Transitional behaviour between biphasic lubrication and soft elastohydrodynamic lubrication of poly(vinyl alcohol)hydrogel using microelectromechanical system pressure sensor

The soft hydrogel material is expected for a candidate material as biomimetic artificial cartilage with synergisticfunctionalities of adaptive multimode lubrication.In boundary lubrication mode of hydrogel material,the biphasiclubrication mechanism cooperatively exerts its functionality.In hydrodynamic lubrication mode,it is preferable that thelubricating surfaces be impermeable to trap the fluid pressure in contact surfaces,whereas the actual biphasic materiallike a hydrogel is a permeable material with surface porosity.lt is indicated that the interstitial fluid pressurisation inthe permeable biphasic material can contribute to significant fluid load support under lower sliding speed condition.So,the authors examined how the contrary fluid pressure effect appears in the transition from the boundarylubrication mode to soft elastohydrodynamic lubrication mode.In the experiment,a small pressure sensor was utilisedto measure the in-situ fluid pressure in sliding condition.Although the experimental condition of this study wasselective,the result showed a possibility of the negative effect of the biphasic surface,in which the permeable surfacediminished the hydrodynamic fluid pressure.This means that one should manage and enhance the biphasic lubricationabilities in wide operation range when the hydrogel material was used as a load bearing material.