Smart responsive injectable hydrogel loaded with icariin inhibits ferroptosis and promotes nucleus pulposus repair in intervertebral disc degeneration

Intervertebral disc degeneration (IVDD) is a leading cause of lower back pain, characterized by the ferroptosis of nucleus pulposus cells (NPCs) and imbalance in reactive oxygen species (ROS) metabolism. Icariin (ICA), an active compound from traditional Chinese medicine, scavenges ROS and inhibits ferroptosis, but its poor water solubility and low bioavailability limit clinical use. A dual-crosslinked hydrogel (HP@ICA) is developed to address these challenges. Cyclodextrin is integrated into polyvinyl alcohol to enhance ICA loading via hydrophobic interactions. Methacrylic acid and phenylboronic acid are incorporated into hyaluronic acid, enabling dynamic bonding with polyvinyl alcohol. Ultraviolet crosslinking creates a secondary crosslinked hydrogel with pH and ROS responsiveness, self-healing properties, and improved ICA solubility, increasing its water solubility tenfold. Enhanced solubility boosts ICA's free radical scavenging capacity by 103 %, suppressing ferroptosis and promoting NP cell regeneration, as demonstrated by reduced iron ion concentrations, lower malondialdehyde levels, and restored glutathione peroxidase 4 activity. Ferroptosis inhibition facilitates type II collagen production in NP cells. Mechanistic studies reveal activation of the Nrf2-GPX4 pathway as key to regeneration. These findings suggest a promising regenerative therapeutic approach for IVDD.