Micro- and nanotexturing on hard biomaterials have shown
advantages
for tissue engineering and antifouling applications. However, a growing
number of studies have also shown that texturing may cause an increase
in friction, demanding further research on the tribological effects
of texturing under physiological conditions. This study investigates
the tribological effects of micro- and nanopore patterns on hard hydrophilic
silicon sliding against soft hydrophobic polydimethylsiloxane (PDMS)
immersed in aqueous liquids with various viscosities, simulating the
sliding of a textured implant surface against soft tissues. The experimental
results show that silicon surfaces with pore textures at both micro-
and nanoscale feature sizes confer a higher coefficient of friction
(COF) than an untextured one. It is attributed to the texture’s
edge effect caused by the periodic pore patterns between the two sliding
objects with a large difference in material stiffness. For the same
solid area fraction, nanopored surfaces show a higher COF than micropored
surfaces because of the significantly higher texture edge length per
unit area. For micropored surfaces with a similar length of texture
edge length per unit area, the COF increases more significantly with
the increase in pore size because of the greater stress at the rims
of the larger pores. The COFs of both micro- and nanoscale pores generally
decrease from ∼10 to 0.1 with an increase in the surrounding
aqueous viscosity, indicating the transition from a boundary lubrication
to a mixed lubrication regime while mostly remaining in boundary lubrication.
In contrast, the COF of an untextured surface decreases from ∼1
to 0.01, indicating that it mostly remains in the mixed lubrication
regime while showing the tendency toward hydrodynamic lubrication.
Compared to a hydrophilic hard probe sliding against a textured hydrophobic
soft substrate, the hydrophobic soft probe sliding against a textured
hydrophilic hard substrate produces a significantly higher COF under
similar physiological conditions due to the larger edge effect.