Mucoadhesive Carboxymethyl Chitosan Hydrogel Eyedrops via Dual Dynamic Covalent Chemistry for Long-Acting Glaucoma Therapy

Abstract

Glaucoma, a leading cause of irreversible blindness, is commonly treated with topical eye drops that reduce intraocular pressure (IOP), but their efficacy is limited by rapid precorneal clearance. To address this, we developed a dynamic hydrogel (CSFP) via Schiff base bonding between carboxymethyl chitosan (CMCS) and 4-formylphenylboronic acid (FPBA) as an advanced delivery vehicle for brimonidine (BRI) and timolol (TIM), two common IOP-lowering agents. The mechanical properties were tunable by adjusting CMCS and FPBA concentrations. The optimized hydrogel exhibited a storage modulus of ∼38.8 Pa (at 1 Hz, 1% strain), excellent self-healing ability, and shear-thinning behavior, facilitating easy administration and resistance to blink-induced clearance. It also achieved near 100% transmittance and a refractive index of 1.339, ensuring optical clarity. Notably, the incorporated phenylboronic acid (PBA) groups enabled selective binding to sialic acid residues on ocular mucins via dynamic phenylboronic ester bonding, prolonging precorneal retention beyond 30 min compared to less than 5 min for the solution control. In a magnetic bead-induced ocular hypertensive rat model, CSFP hydrogel loaded with either BRI or TIM induced greater and long-lasting IOP reduction than the free drug solutions. This work highlights the potential of mucoadhesive dynamic covalent hydrogels for advanced ocular drug delivery.