samples with depleted surfaces.…”

Functions for fish mucus

“…In many areas of biology such measurements are used to support the development of 'models' of functioning. For example, the role of synovial fluid in lubrication of vertebrate limb joints is well documented and supported by measurements of its viscosity (Linn and Radin, 1968), hydrophobicity of articular surfaces (Chappuis et aL, 1983), the coefficient of friction in joints (for example, Little et al, 1969) and other parameters (Hills, 1988). As will be described in following sections, there are few well-developed models of functioning applied to fish mucus supported by measurements of fundamental parameters.…”

Hydrostatic and boundary lubrication of joints; nature of boundary lubricant.

“…After the removal of any adherent fluid, all sliding tissue surfaces have hydro phobic properties. This is confirmed by the be ha viour of a drop of saline solution on the zjo lo gicz ne go so li na nie sio nej na po wierzch nię chrząst ki sta wo wej po wy płu ka niu jej z pły nu sta wowe go -roz twór so li nie roz pły wa się na po wierzch ni chrząst ki [11,12]. Pod da nie po wierzch ni chrząst ki stawo wej dzia ła niu roz pusz czal ni ka tłusz czu lub en zymów tra wią cych tłuszcz po wo du je sil ny wzrost war tości współ czyn ni ka tar cia [10].…”

“…Stę że -nie lu bry cy ny w pły nie ma zio wym wy no si oko ło 200 μg/ml [21]. Ru ty no we okre śla nie po zio mu lu bry cycartilage surface after the synovial fluid has been rinsed off, where the saline solution does not spill on the carti lage surface [11,12]. When the cartilage surface is subjected to a fat solvent or fat-digesting enzymes, the coefficient of friction rises rapidly [10].…”