Purely Zwitterionic Polymer Injectable Hydrogels for Vitreous Substitutes
Current clinical vitreous substitutes, including inert expansile gases, silicone oil, and perfluorocarbon liquids, are associated with complications such as emulsification, cataract formation, glaucoma, and inflammation, necessitating safer alternatives. This study reports a purely zwitterionic polymer hydrogel constructed entirely from carboxybetaine ureido acrylate (CBUIA) without covalent cross-linkers or non-zwitterionic segments. The hydrogel self-crosslinks via multivalent hydrogen bonding and dipole-dipole interactions, forming a supramolecular network of poly(carboxybetaine ureido acrylate) (PCBUIA). The PCBUIA hydrogels exhibit shear-thinning injectability and rapid self-healing, with density (1.016–1.021 g/cm³), refractive index (1.3359–1.3389), and transmittance (>90%) matching native vitreous. The zwitterionic hydration layer confers ultralow protein adsorption and suppresses cell attachment, with no foreign-body reaction or fibrotic capsule formation. After one month of implantation in rabbit eyes, the hydrogels maintained optical transparency, preserved retinal morphology, and did not elevate intraocular pressure or cause inflammatory responses. These findings demonstrate the potential of purely zwitterionic polymer hydrogels as vitreous substitutes, though further long-term in vivo studies are required to evaluate stability and functional performance.