Impact of Tribological Conditions on Collagen Coating Self-Healing

The study examined the correlation between collagen coating damage and self-healing under various tribological conditions. It confirmed that the friction coefficient and degree of damage on the collagen coating varied based on contact and sliding conditions. The friction coefficient, measured at 0.56 for a single sliding cycle under a 350 mN normal load, demonstrated a notable decrease to 0.46 for 2295 cycles under 30 mN, further reducing to 0.15 for 90 cycles under a 20 mN normal load. As the normal load increased, the friction coefficient decreased, and with repeated sliding cycles under the same load, the coefficient also decreased. Water droplets induced a self-healing effect on collagen coating, causing wear tracks to vanish as fibers absorbed water. Severe wear tracks, with broken fibers and peeled coating, showed limited self-healing. In contrast, mild wear tracks, with compressed yet connected fibers, exhibited the self-healing phenomenon, making the wear tracks disappear. Real-time observations during 90 cycles under a 20 mN normal load highlighted the formation of mild wear tracks with intact collagen fibers, providing quantitative insights into self-healing characteristics. To preserve the self-healing effect of the collagen coating, it is essential to ensure tribological conditions during contact and sliding that prevent the disconnection of collagen fibers.