Hydrogels of Poly(vinyl alcohol) and Nanocellulose for Ophthalmic Applications : Synthesis, Characterization, Biocompatibility and Drug Delivery Studies

Sammanfattning: Hydrogels are commonly used materials in ophthalmic care as contact lenses, bandage lenses, corneal implants, and cornea regeneration scaffolds. Hydrogels can be produced by physical, chemical, or radiation crosslinking of hydrophilic polymers. Poly(vinyl alcohol) (PVA) is a hydrophilic polymer that has been long known to the scientific community and is used in ophthalmic formulations.In this thesis, PVA was reinforced with nanocellulose to obtain self-standing hydrogels. Cryo-gelation technique was used to obtain transparent hydrogels from PVA dissolved in DMSO-water mixed solvent. The properties of these hydrogels were analyzed to explore the possibility of their application for ophthalmic use as a drug delivery vehicle and as cornea regeneration implant.The results indicate that oxidized nanocellulose can be combined with PVA to produce transparent, elastic, macroporous and high-water content hydrogel lenses. The water-filled macroporous structure of these hydrogels aids with oxygen transport and can enhance comfort while worn. The developed hydrogel also features moderate UV-light blocking properties in addition to high transparency. Furthermore, it was observed that the light scattering due to surface roughness of the hydrogel increases with measurement time, due to the rapid evaporation of the water layer from the surface of the hydrogel film.Mechanical analysis results revealed that the hydrogels exhibited a strain-induced stiffening behavior, which is usually noticed in hyper-elastic materials and collagenous soft tissues. The results of this study suggest that in order to mimic collagenous behavior, the material should possess high water content and a specific structural architecture combining soft and rigid elements as building blocks.Furthermore, PVA-CNC composite hydrogel showed no toxic effects on the corneal cells in both direct and indirect contact studies. It was found that the hydrogel promoted cell attachment and was stable when sutured ex vivo to a porcine excised cornea.To study enzyme-triggered drug release, hydrogel lenses loaded with chitosan-poly(acrylic acid) nanoparticles were exposed to lysozyme, an enzyme present in the eye. Nanoparticles were shown to disintegrate due to the hydrolysis of chitosan chains by lysozyme. Overall, with these distinctive properties, PVA-CNC hydrogel has great potential as an ophthalmic biomaterial for therapeutic and cornea regeneration applications.