Start-up friction properties of poly(vinyl alcohol)/nano-hydroxyapatite/silk composite hydrogel

Poly(vinyl alcohol)/nano-hydroxyapatite/silk composite hydrogel was synthesized by repeated freezing and thawing with polyvinyl alcohol (PVA), nano-hydroxyapatite (HA) and silk. Friction tests between PVA-HA-Silk composite hydrogel and bovine knee articular cartilage were performed on a Micro-tribometer. Start-up friction mechanism of PVA-HA-Silk composite hydrogel was investigated under different conditions. The results demonstrated that mechanical properties of PVA-HA-Silk composite hydrogel are enhanced with the adding of HA and silk and start-up friction coefficient decreases with the increase of silk. Normal displacement and start-up friction coefficient increase with the increase of contact loads and contact time. Temperature and lubrication solution have less impact on normal displacement. The liquid flowability of PVA-HA-Silk composite hydrogel is improved with the increase of temperature, which causes the decrease of start-up friction coefficient. In a 25% bovine serum solution, proteins form a boundary film on friction surface to decrease friction effectively.