Boundary Lubrication by Associative Mucin
- Publication date
- 2015
- Publisher
Abstract
Mucus
lubricants are widely distributed in living organisms. Such
lubricants consist of a gel structure constructed by associative mucin.
However, limited tribological studies exist on associative mucin fluids.
The present research is the first to investigate the frictional behavior
of a typical intact vertebrate mucin (loach skin mucin), which can
recover the gel structure of mucus via hydrophobic association under
physiological conditions (5–10 mg/mL loach skin mucin dissolved
in water). Both rough hydrophobic and hydrophilic polydimethylsiloxane
(PDMS) rubber plates were used as friction substrates. Up to 10 mg/mL
loach skin mucin dissolved in water led to a 10-fold reduction in
boundary friction of the two substrates. The boundary-lubricating
ability for hydrophilic PDMS decreased with rubbing time, whereas
that for hydrophobic PDMS remained constant. The boundary-lubricating
abilities of the mucin on hydrophobic PDMS and hydrophilic PDMS showed
almost similar responses toward changing concentration or sodium dodecyl
sulfate (SDS). The mucin fluids reduced boundary friction coefficients
(μ) only at concentrations (<i>c</i>) in which intermucin
associations were formed, with a relationship shown as μ ∼ <i>c</i><sup>–0.7</sup>. Destroying intermucin associations
by SDS largely impaired the boundary-lubricating ability. Results
reveal for the first time that intermolecular association of intact
mucin in bulk solution largely enhances boundary lubrication, whereas
tightly adsorbed layer plays a minor role in the lubrication. This
study indicates that associated mucin should contribute considerably
to the lubricating ability of biological mucus in vivo